Experimental Study On Crack-and Impermeable Hybrid Fiber Concrete In Subway Station

Concrete is a common traditional building material.However,concrete materials also have deficiencies,such as underground structure concrete construction process is easy to produce leakage,resulting in the concrete internal structure crack anti-seepage performance deteriorates,in order to solve the above practical engineering problems.In this paper,based on the orthogonal experimental design of Shuangliu Airport station of Chengdu Metro Line 19,basalt fiber,polypropylene fiber and fly ash as research factors,and based on the orthogonal test method,design groups were conducted to study the working performance,mechanical properties,crack and permeability resistance and NMR pore structure characteristics of different proportions of concrete.The influences of various factors on the main properties of concrete are analyzed and expounded.A hybrid fiber concrete mix with good anti-seepage and crack performance and suitable for continuous pouring is obtained,which provides design basis and construction experience for subsequent subway engineering applications.Specific research work and conclusions are as follows:(1)Under the influence of a single factor,the working performance of concrete mix will deteriorate with the increase of the volume content of basalt fiber and polypropylene fiber,and adding fly ash can make the fluidity of concrete mix better;With the increase of fly ash content,the mechanical properties first increase and then decrease.Both kinds of fibers can effectively improve the mechanical properties of concrete.Among the three factors,polypropylene fiber has the greatest influence on the mechanical properties of concrete,followed by basalt fiber and fly ash.Through range analysis,it can be seen that the optimal ratio of 28 d compressive strength is A2B1C2.The optimal ratio of 28 d splitting tensile strength is A3B1C2.The optimal ratio of28 d flexural strength is A2B2C2.(2)According to the orthogonal analysis,when the volume content of polypropylene fiber and basalt fiber is 0.15% and the fly ash content is 20%,the total cracking area of concrete test block is the minimum.The addition of fiber in concrete can effectively inhibit the shrinkage cracking of concrete,and the crack cracking area per unit area can be reduced by 70%～89.2%compared with that of the benchmark concrete,and the cracking resistance effect is significant.(3)According to the impermeability test,when the volume content of the two fibers is0.10% and the fly ash content is 20%,the average seepage height of the concrete cylinder test block is the minimum,and the impermeability improvement is the best.This is because the two fibers form a "spatial grid structure" in the concrete matrix,which hinders the migration of water in the cement slurry.The hydration products of fly ash can effectively fill the microscopic pores inside the concrete and improve the weak interface at the aggregate interface.The NMR T2 spectral peaks of concrete all show a three-peak structure.With the addition of fly ash,basalt fiber and polypropylene fiber,the internal porosity of concrete can be effectively reduced.The internal pore size types are mainly non-capillary pores and capillary pores,and the cementation pores are less.(4)suggest that hybrid fiber concrete mixing ratio for stone cracking impermeability: river sand: tap water: cement,fly ash,water reducing agent,basalt fiber,polypropylene fiber = 1037,571:180-450:113-5.63: Compared with the 28 d compressive strength,28 d splitting tensile strength,28 d flexural strength,28 d cracking and seepage resistance of the reference concrete,it can increase 8.31%,42.35%,22.79%,65.52% and 75.44%,respectively.(5)From the economic cost analysis,although the cost of hybrid fiber concrete is 5.86%higher than that of ordinary concrete,combined with the later maintenance and reinforcement costs,it is concluded that hybrid fiber concrete is the first choice for practical engineering.