Microfibrillated cellulose as a new approach to develop lightweight cementitious composites: rheological, mechanical, and microstructure perspectives

Lightweight cementitious composites have a broad range of applications, such as filling or thermal insulation, and should display minimal mechanical properties. Our approach was to prepare mixtures of ordinary Portland cement (OPC) and micro- and nanofibrillated cellulose (CNF) at different water to cement ratios (W/C) to optimize a composite with low density, and either high compressive or flexural strength. The rheological data of W/C = 1 CNF-OPC paste confirmed that the viscosity and yield stress of the sample containing 1.1 wt% cellulose fiber was abruptly increased in comparison to the sample without fibers. The results also confirmed the well miscibility (dispersion/distribution) of the OPC in high-water content (98 wt%) fiber medium due to absence of aggregation or agglomeration signatures in plotted rheological data. The dry densities of the CNF-OPC specimen were obviously reduced from 800 kg/m³ to 450 kg/m³ by increasing the content of fiber from 1.1 wt% (W/C = 1) to 1.8 wt% (W/C = 4), respectively. However, the compressive strengths of the CNF-OPC mixtures were dramatically dropped at higher W/C. Based on the results of mechanical testing, the used lightening technique had less effect on flexural strength loss compared to that of compressive strength, which is related to the bridging action of micro- and nanofibrillated cellulose in the matrix.