In the field of infrastructure engineering such as construction and roads, stone is the core aggregate of concrete, and its quality directly affects the quality of the project. The essential difference between shaped and unshaped stone lies in physical properties and engineering applicability, which can be compared in the following dimensions:
1. Difference in physical properties
Particle shape characteristics
Unshaped material: sharp edges and corners, needle-like particles often account for more than 15% (length>2.4 times the average particle size, thickness<0.4 times the average particle size);
Shaped material: after impact crushing or vertical axis shaping, it presents a cubic shape, and the needle-like content drops to less than 5%.
Grading and density
The gradation of unshaped material is highly discrete, and the bulk density is 100-200kg/m³ lower than that of shaped material, and the void ratio is 10% higher;
Shaped material is continuously graded through mechanical screening and secondary crushing, and the compacted density is increased by 5%-15%, and the crushing index is reduced by 30%-40%.
2. Impact of engineering application
Concrete performance
Unshaped materials are prone to concrete segregation and bleeding due to many microcracks and high water absorption, and the strength is reduced by 15%-20%;
The surface smoothness of shaped materials is improved, the bonding strength between aggregate and cement paste is enhanced, and the impermeability of high-strength concrete above C60 is increased by 30%.
Construction adaptability
Unshaped materials need to increase the amount of cement by 10%-15% to make up for the lack of fluidity, and the water consumption of single cubic meter of concrete increases by 5%-8%;
The proportion of spherical particles in shaped materials is increased, the thickness of slurry coating is reduced, and the slump retention rate of pumped concrete is increased by 25%.
3. Comparison of economic value
Production cost
The shaping process increases power consumption by about 0.5-0.8 yuan/ton, but the premium of finished products reaches 20 yuan/ton, and the annual income increases by more than 30%;
Unshaped materials need to be sold at a price reduction of 10%-15% due to limited application, and there is a waste rate of more than 20%.
Environmental benefits
The shaping process reduces the amount of waste rock in mines, and the comprehensive utilization rate of aggregates is increased from 60% to 85% ;
Qualified grading reduces the energy consumption of concrete mixing, and the CO₂ emissions per cubic meter are reduced by 8%-12% .
4. Application scenario selection
Scenarios where shaping is necessary
Highway surface materials, high-speed rail sleeper concrete and other high-grade projects that require > C60 ;
Harsh environments such as water conservancy dams and nuclear power facilities that require > P12 for impermeability .
Simplified shaping scenarios
Low-strength demand projects such as ordinary house foundation cushions and rural roads ;
Non-structural load-bearing parts such as temporary construction access roads and garden paving .
Current mainstream shaping equipment (such as vertical shaft impact crusher and dual-rotor shaping machine) can achieve synchronous optimization of 0-5mm fine aggregate by adjusting the rotor speed and the grate plate gap . When selecting materials for a project, it is necessary to make a comprehensive decision based on the standards of "Construction Sand" and "Sand and Gravel for Concrete" and combine the project budget and quality requirements .
