Study On The Preparation And Properties Of Hybridization Fibers/Cement Composites

Cement-based materials like cement mortar and concrete are currently the largestman-made materials. However, cement mortar and concrete have some disadvantages, such asthe low tensile strength, high shrinkage ratio, poor impact resistance and impermeability.When cement mortar and concrete suffer effects from the external factors, their mechanicsstrength and durability will be decreased. Therefore, cement-based materials need to be highperformance. In the cement matrix, fibers can restrain cracks emergence and expansioneffectively, and improve the strength and toughness of the cement-based materials. Howeverthe reinforcement effects of fibers are different because of the differences of the fiber types,performances and sizes. The different hybridization fibers were chosen to reinforcecement-based materials, and the reinforcement effects of hybridization fibers would besuperior to these of single fiber.This thesis mainly includes the following several research contents: the fine steel fiber,Kevlar fiber and polypropylene fiber are adopt as the reinforcement fiber, and the effects ofdifferent hybridization fibers adding technologies on the dispersity of fibers in the cementmatrix are studied, and the optimal hybridization fibers adding technology is confirmed; theeffects of the fine steel fiber, Kevlar fiber, polypropylene fiber and fly ash on the cementmortar’s performances are studied by the way of orthogonal experiment, and the optimal mixproportion is confirmed; on the basis of orthogonal experiment, the effects of single fiber andhybridization fibers on the compressive strength, flexural strength, impact resistance,shrinkage ratio, impermeability and frost resistance of cement mortar are studied respectively;the microstructure and pore structure are observed respectively by using the scanning electronmicroscope and mercury intrusion porosimeter, and the mechanism of action is discussed.Studies have shown, the optimal technology for the steel fiber and polypropylene fibersystem is that polypropylene fiber was first dispersed in water then the steel fiber was addedafter the cement and sand mixed; the optimal technology for the Kevlar fiber andpolypropylene fiber system is that Kevlar fiber and polypropylene fiber were first dispersed inwater then the cement and sand mixed; the optimal mix proportion was confirmed through theorthogonal experiment, and optimal mix proportion of steel fiber and polypropylene fiber hybridized reinforcing cement mortar was1.0%fine steel fiber,0.6%polypropylene fiber and20%fly ash; and the optimal mix proportion of Kevlar fiber and polypropylene fiberhybridized reinforcing cement mortar was0.5%Kevlar fiber,0.6%polypropylene fiber and10%fly ash.On the basis of the orthogonal experiment, the effects of single fiber and hybridizationfibers on the performances of cement mortar. The results have shown that the action effect ofsingle fiber and hybridization fibers on the compressive strength wasn’t obvious; the singlefiber and hybridization fibers could improve the flexural strength, impact resistance,impermeability and frost resistance, and reduce the shrinkage ratio of cement mortar; thereinforcement effects of hybridization fibers on the strength and toughness of cementcomposite was more obvious because of the fiber superposition effect; fly ash improved thedurability of cement composite to a certain extent. The results of the scanning electronmicroscope and mercury intrusion porosimeter have shown, there are many micro-cracks andlarger diameter pores in the cement mortar without fibers, and the structure of cement mortarwith fibers and fly ash is denser.