Implementation of the Hydraulic Fracture Test at MnDOT. -Final Reportby

Transcription

1 Implementation of the Hydraulic Fracture Test at MnDOT -Final Reportby Mark B. Snyder, Engineering Consultant prepared for The Minnesota Department of Transportation Transportation Building, Mail Stop John Ireland Boulevard St. Paul, Minnesota June 23, 2005

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3 ACKNOWLEDGMENTS The author would like to express his appreciation to the Minnesota Department of Transportation (MnDOT) for its financial and technical support of the implementation effort described herein. Special thanks are offered to Rebecca Embacher, Bernard Izevbekhai and Douglas Schwartz for their technical support and guidance in the conduct of this effort. The author also thanks Daniel Squires for his enthusiastic assistance in preparing the lab for (and helping with) the apparatus set up, and Kevin Rosaasen for his help in fabricating a test stand and making several minor modifications to the test equipment to improve their function. The author also acknowledges the contributions of Dr. Donald Janssen of the University of Washington Department of Civil Engineering, the original developer of the hydraulic fracture test concept for assessing concrete aggregate freeze-thaw durability.

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5 TABLE OF CONTENTS Page Background and Summary of Previous Work...1 Expected Users and Benefits of the HFT...1 Project Work Task Descriptions and Products...1 Task 1: Develop a Specification for Using the HFT...2 Task 2: Assemble and Set Up HFT Test Apparatus...2 Task 3: Program MnDOT s Equipment for Determining HFT Release Rates...2 Task 4: Calibrate the Small and Large HFT Apparatus...4 Task 5: Develop Test Protocol Documents...4 Task 6: Create a Framework for a Database of HFT Test Results...4 Task 7: Document Procedures for Developing a Large Chamber Dilation Prediction Model...7 Task 8: Train MnDOT Personnel...7 Task 9: Final Report...8 Conclusions and Recommendations...8 References...8 APPENDICIES Appendix A Standard Test Method for Hydraulic Fracture of Coarse Aggregate for Portland Cement Concrete Appendix B Hydraulic Fracture Test Protocol Appendix C Procedures for Developing Dilation Prediction Models for Alternate Pressure Chambers or Alternate Freeze-Thaw Tests

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7 LIST OF FIGURES Figure 1. Photo of large chamber set up in MnDOT concrete lab....3 Figure 2. Photo of small chamber set up in MnDOT concrete lab...3 Figure 3. HFT data collection form...5 Figure 4. Example screen print from HFT data entry and analysis spreadsheet...6 Figure A1. HFT apparatus calibration target pressure release rate curve.... A-10 Figure A2. Example plot of pressure release rate profiles for various actuator pressure settings... A-11 Figure B1. Photos of large chamber cylinder assembly...b-1 Figure B2. Photos of chamber pressure regulator and gages (left) and actuator pressure regulator and gages (right)...b-2 Figure B3. Photo of large chamber with drain line attached to quick connect fitting....b-3 Figure B4. Large chamber fill valve assembly....b-3 Figure B5. Photos of small chamber cylinder assembly (top plate removed) and stand...b-5 Figure B6. Small chamber fill valve assembly....b-7 Figure B7. Photo of small chamber pressurization and drain assemblies...b-7 Figure B8. Photo of drain valve assembly, including drain tube on inside of chamber....b-8 Figure B9. Aggregate washer and oven in MnDOT concrete lab...b-9 Figure B10. Photos of double boiler and silane under MnDOT fume hood and treated sample draining in double boiler...b-10 Figure B11. Photos of typical aggregate tumbler with sample in drum (left) and large tumbler in MnDOT lab (right)...b-10 Figure B12. Assembly of large chamber bottom plate and fill with aggregate sample, including strike-off...b-12 Figure B13. Removal of large chamber assembly pins and tightening of assembly bolts....b-13 Figure B14. Small chamber, ready to be filled with aggregate sample....b-14 Figure B15. Tightening of small chamber assembly bolts...b-15 Figure B16. Connecting the drain/overflow line (left) and opening the fill valve (right)....b-16 Figure B17. Removing trapped air bubbles using rubber mallet...b-16 Figure B18. Pressurization of chamber (left) and installation of muffler (right)...b-17

8 Figure B19. Pressure release operation: close pressure isolation valve, then flip electric switch...b-18 Figure B20. Opening the large chamber drain valve....b-18 Figure B21. Attaching the fill overflow line (left) and opening the fill valve (right)...b-20 Figure B22. Dislodging attached air bubbles from the inside of the small chamber...b-21 Figure B23. Closing the pressure release valve and fill valve (left) and removing the fill overflow line (right)...b-21 Figure B24. Closing the pressure release valve and fill valve (left) and removing the fill overflow line (right)...b-22 Figure B25. Release of pressure from small chamber by closing pressure isolation valve, then flipping electric switch...b-23 Figure B26. Removing water from small chamber by closing pressure release valve and nitrogen bottle valve, opening drain valve and slowly opening pressure isolation valve...b-23 Figure B27. HFT data collection form...b-26 Figure B28. HFT apparatus calibration target pressure release rate curve....b-28 Figure B29. Connecting pressure transducer to dynamic signal analyzer...b-29 Figure B30. Example plot of pressure release rate profiles for various actuator pressure settings...b-30 LIST OF TABLES Table A1. HFT Apparatus Calibration Target Pressure Release Rate Data.... A-10 Table B1. HFT Apparatus Calibration Target Pressure Release Rate Data Table....B-27 Table C1. Summary of aggregate sources used in U of Mn study (including their locations and freeze-thaw durability factors)...c-3

9 Background and Summary of Previous Work D -cracking and other forms of aggregate-related freeze-thaw damage have often been associated with concrete pavements in Minnesota. The best approach for preventing these types of distress is to avoid using aggregate sources that are known to be susceptible to freeze-thaw damage in concrete applications. The most widely accepted methods of evaluating aggregate freeze-thaw durability involve the preparation and freeze-thaw testing of concrete beams that contain the aggregate in question. These tests are generally time-consuming, sometimes requiring months to complete, and often require the use of expensive equipment and/or highly skilled operators. Furthermore, the variable nature of many aggregate sources necessitates frequent testing to ensure the adequate freeze-thaw resistance of material being produced at any given point in time. A more rapid test of aggregate freeze-thaw durability was developed under the Strategic Highway Research Program in This test, called the Washington Hydraulic Fracture test (WHFT), was relatively inexpensive and allowed a single laboratory technician to assess the freeze-thaw durability of several samples of aggregate in as few as seven working days. Broader evaluations of the WHFT revealed several deficiencies, however. Subsequent research studies were performed between 1996 and 2002 at Michigan State University and the University of Minnesota for the Michigan Department of Transportation (MDOT) and Mn/DOT, respectively. These efforts resulted in the refinement and validation of the test procedures and apparatus using Minnesota aggregates. The most significant improvements included the modification of the test apparatus and procedures, and the replacement of the hydraulic fracture index with a model that predicts ASTM C 666 freezethaw test dilation as a function of the distribution of particle mass retained on various sieves after hydraulic fracture testing. These changes greatly improved the efficiency and accuracy of the test. In addition, a large test chamber was developed to allow the testing of aggregate samples five times larger than those tested in the original small chamber, thereby allowing aggregate durability characterization of one representative sample with a single test run. It is believed that the hydraulic fracture test is now ready for implementation in Minnesota as an accurate screening tool for concrete aggregate freeze-thaw durability. Expected Benefits and Users of the HFT The implementation effort performed under this contract provides Mn/DOT with the ability to rapidly and accurately evaluate the freeze-thaw durability of coarse aggregate sources intended for use in Portland cement concrete applications. This will aid in increasing the utilization of existing aggregate sources that are not currently accepted for concrete aggregate production, while ensuring acceptable freeze-thaw durability and performance potential. In the context of the decreasing availability of suitable concrete aggregate sources, the ability to make better use of existing local aggregate sources will forestall expected increases in aggregate costs that will result from transportation over increasingly great distances. Project Work Task Descriptions and Products This project included nine work tasks. Descriptions of these task activities and the resulting deliverables are provided below. 1

10 Task 1: Develop a Specification for Using the HFT The original goal of this task was to document standard sampling and testing procedures and acceptance/rejection criteria for use by Contractors and Mn/DOT, thereby helping to ensure consistent test results among operators and between test apparatus. The specification was to provide a detailed description of the required test equipment and procedures, including (but not limited to): Sampling of coarse aggregate (e.g., details concerning the requirements for test sample numbers, sizes, retrieval locations and handling). Sample submittal details (e.g., sample handling and labeling, lead time required prior to paving for source approval). Preparation and testing of the aggregate sample (including sample size reduction, pre-test treatments and all test procedural details). Acceptance / Rejection criteria based on percent dilation per 100 cycles. Number of test results upon which the acceptance / rejection criteria are to be based. As the project progressed, it became clear that there was potential overlap between the content of this proposed specification and the test protocol being developed under Task 5. It was decided that MnDOT would be better served by developing the Task 1 specification with a content and format that closely matched that of a standard ASTM or AASHTO specification. The resulting specification, provided in Appendix A, defines appropriate parameters for test equipment and operations in a general sense that should allow the development and use of improved or modified equipment. In other words, the specification is intended to ensure that various users of generic hydraulic fracture test equipment produce comparable test results. Step-by-step instructions specific to the use of the current MnDOT test apparatus are provided in the Appendix B Test Protocol. Task 2: Assemble and Set Up HFT Test Apparatus The scope of this task was to assemble and set up one small chamber (2-in inside height, 10-in inside diameter) and one large chamber (10-in inside height, 10-in inside diameter) hydraulic fracture test apparatus using equipment available Minnesota Department of Transportation Office of Materials laboratory. This task was accomplished with the help and assistance of MnDOT staff. Figures 1 and 2 are photos of the assembled apparatus in the MnDOT Concrete Testing Lab. Task 3: Program MnDOT s Equipment for Determining HFT Release Rates The goal of this task was to program MnDOT s existing dynamic signal analyzer (a Hewlett- Packard model 35565) and computer equipment for use in determining HFT chamber pressure release rates (for test chamber calibration and monitoring procedures). This was necessary because MnDOT s signal analyzer is of a different brand and requires different software programming than those used under previous research efforts. This goal was accomplished with the development of two tools: 1) a file containing the correct settings for the signal analyzer (HFT.STA), and 2) a spreadsheet (CALIBRATE.XLS) that automatically produces a calibration comparison plot when the user enters pressure release data obtained from signal analyzer. These software tools were provided (on a CD) to the MnDOT project technical liaison. 2

11 Figure 1. Photo of large chamber set up in MnDOT concrete lab. Figure 2. Photo of small chamber set up in MnDOT concrete lab. 3

12 Task 4: Calibrate the Small and Large HFT Apparatus The goal of this task was to calibrate the small and large chambers by determining and documenting actuator and chamber pressures that consistently produce pressure release rates that match those of the target data. This was accomplished with the following results: Small chamber settings: Chamber pressure = 1150 psi, Actuator pressure = 155 psi Large chamber settings: Chamber pressure = 1300 psi, Actuator pressure = 240 psi Task 5: Develop Test Protocol Documents The goal of this task was to develop test protocol documents to provide MnDOT personnel with complete plain language details (to supplement the specifications developed in Task 1) describing how tests and calibrations should be performed. This was accomplished and the resulting document is presented in Appendix B. A data collection/reporting form was developed using Excel and is shown in figure 3. The file used to produce this form is called HFT Data Collection Form.xls and is contained on the project CD that was provided to the MnDOT Technical Liaison. A spreadsheet was also developed to allow operators to enter data collected using the above form and automatically calculate predicted dilation per 100 cycles of freezing and thawing (using ASTM C 666 Procedure B modified with cloth wraps). A screen print of this spreadsheet is provided in figure 4 and the file (called HFT Data Entry and Analysis.xls ) is contained on the project CD that was provided to the MnDOT Technical Liaison. Task 6: Create a Framework for a Database of HFT Test Results The creation of a well-designed database is essential for monitoring aggregate source durability over time. Database trends can also be used to identify possible systematic problems with consistency between operators or equipment calibration, so a functional database will be essential to the successful implementation of the HFT at MnDOT. With this in mind, the original goal of this task was to create a framework for establishing a database of hydraulic fracture test results (e.g., field names), and the engineering consultant was to assist Mn/DOT personnel in developing suitable data reporting forms and an ORACLE table for storing HFT test data. As the project progressed, MnDOT s Technical Liaison determined that MnDOT s database needs might be better served in the short term with an Excel spreadsheet rather than an Oracle database. A file called HFT Database.xls was created and is contained on the project CD that was provided to the MnDOT Technical Liaison. Data entry columns in this spreadsheet include: MnDOT Source Designation Source Common Name Area or Ledge 4

13 HFT Data Collection Sheet Replicate Number Silane Treatment Date Initial Mass, g Test Date: M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g 10 Cycles M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g 20 Cycles M 5/16" (ret), g 30 Cycles M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: Test Date: M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g 40 Cycles M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g 50 Cycles M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: M 3/4" (ret), g Source: Submitted by: M 5/8" (ret), g M 1/2" (ret), g Date Rec'd: Carbonate Content (%): M 3/8" (ret), g M 5/16" (ret), g Test Technician: Equip No: M 1/4" (ret), g M #4 (ret), g Chamber Pressure (psi): Solonoid Press. (psi): M pan, g Mass Check: Comments: Figure 3. HFT data collection form. 5

14 HFT Data Entry and Analysis Sheet Replicate Number Combined Silane Treatment Date 06/10/05 06/13/05 06/14/05 06/15/05 06/16/05 Initial Mass, g Test Date: 06/13/05 06/14/05 06/15/05 06/16/05 06/17/05 Comb M Ret M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g Cycles 20 Cycles 30 Cycles 40 Cycles 50 Cycles M 3/8" (ret), g M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: 06/14/05 06/15/05 06/16/05 06/17/05 06/20/05 Comb M Ret M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: 06/15/05 06/16/05 06/17/05 06/20/05 06/21/05 Comb M Ret M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: 06/16/05 06/17/05 06/20/05 06/21/05 06/22/05 Comb M Ret M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Test Date: 06/17/05 06/20/05 06/21/05 06/22/05 06/23/05 Comb M Ret M 3/4" (ret), g M 5/8" (ret), g M 1/2" (ret), g M 3/8" (ret), g M 5/16" (ret), g M 1/4" (ret), g M #4 (ret), g M pan, g Mass Check: Predicted Dilation/100 cycles Source: Example 1 Submitted Quarry A Date Rec'd: 16-Jun-05 Carbonate Content (%): 100 Test Technician: Tech 1 Equip No: Small 1 Chamber Pressure (psi): 1150 Solonoid Press. (psi): 155 Figure 4. Example screen print from HFT data entry and analysis spreadsheet. 6

15 HFT Test Data Test Start Date Test Operator Predicted Dilation/100 cycles (%) Absorption Capacity Test Date Absorption Capacity (%) Petrographic Examination Examination Date Carbonate Content (%) ASTM C 88 (Magnesium Sulfate) Test Data Test Date Mass Loss ASTM C 666 (Rapid Freezing and Thawing) Test Data Test Start Date Test Procedure (A, B, etc.) Testing Lab Number of Specimens Tested Average Durability Factor Average Dilation/100 cycles (%) Average Mass Loss (%) 14-day Compressive Strength (psi) 14-day Elastic Modulus (ksi) Task 7: Document Procedures for Developing a Large Chamber Dilation Prediction Model Only a few aggregate sources have been tested using the modified large HFT chamber 4. While the dilation prediction model should be good for any properly calibrated test chamber, it would be good practice to verify this fact and, if necessary, modify the dilation prediction model so that it provides the highest possible accuracy when using data obtained from the large chamber. Furthermore, it was determined that it would be most useful if guidance was provided to allow for the development of durability prediction models for other test chamber configurations and other durability test results (e.g., durability factor or dilation performed in accordance with ASTM C 666 Procedure A or B). Therefore, while the original goal of this task was to document procedures for developing a large chamber dilation prediction model, the final goal became to document procedures for developing durability prediction models for situations where either the durability measure is different from the one currently used and/or when any chamber other than the original small chamber is used or modified. This was accomplished and the resulting procedures are documented in Appendix C of this report. Task 8: Train MnDOT Personnel The goal of this task was to train Mn/DOT personnel to use the small and large HF chambers. This was accomplished through the delivery of a 2-hour presentation on the test development and conduct (made to more than 30 MnDOT staff engineers and technicians, along with several 7

16 interested industry representatives), followed by a half week of hands-on training for a group of 4 engineers and technicians to ensure the proper and consistent implementation of the HFT test. Training included all aspects of test apparatus management, operation and repair, as well as evaluation of test results and completion of test reporting and data storage documents. The powerpoint files used for the presentations to MnDOT staff are titled MnDOT HFT Orientation and MnDOT HFT Training and they are included on the CD that was provided to the MnDOT technical liaison. In addition, a full day was spent filming a DVD video of both the presentations and actual operation of the test equipment in the lab. Copies of the DVD video should be available from MnDOT s Office of Communication and Workforce Development. Task 9: Final Report The goal of this task was to assemble and organize all of the documents prepared under tasks 1 through 8 into a single document that describes the entire implementation effort. This report is that document. Conclusions and Recommendations The Hydraulic Fracture Test equipment (both large and small chambers) were successfully installed in the MnDOT Concrete Laboratory, MnDOT staff have been trained in the use of the equipment, and supporting documents and software have been developed. Everything is in place to initiate a full implementation of the test using the small chamber, and procedures are available to validate the large chamber or develop a new model for the large chamber. It is recommended that MnDOT begin to collect and test aggregate samples using the HF apparatus and freeze-thaw tests (at the same time as standard sulfate soundness tests are performed). It will be necessary to either adopt the same freeze-thaw test procedure that was used during the University of Minnesota study, or to adopt an existing standard (e.g., AASHTO T161 Procedure A or B) for all future tests. When sufficient HF and freeze-thaw data have been collected to validate the existing model (or develop a new model) for the large chamber, the HF test should be fully implemented with periodic checks of continued model accuracy when compared to the results of freeze-thaw tests. References 1. D. J. Janssen and M. B. Snyder, SHRP C-391: Resistance of Concrete to Freezing and Thawing (Washington, DC: Transportation Research Board, 1994). 2. M. B. Snyder, D. J. Janssen and W. Hansen, Adoption of a Rapid Test for Determining Aggregate Durability in Portland Cement Concrete (Ann Arbor, MI: University of Michigan Department of Civil Engineering, 1996). 3. J. J. Hietpas, Refinement and Validation of the Washington Hydraulic Fracture Test (Minneapolis, MN: University of Minnesota Department of Civil Engineering, 1998). 4. R. A. Embacher and M. B. Snyder, Refinement and Validation of the Hydraulic Fracture Test (St. Paul, MN: Minnesota Department of Transportation, 2003). 8

17 APPENDIX A Standard Test Method for Hydraulic Fracture of Coarse Aggregate for Portland Cement Concrete

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19 Standard Test Method for Hydraulic Fracture of Coarse Aggregate for Portland Cement Concrete (draft prepared for MnDOT by Mark B. Snyder, Engineering Consultant rev 6/24/2005) 1. Scope 1.1 This test method covers the resistance of aggregates to fracture under the effect of internal pressure expelling water from aggregate pores. The procedure is intended to assist in the identification of aggregates that cause deterioration in concrete when exposed to repeated cycles of freezing and thawing (D-cracking). 1.2 The values state in either inch-pound or SI units shall be regarded separately as standard. The SI units are shown in brackets. The values stated may not be exact equivalents; therefore each system must be used independently of the other. Combining values from the two units may result in nonconformance. 1.3 This procedure may involve hazardous materials, operations and equipment. This procedure does not purport to address all the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 AASHTO Standards T 2 Sampling Aggregates T 161 Resistance of Concrete to Rapid Freezing and Thawing M 92 Wire Cloth Sieves for Testing Purposes M 231 Weights and Balances Used in the Testing of Highway Materials 2.2 ASTM Standards C 666 Resistance of Concrete to Rapid Freezing and Thawing C 702 Method for Reducing Field Samples of Aggregate to Testing Size D 3665 Practice for Random Sampling of Construction Materials 3. Significance and Use 3.1 As noted in the scope, the procedure described in this method is intended to aid in the identification of coarse aggregate sources that may be susceptible to D-cracking. Aggregate particles that exhibit a high rate of fracturing under repeated pressurization cycles are considered to be more susceptible to D-cracking when critically saturated and subjected to cycles of freezing and thawing in field applications. 3.2 The relatively short time required for completion of this procedure (approximately eight working days) makes it suitable for use as a screening test to identify aggregate sources that should be subjected to more traditional (and more time-consuming) testing prior to approval. 3.3 The results of this test, like D-cracking susceptibility, are sensitive to the size of the aggregate particles tested. Therefore, this test may be appropriate for identifying aggregate sources that should be reduced in size to avoid D-cracking in field applications. 3.4 The results of this test are also sensitive to the number of soft or nondurable particles (e.g., sandstone, clay ironstone, etc.) in the test sample. Therefore, this test may be appropriate A-1

20 for determining the amount of durable aggregate that must be blended with nondurable aggregate to produce a blend with sufficiently low D-cracking potential to provide acceptable performance. 3.5 This test is not considered useful in identifying the potential for coarse aggregate popouts caused by the freezing and thawing of saturated particles of chert in concrete. 4. Apparatus 4.1 Tumbling Apparatus The tumbling apparatus (hereafter referred to as the tumbler) shall consist of a rubber drum (for holding the sample) and a motorized drive unit The rubber drum shall have inside dimensions appropriate for tumbling the test sample. The inside shall be faceted to facilitate tumbling of the aggregate particles. The drum shall have a removable cover (so that the sample can be placed in the drum), and the cover should not interfere with the rotation of the drum when it is mounted in or on the motorized drive unit. Note 1 - Suitable tumblers of various sizes are available commercially for polishing rocks. Internal dimensions of approximately 6.75 in (171 mm) in diameter by 8 in (200 mm) deep have been used successfully, but larger drums may be more useful and efficient for samples weighing more than about 6 lbs (3 kg). 4.2 Pressurization Apparatus The pressurization apparatus shall include a pressure chamber of sufficient volume for testing aggregate samples of the desired size. The chamber must be certified for safe operation at pressures of up to 1500 psi (10,000 kpa). Note 2 - Shop-built pressure chambers are not recommended for use in this test due to the difficulty in obtaining pressure-tight seals at the high pressures involved, as well as the hazards associated with their operation at high pressures. If a shop-built pressure chamber is used, it should be pressure-certified to provide a safety factor of at least 5 to The inside surfaces of the pressure chamber shall be suitably treated to prevent the physical fracture of aggregates by the expansion and recovery of the chamber during pressurization/de-pressurization cycles. Note 3 - For cylindrical steel chambers with 1-in (25-mm) thick walls and having inside dimensions of 10 in (250 mm) diameter, in (0.8 mm) thick neoprene rubber sheets, glued to the insides of the flat chamber ends, has proven sufficient to prevent aggregate crushing by chamber expansion and recovery. It is not necessary to coat or otherwise treat the inside wall of this cylindrical chamber The pressure chamber shall be fitted with valves and fittings to permit the pressurization of the chamber (pressurization valve), release of chamber pressure (ball-type pressure release valve), filling with water (fill valve), and draining (drain valve). Valve and fitting sizing and location must be selected to ensure proper function of the apparatus and to achieve the necessary pressure release rate. The apparatus must be capable of producing a pressure drop of at least 300 psi (2,100 kpa) during the first 0.01 second of the opening of the pressure release valve A compressed nitrogen gas supply shall be provided to pressurize the test chamber. The available nitrogen gas supply pressure must be greater than the specified test pressure A pressure gauge and regulator shall be provided to attach directly to the compressed nitrogen gas cylinder and control the level of pressure induced in the chamber. The regulator shall have an output capacity of at least 1500 psi (10,000 kpa). The regulator outlet pressure A-2

21 gauge shall have a precision of 0.25 percent of full scale and shall be properly calibrated and certified at least once every 12 months An electrically triggered pneumatic actuator shall be provided to open and close the test chamber pressure release valve at a speed that provides consistent pressure release rates A second compressed nitrogen gas supply shall be provided to provide a source of pressure for the pneumatic actuator A second pressure gauge and regulator shall be provided to attach directly to the second compressed nitrogen gas cylinder and control the level of pressure used to operate the pneumatic actuator. The regulator shall have an output capacity of at least 250 psi (1500 kpa). The regulator outlet pressure gauge shall have a precision of 0.25 percent of full scale and shall be properly calibrated and certified at least once every 12 months The test chamber assembly shall be mounted on a stand that permits rotation of the pressurization apparatus through all positions necessary for proper operation. 4.3 Drying Oven - The drying oven should allow free circulation of air through the oven and should be capable of maintaining a temperature of 230 o F + 9 o F (110 o C + 5 o C). 4.4 Balance - The balance should conform to the requirements of AASHTO M 231 for the class of general purpose balance required for determining the principal mass of the sample being tested. 5. Special Solutions Required 5.1 A solution of alkylakoxysilane in water (referred to as silane solution) is used in preparing aggregate test samples, as described in section 7.3. Note 4 - Some aggregates absorb water at a very rapid rate, which may prevent them from being fractured by this test. The silane treatment described in section 7.3 reduces the absorption rate by making the aggregates more hydrophobic. This treatment has been demonstrated to have no effect on the hydraulic fracture performance of aggregates with slower absorption rates. Note 5 - An appropriate silane solution is available commercially as Enviroseal 40 from Hydrozo, Inc. Other sources may provide suitable results as well. 5.2 Appropriate precautions should be observed in handling the silane solution. 6. Pressurization Cycle 6.1 Each pressurization cycle consists of pressurizing the water-filled chamber containing the test sample, holding the specified pressure for the specified time (see sections 9.10 and 9.14), and releasing the pressure. 6.2 The pressure release rate must closely match the standard pressure release rate curve presented in Appendix A. It is especially important to achieve a chamber pressure drop of at least 300 psi (2100 kpa) during the first 0.01 second of depressurization. Note 6 Calibration of the test apparatus consists of identifying a pneumatic actuator pressure that results in the desired pressure release rate. A procedure for measuring pressure release rate is described in Appendix A. It may be necessary to modify outlet and valve sizes to achieve the desired release rate curve. Note 7 Each successive pressurization cycle increases the degree of saturation of the aggregate particles. When the particles are saturated, pressurization cycles do not produce significant internal stresses and particle A-3

22 practures. For this reason, a maximum of 10 pressurization cycles can be performed on a given sample on a given day. 7. Test Specimens 7.1 Representative samples of aggregate sources should be obtained by appropriate means and in accordance with accepted procedures such as AASHTO T 2 and ASTM C 702 and D Each aggregate sample to be tested should be screened and split to produce one or more test samples consisting of the desired particle sizes (see section 7.1). The size fraction recommended for indicating D-cracking potential contains only particles retained on the ¾-in (19-mm) sieve. 7.3 Replicate specimens may be run to determine test variability, and sufficient material should be collected in the initial sampling to provide the necessary number of particles in each particle size range being evaluated. Note 8 Research indicates that 600 to 800 coarse aggregate particles must be tested to provide a reasonably accurate estimate of D-cracking potential for a given source. 8. Preparation of Test Specimens 8.1 Obtain a sample of the desired particle size distribution (e.g., ¾-in (19-mm) plus) by sieving to refusal using appropriate wire screens (AASHTO M 92). Individual test samples should contain sufficient quantities of aggregate to fill the pressure chamber. 8.2 The aggregate sample should be washed thoroughly, dried to a constant mass at a temperature of 230 o F + 9 o F (110 o C + 5 o C), and allowed to cool to room temperature. Note 9 - Adequate ventilation should be supplied for the following three steps. The use of a fume hood may be appropriate. 8.3 Place the aggregate sample in the silane solution, making sure that all aggregate particles are submerged. Allow the specimen to remain in the silane solution for seconds. 8.4 Remove the specimen from the silane solution and allow excess solution to drain. Note 10 - Strainers or double boilers suitable for immersing the aggregate in the silane solution and draining are readily obtainable from restaurant supply sources. Note 11 - The silane solution may be re-used if it is placed in a sealed container between uses. The solution should be discarded if it begins to thicken. 8.5 Dry the specimens to a constant mass at a temperature of 230 o F + 9 o F (110 o C + 5 o C), and allow to cool to room temperature. 9. Procedure 9.1 Place enough aggregate in the tumbler to fill it approximately half full. Tumble the aggregate for revolutions of the tumbler. Remove the aggregate from the tumbler and discard any pieces whose size is not within the selected size range (e.g., ¾ 1.5 [19-38 mm]). Repeat until the entire aggregate test sample has been tumbled. A-4

23 9.2 A qualified petrographer should examine the sample to estimate the carbonate content (by percent mass) of the aggregate sample. 9.3 Fill the test chamber with aggregate particles, being careful not to overfill the chamber (which may result in particle fracture due to closure of the chamber rather than due to the hydraulic fracture mechanism). Remove the aggregate from the test chamber and determine the mass of the test sample. Record this number as the initial specimen mass. 9.4 Place the specimen in the pressure chamber; then close and seal the chamber. 9.5 Rotate the apparatus from the filling position (typically horizontal) to the testing (typically vertical) position. 9.6 Close the pressure valve and open the main valve on the nitrogen tank that is used to pressurize the chamber. The pressure regulator for this tank should be set to the pressure indicated on the most recent calibration sheet for the equipment. Note 12 - A chamber test pressure of 1150 psi (7,930 kpa.) is currently recommended. 9.7 Open the main valve on the nitrogen tank that is used to operate the pneumaticallyactuated pressure release valve. The pressure regulator for this tank should be set to the pressure indicated on the most recent calibration sheet for the equipment. 9.8 Connect the fill overflow line to the pressure release line. Open the fill and pressure release valves and fill the pressure chamber with water using the procedures described in the manufacturer s instructions. After the chamber is full and as water is flowing through the chamber and drain line, remove air bubbles from the chamber walls by pivoting the chamber to approximately 45degrees on either side of the testing position and tapping the exterior of the chamber smartly with a rubber mallet. 9.9 After the chamber has been filled and the air bubbles removed, close the pressure release valve and close the fill valve. Remove the fill overflow line from the end of the pressure release valve. This process should be completed in 2 minutes (+ 5 seconds) Ensure that all chamber valves are initially closed. Pressurize the chamber for 5 minutes (+ 5 seconds) by opening the pressure valve. Adjust the pressure regulator as necessary to maintain the required pressure. After about 4.75 minutes, close the pressure valve After about 4.9 minutes of pressurization, close the pressure valve; after 5 minutes (+ 5 seconds) of pressurization, operate the electropnuematically actuated pressure release valve to produce the prescribed pressure release. Note 13 A muffler may be attached to the pressure release line to reduce the noise associated with the explosive decompression of the pressure vessel, provided that it does not prevent the achievement of the target pressure release rate. Appropriate hearing protection should be used during pressure release, especially if a muffler is not used Re-attach the drain line to the pressure release line (which is now open), open the fill valve, and turn on the water supply to refill the chamber with water as before. Allow water to fill for approximately 30 seconds, rotating the chamber to 45 degrees either side of the test position and using the rubber mallet to remove any gas bubbles from the sides of the chamber. Close the pressure release valve, then the fill valve, and remove the drain line Re-pressurize the chamber after a total elapsed time of 1 minute (+ 5 seconds) without pressure. Adjust the regulator as necessary to maintain the desired pressure. A-5

24 9.14 After about 1.9 minutes of pressurization, close the pressure valve; after 2 minutes (+ 5 seconds) of pressurization, operate the electropnuematically actuated pressure release valve to produce the prescribed pressure release Repeat steps 9.12 through 9.14 eight additional times for a total of ten pressurizationdepressurization cycles Rotate the pressure chamber back to the aggregate fill position to drain the chamber and remove the aggregate test sample Close the pressure release valve. Turn off the valve on the nitrogen bottle and open the drain valve. Drain the water from the pressure chamber by slowly opening the pressure valve and allowing the compressed gas in the line to force water out of the chamber. Close the drain valve when draining is complete Open the chamber and remove the test sample. Dry the specimen to a constant mass at a temperature of 230 o F + 9 o F (110 o C + 5 o C), and allow it to cool at room temperature Place enough aggregate in the tumbler to fill it approximately half full. Tumble the aggregate for 30 (+ 5) revolutions. Remove the aggregate from the tumbler, retaining all particles. Repeat until the entire aggregate test sample has been tumbled Sieve the sample and determine (to the nearest 0.1g) the masses retained on the ¾-in (19.0-mm), 5/8-in (16.0-mm), ½-in (12.5-mm), 3/8-in (9.5-mm), 5/16-in (8-mm), ¼-in (6.25- mm) and #4 (4.75-mm) sieves. Record these values. Remove all particles passing the #4 (4.75- mm) sieve from the testing procedure, determine their mass to the nearest tenth of a gram, and save in a labeled container Repeat Steps 9.4 through 9.20 for a total of 50 pressurization cycles per test sample If necessary, test replicate samples of the same aggregate source until a sufficient quantity of material has been tested to provide a reasonably accurate estimate of coarse aggregate D-cracking potential (currently considered to be aggregate particles, about 33 lbs of ¾- 1.5-in coarse aggregate). 10. Calculation 10.1 Determine the combined mass of particles retained on the ¾-in (19.0-mm), 5/8-in (16.0- mm), ½-in (12.5-mm), 3/8-in (9.5-mm), 5/16-in (8-mm), ¼-in (6.25-mm) and #4 (4.75-mm) sieves along with the mass of all particles passing the #4 (4.75-mm) sieve after 50 cycles of pressurization for all replicate test samples representing a given aggregate source Estimate the dilation that would occur in a concrete prism containing this aggregate source and tested using AASHTO TP17 using the following equation: % Dil/100 cycles = C 3 *(6.7147E E-9*M 3/4 in E-7*M 5/8 in where: C E-7*M 1/2 in E-7*M 3/8 in E-6*M 5/16 in E-6*M 1/4 in E-7*M #4 ) = Carbonate content of source, percent; M 3/4 in = Cumulative percentage of mass passing the ¾-in (19.0-mm) screen = 100 Percentage of original mass retained on the ¾-in (19.0-mm) screen; A-6

25 M 5/8 in M 1/2 in M 3/8 in = Cumulative percentage of mass passing the 5/8-in (16.0-mm) screen = M 3/4 in Percentage of original mass retained on the 5/8-in (16.0-mm) screen; = Cumulative percentage of mass passing the ½-in (12.50-mm) screen = M 5/8 in Percentage of original mass retained on the ½-in (12.50-mm) screen; = Cumulative percentage of mass passing the 3/8-in (9.50-mm) screen = M 1/2 in Percentage of original mass retained on the 3/8-in (9.50-mm) screen; M 5/16 in = Cumulative percentage of mass passing the 5/16-in (8.00-mm) screen = M 3/8 in Percentage of original mass retained on the 5/16-in (8.00-mm) screen; M 1/4 in M #4 = Cumulative percentage of mass passing the ¼-in (6.35-mm) screen = M 5/16 in Percentage of original mass retained on the ¼-in (6.35-mm) screen; = Cumulative percentage of mass passing the #4 (4.75-mm) screen = M 1/4 in Percentage of original mass retained on the #4 (4.75-mm) screen Apply appropriate acceptance or rejection criteria to the results of the analysis to determine the suitability of the given aggregate source or to suggest the need for additional or supplemental testing using this or other tests of concrete coarse aggregate freeze-thaw damage potential (e.g., ASTM C 666/AASHTO T161 or TP17, etc.). Note 14 It is not uncommon to use 0.04 percent dilation per 100 cycles of freeze-thaw testing as the maximum acceptable value based on AASHTO T 161 and ASTM C 666 tests. 11. Report 11.1 Test reports shall include, as a minimum, the following information and data: 11.2 Sample Identification: Report the person or agency submitting the sample for testing List the source or identifying code for the aggregate sample Initial Sample Parameters: Report the particle size range tested Report the estimated carbonate content of the sample, as determined in section 9.2 above Report the initial mass of the sample, as determined in section 9.3 above Mass Retained Report the mass retained on each required sieve and pan after each series of ten pressurization cycles When multiple specimens are tested from the same source and particle size range, report both individual and combined specimen values Predicted Dilation/100 Cycles Report the predicted dilation per 100 cycles computed using the test data and the model presented in section When multiple specimens are tested from the same source and particle size range, report both individual and combined specimen values. A-7

26 12. Precision and Bias 12.1 Sufficient data for precision and bias statements are not currently available. 13. Keywords 13.1 accelerated testing; concrete-weathering tests; conditioning; freezing and thawing; resistance-frost A-8

27 Appendix A. Calibration of the Hydraulic Fracture Test Apparatus The Hydraulic Fracture Test (HFT) apparatus must be operated in a manner that produces aggregate fracture rates that are consistent with those that were used in the development of the dilation prediction model. Previous research 1-3 has found that aggregate fracture rates useful in durability prediction can be obtained consistently by controlling the rate of release of pressure from the test chamber. Higher pressure release rates correspond with higher fracture rates. Therefore, the parameter used to calibrate the HFT apparatus is the maximum pressure release rate, computed over and plotted against various time intervals. Generation of a maximum pressure release rate vs. time interval graph or profile begins with measurement of chamber pressure vs. time during the pressure release event. Pressure release rates can be monitored using an appropriate chamber-mounted pressure transducer with a dynamic signal analyzer. Chamber pressure during the release event should be sampled at a rate of approximately 500 Hz (i.e., one pressure measurement every seconds). The data are then used to compute the average pressure release rate (psi/sec) during each second time interval and the highest rate is selected and recorded as the maximum pressure release rate over a second time interval. This analysis process is repeated for successively larger time intervals (e.g., seconds, seconds, etc.), and the maximum pressure release rate for each time interval is plotted against the respective time intervals. Figure A1 presents the plot of maximum pressure release rate vs. time interval that was used to calibrate the test apparatus used in developing the current dilation prediction model. Table A1 summarizes the data used to create Figure A1. Previous research 1-3 indicates that it is most important to match the target maximum pressure release rate profile at 0.01 seconds, although the overall maximum pressure release profile should closely resemble that of the target. Release rates can be varied most easily by modifying the pressure used to operate the actuator that opens the pressure release valve, with higher actuator pressure corresponding to faster release rates. Release rates can also be accomplished by modifying the test chamber plumbing (i.e., modifying pressure release port sizes, pipe and valve sizes, etc.) and/or chamber operating pressure (although pressures less than 1150 psi may not produce aggregate fractures and pressures significantly higher than 1150 psi may produce too much aggregate fracture). Maximum pressure release rate profiles for each actuator pressure setting (or chamber modification) can then be compared with the target curve as shown in Figure A2. The pressure settings and/or chamber configurations that produce the maximum release rate profile closest to the target profile should be selected for test operation (actuator pressure of 145 psi in the example shown in Figure A2). A-9

28 Target Pressure Release Rate Profile for Calibrating HFT Apparatus (from original University of Washington HFT Apparatus) Release Rate, psi/sec Time Interval, sec Figure A1. HFT apparatus calibration target pressure release rate curve. Table A1. HFT Apparatus Calibration Target Pressure Release Rate Data Table Time Interval (sec) Max Pressure Release Rate (psi/sec) Time Interval (sec) Max Pressure Release Rate (psi/sec) Time Interval (sec) Max Pressure Release Rate (psi/sec) A-10

29 Release Rate (psi/sec) Time (sec) U Wash 90 psi 100 psi 120 psi 140 psi 145 psi 150 psi Figure A2. Example plot of pressure release rate profiles for various actuator pressure settings. References 1. M. B. Snyder, D. J. Janssen and W. Hansen, Adoption of a Rapid Test for Determining Aggregate Durability in Portland Cement Concrete (Ann Arbor, MI: University of Michigan Department of Civil Engineering, 1996). 2. J. J. Hietpas, Refinement and Validation of the Washington Hydraulic Fracture Test (Minneapolis, MN: University of Minnesota Department of Civil Engineering, 1998). 3. R. A. Embacher and M. B. Snyder, Refinement and Validation of the Hydraulic Fracture Test (St. Paul, MN: Minnesota Department of Transportation, 2003). A-11

30 A-12

31 APPENDIX B Hydraulic Fracture Test Protocol

32

33 Assembling and Operating the MnDOT Hydraulic Fracture Test Apparatus: A Test Protocol for Operators Description of Parts Large Chamber The large chamber apparatus for the Washington Hydraulic Fracture Test consists of a number of individual pieces. Cylinder Assembly -The cylinder assembly includes the cylinder portion of the pressure chamber containing the valves and fittings, along with the attached pivot collar and stand. The cylinder portion has a machined channel for the O-ring seal (called an O-ring channel) on each end. The "bottom" of the cylinder is the end closest to the three sets of valves and fittings. A handle is attached to the pivot shaft on one side of the stand. A locking bolt or rod on the handle can be pushed in to engage one of three positioning holes in the stand when required to prevent the cylinder assembly from rotating. The large chamber cylinder assembly is shown in figure B1. Figure B1. Photos of large chamber cylinder assembly. O-Rings - Two O-rings are used to seal the pressure chamber when it is assembled and pressurized. The O-rings should be regularly inspected for cuts and embedded rock particles. The O-rings should be replaced when necessary. End Plates - Two interchangeable end plates (with or without handles) complete the pressure chamber portion of the apparatus. B-1

34 High-Strength Bolts - Sixteen high-strength bolts are used to hold the end plates to the cylinder. These bolts are tightened to approximately 60 to 80 inch-pounds (6.8 to 9.0 newton-meters). Assembly Rods - Two 3/4-in (19-mm) diameter threaded rods, 14 in (356 mm) long, are used to assemble the pressure chamber. Each rod has holes located approximately 5 in (125 mm) from each end through which ¼-in (6-mm) diameter rods or cotter pins are inserted during the assembly process. Pressure Regulator No. 1 - A pressure regulator ( psi outlet pressure) with inlet and outlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder (user-supplied) and connects to the pressure chamber via a flexible pressure line, as shown in figure B2. Pressure Regulator No. 2 - A pressure regulator (0-300 psi outlet pressure) with inlet and outlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder (user-supplied) and connects to the pneumatic actuator (attached to the pressure chamber via a flexible pressure line, as shown in figure B2. Figure B2. Photos of chamber pressure regulator and gages (left) and actuator pressure regulator and gages (right). Drain Line - A flexible plastic water line connects to the pressure chamber (through a quick-connect fitting) and leads to a free end at a water drain, as shown in figure B3. Water Fill Line - A flexible plastic water line connects the pressure chamber to a water source. The water line connection should comply with local plumbing codes and regulations, as shown in figure B4. B-2

35 Figure B3. Photo of large chamber with drain line attached to quick connect fitting. The specific valve and fitting assemblies are described below: Fill Assembly - This assembly consists of a brass T connection. One leg of the T connects to the fill valve and the connection to the water line. The second leg attaches to the pressure vessel. The third leg houses the pressure transducer that is used in calibrating the apparatus. The fill assembly is shown in figure B4. Figure B4. Large chamber fill valve assembly. Fill Valve - This is a ball valve with a black lever handle and is the only valve on one side of the bottom of the pressure chamber. Opening and closing are accomplished by 90-degree turns. Occasional maintenance includes replacing worn or damaged O-rings on the valve plug, and applying a thin film of silicone grease when the valve is reassembled. B-3

36 Water Line Connection A serrated brass nozzle fitting attaches to the fill valve through a standard threaded connection. The plastic water line slides over the nozzle and is secured with a worm clamp. Pressure Transducer Assembly A small pressure transducer is installed in a stainless steel adapter, which is, in turn, installed in the bottom leg of the fill assembly T connector. Details concerning the pressure transducer are provided in the list of vendors at the end of this document. Pressurization and Drainage Assembly - This assembly includes three valves and connections for pressurization and depressurization as well as chamber drainage. This assembly can be seen in figure B3. Pressure Isolation Valve - This is a ball valve with a black lever handle located between the chamber and the flexible nitrogen pressure line. Maintenance for this valve consists of periodically tightening the packing around the ball whenever a leak develops. This is accomplished by removing the lever handle (which is attached with a set-screw) and using a wrench to tighten the two-sided nut exposed under the handle. The nut should be tightened in 1/16th turns until leaking stops. Pressure Release Valve - This is a ball valve located beneath and operated by the pressure-driven actuator; there is no handle accessible to the operator. Maintenance is the same as for the pressure isolation valve described above. Electrically-operated Pneumatic Actuator The pneumatic actuator mounts on and operates the valve stem for the pressure release valve. The actuator turns the valve stem 90 degrees in either direction through bursts of pressurized nitrogen gas that are triggered by a standard two-pole electrical power switch. Pressure Release Connector - This is the female half of a quick-connect assembly. The drain line is connected here (using the male half of a quick-connect assembly) while the pressure chamber is being filled with water. For pressure release, the drain line is disconnected and a muffler (optional) can be connected to reduce the noise of chamber decompression. Drain Valve - This valve is located to the right of the pressure release assembly (when viewing the chamber from the top). It is identical to the fill valve described previously. Drain Line Connection The large chamber drain line connects the drain valve to the pressure release line at a point past the pressure release valve. Description of Parts Small Chamber The small chamber apparatus for the Washington Hydraulic Fracture Test consists of a number of individual pieces. B-4

37 Cylinder Assembly -The cylinder assembly includes the cylinder portion of the pressure chamber containing the valves and fittings. The cylinder has a machined channel for an O-ring seal (called an O-ring channel) on each end. The "bottom" of the cylinder is the end closest to the internal drain tube inlet (described below). The small chamber cylinder assembly is shown in figure B5. Figure B5. Photos of small chamber cylinder assembly (top plate removed) and stand. O-Rings - Two O-rings are used to seal the pressure chamber when it is assembled and pressurized. The O-rings should be regularly inspected for cuts and embedded rock particles. The O-rings should be replaced when necessary. End Plates There are two end plates, each with a replaceable neoprene pad centered on the interior face. The bottom end plate is attached to a pivot assembly, which attaches to the test stand through a pair of pivot shafts. A handle is attached to the pivot shaft on one side of the stand. A locking bolt or rod on the handle can be pushed in to engage one of three positioning holes in the stand when required to prevent the cylinder assembly from rotating. The top end plate has a handle to facilitate chamber assembly. B-5

38 High-Strength Bolts - Sixteen high-strength bolts (approximately 5 inches [125 mm] in length) are used to assemble the small chamber assembly. These bolts are tightened to approximately 60 to 80 inch-pounds (6.8 to 9.0 newton-meters). Pressure Regulator No. 1 - A pressure regulator ( psi outlet pressure) with inlet and outlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder (user-supplied) and connects to the pressure chamber via a flexible pressure line, as shown previously in figure B2. Pressure Regulator No. 2 - A pressure regulator (0-300 psi outlet pressure) with inlet and outlet pressure gages attaches directly to a high-pressure compressed nitrogen cylinder (user-supplied) and connects to the pneumatic actuator (attached to the pressure chamber via a flexible pressure line, as shown previously in figure B2. Overflow Line - A flexible plastic water line connects to the pressure chamber (through a quick-connect fitting) and leads to a free end at a water drain, as shown previously in figure B3. Drain Line - A flexible plastic water line fits over a serrated brass nozzle fitting that is attached to the drain valve through a standard threaded connection. One end of the water line is secured to the nozzle with a worm clamp and the other end is placed near a water drain. Water Fill Line - A flexible plastic water line connects the pressure chamber to a water source. The water line connection should comply with local plumbing codes and regulations. The specific valve and fitting assemblies are described below: Fill Assembly - This assembly consists of a brass T connection. One leg of the T connects to the fill valve and the connection to the water line. The second leg attaches to the pressure vessel. The third leg houses the pressure transducer that is used in calibrating the apparatus. The fill assembly is shown in figure B6. Fill Valve - This is a plug valve with a small green lever handle and is the only valve on one side of the pressure chamber. Opening and closing are accomplished by 90-degree turns. Occasional maintenance includes replacing worn or damaged O-rings on the valve plug, and applying a thin film of silicone grease when the valve is reassembled. Water Line Connection A serrated brass nozzle fitting attaches to the fill valve through a standard threaded connection. The plastic water line slides over the nozzle and is secured with a worm clamp. B-6

39 Figure B6. Small chamber fill valve assembly. Pressure Transducer Assembly A small pressure transducer is installed in a stainless steel adapter, which is, in turn, installed in the bottom leg of the fill assembly T connector. Details concerning the pressure transducer are provided in the list of vendors at the end of this document. Pressurization Assembly - This assembly includes two valves and connections for pressurization and depressurization. This assembly can be seen in figure B7. Figure B7. Photo of small chamber pressurization and drain assemblies. Pressure Isolation Valve - This is a ball valve with a black lever handle located between the chamber and the flexible nitrogen pressure line. Maintenance for this valve consists of periodically tightening the packing around the ball whenever a leak develops. This is accomplished by removing the lever handle (which is attached with a set-screw) and using a wrench to tighten the two-sided nut exposed under the handle. The nut should be tightened in 1/16th turns until leaking stops. B-7

40 Pressure Release Valve - This is a ball valve located beneath and operated by the pressure-driven actuator; there is no handle accessible to the operator. Maintenance is the same as for the pressure isolation valve described above. Electrically-operated Pneumatic Actuator The pneumatic actuator mounts on and operates the valve stem for the pressure release valve. The actuator turns the valve stem 90 degrees in either direction through bursts of pressurized nitrogen gas that are triggered by a standard two-pole electrical power switch. Pressure Release Connector - This is the female half of a quick-connect assembly. The drain line is connected here (using the male half of a quick-connect assembly) while the pressure chamber is being filled with water. For pressure release, the drain line is disconnected and a muffler (optional) can be connected to reduce the noise of chamber decompression. Drain Valve Assembly - This assembly includes one valves and connection for chamber drainage following testing. This assembly can also be seen in figure B7. Drain Valve - This valve is located to the left of the pressure release assembly (when viewing the chamber from the top). It is identical to the fill valve described previously. Drain Tube This is a small copper tube that is mounted over the drain outlet on the inside of the pressure vessel, as shown in figure B8. This tube is bent so that the inlet end of the tube nearly touches the bottom end plate when the chamber is assembled. This assists in draining water to very near the bottom of the chamber prior to disassembly. Drain Line Connection The small chamber drain line connects the drain valve to the drain line, which leads to an open end (to be placed near a water drain). Figure B8. Photo of drain valve assembly, including drain tube on inside of chamber. B-8

41 Sample Preparation The following steps describe procedures for obtaining and preparing aggregate samples prior to testing them in the hydraulic fracture test apparatus. 1. Obtain a coarse aggregate sample using standard sampling techniques to ensure that the sample is representative of material that will be used in concrete production. If various ledges of a particular quarry or various areas of a given pit will be used, separate samples must be obtained and tested from each ledge or area. 2. The sample size must be large enough to produce at least 40 lbs of ¾-in plus material, plus whatever additional material is required for companion tests (for example, sulfate soundness, absorption capacity, freeze-thaw beams, etc.). 3. The HFT test sample should be obtained by splitting the original sample as necessary and sieving to refusal over a ¾-in (19-mm) sieve. The HFT sample should weigh at least 40 lbs before proceeding further. 4. The aggregate sample should be washed thoroughly (until water runs clear from the aggregate washer), dried to a constant mass (usually about hours) at a temperature of 230oF + 9oF, and allowed to cool to room temperature (see figure B9). Figure B9. Aggregate washer and oven in MnDOT concrete lab. 5. The water-based silane solution should be placed in a double boiler in an area with good ventilation, such as under or within a fume hood (as shown in figure B10). 6. Place the aggregate sample in the strainer portion of the double boiler that contains the silane solution. Lower the strainer into the silane solution, making sure that all aggregate particles are submerged. It may be necessary to split the B-9

42 sample into smaller portions for proper treatment coverage. Allow the specimen to remain in the silane solution for 30 seconds. 7. Remove the specimen from the silane solution and allow excess solution to drain (as shown in figure B10). Figure B10. Photos of double boiler and silane under MnDOT fume hood and treated sample draining in double boiler. 8. The silane solution should be placed in a sealed container between uses and should be discarded if it begins to thicken. 9. Dry the sample to a constant mass (usually hours) at a temperature of 230oF + 9 of, and allow it to cool to room temperature. 10. Place enough aggregate in an aggregate tumbler to fill it approximately half full. Tumble the aggregate for revolutions of the tumbler. Remove the aggregate from the tumbler, screen the sample over the ¾-in sieve and discard any pieces passing the sieve. Repeat until the entire aggregate test sample has been tumbled. Figure B11. Photos of typical aggregate tumbler with sample in drum (left) and large tumbler in MnDOT lab (right). B-10

43 11. A qualified petrographer should examine the sample to estimate the carbonate content (by percent mass) of the aggregate sample and to ensure that the aggregate does not contain significant quantities (e.g., more than 1% by weight) of chert. 12. Fill the test chamber with aggregate particles, being careful not to overfill the chamber (which may result in particle fracture due to closure of the chamber rather than due to the hydraulic fracture mechanism). Remove the aggregate from the test chamber and determine the mass of the test sample. Record this number as the initial specimen mass. 13. The specimen is now ready for testing. Extreme care must be taken from this point forward to avoid losing aggregate particles due to mishandling or any other process other than the hydraulic fracture mechanism. Large Chamber Assembly The pressure chamber is assembled by the following steps: 1. Rotate the pressure cylinder to the inverted position (bottom of cylinder up) and lock it in this position. Clean the bottom O-ring channel and remove and dirt, dust or rock chips. Place an O-ring in the channel. 2. Place an end plate on the bottom of the cylinder and visually align the holes in the end plate with the holes in the pivot collar surrounding the cylinder. 3. With a nut turned onto one end of an assembly rod, insert the assembly rod through one of the holes in the end plate and the corresponding hole in the pivot collar. Insert an assembly or cotter pin into the hole in the assembly rod on side of the pivot collar furthest from the plate. Repeat this procedure with the second assembly rod, using the hole in the end plate that is directly opposite the one used for the first assembly rod. Finger-tighten the nuts on each of the assembly rods as shown in figure B Rotate the pressure cylinder right-side up and lock it in position. If a test of aggregate durability is to be performed, place the aggregate specimen into the pressure cylinder. The large chamber will accommodate approximately 33 lbs (15 kg) of typical aggregate. Use a strike-off bar to ensure than no aggregate particles protrude above the top of the chamber where they could be crushed during assembly, as shown in figure B12. (If a chamber calibration is to be performed, there is no need to fill the chamber with aggregate. Assemble the chamber empty and follow instructions for calibration.) B-11

44 Figure B12. Assembly of large chamber bottom plate and fill with aggregate sample, including strike-off. 5. Clean the top O-ring channel and install an O-ring. Place the remaining base plate over the protruding ends of the assembly rods and onto the pressure cylinder. 6. (Optional) Place a nut on each of the protruding assembly rod ends and fingertighten. Pivot the pressure chamber 90 degrees into the test position and continue assembly. 7. Insert 14 of the bolts into the holes in one of the base plates, through the pivot collar, and through the other base plate. Place nuts on all of the bolts and fingertighten them. 8. Remove the assembly rods, place the remaining two bolts in the holes vacated by the assembly rods, and place the remaining nuts on the remaining bolts. 9. Tighten all of the nuts to in-lbs ( N-m) using the following pattern to ensure uniform compression of the O-rings: Tighten two nuts on opposite sides of the pressure cylinder (nuts 1 and 9, if the nuts are numbered consecutively around the cylinder). Next, tighten the nuts on each side and midway between the nuts already tightened (e.g., nuts 5 and 13). Next tighten the halfway between those already tightened (e.g., nuts 3, 7, 11, and 15). Then tighten the remaining nuts. It will probably be necessary to complete this tightening pattern at least twice because the nuts tightened first will often B-12

45 develop some looseness as subsequent nuts are tightened and the O-rings are compressed. Figure B13. Removal of large chamber assembly pins and tightening of assembly bolts. Small Chamber Assembly The small pressure chamber is assembled by the following steps: 1. Rotate the bottom end plate to a vertical position (perpendicular to the floor). 2. Clean the O-ring channels of the pressure cylinder, removing all dirt, dust or rock chips. Place an O-ring in the bottom channel. 3. Place the pressure cylinder against the bottom end plate, making sure that the Oring remains properly seated in the channel between the cylinder and end plate. 4. While holding the cylinder in place, rotate the cylinder-bottom plate assembly to the horizontal position (parallel to the floor) and lock it in place. Verify that the cylinder and O-ring are properly seated against the bottom plate. 5. Rotate the cylinder on the end plate as needed to ensure that no valve assemblies block the bolt holes. 6. If a test of aggregate durability is to be performed, place the aggregate specimen into the pressure cylinder. The small chamber will accommodate approximately 7 lbs (3 kg) of typical aggregate. Use a strike-off bar to ensure than no aggregate particles protrude above the top of the chamber where they could be crushed B-13

46 during assembly. (If a chamber calibration is to be performed, there is no need to fill the chamber with aggregate. Assemble the chamber empty and follow instructions for calibration.) Figure B14. Small chamber, ready to be filled with aggregate sample. 7. Clean the top O-ring channel and install an O-ring. Place the top end plate on the pressure cylinder and visually align the holes with those in the pivot assemblies and bottom base plate. 8. Insert the 16 high-strength through the holes in the bottom base plate, through the pivot assemblies (where necessary), and through the other base plate. Place nuts on all of the bolts and finger-tighten them. 9. Tighten all of the nuts to in-lbs ( N-m) using the following pattern to ensure uniform compression of the O-rings: Tighten two nuts on opposite sides of the pressure cylinder (nuts 1 and 9, if the nuts are numbered consecutively around the cylinder). Next, tighten the nuts on each side and midway between the nuts already tightened (e.g., nuts 5 and 13). Next tighten the halfway between those already tightened (e.g., nuts 3, 7, 11, and 15). Then tighten the remaining nuts. It will probably be necessary to complete this tightening pattern at least twice because the nuts tightened first will often develop some looseness as subsequent nuts are tightened and the O-rings are compressed. B-14

47 Figure B15. Tightening of small chamber assembly bolts. Large Chamber HFT Apparatus Operation The following instructions assume that the chamber has already been charged with aggregate, completely assembled and is rotated into the horizontal testing position (i.e., end plates are positioned on their edges, the pressure release assembly is on top and the fill line is on the bottom). 1. If the apparatus has not been used in the past 30 minutes, warm up the pressure release valve by turning the electrical switch on and off 20 times. 2. Attach the drain line to the pressure release connector. 3. Open the fill and pressure release valves and fill the chamber with water by turning on the water source (see figure B16). 4. After the chamber is full (overflow water is coming out of the drain line that is connected to the pressure release valve), fill the copper drain pipe by briefly opening the drain valve until a small amount of water comes out. Close the drain valve. B-15

48 Figure B16. Connecting the drain/overflow line (left) and opening the fill valve (right). 5. Remove any air bubbles in the pressure chamber by pivoting the chamber back and forth, leaving the bottom end (the end closest to the valves and fittings) slightly higher than the top end. While pivoting the chamber, use a rubber mallet to sharply rap the end plates to dislodge trapped air bubbles (see figure B17). Figure B17. Removing trapped air bubbles using rubber mallet. 6. Close the pressure release valve, close the fill valve and disconnect the drain line. All valves on the chamber should be shut. The chamber is now ready for pressurization. B-16

49 7. If it has not already been done, open the valves on the top of the compressed nitrogen cylinders. The pressure regulators for these tanks should be set to the pressures indicated on the most recent calibration sheet for the equipment. 8. Pressurize the chamber by fully opening the chamber pressure valve with a 90degree turn and simultaneously start the timer or stop watch. The first pressurization cycle for each sample on each day of testing lasts 5 minutes while the remaining 9 cycles each day last 2 minutes (see figure B18). 9. (Optional) Install the muffler (see figure B18). Figure B18. Pressurization of chamber (left) and installation of muffler (right). 10. A few seconds before the end of the pressurization cycle, close the pressure isolation valve. At the end of the pressurization cycle, release the chamber pressure by flipping the electric switch that controls the pneumatic actuator (See figure B19). Note: it is advisable to wear hearing protection if a muffler is not used during depressurization. 11. Remove the muffler (if used) and repeat steps 2 through 10 until 10 pressurization-depressurization cycles have been completed. 12. After 10 pressurization-depressurization cycles have been completed, remove the muffler (if used) and attach the drain/overflow line to the quick-release connector. 13. Pivot the pressure chamber back to the upright position (bottom plate parallel to the floor) and lock the chamber in this position. 14. Use the electrically-operated pneumatic actuator to close the pressure release valve. Open the drain valve (see figure B20). B-17

50 Figure B19. Pressure release operation: close pressure isolation valve, then flip electric switch. Figure B20. Opening the large chamber drain valve. B-18

51 15. Close the valve on the nitrogen cylinder. Slowly open the pressure isolation valve to allowing the gas pressure remaining in the line to force the water out of the pressure chamber. 16. If necessary, close the pressure isolation valve, open the valve on the nitrogen cylinder to repressurize the pressure line, and then close the valve on the nitrogen cylinder. Slowly open the pressure isolation valve. Repeat this process until mostly gas (and little water) is passing through the drain/overflow line. 17. When all the water has been removed from the pressure chamber, close the pressure isolation valve. 18. (Optional) Pivot the chamber to the sideways position. 19. Remove two bolts on opposite sides of the pressure chamber and replace them with assembly rods. Insert the assembly/cotter pins into the holes in the assembly rods on the top side of the pivot flange. 20. Finger tighten nuts on the assembly rods (on both ends if the sideways position is being used). 21. Loosen the nuts on the remaining bolts and remove the bolts. 22. If necessary, rotate the chamber back to the upright position and remove the nuts on the top ends of the assembly rods. 23. Remove the top end plate. 24. Take the O-ring out of the top O-ring channel. 25. Remove the aggregate specimen from the pressure chamber. Continue processing the aggregate as described in Specimen Testing Summary below. 26. Clean both the O-ring and the top O-ring channel. 27. Invert the pressure cylinder, loosen the remaining nuts on the assembly rods, remove the assembly pins, and remove the assembly rods. 28. Remove the bottom base plate and clean the inside faces of both base plates. 29. Remove the bottom O-ring from the O-ring channel, and clean the O-ring and the O-ring channel. 30. If no further testing is to be performed, thoroughly dry the chamber (inside and out, especially in the O-ring channels) and end plate surfaces. Store the parts in a manner that will permit further air-drying to minimize the formation of rust. B-19

52 Small Chamber HFT Apparatus Operation The following instructions assume that the chamber has already been charged with aggregate, completely assembled and is rotated into the testing position (i.e., end plates are positioned on their edges, the pressure release assembly is on top and the fill line is on the bottom). 1. If the apparatus has not been used in the past 30 minutes, warm up the pressure release valve by turning the electrical switch on and off 20 times. 2. Attach the fill overflow line to the pressure release connector (see figure B21). Figure B21. Attaching the fill overflow line (left) and opening the fill valve (right). 3. Open the fill and pressure release valves and fill the chamber with water by turning on the water source. 4. After the chamber is full (overflow water is coming out of the line that is connected to the pressure release valve), fill the drain valve assembly with water by briefly opening the drain valve until a small amount of water comes out. Close the drain valve. 5. Remove any air bubbles in the pressure chamber by pivoting the chamber back and forth. While pivoting the chamber, use a rubber mallet to sharply rap the end plates to dislodge trapped air bubbles, as shown in figure B Close the pressure release valve, close the fill valve and disconnect the overflow line (see figure B23). All valves on the chamber should be shut. The chamber is now ready for pressurization. B-20

53 Figure B22. Dislodging attached air bubbles from the inside of the small chamber. Figure B23. Closing the pressure release valve and fill valve (left) and removing the fill overflow line (right). B-21

54 7. If it has not already been done, open the valves on the top of the compressed nitrogen cylinders. The pressure regulators for these tanks should be set to the pressures indicated on the most recent calibration sheet for the equipment. 8. Pressurize the chamber by fully opening the chamber pressure valve with a 90degree turn and simultaneously start the timer or stop watch. The first pressurization cycle for each sample on each day of testing lasts 5 minutes while the remaining 9 cycles each day last 2 minutes (see figure B24). 9. (Optional) Install the muffler (see figure B24). Figure B24. Closing the pressure release valve and fill valve (left) and removing the fill overflow line (right). 10. A few seconds before the end of the pressurization cycle, close the pressure isolation valve. At the end of the pressurization cycle, release the chamber pressure by flipping the electric switch that controls the pneumatic actuator (see figure B25). Note: it is advisable to wear hearing protection if a muffler is not used during depressurization. 11. Remove the muffler (if used) and repeat steps 2 through 10 until 10 pressurization-depressurization cycles have been completed. 12. After 10 pressurization-depressurization cycles have been completed, remove the muffler (if used) and attach the drain/overflow line to the quick-release connector. 13. Pivot the pressure chamber back to the upright position (bottom plate parallel to the floor) and lock the chamber in this position. 14. Use the electrically-operated pneumatic actuator to close the pressure release valve. Open the drain valve. B-22

55 Figure B25. Release of pressure from small chamber by closing pressure isolation valve, then flipping electric switch. 15. Close the valve on the nitrogen cylinder. Slowly open the pressure isolation valve to allowing the gas pressure remaining in the line to force the water out of the pressure chamber (see figure B26). Figure B26. Removing water from small chamber by closing pressure release valve and nitrogen bottle valve, opening drain valve and slowly opening pressure isolation valve. B-23

56 16. If necessary, close the pressure isolation valve, open the valve on the nitrogen cylinder to repressurize the pressure line, and then close the valve on the nitrogen cylinder. Slowly open the pressure isolation valve. Repeat this process until mostly gas (and little water) is passing through the drain/overflow line. 17. When all the water has been removed from the pressure chamber, close the pressure isolation valve. 18. Loosen the nuts on the chamber assembly bolts and remove the bolts. 19. Remove the top end plate. 20. Take the O-ring out of the top O-ring channel. 21. Remove the aggregate specimen from the pressure chamber. Continue processing the aggregate as described in Specimen Testing Summary below. 22. Remove the pressure cylinder and clean both O-rings and O-ring channels. 23. If no further testing is to be performed, thoroughly dry the chamber (inside and out, especially in the O-ring channels) and end plate surfaces. Store the parts in a manner that will permit further air-drying to minimize the formation of rust. Specimen Testing Summary Sampling and Specimen Preparation Aggregate sampling and specimen preparation should be performed as described in Sample Preparation above. Key points include: Good sampling techniques must be used to ensure that the sample obtained is representative of material that will be used in concrete production. The sample obtained must contain at least 33 lbs ( particles) of ¾-in plus material for hydraulic fracture testing, plus any additional material required for companion tests (such as magnesium sulfate testing, absorption capacity, freezethaw beams, etc.). If various ledges of a particular quarry or various areas of a given pit will be used, separate samples must be obtained and tested from each ledge or area. The aggregate sample should be washed thoroughly, then dried to a constant mass. The sample is then soaked in a water-based silane solution for 30 seconds, drained and again dried to a constant mass. The sample is then placed in an aggregate tumbler, which is operated for 30 revolutions. Upon removal, the aggregate is screened over the ¾-in sieve and the particles that pass the sieve are discarded. A qualified petrographer should examine the sample to estimate the carbonate content (by percent mass) of the aggregate sample and to ensure that the B-24

57 aggregate does not contain significant quantities (e.g., more than 1% by weight) of chert. The test chamber should then be filled (but not overfilled) with aggregate particles to determine the size of the test sample. The aggregate is then removed and weighed to determine the initial mass of the test specimen. Extreme care must be taken from this point forward to avoid losing aggregate particles due to mishandling or any other process other than the hydraulic fracture mechanism. Testing Procedures The hydraulic fracture test process consists of two parts: the pressurizationdepressurization cycles, and the post-pressurization sieving and mass measurement. The steps involved in completing the test are described below: 1. A total of 50 pressurization-depressurization cycles are performed at a rate of 10 per day over five days of testing. Detailed procedures for performing the pressurization cycles are described for each of the available pressure chambers in sections titled Large Chamber HFT Apparatus Operation and Small Chamber HFT Apparatus Operation. th 2. After the 10 pressurization cycle for any particular test specimen on any particular day, the sample must be removed from the test chamber (taking care to remove all aggregate particles) and dried to a constant weight (typically hours in an oven operating at 230oF + 9oF). 3. After the aggregate has cooled, place enough aggregate in an aggregate tumbler to fill it approximately half full. Tumble the aggregate for revolutions of the tumbler. Remove the aggregate from the tumbler being careful not to lose any particles or pieces. Repeat until the entire aggregate test sample has been tumbled. 4. Sieve the sample and determine (to the nearest 0.1g) the masses retained on the ¾-in, 5/8-in, ½-in, 3/8-in, 5/16-in, ¼-in and #4 sieves. Record these values on the standard data collection sheet provided (see figure B27). Determine and record the mass of all particles found in the pan and save these particles in a labeled baggie or other container. 5. All particles retained on any of the sieves must be returned to the test apparatus for 10 additional pressurization cycles (unless the sample has already been subjected to 50 pressurization cycles; in this case, the testing is complete). Data Reporting, Data Entry and Calculations (All Chambers and Devices) All data are initially recorded manually on a standard data collection form (see figure B27), which includes entry spaces for aggregate source and sample identification, sample submittal and testing dates, estimated carbonate content, initial test sample mass and masses retained on each sieve after each 10 cycles of testing. Data can be recorded on a single sheet for up to 5 samples from each aggregate source. The data can be transferred to an Excel spreadsheet titled HFT Data Entry and Analysis.xls. This spreadsheet automatically performs all calculations necessary to B-25

58 HFT Data Collection Sheet Replicate Number Silane Treatment Date Initial Mass, g Test Date: Test Date: M3/4" (ret), g M 3/4" (ret), g M5/8" (ret), g M 5/8" (ret), g M1/2" (ret), g M 1/2" (ret), g M3/8" (ret), g 10 Cycles M5/16" (ret), g 20 Cycles 1 40 Cycles M 3/8" (ret), g M 5/16" (ret), g M1/4" (ret), g M 1/4" (ret), g M#4 (ret), g Mpan, g M #4 (ret), g M pan, g Mass Check: Test Date: M3/4" (ret), g Mass Check: Test Date: M 3/4" (ret), g M5/8" (ret), g M 5/8" (ret), g M1/2" (ret), g M 1/2" (ret), g M3/8" (ret), g M5/16" (ret), g 50 Cycles M 3/8" (ret), g M 5/16" (ret), g M1/4" (ret), g M 1/4" (ret), g M#4 (ret), g Mpan, g M #4 (ret), g M pan, g Mass Check: Test Date: M3/4" (ret), g Mass Check: Source: Submitted by: Date Rec'd: Carbonate Content (%): Test Technician: Equip No: M#4 (ret), g Mpan, g Chamber Pressure (psi): Solonoid Press. (psi): Mass Check: Comments: M5/8" (ret), g M1/2" (ret), g 30 Cycles M3/8" (ret), g M5/16" (ret), g M1/4" (ret), g Figure B27. HFT data collection form. B-26

59 predict freeze-thaw dilation (%/100 cycles) for each individual sample. It also estimates an overall dilation value based on the combined values of all individual samples tested. NOTE: It is important to use the Save As function to store the data with a filename that will be associated with the sample tested (for example, Bryan Red Rock Large Chamber June 2005.xls ) When testing and calculations are complete, the aggregate source can be accepted or rejected based on the results obtained. A value of 0.4 percent dilation per 100 cycles of freeze-thaw testing is often used as the maximum acceptable value for freeze-thaw testing. NOTE: Rather than rejecting sources that exceed this value, it may be appropriate to recommend supplemental testing (for example, actual freeze-thaw testing) to ultimately determine the suitability of a particular aggregate source. Calibrating the HFT Chambers The Hydraulic Fracture Test (HFT) apparatus must be operated in a manner that produces aggregate fracture rates that are consistent with those that were used in the development of the dilation prediction model. This is done by matching a graph of the maximum rate of release of pressure vs. time interval for the test chamber with a similar standard graph. Generation of a maximum pressure release rate vs. time interval graph or profile begins with measurement of chamber pressure vs. time during the pressure release event. Pressure release rates can be monitored using the chamber-mounted pressure transducer (installed in the bottom leg of the brass T that also connects to the fill valve) and the dynamic signal analyzer (a HP in the MnDOT concrete lab). The signal analyzer can be programmed for this task by loading a state file called HFT.STA into the signal analyzer using a 3.5-in floppy disk. Chamber pressure during the release event should be sampled at a rate of approximately 500 Hz (i.e., one pressure measurement every seconds; the signal analyzer program HFT.STA is already set for this sample rate). The collected data are then used to compute the average pressure release rate (psi/sec) during each second time interval and the highest rate is selected and recorded as the maximum pressure release rate over a second time interval. This analysis process is repeated for successively larger time intervals (e.g., seconds, seconds, etc.), and the maximum pressure release rate for each time interval is plotted against the respective time intervals. The computation process is done automatically by the spreadsheet program CALIBRATE.XLS, but the operator must enter the collected chamber pressure vs. time data into the spreadsheet manually. Table 1 presents the standard maximum pressure release rate data that have been adopted for calibrating the HFT apparatus. These data are summarized graphically in figure 28. It is most important to match the target maximum pressure release rate profile at the 0.01-second time interval value, although the overall pressure release profile should closely resemble that of the target. The steps involved in calibration are as follows: 1. Turn on the signal analyzer. Insert the disk containing the file HFT.STA into the disk drive. B-27

60 2. Press the Save/Recall button on the signal analyzer and look on the right of the display screen for the words Recall State. Push the button closest to these words and then use the buttons on the front of the analyzer to enter the file name HFT.STA. Use the backspace and erase keys to eliminate the file name that appeared by default. 3. Use the special cable to connect the pressure transducer to Channel 1 of the signal analyzer (see figure 29). Table 1. HFT Apparatus Calibration Target Pressure Release Rate Data Table Time Interval (sec) Max Pressure Release Rate (psi/sec) Time Interval (sec) Max Pressure Release Rate (psi/sec) Time Interval (sec) Max Pressure Release Rate (psi/sec) Assemble the chamber (with or without aggregate), fill it with water, and perform a standard pressurization-depressurization cycle (without the 2-minute or 5-minute pressure hold). 5. When the pressure is released, the signal analyzer will automatically produce a trace of pressure vs. time. The wheel on the front of the analyzer can be used to move a cursor along the trace, displaying both pressure and time coordinates as it moves from data point to data point. B-28

61 Target Pressure Release Rate Profile for Calibrating HFT Apparatus (from original University of Washington HFT Apparatus) Release Ra te, psi/sec Time Interval, sec Figure 28. HFT apparatus calibration target pressure release rate curve. Figure 29. Connecting pressure transducer to dynamic signal analyzer. 6. Manually record pressure and time values for at least 50 data points that capture the initial release of pressure from the chamber. 7. Open the excel spreadsheet called CALIBRATE.XLS. Click on the tab labeled PRESSURE RELEASE DATA. Enter the manually collected test data into one of the open fields and enter the regulator settings (e.g., 1150 psi/150 psi) into the cell that lies B-29