Use of a rubber wood fly ash-based geopolymer for stabilizing marginal lateritic soil as green subbase materials

Abstract

Rubber wood fly ash (RWFA) is one of the main components of biomass ash materials. This research investigates the possibility of using RWFA geopolymer (RWFAG) to stabilize marginal lateritic soil (MLS) as green subbase materials. RWFA was used as a starting material.The studied influence factors included MLS:RWFA ratio, sodium silicate (NS):sodium hydroxide (NH) ratio, soaked and unsoaked conditions, and curing time. The study involved testing the unconfined compressive strength (UCS), indirect tensile strength (ITS), and conducting microstructure. The test results revealed that the optimal liquid content for the MLS-RWFAG specimens ranged between 12-24% for all ingredients. As the RWFA content increased, the maximum dry unit weight of the MLS-RWFAG decreased due to the lower specific gravity of RWFA. The MLS-RWFAG specimen with 30% RWFA content and an NS:NH ratio of 70:30 yielded the maximum UCS and ITS. The SEM-EDS analysis demonstrated the production of C-S-H and N-A-S-H gels, resulting in a dense and homogeneous matrix in the MLS-RWFAG specimens. Considering cost-effectiveness, the optimum ingredients for the MLS-RWFAG specimen were identified at an MLS:RWFA ratio of 70:30 and an NS:NH ratio of 10:90, meeting the 7-day soaked UCS requirement for pavement subbase materials. Moreover, the CO2-eq emissions from MLS-RWFAG specimens were lower compared to those from 3% cement-stabilized MLS samples. These findings strongly support the use of RWFAG as a viable alternative to Portland cement for stabilizing MLS in subbase materials.

Mechanical Response and Deterioration Mechanisms in Freeze–Thaw Environments for Crushed Stone Stabilized with Industrial Solid Waste

“…On the one hand, a large number of hydration products covers the surface of the stabilized material to form a solid matrix, which also makes the loose particles interconnected and aggregated into one, so that the mixture forms strength. On the other hand, the hydration products generated by the geopolymer raw materials after alkali excitation effectively fill the pores and other structures inside the stabilized material, which enhances the compactness of the stabilized material and makes the mixture form strength [5,8,12,15]. In addition, it is worth noting that the dosage of geopolymer generally has an optimal value.…”

“…In addition, the geopolymer significantly reduced the leaching of harmful heavy metals. Tabyang W et al [12] used rubberwood fly ash to prepare a geopolymer for the preparation of geopolymer-stabilized marginal laterite subgrade material and tested its mechanical properties. The results showed that the UCS and ITS (indirect tensile strength) of this base material were optimized when the dosage of the geopolymer was 30% and the ratio of sodium silicate to sodium hydroxide was 7:3.…”

“…The results of the above research are summarized and analyzed, and then potential researchable content is identified. Firstly, existing research used geopolymers as a cementitious material, which can be used for roadbed construction and road construction in mining areas, with certain environmental and economic benefits, as the raw materials used are mostly industrial solid wastes [9][10][11][12]15,16]. Secondly, considering the existing research on geopolymer-stabilized road building materials' mechanical strength, frost resistance, environmental impact and other aspects, the results show the following: the geopolymer, as road building materials, has good mechanical strength, with a certain degree of frost resistance, and the geopolymer effectively reduces the leaching rate of the heavy metals contained in industrial solid waste materials [11,20,21].…”