The Study On Early Cracks Classification Control System Of Ready-mixed Concrete

Concrete structural members generally work with cracks,and there is no concrete without cracks,However,sometimes because of the criticality class of buildings and the needs of external environment,it is demanded to prepare the anti-crack concrete which has a relatively strict requirement with the early cracks;According to the strict degree of crack control,the anti-crack concrete is graded and the ready-mixed concrete with different cracking grades is prepared,which is beneficial to the “good quality and higher price”of the ready-mixed concrete.What's more,it is not only beneficial to clarify the responsibility of concrete cracking on site and maximize the benefits,but also save costs for construction enterprises.The industry standard of?the Technical Specification to Control Cracks in Architectural Engineering ?implemented by Ministry of Construction for Housing and Urban and Rural on October 1st,2014,numbered JGJ/T317-2014,classified the crack resistance of ready-mixed concrete and divided it intofive grades.However,there are still some deficiencies in the application process.In view of its deficiencies,the new anti-crack classification standard of ready-mixed concrete is tentatively proposed in this paper,which can not only overcome the deficiencies of the 2014 edition for the anti-crack classification standards,but also benefits the popularization and application of crack classification standard of the new ready-mixed concrete in site engineering.In order to study the early cracks classification control system of the ready-mixed concrete,the following works are done in this paper:1.The concept of early cracks classification control system of ready-mixed concrete is put forward by studying the control measures of early cracks of ready-mixed concrete and investigatingin practical engineering.2.The effects of water-binder ratio,content of fly ash,fiber and other factors on the early-cracking of ready-mixed concrete are studied.The experimental results show that with the increase of water-binder ratio,the early-cracking index of concrete gradually decreases,the anti-cracking performance of concrete is related to the content of fly ash,and the two are nonlinear and the incorporation of fiber can effectively inhibit the early-cracking of concrete.the effect of crack resistance of layered hybrid fiber reinforced concrete is better than that of integral and single fiber reinforced concrete.3.Through the analysis of the test results of the factors influencing the early cracking of ready-mixed concrete,the parameters of critical control points of grading crack resistance of each factor under the classification of crack resistance system are obtained.4.In the classification of anti-crack system,the on-site environmental conditions are comprehensively taken into account,and the treadmill test is carried out in the field.According to the concrete with different crack resistance grades,the cracksof plate specimen and concrete structure developed with age are observed.The correspondence for the early-cracking between the anti-crack concrete members at different levels and the plate specimens under the classification of crack resistance system is obtained,and the feasibility of implementing the anti-crack classification of the ready-mixed concrete under field conditions is verified,which provides a basic for judging the anti-crack grades of ready-mixed concrete according to the development of cracks of the concrete memberson site.5.Through the analysis of the field test results and the summary of the relevant measures in each stage of project,the countermeasures for the classification of early-cracking of ready-mixed concrete which is suitable for engineering site is put forward.