Mechanistic pathways for early-age mechanical enhancement of high-belite cement via alkali-metal oxide doping from polymorph stabilization to strength gain: The role of R2O in stabilizing α-C2S

As a new type of low-calcium and low-carbon cement, high-belite cement has advantages such as low calcination temperature, lower CaO content, and low requirements for raw material. Given the low calcium requirement of high-belite cement, a large amount of solid waste containing CaO can be used to prepare it. This approach has dual advantages: first, it can reduce the consumption of limestone and improve the utilization rate of solid waste; second, the mineralization and lattice modification effects of impurity ions in the solid waste can decrease the calcination temperature, activate the clinker minerals, and enhance the reactivity of high-belite cement. This study aims to stabilize the high-temperature crystal form of C 2 S through the synergistic effect of phosphorus slag and alkali metal oxides(R 2 O), thereby enhancing the early mechanical strength of high-belite cement. The investigation focused on studying the combined effect of 8 % phosphorus slag and 0–2.0 % R 2 O on the activation and early performance of high belite clinker. Little amounts of P 2 O 5 and F - in phosphorus slag enhanced the burnability of high-belite cement raw meal, but the burnability deteriorated after the addition of R 2 O. With the addition of alkali metal oxides, the contents of α-C 2 S, C 3 S, and C 3 A in high-belite cement clinker increased, while the contents of β-C 2 S and C 4 AF decreased. Adding 1.0 % Na 2 O and 1.5 % K 2 O made the α-C 2 S content in high-belite cement clinker reach 32.15 % and 40.82 %, respectively. It was found that the R 2 O phase preferred to dissolve in the intermediate phase, followed by C 2 S. Meanwhile, extensive Na 2 O entered the C 3 S crystals. Mechanical property test results showed that both 1.0 % Na 2 O and 1.5 % K 2 O can improve the early mechanical properties of high belite cement. Based on the obtained results, it could be concluded that P 2 O 5 and F - in phosphorus slag significantly enhanced the role of R 2 O in the formation and stabilization of the high-temperature α-C 2 S polymorphs.