There are generally two forms of production of crushed sand. One is the specially produced crushed sand, which has a higher gradation and fineness modulus than natural sand, and the gravel has a very similar grain size to natural sand. The other is the production of manufactured sand from various tailings, which is an incidental product.
Most of the sand is made by processing and screening the stone chips that are produced after the production of crushed stone. The cost of sand made from stone chips is very low and the quantity is relatively large. Grading and granularity of substandard stone chips are used as fine aggregates, which will make the commercial concrete consistency and strength poor. Therefore, many people will think that the poor quality of crushed sand cannot replace natural sand, which in turn makes it more difficult to promote crushed sand. In fact, when choosing crushed sand, as long as you choose those made with advanced equipment and technology, it can completely replace the natural sand.
The characteristics of crushed sand
The surface of crushed sand is relatively rough and angular. Therefore, it has poor mixing consistency and can increase the water retention rate of commercial concrete. However, the presence of rock flour in the sand can improve the performance of the concrete. In the same construction site, the crushed sand and gravel are often made from the same type of parent rock and made. The chemical and thermal properties of the two are the same, which is more evident in large-area concrete construction techniques.
Crushed sand is a type of sand with excellent grain size gradation. One fineness modulus of sand can correspond to only one grade of sand and the fineness modulus of the crushed sand is linearly related to the single sieve margin. A type of sand has to be tested first to establish the relationship equation. The fineness modulus can be calculated by simply determining the single sieve margin. The amount of stone dust in the sand will change with the fineness modulus. The two are inversely proportional to each other.
If the sand is divided according to the fineness modulus, it can be divided into coarse sand and medium sand. The sand particles not larger than 0.075mm are stone dust. Generally, it is divided according to the nature of the sand or its role in commercial concrete. The nature of the mud content inside the natural sand is not the same.
The application of crushed sand in commercial concrete
Crushed sand and river sand in the case of the same water-cement conditions, in the crushed sand inside less than 0.075mm sand powder content is generally less than 30%, except for high-grade concrete compressive strength is slightly lower than the river sand concrete, all other properties are higher than the river sand.
The strength of commercial concrete is an important indicator for testing the performance of concrete. Under the same conditions, the strength of commercial concrete of crushed sand is higher than that of natural sand concrete. It is mainly because the crushed sand is formed by crushing limestone. The main component of crushed sand is calcium carbonate. Calcium carbonate is inside a high concentration of calcium hydroxide, and a chemical reaction occurs on the surface of the crushed sand.
Natural sand has a higher content of silica inside, and generally, a similar chemical reaction does not occur. And the texture of crushed sand is harder. Its surface is rougher and more angular, which can greatly improve interfacial adhesion.
Modulus of elasticity
It is rougher and more angular. In the mortar, the sand particles have the role of the skeleton, which inhibits the deformation of cement stone and the sliding of the aggregate particles between each other. The interface between the sand and the cement stone is well-bonded. The pores of the interface are fewer, and the stress concentration is greatly reduced.
The density of the crushed sand is relatively large and the voids are relatively small, which greatly improves the compressive elastic mode of commercial concrete. In the case of the water-cement ratio and the same amount of cement, the elastic modulus of commercial concrete of crushed sand is much higher than that of ordinary concrete.
Dry shrinkage performance
The dry shrinkage rate will increase with the increase of stone powder content. It is mainly because the very fine particles in the stone powder will keep increasing with the increase of the stone powder content. These very fine particles in the commercial concrete mixture can increase the content of cement paste. The dry shrinkage of commercial concrete is mainly due to the dry shrinkage of cement paste. Therefore, the increase in cement paste per unit volume will lead to an increase in the dry shrinkage of concrete.
Seepage resistance The seepage resistance of commercial concrete is related to the pore structure of concrete, and the stone powder inside the crushed sand is considered to be the most important reason for improving the seepage resistance in commercial concrete in two ways.
One argument is that the stone powder inside the crushed sand is just a filler, although the stone powder does not have activity, it is effective to improve the compactness of commercial concrete and improve the cement stone and aggregate interface adhesion. There is also a saying that stone powder can effectively improve the structure of cement stone pores, to improve the permeability of commercial concrete.
When formulating commercial concrete, companies use 50% of stone chips instead of natural sand to improve the frost resistance of commercial concrete, which has achieved very good results. After 200 cycles of freezing and thawing, the strength of the concrete is about 10% less than that of the concrete without the replacement. The application of stone dust effectively improves the structure of commercial concrete capillaries, which in turn greatly improves the frost resistance of commercial concrete.
Crushed sand commercial concrete shows superiority in workability, impermeability, strength, frost resistance, and durability. Especially in the low standard of commercial concrete, the stone powder acts as a filler of micro-aggregates, which effectively improves the structure of commercial concrete pores and makes the crushed sand commercial concrete higher than natural sand commercial concrete in many aspects. The application of crushed sand commercial concrete admixture can effectively meet the performance of commercial concrete mixes.