Research On The Strengthening-toughening Of Supporting Cement-based Composite Materials

The tunnel support has become one of the technical problems with the increasing excavation depth. Among them, the developments of the materials which are used for tunnel support have been increasingly significant, especially for preparation of the high performance cement-based composite materials. As we all know, the cement-based materials have some disadvantages, such as high brittleness, low flexural and low tensile strength, and these shortcomings can be improved by modification of polymers and reinforcement of fibers. The main contents and research results are as followed:(1)Synthesis of polymer modifier:the polybutadiene grafted polystyrene emulsion (PB-g-PS) with core/shell structure were synthesized via semi-continuous seed emulsion graft polymerization method and characterized by FTIR,TEM.(2)For the modification of polymers, the modification effects of the ploymer-binder ratio(A), water-binder ratio(B), sand-binder ratio(C) and amount of composite auxiliaries(D) were investigated through four factors-four levels orthogonal experiment. The optimal formula combination was obtained:ploymer-binder ratio is 10%, sand-binder ratio is 0.37, the amount of composite auxiliaries is 1.2%, and water-binder ratio is range 0.3 to 0.35.(3) The problem of the concrete crack, poor flexural/tensile properties can be effectively solved by reinforcement of fibers. Based on the fibers reinforcement mechanism, the effects of sand-binder ratio, cement-binder ratio, reinforced material ratio and fiber volume content were investigated through four factors-three levels orthogonal experiments. Moreover, the compressive strength,flexural,splittingtensile strength and bending-toughness were analyzed and obtained the optimal formula:sand-binder ratio is 1, cement-binder ratio is 0.4, reinforced material ratio is 0.05 and the amount of fiber chooses 2.4%.(4)Based on the experiment of fiber reinforced cement-based material, the effects of the kind, the length and the volume content of the fiber were investigated and the preformulation was optimized. The experiment results showed that Japan PVA fiber, fiber length of 9 mm and the volume content of 2.2% have good enhancing effect on cement-based material. Also, the elastic modulus and poisson’s ratio of the various types of fiber cement base material were measured.(5)Using the FLAC3D software to analyze the support effect, the numerical simulation calculation results show that the fiber reinforced cement-based materials have improved greatly on the effect of tunnel supporting, can resist large deformation and release the rock stress.