Study On Mechanical Properties Of Fiber Reinforced Coral Cement Matrix Composites

The construction of Marine islands and reefs requires a large number of building materials,among which the demand for sand and stone is particularly significant.The transportation of raw materials from the inland to the islands is not only expensive but also affects the schedule of the project.Therefore,the preparation of coral concrete using the raw materials such as coral reef,sand and sea water,which exist in large quantities near the islands and reefs,can not only relieve the pressure of resources,but also greatly save the construction cycle.However,the problems of large shrinkage deformation,brittleness,low elastic modulus and bending strength of coral concrete greatly limit its application in the field of development and application.Addition of polyvinyl alcohol(PVA)and polypropylene(PPF)fibers with high elastic modulus into coral concrete can well solve the shortcoming of brittle failure of coral concrete,and enhance the ultimate tensile strain and crack control of coral concrete to some extent.Fiber reinforced coral cement-based composites with light weight,high compressive strength,excellent tensile and bending properties can be developed.Therefore,this paper studied the mechanical properties of fiber reinforced coral concrete by changing the length-diameter ratio and fiber volume dosage of PVA and PPF fibers,and determined the optimal length-diameter ratio and fiber volume dosage of the two fibers,which will provide a basis for the research and promotion of fiber reinforced coral cement based materials in the future.The main research contents and experimental results are as follows:(1)The compressive properties of coral concrete cube and prism block reinforced by PPF fiber with length-diameter ratio of(150,225,300)and length-diameter ratio of(55,88,111)were tested.The effects of fiber types,fiber content and fiber length-diameter ratio on the compressive properties of coral cement based composites were investigated.The conversion relationship between the axial compressive strength and the cube compressive strength index is established.According to the stress-strain test curve,the stress-strain relationship is reasonably simplified,and the corresponding constitutive equation is given.In this paper,the working performance of coral fiber cement-based composites was explored.By adding appropriate thickening agent,the working performance of coral fiber cement-based composites was improved,and the influence of different length-diameter ratio and dosage on the slump of fiber cement base was explored,laying a foundation for the subsequent mechanical properties test research.(2)The bending strength tests of prisms and thin plates were carried out to investigate the influences of fiber types,fiber volume content and fiber length-diameter ratio on the bending performance of fiber coral cement-based composites.The optimal length-diameter ratio and fiber content were determined to provide a basis for the research and promotion of fiber reinforced coral cement-based composites in the future.The crack characteristics of prism and thin plate under bending were described reasonably,the whole curve of bending load-deflection of thin plate was analyzed,and the bending toughness of thin plate at four points under bending was evaluated by using bending toughness index method.(3)The influence of fiber type,fiber volume content and fiber length-diameter ratio on the tensile properties of coral-cement based composites was investigated by direct tensile tests.The conversion relationship between bending strength and bending strength is established.The development of strain-hardening and crack in the tensile process is reasonably described,and the stress-strain relationship is reasonably simplified according to the tensile stress-strain test curve,and the corresponding tensile constitutive equation is given.