The use of supplementary cementitious materials as a partial replacement for Portland cement is the most effective way to reduce the carbon footprint of the concrete industry. Raw clays containing kaolinite (kaolin) are promising substitute materials. In the field, raw clays are often mixed with calcite and this is thought to affect their behaviour after calcination. This study explores the influence of calcite impurities on the mineralogy and reactivity a kaolinitic clay. A kaolin sample was blended with different quantities of calcite. The results show that during calcination calcite is decomposed, but no significant amount of free lime or amorphous calcium carbonate are formed. A granular deposit was observed that partially covers the kaolinite particles. The decomposition of calcite and formation of the deposit is associated with a reduction in specific surface area, which increases with the amount of calcite that is intermixed in the raw clay. TEM-EDS analysis showed that the deposit corresponds to a new phase formed from the interaction of kaolinite and calcite, with an Al/Si ratio ranging from 0.74 to 0.88 and Ca/Si ratio between 0.86 and 1.65. Reduction of the calcination temperature to 700 °C reduces the calcite decomposition and the negative impact on reactivity.

中文翻译：

---

含高岭石粘土中方解石杂质对其煅烧后在水泥中反应活性的影响

使用补充胶凝材料作为硅酸盐水泥的部分替代品是减少混凝土行业碳足迹的最有效方法。含有高岭石（高岭土）的生粘土是很有前途的替代材料。在现场，生粘土通常与方解石混合，这被认为会影响它们在煅烧后的行为。本研究探讨了方解石杂质对高岭土矿物学和反应性的影响。高岭土样品与不同数量的方解石混合。结果表明，在煅烧过程中方解石分解，但没有形成大量游离石灰或无定形碳酸钙。观察到部分覆盖高岭石颗粒的粒状沉积物。方解石的分解和沉积物的形成与比表面积的减少有关，比表面积随着混合在生粘土中的方解石的量而增加。TEM-EDS 分析表明，沉积物对应于高岭石和方解石相互作用形成的新相，Al/Si 比在 0.74 至 0.88 之间，Ca/Si 比在 0.86 至 1.65 之间。将煅烧温度降低到 700 °C 会减少方解石分解和对反应性的负面影响。