压蒸条件对外掺MgO水泥砂浆和混凝土压蒸膨胀率的影响

Influence of pressure-braise system on the pressure-braise expansion ratio of concrete and cement mortar mixed with MgO

通过对各种压蒸条件、不同养护龄期和温度、采用干湿筛法成型及长龄期养护、掺不同MgO的砂浆和混凝土试体进行压蒸试验研究,结果表明:不同压蒸条件下的压蒸试验结果不相同,即压力和温度越高,压蒸膨胀率越大,压力和温度是MgO能否水化膨胀完毕最主要的决定因素,压时次之;高温养护能提高基体的强度,增强其抵御膨胀的约束能力,对压蒸试验有利。在分析研究了大量先低压后标压试验结果的基础上,提出了合理的压蒸方法,即温度采用200℃,压力为1.5MPa,压时为4 h。基于该压蒸方法,一级配混凝土的压蒸膨胀率可达到原标压试验结果的95%(砂浆达到9 8%)以上,满足绝大部分MgO都能水化完毕的要求,又可大幅度降低原标压试验带来的不利影响。

Pressure-braise tests were conducted on test samples of concrete and mortar mixed with different proportions of MgO with different pressure-braise systems, curing durations, and temperatures using the dry/wet screening method. The results of the pressure-braise tests vary with different pressure-braise systems. The higher the pressure and temperature are, the higher the pressure-braise expansion ratio will be. Pressure and temperature are the most important factors in whether MgO can be completely hydrated and expanded, followed by time. High-temperature curing can raise the strength of the substrate and enhance its resistance to expansion and is good for pressure-braise tests. On the basis of results of tests conducted first under a low pressure and then under normal pressure, reasonable pressure-braise conditions are put forward： 200℃, 1.5 MPa and durations of four hours. With this pressure-braise method, the pressure-braise expansion ratio of grade 1 concrete may exceed 95% of the result of the original normal-pressure test （98% for met-tar）. It can meet the requirement of hydration of most of the MgO and, meanwhile, may significantly alleviate the ill impact of the original normal-pressure test.