Study On The Fracture Properties Of Carbon Fiber Reinforced Concrete

With the unceasing development of the Material Science and Engineering technology,higher requirements were proposed to intensity, durability and workability of concrete in modern engineering.As a new cement-based compound material produced in concrete modified process,fiber reinforced concrete(FRC) won the favor of many engineers and technicians,because of its unique superiority in strengthening,anti-cracking and toughening.Now the research on FRC is focus on its intensity and durability,but the research on its fracture mechanics and fracture properties is not enough.Taking the fracture properties of carbon fiber reinforced concrete(CFRC) as main object,the following works have been accomplished in this paper:(1)By the compressive strength test and splitting tensile test of CFRC in different carbon fiber volume content,the impacts of carbon fiber volume content on its intensity have been studied.Through the comparison of CFRC and plain concrete in intensity,laod~displacement curve and surface condition after test,the strengthening, anti-cracking and toughening mechanics of CFRC have been analyzed.The test results indicated that the addition of carbon fiber is helpful in increasing compressive strength,splitting tension strength,peak strain and ultimate strain of CFRC.When CF volume content is 0.3%,compressive strength increase 80%,splitting tension strength increase 61%,peak strain increase 88% and ultimate strain increase 152%.More,the addition of carbon fiber can improve interface characteristic between aggregate and cement mortar,optimizing its internal structure,improving its integrity.The main function of carbon fiber to concrete displays in strengthing when fiber volume content is lower(≤0.3%),but in toughening when fiber volume content is higher.(2)By the three-point bending beam test on CFRC with the size of 100mm×100mm×400mm,the impacts of carbon fiber volume content upon the fracture parameters,such as fracture toughness( K IC),fracture energy( G F),as well as critical crack mouth opening displacemeng( CMODC ) of CFRC have been researched.The test results indicated that the addition of carbon fiber is helpful in improving fracture properties.When CF volume content is 0.5%, K IC, G F and CMODC of CFRC is 2.67,5.14 and 4.51 times of that of plain concrete.Each fracture parameter increase linearly fiber volume content increasing,Through data regression,we obtain a uniform formula displating the relation of CF volume content and fracture parameters.(3)By the mechanical test and three-point bending beam test on hybrid (carbon and polypropylene) fiber reinforced concrete(C-P HFRC) with the size of 100mm×100mm×400mm,the compressive strength and splitting strength have been researched, K IC, G F,as well as CMODC of HFRC and the hybrid effect been investigated.The test results indicated that C-P HFRC is superior to CFRC.Whenρf is invariable and V f is 0.3～1.2kg/m3,Fracture parameters increase with V f increasing, V f is 0.9kg/m3 having best effects.When V f is invariable(0.9kg/m3) andρf is 0.1%~0.5%, Fracture parameters increase withρf increasing,ρf is 0.3% having best effects for K IC and G F,ρf is 0.3% having best effects for CMODC .Taking into account economic factors,we considerρf is 0.3% having best effects.(4)Carbon fiber plays a main role in improving fracture properties of C-P HFRC,but polypropylene fiber's effects is not very obvious.When polypropylene dosage is 0.9kg/m3 and carbon fiber volume content is less than 0 .3%,the impacts of hybrid fiber upon fracture parameters display good hybrid effect.