高温后全轻页岩陶粒混凝土与钢筋的拉拔试验研究

Experimental Study on Pullout Tests between All-lightweight Shale Ceramsite Concrete and Steel Bars after High Temperatures

钢筋与混凝土的高温粘结性能是结构抗火设计和灾后评价的依据。通过全轻页岩陶粒混凝土(ALWSCC)与335级Φ16 mm月牙肋钢筋(CRB)和光圆钢筋(PSB)分别经历20℃(常温)、300℃、400℃、500℃后的拉拔试验,分析了高温导致粘结性能劣化的特征参数,并与普通混凝土(NWC)和再生混凝土(RAC)进行了比较。结果表明:高温不仅造成混凝土色泽变化、表面疏松、缺棱掉角现象及沿CRB顺筋裂纹(宽度分别为0.03~0.1 mm、0.1~0.18 mm和0.18~0.22 mm),而且破坏形式从拔出破坏到劈裂破坏和劈裂-拔出破坏;τ-S曲线整体下降、峰值粘结应力残余强度(ατ0)降低、峰值滑移系数(βS0)增大和峰前耗能减小;但月牙肋对拉拔荷载的贡献率却均在85%左右;以ατ0和βS0作为评判指标,上述三种混凝土中ALWSCC具有更好的抗火性能;以抗压和劈拉残余强度及上述粘结性能指标作为判断条件,可将500℃作为临界温度以指导试验设计和火灾评价。

The bonding performance of concrete and steel bars is the principles for fire resistance design and fire risk assessment of structures after high temperature.The pullout tests were carried out between all-lightweight shale ceramsite concrete(ALWSCC)and steel bars,which includes hot rolled crescent ribbed bars(CRB)and hot rolled plain steel bars(PSB)for grade 335 and diameter 16 mm,under four temperatures of 20℃(room temperature),300℃,400℃and 500℃.The characteristic parameters reflecting the deterioration of bonding performance caused by high temperature were analyzed,and also compared with normal weight concrete(NWC)and recycled aggregate concrete(RAC).The results show that the high temperature can cause the change of concrete color,the loose surface of concrete,the edges and corners of specimen incomplete,and cracks along rebar(the width is 0.03-0.1 mm,0.1-0.18 mm and 0.18-0.22 mm,respectively),and also the failure modes from pullout failure(POF)to splitting failure(SF)and split-pull out failure(POF+SF).Theτ-S curves are the overall downward trend.The residual strength of peak bond stress(ατ0)reduces.The coefficient of peak slip(βS0)increases.The pre-peak energy dissipation decreases.But the contribution ratios of crescent-shape ribs to pullout load are 85%or so.The fire resistance performance of ALWSCC is more better than that of NWC and RAC assessed byατ0 andβS0.The temperature of 500℃can be critical temperature to guide test design and fire risk assessment assessed by the residual strengths of compressive strength(f cu)and splitting tensile strength(f ts)and the above indexes of bonding performance.