The cracking of concrete and mortar is a quality accident that often occurs in engineering. This is caused by the large self-shrinking deformation of high-performance concrete with a low water-to-binder ratio and active mineral admixture.
The root cause of self-shrinkage deformation is the self-drying inside the concrete. The structure of high-performance concrete is dense, and it is difficult for external curing water to enter the interior of the concrete, and the water required for cement hydration in the later stage cannot be replenished, which intensifies the self-drying phenomenon inside the cement stone.
Therefore, in order to alleviate the internal self-drying of concrete, the method of internal curing is often used, and pre-water-absorbing ceramsite or ceramic sand, or other water-absorbing artificial lightweight aggregates are used instead of ordinary aggregates. However, the water absorption rate of artificial lightweight aggregate is limited, and the effect of relieving drying and reducing shrinkage is not obvious.
Internal curing of concrete after absorbing water with acrylic polymer superabsorbent resin is a cost-effective method.
Studies have shown that the particles of superabsorbent polymer are smaller, disperse evenly in concrete, and absorb large water, which can effectively supplement the digestion water in cement stone.
The self-shrinkage deformation of concrete is significantly reduced after adding pre-absorbent superabsorbent polymer to the mortar.
However, after the concrete is hardened, the superabsorbent polymer leaves closed pores with relatively regular shapes inside the concrete, which reduces the strength of the concrete to a certain extent.
Jensen M and Hansen P F of the Technical University of Denmark jointly proposed that adding ultra-high
Strongly water-absorbing polymers can effectively improve self-drying, and this method has been widely recognized by the international academic community. When the hydration of concrete is affected by the decrease of the internal humidity of concrete due to concrete hydration, the polymer material can release the stored water, provide water for further hydration of concrete, and delay the self-drying process of concrete.
In the construction industry, SAP can also be mixed with natural rubber or synthetic rubber, and then add surface active
Additives to improve their compatibility and make sealing materials.
SAP expands sharply when it encounters water or other aqueous fluids, quickly fills the gap, forms a tight seal, and maintains good mechanical strength.
This sealing method has strong resistance to strong acid and strong alkali, especially in the sealing of oil and gas pipelines.
This has been applied in the construction of subsea tunnels in Britain and France, with satisfactory results. In addition, in the emergency rescue of rivers, reservoirs, dams, mines, and other waterproof plugging projects, the application of SAP-containing water plugging agents can greatly improve safety.