Use of red gypsum in soil mixing engineering applications

This paper describes a laboratory trial to test the effectiveness of a waste-based binder as a cement replacement for deep in situ soil stabilisation. The binder is composed of red gypsum, a co-product of the production of white pigment titanium dioxide, and ground granulated blast furnace slag (GGBS), with a small addition of lime to increase soil pH and enable pozzolanic reactions to occur. The waste binder was mixed with a number of typical UK soils and cured for 7, 14, 28, 56 and 112 days in wet and dry conditions. Samples were then tested for undrained shear strength and stiffness, and results compared with values exhibited by soils mixed with Portland cement. Selected samples were also subjected to X-ray diffraction analysis. Results showed that, while not achieving strengths as high or hardening as rapid as samples mixed with Portland cement, samples mixed with the gypsum–GGBS binder achieved high strengths and stiffness, and demonstrated that gypsum–GGBS binders have the potential to be used as cement replacements in ground improvement.