System Balance Problem Of Mixture After Concrete Pouring

For concrete with heavier bleeding and segregation, the mixture system is an unstable system. Because of the large water-filled space, the mixing water filled with the water-filled space can’t sustain the weight of the system. Under the effect of its own weight, the spare mixing water is squeezed out until the water-filled space is small enough to sustain the weight of the system. This is a process in which the system transforms from imbalance to balance. But this balance is short-lived.

Bleeding segregation causes large bleeding channels and many weak structures inside the concrete, which destroys the uniformity of the concrete. These bleeding channels and weak structures are difficult to be filled and compacted by hydration products, which easily cause internal stress and destroy the balance of the system.

The high performance concrete mixture is a well-balanced system with good stability. Its water-to-binder ratio is small, no bleeding, no segregation, and good uniformity. The water-filled space is small enough to sustain the weight of the system and maintain the uniformity of the concrete under the effect of its own weight. At this time, the concrete has no internal stress and the system is stable. But after the concrete is poured and formed, if the system loses water and there is a water loss channel, internal stress will take place, causing the system to deviate from the original balance, and the system will become unstable. This is why high performance concrete will come out with early cracking.

Therefore, establishing a stable balance system for concrete before initial setting is very important to improve the quality of hardened concrete. For high performance concrete, instant curing can be used to prevent the loss of mixing water, and the balance of the system can be maintained.

If the concrete has lost water, no matter how much water is lost, secondary plastering should be used to completely eliminate the water loss defect before initial setting. Elimination of water loss channels also eliminates internal stress. The concrete in the dehydrated part becomes denser after plastering and pressing, and the water-filled space is completely filled with mixing water again, and the hydration product can completely fill and compact the water-filled space, so that the concrete can achieve high impermeability.

Bleeding concrete is not suitable for immediate curing because of the existence of bleeding channels. The water secreted on the surface should be drained in time, and the concrete surface should be repeatedly pressed before initial setting to seal the bleeding channel and the water loss channel. For concrete with serious bleeding and segregation, the interior is full of defects, and it is best to use the secondary vibration process for this kind of concrete.

Only the secondary vibration before the initial setting can completely eliminate the defects in the inner depth, improve the uniformity of the mixture, and make the water-filled space of the concrete small enough. The defects are eliminated, the internal stress is also eliminated, and the concrete system before initial setting becomes a stable balance system.

System Balance Problem During Concrete Hardening

The mixture system balance before initial setting lays the foundation for establishing the system balance of hardened concrete. From the initial setting, the concrete enters the hardening stage. The generation of internal stress at this stage is mainly caused by the loss of mixing water. Therefore, the loss of mixing water must be strictly controlled after the secondary vibration and secondary pressing. We emphasize the need to cover while wiping and pressing, and then water to moisturize, so that the cover is full of water, that is, to prevent the loss of mixing water. After the secondary plastering and covering are completed, the concrete should be poured with sufficient water for curing, or stored for 3-7 days to ensure that the concrete does not lose water during the curing period, and the overall concrete can achieve high impermeability, thereby eliminating or reducing the maximum amount of water and decrease the concrete stress. This creates a stable and balance system for the hardened concrete.