Utility of pH-sensitive superabsorbent polymers in concrete repair

摘要

The largest issue with concrete is that cracks can occur due to its relatively low tensile strength. These cracks can generate an entrance for harmful compounds which are dissolved in fluids and gases and endanger the durability of concrete. The cost for crack repair is very high. Alternatively, introducing a polymer during concrete mixing can create a self-sealing material. Fresh cement pore solution possesses a pH value of 12.8, but when a crack occurs, the pH drops to 9 - 10 or even lower, depending on the environment. At this lower pH value, the swelling degree of the hydrogel incorporated must be sufficiently high in order to fill up the crack. As a result, a cross-linked pH-sensitive copolymer of acrylic acid and acrylamide has been synthesized in the present work. The chemical structure has been characterized and sorption and desorption effects have been investigated using dynamic vapour sorption experiments. In addition, a swelling curve was established over the entire pH-range (pH 1-13). Interestingly, the hydrogel developed possessed a maximal swelling capacity of more than 400 times its own weight. Next, water permeability and flexural and compressive strength tests were performed on these samples. The significant decrease in water permeability of hydrogel containing cracked concrete relative to the cracked reference concrete is a quantitative indication of the sealing capacity of the applied hydrogel.The uptake of mixing water by the hydrogel will reduce the effective water/cement ratio of the cementitious matrix. This water will then be released later-on and will cause internal curing. In the present work, experiments have been performed using additional mixing water. Additional mixing water resulted in a higher apparent water/cement factor during internal curing and, together with macro-pore formation, in a lower strength. The results indicate that the polymer developed can be promising to introduce crack-sealing potential in concrete.