| In view of the poor external maintenance effect and cracking of concrete caused by the environmental conditions in the arid area of Northwest China.Based on the theoretical analysis,macro performance test and engineering application,the internal maintenance agent of concrete Super Absorbent Polymer(SAP)suitable for the environment of northwest arid area was developed in this study.Meanwhile,the effect of self-developed SAP on concrete properties was studied and the site construction technology of SAP internal maintenance concrete was put forward.The research provides an important reference for promoting the development of concrete crack resistance technology in northwest arid area and the application of SAP internal maintenance in practical engineering.The work and conclusions of this study area as follows.Firstly,polyacrylic acid acrylamide superabsorbent resin was prepared by solution polymerization and step heating method.Based on the fuzzy orthogonal method,the process parameters of the synthesis of polyacrylic acid acrylamide superabsorbent resin were optimized.The water absorption ratio of SAP prepared under the optimal conditions is 626g/g.Furthermore,through the fluidity test of cement paste and the slump test of concrete,the reasonable content of SAP was determined to be 0.1% ~ 0.5%.It can be seen from the study on the influence of SAP content and mixing method on the mechanical properties of concrete that there is a reasonable SAP content in the inner maintenance concrete.After water absorption treatment,SAP will have a negative effect on the compressive strength of concrete,and the mixing method was determined as dry mixing.The influence of SAP on the volume stability of concrete was studied.The results shows that SAP can effectively improve the self-shrinkage and crack resistance of concrete,and with the increase of SAP content,the self-shrinkage of concrete gradually decreases and crack resistance gradually increases.Compared with the internal maintenance mode,the combination of steam maintenance and SAP internal maintenance modes has a better effect on improving cracking resistance.Through the hydration heat test of cement slurry,it is found that adding SAP into concrete can delay the hydration reaction of cement and reduce the total heat produced by the hydration reaction,and the effect is more obvious with the increase of SAP content;It can be seen from the study of the influence of SAP on the frost resistance and chloride penetration resistance of concrete that the addition of SAP can significantly improve the frost resistance and chloride penetration resistance of concrete.Thirdly,the results of mercury intrusion porosimetry(MIP)test and nuclear magnetic resonance(NMR)test show that the most probable pore diameter and porosity of concrete gradually increase with the increase of SAP content.Excessive SAP will have a negative impact on the pore structure of concrete,resulting in the reduction of concrete strength.Compared with the test results of shrinkage cracking of concrete and pore structure,it is found that adding appropriate amount of SAP can increase the number of small pores in concrete.Meanwhile,the increase of small pores is more conducive to improving the shrinkage of concrete,thus reducing the cracking of concrete.Finally,the application experience of self-made superabsorbent resin in practical engineering is summarized in the engineering application of SAP internal maintenance concrete.The whole construction scheme of SAP internal maintenance concrete is determined from raw material selection,concrete mixing,transportation,pouring and concrete quality inspection,etc.The economic benefits of self-made superabsorbent resin and common superabsorbent resin are compared and analyzed.The results show that the cost of self-made superabsorbent resin is far lower than that of the same type of superabsorbent resin on the market,showing greater economic benefits. |
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