压蒸条件对外掺MgO水泥砂浆和混凝土压蒸膨胀率的影响

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。

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

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.Hightemperature 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 mortar).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.