不同碱度液体速凝剂的高低温适应性及促凝机理

Influence of Liquid Accelerator with Different Alkalinity on Setting Behavior and Mechanical Properties of Cement Pastes at Different Temperatures

研究了偏铝酸钠、硅酸钠、硫酸铝3种典型液体速凝剂常用组分在高低温下对水泥浆的促凝规律、温度敏感性及其对水泥水化的影响机理。结果表明:铝酸钠和硫酸铝掺量为3%,硅酸钠速凝剂掺量为5%时可满足JC477—2005的初凝时间≤5 min、终凝时间≤12 min的要求;硅酸钠速凝剂的促凝性能受温度的影响较大;两类碱性的速凝剂(偏铝酸钠和硅酸钠)能够有效提高砂浆块的早期抗压强度,而硫酸铝对早期强度的影响较小;偏铝酸钠对28 d抗压强度的不利影响较大,其它两类速凝剂对28 d抗压强度的影响较小;偏铝酸钠速凝剂通过消耗石膏,生成铝相水化产物来促进凝结;硫酸铝通过形成大量钙矾石晶体搭接使水泥浆体失去流动性;硅酸钠通过消耗石膏和生成早期水化硅酸钙达到速凝效果。

Sodium aluminate （SA）, aluminum sulfate （AS） and sodium silicates （SS） are three main components of liquid accelerators. The influence of these three accelerators on the setting behavior and mechanical properties of cement pastes at different temperatures was evaluated. To meet the requirements of initial setting time ≤ 5 min and final setting time ≤ 12 rain, the minimum dosages for SA and AS are 3% and the dosage for SS is 5%, respectively. The two alkaline accelerators, i.e., SA and SS, enhance the early strength of hardened cement pastes, while the non-alkaline AS has little effect on the early strength growth. SA exhibits a negative impact on the 28-d compressive strength, and the other two accelerators present much less effect on the 28-d strength. SA accelerates the setting by quickly consuming gypsum to eliminate its retarding effect and producing the amorphous C-A-H hydrate that consumes the free water and thus reduces the fluidity of cement paste. AS promotes the precipitation of ettringite crystals, which connect cement grains in a compact mass and hence accelerate the setting of cement paste. The quick setting promoted by SS is mainly due to the result of the quick consumption of gypsum and the consumption of water caused by the C-S-H formation.