电伴热预养护条件对混凝土受冻临界强度的影响

电伴热预养护是一种保证预拌混凝土冬期施工养护温度和强度增长的简单高效的方法。本文采用7 d恒负温(-5 ℃、-10 ℃、-15 ℃)一次冻结转标准养护的试验,研究电伴热预养护不同温度和时间对一种高坍落度C30普通混凝土抗压强度的影响。依据混凝土受冻临界强度的定义,确定基于电伴热预养护条件下的混凝土受冻临界强度值及其合理的预养护时间。结果表明:与标准养护相比,经电伴热高温预养护的混凝土抗压强度均得到了提高,但电伴热预养护温度宜控制在30 ℃,较高的预养护温度下强度发展速率和R_-7+28(负温养护7 d再转标养28 d的抗压强度)值反而降低;当预养护温度为30 ℃,硬化温度不低于-15 ℃时,合理的预养护时间在36～48 h之间;恒负温(-5 ℃、-10 ℃、-15 ℃)硬化条件下,采用电伴热预养护的混凝土受冻临界强度的范围是6.6～17.8 MPa,为混凝土立方体抗压强度标准值的22.0%～59.3%。研究旨在比较电伴热预养护制度对普通混凝土力学性能的影响,进而指导相关工程应用。

Effect of Electric Heat Tracing Pre-Curing Condition on Critical Strength of Concrete

Electric heat tracing pre-curing is a simple and efficient method to ensure the curing temperature and strength development of ready-mixed concrete in cold weather. The research analyzed the effects of pre-curing temperature and aging on the compressive strength of a high slump C30 normal concrete. Tests of 7 d constant negative temperature (-5 ℃, -10 ℃, -15 ℃) once-freezing to standard curing pretreatment test were reported. According to the definition of critical strength, the reasonable critical strength values and pre-curing time under the electric heat tracing pre-curing treatment were acquired. The results show that concretes pre-cured by electric heat tracing subjected to high temperatures attain higher compressive strengths than concretes subjected to normal temperature. Nevertheless, the pre-curing temperature should be controlled at 30 ℃, because the rate of strength development and R_-7+28 (compressive strength of negative temperature curing for 7 d and then standard curing for 28 d) are reduced at higher pre-curing temperatures. When the pre-curing temperature is 30 ℃ and the hardening temperature is not lower than -15 ℃, the pre-curing time is between 36 h and 48 h. Under the hardening condition of constant negative temperature (-5 ℃, -10 ℃, -15 ℃), the critical strength of concrete pre-cured with electric heat tracing is in the range of 6.6 MPa to 17.8 MPa, which is 22.0% to 59.3% of the standard value for the compressive strength of concrete cubes. This paper aims to compare the influence of electric heat tracing pre-curing treatment on the mechanical properties of common concrete and to guide the relevant engineering applications.