Novel fly ash based one-part geopolymer for stabilization of expansive road subgrade

Abstract

Expansive soils present significant challenges in road construction on account of their volumetric changes and low unconfined compressive strength (UCS). The conventional technique for soil stabilization entails the use of a chemical stabilizer like ordinary Portland cement (OPC), which is the most commonly used binder. However, the sustainability of OPC is hindered by greenhouse gas emissions. Alkali-activated geopolymers have emerged as sustainable alternatives. Geopolymers, which are formed by activating aluminosilicate precursors in an alkaline environment, come in one-part (OP-G) and two-part (TP-G) forms, with OP-Gs offering convenience and lower costs for transportation over TP-Gs. This study aims to evaluate the strength and swell characteristics of an expansive road subgrade material stabilized with OP-G. First, a comprehensive experimental program was undertaken for the mix optimization of OP-G stabilized soil based on UCS and cost. Altogether 16 UCS tests were conducted by varying binder/dry soil and solid NaOH/Fly ash (FA) ratios. Based on the findings, the optimal OP-G mix was determined at binder/dry soil = 0.2 and solid NaOH/FA = 0.1. In the second part of the study, the strength and swell characteristics of the optimum OP-G were compared with the optimum TP-G and OPC mixes. Laboratory tests, including the Atterberg limits, swell pressure, UCS, and California bearing ratio (CBR), were conducted on all three stabilized mixtures. The UCS values of the OP-G, TP-G, and OPC-treated samples were 1.23, 0.98, and 2.77 MPa, while the CBR values were 24%, 16%, and 81% respectively. All three stabilizers satisfied the ICTAD requirements for subgrade materials (UCS from 0.75 MPa to 1.5 MPa and CBR ≥ 15%). Despite the superior UCS and CBR of OPC, the OP-G can be a viable alternative, surpassing OPC in swell control and environmental impact. The outcomes reflect the effectiveness of OP-G in stabilizing expansive road subgrades.