Showing papers by "Arul Arulrajah published in 2023"

Improved fatigue properties of cement-stabilized recycled materials – lateritic soil using natural rubber latex for sustainable pavement applications

Abstract: This research project investigates the role of a new recycled pavement material and natural rubber latex (NRL), in improving the resilient and fatigue performances of cement-stabilized recycled materials and lateritic soil (LS) blends under traffic loads. Two types of recycled materials, being steel slag (SS) and recycled concrete aggregate (RCA) and 5% cement content by weight were studied in this research. The dry rubber content in NRL to cement (r/c) ratios of 0%, 3%, 5%, 10%, and 15% were designed as the influence factor. The results indicated that mechanical strength properties namely unconfined compressive strength (UCS) and indirect tensile test (ITS), as well as fatigue properties namely indirect tensile resilient modulus (IT Mr) and indirect tensile fatigue (ITF) were enhanced with the NRL additive. Beyond the optimum r/c ratio, the excessive amount of NRL generated thick NRL films and retarded the cement hydration products, resulting in low strength and performance improvement. The r/c ratios of 3% and 5% were found to be the optimum r/c ratios for cement-NRL stabilized SS:LS and RCA:LS blends, respectively. The brittleness and permanent deformation of cement-stabilized SS/RCA:LS blends were significantly improved by the NRL additive. The superior mechanical and physical properties of SS and RCA were also attributed to the enhancement of fatigue characteristics of the cement-NRL stabilized blends. Finally, the mechanistic and fatigue models of cement- and cement-NRL stabilized soil with recycled material replacements were proposed, which are important for pavement designers and engineers when using a mechanistic-empirical pavement design approach.

Hemp Fiber-Modified Asphalt Concretes with Reclaimed Asphalt Pavement for Low-Traffic Roads

Abstract: Reclaimed asphalt pavement (RAP) contributes substantially to the volume of recycled waste in the world. This research aims to evaluate the mechanistic performance of asphalt concrete with 100% RAP (RAP-AC) modified with natural hemp fiber (HF) reinforcement. The effects of HF lengths and HF contents on the mechanistic performance were investigated. The static tests included Marshall stability, strength index (SI), and indirect tensile strength (ITS), whilst the cyclic tests included indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), and rutting resistance tests. The microstructural analysis revealed that HF could absorb more asphalt cement and function as a reinforcement. The 0.05% HF with a 24 mm HF length was suggested as the best ingredient. For various stress levels, the higher resilience properties—due to the addition of HF—contribute to higher levels of ITFL and rutting resistance. Based on a critical analysis of the cyclic test data, the distress model for HF-RAP-AC was developed for mechanistic pavement design. The outcome of this research promotes the usage of HF-RAP-AC as a greener material for low-traffic roads, which account for over 70% of the total roads worldwide.

Improved Fatigue Performance and Cost-Effectiveness of Natural Rubber Latex–Modified Cement-Stabilized Pavement Base at Raised Temperatures

Abstract: The increased temperature at the early state of curing affects the fatigue properties of pavement base materials. The fatigue properties of stabilized pavement bases and subbases govern the performance and service life of pavement structures. This research study utilized natural rubber latex (NRL) to enhance the tensile fatigue properties of cement-stabilized base materials at various temperatures. The effects of influence factors such as cement content (3%, 5%, and 7%), NRL replacement ratio (0%, 10%, 15%, 20%, 25%, and 30%), and temperature (25°C, 40°C, and 60°C) on indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) were studied in this research. NRL replacement was found to improve the UCS, ITS, IT Mr, and ITFL of cement (C)-stabilized soil up to the highest values at the optimum NRL replacement ratios, which were 20%, 15%, and 10% for cement contents of 3%, 5%, and 7%, respectively. The cement-NRL (C-NRL)-stabilized samples were found to have superior ITS, IT Mr, and ITFL values compared with C-stabilized samples for the same cement content but had the same rate of reduction in ITS due to the raised temperature. For the NRL replacement ratio on the dry side of optimum, the C-NRL-stabilized samples had lower rate of IT Mr reduction than the C-stabilized samples, although they had the same ITS due to the higher toughness. Therefore, the rate of ITFL reduction of C-NRL-stabilized samples was lower than that of the C-stabilized samples. It was proven in this research that the NRL replacement could reduce the thickness (superior IT Mr) of a cement-NRL-stabilized base course for a given traffic volume and service life, and therefore the construction (material and operation) cost by 17.26% benchmarked to a C-stabilized base course. Finally, the cost-effective design method for C-NRL-stabilized bases course was proposed, which will promote the use of NRL as an alternative green additive instead of synthetic polymer.

Mechanical Performance of Porous Asphalt Concrete Incorporating Bottom Ash as Fine Aggregate

Abstract: Porous asphalt concrete (PAC) is an open-graded asphalt concrete with a high air void, which functions as permeable pavement with high surface frictional resistance. PAC typically requires a high amount of coarse aggregate to provide the required porous structure. An expensive high-quality polymer-modified asphalt (PMA) is commonly required to prevent draindown issues and to improve the performance of PAC. Bottom ash (BA), a high-porosity byproduct from coal-fired power plants, is used as a greener product to improve the quality of traditional asphalt cement penetration grade 60/70 (AC 60/70) for producing low-cost PAC in this research. The effect of the BA replacement ratio (0%, 10%, 15%, 20%, and 25% by total weight of fine aggregate) on the draindown, loss of particle, Marshall properties, indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), permanent deformation (PD), rut depth, and skid resistance of BA-AC60/70-PAC were measured and compared with PMA-PAC. The draindown and particle loss values of BA-AC60/70-PAC were found to decrease with an increase in the BA replacement ratio. The BA replacement improved the Marshall properties, strength index, ITS, IT Mr, ITFL, PD, rut depth, and skid resistance of PAC up to the highest value at the optimum BA replacement ratio of 20%. The improved ITS is associated with the improved IT Mr in a linear relationship for all BA replacement ratios. The change in ITFL was found to be linearly related to IT Mr at a specific stress level. At the same design criteria, the 20% BA replacement ratio yields the reduction of total construction cost of BA-AC60/70-PAC surface course by 33% benchmarked to the conventional PMA-PAC surface course.

Geothermal Pavements: Experimental Testing, Prototype Testing, and Numerical Analysis of Recycled Demolition Wastes

Abstract: Geothermal pavements have the potential to reduce the pavement surface temperature by circulating fluid in pipes within the pavement structure. This research investigated an innovative geothermal pavement system with multiple benefits, such as reducing the surface temperature and harvesting heat energy for power generation. This research aimed to provide an understanding of the mechanical properties of geothermal pavements constructed with construction and demolition (C&D) waste materials through large-scale physical testing, experimental testing, small-scale prototype testing, and numerical simulation. The mechanical properties of the geothermal pavement system were assessed under long-term traffic loading conditions using a prototype test system. The repeated load triaxial and repeated-load California bearing ratio tests were also undertaken to evaluate the effect of pipe inclusion on the permanent deformation, stiffness, and strength of the pavement base. A numerical model was subsequently developed and calibrated using the data from small-scale prototype testing. In addition, the effects of the flow rate and pipe materials on the thermal performances of the geothermal pavements were also investigated in this research. The inclusion of pipes in the pavement base layer was found to have negligible detrimental effects on the deformation behavior of RCA. The resilient moduli of recycled concrete aggregate (RCA) samples slightly decreased with the inclusion of pipes. An HDPE pipe reduced the stiffness of the RCA + HDPE mix. On the other hand, a copper pipe’s high stiffness improved the mix’s strength. The numerical simulations indicated that for the HDPE pipe, increasing the flow rate from 500 mL/min to 2000 mL/min reduced the surface temperature by approximately 1.3%, while using the copper pipe resulted in an approximately 4% further decrease in the surface temperature compared to the HDPE pipe.