基于单轴约束试验的早龄期混凝土开裂行为评价

Evaluation of cracking behavior of early-age concrete using temperature stress testing machine

早龄期阶段,大体积混凝土由于自身变形受到相邻构件或地基的约束产生温度应力,一旦拉应力超过混凝土自身强度,混凝土便会开裂。鉴于传统的约束圆环法和平板法无法考察温度历程对大体积混凝土温度开裂行为的影响,基于研制的新型开裂全过程仿真试验机在实验室内实现了对混凝土日降温0.3℃的速率控制,重现了大体积混凝土浇筑后的真实温度历程,测量了不同龄期(3、7和14 d)快速温降条件(0.5℃/h)下混凝土的温度应力,并基于开裂温差分析了龄期和水泥类型对早龄期混凝土抵抗快速温变性能的影响。试验结果表明,混凝土抵抗快速温变的能力与龄期(强度)正相关,松弛能力随加载龄期的推迟逐渐减弱;低热水泥混凝土较中热水泥混凝土应做好更严格的早龄期阶段表面保温措施。

At early ages,considerable concrete restrained stress can be generated once the deformation is restrained by adjoining members or foundation.Concrete will crack when the tensile stress exceeds its tensile strength.Due to the fact that temperature control function can not be achieved by restraint ring and flat plate method,the actual temperature evolution of mass concrete(0.3℃/d)was achieved in the lab based on the newly developed temperature stress testing machine(TSTM).Furthermore,we also investigated the restrained stress of concrete made with different cement compositions with different cooling ages(3 d,7 d and 14 d)under the rapid temperature variation history(0.5℃/h).The temperature difference criterion was adopted to evaluate the cracking behavior of concrete.Results show that the cracking temperature difference is proportional to the concrete age(strength)and the relaxation degree decreases with the increasing loading age.Finally,stricter surface protection should be carried out for concrete made with low heat cement(LHC).