Good quality control 2005.pdf

8/11/2019 Good quality control 2005.pdf

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A guide to good quali ty cont rol pract iceson asphalt productios and construction

Cawangan Jalan, Ibu Pejabat JKR, K.L

FOR INTERNAL USE ONLY


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TABLE OF CONTENTS

Item Page

Rocks and aggregates 1Classification of rocks 2

Aggregate stockpiles 4 Aggregates 7

Bitumen 8

Mix design 10Compliance 11

Mixing plants 12Batch plant mixing operation 14

Site preparation 17

Delivery of asphalt 21

Laying of asphalt 23

Hand casting 26

Compaction of asphalt 28

Construction joints 31Joint preparation 32Transverse joint construction 35Longitudinal joint construction 37

Surface waves and roughness 39

Checklist 41


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Rocks and aggregates

Rocks are classified relative to their geological origins and these are termedigneous, sedimentary and metamorphic.

Igneous rocks - formed from hot liquid or magma, cooling either above or beneath the earth's surface. Typical examples are granite and basalt.

Sedimentary rocks - the action of wind or-water on a rock's surface results inthe formation of smaller particles. These particles are deposited on river or seabeds or depressions in the earth's surface. This sediment accumulates and isburied - compaction and cementation over the years removes the air and water to form sedimentary rocks. A typical example is limestone.

Metamorphic rocks - heat, pressure and chemical substances deep beneaththe earth's surface act on existing igneous and sedimentary rocks to form anew type called metamorphic rocks, eg. marble.

In the tropics, the minerals in surface deposits of igneous rocks are alwayslikely to be weathered. High temperatures and high humidity can producephysical and chemical changes to a considerable depth. The weathering mayonly be slight as in the brown staining often evident in spots on granite mason-ry. In more humid areas, chemical weathering may proceed quite rapidly andmany of the rock minerals will be found to be at least partially weatheredtowards their ultimate clayey form. Such deterioration may not be obvious byhand inspection but the consequences of using such weathered rocks in roadsmay be disastrous.

There are relatively simple laboratory tests which can be used to indicatewhether the aggregate contains particles of suspect hardness and durability.The best known of these is the soundness test as per BS 812 or ASTM C88.This test will identify aggregates which are weak and porous. However, its useto identify aggregates that are partially weathered is less certain since some of

the aggregates may not be porous. Magnesium sulphate is prferred to sodiumsulphate because of the greater penetrating power of the saturaed solution.

Aggregates must have certain properties to withstand the stresses imposed onthe road surface and sub-surface layers. For every stockpile that prduces2,500 tonnes of mix, all coarse and fine aggregates should conform to thephysical and mechanical quality requirements as per Clause 4.2.4.2 (a) of SPJ.



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Classification of rocks

Typical types of rock.Pic, from left weathered granite, basaltand unweathered granite. In tropical

region, high temperatures and humiditycan produce physical and chemicaldecomposition as evident by

brown discolouration on the surface.

Weathered andunweathered rocks.Weathered rocks should not be used inroads, neither as coarse and fine

aggregates nor as roadbase crusher run.Aggregates suspected of weatheringshould undergo soundness test as perClause 4.2.4.2 (a) of SPJ.

Typical aggregates.Granite (pic), a coarse grained igneousrock, is siliceous and susceptible tostripping. Bitumen stripping test should

be regularly carried out if granite is usedas aggregate. Basalt, a fine grainedigneous rock, contains less silica and has

better affinitywith bitumen but can be brittle and splintery. Limestone, a calcer-oussedimentary rock, is softer than igneousrock but usually has adequate strength foruse in roads. However, the material issusceptible to polishing under trafficand therefore should not be permitted for use in wearing course as per Clause4.2.4.2 (a) of SPJ



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Classification of rocks

Weathered granite.The brown staining on the surface givesan indication that some degree of weath-ering may have taken place on this gran-ite.

Weathered granite.This granite is obviously porous, an indi-cation that the weathering may have beensubstantial.

Weathered rocks.Weathered rocks should not be used inany of the pavement layers.



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Aggregate stockpiles

Good separation of stockpil es.Quality control of asphalt begins withaggregate stockpiles. Different sizes of aggregate should be kept separated.

Clean and stable stockpilebase .Aggregates should be stockpiled on aclean surface. Paved pads should be used to facilitate drainage and to avoid contami-nation with soil. Stockpiles of fine aggre-gates shall be kept dry using waterproof covers and other means as necessary as

per Clause 4.2.4.5 (c) of SPJ.

Building aggregate stockpiles .Stockpiles should be built in horizontal or

gently sloping layers to minimise segrega-tion. Conical stockpiles will cause thecoarser aggregates to roll down the sidesresulting in segregation.



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Contaminated stockpile.This aggregate stockpile has been severelycontaminated and should be discarded.

Contaminated stockpile. No foreign objects should be dumped onto aggregate stockpiles.

Contaminated stockpile.Without proper foundation and drainage,this stockpile is susceptible to contamina-tion by the surface water.



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Feeding the cold bins.The cold bins must contain the nominalaggregate size for which they are intend-ed, otherwise problems with unbalanced hot bins and excessive aggregate carry-over may occur (refer to page 16).

No intermingling o f aggre-gates.Intermingling and overflow of aggre-gates in the cold bins should be avoid-ed.

Aggregate feeder units.Aggregate feeder units located beneath the

cold bins should provide a uniform flow of aggregates to the elevator. The rate of feed shall be such that the screens at the hot binsshall never be overloaded.



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Aggregates

Contaminated aggregates.Coarse aggregates should be screened

hard rock, angular in shape and free fromdust, clay, vegetative and other organicmatter, and other deleterious substances.Cleanliness of aggregates is important for good bitumen adhesion. Impurities cancause incomplete bitumen films or weak

bonding. Coarse aggregates should con-form to physical and mechanical qualityrequirements as per Clause 4.2.4.2 (a) of SPJ.

Fine aggregates.Fine aggregates should be screened quarrydust, or clean natural sand or mining sand.Mining sand should be thoroughly washed

before use. Fine aggregates should con-form to physical and mechanical qualityrequirements as per Clause 4.2.4.2 (a) of SPJ.

An ti -st ripping agent.Ordinary Portland cement or lime based

product should be added to the combined aggregates to serve as an anti-strippingagent cum filler. This is to prevent strip-

ping of aggregates by the action of trafficand water which can lead to disintegrationof the surfacing as shown in pic.



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Bitumen

Bitumen is a dark brown or black sticky substance which occur in nature or is obtained from the refining of crude oil. It is semi-solid at room temperatures but becomes fluid

when heated. It is commercially available in several standard grades. For many years,grades of bitumen are designated by the penetration values. They are five standard grades:40-50, 60-70, 80-100, 120-150 and 200-300 with the numerical grade indicating theallowable ranges of penetration for each grade. In Malaysia, grade 80-100 conforming toMS 124 is used as per Clause 4.2.4.2 (c) of SP J.

In the production of asphalt, both the bitumen and the aggregates are heated to relativelyhigh temperatures to liquidify the bitumen and dry the aggregates before they are mixed together. For some processes, it is either not convenient or not possible to heat the bitumenand/or aggregates, for example, in surface dressing and in priming a surface. Therefore,

cutback bitumen and bitumen emulsion are used.

Cutback bi tumen is produced by fluxing bitumen with a lighter fraction oil. It canthen be applied either at ambient temperature or heated to relatively low temperatures. Itstarts to harden by the volatilisation of the flux oil. The rate of hardening is determined bythe volatility of the flux oil. Where rapid hardening is needed, as in surface dressing, alight oil such as kerosene is used. Where slow hardening is needed, as in patching materi-als and soil stabilisation, a less volatile oil such as diesel is used. Cold application cutback

bitumen may contain up to 30 percent of flux oil where as cutback bitumen which isapplied warm contains less.

Cutback bitumen is available by type and grade. The types (rapid-curing RC, medium-cur-ing MC and slow-curing SC) indicate the relative speed of evaporation while the grades(30, 70, 250 and 3000) indicate the minimum allowable kinematic viscosity in centistokeat 60 C. Cutback bitumen shall comply with MS 159. Clause 4.2.1.2 of SPJ stipulates that

prime coat material shall be cutback bitumen of grade MC-70.



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Bitumen

Bitumen emulsion is dispersion in water of minute drops of bitumen of average diam-eter about 2 microns. It provides a means of using bitumen at ambient temperature. The

water evaporates shortly after the emulsion is exposed to the atmosphere. It is muddy brown in colour and the breaking' of the emulsion is indicated by the appearance of aglossy black film of bitumen on the surface to which the emulsion is applied. It can bedivided into four classes of which the first two are the most widely used; anionic, cationic,non-ionic and clay-stabilised.

Bitumen emulsion shall comply with MS 161. The requirements for anionic bitumenemulsion are excluded from MS 161 as this type of emulsion is not used in road construc-tions. Cationic emulsion in general is more versatile. It can be used over a broader rangeof aggregate than the anionic emulsion.

Bitumen emulsion is classified into three types: rapid setting (RS), medium setting (MS)and slow setting (SS). Each type is classified into various grades, based largely on bitumencontent and viscosity. RS-1K and RS-2K are recommended for tack coating, RS-3K for surface dressing, MS-1K and MS-2K for penetration macadam, and SS-1K for slung sealand prime coating. Clause 4.2.1.2 of SPJ stipulates that prime coat material shall be bitu-men emulsion of grade SS-1K whereas Clause 4.2.2.2 of SPJ stipulates that tack coatmaterial shall be bitumen emulsion of grade RS-1 K.



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Mix design


Loratory mix design.Using the aggregate gradation and bitumen content as allowed for in Table 4.8 and Table 4.9 of SPJrespectively, five set of three Marshall specimens with bitumen content increasing at an increment of typically 0.5% shall be prepared as per Clause 4.2.4.3 of SPJ. The design bitumen content is theaverage bitumen content which gives the maximum stability and density, and the median flow, air voids in aggregate filled with bitumen and air voids in the mix as allowed for in Table 4.10 of SPJ.

Plant trials. A minimum of 10 tonnes of mix shall be placed in trial areas to demonstrate that themixing, laying and compacting equipment conform to the requirements of SPJ and that the proposed mix is satisfactory. A comprehensive sampling and testing of the trial mix shall be carried out to check for satisfactory compliance with the job mix formula and satisfactory degree of compaction.


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Compliance


Job mix for mula. As a result of the plant trials, the mix shall be approved for fullscale production. The gradation and bitumen content, with the allowable tolerances setforth in Table 4.11 of SPJ then becomes the job mix formula for use in full scale produc-tion. The mixing, laying and compacting temperatures, and the types of roller and number of roller passes should be consistent with the plant trials.

Sampling and testing. During the production of mix, it is required that a comprehensiveMarshall method test and analysis as per Clause 4.2.4.3 (a) of SPJ together with aggregate gra-dation and bitumen content analysis be carried out for every 200 tonnes of mix produced and atleast once for each plant operating session. Gradation analysis of aggregates from the hot binsshould be carried out once for each bin per day of production.


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Mixing plants

Mixing plant shall be either a batch plant, a continuous plant or a drum mix plant.

In a batch plant, aggregates are fed from the cold bins into a dryer in controlled amounts. After they are dried and heated, the aggregates are passed over a screening unitthat segregates the material into different sizes and kept in hot bins. The aggregates and mineral filler are then fed into a pugmill in fixed proportions and mixed with a knownquantity of hot bitumen as a batch. The mix is loaded into tip-trucks and delivered to the

paving site.

In a continuous p lant, the process is similar up to the hot bins but differs from the batch plant in the procedure for combining the materials for mixing. The plant uses a con-tinuous flow of aggregates into the pugmill with the amount of each size fraction con-

trolled by adjustable gate openings. Hot bitumen is sprayed into the pugmill continuously.Mixing is thus a continuous process. The tip-trucks are loaded by continuous dischargefrom the pugmill.

In a drum mix plant, aggregates with controlled gradation are stored in the cold binsfrom which they are continuously fed in exact proportions on to a conveyor. An automaticaggregate weighing system monitors the amount of aggregates flowing into the drummixer. The weighing system is interlocked with the controls on the bitumen storage pumpwhich draws bitumen from a storage tank and introduces into the drum mixer where bitu-men and aggregates are thoroughly blended by the rotary motion of the drum. As theingredients mix, they move slowly towards the discharge end of the drum. By the timethey reach the end, they are thoroughly mixed. From the drum, the hot mix is transported

by a conveyor to a surge silo from which it is loaded into tip-trucks.



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Batch plant mixing operation

Bitumen heating.The temperature of bitumen should be inthe =s range of 140 C to 160 C whendelivered to the pugmill as per Clause4.2.4.5 (d) of SPJ. ASTM D 3515 recom-mends that bitumen shall not be exposed during storage and mix production to tem-

peratures of more than 350F (177 C).

Mix producti on temperatures.The temperature of mix immediately after discharge from the pugmill may be as lowas can be demonstrated to get good coat-ing and compaction to reduce binder hard-ening. However, the temperature immedi-ately before unloading from the tip-truck should not be less than 125 C and at thecommencement of initial rolling should

not be less than 110 C as per Clause4.2.4.5 (f) and 4.2.4.5 (g) of SPJ respec-tively. On the upper limit, Asphalt Instituterecommends that the temperature shall benot more than 325 F (163 C).

Dry and wet mixing times.The dry mixing time of aggregate and filler in the pugmill should be minimal -

usually not more than 10 seconds. Thewet mixing time of bitumen, aggregateand filler should be no longer than needed to uniformly mix the aggregate and coatthe aggregate with bitumen - usuallyabout 30 to 35 seconds.Unnecessary longwet mixing time reduce plant output and

promote additional age hardening of themix.



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The pugmill live zone.Aggregates, mineral filler and bitumenare mixed in the pugmill. It should be

operated at or just below nominalcapacity; overloading and underload-ing the pugmill will decrease the effi-ciency of the mixing process.

Overloading the pugmil l. Non-uniform mixing will occur if the pugmill is overloaded. At maximumoperating efficiency, the paddle tipsshould be barely visible in the materialat the top during mixing. Materialabove this level tends to float abovethe paddle and is not mixed.

Underloading the pugmil l.An insufficient batch will not bemixed properly because there is notenough material to carry around in the

paths of the paddle tips.



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In a batch plant, vibrating screens are used to separate hot and dry aggregates into frac-tions of specified sizes and deposit each into separate hot bins. The separation should bemade so that the amount of material in each hot bin is in balance. Imbalance hot bins sig-

nal a need for corrective action elsewhere, usually in the cold aggregate feed.

If screen openings are plugged or if too much aggregates are fed to the screens, carry-over ie. depositing of fine aggregates into larger aggregate bins will result. Varying cant'-over will cause a lack of uniformity in the aggregate gradation. Excessive cant'-over will resultin a dry mix due to an increase in the amount of fine aggregates in the mix. Correctivemeasures include cleaning screens and adjusting the cold aggregate feed.

If screens are excessively worn out, oversize aggregates will be deposited into fine aggre-gate bins.

Each hot bin should be large enough to prevent depletion of aggregates during full capaci-ty operation of the mixing plant. Each bin should have an overflow pipe to prevent aggre-gates from backing up into other bins and avoid overfilling to the point where the vibrat-ing screen will ride on the aggregate. Should this happen, it will result in a heavy cant'-over and damage to the screen.

Worn gates at the bottom of the bins will allow leakage of aggregates into the weigh hopper and affect the specified aggregate gradation.



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Site preparation

Paving work should only be carried out on dry surface or if so specified, has received a

bituminous tack coat which should have a satisfactory degree of tackiness.

Immediately prior to applying bituminous tack coat, the full width of the surface to betreated should be swept using a power broom followed by a compressed air blower, and if necessary, scraped using hand tools to remove all dirt, dust and other objectionable materi-als.

Bituminous tack coat should only be applied to a clean, dry, bituminous or bitumen primed surface. It should be applied as far in advance as is necessary to achieve a satisfac-tory degree of tackiness before the overlying material is placed.

The rate of application of bituminous tack coat is typically in the range 0.25 to 0.55litres/sq.m. It should be distributed uniformly over the surface without streaking (see pic

below).

Traffic should be kept off the tack coat at all times.



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S ite preparation

Surface preparation and clean-ing.Bituminous tack coat should beapplied only to a clean and dry bitumi-nous or bitumen primed surface. Thesurface should be thoroughly cleaned of all dirt, dust and other objectionablematerial including loosely scattered cold mix as per Clause 4.2.2.4 (b) of SPJ.

No loose materials.Loosely scattered cold mix should beremoved prior to the application of tack coat.

Tack coat.Tack coat material should be rapid set-ting bitumen emulsion of grade RS-1K. The rate of application is usually

between 0.25 to 0.55 litres/sq.m, dis-tributed uniformly over the surfacewithout streaking (not as shown in pic)as per Clause 4.2.2.4 (c) of SPJ. Tack coat of inferior grade such as RS-OK or K1-40 should not be used.



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Site preparation

Too much tack coat.Too much tack coat will promote slip-

page of the new layer on the old pave-ment or bleeding into the new layer.

Too little tack coat.Too little tack coat or non-uniform dis-tribution will not provide the needed

bond between the old and new layers,and will promote slippage and crack-ing in the new layer.

Surface protection.Traffic should be kept off the tack coatat all times prior to the placement of asphalt. Thus tack coat should only beachieve a satisfactory degree of tacki-ness.



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Site preparation

No paving in the rain. Paving work should only be carried out in dry weather. Rainwill reduce mix temperatures and thus affect compaction. Cavities will also be formed once the trapped moisture eventually evaporates.



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Belivety of asphalt

The contractor should provide a suitable number of tip-trucks of a type approved by theS.O. for transporting asphalt from the mixing plant to the site.

The trucks should have trays with smooth, flat beds and sides with tailgates.

The truck bed should be free of material that may be detrimental to asphalt. Any debris inthe bed from previous use of the truck should be removed.

After being cleaned, the inside surface of truck bodies shall be treated with a thin coatingof a non-petroleum based release agent such as soap or detergent solution to preventasphalt from sticking. Petroleumbased materials such as diesel may change the propertiesof the asphalt.

Each truck should be equipped with a tarpaulin which should be large enough to cover the bed and wrap over the sides and ends. This is to protect the asphalt from contamination bywater, dust, dirt and other deleterious materials, and to maintain the temperature. The tar-

paulin should be made of water repellent material and should be of sufficient strength and weight to resist tearing.

Care should be taken in the truck loading, hauling and unloading to prevent segregation of the mix.



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Delivery of asphalt

Loading the tip-truck.The truck should be loaded in multipledrops of mix on to different parts of

the truck bed. This method will min-imise the distance that any coarseaggregates can roll and thus reducesegregation.

Delivering mix to paver.In delivering mix to the paver, the tip-truck should be reversing and stopshort of the paver. The paver thenshould move forward to pick up thetruck. The truck should never back into and bump the paver.

Discharging mix intopaver hopper.Only the rear wheels of the tip-truck should be in contact with the paver

push rollers. The truck bed when raised should not be in contact with the hop-

per and should not press down the paver. The truck bed should be raised smoothly to reduce segregation.



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laying of asphalt

There are three main types of paver;

Fixed screed paver. Normally used for laying a concrete pavement. Have a screed which is fixed at the beginning of the paving operation and cannot be adjusted while the paver is in motion. The height of the screed and thus the thickness of the mat produced is determined by road forms upon which the paver runs. The road forms also form the edge of the mat.

Slipfor rn paver.Also a concrete paver but does not need road forms to contain the material. The edge of the mat iscontained by long forms which travel with the paver and are connected to the sides of the paver atits varying laying widths.

Floating screed paver.Most associated with the laying of asphalt pavement. The paver may be fitted with a fixed screed or a hydraulically extendable screed which can lay varying widths. The screed can be mounted oneither wheels or tracks. There are three types of screed; vibrating screed, tamping screed, combina-tion vibrating/tamping screed. The screed strikes off, partially compacts and irons the surface of the mat as it is pulled forward.

Generally, each paving layer should have a compacted thickness of not less than twice the nominalmaximum aggregate size of the mix and not more than 100 mm.

Laying should commence along the lower side of the carriageway and progress to the higher side.

Laying should not be carried out in a downhill direction along any section of the road.

As the paver spreads its load, the mat should be frequently checked for thickness. The texture of the unrolled surface should be uniform. If it is not, screed adjustments may be necessary. Theadjustment of the screed, tamping bars or vibrators, spreading screw hopper feed and other adjust-ments should be checked frequently to ensure uniform spreading of the mix.

The paver screed is usually equipped with heaters to prevent the mix from sticking to the screed plate. They are used to heat the screed at the start of paving operation. They should never be used to heat the mix being delivered to the paver.



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Laying of asphalt

The amount of mix carried ahead of the screed should be kept uniform; variation mayresult in surface roughness. This will require maintaining sufficient material in the hopper

to supply the spreading screws with enough mix to cover at least 2/3 of the depth of thescrews out to their ends.

When the next truck is ready to move into position, the hopper wings can be folded to pre-vent excessive build-up of cold mix in the hopper corners. If excessive, this cold materialmay result in a poor surface texture and an area prone to ravelling.

When automatic screed controls are used to control the grade and slope of the pavementlayer being constructed, all sensors should be checked regularly.

If a stringline is used as the grade references, the line should be very taut. Every effortshould be made to keep personel and equipment from comming in contact with the string-line and disturbing it.



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Laying of Asphalt

Continuous paving.The paver should be operated continu-ously at a uniform speed. The supply

of bituminous mix should be regulated so as to enable continuous paving.Intermittent stopping and restarting of the paver should be avoided and trans-verse joints kept to a minimum (Clause4.2.4.5 (g) of SPJ).

Constant feed of mix toscreed.Substantial fluctuation of the quantityof mix in front of the paver screed willcause the screed to fall and rise inresponse to the change of forces actingon it. Uncontrolled falling and rising of the screed will cause a change in matthickness and the formation of surfacewaves.

Operating hopper wings.The hopper wings should be folded only when necessary to prevent exces-sive build up of cold mix in the hopper corners. The cold mix may result in

poor surface texture and an area proneto ravelling. The paver hopper should

be about one third to half full when thewings are folded. Dumping of mixfrom the wings into a relatively emptyhopper promotes segregation and poor surface texture.



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Hand casting

As far, as is practicable, laying should be carried out using a paver. Hand casting of mixon to the paver finished surface for correcting localised blemishes and irregularities should

be kept to a practicable minimum. If the defects are substantial, paving should be stopped and mix composition, delivery and placement should be reviewed.

If the paver is in good condition and properly adjusted, and if the paver is not spreadingthe mix at an excessive rate or speed, there should be little or no need for hand casting.

Surplus mix should not be cast on to the mat surface as this will result in poor surface tex-ture even after proper compaction is obtained. In addition, coarse aggregates on the sur-face tend to crack under the roller, will not bond properly with the mix placed by the paver and tend to be dislodged by traffic. The surplus mix shall be added back into the paver

hopper.

Only in areas inaccessible to the paver shall laying be carried out by hand methods usingrakes, lutes and other approved hand tools.



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Hand casting

Minimum hand casting.The most uniform surface texture can beobtained by keeping hand casting behind the paver to a minimum as per Clause4.2.4.5 (g) of SPJ. If the mat placed by the

paver shows substantial blemishes and irregularities, mix composition, deliveryand placement should be reviewed and corrected.

No excessive hand casting.Excessive hand casting and raking to cor-rect blemishes and irregularities, and man-ual addition or removal of mix to correctlevels will result in poor surface textureand inadequate functional performance of the pavement even after proper com-

paction is obtained.

Discard coarse aggregates.If occasional hand casting of mix isrequired to correct localised blemishesand irregularities. coarse aggregates caston top of the mat must be removed and discarded by arake because they tend tocack under the roller and will not bond

properly with the mix placed by the paver.



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Compaction of asphalt

Compaction is the densification of asphalt by the application of pressure initially from the paver tamper and subsequently from the rollers.

The performance and durability of the pavement depend largely on the degree of compactionachieved. Good compaction improves structural strength and resilience of the pavement, increasesresistance to rutting and reduces moisture penetration and age hardening.

For each layer of mix, compaction by rolling should commence as soon after laying as the materi-al will support the rollers without undue displacement. As a guide, the temperature at which rolling

begins for normal asphalt is usually between 125 C to 135 C. It should not be less than 110 C as per Clause 4.2.4.5 (i) of SPJ because even if the density is adequate, compaction at low tempera-tures could induce excessive strains in the binder film which result in hair-line cracks. Too high atemperature is also not advisable as the mix will tend to flow under the rollers, resulting in anuneven surface and many fine cracks.

Initial or breakdown rolling should be carried out with an approved steel wheel roller. The princi- pal heavy rolling should then follow immediately with an approved pneumatic tyre roller. Thefinal rolling should be carried out with an approved steel wheel roller to eliminate minor surfaceirregularities or roller marks left by the pneumatic tyre roller.

All rollers should operate in a longitudinal direction with their driven wheels towards the paver.Rolling should generally commence at the lower edge and progress uniformly to the higher edgeexcept where there is a longitudinal joint which should be rolled first.

If the rollers can not keep up with the speed of the paver, more rollers should be used or the paving operation be slowed down.

Compaction should be carried out in such a mannerthat each section receives equal compactiveeffort and that no roller marks are visible after final rolling.



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Establishing compactive effort.Rolling temperatures, rolling pattern, and the type and weight of rollers should beestablished during the plant trial. As aguide, the temperature at the commence-ment of rolling for normal asphalt is usual-ly between 125 C to 135 C. The rolling

pattern should not only include the number of passes but also the location of the first

pass, the sequence of succeeding passesand the overlapping between passes.

Steel wheel roller.Steel wheel roller can be either two-axletandem or three-wheeled. The operatingweight should be in the range of 8 to 10tonnes and its driven roller drum should exert a rolling force of not less than 3.5tonnes per metre width of roller drum as

per Clause 4.2.4.4 (e) of SPJ. The roller

should be regularly checked for wear of the wheel rims.

Pneumatic tyre roller.The operating weight of pneumatic tyreroller should be not less than 15 tonnes as

pe Clause 4.2.4.5 (i) of SPJ. All tyres must bE inflated to an equal pressure and should be not less than 0.7 Mpa.

Also note that the speed of all types of roller should not exceed 5 km/h. Sharpturns and quick starts or stops should beavoided.



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Taking core samples.Within 24 hours after compaction, coresamples should be obtained at a rate of 1sample for every 500 sq.m of mix laid butnot less than 2 samples for each pavingsession as per Clause 4.2.4.5 (i) of SPJ.The core samples should be used to deter-mine the compacted thickness and densityof the mix.

Density & thickness require-ments.The required compacted density is 98-100% of the Marshall density for wearingcourse and 95-100% of the Marshall den-sity for binder course as per Clause 4.2.4.5(i) of SPJ. The average thickness over any100 metre length should be not less thanthe required thickness and the minimumthickness at any point should be not lessthan the required thickness minus 5 mm as

per Clause 4.2.4.5 0) of SPJ.

Opening to traffic. Newly laid mix should not be opened totraffic until compaction has been complet-ed and the material has thoroughly cooled and set. This will usually be not less than4 hours after the commencement of rollingas per Clause 4.2.4.5 (k) of SPJ.Premature opening to traffic will promotesecondary compaction and thus deforma-tion along the wheelpaths.



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Construction joints

Construction joints are generally the weakest part of a pavement; every effort should be made tokeep the total number of longitudinal and transverse joints as low as practicable.

Joints are typically constructed either as hot joints (longitudinal only) or cold joints.

True hot joints are produced with pavers operating in echelon.

Paving in echelon is often not feasible because of traffic restrictions and/or the plant is not capableof producing sufficient mix for more than one paver. In this case, a paver is operated on a laneover some distance before it is shifted back to pave an adjacent lane. This technique is calledsemi-hot joint construction.

There are no firm rules on semi-hot joint construction. As a guide, lanes of approximately 300 mlength (or about 2 hours paving time) have been constructed successfully without joint treatment.

Where cold longitudinal or transverse joints are required, the material first laid and compacted should be cut back to a vertical face for the full thickness of the layer on a line satisfactory to theS.O. before the adjacent area is paved.

At all construction joints, a thin uniform coating of bitumen emulsion of grade RS1K should be brushed on to the vertically cut joint faces before laying the adjacent section to ensure good bond-ing. All contact surfaces of kerbs, manholes etc should also be treated similarly.

Construction jpints should be pffset from those in any immediately underlying layer by at least100 mm for longitudinal joints and 500 mm for fransverse joints as per Clouse 4.2.4.5 (h) of SPJ.



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Joint preparation

Cut joint f aces must be pro-tected.Cutting and preparation of joints should

be carried out only as far in advance of paving as is necessary. Cut joints must beadequately protected from constructionmachinery and traffic.

Applying tack coat to cutfaces.At all construction joints, a tack coatusing RS-1K should be brushed or sprayed neatly on to the vertically cut

joint faces. Vertical faces of existing pave-ment such as kerbs and manholes should

also be tre; similarly as per Clause 4.2.4.5(h) of SPJ.

Shoddy practice.

The aftermath of spraying the cut jointfaces with tack coat material at an uncon-trollable rate.



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Joint preparation

An example of a neatly cut and prepared longitud inal jo in t.



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Transverse joint construction

Starting blocks .The screed of the paver must be set onstarting blocks on the cold side of a trans-verse joint to provide space above the sur-face of the compacted lane and thus allow

placement of mix of sufficient thickness.The excess material should be pushed

back with an appropriate hand tooltowards the joint. The thickness of theoverlap should be about one-fourth of thedesired compacted thickness. It is animproper and a very poor practice to setthe screed directly on the cold mat.

No excessive hand work.Placement of hot mix at the joint by hand and excessive raking to correct levels inthe absence of starting blocks will resultin poor joints.

Compacting transverse joints.Ideally, a transverse joint should be com-

pacted in a transverse direction with aroller. The roller should operate on thecompacted lane and overlap the joint byabout 150 mm over the uncompacted lane. The roller is gradually shifted acrossthe joint until the entire roller drum is onthe new mix.



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Transverse joint construction

Bond breakers.To allow for easier removal of materialdownstream of a transverse butt joint, a

bond breaker in the form of thick paper or sand shall be used, otherwise the materialmust be sawed. Alternatively, a bulkhead shall be inserted before the material isrolled (see pic). Unless the bulkhead isfirmly placed, this method shall not beencouraged as it may be dislodged by traf-fic.

Surface roughness.Poorly constructed transverse joints con-tribute towards surface roughness and rid-ing quality of the pavement.

A bad jo in t.An example of an unsatisfactorily con-structed transverse joint.



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Longitudinal joint construction

Constructing longitudinal joints.During the construction of longitudinal

joints, the end plate of the screed should overlap the compacted lane by about 25to 50 mm; the excess material should be

pushed back with an appropriate hand tool towards the joint. The thickness of the overlap should be about one-fourth of the desired compacted thickness.

Compacting longitud inal joints.During the compaction of longitudinal

joints, the roller should operate on thecompacted lane and overlap the joint byabout 150 mm over the uncompacted lane. The roller should continue to operatealong this line, its position being shifted

gradually across the joint until a thor-oughly compacted neat joint is obtained.

No excessive hand work.Excessive raking during the construction

of longitudinal joints should not beallowed except to push excess materialtowards the joint.



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Surface waves and roughness

There are two primary types of waves in asphalt surfacing; short waves and long waves. Shortwaves are generally 0.5 to 1.0 m apart. Long waves are considerably further apart. A washboard effect is a defect which is typically caused by improper operation of the vibratory roller. The dis-tance between this type of waves is generally small, typically less than 0.5 m.

Clause 4.4.3 of SPJ terms surface roughness as longitudinal irregularity and is defined as a varia-tion in profile of the road surface as measured by a rolling straight edge or a straight edge deviceand a wedge. The maximum permissible number of longitudinal irregularities over a traverse

length of 300 m for depth exceeding 4 mm and 7 mm is given in Table 4.14 for three classes of surface regularity. The maximum permissible depth of transverse irregularities for three classes of surface regularity is also given in Table 4.14 of SPJ.



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Surface waves and roughness

Short waves.The waves are generally 0.5 to 1.0 mapart. Possible causes are;- Fluctuating head of material in front of

paverscreed.- Frequent changes in paver speed.- Poor mechanical condition of screed.- Improper mounting or use of automatic

grade control devices.- Bumping of paver by tip-trucks.- Improper rolling technique.- Excessive hand casting.

Long waves.The waves are considerably further apart(greater than 3 m) and are frequently asso-ciated with overall lack of bearing capaci-ty of the subgrade. They may also corre-spond to the distance between tip-truck loads of mix. Variation in mix composi-

tion or temperature may be the cause.

Washboard effect .This defect is typically caused by improp-er operation of the vibratory roller.Overrolling, rolling when mix is too hotor roller travelling too fast may be thecause. The distance between waves isgenerally less than 0.5 m.



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CHECKLISTCHECKLIST



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A guide to good quali ty cont rol pract iceson asphalt productios and constructionFOR INTERNAL USE ONLY

Good quality control 2005.pdf

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