Study on Influence of Heat and Humidity on The Adhesive Performance of Base Mortar of External Wall.

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In the sequence from last year, the experiments have been carried out on the concrete walls finished by mortar. Some of them have been heated upto 80ﾟC at the face by infrared lamps and cooled down to circumstane temperature (or+humidity) and others exposed out door.The contact planes with mortar and concrete wall have been in two conditions, "normal" and "having partially pre-cracking" (Ref.fig-1, Type1).In this year, additional experiments have been done. The specimens with pre-crackings (Type1,2) have been heated up as same as above and the behavior of pre-cracking have been inspected.The exprimental results have been as follows ;(1) The adhesive strength with mortar and concrete wall has been lowered 40% after a month in the case of only heating up.(2) The drop in adhesive strength of "normal" was amaller in the case of (heating+giving humidity) than in the case of only heating. On the other hand, the drop in the adhesive of "pre-cracking Type-1" was much larger in the case of (heating+giving humidity) than in the case of only heating.(3) The adhesive strength of "normal" have been lowered 7% after 90 days from exprimental start and that of "pre-cracking Type-1" have been lowred 37%.(4) The cracking in mortar have been observed in all the specimens, especially the specimens with "pre-cracking Type-1" have had wider cracking.(5) At the roots of "pre-cracking Type-1,2", the extention of that have ben observed. These are a mechanical reason of mortar pealing off concrete wall.2) The temperrature distributions in the specimen which have been heated up infrared lamps have been analyzed by F.E.M.. The calculated results have agreed with the mesured temperature.3) The calculation of stress distribution in the specimen have been carried out based on the temperature distribution calculated in item 2). They are shown that the enough magnitude of tensile stress for cracking to occur exists in mortar.