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1 引言 混凝土结构的强度和耐久性是两个重要指标。现行规范对强度指标有详细的计算和试验方法,达不到指标即为不合格产品。而对耐久性,却没有可供事先控制的试验方法 同一强度指标的混凝土的实际耐久性又可能相差很大。所谓安全使用年数即是不要大修的使用年数。大跃进时期采取了一些不适当的节省水泥用量的措施,造成不少建筑物的耐久性差,被迫提前加固。目前施工单位都在推广使用泵送混凝土浇筑建筑物,为防止泵送时混凝土堵塞输送管道,除掺和外加剂外,常常采取提高水泥用量,使在保持一定水灰比和满足规范或标书要求时,实际用水量增加,同时将石子和砂的用量减少,达到较大的砂率。这样做的目的是满足了混凝土的强度,提高了混凝土的和易性,
1 Introduction The strength and durability of concrete structures are two important indicators. The current specification of the strength indicators have a detailed calculation and test methods, failing to meet the targets is unqualified products. However, the durability of concrete without the same controllable test methods for the same strength may in fact be quite different. The so-called safe to use the number of years that is not overhaul the use of years. The Great Leap Forward took some inappropriate measures to save the amount of cement, resulting in the durability of many buildings is poor, forced to advance reinforcement. At present, construction units are promoting the use of pumped concrete pouring buildings. In order to prevent concrete from clogging the pipeline during pumping, in addition to admixture admixture, the cement dosage is often increased so as to maintain a certain water-cement ratio and meet the requirements of specifications or tenders When the actual water consumption increases, while reducing the amount of stones and sand, to achieve a larger sand rate. The purpose of doing so is to meet the concrete strength and improve the workability of concrete,