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The mechanical performance of Masterbatch Natural Rubber (MNR)-modified asphalt concrete (MNR-AC) was investigated and is presented in this paper. When compared to conventional asphalt concrete (AC), MNR-AC exhibits significantly superior performance across key mechanical parameters, including Marshall stability, indirect tensile strength (ITS), resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), and rutting resistance. The most pronounced enhancements are observed at the optimal dry rubber to asphalt cement (r/b) ratio of 3%, at which MNR-AC demonstrates peak performance in all evaluated tests. The fatigue distress models for MNR-AC and AC reveal distinct logarithmic relationships, with an intersection point occurring at an r/b ratio of approximately 3%. This suggests that MNR-AC with an r/b ratio of 3% or less exhibits a markedly superior fatigue life compared to conventional AC under equivalent applied-stress conditions. MNR offers significant practical advantages over liquid natural rubber, including more consistent mixing, and simplified storage and transportation, positioning it as a promising and sustainable advancement in pavement material technology. [ABSTRACT FROM AUTHOR]

There are ongoing research challenges for the addition of the blend of PET and crumb rubber in polymer-modified concretes, which aims to leverage the benefits of both materials. In this study, various percentage combinations of waste aggregates, such as PET and crumb rubber, were used to replace coarse and fine aggregates in natural rubber latex (NRL)-modified concrete. Engineering properties such as compressive and flexural strengths, modulus of elasticity, and toughness obtained from compressive- and flexural stress-strain curves were investigated. Scanning electron microscopy (SEM) analysis was performed to examine the microstructural properties and study the strength development of the studied concretes. The results revealed that the compressive and flexural strengths of NRL-modified concretes with PET and crumb rubber aggregate replacements decreased with increasing replacement ratios. SEM analysis indicated that PET and crumb rubber (hydrophobic and non-polar materials) can affect the microstructure of the studied concrete by creating a weak interface between the aggregate and cement pastes, leading to reduced strength development. With the addition of the NRL additive, the film formation was found to act as a bridge and improve the bond strength of aggregates and hydration products in NRL-modified concrete. Furthermore, the integration of PET and crumb rubber aggregate can enhance the ability of the concrete to absorb energy and improve ductility. It was found that 10% of PET and crumb rubber aggregate replacement can be used for NRL-modified concrete as a rigid pavement, as its mechanical strengths satisfy the requirements set by the Department of Highways (DOH) in Thailand. This research helps repurpose waste materials and reduce the environmental footprint of concrete production. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Road networks are major infrastructures that support the economic development in both developed and developing countries. Bottom ash (BA) is a by-product from coal-fired powerplants, which is composed of a lipophilic molecule with effective reactivity to bituminous binder. BA was adopted in this research, as a green fine aggregate, to improve the mechanistic performance of asphalt concretes in this research. The effect of BA-replacement ratio (0%, 10%, 15%, 20% and 25%, by total weight of natural fine aggregate) on the Marshall stability and flow, indirect tensile strength (ITS), and mechanistic performance of BA-asphalt concrete, were examined. The mechanistic performance tests included the indirect-tensile condition (indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL)) and compressive condition (permanent deformation (PD), rut depth, and skid resistance). BA replacement improves the Marshall stability and flow, strength index, and ITS, up to the optimum BA-replacement ratio, of 5%. The change in IT Mr was found to be linearly proportional to the change in ITS, for all BA-replacement ratios. The ITFL is dependent upon the repeated stress level and can be estimated in terms of IT Mr. For the compressive condition, the PD, rutting, and skid resistances were found to be improved by the BA replacement. The lowest PD and rut depth as well as the highest skid resistance, for IT Mr and ITFL, were found at the optimum BA-replacement ratio, of 5%. The outcome of this research will promote the usage of BA as a cleaner additive in asphalt concrete pavement, which is useful in terms of engineering and environmental perspectives. [ABSTRACT FROM AUTHOR]

The growth of the global economy in recent years has resulted in an increase in infrastructure projects worldwide and consequently, this has led to an increase in the quantity of waste generated. Two recycled materials, namely garnet residues (GR) and tire-derived aggregates (TDA), were used to improve mechanical properties of soft clay (SC) subgrade in this study. GR was evaluated as a replacement material in SC prior to Type I Portland cement stabilization. TDA was also studied as an elastic material in cement-stabilized SC–GR. The laboratory tests on the cement–TDA-stabilized SC–GR included unconfined compressive strength (UCS), indirect tensile stress (ITS) and indirect tensile fatigue (ITF). Microstructural analysis on the cement–TDA-stabilized SC–GR was also performed to illustrate the role of GR and TDA contents on the degree of hydration. The UCS of cement-stabilized SC–GR increased when cement content increased from 0% to 2%. Beyond 2% cement content, the UCS development was slightly slower, possibly due to the presence of insufficient water for hydration. The GR reduces the specific surface and particle contacts of the SC–GR blends to be bonded with cementitious products. The optimum SC:GR providing the highest UCS was found to be 90:10 for all cement contents. Increased amounts of GR led to a reduction in UCS values due to its high water absorption, resulting in the insufficient water for the cement hydration. Moreover, the excessive GR replacement ratio weakened the interparticle bond strength due to its smooth and round particles. The TDA addition can enhance the fatigue resistance of the cement-stabilized SC–GR. The maximum fatigue life was found at 2% TDA content. The excessive TDA caused large amounts of micro-cracks in cement–TDA-stabilized SC–GR due to the low adhesion property of TDA. The SC:GR = 90:10, cement content = 2% and TDA content = 2% were suggested as the optimum ingredients. The outcome of this research will promote the usage of GR and TDA to develop a green high-fatigue-resistant subgrade material. [ABSTRACT FROM AUTHOR]

In this research, large direct shear tests were conducted to evaluate the interface shear strength between reclaimed asphalt pavement (RAP) and kenaf geogrid (RAP–geogrid) and to also assess their viability as an environmentally friendly base course material. The influence of factors such as the gradation of RAP particles and aperture sizes of geogrid (D) on interface shear strength of the RAP–geogrid interface was evaluated under different normal stresses. A critical analysis was conducted on the present and previous test data on geogrids reinforced recycled materials. The D/FD, in which FD is the recycled materials' particle content finer than the aperture of geogrid, was proposed as a prime parameter governing the interface shear strength. A generalized equation was proposed for predicting the interface shear strength of the form: α = a(D/FD) + b, where α is the interface shear strength coefficient, which is the ratio of the interface shear strength to the shear strength of recycled material, and a and b are constants. The constant values of a and b were found to be dependent upon types of recycled material, irrespective of types of geogrids. A stepwise procedure to determine variable a, which is required for analysis and design of geogrids reinforced recycled materials in roads with various gradations was also suggested. [ABSTRACT FROM AUTHOR]