Study on frost resistance of rapid-hardening magnesium phosphate-ferro-aluminate composite cement北大核心CSCD

随着冬季抢修抢建混凝土工程的增多，研发适用于严寒地区具有良好抗冻性的快硬水泥意义重大。磷酸镁水泥具有早期强度高、初凝时间短、与混凝土相容性好等特点，被视为混凝土工程的良好快修快建材料。然而，磷酸镁水泥制备的水泥砂浆或混凝土在北方地区的冬季往往会受到冻融循环作用，导致其耐久性和强度出现不同程度的退化。为增强磷酸镁水泥的抗冻性，在磷酸镁水泥制备中用铁铝酸盐水泥代替一定数量的过烧氧化镁，制备出快硬磷酸镁-铁铝酸盐复合水泥。通过冻融循环前后磷酸镁-铁铝酸盐复合水泥砂浆试件的质量损失测试、强度试验、孔隙率测试及SEM-EDS测试，得出：铁铝酸盐水泥代替氧化镁的数量在30%~40%时，制备的磷酸镁-铁铝酸盐复合水泥砂浆试件冻融循环后的质量损失率最小，抗压强度和抗折强度达到峰值，抗压强度和抗折强度剩余率最高，孔隙率最小，因而该配合比的磷酸镁-铁铝酸盐复合水泥具有最好的抗冻性。由SEM-EDS测试可知磷酸镁水泥砂浆试件冻融循环后，基体中的胶凝材料K-鸟粪石部分溶解，试件整体结构疏松，晶体间存在大量间隙；磷酸镁水泥制备中掺入铁铝酸盐水泥后，制得的磷酸镁-铁铝酸盐复合水泥水化生成大量晶体填充于砂浆试件基体内部，无定形水化产物对砂浆试件的强度有一定补偿作用，使得磷酸镁-铁铝酸盐复合水泥砂浆试件在冻融循环后孔隙率大幅减小，密实度得到提高，使得磷酸镁-铁铝酸盐复合水泥的抗冻性能得到了显著增强。磷酸镁-铁铝酸盐复合水泥为北方严寒地区冬季混凝土抢修抢建工程提供了一种新材料。

Study on frost resistance of rapid-hardening magnesium phosphate-ferro-aluminate composite cement

With the increase of rapid repair and construction of concrete projects， it is significant for fast hardening cement with good frost resistance in the cold regions of China. Magnesium phosphate cement has the characteristics of high early strength， short initial setting time， good compatibility with concrete， and thus is seen as an excellent material for the concrete engineering required rapid construction. However， the cement mortar or concrete made of magnesium phosphate cement often suffers from freezing and thawing cycles in winter in northern China thereby causing various degrees of degeneration in its durability and strength. In order to enhance the frost resistance of magnesium phosphate cement， a certain amount of ferro-aluminate cement was used to replace over-burning magnesium oxide to prepare magnesium phosphate-ferro-aluminate composite cement during the preparation of magnesium phosphate cement. A conclusion can be drawn based on the quality loss test， strength test， porosity test and SEM-EDS test of magnesium phosphate-ferro-aluminate composite cement mortar specimens before and after freeze-thaw cycles. When the substitution rate of ferro-aluminate cement for MgO is 30%~40%， the loss rate of mass attains the minimum， and the compressive strength and flexural strength reach the peak， and the residual rates of the compressive strength and flexural strength achieve the highest， and the porosity is lowest for the prepared magnesium phosphate-ferro-aluminate composite cement mortar specimens after freeze-thaw cycles， and thus the frost resistance of the magnesium phosphate-ferro-aluminate composite cement prepared under the above mix ratio is optimal. The SEM-EDS tests show that for the magnesium phosphate cement mortar specimen after freeze-thaw cycles， the gel materials K-struvite existing in its matrix are partly dissolved， which results in a loose structure with plenty of gaps between the crystals. Magnesium phosphate-ferro-aluminate composite cement， which is prepared by adding ferro-aluminate to magnesium phosphate cement， generates a large number of crystals during the hydration reaction to fill in the matrix of the mortar specimen， and the amorphous hydration products have a certain compensation effect for the strength， which result in a great drop in the porosity and increase in the density and thus dramatically improves the frost resistance for magnesium phosphate-ferro-aluminate composite cement. Magnesium phosphate-ferro-aluminate composite cement provides a new material for concrete construction projects required rapid completion in winter in the northern cold areas of China.