Search Results (4)

The global market for tires is ever-growing, and partially replacing sand with crumb rubber (CR) as fine aggregates in concrete could reduce environmental pollution. However, the main barrier to the complete usage of recycled tire crumbs in construction is the deterioration effect of CR on the mechanical properties of cement-based composites. Therefore, this paper attempts to improve the fresh and hardened properties of crumb rubber mortar (CRM) by incorporating polypropylene-polyethylene synthetic fibers with coconut and kenaf natural fibers as reinforcements. A total of 18 mix designs were developed with varying fiber combinations and rubber crumb replacement. Subsequently, parametric studies with chemical admixture were conducted at 3, 7, and 28 days to improve the flowability and resulting mechanical properties of the fiber-reinforced CRM. According to the results, the single and hybrid fibers positively improved the mechanical properties of cement mortar at 5–15% CR replacement. It can be concluded that adding single and hybrid fibers enhanced the performance of cement mortar modified with tire crumb rubber aggregates by providing varying degrees of improvement. Full article

This paper presents a mesoscale model to study the influence of rubber particles on the mechanical performance of crumb rubber mortar (CRM). The indirect tensile and flexural behaviors of CRM with different rubber replacement rates, shapes, and sizes were investigated. Rubber mortar is assumed to be a three-phase material composed of rubber aggregate, a mortar matrix, and an interface transition zone (ITZ). Numerical analysis showed that rubber content was the governing factor affecting the reduction rate of indirect tensile and flexural strength. The effect of the ITZ on the tensile strength of CRM was within one percent, which could be ignored. The influence of rubber particle size was investigated by analyzing CRM models containing five different rubber sizes from 0.86 mm to 7 mm. For each size, six different models with randomly distributed rubber particles were set up. CRM models presented a similar average strength even with different rubber particle sizes. However, the strength variation among the random models became higher when the rubber particle size increased. Numerical results also proved that treating rubber particles as pores in modeling led to negligible errors. Then, a prediction formula after considering the increase in air content is provided. Finally, the accuracy of numerical simulations was verified through a series of experimental studies. Full article

Crumb rubber (CR) from scrap tires is used as a partial replacement of fine aggregates in cement paste. This promotes the sustainable development of the environment, economy, and society, as waste tires are non-biodegradable and flammable. They occupy large landfill areas and are breeding grounds for mosquitoes and rodents. Inclusion of CR in mortar leads to several improvements on the mixture properties such as ductility, toughness, and impact resistance. However, it exhibits lower strengths and Modulus of Elasticity (ME). Therefore, to promote the use of mortar containing CR, it is vital to improve its mechanical strength. Past studies proved that nano-silica (NS) improves the strength of concrete due to the physico-chemical effects of NS. This study aims to examine the mechanical properties of crumb rubber mortar containing nano-silica (NS-CRM) and to develop models to predict these properties using Response Surface Methodology (RSM). Two variables were considered, CR as partial replacement to sand by volume (0%, 7.5%, 15%), and NS as partial replacement to cement by weight (0%, 2.5%, 5%). The results demonstrated a significant improvement in the mechanical properties of CRM when incorporating NS, and the models developed using RSM were acceptable with a 2% to 3% variation. Full article

Studies on the properties and applications of rubber cement-based materials are well documented. The sizes of rubbers used in these materials varied. However, information about the effects of rubber size on the properties of rubber cement-based materials, especially pore structure, mechanical strengths, and drying shrinkage properties, remains limited. Three groups of rubber with major particle sizes of 2–4 mm, 1–3 mm, and 0–2 mm were selected in this study. This paper presents experimental studies on the effects of rubber size on the consistency, fresh density, pore structure, mechanical properties, and drying shrinkage properties of crumb rubber mortars (CRMs). Results demonstrated that the consistency and fresh density of CRMs decreased with the rubber size. As to the pore structure, the total pore volume increased with the decrease of the rubber size. By contrast, the influence of the rubber size on the mesopore (<50 nm) volume is not as significant as that of the rubber content. The mechanical properties of CRMs decreased with the rubber size. Low rubber stiffness and large pore volumes, especially those of small sized rubbers, contribute to the reduction of CRMs strength. The drying shrinkage of CRM increases as the rubber size decreases. The influences of rubber size on capillary tension are not significant. Thus, the shrinkage increases with the decrease of rubber size mainly because of its function in the deformation modulus reduction of CRMs. Full article