Effect Of Steam Curing On Mechanical Properties Of High Ductile Concrete

High Ductile Concrete(HDC)is a new type of structural material with high strength,high toughness and high damage resistance.In recent years,it has been widely used in civil engineering due to its excellent mechanical properties.However,since HDC contains mineral admixture with slow hydration such as fly ash,its curing age is over 60 d.Steam curing can accelerate the hydration rate of cementing materials and promote the development of concrete strength.Therefore,studying on the mechanical properties of HDC after steaming and using it as a rapid curing method is of great significance for the further promotion and application of HDC.Based on the previous research of the research group,this paper studies the compressive strength,flexural toughness,flexural strength,material hydration mechanism and microstructure of HDC after steaming.The main contents are as follows:(1)The compressive strength of HDC cubes and the flexural strength of prisms after steam curing were studied.The effects of constant temperature,constant temperature time and steaming mode on the compressive strength and flexural strength of HDC with three strength grades were analyzed by taking the corresponding strength of the room temperature curing test block as the control;Through regression analysis of test data,the correlation formulas of compressive strength with constant temperature and time were established,which provided a basis for predicting compressive strength of HDC autoclaved.(2)A four-point bending test study of HDC prisms was carried out.The influences of three factors,namely curing method,constant temperature and time,and steaming mode,on the flexural toughness of HDC were analyzed.The results were mainly related to the high temperature hydration of fly ash;the flexural and tension conversion formula were established.The tensile properties of HDC after steaming were evaluated by four-point bending test results.Among them,the change of the ultimate tensile strain is mainly related to the flexural toughness,and the variation degree of the tensile strength is basically similar to the compressive strength.(3)The Micro-properties of materials such as X-ray diffraction and scanning electron microscopy were tested.The phase composition and microstructure of HDC slurry under room temperature and steam curing were compared and analyzed.XRD and SEM test results are consistent with the corresponding macroscopic mechanical performance.Among them,insufficient hydration of cement and micro-cracks in hardened paste are important factors affecting macro-mechanical properties of HDC after steam curing.(4)Based on the nine steam curing systems explored in the experiment,the optimum steam curing systems corresponding to the three strength grades of HDC were determined by synthesizing the test results of compressive strength,flexural toughness and flexural strength of HDC;It is pointed out that the HDC steaming system should select the corresponding steaming mode according to the early strength before steaming;achieve the optimal matching of constant temperature and constant temperature time;reasonably control the rising and cooling rates,and ensure the high relative humidity during the steaming process.