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冬期施工中,在混凝土及砂浆中使用外加剂已较广泛,一般都以防冻外加剂为主,以降低外加剂溶液冰点,使其存在一定量的液相水,维持水泥水化,来获得强度增长。随着环境温度的降低,不得不增加外加剂掺量来获得较低冰点值。目前降低冰点效果较好、使用较广的还是氯盐,但由于氯盐对钢筋的严重锈蚀,其掺量在有筋混凝土工程中有使用限制;砌筑砂浆中掺量虽可适当加大,但析盐现象严重,因此在抹灰工程中的应用就受到了一定限制。外墙抹灰工程虽可以通过雨淋逐年消除析盐痕迹,允许使用于中、低级外墙抹灰工程,而内墙却不具备这个自然条件。大面积的析盐不仅影响面层浆体的附着,还造成墙面常年泛潮、发黄等严重弊病。为此,国家规范规定,冬季室内抹灰必须在+5℃以上的环境温度下施工及养护。
In the winter construction, the use of admixtures in concrete and mortar has been extensive. Generally, antifreeze admixtures are mainly used to reduce the freezing point of the admixture solution so that a certain amount of liquid-phase water exists, and the cement hydration is maintained to obtain strength. increase. As the ambient temperature decreases, the amount of admixture has to be increased to obtain a lower freezing point value. At present, the effect of reducing the freezing point is better and the chlorine salt is widely used. However, due to the severe corrosion of the steel bar by the chloride salt, the amount of the salt used in the reinforced concrete works is limited; the addition amount of the masonry mortar can be appropriately increased. However, the phenomenon of salt precipitation is serious, so its application in plastering works has been limited. Although the external wall plastering project can eliminate the traces of salt precipitation through rain, it is allowed to be used in middle and low-grade exterior wall plastering works, but the internal walls do not have this natural condition. The large area of salt precipitation not only affects the adhesion of the surface layer slurry, but also causes serious problems such as the annual flooding and yellowing of the wall surface. For this reason, the national regulations stipulate that winter indoor plaster must be constructed and maintained at an ambient temperature of +5°C or higher.