混凝土中孔隙大，所以传热性低，透水性好。 Due to the large pores in the sandless concrete , the heat transfer is low and the water permeability is good. In water conservancy projects, it is mainly used to make drainage ditches and drainage pipes for drainage bodies. 混凝土与普通混凝土的主要不同之处，就是没有细骨料，只用粗骨料。 The main difference between sandless concrete and ordinary concrete is that there is no fine aggregate and only coarse aggregate is used. The cement is used to cover the surface of the coarse aggregate and acts as a cement instead of filling the gaps. Therefore, the amount of cement is less than that of ordinary concrete, generally 70 to 150 kg / m3. Coarse aggregate is best selected with medium particle size (10-20mm), and gravel or crushed stone with uniform particles should be used.
For the preparation of sand-free macroporous concrete, generally higher grades of ordinary cement are used. When the blending ratio is 1: 8 to 1:20, the strength can reach 100 to 500kPa and the density is 1600 to 1950kg / m3.
When making sand-free and large-pore concrete, the water consumption should be strictly controlled. If too much water is used, the cement slurry will flow down along the coarse aggregate, resulting in uneven concrete and easy cracking of weak points.
The sandless concrete is basically not vibrated and can only be vibrated for a short time. Otherwise, the cement slurry will escape from the aggregate and be lost. Therefore, sandless concrete has no mention of workability, as long as the water-cement ratio is appropriate, all particles can form a smooth cladding.
The compressive strength of sandless concrete is mainly related to density and depends on the amount of cement. The water-cement ratio is not as controlling as ordinary concrete, but because the water-cement ratio controls the density, there is also a certain optimal water-cement ratio range. The water-cement ratio is higher than the optimal value, and the cement slurry is easy to flow; if the water-cement ratio is too low, and the cement slurry is too thick, it is not easy to achieve a certain degree of compactness.
The control range of the optimal water-cement ratio is difficult to predict. It is greatly affected by the type of aggregate and water absorption, and it is also related to the amount of cement. Therefore, it should be determined through experiments, generally between 0.40 and 0.55. The shrinkage of sandless concrete is lower than that of ordinary concrete and generally can be ignored; the coefficient of thermal expansion is 0.6 to 0.8 of ordinary concrete; the water absorption is high, up to 50% by weight.
Sandless concrete is generally not used as reinforced concrete. Although the strength of this kind of concrete is not high, it is very popular for building construction due to its small density (if light aggregate is used, the density can be reduced to 640kg / m3).