The Principles of Asphalt Laying Works From A ~ Z

1- Introduction

There are two types of asphalt paving mixtures most famous in terms of components, specifically, the binder, which is bitumen of petroleum origin 60/70 and the other is polymers.

2- The scope of this article.

In this article, we will talk about individual asphalt paving mixes from materials that make up the mixture and how to properly lay them out. But we will not discuss how to design the asphalt mixture.

3 Materials for Asphalt paving Works

???3.1 Fine Aggregate for Asphalt Works?

1. ?Fine aggregate shall be in compliance with project specifications.

?????3.2??Coarse Aggregate for Asphalt Work

1. Coarse aggregate shall be in compliance with project specifications

??????3.3?????Mineral Filler

1. Mineral filler, when supplied from and external Source, shall be in compliance with project specifications

??????3.4?????Bitumen

1. The bitumen specified for use in the asphalt mixes shall be 60-70 penetration grade in accordance with ASTM D 946 and as per table 5.4 requirements and shall only be obtained from approved sources.
2. The refining of petroleum is producing The bitumen. It shall be uniform in character and shall not foam when heated to 1750C. The blending of bitumen materials from different refineries will be used only with the written approval of the Engineer.

3.5?Prime Coat Material

1. The liquid asphalt to use in Asphalt works shall be MC 70 medium curing cutback asphalt as per project specifications and in accordance with AASHTO M 82.
2. The prime coat shall be cutback bitumen consisting of a 60/70 penetration grade bitumen and Kerosene. The residue from the distillation test, carried out to 360 °C in accordance with ASTM D 402 shall be minimum 55% (by volume), as determined by the difference method. One sample shall be tested every 5 tons.

1. ?Immediately after cleaning the previous laid and approved Aggregate road base / subbase?surface, the Prime Coat shall be applied by means of the distributor at the temperature and rate in accordance with project specifications. Air Compressor and hand brush / Mechanical broom shall be provided for cleaning as and when required.
2. The rate of application of PC shall be determined in advance by setting the speed of Distributor to apply required quantity/rate at all time. Prime coat rate shall be between 0.45 to 0.75 Kg/m2. Excessive application of prime coat shall be avoided.
3. The application temperature for the MC-70 liquid asphalt shall be between 60°C and 85 °C.
4. The Implementation rate for spraying prime coat shall be controlled by placing a square of wood on the surface being sprayed that the tanker then drives over and then subsequently removed and weighed to check that the application rate is correct.
5. The prime coat to the aggregate base layer shall be left until the required curing time – being 48hrs or such lesser time as may be approved by the Engineer.
6. No traffic is allowed on the primed surface for a period a minimum of 48 hrs or lesser time as approved by the Engineer.
7. No prime coat application shall be done in bad weather condition such as heavy wind, Dust etc.

3.6 Tack Coat Material

1. Emulsified asphalt for use in asphalt works shall be CSS-1h or CRS-2 cationic emulsified asphalt as specified in project specifications, in accordance with AASHTO M208 or SS-1h anionic emulsified asphalt in accordance with ASTM D977 or AASHTO M140 unless otherwise designated.
2. The emulsified asphalt shall be of the slow-setting cationic or anionic type of the CSS-1h or SS-1h grades respectively and shall conform to the designated requirements. One sample shall be tested every 5 tons.

???Tack coat application.

1. Immediately after cleaning the laid and approved asphalt Base Course surface, the tack coat shall be applied by means of the distributor at the temperature and rate in accordance with project specifications and as directed by the engineer.

2. The tack coat shall be applied at a rate between 0.15 to 0.38 kg / m2?in accordance with project specifications and as directed by the Engineer. Tack coat rate of application shall be determined by setting the speed of the distributor will be prefixed in such a manner to apply the required quantity always.

3. The application temperature for the Tack coat shall be between 10?0C and 60?0C in accordance with project specifications and as directed by the Engineer.

4. The tack coat shall not be applied when the ambient temperature is less than 130C nor during rain, fog, dust storm or other unsuitable weather.

4. Construction Methodology

4.1 Sequence of Work

1. Daily Schedule shall be agreed with the Main Contractor in order to enable request for inspection (RFIs / INRs) to be raised and issued to the Consultant by the Main Contractor with sufficient notice period at all stages of activity.
2. In advance of the start of the surfacing works, prepared areas of the specified portion shall be jointly inspected by the Supervisor and the Customer’s Site Engineer and agreed ready for laying operations to commence by signing off the inspection checklist.
3. Prior to the commencement of delivery of the mix, reference guide pins shall be erected and maintained for controlling the levels of the laid mix. The reference guide pins shall be spaced at intervals of not More than 10 meters apart.

Note: Guide Pins shall NOT be used when laying utilizing the Multiplex systems manufactured and supplied by Vogele as these ‘conflict’ with the averaging function of this system.

4. Sufficient plant capacity, haul vehicles and storage shall be provided so that adequate supplies of the mixture are delivered to site to ensure that continuous paving can be achieved.

5. The dispatching of the hauling vehicles to the job site shall be so scheduled that all material delivered may be placed in daylight, or under sufficient artificial light as and when necessary. Delivery of material shall be at a uniform rate and in an amount well within the capacity of the paving and compacting equipment.

6. All asphalt vehicles shall be reversed with the aid of a banks man through the site. The bank's man’s dual functions shall be to both ensure that the reversing operations are conducted safely and wherever possible, to also ensure that the paving machine runs to the Asphalt vehicle, rather than asphalt vehicle reversing to the paver. Asphalt lay can commence once the paver reached the delivery truck. Paver speed shall be adjusted in accordance with the paving width.

7. The hauling vehicle shall not be permitted to carry out tight turns on the Asphalt surface, freshly laid.

8. The mixture at delivery to the paver shall be within 140C of the Job Mix Formula temperature and above a temperature of 135?Material which has fallen below the minimum temperature of 135?0C before discharge and 120 C before rolling shall be rejected and immediately removed from the site. Delivery temperature shall not exceed the maximum temperature specified for mixing at the plant.

9. Should a significant proportion of the mixture delivered to the paver fail to meet this requirement, or should cold lumps be found in the mixture, the Engineer shall order that paving operations be suspended until measures are taken, to the approval of the Engineer, to ensure compliance.

10. Delivery Notes’ of the asphalt materials delivered to the site shall be forwarded to the Main Contractor’s QC at the site or as directed by the Client / Engineer.

11. Inspection and control shall be in accordance with the project’s specifications.

4.2 Spreading and Finishing

1. The use of motor grader or hand spreading of the asphalt mix shall not be permitted except in places where it is impractical to use?pavers and shall be only with the specific permission of the Engineer. The asphalt mix shall comply with all conditions regarding trueness of level, thickness and homogeneity of the mix.
2. Asphalt pavement Base and Wearing Courses shall be constructed to the designated lines, grades and thickness. The total thickness of all courses shall not be less than specified per project’s specifications in no case shall construction of a new asphaltic wearing course begin until the previously laid base course has been tested and approved unless otherwise approved in writing by the Engineer.
3. The mix shall be laid upon an approved surface and only when weather conditions are suitable and as designated. Upon arrival at the point of use, the asphalt mix shall be spread and struck off to the grade, elevation and cross-section shape intended, either over the entire width or over such partial width as may be required.
4. If during lay, the paver is repeatedly delayed because of lack of mixture or if the paver stands at one location for more than thirty minutes (for any reason), a transverse joint shall be constructed. Paving shall not recommence until the paver will proceed uninterrupted and until at least four loaded vehicles (or sufficient to complete if fewer) have arrived at the paving site.

5. Longitudinal joints in Wearing course should be set to run under the white lining marks where possible.

6. The levels and regularity of the finished surface of the Wearing Course Asphalt and underlying layers of Asphalt shall, wherever reasonably practicable, be controlled by the Multiplex levelling systems manufactured and supplied by Vogele and which shall be fitted to the Asphalt Paving Machines. Consisting of ultrasonic averaging beams, the system ensures that any minor irregularities in the surface finish are progressive ‘averaged-out’ as each subsequent layer of asphalt is laid, in order to ensure that the surface level of the finished Wearing Course asphalt layer meets the Specification requirement

7. When laying in Echelon, the lead Paving Machine shall be equipped with two Averaging Beams, one on each side of the Paver with the second, following, Paving Machine being equipped with an averaging beam picking-up the levels set by the Lead Paver.

8. The levels shall be checked by the asphalt supervisor using offset steel level pins normally at 10 - 5meter intervals.

4.3 Compaction of Mixes

1. At least three rollers shall be required at all times, two self-propelled pneumatic-tyred and one self-propelled steel-wheeled. As many additional rollers shall be used as necessary to provide specified asphalt course density and surface characteristics in an orderly, efficient and continuous manner.
2. Before commencement, unless otherwise agreed with the Engineer, laying & compaction trials shall be undertaken to establish an approved compaction procedure.
3. The compaction trials shall involve all procedures specified for the permanent works including testing as specified for the asphaltic wearing course under consideration and any equipment, processes or procedures proposed which are not designated shall be agreed by the Engineer.
4. Immediately after the asphalt mix has been spread and struck off, the surface shall be checked and any irregularities adjusted and then compacted thoroughly and uniformly by rolling.
5. After the longitudinal joints and edges have been compacted, rolling shall start longitudinally at the sides of the road and shall gradually progress towards the Centre. On superelevated sections, roller shall begin on the low side and progress to the high side, overlapping on successive trips by at least one-half the width of tandem rollers and uniformly lapping each proceeding track. The roller shall move at a slow but uniform speed with the drive wheels nearest the paver. The speed shall not exceed 4-5 km/h for steel-wheeled rollers or 8 km/h for Pneumatic-tyred rollers.

6. Field density of core sample shall be determined as per project’s specifications, for example, minimum 97% for base course and 98%for Intermediate and Wearing course and maximum 101.8% of the?Daily Marshall Density.

7. The thickness, level and evenness of the asphalt layer and surface shall comply with the project’s specifications.

????4.4?????Paving Edges.

1. The edges of the asphalt course shall be rolled concurrently with or immediately after rolling the longitudinal joint.
2. Care shall be exercised in consolidating the course along the entire length of the edges. Before it is compacted, the material along the unsupported edges shall be slightly elevated with hand tools. This will permit the full weight of the roller wheel to bear on the material to the extreme edges of the mat.

????4.5?????Breakdown Rolling.

1. Breakdown rolling shall immediately follow the rolling of the longitudinal joints and edges. Rollers shall be operated as close to the pavers as possible to obtain adequate density without causing undue displacement. In no case shall the mix temperature be allowed to drop below 120 0C before breakdown rolling.
2. If the breakdown roller is steel-wheeled, it shall be operated with the drive wheel nearest the finishing machine. Pneumatic-tyred rollers may be used as breakdown rollers.

????4.6?????Intermediate Rolling.

1. Pneumatic-tyred rollers or steel-wheeled rollers shall be used for the intermediate rolling.
2. The intermediate rolling shall follow the breakdown rolling as closely as possible and while the paving mix is still hot. Rollers shall be used continuously after the initial rolling until all of the mix placed has been thoroughly compacted. Turning of rollers on the hot paving mix which cause undue displacement shall not be permitted.
3. The pressure range for the pneumatic tyred rollers shall be in accordance project’s specifications.

?????4.7??Transverse Joints.

1. Transverse joints shall be carefully constructed and thoroughly compacted to provide a smooth riding surface and to be checked by the straight edge to assure smoothness and true alignment. Joints shall be formed with a bulkhead, such as a board to provide a straight line and vertical face.
2. The roller shall be placed on the previously compacted material transversely so that not more than150 mm of the rear rolling wheel rides on the edge of the joint. The roller shall be operated to pinch and press the mix in to place the mix at the transverse joint. The roller shall continue to roll along this line, shifting its position gradually across the joint, in 150 to 200 mm increments, until the joint has been rolled with the entire width of the roller wheel. Rolling shall be continued until a thoroughly compacted, neat joint is obtained.

4.8??Longitudinal Joints.

1. Longitudinal joints shall be rolled directly behind asphalt Paving operation after completion of the transverse joint. When the butting line has not been placed in the same day, or the joints distorted during the days work, the edge of the line shall be carefully trimmed to lane, cleaned and painted with a thin coating of tack rapid cure before the adjacent line is placed.
2. The roller shall be shifted over onto the previously placed lane so that not more than 150 mm of the roller wheel rides on the edges of the newly laid lane. The rollers shall then be operated to pinch and press the fine material gradually across the joint. Rolling shall be continued until a thoroughly compacted, neat joint is obtained

4.9 Finish Rolling.

1. The finish rolling shall be performed with a steel wheel roller. Finish rolling shall be accomplished while the material is still warm enough for the removal of roller marks.
2. All rolling operations shall be conducted in close sequence.
3. In place inaccessible for the operation of standard rollers as specified, compaction shall be performed by manual or mechanic tampers.
4. ?After the final rolling, the smoothness, levels, cross falls, density and thickness shall be checked and any irregularity of the surface exceeding the specified limits and any areas defective in texture, density or composition shall be corrected as directed by the Engineer.

5. Protection of Laid Courses

1. Sections of the newly finished works shall be protected from the traffic of any kind until the mix has been properly compacted and cooled. In no case shall traffic be permitted less than 48 hours after completion of the asphalt course unless a shorter period is authorized by the Engineer.

6. Major Plant and Equipment-?Spreading and Finishing Equipment

????6.1???Asphalt Paving Machine

1. The asphaltic mixture shall be fed to the paver by end tipping of the truck or where practicable via the Road tech Shuttle buggy Material Transfer Vehicle (see 6.1.1 above). The equipment for spreading and finishing the asphaltic paving mixtures is an approved mechanical, self-powered electronic controlled floating screed type, capable of spreading and finishing the mixture true to line, grade and required a crown.

??6.2??Rolling Equipment

1. Rolling equipment will consist of vibratory steel-wheeled rollers and pneumatic-tired rollers as required for proper compaction and finishing of the asphalt paving surface.

?6.3???Liquid Bitumen Distributor

1. The liquid bitumen distributor truck is pressure type with insulated tank. The gravity distributor trucks will not be used. Also, the characteristics of the truck will be in accordance with the project’s specifications.

?Rolling pattern

Rolling patterns for asphalt paving shall be conducted as per the following explanation, to confirm that laid and rolled asphalt has reached the required compaction density shall be minimum 97% for BC and 98% for IC and SC and 101.8% maximum of?Daily Marshall density,?as per project’s specifications requirement.

One?Rolling Pass?is defined as being the movement of a Roller from the start-point, or joint, to the asphalt-paver and back to start-point,?noting that Rollers must keep a five-metre‘ safety distance’ from any plant or personnel in the direction of travel.

Care must be taken to avoid changes in the Direction of Rolling (ie halfway through a Rolling Pass) at the same chainage-point along the carriageway for each subsequent Rolling Pass

?All rolling shall be parallel to traffic-flow/travel unless in the case of cross-rolling a cold-formed joint (across the carriageway) which shall be undertaken as directed.

Aggressive braking and sudden changes in direction of all Rollers shall be avoided

All Rollers must be parked off the mat when not in use and under no circumstances shall a Steel Wheel Vibrating Roller (SWR) be stopped on the mat with vibration turned-on

The number of Rollers shall be as described in the method statement. There shall be a minimum of 1 SWR (this will be the ‘Lead Roller’) and 2 Pneumatic Tyred Rollers (PTR) per asphalt Paving Machine.

Break Down Rolling

Unless varied by written instruction, Rolling shall only commence when the asphalt Paving being laid is at the required temperature of?135oC - 140?°C for?Base Course only?and?no rolling shall commence when the laid asphalt is above these temperatures. Rolling will start first from Transverse and then longitudinal joints, if any, prior to starting rolling off the mat. In no case shall the mix temperature be allowed to drop below 120oC before breakdown rolling.

Rolling shall start with the Lead Roller (SWR) without vibrating the asphalt Paving and shall be started from the low side of the asphalt mat –?the length of a Rolling Pass shall be determined by the temperature of the laid asphalt?Paving. This initial Break-Down Rolling shall proceed by moving the SWR half a Roller-Width across the preceding Rolling Pass for each subsequent Rolling Pass (see Fig 1 below); shall be undertaken such that the SWR(s) does not stop at the same chainage for each Rolling Pass and shall continue until the asphalt has been rolled the full width of the asphalt mat being laid by the paver.

Following this Break-Down Rolling, the SWR shall start rolling?with vibration mode?from the low side of the mat and, as above, shall move half a Roller-Width across for each subsequent Rolling Pass (see Fig 1 below) across the full width of the mat laid by the Paving Machine. This shall be repeated up to three times or until such times the asphalt mat start to produce small fine cracks on the surface. In no case shall the mix temperature be allowed to drop below 120oC before breakdown rolling.

PTR Rolling

Following SWR Vibration Rolling, the SWR(s) shall be withdrawn from the mat until final ‘Back Rolling’ or moved further up the Mat (subject to the mat being at the correct temperature of?no more than 135oC for Base Course)?and compaction utilising the PTRs shall commence. There shall be no less than two PTRs per asphalt Paving Machine and PTR rolling shall be undertaken with the same five-metre safety gap in the direction of travel as above. PTR rolling shall start from the low side of the mat laid by the Paving Machine and shall continue by moving across the full width of the mat by half the width of the PTR’s on each subsequent Rolling Pass (see Fig 1 below). This shall continue for up to three Rolling Passes across the full width of the mat, or until such times that the required density is achieved.

PTR Rolling of the asphalt Paving mat shall only be undertaken on areas compacted by the SWR(s) and under no circumstances shall PTR rolling be undertaken where a PTR(s) creates visible ruts in the mat.

?PTRs must never stop at the same chainage on each Rolling Pass; aggressive braking and rapid changes of direction shall be avoided.

Final ‘Back Rolling’

Final ‘Back-Rolling’ shall be undertaken after the PTRs have completed their rolling and shall be undertaken with an SWR(s) without any vibration being used. Again, Back Rolling shall start from the low side of the mat and shall proceed by moving half an SWR-width per Rolling Pass until the required smoothness is achieved across the full width of the mat.

If two asphalt Paving Machines are laying in echelon, then two SWRs shall undertake the final Back Rolling for smoothness. The requisite number of SWRs shall work in echelon pattern across the full width of the carriageway; shall proceed across the full width of the carriageway by moving across by half an SWR width on each subsequent Rolling Pass (see Fig 1 below) and shall maintain a five-metre Safety Gap from all other Plant and Personnel in the travel of direction.

Areas inaccessible for the operation of standard rollers as specified, compaction shall be performed by manual or mechanical tampers.

After the final rolling, the smoothness, levels, cross falls, density and thickness shall be checked and any irregularity of the surface exceeding the specified limits and any areas defective in texture, density or composition shall be corrected as directed by the Engineer.

The thickness, level and evenness of the asphalt layer and surface shall comply with project specifications.

7. Particular Safety Precautions.

The attached Job Safety Analysis/Risk Assessment gives generic information about particular Safety precautions measures for Infrastructure of Pavement Works and shall be subject to a Site Specific Assessment of Hazards prior to work commencing.

All key personnel on this section of works are experienced in asphalt pavement works and shall be included into this method statement. Records of attendance at the toolbox meeting shall be kept and filed on site.

Before commencing any work the safe operation of the related equipment, as well as a safe method of doing asphalt pavement, shall be explained to all personnel that are involved at a toolbox meeting by the Asphalt supervisor responsible for that area. All Plant and Equipment are to be inspected and approved as required by the contract requirements.

8. Particular Environmental Protection Measures.

The environmental protection measures relating to the works, other special environmental protection measures need to be considered other than to keep the dust control to a level as appropriate to the surrounding environment.