Effect of super absorbent resin on concrete performance
1. Impact on the performance of concrete
The research shows that the pre-absorbed superabsorbent resin can improve the working performance of freshly mixed concrete, while the dry mixing of superabsorbent resin will reduce the workability of the freshly mixed slurry because the superabsorbent resin will absorb some of the free water in the concrete. . The addition of pre-absorbent superabsorbent resin is beneficial to improve the performance of concrete. The pre-absorbent treatment can make the superabsorbent resin absorb and store a large amount of water inside. During the hydration of concrete, as the internal pH of the concrete increases, the superabsorbent resin starts to release the pre-absorbed water inside and increase the amount of concrete. Of free water, thereby improving the performance of concrete.
2. Impact on concrete shrinkage and cracking performance
Due to the loss of water inside the concrete, the water surface inside the capillary hole drops, and the curvature of the meniscus becomes larger, resulting in increased surface tension and pressure on the capillary tube wall. The concrete is in an increasingly compressed state, resulting in a reduction in the appearance volume of the concrete . During the hydration of concrete, the superabsorbent resin will release its pre-absorbed water. Make the internal moisture of the concrete properly supplemented, slow the increase of the capillary tension, and thus improve the concrete
3. Influence on the mechanical properties of concrete
1) Compressive strength
The superabsorbent resin can release water to its surrounding environment for a longer period of time, which improves the degree of cement hydration and the structure of the hydration product is more dense, so the strength of the mortar is greatly improved. The addition of superabsorbent resin makes the strength of concrete at different ages increase in varying degrees.
The role of super absorbent resin in concrete can be considered from two aspects:
First, the high water absorption and high water retention of the superabsorbent resin make it continuously provide water during the hydration process of concrete, which is beneficial to improve the degree of hydration of concrete and make the overall hydration of concrete more uniform. The intensity of the effect plays a positive role. Second, due to the reduction of its own volume after the water release in the superabsorbent resin, pores are left in the concrete, some of which are harmful pores, and the preabsorbent treatment of the superabsorbent resin virtually increases the effectiveness of the concrete The water-binder ratio increases the porosity of the concrete, reduces the effective bearing area of the concrete, and has a negative effect on the strength of the concrete. Therefore, to analyze the effect of superabsorbent resin on the compressive strength of concrete, it depends on which of these two aspects plays a major role
2) Modulus of elasticity
There is a clear correlation between the elastic modulus and compressive strength of high-strength concrete, and the influencing factors of the two are also about the same. Therefore, there are many opinions on the influence of superabsorbent resin on the elastic modulus of concrete. Some scholars believe that internal curing can promote cement hydration and improve mechanical properties, such as strength and elastic modulus. Most studies believe that considering the influencing factors of concrete elastic modulus is mainly the elastic modulus of cement stone and the elastic modulus of aggregate, and the elastic modulus of cement stone mainly depends on its porosity and pore size distribution. The superabsorbent resin releases water and leaves a lot of pores in the concrete, and the porosity of the cement stone increases, thereby reducing the elastic modulus of the concrete.
4. Impact on the durability of concrete
1) Frost resistance
After releasing water, the superabsorbent resin shrinks in volume, leaving a large number of tiny spherical holes in the concrete, and evenly distributed in the concrete. There is a more appropriate spacing factor, which increases the air content of the concrete, which is similar to the air-entraining agent. effect. As the main factor affecting the frost resistance of concrete, the increase in porosity is conducive to improving the frost resistance of concrete. In addition to high suction
In addition to the pores left by the shrinkage of the waterborne resin itself, the surfactant added during the production of the superabsorbent resin will additionally introduce air to increase the porosity of the concrete, thereby improving the frost resistance of the concrete.
2) Penetration performance
The addition of super absorbent resin will increase the porosity of concrete. However, since most of these holes are not connected holes, they have little effect on the permeability of concrete. On the contrary, the addition of superabsorbent resin makes the concrete more hydrated, more uniformly hydrated, and more densely packed concrete, so that the permeability resistance of concrete has been improved. Coupled with the fact that the superabsorbent resin gel loses its water and does not restore its original morphology in the dry state, it forms an organic film covering the pore walls, which will further affect the permeability of the concrete. Incorporating super absorbent resin can greatly improve the impermeability of concrete.
3) Corrosion resistance
Using the characteristics of superabsorbent resin to absorb water expansion, compact micro-cracks or pores, the surface treatment of concrete can cut off the transmission path of sulfate and other aggressive media, and improve the resistance of concrete to sulfate corrosion.