Study On Mechanical Properties And Microscopic Mechanism Of Hybrid Fiber Modified Concrete

In the field of modern civil engineering,concrete has many advantages,such as high compressive strength,good durability,easy construction and so on.It occupies a very important position in the construction industry with the largest amount of concrete.But it also has some shortcomings such as self-weight,poor ductility,poor crack resistance and low tensile strength.At present,the building structure is developing towards light,long-span and super-high direction,and new requirements are put forward for the performance of concrete.The crack resistance and strength of concrete are improved to meet the needs of modern engineering for concrete.The mechanical properties of concrete can be further improved by adding a variety of fibers to make up for their weaknesses.In this paper,a series of studies on the basic mechanical properties and micro-mechanism of carbon-polypropylene-aramid ternary hybrid fiber concrete are carried out based on the existing research results of fiber reinforced concrete.The effects of hybrid fibers on the strengthening and toughening of concrete,the constitutive relationship and the micro-structure are analyzed.The main contents and conclusions are as follows:(1)Through the compressive test,splitting tensile test and the flexural test of 310 concrete specimens with the size of 100 mm x 100 mm x 100 mm and 155 concrete specimens with the size of 100 mm x 100 mm x 400 mm,the effects of fiber length-diameter ratio,volume fraction,mixing ratio on the cubic compressive strength,splitting tensile strength,flexural strength,failure characteristics and reinforcement machine of hybrid fiber concrete are studied respectively.The strength model of the influence of the content of hybrid fibers on the strength of concrete is established.(2)Through uniaxial compression tests of 25 prismatic concrete specimens with the size of 100 mm x 100 mm x 300 mm,the constitutive relations of ordinary concrete,single fiber concrete and hybrid fiber concrete are studied,the stress-strain curves of fiber concrete are drawn and analyzed,and the mathematical model of stress-strain constitutive relationship of fiber concrete under uniaxial compression is established,and the constitutive relations of fiber concrete under uniaxial compression are also studied.The results show that the fitting effect is good.(3)The micro-morphology of concrete paste and interface of transition zone after compression damage was observed by SEM.The difference of micro-structure between fiber reinforced concrete and ordinary concrete was analyzed from the quantity of hydration products,the number and development of cracks and fiber crack resistance.The failure mechanism of fiber reinforced concrete was analyzed,and the micro-structure model of fiber reinforced concrete was established.