Experimental Study On Anti-crack Performance Of Hybrid Fiber Reinforced Concrete

When fiber is added into concrete matrix, mechanical properties, wear resistances and durability of cement-based concrete could be improved, because of this, more and more research personnel's attention is attracted by fiber reinforced concrete. The concrete is a heterogeneous compound material, when some single material is mixed; some performances of concrete are improved. But such enhancement of the performance is based on a specific level, and the multi-phase and multi-level performance of concrete is not improved comprehensively. This is the reason of its limitation. If the overall performance of the concrete wants to be enhanced with greater degree, the added fiber is also multi-level, so hybrid fiber concrete is formed.If a single fiber is adopted to strengthen the reinforced concrete, its effect is limited, while the application of hybrid fiber can make up for one's deficiency by learning from other strong points. But at present researches and engineering applications about the hybrid fiber concrete are not sufficient, particularly about the hybrid effects of different fibers are not clear and the interpretation model of strengthening mechanism has not formed its system.This thesis centering on the goal of enhancing crack resistance performance of concrete, aiming at the plain concrete, polypropylene fiber reinforced concrete, steel fiber reinforced concrete and hybrid fiber reinforced concrete, passing through the orthogonal test and combining with some aspects'consideration about economy and process's complexity studies on adding different type of fiber to enhance the crack resistance performance and effect of ordinary concrete and explore hybrid effect and strengthening mechanism of different fiber.The test result showed that:(1) In stir process of the concrete, the steel fiber is more easily spread than the polypropylene fiber. To make hybrid fibers in concrete matrix achieve uniform dispersion, it should be noted the placement order of different materials and fibers in the stirring.(2) After incorporation of hybrid fibers, the slump of concrete has differently decreased.(3) Hybrid fiber has no significant contributions for the compressive strength of concrete. On the contrary, when the fiber mixing amount is gradually increased, the compressive strength of concrete is decreased a little. But hybrid fiber improves the deformation performance of concrete members; the brittle failure of concrete is changed into ductile failure.(4) After incorporation of hybrid fibers, flexural toughness of the concrete is significantly improved. Among them, polypropylene fibers can effectively improve the initial cracking deflection of the small beam specimens and steel fibers have an important contribution for the residual strength of small beam specimens. Moreover, the collaborative effect of two fibers is better than any single-doped fiber. Based on test results analysis, the volume quantities with 1% steel fiber and 0.1% polypropylene fiber are the optimal mixing ratio of fiber.(5)Hybrid fibers have a significant crack arresting effect for early-age shrinkage of concrete mortar. Polypropylene fibers are remarkable function for the concrete's early crack resistance, but steel fibers have an important contribution for the inhibition of post crack propagation.