Hygrothermal and strength properties of cement mortars containing cenospheres

This study characterizes the hygrothermal and microstructural properties of cement composites containing aluminosilicate cenospheres. It involved the preparation of six mortar mixtures based on CEM I 42.5R cement, in which cenospheres accounted for 0 to 100 % of the aggregate content. The research included measurements of thermal properties, compressive and bending strength tests, density tests on the cured mortars, determination of pore distribution and total porosity, and qualitative assessment of the cenosphere-cement matrix contact zone. However, the main emphasis was on moisture-related parameters. The publication discusses the effect of using cenospheres as a substitute for natural sand on water absorption, capillary absorption, and the sorption and desorption of water by the tested composites, along with the influence of individual microstructural properties on moisture properties. The results showed that increasing the amount of cenospheres added as a sand substitute contributed to an increase in the water absorption of the composite and in parallel reduction in the capillary rise coefficient. The increase in the content of cenospheres caused also a clear increase in the sorption capacity of mortars. Moreover as the statistically average distances between the pores decreased, the thermal conductivity of the composites also decreased. Both when considering the porosity and the spacing factor, the conductivity decrease with wet composites was faster than with dry ones. With decreasing distances between the pores, the compressive strength also decreased significantly. Higher content of cenospheres also reduced the density of the composite and at the same time, increased the specific surface area, which contributed to the reduction in the capillary absorption coefficient and the increase in the durability of the entire composite. In addition, relatively good insulating properties of these composites (λ as low as 0.25 W/mK) in comparison to ordinary cement-based mortars make them interesting alternative to traditional solutions, while the appropriate mechanical strength (compressive strength in the range of 37.68 to 17.74 MPa) makes them suitable even for use as structural elements.