Workability and Mechanical Properties of Superplasticized Microfine Cement Grouts.

Superplasticizer (SP) is essential to enhance the groutability of microfine cement (MC) in civil engineering, however, combined effects of cement type, SP type, amount of SP and water-solid ratio (W/S) on engineering performance of MC are not clear currently. In this research, workability and mechanical properties of superplasticized microfine cement grouts (SMCG) with various SPs are evaluated systematically. Three different MCs (CEM I, CEM II/B-M and CEM III/B based on EN 197-1) and four SPs (one naphthalene-based (N), one melamine-based (M) and two polycarboxylate-based (PCE)) were used to study the effect of grout formulation. The properties investigated included rheological behavior (mini-slump, flowability, time-dependent viscosity and initial viscosity), fresh-state property (bleeding, effective W/S and final setting time), mechanical performance (shrinkage, flexural strength (FS), unconfined compressive strength (UCS), and FS/UCS) and microstructure. The new method of static viscosity was adopted and viscoelasticity was evaluated. The ranges of W/S and SP content were 1.0-2.0 and 0-2.5%, respectively. The results show that the dispersion effects of SP on rheological behavior were followed by PCE, M and N in order of the influence degree. The instability, long-setting and oversaturation were easily caused by excessive SP. SP could be helpful for improving FS or bending toughness. Considering workability and mechanical performance of SMCG, the W/S is suggested to be within 1.5, the optimal amounts of N, M and PCE are recommended as 1.5-2.0%, 1.2-1.5% and 0.9-1.2%, respectively.