Development of Rice Husk Ash as a Cement Substitute for Environmental Conservation and Its Effective Use in Green Infrastructures

Abstract

In recent years, there has been a growing demand for the development of structural materials capable of introducing vegetation in order to solve environmental problems and achieve sustainable development of society. The authors have been developing a cement-based greening base material using “rice husk ash”, which is incinerated ash from rice husks, an agricultural by-product. The reason for focusing on rice husks is that most of them are not utilized despite their abundance in the world. In addition, the advantage of rice husk ash is not only the reuse of resources but also its ability to accelerate hardening reactions as a cement substitute due to its pozzolanic activity. The greening base material is a porous material that must have both stability as a soil material and a pore structure that does not inhibit the development of plant root systems. The problem with the mechanical properties of porous materials is that fracture occurs due to stress concentration at the site of minimum strength in various stress fields. Therefore, in addition to the strength value, which is the maximum stress, it is necessary to clarify the cracking kinetics that appear during the fracture process. Previous studies have quantified the cracking behavior using fracture mechanics parameters and evaluated the material properties based on particle bonding. However, these studies have not been sufficiently conducted for greening base materials. In this study, we report the results of cracking and tensile strength tests of cementitious greening base materials with five different rice husk ash replacement ratios, and the evaluation of material properties using acoustic emission (AE) energy indices. In addition, planting tests were conducted on these materials and the relationship between the materials and the development of plant rhizosphere was discussed. Thus, the results indicated that the particle binding strength decreased as the rice husk ash replacement ratio increased, and that the change in fracture behavior could be evaluated from the AE energy index. The planting tests revealed a close relationship between the development of the rhizosphere and the material represented by the pore distribution by the replacement ratio. Therefore, rice husk ash is useful as a cement substitute, enabling both material strength and plant growth in service green infrastructure.