Aggregate is the most exploited material in the world. It is an important component of concrete and asphalt concrete, accounting for 70% of the volume of concrete. It can inhibit the shrinkage and cracking of concrete and enhance the strength of concrete.
Aggregates are divided into natural aggregates and artificial aggregates. According to the degree of thickness, they are divided into coarse aggregate (crushed stone or gravel) and fine aggregate (sand).
Due to the non-renewable resources, the mining of natural aggregates is increasingly restricted. Now, in many countries and regions, the amount of artificial aggregate has exceeded the amount of natural aggregate, and it is widely used in various concrete industries.
What is Artificial Aggregate(Manufactured Aggregate)
Manufactured aggregate mainly refers to machine-made aggregate(manufactured sand and crushed stone).
Rock particles (excluding soft and weathered rock particles) processed by natural rock, river pebble stone or mine waste rock through mechanical crushing, shaping, screening, powder control and other processes, including:
Crushed stone: >4.75 mm particle size
Artificial sand: <4.75 mm particle size
Types of Manufactured Aggregate Processing Technology
The processing technology of manufactured aggregate is divided into 3 categories
- Wet process
- Dry process
- Semi-dry process
Wet Processing Technology
The wet processing technology refers to washing with water during the screening and crushing of materials, and washing the coarse and fine aggregates with the stone washing machine and sand washing machine. Generally used for raw materials containing mud or more weak particles. When the finished sand and crushed stone powder content is too high, wet production can also be used to remove part of the stone powder.
According to the nature of the soil contained in the raw materials, the sand and stone washing methods can be divided into screen surface washing and sand washing machine washing. Which stone washing method to use can be determined according to factors such as the mud content of the raw materials, the nature of the soil, and the processing volume.
Less dust pollution, high washing and screening efficiency.
High water consumption, high cost of machine-made sand and crushed stone powder recovery and sewage treatment, serious loss of fine sand and crushed stone powder, and difficulty in dehydration of finished sand; when vertical shaft impact crushing machine-made sand is used, the sand formation rate is low.
The wet production process is suitable for applications in areas with abundant water resources.
Semi-Dry Processing Technology
Generally, it means that the pre-screening is produced by wet method and the moisture content of the discharged material is controlled, and the sand making and screening system of shaping adopts the dry production process.
The water consumption is relatively small compared with the wet method, the wastewater treatment volume is not large, the loss of stone powder is small, and the dust pollution is also small.
After the sand-making raw materials are washed with water, they must be dehydrated mechanically or naturally to ensure that the moisture content of the raw materials entering the sand-making machine is not more than 3%, otherwise the sand-forming rate and screening efficiency of the sand-making machine will be low.
It is mainly suitable for concrete dam sand with low mud content in raw materials and high powder content in finished sand.
Dry Processing Technology
It refers to a process that basically does not use water in the process of the entire production line except for the spray water in the dust removal process.
No water or very little water consumption, less stone powder loss, dry processing technology is mainly used for raw material cleaning, high sand rate, low stone powder content machine-made sand and stone system.
(1) Due to the high moisture content of the dry processing raw materials or the high soil content of the raw materials, the fine aggregate is not easy to sieve through, and the soil content or fine powder content exceeds the requirements of relevant standards.
(2) The dust in each processing point of dry processing is relatively large, and the investment and operating costs of the dust removal system are relatively high.
(3) When the fine powder separation device is not installed, the fine powder content of the finished sand exceeds the standard.
Manufactured Aggregate Processing Flow
Whether using dry, wet or semi-dry processing of manufactured aggregate, the main equipment for crushing and screening is almost the same as that of manufactured sand.
Feeder→soil removal→coarse, medium and fine crushing→screening→sand making→screening→fine powder separation→online monitoring.
Crushing and Screening
Different types of raw materials, using different crushing equipment:
- When using medium-soft materials such as limestone, the impact crusher can be used for coarse and medium-fine crushing.
- When using hard rock materials such as granite, jaw crushers or gyratory crushers are generally used for coarse crushing, and cone crushers are used for medium and fine crushing.
Shaping Sand Making, Screening and Fine Powder Separation
The 40 mm clean aggregate produced by multiple crushing and screening enters the sand making system. Sand making equipment generally uses a vertical shaft impact crusher. The principle of sand making is that some or all of the raw materials enter the high-speed rotating impeller and quickly rotate, and shoot out at high speed from the evenly distributed launch ports around the impeller. The flow or the raw materials piled in the cavity are broken by repeated high-speed collisions.
After screening and fine powder separation system sorting, qualified machine-made sand and gravel are processed. Fine powder separation is divided into two types according to different processing techniques:
- Wet sand washing and sewage treatment system
- Dry fine powder separation and dust control system
Wet Sand Washing and Sewage Treatment System
Wet sand washing generally adopts a flat layout. The screened artificial sand flows into the sand washing machine for sand washing, and the washed fine powder and soil enter the integrated fine sand recovery and dehydration system for fine sand recovery.
The separated mud and stone powder enter the high-efficiency thickener for concentration and dehydration, and the concentrated and precipitated mud powder is pressed into a mud cake through a filter press.
The recovered fine sand and the sieved coarse sand are combined and stacked evenly for dehydration.
The operating cost and floor space of a complete set of wet-process artificial sand making and sewage treatment equipment are about twice that of the dry process. Due to the high cost of equipment investment and land occupation rent, sewage treatment and dewatering waste residue discharge are also very expensive, so dry sand making has been rapidly developed.
Dry Fine Powder Separation and Dust Control System
The dry sand making fine powder separation system can be set up before or after screening. The plastic sand making machine and the screening fine powder separation system are connected to the large dust collector through a pipeline. The excess fine powder in the screened sand is collected by the dust collector and stored in the fine powder tank, which is regularly transported by the tanker for later application.
The sieved manufactured sand can be evenly mixed with water in a humidifier and used in a concrete mixing station. It can also be stored directly for dry-mix mortar.
Dry sand making can be arranged in a flat layout or a three-dimensional layout in a tower. Since the tower-style complete set of equipment occupies only one-fifth of that of the traditional wet method and one-third of the traditional dry method Therefore, the tower-type machine-made artificial sand system is very suitable for building with concrete mixing plants or dry-mixed mortar mixing plants, reducing the transportation cost of finished artificial sand and crushed stone aggregates and storage facilities.
Contact us for the types, specifications and prices of manufactured aggregate processing equipment.