Sand and gravel are the key raw materials for the construction of concrete skeleton, and also the highest proportion of concrete raw materials, accounting for about 75%. The quality of sand and gravel will have a great impact on the quality, stability and performance of concrete.
With the tightening of natural sand resource constraints and the strengthening of environmental protection, machine-made sand has gradually become the main source of sand for construction. Machine-made sand is made of rock, pebble, mine waste rock and tailings as raw materials, after soil removal treatment, by mechanical crushing, shaping, screening, powder control and other processes, the gradation, particle shape and stone powder content meet the requirements and the particle size is less than 4. 75 mm.
Through the five indexes of stone powder content of machine-made sand, fineness modulus of sand, mud content of sand and gravel, crushing value of gravel and needle and flake content of gravel, we can understand the actual impact of the characteristics of sand and gravel on concrete. Stone powder content
of machine-made sand Machine-made sand needs to go through crushing, screening, sand making and other processes in the production process, which inevitably produces a large amount of stone powder. Stone powder content refers to the content of particles with particle size less than 75 μm in machine-made sand. The appropriate content of limestone powder will play a positive role in the mechanical properties and workability of concrete under the action of hydration, but when it exceeds a certain level, the limestone powder will seriously affect the fluidity of concrete and play a reverse role in the workability of concrete. Fineness modulus
of
sand Fineness modulus is an index to measure the fineness of sand. If the fineness modulus is too large, it means that the coarser the sand is, the poorer the workability of concrete such as segregation, bleeding and poor wrapping will be easily caused; if the fineness modulus is too small, it means that the finer the sand is, the lower the fluidity of concrete will be easily caused and the loss of slump will be too large.
In terms of quality, the mud content
of sand and gravel is on the high side, and the mud particles in sand and gravel will reduce the compactness of concrete, thus affecting the strength of concrete, and cracks are prone to occur; In terms of working performance, clay particles will adsorb admixtures and water, accelerate slump loss, and easily cause the working performance of concrete on construction site to fail to meet the construction requirements. The crushing value
of
gravel is like the skeleton of concrete. Whether the concrete resists beating depends on whether the "bone" is hard or not. Therefore, the crushing value of crushed stone directly affects the compressive strength of concrete. The crushing value of crushed stone refers to the proportion of the mass of particles with a particle size of less than 2.5mm to the total mass after crushing, that is to say, the crushing value is the proportion of the crushed part, so the smaller the value is, the more compressive it is. In terms of quality, the needle-like content
of
gravel can not really "unite" because of its unique personality, and it is easy to be broken by external forces. Therefore, the high content of needle and flake will reduce the strength of concrete. In terms of working performance, the rolling ability of needle-like gravel is far better than that of regular gravel. The high content of needles and flakes will also reduce the fluidity of concrete.
Know your enemy and know yourself, and you can fight a hundred battles with no danger of defeat. Each characteristic of aggregate will affect the performance of concrete at different levels. Fully understanding the characteristics of raw materials can help us better grasp the character of concrete, so as to produce better quality concrete.
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