Investigation of viscous behaviour and strength of microfine-cement-based grout mixed with microfine fly ash and superplasticiser

In order to obtain grouts with reduced leaching, desirable fluidity and sufficient penetrability for the filling of sand voids or microcracks, a microfine-cement-based grout (MCG) with microfine fly ash (MFA) was prepared and the maximum grain size (d_max) was controlled at 20 μm. The viscosity, hydration temperature, spreading ability, fluidity, flexural strength and unconfined compressive strength of MCGs with MFA and naphthalene-based superplasticiser (SP) were investigated. The relatively new concept of ‘static viscosity’ was considered. The ranges of water/MCG (w/MCG) ratios, MFA contents and SP contents were 0·8–3·0, 0–50% and 0·5–3·0%, respectively. The viscosity, hydration temperature and flow time were found to decrease with increasing w/MCG ratios, MFA and SP contents, but mini-slump diameter, bleed capacity and setting time increased. The effects of MFA were not as obvious as those of SP. The addition of 2·0% SP decreased the flexural strength and the compressive strength, while 40% MFA increased the flexural strength and decreased the compressive strength. The optimum w/MCG ratio, MFA and SP contents are recommended as 1·0–1·5, 30–40% and 1·5–2·0%, respectively. A low initial viscosity of the optimised MCG ensured desirable rheology properties and satisfactory mechanical properties of the hardened grout. To avoid instability, oversaturation or long setting times, SP dosages should not be excessive.