Hot Mix Pav ing in Ad verse Weather

Transcription

1 ot ix Pav ing in Ad verse Weather anual 22 Second edition ay 2007 Pub lished by Sabita Postnet Suite 56 Pri vate bag X21 oward Place 7450 ISB

2 anu als pub lished by Sabita an ual 1 an ual 2 an ual 5 an ual 7 an ual 8 an ual 9 an ual 10 an ual 11 an ual 12 an ual 13 an ual 14 an ual 16 an ual 17 an ual 18 an ual 19 an ual 20 an ual 21 an ual 22 an ual 23 an ual 24 an ual 25 an ual 26 Construction of bitumen rubber seals Bituminous products for road construction anufacture and construction of hot mix asphalt SuperSurf: Economic warrants for surfacing unpaved roads Safe and responsible handling of bituminous products Bituminous surfacings for temporary deviations Appropriate standards for bituminous surfacings abour enhanced construction for bituminous surfacings ethods and procedures - abour enhanced construction for bituminous surfacings ABS - The design and use of large aggregate mixes for bases GES - The design and use of granular emulsion mixes REACT - Economic analysis of short-term rehabilitation actions The design and use of porous asphalt mixes Appropriate standards for the use of sand asphalt Technical guidelines for bitumen-rubber asphalt Sealing of ac tive cracks in road pavements ETB: The design and use of emulsion treated bases ot ix Pav ing in Ad verse Weather Bitumen auliers Code: Guidelines for loading bitumen at refineries User guide for the design of hot mix asphalt Quality management in the handling and transport of bituminous binders In terim guidelines for primes and stone precoating fluids Training Guides TRIP A SE CEP Technical Recommendations in Prac tice ot mix Asphalt Training Series ealth, Safety and Environmental Guidelines for bitumen and coal tar products Councillor Empowerment Programme 2

3 Sabita Video Se ries Testing of bituminous products Bi tu men AV-1 Pen e tra tion test / Softening point (ring and ball) AV-2 Spot test / Rolling thin film oven test AV-3 Brookfield vis cos ity / Duc til ity Bitumen Emulsion AV-4 Saybold furol vis cos ity / Wa ter con tent of emul sions AV-5 Sed i men ta tion value of emul sions / Res i due on siev ing AV-6 Co ag u la tion value with chip pings / Co ag u la tion value with Portland cement AV-7 Binder con tent of slurry / Par ti cle charge test ot ix As phalt AV-8 Op ti mum binder con tent for as phalt AV-9 ar shall test AV-10 Binder con tent / ois ture con tent AV-11 Static creep test / Im mer sion in dex AV-12 Rice s den sity and binder ab sorp tion/bulk rel a tive den sity and voids Bitumen Rubber AV-13 Ball pen e tra tion and re sil ience test / Dy namic vis cos ity AV-14 Com pres sion re cov ery / Flow test AV-15 Bulk den sity of crumb rub ber / Grading and loose fi bre test of crumb rub ber Black top Roads AV-22 Black top sur fac ing and re pair (with In struc tor Training an ual) AV-23 Pave ment sur fac ing and re pair for black top roads ot ix As phalt AV-25 anufacture AV-26 Paving AV-27 Com pac tion ealth, Safety and En vi ron men tal Conservation AV-28 BitSafe - The safe han dling of bi tu men (DVD) 3

4 DIS CAIER Con sid er able ef fort has been made to en sure the ac cu racy and re li abil ity of the in for ma tion con tained in this pub li ca tion. ow ever, nei ther Sabita nor SAT nor a any of their mem bers can ac cept any li a bil ity what so ever for any loss, dam age or in jury re sult ing from the use of this in for ma tion. The con tents of this pub li ca tion do not nec es sar ily rep re sent the views of all mem bers of Sabita and SAT. 4

5 COTETS Pref ace 6 Introduction, purpose of this manual 7 1. Im por tant fac tors af fect ing the cool ing of as phalt ixing and trans port Site con di tions 9 2. In for ma tion about these fac tors As phalt layer or mat Wind Wa ter Trapped wa ter Wet gran u lar base Trans port Recommendations for adverse paving conditions Ground rules Prime, tack, bi tu men, mix ing tem per a ture an aging the ef fects of rain on gran u lar bases in i mum base and air tem per a tures in i mum lay-down tem per a tures Trans porting the hot as phalt Com pac tion man age ment Tech niques for pav ing when caught in rainy con di tions Fac tors to be con sid ered in as sess ing the over all risk Risk As sess ment As sump tions Def i ni tions Rec om men da tions Risk As sess ment 20 Ref er ences 22 Appendix #1 Guide for as sess ing com pac tion win dow time 23 Appendix #2 Sum ma rised Field Guide 27 5

6 PREFACE Driven by the wide vari a tion of spec i fi ca tion re quire ments for pav ing in windy, cold or wet con di tions, Sabita held a sem i nar in o vem ber 1998 which fo cussed on the ef fects of weather and cli mate on hot mix as phalt pav ing. The out come of this work shop was the for ma tion of a com bined work ing group of Sabita and the South ern Re gion of the So ci ety for As phalt Tech nol ogy, which was tasked to pro duce a prac ti cal guide line for use by site staff when ad verse weather con di tions pre vail or are likely to oc cur. It was in tended that this guide line should cap ture lo cal and in ter na tional experience to formulate practical recommendations applicable to southern African environmental and operating conditions. The ex pe ri ences of the broader south ern Af rica have been in cor po rated into these rec om men da tions, and are of fered as back ground and ad vice to im prove prac tice and pro mote ef fi ciency for the ben e fit of both cli ent and con trac tor. Read ers should note that a sig nif i cant por tion of the con tent of this man ual is based on selected ational Asphalt Paving Association (APA) publications, and is therefore applicable to continuously graded asphalt. owever, in conjunction with local experience, the range of applicability has been broad ened, and the rec om men da tions should there fore be con sid ered valid for a wider spec trum of dense-graded mix types. PA yburgh Chief Ex ec u tive Of fi cer Sabita 6

7 ITRODUCTIO ost current specifications do not deal comprehensively with the complexity as so ci ated with the lay ing of hot mix as phalt in ad verse weather con di tions such as rain, wind and low tem per a tures in win ter rain fall ar eas, or thun der storms and low win ter tem per a tures in sum mer rain fall ar eas. ost specifications restrict paving to favourable weather con di tions, leav ing no specific boundaries between favourable and ad verse weather con di tions. or do they take into con sid er ation dif fer ent mat thick nesses or base lay ers. Pro ce dures should be adopted to pro mote ef fi ciency, de crease waste ful prac tice, and to re duce risk. Pur pose of this man ual To set out guide lines to as sist resi dent en gi neers, clerks of works, main con trac tors, site agents, site fore men, pav ing con trac tors, pav ing fore men and asphalt suppliers in applying specifications judiciously. Information and recommendations are provided on: Good paving practices; Risks involved; imiting conditions for paving; Precautions required. What are the ma jor ar eas of con cern and risk? RAPID COO IG RAPID COOIG and WET BASE RAPID COOIG and TRAPPED WA TER 7

8 Rapid cool ing due to loss of heat from the as phalt through the ef fects of wind, wa ter and low am bi ent tem pera tures causes the avail able pav ing and com pac tion time win dow to shrink. oisture in a granu lar base in tro duces weak nesses which make ade quate com pac tion dif fi cult to achieve. Trapped wa ter in the as phalt can cause a loss in du ra bil ity or strip ping of the bi tu men from the aggregate, lead ing to failures. All these con cerns in crease the risk of in ad e quate com pac tion This guide line is a re vi sion of ot ix Pav ing in Ad verse Weather In terim Recommendations, pub lished in We ex press our sin cere ap pre ci a tion to Julian Wise for the re fine ments encapsulated in this revision. 8

9 1 IPORTAT FACTORS AFFECTIG TE COO IG OF AS PAT 1.1 ix ing and Trans port ixing temperature at the plant and delivery temperature at site; Size of load; ength of haul; Use of tarpaulins (particularly important for long hauls in cold conditions). 1.2 Site conditions Un con trol la ble Con trol la ble Temperature of base Thick ness of mat Air temperature Wind velocity ay down temperature Water deposited by rollers Other weather con di tions (rain, cloud, shade from trees, build ings or bridges 9

10 2 IFORATIO ABOUT TESE FACTORS In gen eral, mat thick ness, air and base tem per a tures, wind speed, amount of rain, ef fect of rain on base and speed of at tain ing ini tial com pac tion, should all be con sid ered. 2.1 As phalt layer or mat at thickness and temperature act together in providing the total heat reservoir. These two plus the initial base temperature largely determine the rate at which the mat will cool (See Figure 1 and Appendix #1 for typical South African conditions); For thin mats (40mm and less), rapid cooling occurs through the entire thickness; ore rapid cooling occurs at the bottom (in contact with the cold base) regardless of thickness. Fig ure 1: Cool ing rate curves - Com pac tion of As phalt Pave ments, CRP: Syn the sis of igh way Prac tice

11 2.2 Wind Wind cools the surface, and as the speed increases, so does its cooling influence; At wind speeds of >15 km/hr, the upper surface of the mat may cool more rapidly than the lower. Cold and wind have a far greater cooling effect on the mat than rain alone. For ex am ple: It may be very risky to pave 25mm mats in windy conditions at ambient temperatures of say 15 0 C. If the sur face and the un der side cool rap idly (say 10mm com bined) only the mid dle 15mm of the mat is at a tem pera ture suit able for nor mal compaction. 2.3 Wa ter On the other hand, there is much less risk to a 60mm mat un der the same con di tions. Rain, apart from its cooling effect, may become a problem if excessive amounts of water enter the mat; Paving over standing water will cause rapid cooling and may allow the water to enter the new mat if not swept away; Drum sprinklers spray up to an equivalent of approximately 0.5mm/hour onto the mat (classified as a drizzle). The first roller cools the surface of the mat by approximately 25% after six passes, but only as measured at the surface. Thin mats are more affected by roller water than thicker mats. 2.4 Trapped wa ter Water trapped in the mat may cause loss of adhesion and stripping, as well as excessive movement under the rollers. This may further result in shear cracks in the mat, making it more permeable and less dense. Thin mats are more vulnerable to rain and standing water than thicker mats. 11

12 2.5 Wet gran u lar base Excessive moisture in a granular base makes compaction of the asphalt difficult. Trapping water in or on the base may affect its stability under traffic, causing heaving and/or crocodile cracking. Thin mats are more susceptible to moving on the wet base than thicker mats. 2.6 Transport The purpose of covering loads with tarpaulins is to obtain better temperature uniformity and reduce crust" thickness, but does not significantly contribute to an increase in the compaction window. On long hauls in cold weather, a crust will form not only on top but all around where the load is in contact with the truck body. Double skin trucks with canopies that close fully are used in Europe, but are seldom required under South African conditions. 12

13 3 RECOEDATIOS FOR ADVERSE PAVIG CO DI TIOS 3.1 Ground rules The fol low ing rules should be con sid ered and agreed be tween the resident engineer, main contractor, supplier and paving contractor before paving starts: Working in adverse weather conditions requires close cooperation, good plan ning and a well organised site team to en sure that qual ity stan dards are main tained When the weather re port in di cates risk of ad verse weather, par ties should dis cuss the day s pav ing op er a tion to reach con sen sus on achieving the required end product without compromising the specification Due con sid er ation should be given to the spec i fi ca tion and rel e vant fac tors af fect ing the cool ing of as phalt (see chap ters 1 and 2) The lay ers be low the aphalt should be fully com pacted and have a low enough mois ture con tent so that the mat will not heave dur ing com pac tion of the as phalt o pav ing should be started on: a granular base showing signs of sponginess; bases with a loose wet surface; existing asphalt containing trapped water There must be suf fi cient work ing time avail able to make pav ing and com pac tion com mer cially vi a ble for the day (see 3.4.2) If pos si ble, in crease mat thick ness to in crease the heat res er voir En sure an un in ter rupted sup ply to the paver Plan and agree times for the first and last trucks to ar rive on site Endeavour to use large trucks (12 tons and greater) to en sure high heat retention All trucks to have full, thick, im per vi ous tar pau lins (such as Sterkolite, not hessian) which should re main in place dur ing tip ping. 13

14 3.2 Prime, tack, bi tu men and mix ing tem per a tures Typ i cal prime types: cut back and emul sion primes (see 3.3.8) Tack coats for wear ing courses are rec om mended at all times even on fresh primes to en sure ad e quate ad he sion. Typ i cal tack type: Stablemix emul sion (60%) mixed 50/50 with wa ter, ap plied evenly at a rate of 0.2 to 0.4 l/m 2 of the di luted emulsion The tack should be ap plied be fore the rain. If tack is not down and broken be fore any rain, pav ing should be de layed To en sure compactibility in cold con di tions, check the (60/70-pen) bi tu men test re sults to en sure that the vis cos ity (af ter RTFOT) at C is not more than 0.7 Pa.s, pref er a bly 0.6 Pa.s For 60/70 pen bi tu men a mix ing tem per a ture range of C C is usu ally re quired to en sure the min i mum lay-down tem per a tures shown in Table For 40/50-pen bitumen, mixing and minimum lay-down temperatures should be 10 0 C higher than for 60/70-pen odified binders can be more sensitive to temperature and are placed at dif fer ent tem per a tures: Con sult the sup plier. 3.3 an ag ing the ef fects of rain on gran u lar bases ois ture in the base layer should be less than 50% OC be fore prim ing or pav ing com mences Check for spongy ar eas with a pneu matic roller (or loaded truck). Re pair before paving, using e.g. BTB, or ac cept the de lay for evap o ra tion to take place. This should be done be fore the pav ing con trac tor es tab lishes to avoid costly de lays A wet gran u lar base with very low PI may re sult in a soft,loose sur face, caus ing trac tion prob lems for the paver and compaction problems (the paving contractor may have to wait for the sur face to dry) Drain age of the base must be good (min i mum 1% fall in a di rec tion that will take wa ter off the sur face). This is a de sign re quire ment Pro tect the base from wa ter dam age by al low ing drain age into catchpits by form ing out lets in the kerbs or chan nels as of ten as nec es sary Sweep wa ter away from in front of the paver be fore pav ing Where pos si ble, pave down hill so that any rain will drain away from the mat. 14

15 3.3.8 Tack coat, in ad di tion to a prop erly ap plied and well cured prime coat (which acts as a tem po rary pro tec tion from rain), is es sen tial for good adhesion. 3.4 in i mum base and air tem per a tures Table 1: in i mum base and air tem per a tures and re lated wind strength for con tin u ously graded wear ing courses and asphalt bases Wind Speed at thick ness 25mm 40-60mm > 60mm Base temp C 10 0 C 4 0 C 0 10 km/h Air temperature 15 0 C 10 0 C 4 0 C > 10 km/h Air temperature 18 0 C 13 0 C 10 0 C In windless, sheltered conditions, paving at ambient temperatures lower than 10 0 C can still be prac ti ca ble for 40-60mm mats. The cool ing ef fect at the sur face is re duced and does not ad versely af fect the high temperature of the mat. This al lows enough time for com pac tion to be achieved (see Ta ble 2). ow ever, harsh, hard to com pact mixes must be avoided in these con di tions At least 4 5 hrs of pav ing time per day is nec es sary to en sure cost effectiveness. 3.5 inimum lay-down temperatures Table 2: inimum lay-down temperatures (related to Table 1) at thick ness (mm) >75 ini mum truck temperature at tipping ( 0 C) inimum mat temperature when roll ing starts ( 0 C) It is vi tal to in sist on at least the min i mum truck temperatures at tipping Tar get a higher average temperature than these minimums. 15

16 3.5.3 These tem per a tures could be ad justed for highly flex i ble mixes (more work able) which com pact more eas ily at lower tem per a tures When be ing tipped, the last por tion of the load is slightly cooler than the bulk of the load, and can come out be hind the paver at a slightly lower temperature (say 10 0 C). 3.6 Trans port ing the hot as phalt Good communication between the paving contractor and the asphalt sup plier should be main tained at all times so that al low ance can be made for sup ply in ter rup tions (see 3.7.7) or mal tran sit time should ide ally not ex ceed 2 hours; preferably 1½ hours (i.e. time from load ing at plant to tip ping on site) Pref er a bly ar range with the sup plier to de liver in tons per hour, not in batches ix ing and trans por ta tion should be ar ranged to match the pav ing speed A trans port fleet of large trucks (12 to 15 tons) should be avail able to en sure con ti nu ity of pav ing and good heat re ten tion igh stan dards for the type, size and use of tar pau lins must be maintained Com pac tion man age ment Choose a pav ing speed which en sures that the roller train re mains close be hind the paver Use wider roll ers and/or pave nar rower widths (e.g. cover mat in two roller widths in stead of three), but en sure that lon gi tu di nal joints do not oc cur in the wheel tracks Use more or heavier roll ers to in crease the compactive ef fort. In addition First roller must roll im me di ately be hind the paver; this helps seal in the heat and seal out wa ter Roll longitudinal joints first ave a standby roller avail able in case of break downs or as an ad di tional roller at the cold est time of day. Some cir cum stances may even re quire a standby paver. This has a cost im pli ca tion for the contractor. 16

17 3.7.7 Empty the paver and form trans verse joints when there is a sup ply de lay to pre vent the mat un der and be hind the paver (the area not yet reached by the roll ers), cool ing be low the tem per a tures shown in Ta ble Tech niques for pav ing when caught in rainy con di tions Re fer to 3.2 on tack coats and prim ing Sur face must drain well Sweep away any stand ing wa ter from in front of the paver Where possible, pave downhill (excluding steep hills) so that rain drains away from the as phalt. Roll ing tech niques must be adapted to pre vent shov ing when pav ing down slopes First roller must roll im me di ately be hind the paver to seal the mat and pre vent in gress of rain Re duce wa ter on the roller drums to an ab so lute min i mum (in some con di tions it may be pos si ble to cease all wa ter ap pli ca tion if pick-up does not oc cur) Fac tors to be con sid ered when as sess ing over all risk Type of rain: Is it light, a con tin u ous driz zle, a sud den down pour or oc ca sional showers? Amount of rain: Con sider that drum sprin klers spray up to 50ml/m 2 /hr with out harm to the as phalt (equiv a lent to rain of 0.5 mm/hr.) Type of mix: Cer tain mixes such as base lay ers could pos si bly be paved in rain. ow ever, this may not be pos si ble with other mixes such as wear ing courses at thick ness: The thicker the mat, the lower the risk of rapid cool ing Base con di tion and whether rain is af fect ing it: Op po sites are as phalt bases and gran u lar bases there is less risk pav ing on as phalt bases than on gran u lar bases in light rain. Coarsely graded base lay ers may trap wa ter, which could take sev eral days to dry Pre vail ing tem per a tures: Ex tremes when rain oc curs may vary from 25 0 C in arch to 10 0 C in July Pre vail ing winds: Ex tremes may range from no wind to a cold 40 km/hr wind Temperature at which asphalt is delivered: See , and

18 eed for high level su per vi sion: When risk is high or me dium, high level su per vi sion linked to good paving experience (usually the responsibility of the site agent) should en sure that all pre cau tions are taken and correct procedures followed at all times ayer thick ness, wind speed and base tem per a ture: These parameters have the great est in flu ence on the mat cool ing rate. Am bi ent tem per a ture, rain and shade have less in flu ence.

19 4 RISK ASSESSET (Based on West ern Cape ex pe ri ence in rainy con di tions. Other re gions may interpret differently.) 4.1 Assumptions Base layer is well compacted, dry enough and primed; Tack has been applied and is ready for paving; Base and air temperatures conform to Table 1; Delivery temperatures are higher than the minimums in Table 2; Enough rollers are available to ensure speedy compaction. 4.2 Def i ni tions Rain type Quan tity Drizzle Up to 1mm/hr ight 1mm 2.5mm/hr oderate 2.5mm 12.5mm/hr eavy > 12.5mm/hr 4.3 Recommendations (Cour tesy of the Cape Town Weather Of fice) il risk () al ways use good pav ing prac tice; ow risk () take precautions to minimise the possibility of failure; edium risk () avoid paving unless absolutely necessary, and then only if risk can be re duced to an ac cept able level.; igh risk () pav ing should not be con sid ered. 4.4 Risk as sess ment 19

20 4.4.1 Con di tion A: Wear ing course on an as phalt base or as phalt base on a cementitious subbase. Table 3: Risk as sess ment for Con di tion A at thick ness 25mm mat 40mm mat 60mm mat/> Weather Wind il > 10km/h il > 10km/h il > 10km/h Air temp: > 24 0 C Drizzle ight rain oderate rain Air temp: C Drizzle ight rain oderate rain Air temp: <18 0 C Drizzle ight rain oderate rain Con di tion B: Wear ing course or as phalt base on a sound, unstabilised gran u lar base e.g. crushed stone. 20

21 Table 4: Risk assessment for Condition B: at thick ness 25mm mat 40mm mat 60mm mat/> Weather Wind il > 10km/h il > 10km/h il > 10km/h Air temp: > 24 0 C Drizzle ight rain oderate rain Air temp: C Drizzle ight rain oderate rain Air temp: < 18 0 C Drizzle ight rain oderate rain ote: Even if well primed and tacked, other gran u lar bases with very low PI s and certain materials such as ferricrete, laterite, or calcrete, may in crease the risks even more, de pend ing on how their sur faces are af fected by rain. 21

22 References 1. CRP: Syn the sis of igh way Prac tice CAPSA 2004 Bul le tin Pa per: A practical guide for estimating the com pac tion win dow time for thin layer hot mix as phalt Julian Wise. 3. ational Asphalt Pavement Association (APA): ot mix pav ing handbook, 2000 P ational Asphalt Pavement Association (APA): Cold weather compaction QIP-115. APPEDIX #1 22

23 A GUIDE FOR ES TI AT IG CO PAC TIO WI DOW TIE The guide con sists of three charts: 1. at thickness versus compaction window time for typical ambient and asphalt temperatures (Chart 1); 2. Re duc tion of this com pac tion win dow time due to dif fer ing wind speeds (Chart 2); 3. A guide to es ti mat ing wind speed. Figure 1: Com pac tion time vs. mat thick ness for wind less conditions. (ote the three as sump tions below the chart). Figure 2: Ef fect of wind on com pac tion win dow time 50 at thickness (mm) Compaction window time (mins) Windspeed = zero 0 at temp behind paver = 135 C 0 Cut-off temp. for compaction = 80 C 0 Air 10 C; Base C 0 Air 200C; Base C 0 Air 300C; Base C 23

24 Windspeed (km/hr) Reduced compaction time (%) Table 1: Estimating windspeed Wind speed km/hr De scrip tion Guide 0-2 Calm Smoke rises vertically 2-4 ight air Smoke drifts in di rec tion of wind 4-7 ight breeze Wind felt on face; leaves rustle 7-11 Gentle breeze Wind ex tends a light flag; leaves in motion oderate breeze Wind raises dust and light paper Fresh breeze Small trees sway, wave lets form on water Strong breeze arge branches sway; whistling in over head wires ear gale Whole trees move; af fects walking 24

25 Us ing the guide: Example 1 Site con di tions at thickness Com pac tion time from Chart 1 Cor rec tion for wind Delivery temp C Temp at screed C Base temp 16 0 C Air temp 13 0 C Windspeed 15km/hr 25mm 9 mins 7 mins 40mm 21 mins 16 mins 50mm 32 mins 24 mins Example 2 Site con di tions at thickness Com pac tion time from Chart 1 Cor rec tion for wind Delivery temp C Temp at screed C Base temp 45 0 C Air temp 30 0 C Windspeed: calm 25mm 11 mins 11 mins 40mm 26 mins 25 mins 50mm 38 mins 36 mins 25

26 Comments 1. A rule of thumb for com pac tion time is a min i mum of 10 min utes, but this is for mixes that com pact eas ily. arsh mixes re quire more time (e.g minutes) 2. For a 25mm mat: In Example 1, there is not enough time to achieve compaction; In Example 2, however, there is enough time. 3. For a 40mm mat: In Example 1, there is just enough time for, say, a harsh COTO medium mix, as long as the rollers are close behind the paver; In Example 2, there is plenty of time. 4. For a 50mm mat: There is al ways suf fi cient time, even if tem per a tures are near zero. 5. ote how the time al most dou bles from a 25mm to a 40mm mat, and more than tre bles from a 25mm to a 50mm mat. 26

27 Sabita mem bers Or di nary em bers AG Thomas (Pty) td AJ Broom Road Products (Pty) td Akasia Road Surfacing (Pty) td Astec - Asphalt Technology cc Bitumen Construction Ser vices (Pvt) td Bitumen Supplies & Services (Pty) td Black Top oldings (Pty) td BP SA (Pty) td Brisk Asphalt Surfacing (Pty) td Chevron South Af rica (Pty) td Colas SA (Pty) td Engen Petroleum td Javseal (Pty) td illing Techniks (Pty) td ore Asphalt uch Asphalt (Pty) td urray & Roberts Construction td ational Asphalt (Pty) td ikamandla Construction (Pty) td yanga Roads (Pty) td Phambili Road Surfacing (Pty) td Polokwane Surfacing (Pty) td Rand Roads (a division of Grinaker-TA td) Roadsmart (Pty) td Sasol Oil (Pty) td Shell SA arketing (Pty) td Spray Pave (Pty) td Tarfix (Pty) td Tosas (Pty) td Total SA (Pty) td Tar Spray cc Van Wyk Tar mac cc Zebra Bituminous Surfacing cc 27

28 As so ci ate em bers Africon Engineering International (Pty) td Arcus Gibb (Pty) td Asch Professional Ser vices (Pty) td BCP Engineers (Pty) td Beosumbar and As so ci ates cc BKS (Pty) td Cape Peninsula University of Technology Dick King ab Supplies (Pty) td G/CPP Consulting Engineers (Pty) td Goba (Pty) td O Africa olcim SA (Pty) td Iliso Consulting (Pty) td Jeffares and Green (Pty) td Kantey & Templer (Pty) td Kaymac (Pty) td t/a Kaytech afarge South Af rica td idwala Consulting Engineers (Pty) td inham Shand (Pty) td PD aidoo and As so ci ates (Pty) td Rankin Engineering Consultants Sasol Technology Fuels Research Sasol Wax (a division of SCI) Siyenza Engineers cc Specialised Road Technologies (Pty) td SSI Engineers and Environmental Consultants (Pty) td The Synthetic atex Co. (Pty) td TPA Consulting cc Tshepega Engineering (Pty) td Unitrans Fuel and Chemical (Pty) td Vaal University of Technology Vela VKE Consulting Engineers (Pty) td WSP SA Civil and Structural Engineers (Pty) td Af fil i ate em bers DV arri smith (Pty) td TTC (Pty) td Salphalt (Pty) td 28

29 OTES 29

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32 32 OTES

33 SUARISED FIED GUIDE WAT ARE TE A JOR AR EAS OF CO CER? RAPID COO IG RAPID COO IG and WET BASE RAPID COO IG and TRAPPED WA TER Ta ble 1: in i mum base and air tem per a tures and re lated wind strength for con tin u ously graded wear ing courses and as phalt bases. Rapid cool ing due to the loss of heat from the as phalt through the ef fects of wind, wa ter and low am bi ent tem per a tures causes the avail able pav ing and com pac tion time win dow to shrink. ois ture in a gran u lar base in tro duces weak nesses which make ad e quate com pac tion dif fi cult to achieve. Trapped wa ter in the as phalt can cause a loss of du ra bil ity or strip ping of the bi tu men from the ag gre gate, lead ing to fail ures. Windspeed at Thick ness 25m m 40-60m m > 60m m Base tem per a ture 18 0 C 10 0 C 4 0 C

34 0 10 km/hr > 10 km/hr Air tem per a ture Air tem per a ture Table 2: inimum lay-down temperatures (related to Table 1 above) Base and air temperatures conform to Table 1; Delivery temperatures are higher than minimums in Table 2; Enough rollers are available to ensure speedy compaction. Definitions at thick ness > 75 in i mum truck temp. at tip ping ( 0 C) in i mum mat temp. when roll ing starts ( 0 C) Rain Type Driz zle ight od er ate eavy Quantity Up to 1mm/hr 1mm - 2.5mm/hr 2.5mm mm/hr > 12.5mm/hr Risk as sess ment Assumptions (Based on West ern Cape ex pe ri ence. Other re gions may interpret differently). Base layer is well compacted, dry enough and primed; Tack has been applied and is ready for paving.; Recommendations (Cour tesy of the Cape Town Weather Of fice) il risk () al ways use good pav ing prac tice. ow risk () take precautions to minimise the possibility of fail ure.

35 e dium risk () avoid paving unless absolutely necessary, and then only if risk can be re duced to an ac cept able level. igh risk () pav ing should not be con sid ered. Table 3: Risk assessment for Condition A at thick ness 25mm 40mm 60mm > Risk As sess ment Weather Wind il > 10 km/hr il > 10 km/hr il > 10 km/hr CO DI TIO A: Wear ing course on an as phalt base or as phalt base on a cementitious subbase. Air temp: > 24 0 C Driz zle ight rain od er ate rain Air temp: C Driz zle ight rain od er ate rain Air temp: < 18 0 C Driz zle ight rain od er ate rain

36 CODITIO B: Wear ing course or as phalt base on a sound, unstabilised gran u lar base, e.g. crushed stone. Table 4: Risk as sess ment for Con di tion B at thick ness 25mm 40mm 60mm > Weather Wind il > 10 km/hr il > 10 km/hr il > 10 km/hr ote: Even if well primed and tacked, other gran u lar bases with very low Pl s and cer tain ma te ri als such as ferricrete, laterite or cal crete, may in crease the risks even more, de pend ing on how their sur faces are af fected by rain. Air temp: > 24 0 C Driz zle ight rain od er ate rain Air temp: C Driz zle ight rain od er ate rain Air temp: < 18 0 C Driz zle ight rain od er ate rain

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