This paper focuses on increasing the efficiency in accelerating the rate of consolidation of prefabricated vertical drains (PVDs) in improved soft Bangkok clay using vacuum and heat preloading. Laboratory model tests were performed in new, large-scale consolidometers with PVD-improved reconstituted specimens using the following four schemes: surcharge preloading (PVD only), surcharge combined with vacuum pressure preloading (vacuum-PVD), surcharge combined with heat (thermo-PVD), and surcharge combined with heat and vacuum pressure (thermo-vacuum-PVD). Subsequently, the flow parameters in terms of the horizontal coefficient of consolidation (C_h) and the ratio between the horizontal hydraulic conductivity in the undisturbed zone (k_h) to the horizontal hydraulic conductivity in the smear zone (k_s), based on Hansbo's method. were investigated by back-calculation. The results show that the values of C_h were 1.93 m²/yr, 2.23 m²/yr, 4.17 m²/yr and 4.37 m²/yr for the PVD, vacuum-PVD, thermo-PVD and thermo-vacuum-PVD, respectively, with corresponding k_h/k_s values of 3.0, 2.7, 1.4 and 1.1, respectively. On the other hand, the increase in C_h of reconstituted specimens using the vacuum-PVD, thermo-PVD and thermo-vacuum-PVD were 15.54%, 116.06% and 126.42%, and the increases in k_h/k_s were 10.00%, 53.33% and 63.33%, respectively. Thus the vacuum-PVD can increase the horizontal coefficient of consolidation, C_h, resulting in a faster rate of settlement at the same magnitudes of settlement, compared with the PVD. The thermo-PVD and thermo-vacuum-PVD can further increase the coefficient of horizontal consolidation, C_h, with associated reduction of k_h/k_s values, by reducing the drainage retardation effects in the smear zone around the PVD, and consequently faster rates of consolidation were obtained. However, higher magnitudes of settlement were obtained upon application of heat owing to the associated collapse of the clay structure, similar to the results of previous investigations.

The use of synthetic fiber and natural fiber for concrete production has been continuously investigated. Most of the materials have become popular for their higher flexibility, durability, and strength. However, the current study explores the engineering properties of cement concrete reinforced with nylon and jute fibers together. Varying proportions and lengths of nylon and jute fibers were utilized in the concrete mixture. Hence, the combined effects of nylon and jute fibers on workability, density, water absorption, compressive, tensile, flexural strength, and drying shrinkage of concrete were investigated. Results showed that concrete with 1% of nylon and jute fibers together by the volume fraction showed a maximum enhancement of the compressive strength, split tensile strength, and flexural strength by 11.71%, 14.10%, and 11.04%, respectively, compared to the control mix of concrete at 90 days. However, the water absorption of concrete increased with increasing nylon and jute fiber contents. The drying shrinkage of concrete decreased with the addition of nylon and jute fibers together after 90 days. Thus, the sparing application of both nylon and jute fiber as discussed in this study can be adopted for concrete production.

Nowadays, the incorporation of natural fiber, such as coir fiber, to high-strength concrete has sparked a lot of attention in the construction materials industry. This is because coir fibers are significantly cheaper and more widely accessible than synthetic fibers. Natural fibers such as bamboo, flax, hemp, and coir have distinct microstructures and chemical compositions from cement-based materials. The physical and mechanical properties of natural fiber, such as coir fiber, are significantly correlated with fiber concentration and cellulose component. However, coir fiber has high stretching to failure, while bamboo, flax, and hemp fibers are very resistant to stress and increase stiffness. Based on these distinctive fiber qualities, it is anticipated that coir fiber would facilitate the development of cement-based materials for advanced concrete building applications. In this paper, coir fiber-reinforced cement-based concretes were evaluated in terms of workability, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and permeability. The relationship between strength and fiber content was analyzed to understand the impact of coir fiber on the properties of coir fiber-reinforced cement-based concrete. Based on the results obtained, it is determined that 2% coir fiber modification offers the highest compressive strength, splitting tensile strength, and flexural strength. Moreover, the modulus of elasticity is increased, and the permeability is plummeted by the volume fractions of coir fiber 1%, 2%, and 3% because the blending of coir fiber has a bridging and dispersing mechanism of the force-carrying capacity in concrete. In conclusion, coir fiber might be a viable choice for improving the strength and durability of concrete. Therefore, the sparing use of coir fiber presented in this research can be implemented for the manufacturing of concrete in the future.