I believe everyone has some understanding of the knowledge of polycarboxylic acid water reducing agent. If you want to use it better, you should also have some understanding of its bleeding knowledge. You must know that the polycarboxylic acid water reducing agent is used improperly. Will cause concrete bleeding, the following is a brief understanding of the reasons for the polycarboxylate water-reducing agent causing concrete bleeding:
(1) The quality of aggregate fluctuates.
In the process of concrete production, the quality of sand and gravel aggregates often fluctuate. For example, the mud content becomes larger or smaller, the water content fluctuates, the aggregate gradation changes, the sand fineness modulus changes, etc., may increase Possibility of concrete bleeding.
(2) Polycarboxylic acid water reducing agent is sensitive to ambient temperature and has slow release properties.
Compared with other water-reducing agents, the water-reducing performance and slump retention performance of polycarboxylic acid water-reducing agents are greatly affected by temperature. When the summer temperature is high, the polycarboxylic acid water reducing agent with good slump retention performance may have a “large slump” phenomenon when the temperature suddenly drops.
(3) Add water reducing agent twice to adjust slump.
When using polycarboxylic acid water-reducing agent for secondary addition and adjustment, sometimes it is not possible to reasonably control the amount of water-reducing agent used. When the amount of water-reducing agent exceeds the theoretical requirement, the excessive water-reducing agent still plays a role after the concrete is poured, which makes the part of the concrete The water is analyzed out.
(4) When the polycarboxylic acid water reducer is compounded, the retarder is used improperly.
In order to obtain good slump retention performance of concrete, the maximum amount of retarding component is often added when compounding polycarboxylic acid water-reducing agent. If the amount of retarding component is too large, or when the temperature is better, the compounded polycarboxylic acid water reducing agent encounters a sudden drop in temperature, too much retarding component will slow down the hydration of cement and cause concrete bleeding.
(5) Compatibility of cement and polycarboxylic acid water reducing agent.
Inconsistent chemical changes between the components of the concrete are complex, especially the compatibility of cement and polycarboxylic acid water-reducing agent, which is particularly prominent. If the compatibility of cement and polycarboxylic acid water-reducing agent is poor, the saturated content of water-reducing agent will be increased, and the excess water-reducing agent will prolong the initial setting time of concrete, and at the same time, the free water in the concrete will be precipitated. In addition, when the soluble alkali in the cement is low, the cement hydration speed becomes slower, and the phenomenon of hysteresis bleeding often occurs.
The above is the reason why polycarboxylic acid water reducer causes concrete bleeding. It should be known that the effect of polycarboxylic acid water reducer on concrete bleeding is very limited, but the impact on concrete durability is very important. It can be known from the mechanism of bleeding that after the water is secreted from the inside of the concrete to the surface, a channel from the inside to the outside is formed in the concrete. These channels will reduce the penetration resistance of the concrete.