5℃时掺低温早强剂水泥的早期水化及微观结构

Early Hydration and Microstructure of Cement Pastes Mixed with Low-Temperature Early Strength Accelerator at 5 ℃

以溴化钙(CaBr2)、溴化锂(LiBr)和三异丙醇胺(TIPA)三组分制备低温早强剂,研究低温下,早强剂对净浆强度、凝结时间、流动度的影响,并从水化热、产物微观结构等角度出发,探讨其作用机理。结果表明:5℃低温时,低温早强剂的掺入使净浆初、终凝时间均略有所缩短,可明显加快试件的强度发展,掺低温早强剂净浆1、3、7、28 d抗压强度较对比样分别提高291%、78%、62%和40%,3 d后各龄期强度已超对比样20℃时强度。低温下,低温早强剂使水泥水化诱导期缩短、加速期提前,最大放热速率较对比样增大78%,12 h、7 d累计放热量则分别增大227%和52%。低温早强剂可促进水泥初期水化反应,使试样中Ca(OH)2含量增加、水化程度增大,水化12 h产物中即有大量Ca(OH)2生成,且生成了含溴C-S-H凝胶和水化溴氧铝酸钙[Ca4Al2O6Br2·10H2O]产物。水化产物相互堆积,细化了水化初期(7 d前)试件的孔径,大孔数量明显减少,净浆1、7 d总孔隙率较对比样分别减小16%、31%,试样微观结构更加致密。

A low-temperature early-strength accelerator was designed with three components,such as calcium bromide(CaBr2),lithium bromide(LiBr)and triisopropanolamine(TIPA).Effect of early-strength accelerator on the strength,setting time and fluidity of cement paste at a low temperature was investigated,and its mechanism of action was discussed based on the perspectives of hydration heat and product microstructure.The results show that the incorporation of low-temperature early-strength accelerator shortens the initial and final setting time of cement pastes,and accelerates the strength development of specimens at a low temperature(i.e.,5℃).The 1-d,3-d,7-d and 28-d compressive strength of cement pastes mixed with the low-temperature early-strength accelerator can be increased by 291%,78%,62%and 40%,respectively,and the strengthat each age after 3 d already exceeds that of the contrast sample cured at 20℃.At a low temperature,the early-strength accelerator can shorten the hydration induction period of cement hydration and advance the acceleration period.Furthermore,the maximum heat release rate can be increased by 78%,compared to the contrast sample.The cumulative heat release is increased by 227%and 52%at 12 h and 7 d,respectively.The early-strength accelerator can also promote the hydration reaction at the initial stage of cement hydration,increase the content of Ca(OH)2 in the sample and increase the hydration degree.Large amounts of Ca(OH)2 are formed in the products at the age of only 12 h,and some products,such as bromine-containing C-S-H gels and hydrated calcium bromoaluminate(Ca4 Al2 O6 Br2?10 H2 O),are also generated.Large amounts of hydration products are accumulated,refining the pore diameter of the specimens at the initial stage of hydration(before 7 d)and decreasing the number of macropores.The total porosity of the cement pastes at 1 and 7 d is decreased by 16%and 31%,respectively,thus leading to the denser microstructure.