蒸压粉煤灰砖砌体干燥收缩试验研究及其预测模型

蒸压粉煤灰砖砌体房屋的裂缝很大程度上由砌筑后使用阶段砌体干燥收缩引起.基于复合材料力学,推导了正交各向异性砌体的干燥收缩与砖和砂浆干燥收缩的关系.理论分析表明,砂浆的干燥收缩对砌体干燥收缩的影响可忽略不计,砌体干燥收缩近似等于砌体中砖在使用阶段干燥收缩.为考察试验方法、上墙含水率、环境相对湿度、体积/暴露面积比对蒸压粉煤灰砖的干燥收缩的影响,进行了试验研究.试验结果表明,按快速法得到的蒸压粉煤灰砖的干燥收缩值比慢速试验法小,且蒸压粉煤灰砖的干燥收缩率随着上墙相对含水率的增大而增大,随着环境相对湿度增大而减小,随着体积/暴露面积比的增大而减小,并由试验结果得到了砌体中砖的干燥收缩预测模型.还对不同上墙含水率和不同环境相对湿度的6片砌体墙干燥收缩进行了试验研究,试验值与理论推导的结果符合良好.

Experimental Research and Prediction Formulation of the Drying Shrinkage of Autoclaved Fly Ash Brick Masonry

Cracks in autoclaved fly ash brick masonry walls are chiefly caused by the drying shrinkage of masonry during the service stage.A prediction formulation of the drying shrinkage of orthogonal masonry was derived on the basis of the mechanics of composite materials.The analysis results showed that the drying shrinkage of masonry could be approximately represented by the drying shrinkage rate of brick in masonry during the service stage,and the effect of the drying shrinkage of mortar on that of masonry was negligible.The effect of test methods,the moisture content,relative humidity,and the ratio of volume/exposed area on the drying shrinkage of autoclaved fly ash bricks was studied.It was showed that the drying shrinkage of autoclaved fly ash brick in RAPID method was smaller than that in SLOW method,and increased with the relative moisture content,decreased with the relative humidity and the ratio of volume/exposed area of brick.The prediction formulation of drying shrinkage of brick in masonry was obtained through the experiment results.The drying shrinkage of 6 masonry walls with different relative moisture contents in different relative humidity was measured,and the theoretical results was in good agreement with the test value.