Asphaltic Concrete on Roads in Malaysia: Is Quality Under Control?
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ASPHALTIC CONCRETE ON ROADS IN MALAYSIA: IS QUALITY UNDER CONTROL? Hanani Mohd Radzi Public Work Department Malaysia E-mail: [email protected] Mohd Hizam Harun Public Work Department Malaysia E-mail: [email protected] Wan Radhiah Wan Hanafi Public Work Department Malaysia E-mail: [email protected] ABSTRACT The introduction of asphaltic concrete in Malaysia has brought with it the problem of a through design process of the mixture composition and subsequent extensive control testing that are required to produce and lay the mixture to the required tolerances. However, it is unfortunate to note that many elements of the design, production and construction of the delicate mixture have been either blatantly ignored or manipulated by the contractors and the supervising consultants. While it is clearly stated in PWD guidelines that the initiation and execution of quality control testing must be not left to the contractor, it is a common practice in Malaysia to let the contractor carry out most or all the testing as a means to control the quality of the materials and construction works. Verification of test results by the supervising consultants is usually done on the basis of more or less effective surveillance, often by site staff with little or no training and experience. As such, PWD is invariably presented with inferior quality of materials and constructed works which include asphaltic concrete as road surfacing material. A total of 21 work sites were surveyed to identify the problems at each site. This paper looks into the problems and suggests ways how they could be mitigated. 1 INTRODUCTION Many contractors tend to believe that design, production and laying of asphaltic concrete mixture are a straight forward task. Consequently, the quality of the mixture produced and subsequent laying of the road surfacing material at the construction sites are often taken for granted without realizing that such practices are bound to create undesirable premature failure to the road surfacing. Based on a study carried out jointly by Public Works Department (PWD) Malaysia and Transport Research Laboratory of United Kingdom on the performance of asphaltic concrete overlays in Malaysia that were designed and constructed to the specification of PWD, it was found that the performance had been dominated by the properties of the road surfacing material rather than the overall strength of the road pavement. A similar study carried out on some experimental bituminous overlays in Kenya had also shown that the performance of the overlays was primarily dependant on the properties of the overlay material itself. 1 It was the concern over by poor quality asphaltic concrete on the road pavements in this country that this study was initiated PWD which the primary aim was to investigate the current level of quality of asphaltic concrete that were being produced and supplied for the on-going road construction and rehabilitation projects of PWD throughout the country with respect to the current standard specification for road works of PWD. 2 OBJECTIVES The main objectives of this study were: i. To review asphaltic concrete quality framework within the current PWD Standard Specifications and Guidelines. ii. To review current practices in on-going road construction and rehabilitation projects of PWD in assuring acceptable standards in the production of asphaltic concrete as actually produced in the projects. iii. A member of on-going road construction and rehabilitation projects which were being undertaken by PWD had been identified throughout the country. Samples of asphaltic concrete produced by respective hot mixing plants were obtained from randomly selected tip-trucks and tested in the laboratory. These results were compared with more recent quality control test results obtained from the various sites visited. iv. To recommend improvements to handling and acceptance procedures of asphaltic concrete at mixing plants and laying sites. 3 BACKGROUND In Malaysia, there is a total of 137,219kilometers of roads which make up the whole road network of the country, 81.1% of which are paved. In the 1940s, paved roads in this country were mainly semi-grout and double surface dressing. Bitumen macadam was only introduced in the 1960s.Subsequently based on recommendations in the Malaysian Highway Maintenance Study in 1967, asphaltic concrete was adopted by PWD. Since then, asphaltic concrete has been widely used throughout the country on both Federal Roads and State Roads while the usage of bitumen macadam has been in general limited to State Roads only. 3.1Bitumen Macadam Bitumen macadam is composed of three (3) fractions of aggregate which are continuously graded, and bitumen. Its strength is primarily achieved through friction and mechanical interlock of the coarse aggregate. Air void contents in bitumen macadam are generally higher than asphaltic concrete and it is thus relatively permeable to air and water, and consequently not as durable as asphaltic concrete. The higher level of air voids ensures the proportions of the mixture are not as critical as for asphaltic concrete, thus easier to produce. As a wearing course material, specification for road work provides two recipes of bitumen macadam viz. nominal size 14mm with allowable binder content 5.0 +/- 0.5% ( BMW14) and nominal size 20mm with allowable binder content 4.9 +/- 0.5% (BMW 20) whereas the Malaysian Standard (MS 512) offers two nominal sizes (¾ “ and 1”) each for open textured and dense mixtures. 2 3.2 Asphaltic Concrete Like dense bitumen macadam, asphaltic concrete is continuously graded but contains less coarse aggregate, fine aggregate and mineral filler, coated with a higher quantity of bitumen. Differ from the recipe method of bitumen macadam, the composition of asphaltic concrete is determined by a thorough standard design procedure the aim of which is to carefully proportion the mixture of coarse aggregate, fine aggregate and mineral filler, and to arrive at optimum bitumen content to coat the aggregate particles for maximum stability and density, and adequate air voids. This results in an economical blend of aggregate and bitumen having high stability under traffic and good durability in service. During laying, the compaction of the material, which is governed by among others the type and size of rollers used, number of roller passes, rolling pattern and rolling temperatures, has to be carefully monitored to ensure that the compacted density achieved exceeds the minimum requirements so as to ensure that the air voids in the field are within the permissible limits. 4 PROBLEM STATEMENTS The introduction of asphaltic concrete in Malaysia has brought with it the problem of a thorough design process of the mixture composition and subsequent extensive control testing that are required to produce and lay the mixture to the required tolerances in the among others, aggregate gradation, bitumen content and air voids. However, from authors’ past observations while doing few rounds of auditing on site, it is unfortunate to note that many elements of the design, production and construction of the delicate asphaltic concrete mixture have been blatantly ignored or manipulated by the contractors and the supervising consultants. PWD Guidelines for Inspection and Testing of Road Works states that as far as practicable, all quality control testing of materials and workmanship should be directed and carried out by the staff of the PWD Superintending Officer (S.O.), or the Engineer responsible for supervision of construction. As a general rule, the initiation and execution of quality control testing must not be left to the Contractor. The Guidelines also states that a project laboratory for the exclusive use of PWD S.O or the Engineer responsible for supervision of construction will be provided for each road works contract. In contrast, it is a common practice in Malaysia to let the contractor carry out most or all the testing as a means to control the quality of materials and construction works. Verification of test results by the supervising consultants is usually done on the basis of more or less effective surveillance, often by site staff with little or no training and experience. With this kind of practice in place, it usually tends to bring the contractor’s focus on obtaining the signature of approval from PWD or supervising consultants rather than on actually controlling the quality of materials produced and the works constructed. This verification procedure is certainly not effective in controlling without fully supervising the conduct of tests. Serious errors made during production and construction will often not be detected or reported. Until premature failure prevails, even quality audits would not be able to detect the discrepancies as the test records indicate compliance and appear ‘verified’ by the consultant. When premature failure does prevail, a contractor’s typical reply is ‘the consultant approved it’. As such, PWD is variably presented with inferior quality of materials and constructed works which include asphaltic concrete for use as road surfacing material. The most common non-compliances that are the results of poor control on the quality during the production of asphaltic concrete which subsequently contribute to poor performance of the road surfacing material in service are: 3 i. Too much or little quantity of bitumen ii. Too coarse or too fine aggregate gradation iii. Too low or too high air voids in the compacted mixture. These are some of the parameters that were being looked into this study in order to determine the level of asphaltic concrete that were being produced and supplied to some on- going PWD road construction and rehabilitation projects throughout the country with respect to the current standard specification of road works adopted by PWD. 5 MIX DESIGN CONCEPTS Asphaltic concrete as specified in PWD specification is of type continuously graded aggregate mixture. The gradation of the combined coarse aggregate, fine aggregate and mineral filler shall produce a smooth continuous curve within and essentially parallel to the gradation limits as specified in PWD specification.