Research And Application Of Crack Control Technology For Concrete Structures In Arid Sandy Areas

Anti-crack concrete adapted to the arid sandy areas was developed by the method of combination of theoretical analysis, indoor micro properties test, macro properties test and verification of field engineering application based on the technical problems of cracking and maintenance difficulties of concrete caused by the great differences in temperature in the arid sandy areas of West China. Packaged technology of crack control of concrete was proposed which provided references for promoting the development and application of cracking resistance technology of concrete in the arid sandy areas. The works and achievements of this paper were:Firstly, environmental conditions and cracking characteristics of concrete structure in the field were investigated. Mechanism and law of cracking of concrete in arid sandy areas were analyzed. The main factor of cracking on the surface of concrete caused by the fast water evaporation and great shrinkage is definite. The technological approach of crack control of concrete that compensating humidity inside and reducing evaporation outside was put forward from the view of engineering practices’need for economy and technicality of concrete.Secondly, super absorbent polymer was prepared by different synthetic processes. Acrylamide SAP as humidity regulating component was optimized selected by the water absorption rate and water absorbency tests in different medium and ionic concentration solution and effect of SAP on the workability and volume stability of concrete. The particle size was determined from 0.12mm to 0.25mm. Internal curing material which could improve the crack resistance of concrete significantly and did not reduce the strength and durability of concrete was developed by the optimize selection of water retention component, shrinkage reducing component and humidity regulating component.12 hours shrinkage reducing ratio of concrete with internal curing agent was 56% and 28 days shrinkage reducing ratio was 25%.Thirdly, watering and cover maintenance were hard to realize and the problem of water desorption of concrete in the early age cannot be solved. The effects of film formation components, inorganic enhancement components and modified components on the water retention properties of curing agent were studiedExternal curing agent whose water retention ratio was greater than 85% was developed based on the environment characteristics of the arid sandy areas. Property evaluation methods of curing agent suitable for field application and evaluation index of curing effect of concrete were proposed.fourthly, preparation technology of high cracking resistance internal curing concrete with internal curing water introduced by moderate SAP through theory calculation of chemical shrinkage compensation and verification of concrete preparation was proposed follow the principle of "three low and one high" (low water consumption, low cementitious material dosage, low slump, high air content) based on the study of effect of supplementary cementitious material and parameters of mix proportion on the workability, mechanical properties, volume stability and durability of concrete. The distribution of water in different phases in the cement paste was analyzed by XRD, TG, pore structure analysis and nuclear magnetic resonance testing technology. The effect of internal curing water on the capillary negative air pressure, hydration degree and pore structure was studied. The function model of SAP with water in the cement paste during the hydration process was proposed and the mechanism of internal curing was revealed.Finally, key engineering application technologies of mixing, transportation, placing, vibrating and curing of high crack resistance internal curing concrete was systematic studied. Internal curing material with shrinkage reducing and crack resistance effect and external curing agent with high water retention effect were used in the concrete engineering of Lanxin high speed railway. The purpose of the crack width of concrete structure in arid sandy areas meeting the requirement of acceptance specification was realized. The disadvantages of poor environmental adaptability and high maintenance dependence of recent crack resistance technology of concrete were made up.