木素磺酸钙对水泥净浆的缓凝机理研究

研究了掺加木素磺酸钙(简称木钙)后水泥净浆液相中钙离子、硫酸根离子和氢氧根离子浓度随水化时间的变化,以及除糖后木素磺酸钙对水泥净浆凝结时间的影响．结果表明,掺加木钙后在水化初期水泥净浆中S042-浓度大幅度上升,OH-浓度变化不大．木钙掺量越大,水泥净浆中游离Ca2 浓度的峰值出现越迟,浆体的初凝时间越长．进一步研究发现木钙的掺加能促进熟料矿物的水解,当木钙掺量为0．5％(质量分数)时,水泥净浆中的总Ca2 浓度峰值比未掺加木钙时增加48％,被络合的Ca2 量峰值较水化开始时增加2倍．在水泥净浆强碱性溶液中木钙的络合能力增强导致Ca(OH)2不能达到过饱和,是造成水泥净浆缓凝的重要原因,木钙对水泥净浆的缓凝机理为“吸附-络合”机理．

Research on retarding mechanism of calcium lignosulfonate to cement paste

In order to discuss the retarding mechanism of calcium lignosulfonate (CLS) , which is a popular water-reducing agent in concrete, the concentrations of Ca2 , SO42- ,OH- in cement paste changing with hy-dration times after added CLS, and the influence of CLS removed sugar on the setting time of cement paste are studied systemically. It is found that, the concentration of SO42- during initial hydration in cement paste blended with CLS increases sharply, while the concentration of OH- changes little. The elapsed time that concentration of free Ca2 reaches the maximum value prolongs with the increasing of CLS dosage, and so does setting time of cement paste. Further studies indicate that CLS can promote the hydrolyzation of clinker minerals. After blending with 0. 5% CLS, the maximum concentration of total Ca2 in cement paste increases by 48% than that without CLS, and the maximum amount of complexed Ca2 is twice more than that at the beginning of hydration. It can be deduced that, the main reason that CLS has retarding property is that under the strong alkaline solution of cement paste, the complexing capacity of CLS enhances. A " Adsorption-complexation" mechanism is put forward to explain the retarding action of CLS.