ASPHALTIC CONCRETE AS ROAD SURFACING MATERIAL IN MALAYSIA: HOW DO WE ASSURE QUALITY?

Transcription

1 ASPHALTIC CONCRETE AS ROAD SURFACING MATERIAL IN MALAYSIA: HOW DO WE ASSURE QUALITY? Nur Maira Adila binti Othman * Assistant Director, Road Facilities Maintenance Branch, Public Works Department Malaysia, Malaysia * Block D, Level 2, Public Works Department (HQ), Kuala Lumpur maira@jkr.gov.my Hanani binti Mohamed Radzi Assistant Director, Road Facilities Maintenance Branch, Public Works Department Malaysia, Malaysia Mohd Hizam bin Harun Senior Assistant Director, Road Facilities Maintenance Branch, Public Works Department Malaysia, Malaysia ABSTRACT: If road pavements are designed adequately and pavement layers are constructed in accordance with design and specifications, the new road surfacing is expected to last for at least 10 years with minimal maintenance. However, there is a concern over the actual quality of asphaltic concrete produced in Malaysia as evident from known cases where the road surfacing have prominently cracked during defect liability period and even when the construction is still on-going. 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 too much or too little quantity of bitumen, too coarse or too fine aggregate gradation and too low or too high air voids in the compacted mixture. Based on a study carried out by the Public Works Department of Malaysia (PWD) on the quality of asphaltic concrete that were actually produced and supplied to a number of on-going PWD road construction and rehabilitation projects throughout the country, it was found that the surfacing materials were indeed of inferior quality and did not comply with the PWD standard specification even though test records obtained from respective sites indicated otherwise. As a follow up from this study, PWD has carried out a systematic audit on asphalt mixing plants, trial lay and completed paving works to ensure that the asphalt material and works are in compliance with the specifications. This paper highlights the findings of this study. KEYWORDS: Quality, asphaltic concrete, bitumen, aggregate, mix design, audit 1. INTRODUCTION Many contractors tend to believe that design, production and laying of asphaltic concrete mixture is 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 PWD 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 structural strength of the road pavement [1]. A similar study carried out on some experimental bituminous overlays in Kenya had also shown that the performance of the overlays was primarily dependent on the properties of the overlay material itself [2]. It was on this concern over poor quality asphaltic concrete on the road pavements in Malaysia that this study was initiated by PWD, the primary aim of which is to investigate the current level of quality of asphaltic concrete that are being produced and supplied for the on-going road construction and rehabilitation projects throughout the country with respect to the current standard specification for road works of PWD. Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 1

2 2. BACKGROUND In Malaysia, there is a total of 157, kilometres of roads which make up the whole road network of the country, 81.1% of which are paved [3]. In the 1940s, paved roads in Malaysia 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[4], 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. PROBLEM STATEMENT 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. JKR Guidelines for Inspection and Testing of Road Works [5] 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 or the Engineer responsible for supervision of construction (presumably the Consultant) and/or the staff of PWD laboratories (the latter category is no longer applicable as the laboratories have all been privatized). As a general rule, the initiation and execution of quality control testing must not be left to the Contractor. 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 the supervising consultant rather than on actually controlling the quality of the material produced and the works constructed. This verification procedure is certainly not effective in controlling the quality of the completed works because test results are often verified 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. These are some of the parameters that were being looked into in this study in order to determine the level of quality of asphaltic concrete that were being produced and supplied to some on-going road construction and rehabilitation projects throughout the country with respect to the current standard specification of road works adopted by PWD. 4. SURVEY PWD had carried out a survey to identify discrepancies with regards to the production and laying on asphaltic concrete in this country. Both qualitative and quantitative data were obtained. 4.1 Qualitative Data Qualitative data were obtained through response given by the respective supervising consultants of the projects visited to a standard questionnaire. This was done by personally interviewing the representative of the consultant, mostly the senior resident engineer, at the site office. In the questionnaire, information regarding mix design, trial lay, Marshall and field density tests were requested from the consultants. Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 2

3 4.2 Quantitative Data Quantitative data include samples of asphaltic concrete which is either the binder course or wearing course depending on the current progress of the project, collected from randomly selected tip-trucks and compilation of some recent results of routine control tests carried out on site by the contractors, consultants or independent laboratory operators, as well as results of tests conducted by IKRAM on the collected samples. In collecting the samples, it was so planned that each selected site is visited three times and at each time, sufficient samples are collected from three different tip-trucks which are randomly selected. Thus, a total of nine samples were collected from each site. A total of only 21 sites were visited in this study out of 30 as initially targeted. This is because some projects have not reached to the stage of producing the asphaltic concrete during the visit while some including the paving sub-contractors for the Federal Roads maintenance concessionaire for the central and eastern zones have already completed their paving works. Altogether, there were 189 samples collected ie. nine samples from each of 21 sites. These samples were subjected to a series of tests at IKRAM s laboratory. 5. RESULTS AND DISCUSSIONS 5.1 Qualitative Data Mix Design: A total of 18 out of 21 quarries surveyed did carry out laboratory mix design on the asphaltic concrete mix manufactured and produced by them. Out of three quarries which did not, two were PWD quarries. Without mix design, quality control simply would not exist as there would be no reference to gauge the quality level of the mix being produced. Trial Lay: There were 24% or five (5) out of 21 quarries which did not carry out trial lay and were uncertain whether they really carried out one respectively. Trial lay is meant to demonstrate that the mixing, laying and compacting equipment conform to the requirements of the specifications and the proposed mix which has undergone laboratory mix design satisfactorily does comply with the design. Without trial lay, one would not know that the initial few batches of mix produced and laid at site are satisfactory or otherwise. Rejection Experience: Only five (5) out of 21 contractors/quarries surveyed have past experience in rejecting the mix for the following reasons; i. Temperature of mix too low (2 cases) ii. Paving in the rain (1 case) iii. Bitumen content too high (1 case) iv. Road surface cracks after open to traffic (1 case) Note that there is only one case of rejection (ie. due to too high bitumen content) which can be related to routine laboratory testing which verify the compliance of material with mix design. 5.2 Quantitative Data Bitumen Content: Comparing bitumen content test results obtained from IKRAM with those from sites, only 20.4% complied with respective job mix formula (ie. +/- 0.2% of design bitumen content) as compared to 56.0% obtained from various sites. In any case, the figures contradict with the fact that only one site have past experience in rejecting the mixture due to non-complied bitumen content. There was a considerable difference in the variation in bitumen content between IKRAM and some project sites. Even the variation in bitumen content for some of these sites, based on the test results obtained from respective sites, is considered too small, taking into consideration the variation in testing and sampling procedures and normal variation in the materials and production process. Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 3

4 Even though test results obtained from IKRAM and various sites were not from duplicate samples, the considerable difference that exist over a relatively short period of time (between one to three weeks) raise some doubts on the genuineness of the test results obtained from respective sites. Aggregate Gradation: Aggregate gradation test results obtained from IKRAM and sites both indicate relatively low percentage of compliance with job mix formula (permissible variation from design aggregate gradation ranging from +/- 5.0% to +/- 2.0%). Compliance with job mix formula means the percentage passing through the test sieves as listed in Table 4.8 of JKR/SPJ are all within the permissible variation for the various fractions of aggregate size as given in Table 4.11 of JKR/SPJ. Air Voids: There is a substantial difference in percentage air voids which are within the limits as stipulated in JKR/SPJ between IKRAM s and sites test results; the figures are 18.0% and 94.0% respectively. It is observed, as expected, that low bitumen contents tend to yield high air voids from IKRAM s test results; the percentage that pass the bitumen content (20.4%) is almost identical to the percentage that pass the air voids requirement (18.0%). However, this trend is not reflected from site laboratories test results. Marshall Stability And Flow: Test results from IKRAM and sites indicate that the Marshall stability of all samples exceed the minimum requirements (ie N for binder course and 5000 N for wearing course) despite the fact that a substantial number of samples do not comply with job mix formula with respect to bitumen content, aggregate gradation and air voids. At the same time, a relatively large number of test results from both IKRAM and sites indicate compliance with Marshall flow requirements (ie mm) 6. FOLLOW-UP ACTIONS 6.1 Audit On Asphalt Mixing Plants To improve the quality of the road paving, audit on asphalt mixing plants have been carried out since November 2011 to ensure that the plants comply with the specification in mixing and supplying asphalt for road paving work. This will be followed by audit on trial lay, paving work while in progress and the completed paving work. To standardize the implementation of the audit on asphalt mixing plants, a checklist has been prepared in accordance with Clause JKR/SPJ. Some of the items listed are; i. Approval of bitumen. ii. Approval of coarse and fine aggregate. iii. Waterproof cover for fine aggregate. iv. Approval of mix design. v. Laboratory facilities. Based on the checklist, the plant is deemed qualified to supply asphalt for road paving work if all mandatory items are complied with. 6.2 Audit On Trial Lay Clause (b) JKR / SPJ states that after the proposed JMF is approved by the S.O., the asphalt shall be mixed, laid and compacted by the contractor in compliance with the proposed JMF. The aims of audit on trial lay are; i. To ensure that asphalt complies with the mix design. ii. To determine and ensure that the laying thickness, laying temperature, rolling temperature and rolling pattern are adequate to achieve the compacted thickness and compacted density as specified. Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 4

5 6.3 Audit On Completed Paving Works Audit on completed paving works are carried out in subsequent to asphalt mixing plants and trial lay to finally ensure that the quality of road paving work are satisfactory and in accordance to the specification. Clause (c) JKR/SPJ states that upon approval of the approved JMF by the S.O., the contractor shall produce, lay and compact the asphalt in accordance to the JMF. It is the responsibility of the contractor to produce asphalt with precise aggregate gradation and bitumen content as specified in the JMF, with permissible tolerance as specified in Table JKR/SPJ. 7. CONCLUSIONS The type of specification and acceptance procedure widely used in this country is the Traditional QC Specifications whereby the Contractor prepares method statements for review and acceptance by the Consultant and the Consultant monitors field work based on the method statements. Proof of compliance with specifications is based on a quality control plan administered by both the Contractor and Consultant, and subsequently supervised by the Consultant. However, the supervision is usually done on the basis of more or less effective surveillance and often so by site staff with little or no training and experience. As a result, the client is bound to be presented materials and constructed work of inferior quality even though test results indicate otherwise. This is well manifested by a statement made by Ir. Dr. Judin Abdul Karim, JKR Deputy Director General II in Buletin Ingenieur, July 1996; Over the last 4 years, there have been barrages of incidents of building failures that made headlines in the news media and even sent shock waves across the nation. Upon closer examination of many of these failures, it is very apparent that they are generally avoidable they occur not through lack of basic knowledge but because of non-application or misapplication of it. The construction process in Malaysia lacks efficient control and monitoring mechanisms. In this study, out of a total 21 construction sites being surveyed, only one site consistently complied with mix design and showed a trend of test results similar to those obtained independently from IKRAM. Even though the test results obtained from IKRAM were not from duplicate samples as tested at the various sites, the considerable difference in the test figures that exist over a relatively short period between the time the samples were taken and tested at IKRAM and purportedly tested by the Contractor/Consultant at sites one to three weeks earlier raise some doubts on the genuineness of the test results obtained from respective sites. In summary, the following conclusions can be deduced from this study; i. Out of 21 construction sites surveyed, and based on nine samples taken at random from each site and tested at IKRAM s laboratory; a. Only one site consistently complied with job mix formula. b. Only one site consistently showed a trend of test results similar to IKRAM s. ii. Three sites do not have mix design; two of them involve JKR quarries. iii. Marshall samples which comply with design binder content and aggregate grading will also comply with Marshall stability and flow requirements. iv. Marshall samples which do not comply with design binder content and aggregate grading may still comply with Marshall stability and flow requirements. v. Marshall samples which comply with design binder content and aggregate grading may have air voids exceeding the allowable limits. However, these samples may still comply with Marshall stability and flow requirements. Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 5

6 REFERENCES: [1] C.R. Jones, G. Morosiuk, H.R. Smith, and A. Mutalif, The effect of material properties on the performance of asphaltic concrete surfacings in Malaysia, Unpublished Project Report PR/ORC/079/95, Transport Research Laboratory, Crowthorne, UK [2] H.R. Smith, and C.R. Jones, Early performance of some experimental bituminous overlays in Kenya. Laboratory Report 1043, Transport and Road Research Laboratory, Crowthorne, UK, [3] Jabatan Kerja Raya Malaysia, Statistik Jalan edisi 2012, JKR , Kuala Lumpur, [4] Kerajaan Malaysia, Kementerian Kewangan Malaysian highway maintenance study, Final Report. Kuala Lumpur, [5] Jabatan Kerja Raya Malaysia, Guidelines for inspection and testing of road works, JKR , Kuala Lumpur, Copyright 2013 IJPC International Journal of Pavements Conference, São Paulo, Brazil Page 6