Properties of sulfoaluminate cement-based grouting materials modified with LiAl-layered double hydroxides in the presence of PCE superplasticizer

Abstract

Sulfoaluminate (CSA) cement-based grouting materials (CBGM), due to their fast hydration rate and high early strength, can be used in repair and reinforcement projects. To obtain a high workability, CBGM has often been modified by a polycarboxylate ether (PCE) superplasticizer with a high water to binder ratio (>0.5), which results in a poor compressive strength. Nano LiAl-LDH has been reported to have excellent properties for improving the mechanical behavior of sulfoaluminate (CSA) cement clinkers. In addition to the physicochemical characteristics of the nanomaterials, the admixtures used in CBGM paste can also affect the properties of the nanomaterials. In this paper, the effect of the PCE superplasticizer concentration on the properties of CBGM modified with LiAl-LDH was investigated, and a possible reason is provided. The results show that low PCE superplasticizer concentrations (0.9 wt% and 1.15 wt%) increased and high PCE superplasticizer concentrations (1.38 wt%, 1.76 wt% and 2.13 wt%) decreased the compressive strength of a CBGM paste modified with LiAl-LDH in comparison with that of the control paste. The PCE superplasticizer did not intercalate into the interlayers of the LiAl-LDH, and the interaction between the PCE superplasticizer and LiAl-LDH was limited to surface adsorption. A small quantity of lithium ions was released from the precipitation-dissolution equilibrium of LiAl-LDH in the slurry. Lithium atoms can enter the vacant octahedral sites of montmorillonite, which is one component of the CBGM, via isomorphous substitution, and the interaction decreased the adsorption quantity of the PCE superplasticizer on the bentonite surface, resulting in the high fluidity of the CBGM paste in the presence of a high PCE superplasticizer concentration.