Study On Experimental Method For Moisture Expansion Of Wall Material And Its Application

The crack prevention of walls is an important problem in multidiscipline fields and structure engineering, but it is almost focused on the restraint of drying shrinkage of blocks and masonry structures. Hygric expansion as a important part of dry-wet cycling is not payed attention. Because lack of the definite test method, drying shrinkage test method always is used in the research and test of hygric expansion, which isn't in conformity with hygric expansion discipline and influnce the measurement precision. Therefore, it's exigent to build up a test principle and method of wall material hygric expansion in order to provideing the scientific data for research and engineering detection. As to the phenomenon of water expansion and moisture expansion, this thesis is to study the expansion discipline and its measuring method. The main research works are as follows:1. The thesis expound systematically moisture expansion mechanism and process. Through the analysis of the mechanism, it's found that the existing drying shrinkage test principle and method can't meet the challenge of water expansion test. So dynamic measuring method of water expansion as a new test method is proposed. Through supposing the water absorption mode, it's successful solved of dynamic measurement of water aborption in water. And solutions of the fixed method, expansion measurement, standard bar of test piece are proposed.2. On basis of dynamic test principle and method of water absorption and expansion, a dynamic moisture expansion measuring equipment (DMEME) as a measuring function of water absorption and expansion is developed, which achieves the measurement of continuity, automaticity and accuracy; DMEME eliminates manual work error, avoids water absorption process interrupted, and water expansion process is hard to measure in initial period of the test.3. Based on water absorption mode supposition and principle and method of the gauge length positioning system, the thesis deduces caculation model of water absorption and expansion, and chooses a aerated concrete brick, lime-sand brick, concrete brick and aerated concrete block to do a dynamic water expansion test. The test finishing criterion is discussed. From the microcosmic aspect, water absorpton process and expansion process of typical wall brick are analysed, and water absorption-time test models and expansion-time test models with the double exponential decay function are fitted respectively. The water expansion discipline is analysed, and the test models of piecewise function on basis of water absorption properties are fitted respectively:the water expansion test models of the aerated concrete brick, lime-sand brick and concrete brick follow the power function growth law in their frist step; those of the aerated concrete brick and lime-sand brick follows the S-type cruve growth law, and the concrete brick follow a straight line model.4. Using the dynamic moisture expansion test method, the thesis chooses a aerated concrete brick, lime-sand brick and concrete brick to do a dynamic moisture absorption expansion test. The test finishing criterion should be decided commonly by expansion change which over a period of 4 d is less than 0.001mm and the curve values which is close to the asymptotic final value. From the microcosmic aspect, moisture expansion process are all analysed in each and whole section, and moisture expansion test models are fitted:the water expansion test models of the aerated concrete brick follows exponential function growth law, and these of the lime-sand brick and concrete brick follow the S-type cruve growth law in constant temperature and 40%-80% relative humidity conditions.