Study On Mechanical Properties And Compressive Stress-Strain Behavior Of Lightweight Aggregate Concrete Reinforced With Hybrid Fibers

As a kind of green building material with good application prospects,lightweight aggregate concrete has a lot of advantages such as light weight,high strength,good insulation properties,energy conservation and environmental protection.An effective enhancement of the mechanical behavior of concrete can be achieved through the incorporation of fibers.The toughness and ductility of LWAC have seen effective improvement by mixing of fiber.And the fatigue resistance and durability significantly of LWAC structures has also been enhanced.Steel fiber is the earliest and most widely used to mix into LWAC,but with a higher density which can not play advantages of LWAC fully.So,synthetic fibers which have high elastic modulus or good ductility are mixed into LWAC to enhance the strength and toughness.Presently,the main factors have been considered in the study of synthetic fiber to improve the mechanical properties of LWAC are the content and length diameter ratio of fibers.Few investigations on the working performance,toughness and uniaxial compressive stress-strain constitutive model of hybrid fiber reinforced LWAC,and that does not form a complete theoretical system yet.Therefore,the mechanical properties and stress-strain curve of hybrid fiber reinforced LWAC are studied in this paper.This paper is study on the impact of carbon and polypropylene fibers in both single and hybrid forms on the mechanical properties and stress-strain curve model of LWAC.By setting three different water-binder ratio and different fiber volume fraction from 0.2% to 0.8%.Light aggregate was designed with high strength crushed stone and LC60 was used as design strength of LWAC.The main contents are:1.The tests of the working performance and mechanical properties of hybrid fiber reinforced LWAC were completed.The effects of water-binder ratio,fiber types and volumes on slump,aggregate floatation,failure mode and mechanical strength were studied.The results show that carbon fiber can reduce the slump and improve strength of LWAC significantly.Polypropylene fiber can inhibit the aggregate floatation effectively and improving the brittle failure of LWAC.Hybrid fiber can enhance the uniformity of LWAC effectively,while improve the failure mode and the mechanical strength also increased.2.Based on the analysis of the splitting compression ratio,flexural compression ratio,toughness ratio and ductility index of hybrid fiber reinforced LWAC,the improvement of the toughness and ductility of LWAC by different fiber types and volumes are studied.The synergy effects and toughening mechanism are analyzed.Research shows that the effect of hybrid fiber on the toughness of LWAC is the most significant under the water-binder ratio of 0.27.The hybrid combination of carbon and polypropylene fibers produces positive synergy effects,and the change of water-binder ratio has little effect on it.Considering the mechanical properties and toughness of hybrid fiber reinforced LWAC,it is suggested that the best content of hybrid fiber is C4P2.3.The test of uniaxial compressive stress-strain curve of hybrid fiber reinforced LWAC was completed.The effects of water-binder ratio,fiber types and volumes for peak stress,ultimate strain,and other characteristic points were analyzed.Based on the the experiment,the relational expression of hybrid fiber reinforced LWAC between axial compressive strength and compressive strength is proposed.The results show that the peak strain and the ultimate strain of LWAC will increase when carbon fiber or hybrid fiber mixed in.The ductility improvement of LWAC which reinforced by carbon fiber or hybrid fiber are better than that of polypropylene fiber,and the improvement is related to the volume fractions of fiber.4.Through the comparison and analysis of the existing constitutive models,a modified model of the stress-strain relationships for hybrid fiber reinforced LWAC under uniaxial compression is established.Based on the regression of the experimental data and considered of interfering factor,the parameter expressions of the ascending and descending branches are obtained.And the relationship between the strain at peak stress and the concrete strength are suggested.The applicability of the modified model was verified.The study on the basic mechanical properties and the uniaxial compressive stress-strain curve model of hybrid fiber reinforced LWAC.These researches have great significance and practical application value for further understanding the mechanical properties of hybrid fiber reinforced LWAC and guiding engineering practice.