Concrete segregation means that the cohesion between the components of the mixture is insufficient, the components of the mixture separate from each other, the coarse aggregate sinks, and the mortar floats, resulting in hardening of the concrete. Later, quality defects such as honeycombs, pitted surfaces, and weak interlayers appeared. There are six main reasons for segregation in concrete:
Cement
The stability of cement quality is directly Affecting the stability of concrete quality, changes in cement quality may cause concrete to segregate.
Changes in cement fineness: The higher the cement fineness, the higher its activity, the greater the water demand, and the adsorption capacity of the cement particles to the water-reducing agent. The stronger it is, the water-reducing effect of the water-reducing agent can be significantly weakened. Therefore, when the cement fineness suddenly decreases, the water-reducing effect of the admixture will be significantly enhanced. At this time, if the amount of admixture remains unchanged, the water consumption of concrete will be greatly reduced. If not adjusted in time, it is easy to cause excessive dosage of admixtures and segregation.
Changes in the alkali content of cement: The alkali content has a great influence on the adaptability of cement and admixtures. The alkali content decreases and the water-reducing effect of water-reducing agents Enhance. When the alkali content of cement changes significantly, it may have a greater impact on the viscosity and fluidity of concrete, resulting in segregation.
Cement storage and storage time: If the cement is not well stored, it is easily affected by moisture, and the water demand will be reduced after getting damp. The longer the cement is stored, the particles will condense into larger particles through adsorption, which reduces the surface energy of the cement particles and weakens the adsorption of the cement particles to the water-reducing agent, which shows that the water-reducing effect of the water-reducing agent is enhanced. If not adjusted in time, it is easy to cause excessive dosage of admixtures and segregation.
Admixture
The dosage of concrete water-reducing agent is too large and the water-reducing rate is too high. High, the water consumption of a single concrete is reduced, and the water-reducing agent may not fully play its role in the mixer, but it will continue to work during the transportation process, causing the slump of the concrete to the site to be greater than the slump when leaving the machine. Produce segregation.
Fly ash
Fly ash is one of the important admixtures of concrete. It can greatly improve the workability, compactness and strength properties of concrete. If fly ash quality fluctuates greatly, concrete quality control will become more difficult and segregation will easily occur.
When the quality of fly ash suddenly becomes better (such as the fineness changes from 19% to 4%), the water demand of fly ash decreases greatly. It is easy to cause concrete to segregate.
When the quality of fly ash suddenly changes (such as the fineness changes from 19% to 38%), a large part of the fly ash has been lost. The function of the cementing material, so the amount of admixture relative to the cementing material is actually increased, and segregation is prone to occur.
Aggregate
Aggregate is the largest amount of material used in concrete, and its quality directly affects Quality of concrete. Fluctuations in aggregate quality can easily cause segregation of concrete.
The increase in coarse aggregate particle size, unreasonable gradation, and single gradation will cause segregation.
Excessive amount of flake stone chips in the sand will affect the workability of concrete and cause segregation.
The moisture content of the aggregate is too high. When the concrete mixture is mixed in the mixer, the water in the capillary tubes on the surface of the aggregate cannot be released in time, which easily causes the mix to collapse. The amount of combined water is too much. During the transportation process, the water in the capillary tubes is continuously released, causing segregation.
Excessive mud content in the aggregate will reduce the bonding force between the cement slurry and the aggregate, and the ability to wrap the aggregate will decrease, causing the aggregate to separate and produce segregation.
Construction
After the concrete is delivered to the construction site, workers add water to the mixture at will. As a result, the water-cement ratio increases, the cement mortar becomes thinner, the cohesion of the mixture becomes worse, and segregation occurs.
Tank truck
The concrete tank truck did not drain out the remaining water from the tank washing tank, causing the concrete to enter After tanking, the water-cement ratio changes, the mixture becomes thinner, and segregation occurs.
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