Properties of the cement containing hybrid micro-fibers and polymer latex using the orthogonal test: A comparative study of freshwater and seawater curing conditions

The enhancement of cement properties through the integration of composite materials has become a prevailing topic, as it offers a solution to the limitations associated with single-material approaches. Our study aims to explore the synergistic potential of calcium carbonate whiskers (CWs), multi-wall carbon nanotubes (MWCMTs), and carboxylated styrene-butadiene rubber latex (XSBRL) in cement under seawater curing conditions, and freshwater conditions are added as the control group. The laboratory tests including fluidity, mechanical strength, and porosity were measured using the orthogonal test design method, and the weight matrix analysis method was used to determine the optimal mix proportion. The results showed that incorporating 5%, 10%, and 15% of XSBRL increased the fluidity by 17.87%, 48.55%, and 133.09%, respectively. On the contrary, the mechanical strength decreased by 8.33%, 10.85%, and 10.09% for seawater conditions at 28d, respectively, accompanied by an increase in porosity. CWs enhanced the mechanical strength by 7.69%, 10.92%, and 12.84%, respectively, and the pore structure was densified. MWCNTs first increased and then decreased the strength, and it may be due to the agglomerative effect. The optimal mix proportions were 3% CWs content, 0.2% MWCNTs, and 10% XSBRL for freshwater conditions, while 3% CWs, 0.3% MWCNTs, and 15% XSBRL for seawater conditions. X-ray diffusion (XRD) and scanning electron microscope (SEM) were used to characterize the phase composition, mineralogy, and microstructure. Results illustrated that CWs, MWCNTs, and XSBRL would not change the mineral phases of cement, and some Friedel's salt and more ettringite were found under seawater conditions. The crack deflection, bridging effect, whisker breaking, and pull-out effect of CWs, the nucleating effect for hydration products and the crack control ability of MWCNTs, and the three-dimensional network structures of XSBRL were responsible for the considerable modification.