Deflection bowl parameters for falling weight deflectometer testing data collection and threshold benchmarking

Feb 2022

Journal: International Journal of Pavement Engineering Taylor & Francis Online, UK. DOI: 10.1080/10298436.2022.2034815

Author(s): T Nguyen, J Y Tan & N Y Ho

Deflection Bowl Parameters (DBP) has been used widely to evaluate pavement structural performance based on deflection data from Falling Weight Deflectometer (FWD). However, due to different pavement layers, materials configuration, test load, and climatic temperature, DBP thresholds need to be established for urban streets in tropical countries like Singapore. Around 130 km of field data in the network was collected every 25 m span, processed using Elmod 6 software before regression analysis. Based on the high coefficient of determinations (R-squared > 0.65), the DBP thresholds were proposed mainly for the middle layer condition (using Middle Layer Index, Lower Layer Index and Maximum deflection) and subgrade condition (via Lower Layer Index). In contrast, there were still some uncertainties in parameters related to HMA surface layers (by using Base Layer Index and Radius of Curvature) due to lower levels of R-squared (≅ 0.5). Our results have filled the research gaps of field-validated DBP thresholds for FWD 50 kN on the thick bituminous base pavement: Hot Mix Asphalt 130-170 mm, Graded Granite Aggregate Base 200-250 mm, and infinite subgrade. The findings have contributed to newly established DBP thresholds for immediate implementation in Singapore and other countries sharing similar pavement configurations.

Automatic pavement crack rating for network-level pavement management system

Jul 2021

Conference: 12^th International Conference on Road and Airfield Pavement Technology (ICPT), 14 - 15 Jul 2021, Colombo, Sri Lanka

Author(s): J Y Tan, T Nguyen, S Kapilan, T T Nyunt, Y H Lim & Y F Leong

Cracking is one of the important distresses that can be used to trigger pavement maintenance treatments. Traditional crack rating is commonly based on the Pavement Condition Index (PCI) appoach involving time-consuming visual inspection and manual classification processes. The emergence of automatic and high-speed laser imaging devices significantly improves the efficiency and productivity of pavement crack data collection but it requires suitable methods and concepts for automatic crack ratings. This paper discusses the development of an automatic pavement crack rating using crack data collected from a high speed 3D sensor. Two levels of crack ratings are proposed: Level 1 provides detailed crack information including cracking extent, crack types and severity, and Level 2 is a macro-indicator of general/overall cracking extent on a pavement section of 10m length. The method and concept were developed and tested initially for Singapore expressway network under the effort of the Land Transport Authority (LTA) of Singapore to integrate crack data into the pavement management system (PMS).

Effects of recycled plastics on the performance of polymer modified bitumen (PMB)

Jul 2021

Conference: 12^th International Conference on Road and Airfield Pavement Technology (ICPT), 14 - 15 Jul 2021, Colombo, Sri Lanka

Author(s): A N W Maung, Y P K Lee, N Y Ho, G W Tiah & K Yi

Polymer modified bitumen (PMB) has been widely used in asphalt mixtures as it provides better performance and durability as compared to unmodified binders. Styrene Butadiene Styrene (SBS) is one of the most common additives used in PMB. With the advent of bitumen technology, PMB can be further enhanced to improve its performance in terms of properties such as viscosity, ageing resistance, stiffness etc. This study aims to evaluate the effects of recycled plastics on the performance of SBS-modified binder. The analysis was conducted using a series of tests which include elastic recovery, dynamic shear test (before and after short term ageing), viscosity test, multi-ple-stress creep and recovery test and storage stability.

Rutting and cracking performance of asphalt concrete incorporating plastic waste and crumb rubber

Jul 2021

Conference: 12^th International Conference on Road and Airfield Pavement Technology (ICPT), 14 - 15 Jul 2021, Colombo, Sri Lanka

Author(s): M A Lwin, Y P K Lee, N Y Ho & X C Wang

Typically, asphalt pavements encounter two major types of distresses, rutting and cracking. Rutting occurs mostly in early stage or immature age while cracking occurs eventually after aging when the pavement becomes stiffer. Generally, stiffer asphalt pavements have good rutting resistance and softer pavements have good cracking resistance. It is important to achieve a balanced asphalt mixture having both good rutting and cracking resistances. This study aims to evaluate the use of two types of recycled materials, plastic waste and granulated crumb rubber, on the rutting and cracking properties of asphalt. Penetration Grade 60/70 binder was used as base binder, and for the control-mix. Different types of samples were prepared with Marshall and gyratory compactors and the asphalt properties were determined with respect to resilient modulus, cracking resistance and Hamburg wheel tracking test, before and after simulated aging in the laboratory.

Effects of construction time on the performance of cement treated base

Mar 2021

Journal: IOP Conference Series: Material Science & Engineering, Vol. 1075, Paper No. 012003, Mar 2021. IOP Publishing, UK. DOI: 10.1088/1757-899X/1075/1/012003. (11^th ICPT Paper)

Author(s): A N W Maung, Y P K Lee & N Y Ho

Cement treated base (CTB) has been widely used as a stabilized base layer in pavement for highways, roads, airports, parking areas and some storage areas. CTB comprises mainly three components, namely, cement, water and either natural soil or aggregates. The mixture will become strong and durable after proper compaction and curing. CTB can be produced in central plant, haul to the laying area by dump trucks or can be mixed in-placed using proper materials and equipment. One of the key factors which can affect the performance of CTB is the construction time which consists of mixing to transportation, laying and compaction. This paper describes a study that was conducted to analyse the effects of construction time on the performance properties of CTB. Laboratory tests were conducted for various CTB mixtures. The CTB mixtures were compacted at different time frames and then tested for dry density and unconfined compressive strength. The results were then analysed to study the effects of construction time.

LCMS-2 Measurements of the Quality of Road Markings

Jul 2020

Conference: 9^th International Conference on Maintenance and Rehabilitation of Pavements (MAIREPAV), , 1 - 3 Jul 2020, Zurich, Switzerland. (Shifted to eConference due to COVID-19)

Author(s): K Drenth, J Y Tan, M Drenth & J K Ong

The assessment of the structural and functional pavement condition is nowadays a fully machine based non-destructive procedure in which equipment covers all the data input required for a modern PMS approach. A LCMS (Laser Crack Measurement System) is a high-resolution transverse profiling system based on 3D Sensors capable of real time continuous measurement of condition data in a single run. One of the images produced by a LCMS is the intensity image, which expresses the reflective properties of the pavement surface. As quality control of road marking often retroreflectometers are used. A limitation of retro-reflectometers is that they can only measure for instance a single edge marking at any time whereas the road surface can have multiple markings. The LCMS captures the reflective properties of the surface over the total width of a lane and as such can measure the reflective properties of all road markings at any transverse location. This paper discusses the results of the correlation of the retroreflectometer measurements with the reflective properties measured by the LCMS-2. This first time study resulted in a very promising correlation showing that the LCMS-2 collected data is very useful in rating the quality of road markings and predicting the need for maintenance.

Evaluation of hot mix asphalt incorporating plastic waste

Jul 2019

Conference: 11^th International Conference on Road and Airfield Pavement Technology (ICPT), 10 - 12 Jul 2019, Kuala Lumpur, Malaysia

Author(s): Y P K Lee, M A Lwin, X C Wang & N Y Ho

In Singapore, about 949,300 tonnes of plastic waste was generated in 2018 according to the Singapore National Environment Agency [1]. Only 4% of the plastic waste is recycled and it is the largest amount of waste disposed in landfill. Looking into global picture, an estimated 6.5 billion tonnes of plastic waste was produced in 2015. Of this huge amount, 9% of plastic waste is recycled, 12% incinerated and 79% accumulated in landfills or the natural environment [2]. To contribute to the plastic recycling rate in Singapore, this paper describes a study that was carried out to investigate the use of recycled plastic waste in hot mix asphalt. Optimal binder content of asphalt mixes incorporating plastic waste was based on 4% air-voids. Samples were prepared and the results were compared with controlled samples. The performance properties were evaluated by means of laboratory tests such as resilient modulus, tensile strength ratio, dynamic creep and wheel-tracking tests.

LCMS-2 based 3D pavement condition surveys

Jul 2019

Conference: 11^th International Conference on Road and Airfield Pavement Technology (ICPT), 10 - 12 Jul 2019, Kuala Lumpur, Malaysia

Author(s): K P Drenth, J Y Tan & M L Drenth

An important characteristic of a pavement surface is texture. Texture, or better macro texture, relates to friction, noise and ravelling. The standard procedure for roads is to measure texture based on the Mean Profile Depth (MPD), which is a single point measurement along a longitudinal track sampled at a high frequency. The Sand Patch Test Method (SPTM) as volumetric procedure results in a Mean Texture Depth (MTD). The MTD is calculated based on the sample volume divided by the average diameter of the area covered by the material. An Estimated Texture Depth (ETD), a value close to MTD, can be calculated based on multiple relationships. Several publications can be found relating MPD’s to ETD’s, however number of publications do match the number of different relationships found which shows that this approach is not very accurate. The latest development in 3D camera technology allows a longitudinal and transverse sampling grid of 1mm x 1mm at speeds up to 100 km/h with a vertical resolution of 0.1mm for a single point measurement and 0.05mm vertical resolution for IRI measurements at 25mm interval. This paper discusses the results of the improved accuracy using the 3D technology especially regarding the rating of macro texture and ravelling of fine textured wearing courses. Several road sections have been surveyed having different types of surface courses. The accuracy as well as the repeatability of ravelling and cracking has improved which are in combination with roughness (IRI) and rutting, the four most important characteristics of the quality of the surface of a pavement.

Bus Ride Index – A refined approach to evaluating road surface irregularities

Jun 2019

Journal: Road Materials and Pavement Design, Taylor & Francis Online, UK. DOI: 10.1080/14680629.2019.1625806

Author(s): T Nguyen, B Lechner, Y D Wong & J Y Tan

The road surface quality can be assessed with ride comfort indices because of their strong correlation. Many studies on ride comfort have focused on cars and trucks, but their results are not applicable to buses, which are characterised by inherently different vehicle dynamics. In this study, a quarter-vehicle simulation concept was used to develop a Bus Ride Index (BRI) for evaluating the effect of road irregularities on bus ride comfort. A BRI model was developed to optimise ride comfort depending on seat configuration and air suspension and validated according to technical data. The results show a good regression relationship between BRI and the International Roughness Index (IRI). New IRI thresholds with regard to ride comfort and bus operating speeds were established to serve as a benchmark to develop better pavement maintenance strategies for bus lanes and to estimate road quality based on acceleration data.

Development of environmental friendly rubberized asphalt

Oct 2018

Conference: 11^th Asia Pacific Transportation and Environment (APTE) Conference, 18 - 19 Oct 2018, Malang, Indonesia

Author(s): M A Lwin, Y P K Lee, N Y Ho & X C Wang

Greenhouse gas emission from the construction of asphalt pavement can affect the environment during the production and laying of hot mix asphalt which are carried out at high temperatures. With the advent of warm mix asphalt technologies, asphalt mixes can be produced and compacted at about 20°C to 40°C lower than the corresponding hot mix asphalt mixes. The lower temperatures reduce greenhouse carbon emission and energy used. In Singapore, about 32,700 tonnes of scrap tyres were produced in 2016 and recycling rate is 91%. The applications of the recycled scrap tires are typically low in economic value and some are disposed in landfills. The disposal of scrap tires caused environmental problems and there is limited land fill space in Singapore. To maximize the use of scrap tires, a previous study was conducted to evaluate the use of crumb rubber (processed from scrap tires) in asphalt mix. The results showed that the rubberized asphalt containing crumb rubber has high potential to be used in Singapore roads. This study is a continuation of the previous research work, and aims to investigate the use of warm mix technologies to reduce the production and compaction temperatures of rubberized asphalt. The rubberized asphalt used in this study is a type of open-graded asphalt mix. Two types of bitumen, straight-run bitumen of penetration grade 60/70 and polymer modified bitumen of performance grade PG76 were used as reference samples for comparison. Different types of warm mix additives were evaluated. The performance of the rubberized asphalt was determined based on various types of laboratory tests which include resilient modulus, Los Angeles abrasion loss, tensile strength ratio and dynamic creep tests.

Study the performance of modified bitumen with polyphosphoric acid

Aug 2017

Conference: 10^th International Conference on Road and Airfield Pavement Technology (ICPT), 8 – 10 Aug 2017, Hong Kong

Author(s): A N W Maung, Y P K Lee & N Y Ho

Bitumen modification has been widely developed to raise the requirement for durability and to achieve long- lasting road surface. There are many types of bitumen modifiers and additives such as polymer (elastomers and plastomers), crumb rubber, natural rubber latex, polyphosphoric acid (PPA) and sulphur. This paper involves a study to evaluate the performance of PPA modified bitumen in comparison with that of styrene-butadiene- styrene (SBS) modified bitumen. The 60/70 penetration grade bitumen was used with different dosages of PPA/SBS to prepare PPA/SBS modified bitumen samples. Standard tests such as rotational viscosity, elastic recovery, dynamic shear (DSR), rolling thin film oven (short term ageing) and multiple-stress creep and recovery (MSCR) were conducted according to performance grade (PG) requirements.

Sampling pavement surface condition data at traffic-speed

Aug 2017

Conference: 10^th International Conference on Road and Airfield Pavement Technology (ICPT), 8 – 10 Aug 2017, Hong Kong

Author(s): K P Drenth, F H Ju & J Y Tan

The assessment of the structural and functional pavement condition is nowadays fully machine based and non- destructive equipment does cover all the data input required for a modern PMS approach. A Multi-Laser Vehicle is capable of real time continuous traffic-speed measurements of condition data regarding cracking, ravelling, rutting, roughness, macro texture and road geometrics in a single run using high-speed line-scan cameras for an automated assessments. The system of the Multi-Laser Vehicle equipped with a Laser Crack Measuring System (LCMS) is the most promising development in 3D camera technology with a progressive improvement of capabilities and quality.

This paper discusses the results of the equipment used and does show the continuous measured macro texture based on the MTD as index using the LCMS device in addition to the automated crack detection. A major advantage is that no conversion is required as the volumetric MTD is a direct output. The LCMS based automated MTD analysis is a machine based result not influenced by a human factor such as the Sand Patch. The results allow as well the automated analysis of loss of aggregate which is a major advantage in rating the severity and extent of ravelling in comparison to the non-consistent wind-screen surveys and manual rating of collected images. In addition the sampling of rutting has been validated against the multi-laser profiler approach as well as the IRI based on Inertial Motion Sensors attached to the LCMS units.

Sampling functional condition indices at traffic-speed

Jul 2017

Conference: 10^th International Conference on the Bearing Capacity of Roads, Railways and Airfields (BCRRA), 28 – 30 Jun 2017, Athens, Greece

Author(s): K P Drenth, F H Ju & J Y Tan

The assessment of the structural and functional pavement condition is nowadays fully machine based and non-destructive equipment does cover all the data input required for a modern PMS approach. A Multi-Laser Vehicle is capable of real time continuous traffic-speed measurements of condition data regard- ing cracking, ravelling, rutting, roughness, macro texture and road geometrics in a single run using high-speed line-scan cameras for an automated assessment. The system of the Multi-Laser Vehicle equipped with a Laser Crack Measuring System (LCMS) is the most promising development in 3D camera technology with a pro- gressive improvement of capabilities and quality.

This paper discusses the results of the equipment used as well as the accuracy and repeatability achieved. Shown is as well the continuous measured macro texture based on the Mean Texture Depth (MTD) as index using the LCMS device in addition to the automated crack detection. A major advantage is that no conversion is required as the volumetric MTD is a direct output. The LCMS based automated MTD analysis is a machine based result not influenced by a human factor such as the Sand Patch. The results allow as well the automated analysis of loss of aggregate which is a major advantage in rating the severity and extent of ravelling in com- parison to the non-consistent wind-screen surveys and manual rating of collected images. In addition to the MTD the sampling of rutting has been validated against the multi-laser profiler approach as well as the Inter- national Roughness Index (IRI) based on Inertial Motion Units (IMU’s) attached to the LCMS sensors.

Use of incineration bottom ash for road construction in Singapore

Jun 2017

Conference: World Sustainable Built Environment (WSBE) Conference, 5 – 7 Jun 2017, Hong Kong

Author(s): N Y Ho, Y P K Lee, C C Yap, K K Tong & C T Lim

Every year, about 600,000 tonnes of incineration ash is produced in Singapore. The ash comprises bottom ash and fly ash. The bottom ash contains less leachable metals of concern and soluble salts and has a great potential for utilization. In 2008, Samwoh participated in a trial initiated by Land Transport Authority to evaluate the use of bottom ash in road construction. The study comprises laboratory tests and field trial to evaluate the properties of the bottom ash which was processed using a patented technology. The bottom ash was used for the construction of road base and subbase. The test results showed that the processed bottom ash meets all the relevant regulatory requirements.

Recycling of scrap tires for use in asphalt concrete in Singapore

Jul 2016

Conference: 8^th International Conference on Maintenance and Rehabilitation of Pavements (MAIREPAV), 27 – 29 Jul 2016, Singapore

Author(s): N Y Ho, Y P K Lee & M A Lwin

In Singapore, a significant amount of scrap tires is generated every year. The applications of the scrap tires are typically low in economic value and some are disposed in landfills. The disposal of scrap tires caused environmental problems and there is limited land fill space in Singapore. Hence, there is a need to recycle scrap tires for more beneficial applications. This paper describes a study that was carried out to evaluate the use of crumb rubber recycled from scrap tires in asphalt concrete. The study was conducted with respect to open-graded wearing course (OGW) which is commonly used for highways in Singapore. Two types of bitumen, straight bitumen of penetration grade 60/70 and polymer modified bitumen of performance grade PG76 were used for controlled samples. The samples were prepared by wet mixing and dry mixing methods and the results were compared with those of controlled samples. The performance properties were evaluated by means of resilient modulus, Los Angeles abrasion loss, tensile strength ratio and dynamic creep tests.

Structural management of airfield pavements using effective tools

Jul 2016

Conference: 8^th International Conference on Maintenance and Rehabilitation of Pavements (MAIREPAV), 27 – 29 Jul 2016, Singapore

Author(s): K Drenth, F H Ju & J Y Tan

The volume of air traffic continues to grow, resulting in an increasing frequency of aircraft movements as well as increase in gross weight. To cope with such growth it is necessary to make optimal use of all available runways, taxiways and aprons. An optimum utilization of such resources also means that maintenance has to be structured into a planned approach making it a prerequisite to have insight knowledge of the performance of the pavements, asphalt as well as concrete. By carrying out the right maintenance at the right time, the airport will reduce the overall need for maintenance, which in turn will produce economic benefits.

The pressure on the availability of all airport pavements at any time does mean that the condition of pavements has to be forecasted based on reliable performance indicators and performance models. For many airports the PCI procedure is the primary tool for forecasting and budgeting. A pavement condition is often periodically evaluated using various condition measurements such as (automated) visual condition surveys, non-destructive deflection testing (PCN), roughness (BBI) and skid resistance. Bringing all this data together in a PMS like PAVER will allow to visualize the condition of the pavement sections in GIS-based maps.

This paper discusses the issues busy international airports do face with the increase in movements approaching saturation levels of the runways leaving ample time for the minimum maintenance required. Machine-based condition measuring tools are required in combination with a long term prediction of the structural as well as functional condition based on proper historic information. This requires proper pavement management to avoid critical maintenance to be executed beyond the point of no return

Traffic-speed MTD measurements of asphalt surface courses

Jul 2016

Conference: 8^th International Conference on Maintenance and Rehabilitation of Pavements (MAIREPAV), 27 – 29 Jul 2016, Singapore

Author(s): K Drenth, F H Ju & J Y Tan

An important characteristic of a pavement surface is texture. Texture does relate to friction, noise and ravelling and does change over time due to aging, contamination and loss of aggregate. As such it is an important characteristic triggering maintenance measures when it does not meet the requirements anymore. The standard procedure is to measure texture based on the Mean Profile Depth (MPD), which is a single point measurement along a longitudinal track sampled at a high frequency. The actual requirement is a volumetric 3D based result to be directly representative for the characteristics required without the need of a conversion from a 2D based test.

This study was conducted to validate at traffic-speed measured MTD’s using a Laser Crack Measurement System (LCMS) with the results of the static Sand Patch Test Method (SPTM). The LCMS does measure the volumetric properties of the road surface continuously over its full width and length based on 250 x 250mm squares. The evaluation did include static SPTM’s, a static ELAtextur device measuring MPD and a traffic-speed road surface profiler equipped with a texture laser measuring MPD as well. The test were conducted over different time periods and multiple runs at a validation site used for calibrating testing equipment operating at roads in Singapore.

This paper discusses the results of the equipment used and does show the very good correlation between the SPTM results and the MTD’s based on the LCMS device. A major advantage is that no conversion is required as the volumetric MTD is a direct output. The LCMS based automated MTD analysis is a machine based result not influenced by a human factor such as the SPTM. The results allow as well the automated analysis of loss of aggregate which is a major advantage in rating the severity and extent of ravelling in comparison to the non-consistent wind-screen surveys and manual rating of collected images. However, the next generation LCMS sensors will require an improved vertical resolution to improve on the reliability of ravelling for finer textured surface courses.

Traffic-speed MTD measurements of asphalt pavements

Jun 2016

Conference: CROW Infra Days 2016, 22 – 23 Jun 2016, Papendal, Netherlands

Author(s): K Drenth, F H Ju & J Y Tan

An important characteristic of a pavement surface is texture. Texture does relate to friction, noise and ravelling and does change over time due to aging, contamination and loss of aggregate. As such it is an important characteristic triggering maintenance measures when it does not meet the requirements anymore. The standard procedure is to measure texture based on the Mean Profile Depth (MPD), which is a single point measurement along a longitudinal track sampled at a high frequency. The actual requirement is a volumetric 3D based result to be directly representative for the characteristics required without the need of a conversion from a 2D based test.

This study was conducted to validate at traffic-speed measured MTD’s using a Laser Crack Measurement System (LCMS) with the results of the static Sand Patch Test Method (SPTM). The LCMS does measure the volumetric properties of the road surface continuously over its full width and length based on 250 x 250mm squares. The evaluation did include static SPTM’s and a traffic-speed road surface profiler equipped with a texture laser measuring MPD as well. The test were conducted over different time periods and multiple runs at a validation site used for calibrating testing equipment operating at roads in Singapore. 

This paper discusses the results of the equipment used and does show the very good correlation between the SPTM results and the MTD’s based on the LCMS device. A major advantage is that no conversion is required as the volumetric MTD is a direct output. The LCMS based automated MTD analysis is a machine based result not influenced by a human factor such as the SPTM. The results allow as well the automated analysis of loss of aggregate which is a major advantage in rating the severity and extent of ravelling in comparison to the non-consistent wind-screen surveys and manual rating of collected images. However, the next generation LCMS sensors will require an improved vertical resolution to improve on the reliability of ravelling for finer textured surface courses.

Use of sedimentary rocks for use in road construction in Singapore

Nov 2015

Conference: 33^rd Conference of the ASEAN Federation of Engineering Organizations (CAFEO), 22 – 26 Nov 2015, Penang, Malaysia

Author(s): N Y, Ho, Y P K, Lee, A L, Moe, P Y C, Leong & W, Zhang

In Singapore, about 3.7 million m3 of sedimentary rocks have been excavated from the Jurong Rock Cavern project. Due to limited landfill space, this posed potential storage problems. Hence, there is a need to use the rock for beneficial applications. This paper describes a study that was carried out to investigate the use of sedimentary rocks in asphaltic concrete for road construction. The study was conducted with respect to asphalt wearing course and binder course. Based on the laboratory tests, the results showed that with some modification, the asphaltic concrete containing sedimentary rocks can provide comparable performance as conventional asphaltic concrete containing granite.

Evaluation of RCA concrete for the construction of Samwoh Eco-Green Building

Jun 2015

Journal: Magazine of Concrete Research, Vol. 65, Issue 12, pp. 633 – 644, Jun 2015. Institution of Civil Engineers (ICE), UK

Author(s): N Y Ho, Y P K Lee, W F Lim, K C Chew, G L Low & S K Ting

This paper describes a study conducted to evaluate the use of concrete containing up to 100% recycled concrete aggregate (RCA) for the construction of a commercial building known as the Samwoh Eco-Green Building in Singapore. The study is a continuation of research which established that concrete produced with RCA can achieve strength comparable to that of normal concrete produced with natural aggregate for structural applications by using a rational mix design approach. The present study was carried out to evaluate the effects of RCA on other engineering and durability properties of concrete, including compressive strength, flexural strength, tensile splitting strength, creep strain, water permeability, initial surface absorption, chloride ingress and sulfate resistance. With normal concrete serving as the basis for comparison, the experimental data showed that comparable compressive strength, flexural strength and tensile splitting strength were attainable for concrete containing up to 100% RCA. Although concrete with 100% RCA exhibited higher creep strain and initial surface absorption rate as well as lower resistance to water permeability, chloride ingress and external sulfate attack, the effects on the concrete performance are insignificant. On the whole, the research study suggests that RCA concrete can be designed to meet the specifications for structural applications which led to the successful completion of the Samwoh Eco-Green building.

Use of high percentage of recycled concrete aggregate in aircraft stand rigid pavement

Jul 2013

Conference: 8^th International Conference on Road and Airfield Pavement Technology (ICPT), 14 – 16 Jul 2013, Taipei, Taiwan

Author(s): N Y Ho, Y P K Lee, T F Fwa, J Y Tan, W F Lim, E S Teoh, S Tan & W S Chew

This paper describes a study that was carried to investigate the use of recycled concrete aggregate (RCA) in aircraft stand rigid pavement at the Singapore Changi Airport. The study aimed to recycle the concrete waste generated from the demolition of the existing aircraft stand rigid pavement to reconstruct the aircraft stand rigid pavement. The study was a continuation of a previous work in which 20% of RCA was used in the rigid pavement. In this study, laboratory tests were carried out to evaluate the use of up to 100% of RCA in rigid pavement. The test properties that were evaluated include compressive strength, flexural strength, drying shrinkage and resistance to chloride ingress. The study showed that it is viable to incorporate high RCA content in concrete.

Efficient utilization of recycled concrete aggregate in structural concrete

Mar 2013

Journal: Journal of Materials in Civil Engineering, Vol. 25, Issue 3, pp. 318 – 327, 1 Mar 2013. American Society of Civil Engineers (ASCE), US

Author(s): N Y Ho, Y P K Lee, W F Lim, T Zayed, K C Chew, G L Low & S K Ting

In Singapore, the applications of recycled concrete aggregate (RCA) are limited to nonstructural concrete, road construction, and backfilling. To realize the beneficial use of RCA, an in-depth study was conducted to evaluate its use in structural concrete. This paper reports the test results of a study that is part of extensive research intended to evaluate the properties of RCA concrete produced by a proposed rational approach in concrete mix design. The key parameters studied include compressive strength, elastic modulus, and drying shrinkage. The results showed that the RCA concrete can be designed to achieve comparable compressive strength and elastic modulus, relative to the corresponding properties of concrete containing natural coarse aggregate (NCA). RCA concrete tends to exhibit higher drying shrinkage strains relative to NCA concrete, but the values are within the recommended limits.

Beneficial use of fine recycled concrete aggregate for utility trench reinstatement

Aug 2011

Conference: 7^th International Conference on Road and Airfield Pavement Technology (ICPT), 3 – 5 Aug 2011, Bangkok, Thailand

Author(s): Y P K Lee, N Y Ho, J Y Tan, S Y Foo, S S M Ang & K K Lee

The Singapore government has been actively promoting the recycling of construction and demolition waste for construction applications with the aim to reduce the reliance on natural aggregates and to alleviate waste disposal problem. The waste can be processed into recycled concrete aggregate (RCA) which can be used as an alternative to natural aggregate. Studies have shown that RCA can be used for many applications such as concreting and road construction works. However, coarse RCA (bigger than 5mm) is largely used in these applications and there is limited usage for the finer RCA. Hence, a joint study was carried out by Samwoh Corporation Pte Ltd, Land Transport Authority and SP PowerGrid to evaluate the use of fine RCA for utility trench reinstatement works which are carried out during maintenance or installation of underground utilities pipes. The study involves laboratory tests and a field trial. The tests results showed that the fine RCA can provide a good alternative to fine natural aggregate for utility trench reinstatement works.

Use of recycled concrete aggregate for the construction of aircraft stand rigid pavement at Singapore Changi Airport

Aug 2011

Conference: 7^th International Conference on Road and Airfield Pavement Technology (ICPT), 3 – 5 Aug 2011, Bangkok, Thailand

Author(s): N Y Ho, Y P K Lee, J Y Tan, C O How, S Y C Koh & S W Ooi

In support of the Singapore government’s goal to achieve sustainable development in the construction industry, Changi Airport Group (CAG) has initiated a project to use recycled concrete aggregate (RCA) that was obtained from the demolition of existing aircraft stand rigid pavement to reconstruct a new aircraft stand rigid pavement at Singapore Changi Airport. The project was carried out by Samwoh Corporation Pte Ltd (Samwoh) and the National University of Singapore (NUS) which involved the demolition of existing aircraft stand rigid pavement, recycling of concrete waste to produce RCA, laboratory tests to assess the quality of the RCA and construction of new aircraft stand rigid pavement using concrete made of RCA. This paper highlights the key considerations involved in the recycling and construction process of aircraft stand rigid pavement using concrete with RCA. The project demonstrates the feasibility of using RCA as an alternative to natural aggregate in concrete for the construction of aircraft stand rigid pavement.

Use of recycled and secondary aggregates in concrete: An overview

Mar 2011

Conference: UK-India Education and Research Initiative (UKIERI) Concrete Congress, 8 – 10 Mar 2011, New Delhi, India

Author(s): R K Dhir, K A Paine, J de Brito, M Etxeberria, N Y Ho, C S Poon & W Y V Tam

This paper written by some of the World’s leading exponents on the use of recycled and secondary aggregates provides a brief overview of the use of recycled and secondary aggregates for new concrete construction.  It is based on a substantial review, dissection and repackaging of the current known knowledge in the field and is based on authors’ own research, findings and experience.  The paper, in particular, draws upon recent knowledge that has been generated in the past five years as standards and specifications have finally started to provide a route by which these materials can be more readily assimilated into construction.  The paper covers production and processing of recycled aggregates, developments in international standards, the effect of recycled aggregates on strength, deformation characteristics and durability of concrete, and concludes with three international case studies in which recycled aggregates have been used in structural and high performing concrete.

Efficient utilization of recycled concrete aggregate for structural concrete applications

Dec 2009

Conference: 27^th Conference of the ASEAN Federation of Engineering Organizations (CAFEO), 30 Nov – 2 Dec 2009, Singapore

Author(s): N Y Ho, Y P K Lee, W F Lim, S K Ting, Y Soh & G L Low

In recent years, the Singapore government has been actively promoting the recycling of construction and demolition (C&D) waste for construction applications due to limited landfill space and the lack of natural materials available in Singapore. The C&D waste can be processed into recycled concrete aggregate (RCA) which contains mainly aggregate and cementitious materials. At present, the applications of RCA are limited to non-structural concrete and road construction. In line with the nation’s goal to promote sustainable development, a full scale evaluation study was carried out by Samwoh Corporation Pte Ltd, Nanyang Technological University (NTU) and the Building and Construction Authority (BCA) to evaluate the use of RCA for structural concrete. The study involves two stages, namely Stage 1 – Evaluation of the properties of RCA, mechanical and durability characteristics of concrete containing RCA and the mix design, and Stage 2 – Construction and structural health monitoring of a three-storey commercial building using concrete containing RCA. This paper presents some of the results obtained in Stage 1 of the project which include the RCA properties and compressive strength test results. The study was carried out using up to 100% RCA as replacement for granite for various concrete strengths ranging from Grade 20 to Grade 60. The test results showed that the concrete with RCA can be designed to achieve similar strength as compared to concrete with granite.

Field study on the use of recycled concrete aggregate for road trenching works in Singapore

Oct 2009

Conference: 2^nd World Roads Conference, 26 – 28 Oct 2009, Singapore

Author(s): Y P K Lee, N Y Ho, J Y Tan, C C Yoong, C J Lim & K K Lee

Over the years, the Singapore government has been promoting the recycling of concrete waste with the aim to alleviate waste disposal problem due to limited land space in Singapore. The concrete waste can be used as an alternative to natural aggregate which is largely imported from overseas. One of the beneficial uses of concrete waste is for road trenching works which is carried out to install or repair utility pipes such as gas, water, sewage, electrical and telecommunication cables which are located beneath the pavement. This paper describes a field study that was carried out to evaluate the field performance of using concrete waste for road trenching works. The study involved laboratory tests and field performance assessment with respect to riding quality and structural strength.

Framework and assessment of carbon footprint for direct and indirect carbon contributory inventories of a road construction project in Singapore

Oct 2009

Conference: 2^nd World Roads Conference, 26 – 28 Oct 2009, Singapore

Author(s): B S Baliyan, Y S Leong & C S Chan

With the increase in population and the significant increase in traffic on Singapore road network, the demand for more roads and upgrading of existing road network is evident. New roads and upgrading of roads need various construction materials. But as known, the construction industry contributes significant amount of CO2 through usage of fossil fuel and demand for the upstream production of the basic construction materials such as steel, cement and bitumen.

The first part of the paper discusses the carbon footprint framework for road construction, which was developed by Land Transport Authority. The second parts discuss the methodology and the study carried out using the said framework to evaluate the carbon footprint of a road widening project at Tampines Expressway. The study results showed that the three major CO2 emission contributors for road construction works are diesel, cement and steel. The extent of the emission depends on the type of project and the emission factors for each individual contributor.

With the identification of the major CO2 emission contributors for road construction, the next challenge will be on how to limit the carbon contribution from the direct and indirect inventories of road construction materials.

Beneficial use of recycled concrete aggregate for road construction in Singapore

Jul 2008

Conference: 6^th International Conference on Road and Airfield Pavement Technology (ICPT), 20 – 23 Jul 2008, Sapporo, Japan

Author(s): N Y Ho, Y P K Lee & J Y Tan

The construction and demolition (C&D) of building structures and infrastructures has generated large amount of wastes in Singapore. The disposal of the waste posed an environmental problem due to limited land space in Singapore and the rate of waste generation has increased significantly over the years. Moreover, there is a strong dependence on natural aggregate which is imported mainly from overseas. As such, the recycling of C&D waste not only helps to alleviate the waste disposal problem but also provide an alternative to natural materials. This paper describes a study that was carried out on the use of C&D waste in base course for road construction. The study involved laboratory tests to evaluate the properties of the recycled concrete aggregate (RCA) obtained from the processing of C&D waste and to analyze the performance of base course produced with RCA. A field trial was also carried out to evaluate the field performance of the base course.

Field evaluation of stone mastic asphalt for runway pavement in Singapore Changi Airport

Jul 2008

Conference: 6^th International Conference on Road and Airfield Pavement Technology (ICPT), 20 – 23 Jul 2008, Sapporo, Japan

Author(s): Y P K Lee, N Y Ho, J Y Tan, Y D Wong, L Somkiat, C O How & T T K Teo

This paper describes a study that was conducted to evaluate the field performance of a stone mastic asphalt (SMA) mix to be used for the airport runways in the Singapore Changi Airport. The study is a continuation of a laboratory study that was conducted to evaluate the performance of the SMA. In this second part of the study, a site trial was constructed on the runway pavement using the SMA as the surface course. The performance of the site trial was assessed with respect to the pavement surface texture, rutting resistance and skid resistance of the SMA.

Recycling of waste materials for road construction in Singapore

Dec 2007

Conference: 5^th Asia Pacific Conference, 7 – 8 Dec 2007, Singapore

Author(s): Y P K Lee & N Y Ho

The recycling of waste materials has become one of the key interests of the Singapore government. The disposal of waste materials posed an environmental problem due to limited land space in Singapore and the rate of waste generation has increased significantly over the years. Moreover, there is a strong dependency on natural aggregate for construction, which is imported largely from overseas. As such, the recycling of waste materials not only helps to alleviate the waste disposal problems but also provide an alternative to natural materials. This paper describes some of the waste materials that can be or has been used for road construction in Singapore. The waste materials discussed include construction and demolition (C&D) waste, asphalt pavement waste and incinerator ash that is generated from the incineration of solid waste.

Evaluation of stone mastic asphalt and dense-graded asphalt mixes for aircraft pavement in Singapore Changi Airport

Mar 2006

Conference: Special International Conference on Road and Airfield Pavement Technology (ICPT) Symposium - Road Construction and Maintenance Technology, 16 – 18 Mar 2006, Beijing, China

Author(s): Y P K Lee, N Y Ho, Y D Wong, L Somkiat & C O How

A study was conducted to evaluate the performance of two types of asphalt mixes, namely, stone mastic asphalt (SMA) as well as a dense-graded hot mix asphalt (HMA). The mix design of the asphalt mixes was determined using the Marshall method. The performance of the asphalt mixes was evaluated with respect to a series of laboratory tests which include (a) wheel—tracking test (b) moisture sensitivity, (c) macrotexture depth (d) skid resistance and (e) fuel-resistance. The results showed that the SMA mix exhibited better rut-resistance and higher macrotexture depth as compared to the HMA mix. On the other hand, the HMA mix showed better resistance to moisture and kerosene. There is no significant difference between the two mixes in terms of skid resistance.