The insufficient strength of concrete has a great impact on actual construction. The strength of cement and the water-cement ratio are the most important factors that determine the strength of concrete. Cement is the cementing component in concrete, and its strength directly affects the strength of concrete. Under the same mix ratio, the higher the strength of cement, the higher the strength of concrete. When the same cement (same variety and strength) is used, the strength of concrete is mainly determined by the water-cement ratio; when the concrete can be fully dense, the greater the water-cement ratio, the more pores in the cement stone, and the lower the strength. The smaller the bonding strength of the aggregate, the lower the strength of the concrete. On the contrary, the smaller the water-cement ratio, the higher the strength of concrete.
1. Poor quality of raw materials
The main reasons for the poor quality of raw material cement are: cement quality problems, poor quality of sand and gravel, unqualified mixing water quality and poor quality of admixtures, etc.
2. Improper mix ratio
The reason why the mix ratio of concrete structures is often inappropriate is that the construction personnel do not design the concrete mix ratio reasonably according to the specifications and standards of engineering construction and apply it at will. The concrete mix ratio makes the quality of the concrete structure unable to meet the engineering construction standards.
3. Problems with construction technology
During the construction process, problems with construction technology are the main factors leading to insufficient concrete strength, which mainly manifest in the following aspects:
First, when mixing concrete, the construction personnel did not strictly follow the engineering construction standards, and there were problems such as the wrong order of adding materials and the mixing time was too short, resulting in poor quality of concrete pouring;
Secondly, during the transportation of concrete, the concrete structure was not properly handled, causing quality problems during transportation;
Thirdly, after the concrete was poured, Later, the construction workers did not vibrate it well, causing the slope of the holes in the concrete structure to be too large;
Fourth, during the curing process, due to improper curing, the temperature and temperature in the concrete structure increased. Humidity cannot meet the standards of engineering construction, resulting in changes in the quality of concrete structures.
Main measures to improve the strength of concrete
1. The concrete mix ratio remains unchanged, and the strength of concrete can be increased by increasing the cement strength grade. The use of early-strength cement helps to increase the early strength of concrete to meet the requirements of rapid construction.
2. Control the water-cement ratio, or use dry hard concrete with small water demand for construction. During construction, the strength of concrete is generally increased by reducing the water-cement ratio. Appropriately reducing the water-cement ratio can effectively control the slurry-to-aggregate ratio and the thickness of the cement slurry layer, so that the skeleton function of the aggregate can be fully exerted, and ultimately the strength of concrete can be enhanced.
3. Optimize the design process flow and mechanize the mixing and vibration of the mixture. If mechanical mixing and strong vibration are used, the concrete mixture can be poured more evenly and densely at a low water-cement ratio, thereby obtaining higher strength.
In recent years, new construction technologies such as high-speed mixing method, secondary feeding mixing method and high-frequency vibration method developed abroad have been applied in domestic projects and have achieved good results.
4. Select high-strength gravel with excellent gradation and moderate sand rate.
5. Use moist heat treatment to maintain concrete.
(1) Steam curing: Curing concrete in normal pressure steam with a temperature below 100°C. Generally, after 16 to 20 hours of steam curing, the strength of concrete can reach 70% to 80% of the strength of 28 days of curing under normal conditions.
(2) Autoclave curing: Place the concrete components that have been resting for 8 to 10 hours in an autoclave with a temperature of 175°C and 0.8MPa for curing.
6. Add appropriate amounts of admixtures and admixtures. To obtain early-strength and high-strength concrete, high-quality concrete admixtures must be added when mixing the mixture.
Early strength agent can improve the early strength of concrete. Adding water-reducing agents, especially polycarboxylate high-performance water-reducing agents, can effectively reduce the amount of water added, improve the durability of concrete, and ensure that the strength of the concrete reaches the standard.
Polycarboxylate water-reducing agent is a highly efficient water-reducing agent that can be used in ready-mixed and precast concrete. It can effectively reduce the shrinkage and shrinkage of concrete during use. Improve the durability of concrete.
In summary, there are many reasons for insufficient concrete strength. When we deal with them, we must first analyze the causes of structural concrete strength insufficient accidents and fundamentally find the corresponding solutions. Solution, only in this way can the quality of the concrete structure be effectively improved to meet the requirements of engineering construction.
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