Study On Mechanical Properties And Toughness Of Steel Fiber High Strength Lightweight Aggregate Concrete

High-strength lightweight aggregate concrete(HLAC)is widely used in high-rise building flexible foundations,hydraulic marine engineering,high-rise and long-span structures,various civil engineering projects due to its high-strength and light-weight performance advantages.However,the brittleness of HLAC is more obvious with the increase of its strength.In order to improve the toughness of HLAC,13 mm micro-type(length to diameter ratio 65),25 mm end hook type(length to diameter ratio 50)and 30 mm corrugated steel fiber(length to diameter ratio 38)are used to improve the mechanical properties of HLAC.(1)Different steel fibers are added to HLAC,and the effects of steel fiber type,volume fraction and hybrid ratio on the basic mechanical properties such as compression,splitting tensile strength and flexural strength are investigated.The research showns that all strengths are improved with the increase of the volume fraction.However,the workability is poorer under large volume fraction.It is recommended that the amounts of micro and large-sized steel fiber are 0.5%~1.0% and 1.0%~1.5% respectively.At the same volume fraction,the micro steel fiber has the best reinforcement effect,especially for splitting tensile strength.The large-sized hooked steel fiber also has better effect on the flexural strength of HLAC,while the corrugated steel fiber has a less reinforcement effect on various strengths,especially for compressive and flexural strengths.The hybrid steel fiber with proper hybrid ratio has positive hybrid effect on the mechanical properties,but the effect is not obvious.(2)The load-displacement curves of non-standard trabecular specimens were collected by four-point bending test.Combined with Japan JSCE-SF4,CECS13:2009 and JG/T 472-2015,the toughness index,bearing capacity variation coefficient and equivalent bending strength ratio of different steel fiber high-strength lightweight aggregate concrete(SFHLAC)are evaluated.The results show that the toughness factor and toughness index of SFHLAC are improved with the increase of fiber volume fraction,and the fiber type has a great influence on the elastoplastic properties of SFHLAC.At the same volume fraction,the micro steel has the best effect on improving the toughness and ductility of HLAC.The hooked steel fiber has poorer toughening effect in the large deflection stage,while the corrugated steel fiber has the worst toughening effect in the whole deflection stage.Appropriate amount of micro and large-sized hybrid steel fiber can improve the toughness of SFHLAC under the large deflection.The equivalent bending strength ratio cannot clearly reflect the toughening difference caused by different fiber volume fraction,sand ratio and water-cement ratio.So,the equivalent bending strength ratio is used to evaluate the toughness depending on the situation.(3)The shear properties of SFHLAC were studied by double-sided direct test.The effects of fiber type and fiber volume fraction on the shear strength and toughness of SFHLAC are investigated.The results show that steel fiber has a great improvement on the shear property of HLAC.The shear strength reinforcing effect is affected by the number of "bridges' fibers" of the sheared fracture surface.The micro steel fiber has a significant improvement on the shear strength and toughness of HLAC,and the shear enhancement at a low volume ratio(0.5% to 1.0%)is better.(4)The strength laws and correlations of SFHLAC are fitted and analyed.The analysis shows that the fitting formula can better reflect the strength law of steel fiber high strength ceramsite lightweight aggregate concrete,which can provide reference for related engineering and research.