焙烧菱镁尾矿制MgO膨胀剂对水泥砂浆膨胀性能的影响

Impact of Expansive Agent from Calcinating Magnesite Tailings on Expansion Performance of Cement Mortar

为降低大体积混凝土收缩现象,将焙烧菱镁尾矿制成MgO膨胀剂,掺入水泥砂浆中,研究了焙烧温度对MgO膨胀剂矿物组成、晶粒尺寸及活性等的影响.采用X射线衍射仪(XRD)、扫描电镜(SEM)、热分析仪等分析了内掺MgO膨胀剂水泥砂浆的矿物组成、水化进程、热稳定性和微观形貌.结果表明:在菱镁尾矿完全分解的条件(焙烧温度1000℃以上,保温1 h)下,随着焙烧温度的提高,MgO晶粒尺寸由27.6 nm增至138.0 nm,其活性从70.8%降至3.3%,MgO水化速率减慢,晶粒尺寸与其反应活性之间存在线性关系;MgO的活性影响水泥砂浆的膨胀限制率,水泥砂浆试样M-C-1000的限制膨胀率最大,在水养20℃条件下,其7、28、120 d的限制膨胀率分别为0.022%、0.037%和0.062%.此外,体系中的水化产物Mg(OH)2在基体中呈片层状生长.

In order to reduce the shrinkage cracking of mass concrete,MgO expansive agent was made by calcinating magnesite tailings.The effects of different calcination temperatures on the mineral composition,particle size and activity of MgO expansive agent were studied.The changes of mineral composition,hydration process,thermal stability and micro morphology of cement mortar with MgO expansive agents were studied by means of X-ray diffraction,scanning electron microscope and thermal analyzer.The results show that under the condition of complete magnesite decomposition(calcination temperature over 1000℃,and constant temperature for 1 h),with the increase of calcination temperature the grain size of magnesium oxide increases from 27.6 nm to 138.0 nm,the activity decreases from 70.8%to 3.3%,and the hydration rate slows down.There is a linear relationship between the grain size of magnesium oxide and the reactivity.MgO activity affects the expansion limit of cement mortar.The expansion limit of cement mortar mixed with MgO expansive agent made of calcination temperature 1000℃is the largest.Under the condition of 20℃water curing,the expansion limit of 7,28,120 d can reach 0.022%,0.037%and 0.062%,respectively.In addition,the hydrated product magnesium hydroxide in the system shows lamellar growth in the matrix.