蔗糖对水泥水化过程影响机理研究

研究了不同掺量蔗糖对水泥凝结时间、水泥砂浆强度发展、化学结合水量、液相离子浓度、AFt含量以及浆体矿物组成的影响.结果表明,蔗糖能促进AFt的生成,当蔗糖掺量较小(0.045%,质量分数,下同)时,对Ca(OH)2和C-S-H的抑制作用较弱,液相中Ca2 ,OH-浓度的降低不明显,AFt的溶度积大,AFt以细小的凝胶状存在,在水泥颗粒的表面形成不易被打破的保护膜,延缓了水泥凝结,但当保护膜被打破,水泥的水化进程会得以恢复,强度继续发展;当蔗糖掺量较大(0.48%)时,液相中Ca2 ,OH-浓度降低,AFt的溶度积小,AFt以结晶完好的针棒状出现,并在水化产物间穿插和搭接,起到了明显的促凝作用,使得C2S,C3S难以正常水化并提供C-S-H,因而阻碍了水泥砂浆的强度发展.提出了2个阈值的假说,蔗糖掺量在0.01%时即可促进AFt的生成,蔗糖掺量在0.20%时明显抑制硅酸钙的水化.

Influence Mechanism of Sucrose on Hydration Process of Portland Cement

The influence of sucrose dosage on Portland cement's setting time,strength development,chemical binding water,ion concentrations in paste liquid phase of AFt content was studied.The results indicate that sucrose accelerates the formation of AFt.When the dosage of sucrose is as low as 0.045%(by mass),the sucrose does not have much detrimental effect on the formation of Ca(OH)_2 and CS-H,the concentration of Ca~(2 ) and OH~-reduces little,the AFt has high solubility product,so that the AFt exists as gel-like products which covers the surface of clinker particles,a shell much thicker than usual is formed,thus the hydration process is restrained until the shell is broken,the sucrose acts as a retarder and does not have negative effect on 3 d strength and succedent strength development of the cement.When the dosage of the sucrose is as high as 0.48%,the sucrose affects adversely the hydration of C_2S and C_3S markedly,so the concentration of Ca~(2 ) and OH~-reduces greatly,the AFt has low solubility product,the AFt exists as well-crystallized needle-like AFt and the penetration and connection between the grains and some other hydration products are promoted,thus the setting process is accelerated,but C_2S and C_3S cannot be hydrated normally and not enough C-S-H can be supplied.The original microstructure of the paste is changed markedly,so that the strength development is baffled.It is proposed that there are two dosage threshold values as the sucrose influences the hydration of the Portland cement,the sucrose dosage of 0.01% is a retardation threshold value where sucrose can accelerate the formation of AFt,the sucrose dosage of 0.20% is a setting acceleration threshold value where sucrose can prohibit the hydration of C_3S and C_2S.