ASPHALT PAVING LEVEL 1

Transcription

1 ASPHALT PAVING LEVEL 1 Module 3: Yield Calculations: Tack Coat and Mix Spread Rate FDOT Course Module 3 1 Welcome the students to the third module in this course that covers tack coat and mix spread rates, or yield. Encourage the trainees to ask appropriate questions and reiterate the desire of the instructors to help the students to get through the course successfully. Release 7, April

2 What You Will Learn Calculating tack coat spread rate Calculating asphalt mix spread rate or yield FDOT Course Module 3 2 Review the learning objectives for this module. The objective of this module is to learn how to calculate the tack coat spread rate and the asphalt mix spread rate, or yield. Tack coat is used to bond layers of asphalt together. It is important to get the right amount. Too much or too little will cause problems. It is also important to be able to calculate the yield or spread rate of the asphalt mix on the roadway. This spread rate is based on a specific mix and thickness. The thickness is established by the pavement designer and is based on the intended traffic the pavement is designed to carry. If the thickness is less than needed to carry the traffic, the pavement will fail prematurely. The project is set up based on established quantities of the different mixes needed. If you overrun the asphalt mix too much, the project will be too expensive and will exceed the budget. Release 7, April

3 Calculating Tack Coat Spread Rate FDOT Course Module 3 3 Transition slide introducing the tack coat spread rate calculation. Release 7, April

4 FDOT Course Module 3 4 Review the slide. The tack coat ensures a good bond between the existing pavement and the overlay. Slippage can occur if a good bond is not formed and the life of the pavement will be reduced. Diluted slow-set asphalt emulsions are typically used. The tack distributor must be working properly for even application. If not properly maintained, an erratic, uneven spray pattern will result. Release 7, April

5 Tack Coat Materials Day time operations generally emulsified asphalt Track less tack products on APL Night time operations use PG or approved emulsion For PG multiply the specification rate by 0.6 for the target application rate. FDOT Course Module 3 5 Review the slide There are two main types of tack coat materials used: emulsions and asphalt cement. An emulsion is a solution of asphalt cement, water, and an emulsifying agent used to keep the asphalt in suspension. Typically, an emulsion contains about 50 to 60% asphalt and is processed into very small droplets that are suspended in the water. The water allows the emulsion to be sprayed very thin and evaporates once applied, leaving a thin layer of asphalt on the surface. Sunny, low humidity days speed the breaking of the emulsion. The specifications call for using an asphalt cement (PG 52-28) at night, since emulsions take longer to break at cooler temperatures. There are provisions for using emulsions at night, if they can be demonstrated to work properly. Most contractors use emulsions at night also. PG contains no water and the specification application rate must be multiplied by 0.6 to get the proper target application rate. For example: if the pavement type calls for a 0.06 gal/sq yd application rate (target), the actual rate for PG should be 0.06 x 0.6 = gal/sq yd. Tack Coat: Unless the Contract Documents call for a specific type or grade of tack coat, use PG 52-28, heated to a temperature of 250 to 300ºF or use an undiluted emulsion listed on the Approved Product List (APL). Heat the emulsion to the temperature recommended by the tack coat manufacturer. For night paving, use PG tack coat. The Engineer may approve an emulsified tack coat for night paving if the Contractor demonstrates, at the time of use, that the emulsion will break and not adversely affect the progress of the paving operation. Starting with the January 2015 specifications, tacks are required to be of the minimal tracking nature. Release 7, April

6 Tack Coat Materials: There are multiple products approved and they can be found on the FDOT Approved Products List (APL). Where is tack required? Unless otherwise authorized by the Engineer, apply a tack coat between successive layers of base material. Place a tack coat on all asphalt layers prior to constructing the next course. In general, the Engineer will not require a tack coat on primed bases except in areas that have become excessively dirty and cannot be cleaned, or in areas where the prime has cured to the extent that it has lost all bonding effect. FDOT Course Module 3 6 Review slide. Note: This specification language is inserted to show changes that allow new tack materials. Tack Coat: Unless otherwise authorized by the Engineer, apply a tack coat between successive layers of base material. Place a tack coat on all asphalt layers prior to constructing the next course. In general, the Engineer will not require a tack coat on primed bases except in areas that have become excessively dirty and cannot be cleaned, or in areas where the prime has cured to the extent that it has lost all bonding effect. Release 7, April

7 Prime Coat Materials: Use a product listed on the Department s Approved Product List (APL), meeting the requirements of 916 2, or other types and grades of bituminous material if specified in the Contract Documents. The Contractor may select any of the approved prime coats unless the Contract Documents indicate the use of a specific material. FDOT Course Module 3 7 Review slide. Note: This specification language is inserted to show changes that allow new tack materials. Prime Coat: For prime coat, use a product listed on the Department s APL. Where prime coats are to be diluted, certify that the dilution was done in accordance with the specific dilution requirements for each product and for each load of material used. The Contractor may select any of the approved prime coats unless the Contract Documents indicate the use of a specific material. Release 7, April

8 Emulsion Un broke emulsion is brown Broke emulsion is black FDOT Course Module 3 8 Review slide. Breaking of the emulsion. An emulsion is a combination of asphalt cement and water. The asphalt cement provides the bond and the water makes it easier to spread. The water does not help bonding, in fact, it can hinder it. Therefore, the water must be removed before the tack is covered by the asphalt mix. The removal of water is accomplished by "breaking" through evaporation. The "breaking" is the separation of the water and the asphalt cement. This permits the water to evaporate into the atmosphere. If tack is covered before it breaks, the water may be trapped and can cause a loss of bond between layers, or cause the tack to bleed up through the new asphalt layer. Release 7, April

9 Tack Coat Application Rate FDOT Course Module 3 9 Review the slide. Shown here are the typical application rates for tack coats. Always check the project s specifications as application rates may change. Tack Coat Application Rates Shown below are the typical application rates for tack coats. Base, structural, or dense graded friction 0.03 min. gal/sq yd newly constructed 0.06 gal/sq yd milled surface 0.08 gal/sq yd concrete pavement OGFC 0.05 gal/sq yd newly constructed 0.07 gal/sq yd milled surface Temperature correction factor Tack tolerance: +/ gal/sq yd (Covered in Paving Level 2) Release 7, April

10 Tack Coat Application Rate Apply temperature correction factor Tack tolerance: +/ 0.01 gal/sq yd (Covered in Paving Level 2) FDOT Course Module 3 10 Review the slide. Check your project Contract documents (Specs., plans, etc.) to ensure they are using the correct spread rates. Tack spread rates are going up by 0.01 gal/sq yd in the July 2015 Specs. Additional information on application rates for tack coats. Check your project Contract documents (Specs., plans, etc.) to ensure they are using the correct spread rates. Tack spread rates are going up by 0.01 gal/sq yd in the July 2015 Specs. Release 7, April

11 Application Rate Good tack coverage FDOT Course Module 3 11 Review the slide. Slide show various tack shots with reasonably uniform coverage. Application rates depend on the existing surface and the type of mix to be placed on top of it. Newly paved, denser surfaces (top right) need less tack coat to allow the new layer to stick to the existing. Milled surfaces (left and bottom right) have more surface area and require higher tack rates Release 7, April

12 Application Rate Poor tack coverage FDOT Course Module 3 12 Review the slide. Slide shows various tack shots with poor, non-uniform coverage. Release 7, April

13 Tack Spread Rate To calculate the tack spread rate, you need: Calibration chart for the distributor Temperature charts Initial and ending tank readings Type of tack material used Area being tacked Tack temperature FDOT Course Module 3 13 Review the slide. It is important to place the correct amount of tack on the pavement. The temperature of the tack must also be taken so the volume can be temperature corrected. We will use the temperature correction charts at the end of this chapter. The only other information you need is the length and width of the shot. Release 7, April

14 Stationing Stations are set up from a reference point The first station is 0+00 Every 100 feet is another station 100 feet from the start is station feet from the start is station 2+00 Station identification stakes (station boards) 1814 is equal to To convert from stationing to feet simply remove the + sign FDOT Course Module 3 14 Review the slide. A primer on stationing. The entire project is based on a set of reference points that run the length of the project, called stationing. Typically, there will be station identifier posts or boards every 100 feet on a project (sometimes 200 foot intervals on a simple resurfacing project). Finding a station and knowing which direction you are facing can orient you to the project and plans. It is important to be able to cross reference your location to the plans as typical sections vary on projects. A rather extensive set of self study materials can be found at if additional information is needed. The following slide helps explain basic directions and lane identification. Release 7, April

15 Stationing Guidelines L1 L2 W or S Centerline N or E R1 R FDOT Course Up Station Module 3 15 Review the slide. Stations increase (up-station) from West to East and South to North. Lanes are numbered from the Center of roadway and increase going outward. R1 is the right inside lane. R2 is the right outside lane. L1 is the left inside lane. Left and Right roadway are determined by facing up-station. Facing up-station, left roadway is on your left side and right roadway is on your right side. If you turn around and face down-station, the left roadway is now on your right side and right roadway is now on your left side. The roadway side designations only agree with your left and right sides when you face upstation. When you face down-station, they are opposite. Confused? Face up-station (in the direction that puts a higher number station in front of you than behind you) and your left and right sides agree with the roadway s left and right designations. Release 7, April

16 Application Rate Gauge FDOT Course Module 3 16 Review the slide. Placing (shooting) the tack coat requires knowing how much tack was used and the area covered. Modern tack trucks are equipped with a computer rate control system that automatically adjusts the spray rate regardless of vehicle speed variations. However, to accurately measure the amount of tack or prime, someone has to climb to the top of the truck and measure the initial volume in the tank, then after the tack is sprayed, measure the volume again. The process of measuring the tack in the tank is called sticking-thetank. The process is the same whether you are applying tack emulsion or PG tack. The differences are in the specifications used. Release 7, April

17 Tack Spread Rate FDOT Course Module 3 17 Review the slide. Checking the tack spread rate starts with getting an accurate temperature of the tack material being sprayed. It is also necessary to know the amount of material in the tank before and after spraying in order to determine the volume of tack used. The tank level gauge shown here is not precise enough for accurate measurements. You will need to stick the tank as shown in the following slides. It is important that the right amount of tack is placed on the pavement. The temperature of the tack must also be taken so the volume of tack can be temperature corrected. We will use the temperature correction charts found in the appendix. The other information you need is the length and width of the shot. Release 7, April

18 Tack Spread Rate Items needed to determine spread rate 1. Area covered = ((Length (ft)x Width (ft)) divided by 9 sq ft/sq yd 2. Tack Type used (emulsion or AC) Volume used Temperature Proper temperature correction table Temperature corrected volume FDOT Course Module 3 18 Review the slide. The slide illustrates the items needed to correctly determine the spread rate of the tack materials. We will go through an example using the following slides to illustrate these points. The process is the same whether you are applying an emulsion, asphalt cement, or asphalt rubber binder. The differences are in the specifications. Release 7, April

19 Tack Spread Rate Problem Milled Surface Start: Station End: Station Shot width: 12 feet Initial tank reading: 11/13 (or 11 & 13/16 ) Final tank reading: 18/14 (or 18 & 14/16 ) Tack temperature: 160 F Type of tack: emulsion Tank Number: 2266 Desired spread rate is 0.06 gal/sq yd FDOT Course Module 3 19 Review the slide. Let s work though this classroom problem step-by-step, but first make sure we have all the information we need. temperature correction charts at the end of this module the tack coat type the tack temperature information needed to calculate the area Let s proceed with the next slide. Release 7, April

20 Tack Spread Rate Step 1 Initial Tank Reading Final Tank Reading FDOT Course Module 3 20 Instructors Notes: Review slide. Prior to placing (shooting) the tack coat you need to get an initial reading on the volume of tack in the distributor tank. Often called sticking-the-tank, this establishes the initial level or starting point for use in your tack spread rate calculations. All measurements must be made when the tank is level. Measure from the top of the tank opening to the surface of the tack in the tank to the closest 1/16th of an inch. The initial tank reading shown here is 11-13/16 (11 inches and 13 sixteenths of an inch). This is written as 11/13 in the tank calibration charts. In the tank calibration charts, the number to the left of the slash is the number of inches and the number to the right of the slash is the number of 16ths of an inch. Release 7, April

21 Tack Spread Rate Step 2 Find the length of the shot. Sta Sta = 2,625 lineal feet FDOT Course Module 3 21 Instructors Notes: Review slide. The next step is to find the length of the shot, which is just subtracting the starting station from the ending station. Release 7, April

22 Tack Spread Rate Step 2 Determine the square yards (area) of the pavement tacked. Square Yards (sq yd ) = lineal feet x width 9 sq ft/sq yd = 2,625 ft x 12 ft = 31,500 sq ft = 3,500 sq yd 9 sq ft/sq yd 9 sq ft/sq yd FDOT Course Module 3 22 Instructors Notes: Review slide. To calculate the square yards of this tack application, we need the distance in linear feet and also the width of the tack shot. In our example, the shot is 12 feet wide. To calculate the area, multiply the distance times the width to get square feet. Divide the square feet by nine to convert square feet to square yards. Release 7, April

23 Tack Spread Rate Step 3 Determine gallons used at 60 o F Step 3a: Determine gallons at 160 o F From the Distributor Chart at the end of this module: Start Reading 11/13 = 1319 gallons End Reading 18/14 = 1140 gallons Gallons used = 179 gallons (tank reading) This is gallons at 160 o F (or hot gallons) FDOT Course Module 3 23 Instructors Notes: Review slide. After the distributor has completed its shot, another tank reading is taken to measure the final level in the tank. Using both the initial and final readings and the tank calibration chart, look up the corresponding gallons. Use the tank calibration chart found in the appendix. Subtract the final gallons from the initial gallons and you will have the uncorrected volume (hot gallons) of tack used for the shot. 11/13 means 11-13/16 inches 18/14 means 18-14/16 inches Release 7, April

24 Calibration Chart Beginning reading Ending Reading FDOT Course Module 3 24 Instructors Notes: Review slide. Students Notes: Here are screen shots from the calibration chart. Find the reading 11/13 and read the gallons to the right (1319). That is the initial tank stick reading in gallons. Then, find the reading 18/14 and read the gallons to the right (1140 gallons). That is the ending tank stick reading in gallons. We just subtract to get the net gallons used = 179 gallons. Now, move to the next step. Release 7, April

25 Tack Spread Rate Step 3 Step 3b: Correct the gallons at 160 F (tank reading) to gallons at 60 F. Using the Emulsified temperature correction chart, find the correction factor for 160 F 160 F correction factor = Gallons at 60 F = gallons at 160 F x correction factor = 179 x = gallons This is gallons at 60 F. FDOT Course Module 3 25 Instructors Notes: Review slide. Take the temperature of the tack Using the proper temperature correction table (either Emulsion or AC/ARB ) and the temperature from the thermometer in the tank, find the temperature correction factor. Multiply the temperature correction factor by the gallons measured (hot gallons) to get the temperature corrected volume (gallons at 60 F) volume. Release 7, April

26 FDOT Course Module 3 26 Instructors Notes: Review slide. Now we use the temperature correction factor charts. VERY IMPORTANT. There are two sets of charts, one for emulsified asphalts, and one for asphalt cement/asphalt rubber binder (AC/ARB). Make sure you choose the correct chart! Using the correct chart, find the temperature of the tack coat (160ºF) and write down the correction factor to the right of it (0.9756). We multiply the uncorrected (hot) gallons (179) by the correction factor (0.9756) to get corrected (at 60ºF) gallons: gallons. Release 7, April

27 Tack Spread Rate Step 4 Spread Rate = gallons used at 60 F square yards covered = gallons 3,500 sq yd = gal/sq yd = 0.05 gal/sq yd FDOT Course Module 3 27 Instructors Notes: Review slide. Now we enter into the home stretch. We divide the corrected gallons by the square yards to get a tack spread rate of 0.05 gal/sq yd. In Paving Level 2, we would continue this problem and compare our calculated rate (0.05 gal/sq yd) to the target rate of 0.06 gal/sq yd. We find we are within the 0.01 gal/sq yd tolerance, though on the low side. In general, round the calculations for tack spread rate to 2 decimal places. Release 7, April

28 Reporting Pay Item No. Grade Of Asphalt Record Of Bituminous Materials FDOT Calibration Tank No. Record on Asphalt Roadway Daily Report of Quality Control or Asphalt Roadway Verification Report Beginning IN Gallons Ending IN Gallons Time of Day after Unloading Temperature F Net Hot Gallons AM PM AM PM AM PM Correction Factor Prev. 60F Today 60F Accum. Gallons SY Spread 60F Covered Gal/SY FDOT Course Module 3 28 Instructors Notes: Review slide. The information collected for the tack coat spread rate calculation would be entered in the either the Asphalt Roadway Daily Report of Quality Control or Asphalt Roadway Verification Report in the appropriate boxes. Release 7, April

29 Tack Spread Rate Classroom Problem 1 Using emulsified asphalt Start: End: ft wide Tank start: 24/7 Tank end: 32/13 Temperature:150 o F Target: 0.06 gal/sq yd Calculate the spread rate: Answer: 0.06 gal/sq yd FDOT Course Module 3 29 Instructors Notes: Review slide. Here is another example problem. Work through it now and make sure you get the right answer. If you have any questions, ask the instructor. Release 7, April

30 Tack Spread Rate Classroom Problem 2 Using emulsified asphalt Start: End: ft wide Tank start: 18/14 Tank end: 23/2 Temperature: 160 F Target: 0.05 gal/sq yd Calculate Spread rate: Answer: 0.04 gal/sq yd FDOT Course Module 3 30 Review the slide. For FC-5, the targets are now 0.05 gal/sq yd (+/- 0.01) for newly constructed or 0.07 gal/sq yd (+/ for milled surfaces. Explain what this means and whether or not the Contractor needs to make an adjustment. Here is another example problem. Work through it now and make sure you get the right answer. If you have any questions, ask the instructor. Release 7, April

31 Calculating the Asphalt Mix Spread Rate (or Yield) FDOT Course Module 3 31 Transition slide introducing mix spread rate. Release 7, April

32 Calculating the Asphalt Mix Spread Rate (or Yield) Why? Structural design thickness Adjusting cross slope and grade FDOT Course Module 3 32 Review the slide It is important to be able to calculate the asphalt mix spread rate or yield in pounds per square yard to ensure adequate placement of the asphalt mix on the project. Pavement designs dictate a certain thickness of each structural material to meet the design called for. Checking the yield is one way of getting there. Understand that we rarely have a perfectly smooth base. Often we are called to correct cross-slope and even do a bit of leveling as we help to improve the smoothness of the existing pavement. A yield calculation will help answer the question as to whether or not we have the thickness necessary to meet the design requirements. The next series of slides walk through the process. The terms spread rate and yield are used interchangeably although spread rate is the more commonly used term. Release 7, April

33 Calculating the Asphalt Mix Spread Rate Calculate the spread rate at the beginning of each day s production and as needed to control operations, A minimum of once per 200 tons placed Control within 5% of Target Spread rate (Covered in Paving Level 2) Use five truckloads to get average Record on Asphalt Roadway Daily Report of Quality Control or Asphalt Roadway Verification Report FDOT Course Module 3 33 Review the slide Monitor the mix spread rate at the beginning of each day s production, and as needed to control the operations, at a minimum of once per 200 tons placed to ensure that the spread rate is within 5% of the target spread rate. When determining the spread rate, use an average of five truckloads of mix. Release 7, April

34 Calculating the Asphalt Mix Spread Rate Spread Rate = Asphalt Weight used (lb) Area Covered (sq yd) FDOT Course Module 3 34 Review the slide Tons Used: Determine the weight of asphalt placed in the area covered (add up truck tickets). The asphalt weight is typically reported in tons, which you ll convert to pounds. There are 2,000 pounds in a ton. Area Covered: Determine the length of the area covered by subtracting the ending station from the beginning station. Multiply the length by the width of paving. This gives you area covered in square feet. Divide by 9 to get the square yards. Release 7, April

35 Asphalt Mix Spread Rate Example Given the following information, calculate spread rate: Net weights of asphalt in pounds 42, , , , ,120 = 199,690 lb Ending Station: Beginning Station: ,385 ft Area covered = 1,385 ft x 12 ft = 16,620 sq ft Convert to sq yd = 16,620 sq ft / 9 sq ft/sq yd = 1, sq yd FDOT Course Module 3 35 Review the slide First, add up the net weights of the truck tickets to get a single total. In our example, the total is 199,690 pounds. Next, determine the distance the mix covered by subtracting the ending station from the beginning station (1,385 feet). Multiply the length (1,385 feet) times the width (12 feet) and you get square feet (16,620 sq ft). We convert square feet into square yards by dividing by 9. The area is 1, sq yd. Now go to the next slide. Release 7, April

36 Asphalt Mix Spread Rate Example Pounds Used: 199,690 pounds Area Covered: 1, sq yd Asphalt weight used (lb) Spread Rate = Area covered (sq yd) Spread Rate = 199,690 (lb) 1, (sq yd) = lb/sq yd FDOT Course Module 3 36 Review the slide Finally, we calculate the yield by dividing the weight (199,690 pounds) by the area ( sq yd) to get a spread rate of lb/sq yd. This would be compared to the target spread rate and should be within 5%. (This is covered in Paving Level 2.) Release 7, April

37 Asphalt Mix Spread Rate Classroom Problem 1 The last five trucks had the following net weights in pounds: 37, , , , ,952 Paving a 12 ft wide lane The first truck began at station The last truck ended at station Answer: lb/sq yd FDOT Course Module 3 37 Review the slide. The answer is lb/sq yd. It is rounded to the nearest tenth. Another spread rate problem. Be sure you can calculate the spread rate and get the correct answer. Release 7, April

38 Asphalt Mix Spread Rate Classroom Problem 2 The last five trucks had the following net weights in pounds: 36, , , , ,220 Paving a 10 ft wide lane The first truck began at station The last truck ended at station Answer: lb/yd FDOT Course Module 3 38 Review the slide. The answer is lb/sq yd. It is rounded to the nearest tenth. Another spread rate problem. Be sure you can calculate the spread rate and get the correct answer. Release 7, April

39 Spread Rate Complications Use of MTV Use of belly dump trucks Placing mainline and shoulder FDOT Course Module 3 39 Review the slide. Straight, constant-width mainline paving is the easiest to calculate spread rate. But what if its not? Add an MTV in the mix and its hard to figure out where one truck starts and another truck ends. When using an MTV or other device that holds additional mix, it is best to find a steady state. Start and end your measurements when the level in the hopper and the MTV is constant. That should null out the mix in the machine. When pulling mainline and shoulder in single pass, you will have to use the full width of the paving in the calculation. If you are paving a different thickness on the shoulder than the mainline, you will need to develop a reasonable solution with the project team to best handle this situation. Release 7, April

40 What We Learned Tack coat spread rate Asphalt mix spread rate FDOT Course Module 3 40 Review learning objectives for this module. This module focused on two items: tack coat spread rate and asphalt mix spread rate. Both are important requirements for an technician to be able to perform. These measurements should become as simple to do as putting on your boots. Release 7, April

41 QUESTIONS? FDOT Course Module 3 41 Ask if there are any final questions before closing this module. Any questions? Release 7, April