粉煤灰掺量对高水胶比混凝土抗裂能力的影响

Effect of Fly Ash Content on Thermal Cracking Behavior of Concrete with High Water-to-Binder Ratio

通过试验对高水胶比(w/b=0.45)条件下,不同粉煤灰替代率(0、20%、50%、80%)对混凝土材料参数和早龄期阶段开裂行为的影响进行了研究。材料参数试验结果表明,随着粉煤灰替代率由0增至80%,混凝土28 d龄期的弹性模量、劈拉强度和抗压强度分别降低了49.4%、68.4%和75.1%。混凝土温度应力试验结果表明,随着粉煤灰替代率由0增至20%、50%和80%,混凝土2d龄期绝热温升分别降低了7.1%、53.6%和72.6%,混凝土开裂时刻的应力与劈拉强度的比值分别为0.62、0.75、0.74和0.64,第二零应力点温度与最高温度的比值平均值为0.9;开裂时刻的温度(即开裂风险)随粉煤灰替代率由0增至50%逐渐减小,继续提高粉煤灰替代率至80%对混凝土开裂温度影响不大。考虑高水胶比混凝土温度开裂风险时,建议粉煤灰替代率不宜超过50%。

The effect of different fly ash replacement levels(0%,20%,50%,80%)on the properties of concrete material and the thermal cracking of concrete with high water-to-binder ratio(w/b=0.45)at early age are investigated.The results of material parameter test show that the elastic modulus,splitting tensile strength and compressive strength of concrete at 28 d age are decreased by 49.4%,68.4%and 75.1%respectively when the fly ash replacement level increased from 0%to 80%.The temperature stress testing results show that,when the fly ash replacement level is increased from 0%to 20%,50%and 80%respectively,the adiabatic temperature rise of concrete at 2 d age is decreased by 7.1%,53.6%and 72.6%respectively,the ratio of cracking stress to splitting tensile strength at the moment of concrete cracking is 0.62,0.75,0.74 and 0.64 respectively,and the average ratio of second-zero-stress temperature to maximum temperature is 0.9.The cracking temperature(i.e.cracking risk)is lowered when the fly ash replacement level increased from 0%to 50%,however,followed by a plateau with a fly ash replacement level of 80%.In a word,for concrete with high water-to-binder ratio,the recommended optimal fly ash replacement level is 50%.