| The external thermal insulation composite system based on expanded polystyrene, which is a kind of widely used external thermal insulation system, has several advantages over other form of thermal insulation. It has a significant energy-saving effect, makes the construction convenient, etc. However, the cracks have been the common problem of the system. They not only affect the appearance of the buildings, reduce the energy efficiency at the infiltration of snow and rain, but also do harm to the durability of the system. The reason, in terms of the materials, is the lack of anti-crack ability of the base coat. The base coat, which is the barrier of the system and the outside, is an important part of the protective covering of the system, it keeps the system from the erosion of snow and rain, improves the anti-impact ability. Presently, the base coat is usually made up of cementing materials adding other addictives. But the proportion of various ingredients is not appropriate, the ratio of the cement is too high to prevent the cracks. Therefore, it is essential to optimize the capacity of the base coat.In this paper, we determine the ingredients and the best mixture ratio of the base coat using the extra fine sand through studying on the anti-crack and construction performance.(mortar's weight percentage) :①Through changing three different strength grade of the cement P.O32.5,P.O42.5,P.O52.5, we found that the higher of the strength grade, the more fragile of the mortar. So we choose P.O32.5 to continue our study.②According to the natural conditions in Chongqing, the main sand used in construction is the extra fine sand with the modulus of fineness 0.7-1.5. The study found, with the increase of the modulus of fineness of the sand, the ratio of compression strength and flexural strength (c/f), and the shrinkage decrease, so we selected the sand fineness modulus 1.4. And by changing the ratio of cement and sand(c/s), we found the ratio of compression strength and flexural strength (c/f) first increased and then decreased from the c/s 1:2.0 to 1:3.0, and at 1:2.6 reach the minimum. We can see an appropriate increase in the amount of sand will help improve the toughness of mortar, so we selected the ratio of cement and sand(c/s) was 1:2.6.③Dispersible polymer can improve the crack resistance and adhesive ability. But when the content of dispersible polymer exceeds a certain range, the dispersion becomes bad. In our experiment, the best content of the dispersible polymer VinnapasRE5044N is 2.0%.④HPMC can improve water retention of mortar, but the solubility will go bad when increasing its viscosity. We found when the viscosity reaches 80000 mPa.s, it has the best performance. And the best content in the mortar is 0.15%.⑤Polypropylene fiber can improve the anti-crack ability of the mortar, but factors such as length and content have something to do with its dispersion. It was found that polypropylene fiber with the length of 12mm , content of 0.15%, in mortar plays the most obvious role on crack resistance.⑥Wood fiber is a natural organic fiber, it can improve the crack resistance of mortar, the best content is 0.30%.⑦Fly ash has a certain crack resistance effect in mortar, when we use it to replace cement. It can be taken good use of and reduce the costs. And the best amount of fly ash we use to replace cement is 15% of the cement's weight.According to the test results, the base coat we made by optimizing compared with the provisions on base coat in JG149-2003 and the base coat chosen at random in the market, has performed obvious advantages and in practical applications, demonstrated good results, too. |
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