Experimental Study On Mechanical Properties And Microstructure Of Plastic-steel Fiber Reinforced Lightweight Aggregate Concrete

Compared with normal concrete, light weight aggregate concrete (LWAC) boastswith various unique advantages such as light weight, high strength, excellent thermalinsulation effect and seismic resistance, as well as without alkali-aggregate reaction etc.However, most of the present LWACs are still weak in compressive strength, shear andtensile strength, which make it easy to lead to such performance deficiency as brittlefailure. This is why LWAC in China still mainly used in bearing structures of low intensity.The present study shows that fiber can improve the concrete crack resistance, reduce thebrittleness coefficient and effectively improve the mechanical properties of concrete.Plastic steel fiber is characterized by high elastic modulus and tensile strength, which cancombine the advantages of steel fiber and polypropylene fiber. The addition of the plasticsteel fiber can improve the strength and deformation properties of LAWC.Since the concrete with a strength grade of C30is widely used, in this paper, theLWAC of LC30without adding plastic steel fiber is used to measure compressive strength,splitting tensile strength, flexural strength, flexural toughness and impact strength of theconcrete with different mixing amount of plastic steel fiber (5kg/m3,7kg/m3,9kg/m3,11kg/m3,13kg/m3respectively). The influencing mechanism of plastic steel fiber on themechanical properties of LWAC is analyzed and the influencing law of the differentmixing amount of plastic steel fiber on the various mechanical properties of LWAC isconcluded. And finally, in light of these mechanical properties, the reasonable mixingamount of plastic steel fiber used in structure LWAC is suggested. The results areconcluded as follows:Plastic steel fiber can help to improve the compressive strength of LWAC to a certaindegree, and can especially improve the strength of concrete at early stage. Plastic steelfiber has no obvious effect on the initial cracking strength of LWAC, but can significantlyimprove the tensile strength, the flexural strength, the impact resistance and the toughness.Based on the various performance indexes, including strength index, brittleness index, anti-cracking index, impact ductility index, it is suggested that the optimal amount of fibermixed in LWAC should be9kg/m3.The macroscopic mechanical properties of reinforced LWAC with plastic steel fiberare the reflection of its microstructure. Using Scanning Electron Microscope (SEM), themicrostructure research of the reinforced LWAC with plastic steel fiber is mainly done inthe two types interfacial transition zone (ITZ). One is ITZ between LWA and hardenedcement paste (HCP), and the other is ITZ between fibers and HCP. It is noted that the ITZbetween fibers and HCP is the Weak zone of reinforced LWAC with plastic steel fiber.