Experimental Study On Flexural-shear Mechanical Properties Of Steel Fiber Reinforced Alkali-activated Slag Concrete Beams

Portland cement is the major raw material of modern civil engineering construction and has extensive applications.However,its manufacturing process is complex,causing problems such as resource and environmental pollution,which is obeied the concept of sustainable development of contemporary resources in China.As a new kind of building material,alkali slag concrete is a new kind of green concrete material formed by taking liquid blast furnace slag as the main cementitious material,stimulating its activity with alkaline water and adding aggregate.It has great properties of energy saving and environmental protection,and meets the requirements of China’s contemporary construction industry for environmental protection.However,the problems of large shrinkage and easy cracking of alkali slag concrete limit its popularization and application.In order to improve the physical and mechanical properties of alkali slag concrete,steel fibers with superior tensile properties are added into alkali slag concrete to form multiphase composites,and to improve the toughness of alkali slag concrete.In order to study the mechanical properties of steel fiber alkali slag concrete members,eight steel fiber alkali slag concrete beams are made with the volume ratio of steel fiber as the variable.Through the three-point loading failure test of simply supported beams,and with the help of finite element analysis method,the bending and shear mechanical properties of steel fiber alkali slag concrete beams are studied.The leading conclusions are as follows:（1）Adding steel fiber can improve the toughness of alkali slag concrete,and its great influence becomes more evident with the raise of steel fiber content;The destroy modes of the beams are resembly,all of which are reinforced failure,but the mid span deflection and surface crack will decrease with the addition of steel fiber.The addition of steel fiber can significantly increase cracking load and ultimate load;From the test results of beam side surface strain,reinforcement strain and deflection,the plane section assumption is still applicable to steel fiber alkali slag concrete beams,and the addition of steel fiber has a good effect on improving the ductility of members;（2）The addition of steel fiber can delay the development of cracks in alkali slag concrete beams,mainly as follows:in the normal service load range,the generation and development of oblique cracks in steel fiber alkali slag concrete beams are later than that in ordinary alkali slag concrete beams.Under the same level of load,the higher the volume ratio of steel fiber,the more the crack width decreases;The existing formula for calculating the inclined crack width of ordinary reinforced concrete beams is still applicable to steel fiber alkali slag concrete,but the reinforcement coefficientβneeds to be introduced for correction due to the addition of steel fiber;The ductility coefficientμis introduced to analyze the ductility of steel fiber alkali slag concrete beams.The results show that:The effect of steel fiber on the ductility of alkali slag concrete beams is obvious,and the maximum ductility is increased by more than doubled;（3）Based on the existing calculation formula of cracking moment in code for design of concrete structures（GB50010-2010）,the plastic coefficient of section resistance moment of steel fiber alkali slag concrete beam β_f is introduced to modify it.The corrected theoretical calculation results are in good agreement with the test results;The existing calculation method of flexural capacity of normal section in technical specification for fiber reinforced concrete structures（CECS38:2004）is still applicable to the test beam,and the calculation formula of cracking shear force of inclined section of the test beam is put forward according to the code and relevant literature.The computed results are fit for the test results;The ultimate failure load of alkali slag concrete beam is deduced from the calculation results of shear capacity of inclined section of alkali slag concrete beam in code for design of concrete structures（GB50010-2010）,and the theoretical results are less than the test results.The ABAQUS finite element results of steel fiber alkali slag concrete beams are tally with the experimental results.