碳酸化改性对CaO-C4A3S膨胀剂熟料矿物组成及水化历程的影响

Effect of Carbonation Modification on Composition and Hydration Process of CaO-C4A3S Expansive Clinker

采用热重-差示扫描量热(TG-DSC)、X射线衍射(XRD)、微量热和测长法等测试方法对经碳酸化改性的氧化钙-硫铝酸钙(CaO-C4A3S)膨胀剂熟料的矿物组成、水化历程及膨胀特性进行分析.结果表明:800℃以下的高温碳酸化改性,使得膨胀剂熟料颗粒表层中的游离氧化钙(f-CaO)转变成碳酸钙,且碳酸化率随着反应温度的升高而增大,对其他矿物组成无影响.改性膨胀剂熟料的水化历程与碳酸化率相关,低碳酸化率可显著降低膨胀剂熟料的放热速率峰值,但不改变累计放热曲线形状;高碳酸化率不仅降低膨胀剂熟料的放热速率峰值,还大幅延缓放热峰值出现时间,并改变累计放热曲线的形状,使早期放热量大幅降低.碳酸化改性对膨胀剂熟料膨胀历程的影响与对水化放热历程的影响趋势基本一致,低碳酸化率条件下,改性主要增加膨胀剂熟料5d前的膨胀量,5d后的膨胀历程与改性前基本一致;高碳酸化率条件下,改性降低膨胀剂熟料3d前的膨胀量,但3~7d间膨胀量迅速增加,7~14d仍有显著膨胀,28d限制膨胀率较改性前提升1.6倍.碳酸化改性显著提高了CaO-C4A3S膨胀剂熟料在水泥基材料硬化阶段的膨胀效能.

The mineral composition,hydration process and expansion behavior of CaO-C4A3S expansive clinker modified by carbonation were analyzed by TG-DSC,XRD,microcalorimetry and length measuring method.The results show that free CaO in the surface layer of expansive clinker particles is transferred to CaCO3 by carbonation modification at high temperature below 800℃,and the carbonation degree increases with the increase of reaction temperature,which has no effect on the composition of other minerals.The hydration process of modified expansive clinker is related to carbonation degree.Under low carbonation degree,the peak value of hydration heat release rate of expansive clinker was significant reduced,while the shape of cumulative heat release curve was the same as that of the unmodified expansive clinker.Under high carbonation rate,not only the peak value of hydration heat release rate of the expansion clinker is significantly reduced,but also the shape of cumulative heat release curve is changed with the early-stage heat release greatly reduced.The effect of carbonation modification on the expansion process of expansive clinker is basically the same as that of hydration process.Cement mortar containing CaO-C4A3S expansive clinker of low carbonation degree shows an increased expansion ratio before 5days compared to that containing unmodified expansive clinker,while after 5days the expansion rate is basically the same.Mortars containing CaO-C4A3S expansive clinker of high carbonate degree shows a reduced expansion ratio before 3days,but a rapidly increased expansion rate from 3 to 7days,and a still expansion trend during 7 to 14days,with the 28-day expansion ratio increased by 1.6 time.Carbonation modification significantly improves the expansion efficiency of CaO-C4A3S expansive clinker in the hardening stage of cement-based materials.