Study on the effect of thermoactivated conditions on the properties of hardened cement powder

Abstract

The performance of thermoactivated hardened cement powder (HCP) is the basis for studying the performance of thermoactivated recycled concrete powder (RCP). Previous studies have mostly focused on thermoactivated RCP, while thermoactivated HCP is taken as the research object in this paper. The effects of different thermoactivated conditions on the mass loss rate, density, initial and final hardening time, standard consistency water powder ratio, and compressive strength of the test block made from thermoactivated HCP were studied. Furthermore, the mineral composition, microstructure, chemical elements, hydration heat, and hydration products of thermoactivated HCP made from different thermoactivated conditions were analyzed. The test results indicated that the average initial harden time of the 600, 800, 1000, and 1200 °C of thermoactivated HCP are 15, 1160, 85, and 13 min, respectively. In terms of phase change of HCP at different heating temperatures, when the heating temperature reached 800 °C, the diffraction peaks of C-S-H and CaCO3 disappear, while the diffraction peaks of C3S, β-C2S, and αC2S began to appear. AFt and Hydrotalcite are completely decomposed and C-S-H loses adsorbed water with temperature from 35.9 to 201.7 °C. Ca(OH)2 is completely decomposed with temperature from 413.3 to 457.4 °C. CaCO3 is completely decomposed with temperature from 457.4 to 731.6 °C. In terms of changes in the proportion of chemical elements after hydration of thermoactivated HCP, the values of Ca/Si of hydrated cement is 1.78. The average values of Ca/Si after hydration of 1000 and 1200 °C thermoactivated HCP are 3.32 and 3.33, respectively, while the average values of Ca/Si after hydration of 600 and 800 °C thermoactivated HCP are 2.74 and 2.6. These research conclusions provide a foundation for the application of thermoactivated HCP. HIGHLIGHTS The mass loss rate, density, and compressive strength of hardened cement powder made from different heating conditions were studied. The standard consistency water powder ratio, initial and final hardening time of hardened cement powder made from different thermoactivated conditions were analyzed. The mineral composition, microstructure, chemical elements, hydration heat, and hydration mechanism of hardened cement powder made from different thermoactivated conditions were revealed.