Assessment of strength development of slag cement stabilized kaolinite

Abstract Due to low strength and high compressibility, soft clay should be improved to increase its strength, and decrease the permeability and the ground settlement for a better construction condition. Nowadays the sustainability is much more important, so recycled materials such as fly ash and slag have been widely used and replaced the part of cement in soft ground improvement. The slag cement has been applied to improve the strength of soft soil in previous studies. The UCS (unconfined compressive strength) at the 28 days is an important index to evaluate the quality for improved soil. Thus, an assessment of the UCS from the early strength is desirable and will be helpful for safety evaluation and analysis of ground improvement under the construction phase. In this study, a series of UC test are conducted on slag cement treated soil with five types of slag cement-to-soil ratios (C/S ratio, is the ratio of binder over dry soil by weight) are 15%, 20%, 25%, 50%, and 75%. In addition, the initial water contents of 1.8 times, 2.0 times, and 2.2 times of the liquid limit of kaolinite is chosen to simulate the condition of soft ground improvement with cement. The UCS was tested at the ages of 3, 7, 14, 28 and 56 days. Test results show that when the curing time reaches 14 days, the development of strength slows down significantly. Thus, the strength of specimens cured longer than 28 days has a slight growth or no increase against the curing time. The UCS rapidly decreases with clay-water/cement ratio wc/c increasing when the value of wc/c less than 6.0, but the trend of reduction becomes smooth when the value of wc/c greater than 6.0. In addition, the UCS increases with cement-to-soil ratio C/S increasing. Thus, the UCS increases as clay-water/cement ratio decreasing and cement-to-soil ratio increasing. Namely, the UCS increases with the amount of slag-cement when the water content and the weight of soil are fixed. Furthermore, on the basis of both Gallavresi’s equation and Abrams’ law, the modified models of UCS are proposed in this study that can predict the UCS at other curing ages from the early strength on Day 3, and the factor of curing age is built in these modified models. From the comparison of UCS values obtained from tests and prediction models, the overall MAPE values are 18.79% and 18.00% for modified Gallavresi’s equation and Abrams’ law, respectively. These two MAPE values are between 10% and 20%. Thus, the prediction models established in this study have a good predictive ability.