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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]

This research delved into the mechanical and fatigue attributes of hemp fiber–reinforced concrete (HFRC) using both natural crushed aggregates (NCA) and recycled concrete aggregates (RCA) for sustainable rigid pavements. The additional hemp fiber ratios were 0%, 0.5%, 0.75%, and 1.0% by volume of concrete. The accelerated setting times were found due to hemp fibers facilitating rapid cement hydration. The compressive strengths were found to typically decrease with increasing hemp content. Mixes with 0.5% hemp (NCA-0.5H-FRC and RCA-0.5H-FRC) met the local road authority's rigid pavement standards, with enhanced energy absorption and ductility. Flexural strength was optimal at 0.5% hemp, with all mixes meeting the standard 4.2 MPa. The flexural fatigue test indicated that higher hemp content significantly improved the fatigue life of HFRC under repetitive loading. Scanning electron microscopy (SEM) analysis demonstrated hemp fibers' role in enhancing bond strength and interactions with cement matrix, thereby improving the concrete performance. While NCA mixes outperformed RCA ones, hemp fiber's reinforcing effect was consistent across both types of aggregates. The study indicated hemp fiber's potential in applications like pavements, highlighting 0.5% as the optimal hemp content for balancing enhanced mechanical properties while mitigating potential drawbacks. This research paves the way for the broader adoption of hemp fiber–reinforced concretes in sustainable construction endeavors. [ABSTRACT FROM AUTHOR]

The expansive development of infrastructure has led to increased consumption of virgin aggregates in road construction, resulting in significant environmental impacts. To address this issue, there is a pressing need for sustainable alternatives that utilize recycled materials in pavement applications. This paper presents a comprehensive review of a decade-long research program focused on the development and evaluation of sustainable pavement materials, such as recycled and waste aggregates, industrial by-products, and natural fibers. The research encompassed a wide range of innovative materials and technologies, such as geopolymer-stabilized recycled aggregates, cement-stabilized waste materials, natural additive-modified cement stabilization, and recycled aggregate-geogrid reinforcement systems. The experimental framework employed a combination of mechanical testing, durability assessment, microstructural analysis, and environmental safety evaluation to assess the performance and sustainability of these materials. The key findings demonstrated the superior mechanical properties, improved durability, and environmental suitability of the recycled materials compared to conventional virgin aggregates. The successful implementation of these sustainable solutions in real-world projects highlights their potential to reduce the environmental footprint of road infrastructure development. Furthermore, the paper discussed the practical implications of the research outcomes for pavement design and construction, as well as future research directions to further advance the field of sustainable pavement engineering. The findings of this research report can be used as guidance for researchers, practitioners, and policymakers seeking to upcycle the widespread adoption of recycled materials in road application and contribute to the development of a more sustainable and resilient transportation infrastructure. [ABSTRACT FROM AUTHOR]

This article investigates the viability of using natural rubber latex (NRL)-modified concrete with bottom ash (BA) as a partial replacement for river sand in sustainable rigid pavements. Concrete mixes with 10% and 20% BA replacement ratios and varying NRL dosages (0%, 1.0%, 1.5%, and 2.0% by weight of cement) were prepared and evaluated for their mechanical and microstructural characteristics. Results showed that BA substitution decreased the compressive strength of concrete. However, the addition of NRL at an optimal dosage of 1.0% significantly improved both the compressive and flexural strengths. The 10%BA+1.0%NRL and 20%BA+1.0%NRL mixes exhibited mechanical properties surpassing the control mix and meeting the minimum requirements for rigid pavement materials. However, excessive NRL content (1.5% and 2.0%) led to a reduction in mechanical strength. Scanning electron microscopy analysis exhibited a denser and more compact matrix in NRL-modified BA concrete, with NRL films enhancing the interfacial bonding and crack-bridging mechanism. Nonetheless, excessive NRL content resulted in the formation of abundant and thicker NRL films, which disrupted the continuity of the cement matrix and created weak zones. X-ray diffraction analysis confirmed the existence of crucial crystalline phases and their optimal balance in the 20%BA+1.0%NRL mix, contributing to its superior performance. Mixes with excessive NRL contents exhibited lower intensities of quartz, calcite, and portlandite peaks, indicating a disturbance in the proper formation and growth of essential crystalline phases. The findings demonstrated the potential of NRL-modified BA concrete as an eco-friendly and high-performance alternative for sustainable rigid pavements when using an optimal NRL dosage, promoting the employment of waste resources and reducing the environmental impact of the construction industry. [ABSTRACT FROM AUTHOR]

The influence of aggregate properties and natural rubber latex (NRL) additive on the performance of natural rubber modified asphalt (NRMA) concrete mixtures was investigated. The NRMA mixtures were prepared using three types of aggregate (granite, limestone, and basalt), asphalt cement AC60/70 and NRL with different rubber to binder (R/B) ratios of 3%, 5%, and 7%. A series of laboratory tests including Marshall stability and flow, indirect tensile strength, indirect tensile fatigue, resilient modulus, wheel tracking test, dynamic creep, and skid resistance tests were conducted to investigate the mechanical properties and mechanistic performance of the NRMA mixtures. Statistical analysis was performed using the NLOGIT software program to evaluate the influence factors including strength, shape, and chemical properties of aggregate and R/B ratio. The R/B ratio of 3% was found to be the optimum value which provided the best mechanical properties and performance. The strength parameters and mineral compound were found to control the Marshall stability. As such, the NRMA mixtures with basalt and granite of high Marshall stability led to the high resilient modulus, rutting resistance, and permanent deformation. Because of the good strength and shape parameters of granite, the NRMA mixture with granite indicated a significant rate of improvement of fatigue life compared with the NRMA mixtures with other aggregates. Limestone's predominant mineral compounds (CaO, MgO, and SiO2) were found to influence the indirect tensile strength and skid resistance of NRMA mixtures. [ABSTRACT FROM AUTHOR]

The stiffness, rutting, and fatigue performance of cement-natural rubber latex (NRL) stabilized recycled concrete aggregate (RCA) were evaluated under cyclic loading. The RCA was stabilized with 3% cement content and dry rubber content to cement (r/c) ratios at 5%, 10% and 15%. The performance evaluation was carried out through advanced experiments, including indirect tensile resilient modulus test, indirect tensile fatigue test, and rutting susceptibility test using a Hamburg wheel tracking device. The results indicated that the r/c ratio of 10% was optimum for cement-NRL stabilized RCA (3C10R-RCA), which exhibited the optimum performance in terms of permanent deformation, fatigue cracking, and rutting susceptibility. The indirect tensile fatigue life of 3C10R-RCA was found to be 79.3% greater than that of the 3% cement stabilized RCA (3C-RCA), while the rut depth of 3C10R-RCA was 8% lower. Although the resilient modulus value of 3C10R-RCA was slightly lower than that of 3C-RCA, the tensile permanent deformation was found to be lower, which is associated with the lower rut depth. As a result of the significant improvement in fatigue life and rutting performance, the resistance to fatigue cracking and premature failure of cement-NRL stabilized RCA were improved. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This research investigated the influence of natural rubber latex (NRL) on the performance of cement stabilised recycled concrete aggregate (RCA) as a pavement base material. The influence factors studied included different cement at contents and dry rubber to cement (r/c) ratios. The NRL replacement enhanced the unconfined compressive strength (UCS) and indirect tensile strength (ITS) of cement stabilised RCA. The highest UCS and ITS of cement-NRL stabilised RCA were found at the optimum r/c ratios. Beyond these optimum r/c ratios, the UCS and ITC values decreased although all UCS values were still greater than the minimum requirement for base material. Microstructural analyses indicated the detected cement hydration products and NRL films, which NRL films were found to improve the adhesion and interparticle bonds of RCA particles. However, the excessive NRL additive retarded the cement hydration, whereby the UCS and ITS development was low when the r/c was greater than the optimum value. [ABSTRACT FROM AUTHOR]

In this research, a natural kenaf geogrid was used to reinforce recycled concrete aggregate (RCA) as a base/subbase material. The interface shear behavior of kenaf geogrid-reinforced RCA was investigated using a large-scale direct shear test (LSDT). The influence of aperture sizes of geogrid, gradations of RCA, and normal stress on the interface friction angle (δ) and adhesion (ca) of kenaf geogrid-reinforced RCA was evaluated. The interface shear strength of kenaf geogrid-reinforced RCA were found to be dependent upon the gradation of RCA and the aperture size of kenaf geogrids (D). The higher D resulted in the higher δ, while exhibited less effect on ca of the large-sized RCA samples. Furthermore, it was found that the higher D resulted in the higher ca of the small-sized RCA samples and indicated less influence on the δ. A practical correlation between the interface shear strength coefficient (α) and D/FD ratio, where FD is RCA particles finer than D, is proposed for the rapid estimation of the interface shear strength between the kenaf geogrid and RCA. The outcome of this research will lead to the promotion of using kenaf geogrids as a natural reinforcement in waste RCA for sustainable pavement base/subbase applications. [ABSTRACT FROM AUTHOR]

Cement stabilised unpaved roads have been implemented worldwide in both developed and developing countries. In this research project, natural rubber latex (NRL) was used to improve the durability against wetting and drying (w-d) cycles of cement stabilised soil, under cyclic tensile loads. The influences of NRL replacement ratio on the indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), and indirect tensile fatigue life (ITFL) prior to and after w-d cycles were studied. Cement-NRL stabilised soil was found to have superior resilient properties to minimise the plastic deformation and prevent sudden damage against the repetitive tensile stresses. The NRL replacement could improve the durability against w-d cycles of cement stabilised soil whereby the highest ITS, IT Mr, and ITFL were found at the optimum NRL replacement ratio of 20% for all number of w-d cycles tested. NRL was found to enhance the service life of cement stabilized soil as an unpaved material against fatigue cracking failure. The outcome of this research will promote the usage of NRL, which is available in plentiful supply in Thailand and other Southeast Asian and South American countries, as a sustainable additive in pavement applications. [ABSTRACT FROM AUTHOR]