Experimental Study On Mechanical Properties And Freeze-thaw Damage Of PVA Fiber Reinforced Concrete

Concrete is the most used and versatile building material nowadays.Concrete has numerous excellent physical properties,but its application in practical engineering is greatly limited by its low tensile strength and poor crack resistance.In addition,in the cold areas of Northeast and North China,serious freeze-thaw damage often occurs to concrete buildings,which greatly undermines the normal use of buildings.The subsequent maintenance and reconstruction also lead to a lot of waste of manpower,material and financial resources.Therefore,under the environment-friendly and economic conditions,how to improve the mechanical properties,crack resistance and frost resistance of concrete has become a research focus of the construction industry.In this thesis,using fiber length(8mm,12mm),fiber content(0.03%,0.05%,0.07%,0.1%)as the main variables and centering around the benchmark and PVA fiber concrete,a series of experimental studies were carried out so as to provide new insights for relevant practical projects and promote the development of PVA fiber concrete.The main contents and achievements of this thesis are as follows:Firstly,physical and mechanical properties tests were carried out around the benchmark and PVA fiber concrete,and then the influence of PVA fiber content on the early crack resistance,compressive strength,flexural strength and splitting tensile strength of concrete was studied.Within the scope of the test,results show that PVA fiber can effectively improve the early cracking of concrete,and the early crack resistance is positively correlated with the dosage.When 0.1% of 8mm PVA fiber is mixed,the crack reduction coefficient reaches 96.77% and the compressive strength of concrete is slightly increased,with the maximum increase being only 2.40%;PVA fiber can effectively improve the flexural strength and splitting tensile strength of concrete,and the larger the dosage,the stronger the strength.After mixing 0.1% 12 mm PVA fiber,the flexural strength and splitting tensile strength of concrete reach the highest level,respectively 6.2MPa and4.07 MPa,which are 31.91% and 38.44% higher than the benchmark.Secondly,the benchmark and PVA fiber concrete are sampled to conduct a SEM scanning test in order to explore the reinforcement mechanism of PVA fiber concrete from the microscopic point of view.It has been found through experiments that PVA fiber can exhibit good adhesion in the matrix,improve the compactness of the concrete itself,hinder the generation and expansion of the crack as well as improve the internal defects of the concrete.It also shows that PVA fiber can be combined with the concrete to subject to the force.Therefore,PVA fiber can improve the performance of concrete.Thirdly,0~200 rapid freeze-thaw cycles around the benchmark and PVA fiber concrete were conducted to study the effects of PVA fiber and its dosage on concrete strength loss rate,mass loss rate and relative dynamic modulus.Combined with mass attenuation and the dynamic modulus decay,the frost resistance evaluation parameter w is established.The study shows that under the action of freeze-thaw cycle,PVA fiber can effectively enhance the anti-flaking ability of concrete,improve the internal structure of concrete after freeze-thaw,and thus improve the frost resistance of concrete.In the scope of this test,the frost resistance of concrete is positively correlated with the dosage of PVA fiber.The frost resistance of concrete is optimal after mixing 0.1% 8mm PVA fiber.After200 freeze-thaw cycles,the mass loss rate is only 1.56% and the relative dynamic modulus is 78.65%.The compressive strength and flexural strength loss rate are 34.99% and30.00% respectively,and the frost resistance evaluation parameter w was 0.320.At last,based on the dynamic elastic modulus,an exponential function,a unary quadratic function and a Weibull distribution function model were established.After comparison,it is found that the function model which is under the Weibull distribution is more suitable for depicting the attenuation process of the dynamic elastic modulus of PVA fiber concrete.