EFFECT OF THE LOW CALCINATION TEMPERATURE AND MgO CONTENT ON THE FORMATION AND EXPANSION CHARACTERISTICS OF C₄A₃$

Research of C₄A₃$ modified Portland clinker is a key solution for the low-carbon cement industry with high-magnesium low-grade limestone as a raw material, in which the coexistence of C₄A₃$ and C₃S at low sintering temperature is key. Thus, this study investigated the effect of a low calcination temperature (1200 °C, 1250 °C, 1300 °C, 1350 °C) on the formation of C₄A₃$, as well as the influence of the MgO content (0%, 1%, 2%, 3%, 6%) on the formation of C₄A₃$ and its hydration expansion under different calcination temperatures. X-ray diffraction (XRD) was used to analyse the phase composition and hydration expansion tests were also conducted. The results showed that the use of a lower calcination temperature at longer holding times promoted the formation of C₄A₃$, where 1250 °C was considered to be the temperature at which C₄A₃$ begins to form at a faster rate. Compared to the formation of C₄A₃$ at the normal calcination temperature (1350 °C), the formation of C₄A₃$ at 1250 °C was only 10% lower. In the C₄A₃$ phase, MgO exists in an interstitial solid solution form, and the addition of 1-2% MgO enhances the formation of C₄A₃$ and reduces the hydration swelling, but the formation of C₄A₃$ decreases slightly with a further increase in the MgO content. This study provides technical support for the research of C₄A₃$ modified Portland clinker using high-magnesium low-grade limestone as the raw material at low calcination temperatures.