Study On High Performance Concrete With Polyformaldehyde Fiber

With the progress of social economy and technology,buildings are constantly developing in the direction of diversification,and the safety performance of buildings is also highly emphasized,so concrete,as one of the main building materials,is constantly moving toward high strength and high durability.However,High Performance Concrete(HPC)has problems such as easily shrinkage cracking and brittle damage,and the fiber composite is an effective way to improve the performance defects.In this paper,the optimal length and amount of polyformaldehyde(POM)fibers are determined by studying the effects of different lengths and amounts of POM fibers on the mechanical properties of high performance concrete.In the background of offshore engineering conditions,the study investigates the possibility of replacing steel fibers with POM fibers in seawater freeze-thaw cycle test.Finally,the performance of POM fiber high performance concrete is further enhanced by taking advantage of fine fibers such as polypropylene(PP)fibers and polyvinyl alcohol(PVA)fibers,the main work is as follows:(1)The effects of different POM fiber lengths and doping amounts on HPC are analyzed by working performance,compressive strength,flexural strength,bending toughness and fracture performance indexes.The best improvement of bending toughness and fracture properties of HPC is achieved when the fiber length is 20 mm and the volume dose is 2%.The theoretical model of fracture energy is derived by analyzing the form of fiber action in HPC,combined with the theoretical equations,and verified by comparing the experimental results to provide reference for the study of fracture energy of fiber concrete.The principal component analysis in SPSS software is used to evaluate the test results comprehensively and determine the best POM fiber group.(2)The effects of POM fiber and steel fiber on the performance of ordinary concrete and HPC against seawater freeze-thaw cycles are compared and analyzed by apparent morphology,mass loss rate,relative dynamic elastic modulus and relative value of compressive strength,etc.According to the test results,it can be found that the performance of POM fiber against seawater freeze-thaw cycles is better than that of steel fiber.(3)According to the optimal POM fiber parameters,the PP fiber and PVA fiber with different doping amounts are used to study the performance improvement effect,and the compressive strength,bending toughness,drying shrinkage and other indexes are analyzed.When the PVA fiber content is 0.2%,the compressive strength is the greatest and the bending toughness is improved significantly;and when the PP fiber content is 0.2%,the reduction of drying shrinkage is the most effective,for 90 d drying shrinkage,compared with the single POM fiber group,the reduction is 13.61%.According to the test results and combined with the analysis of the formula for calculating the cost performance,it is found that the PVA fiber with 0.2%volume admixture has the best effect on the overall performance improvement,and the PP fiber with 0.2%volume admixture has the highest cost performance.