早期受冻混凝土服役期黏结性能研究

Bond properties during service period of early frozen concrete

为准确评估混凝土早期受冻对其与钢筋间服役期黏结性能的影响,考虑受冻环境(起冻时刻、受冻温度、受冻时长)、混凝土强度、钢筋直径等因素,采用中心拉拔试验方法研究早期受冻混凝土试件的服役期黏结性能,给出了试件的典型破坏形态及钢筋与混凝土间黏结强度、黏结应力-滑移关系曲线。研究结果表明:早期受冻拉拔试件服役期黏结破坏形态为钢筋拔出破坏或混凝土劈裂破坏;起冻时刻造成的黏结强度损失程度从大到小依次为2 h、0.5 h、8 h、1 d、3 d;受冻温度为-5℃和-9℃的试件黏结强度损失接近,受冻温度为-1℃的试件黏结强度损失较小;受冻时长越长,早期受冻造成的黏结强度损失越大,自由端出现滑移时的黏结应力越小;混凝土强度等级越高,早期受冻造成的黏结强度损失程度越小,自由端出现滑移时的黏结应力越大,不同起冻时刻的曲线越靠近;钢筋直径越小,早期受冻造成的黏结强度损失程度越大,黏结应力-滑移曲线降低越明显。

To evaluate the effect of early frozen on the bond properties between concrete and rebar during service period,concentric pull-out tests with consideration of the influence of frost environment factors(frost onset time,frost temperature,frost duration),concrete strength grade and diameter of rebar were carried out.The failure modes,bond strength and the bond stress-bond slip curves of the specimens were obtained.The test results show that the failure modes of early frozen specimens are pull-out failure and splitting failure.2 hr is the most unfavorable frozen onset time,followed by 0.5hr,8hr,1 day and 3 day with decreasing degradation effect on the bond strength.At the frost temperatures of-5℃ and-9℃,the degradation on the bond strength are similar,which is obviously greater than that at-1℃.With the increasing frost duration,the deterioration of bond strength increases while the bond stress at the occurrence of free-end slippage decreases.With the increasing concrete strength grade,the deterioration of bond strength decreases while the bond stress at the occurrence of free-end slippage increases,and the bond-slip curves of the specimens with different frost onset time tend to be closer to each other.The smaller the diameter of rebar,the greater the deterioration of bond strength and more obvious decrease in the bond-slip curves.