Natural sand resources are limited, long-term large-scale excavation will damage the ecology and affect the environment, machine-made sand can replace part of natural sand, solve resource and environmental problems, and reduce the cost of concrete.
Utilization trend of machine-made sand
Manufactured sand is also called artificial sand, which is made of rock mining, mechanical crushing, and screening. It is a rock particle powder with a nominal vertical diameter of less than 5mm. Because it contains a small amount of mud, there are many equipments that can wash it. Sand is the main material of concrete. With the development of the construction industry, the amount of sand used is increasing, and the quality requirements are getting higher and higher, while natural sand resources are becoming less and less. The use of machine-made sand can reduce the resources of natural sand. Environmentally friendly and economical.
Characteristics of machine-made sand
The main characteristics of machine-made sand are: the particles of machine-made sand are irregular in shape after crushing treatment, and the specific surface area is larger than that of natural sand; the quality of machine-made sand is hard; High, mostly above 3.0, particles above 1.25mm generally account for 48-55% of the total, and particles of 0.315-0.16mm account for about 10%.
In addition, the machine-made sand has many edges and corners, and the surface is relatively rough. It is difficult to meet its workability requirements when used alone in concrete. It can be mixed with natural sand to fill the middle part of the particle gradation, so that the fineness modulus and fineness of the machine-made sand Grading meets requirements. Although the vertical diameters of the stone powder and mud contained in the machine-made sand are both less than 0.075mm, their composition is different, and the fineness is also quite different. Adsorbed on the surface of sand, it hinders the bonding of sand and cement, and an appropriate amount of stone powder can be filled in the gaps between cement and fine sand to enhance the workability of machine-made sand concrete. In the process of machine-made sand production, in order to remove most of the stone powder, most of the particles below 300mm are often removed, resulting in poor gradation of machine-made sand particles and a large fineness modulus. At this time, it must be used in conjunction with natural sand. , to ensure the workability of concrete and other properties.
Application of machine-made sand in concrete
Ordinary concrete and high-strength pumping concrete can be prepared with machine-made sand. Under the premise of strictly controlling the quality of raw materials and strictly following the design and construction of the mix ratio, the prepared machine-made sand concrete can ensure the workability, fluidity and pumpability of concrete. , strength, impermeability and other properties, and can also ensure that the concrete does not crack.
Matching of fineness modulus of machine-made sand and natural sand
Manufactured sand can be used in conjunction with natural sand with a fineness modulus of 1.7 to 2.5. The fineness modulus of machine-made sand is between 3.0 and 3.8, and the fineness modulus of natural sand is between 1.8 and 2.2. good. No matter from the perspective of concrete slump, workability and strength, this combination can exert the best effect. For some non-pump roads and other projects, under the premise of not hindering the construction, the amount of machine-made sand is too much, the workability is biased, and its strength is significantly reduced.
Water demand performance of machine-made sand concrete
Due to the rough surface of machine-made sand, although it has been washed to a certain extent, there is still a small amount of stone powder content. Even in the mix ratio of low-grade concrete, its water consumption is higher than that of natural sand. But on the basis of the same material, the strength of machine-made sand concrete is higher than that of natural sand concrete. Concrete prepared with machine-made sand will increase water by 5-10kg per square meter, and the corresponding water-binder ratio will increase by 0.01-0.02. When using machine-made sand and natural sand to prepare concrete, the sand rate should be 1-2% higher than that of natural sand concrete.
Related Factors Affecting Machine-made Sand Concrete
Impact on water consumption of machine-made sand: In addition to the composition of machine-made sand itself, the water consumption of machine-made sand is most importantly related to the content of stone powder in machine-made sand.
When the stone powder content is 0-4%, there is no significant increase in water consumption for machine-made sand. When the stone powder content is 4-6%, the water consumption increases by 0-5kg. When the stone powder content is 6-10%, the water consumption increases by 5-10kg. When the content is 10-15%, the water consumption will increase by 10-20kg. As the content of stone powder in machine-made sand increases, its water consumption also increases accordingly, resulting in changes in the water-binder ratio of concrete.
The influence of the crushing value of the machine-made sand on the strength: For the machine-made sand produced by unqualified stone materials, the strength of the stone itself is low. As a result, the crushing value of the machine-made sand is too large, which will have a certain adverse effect on the strength of the concrete. Therefore, we should strictly follow the standard requirements in the detection of machine-made sand.
Influence of machine-made sand on the physical properties of concrete
A large number of tests have proved that the flexural, compressive and elastic modulus of machine-made sand concrete are close to or higher than those of natural sand concrete with the same mix ratio (under the same material conditions). In addition, the mechanism was found during the trial mixing of concrete. The addition of sand increases water consumption, and the initial setting time of machine-made sand concrete is 10-25 minutes longer than that of natural sand concrete. For the mixing of machine-made sand that meets the requirements of stone powder content into concrete, the hydration degree of cement in machine-made sand concrete is higher than that of natural sand concrete, and the compactness is better. Therefore, the creep performance of machine-made sand concrete is better than that of natural sand concrete. Due to its good compactness, the freeze-thaw resistance of machine-made sand concrete is also better than that of natural sand concrete.
