The Influence Of Chemical And Mineral Addictives On Drying Shrinkage Of Cement-Based Materials

With the development of architectural technology and theory, the issue ofdurability has drawn more and more attention of the scholars in the field all over theworld. In general, various factors can lead to nonstructural cracks, which won’tinfluence the safety and bearing capacity of structures. However, such cracks may havea bad effect on the massive character and durability of structures. Besides, thenonstructural cracks may also cause some problems of the people’s sense andpsychology, as a result, the research on the shrinkage and cracks of the concrete will beof great necessity.As we know, the deformation of concrete under load can not be avoided, but, bytechnical means, the volume deformation, which is caused by expansion, shrinkage andthe variation of temperature, can be decreased in a degree, and even can be avoided.In this thersis, two kinds of cement-based materials, concrete and mortar, wereinvestigated. The experiments on mortar are as follows: drying shrinkage experiment,elastic modulus test, three-point bending test, compressive strength test. In these tests,chemical and mineral addictives, such as silane emulsion, silica fume, NaCl, etc.,weremixed into the samples respectively. The influence of chemical and mineral addictivescontent on compressive strength, bending strength and elastic modulus of the specimenswas studied. In addition, moisture diffusion and drying shrinkage were particularlyinvestigated. For mortar, the application of diffusion software, which was developed byprofessor V. Slowik of Leipzing University of Applied Sciences in Germany, wasinvolved. By using this software to analyze the data obtained during experiment, morein-depth and accurate research on moisture diffussion and drying shrinkage of cementbased materials can be carried out.Results indicate that addition of silane emulsion can decrease the rate of water loss,but no obviously change of drying shrinkage was found. With the increase of humidity,the amount of water loss and drying shrinkage of the cement based material increasedobviously. And the increas of water-cement ratio had the same influence with theenvironmental humidity. When mixed with10%silica fume by mass of cement, the mortar specimen had an obviously higher degree of water loss and drying shrinkagethan the reference specimens, but when the amount of the silica fume reached to20%and30%, the water loss and drying shrinkage just changed a little. The water loss anddrying shrinkage of mortar increased with addition of2.0%NaCl. Addition of fly ashreduce the waterloss and drying shrinkage of concrete specimens, and with theincreasing amount of NaCl, the water loss and drying shrinkage kept decrease. Besides,the result analyzed by the Diffusion software was quite similar with the data obtained byexperiment.