AbstractThe use of carbide sludge (CS)-ground granulated blast furnace slag (GGBS) for clay slurry treatment has shown superior strength performance compared to ordinary Portland cement (OPC). To achieve a maximum level of unconfined compressive strength (UCS) of the CS-GGBS-treated slurry, there is an optimal level of CS, but this content varies with soil type and GGBS content. Optimal CS content is conventionally assessed by evaluating the UCS at 28 or 56 days. In this study, a rapid test method is proposed to estimate the optimum CS content in a few hours by measuring the pH, instead of UCS, of the CS-GGBS-treated slurry. Results show that the 28-day and 56-day UCS versus CS content curves of CS-GGBS-treated slurries are quite similar to their one-hour pH profiles. Hence, the pH versus CS content profile could be used to estimate the optimum CS content, i.e., the minimum CS content required to obtain a saturated Ca(OH)2 solution was estimated as the optimum CS content. The CS-GGBS-treated slurry with an estimated optimum CS content based on initial pH achieved a high strength level (≥91% of the maximum UCS) after curing for 28 and 56 days. Furthermore, the thermogravimetric analysis (TGA) results indicate that excess CS addition beyond the optimum CS content led to the generation of more hydrotalcite phases, but less calcium silicate hydrate (CSH), which contributed to the strength difference.