Influence of initial casting temperature on the properties and microstructure of ultra-light cement-based foam composites for energy-saving buildings

The application of ultra-light cement-based foam composites (ULCF) in buildings has been verified as an effective way to achieve energy conservation in the building sector. However, the production process of ULCF is difficult to complete at the ideal constant temperature during practical industrial production due to cost control and other factors. The sun exposure and residual heat from the machines will cause the initial casting temperature of ULCF to be raised in the preparation process, which will inevitably have an impact on the macroscopic properties of ULCF. In this study, a series of tests were conducted to explore the effect of initial casting temperature (30–55 °C) on the macroscopic properties and microstructure of ULCF for the first time. The results indicated that the 28-day compressive strength of ULCF exhibited a tendency to first increase and then decrease with the increase of initial casting temperature, which was attributed to the variation of its internal pore structure. The thermal conductivity test shows that the thermal conductivity of ULCF existed a minimum value of 0.0651 Wm −1 K −1 when the initial casting temperature reached 40 °C. Meanwhile, SEM and XRD were employed to examine the microstructure and hydration products of ULCF with different initial casting temperatures. Furthermore, the internal pore structure parameters of ULCF were quantitatively analyzed through Image-Pro Plus software, and the results demonstrated that there is a critical value for the initial casting temperature of ULCF, which allows the internal pore structure of ULCF to have characteristics of small size and approximate spherical shape.