Synthesis Of Modified Polyacrylamide Water Absorbent Resin(SAR) And Impermeability Of Concrete Cracks Treated By SAR

The complexity of the concrete materials and the diversity of the environment in which the structure is located make it concrete difficult to avoid cracking. When the crack width of concrete exceeds the standard, it will affect the quality and service life of the concrete structure. In this study, combined with the swelling characteristics of water absorbent resin(SAR) when meeting water, the concrete cracks were repaired using the SAR synthesized in cracks. The research results have important significance and application value for the improvement and development of concrete crack repair technology.The traditional polyacrylamide has the advantages of super absorbent resin, high water absorption rate, high water absorption rate and high water absorption capacity, but it has the disadvantages of high brittleness and brittle fracture after water absorption, which is difficult to meet the special requirements of the treatment of concrete cracking. Therefore, in order to improve the applicability of polyacrylamide absorbent water resin to concrete crack treatment, the modified polyacrylamide water absorbent resin was synthesized by adjusting the crosslinking density and optimizing the structure of the gel network with adding the polymerization surfactant agent based on Flory swelling theory.In this paper, acrylamide(AM) as monomers, N, N- methylene bisacrylamide(MBA) as crosslinking agent, tetramethylethylenediamine(TDMA)- ammonium sulfate(APS) as the oxidation reduction initiator, 2- acrylamido 2 methyl propane sulfonic acid sodium(AMPS-Na), 3- ene propylene oxygen radical- 2- hydroxy- 1-tightening propane sulfonic acid sodium salt(HAPS) and polyvinyl alcohol(PVA) as modifiers, were used to synthesized the different modified polyacrylamide absorbent resin(SAR) by solution polymerization. The testing results show that:(1) with the increasing of the dosage of the crosslinking agent MBA, the cross-linking density of SAR increases, which results in the increasing of the water absorption of SAR, the reducing of the rate of salt solution absorption and brittleness resistance, but no significant change in the rate of polymerization;(2) with the increase of AMPS content, the rate of polymerization reaction, the rate of water uptake, the rate of water absorption and the brittleness resistance of SAR were all decreased, but the rate of absorbing water was increased;(3) with the increase of HAPS content, the rate of polymerization reaction rate and water absorption(salt) ratio of SAR were decreased and the brittleness resistance was increased, but the water absorption rate had no significant change;(4) with the increase of PVA content, the PVA modified SAR water absorption(salt) ratio and the breaking resistance were improved, and the rate of polymerization was not changed. Based on the comprehensive performance of midified SAR in water absorption and brittleness resistance, the optimum composition of SAR pre polymer monomer solution is as follows: AM(20 unit), APS(0.08 unit), TMDEA(0.08 unit), MAB(0.02 unit) and deionized water(80 unit); the dosage of three modifiers is AMPS(1 unit), HAPS(3 unit) and PVA(4 unit), respectively.Secondly, the impermeability of mortar cracks with different widths(0.2mm, 0.4mm, 0.6mm and 1.0mm, 1.2mm, 1.4 mm, 1.8 mm and 2.4 mm) treated by modified SAR was conducted. The results show that:(1) the impermeability of cracks treated by SAR modified with HAPS, PVA and AMPS decreases in turn;(2) when the crack width is 0.4mm ~ 1.2mm, the impermeability of cracks is the best for all the modified SAR;(3) with the increase of the number of wet and dry cycles, the impermeatbility of cracks treated by modified SAR is slightly decreased.