Effects of the Water-Cement Ratio and the Molding Temperature on the Hydration Heat of Cement

The effects of the water-cement ratio and the molding temperature on the hydration heat of cement were investigated with semi-adiabatic calorimetry.The specimens were prepared with water-cement ratios of 0.31,0.38,and 0.45,and the molding temperature was specified at 10 and 20℃.The experimental results show that,as the water-binder ratio increases,the value of the second temperature peak on the temperature curve of the cement paste decreases,and the age at which the peak appears is delayed.The higher the water-cement ratio,the higher the hydration heat release in the early period of cement hydration,but this trend reverses in the late period.There are intersection points of the total hydration heat curve of the cement pastes under the influence of the water-cement ratio,and this law can be observed at both molding temperatures.With the increase in the molding temperature,the age of the second temperature peak on the temperature curve of the cement paste will advance,but the temperature peak will decrease.The higher the molding temperature,the earlier the acceleration period of the cement hydration began,and the larger the hydration heat of the cement in the early stage,but the smaller the total heat in the late period.A subsection function calculation model of the hydration heat,which was based on the existing models,was proposed in order to predict the heat of the hydration of the concrete.

负温条件和矿物掺合料耦合作用对混凝土强度和抗渗性影响

为研究矿物掺合料在负温养护条件下对混凝土抗压强度和抗渗性的影响规律,并从微观角度解释其内在机理,进行-3℃养护条件下双掺不同掺量粉煤灰、矿粉和三掺不同掺量粉煤灰、矿粉、硅灰对混凝土抗压强度、孔隙结构和电通量的试验。试验结果表明:在-3℃养护条件下,掺入矿物掺合料均降低了混凝土早期的抗压强度,但在双掺10%粉煤灰和10%矿粉的基础上,掺入不同掺量的硅灰,掺量为1%时,可有效改善混凝土早期抗压强度;从其渗透性来看,矿物掺合料可以有效改善混凝土的细观孔结构和抗氯离子渗透性能。

-3℃养护条件下矿物掺合料对混凝土强度和孔隙结构的影响研究

为了研究不同养护条件下矿物掺合料对混凝土强度和孔隙结构的影响,进行-3℃和标准养护条件下,复掺粉煤灰、矿粉和硅灰对混凝土抗压强度、孔隙结构的试验。结果表明:与标准养护相比,在-3℃养护条件下,矿物掺合料的掺入对混凝土抗压强度有下降趋势,但对其孔径均有优化作用。基准组、复掺10%粉煤灰+10%矿粉+1%硅灰组、复掺10%粉煤灰+10%矿粉+3%硅灰组,28 d龄期标准养护下出现细小孔的频率是负温养护1.122~1.259倍,56 d龄期标准养护下出现细小孔的频率是负温养护1.108~1.180倍,矿物掺合料对混凝土硬化含气量和平均气泡间距均有改善作用,在标准养护条件下的优化作用明显优于负温养护条件。

-3℃养护环境下粉煤灰对混凝土的强度和孔结构影响

试验研究了负温(-3℃)养护环境下,粉煤灰掺量对混凝土抗压强度和孔径分布的影响,确定了抗压强度和小孔含量之间的关系,并将结果与标准养护(20℃)条件下试件测试结果相比较。结果表明:负温养护环境与标准养护相比,混凝土抗压强度和孔结构都变差;随着粉煤灰掺量的增加,混凝土的抗压强度越来越差,但孔径分布却得到了优化,细小孔径出现的比例增多,强度和孔径分布之间呈负相关,这与标准养护下的规律不一致。因此,养护温度是影响抗压强度与孔结构规律的重要因素。

WN胶和碳纤维布加固混凝土棱柱体试件受压性能的试验研究

研究了WN胶和不同层碳纤维布加固混凝土棱柱体的受压性能。WN胶和碳纤维布横向加固混凝土试件,至其完全固化后,测定了抗压强度和加载时间,接着分析了破坏过程中的受力状态和破坏形态,最后讨论了抗压强度与加载时间的相关性和最优加固措施。结果表明:WN胶和碳纤维布加固混凝土棱柱体后,(1)抗压强度和加载时间都得到改善,而且碳纤维布层数越多,抗压强度和加载时间改善越多;(2)加载过程中,混凝土棱柱体处于"伪"三轴受压状态,改善了原有的受压特性,提高了混凝土的抗压性能和加载时间;加载完成后,混凝土棱柱体局部碳纤维布开裂,上下表面边缘产生微裂缝;(3)抗压强度增长率与加载时间增长率高度相关,相关系数0.988 4;(4)WN胶和两层碳纤维布为最优加固措施,其碳纤维布约束作用发挥较完全。