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砂子是混凝土的基本材料之一,它不仅影响混凝土的性能,而且在决定混凝土的经济效果方面也有相当作用。对于混凝土各组份来说,其中砂子不仅价格便宜且不需要耗费许多能源,是一种廉价的原料。此外,砂子对于改善混凝土的稳定性,收缩等也有良好的作用。重庆地处长江和嘉陵江岸,有丰富的河砂资源,为混凝土生产的发展提供了一定条件,但这里所产砂子系属特细砂,其特点是:1.颗粒细,其细度模量为0.6～1.2(大量的是在0.7左右),巨细颗粒比例有日益增加的趋势;2.空隙率大,一般在50%以上;3.颗粒软弱,粉尘较多。所以,这种砂子一般不宜用来配制高强混凝土,在配制普通混凝土时。其中水泥用量也要较由粗、中砂配制的混凝土为多(可高出10～30%)。为了充分利用地方资源,对于特细砂在混凝土中的应用,由重庆建筑工程学院等单位,早在50年代就开展了不少研究工作,并取得了一定的成绩,提出了一系列措施来改善特细砂混凝土的性能。在各项措施中,使用塑化剂(即减水剂)是行之有效的办法之一。但是,由于过去采用的减水剂其塑化能力不高,因而对改善特细砂混凝土性能的效果还不够显著。
Sand is one of the basic materials of concrete. It not only affects the performance of concrete, but also plays a considerable role in determining the economical effect of concrete. For concrete components, sand is not only cheap but does not require much energy, and is a cheap raw material. In addition, sand also has a good effect on improving the stability and shrinkage of concrete. Chongqing is located on the banks of the Yangtze River and the Jialing River. It has abundant river sand resources and provides certain conditions for the development of concrete production. However, the sand produced here is a special fine sand characterized by: 1. Fine particles with fine modulus. For 0.6 to 1.2 (a large number is around 0.7), the proportion of large and small particles has an increasing trend; 2. The porosity is large, generally more than 50%; 3. The particles are weak and dust is more. Therefore, this type of sand is generally not suitable for the preparation of high-strength concrete, in the preparation of ordinary concrete. The amount of cement used was also higher than that of concrete prepared from coarse and medium sand (up to 10-30% higher). In order to make full use of local resources, for the application of ultra-fine sand in concrete, a number of research projects have been carried out by the Chongqing Institute of Architecture and Civil Engineering as early as the 1950s, and certain achievements have been made. A series of measures have been proposed to improve Superfine sand concrete performance. Among various measures, the use of plasticizers (ie, water reducers) is one of the effective methods. However, since the water-reducing agent used in the past has a low plasticizing ability, the effect of improving the performance of the ultra-fine sand concrete is not significant enough.