Experimental Research And Analysis On Mechanical Properties Of Ocean Aggregate Concrete Members With GFRP Bars

Ocean aggregate concrete(OAC)is a new type of concrete,and it is made of coral reef broken and screened as coarse aggregate and fine aggregate(sea sand,coral sand,river sand),sea water and cement in a appropriate proportion.The research,development and utilization of OAC not only effectively save the transportation cost of coarse aggregate,fine aggregate and fresh water in the construction of islands and reefs,but also effectively solve the environmental problems caused by the stacking and occupation of abandoned coral debris,and can promote the development process of island and reef engineering construction,and effectively improve the the economic benefits of military and civil engineering construction of the South China Sea Islands.At the same time,the consumption of river sand and fresh water resources in our country is huge,and the supply is short in some areas.However,there are abundant sea sand and sea water resources in the ocean.The development and utilization of sea sand and sea water resources can alleviate the shortage of construction sand and fresh water.Glass fiber reinforced plastic(GFRP)material has the characteristics of corrosion resistance,lightweight and high strength.The combination of GFRP bars and OAC forms the OAC structure with GFRP bars.The intensive research on the mechanical properties of OAC and OAC members with GFRP bars(GOAC)or anti corrosion reinforcements has great significance to the construction of offshore islands and reefs and offshore engineering,and it has great application value and promotion prospect.The main contents and conclusions of this paper are as following.To this end,we carried out relevant research,the main research work and results are as follows.Based on the axial compression tests of 252 OAC(coral,sea sand and sea water)blocks and 56 short column specimens,the effects of variable parameters on the axial compression properties of the specimens were investigated,such as sea sand percentage,concrete strength,mass ratio of water reducing agent to cement,water for mixing and curing,type of mineral admixtures,anti rust method,longitudinal reinforcement ratio,stirrup spacing,section size,strain patch method and exposure age in marine tidal zone.The physical and mechanical performance indexes,failure modes,longitudinal reinforcement strain,stirrup strain,and load-displacement curves of the specimens were obtained,and the influence rules of various parameters on the physical and mechanical performance indexes were analyzed.The grey theory was used to analyze the influence degree of the various parameters on the mechanical properties of the specimens.At the same time,the relationship between the compressive strength of OAC cylinder and cube,the stress-strain constitutive equation of OACunder uniaxial compression and the stress-strain constitutive model of OAC(SSSWC)column confined by GFRP bars were fitted.The results show that the strength and slump of OAC can meet the needs of construction engineering.The main failure modes of OAC are aggregate splitting failure and cement stone cracking failure.The dry density of OAC is between 1983 and 2143kg/m~3.The load-circumferential strain curve of GFRP bars is bilinear.The influence of the sea sand percentage and the amount of water reducing agent on the mechanical properties of OAC is fluctuating.The type of mixing and curing water(sea water and fresh water)has no significant effect on the mechanical properties of the specimens.Mineral admixtures can improve the mechanical properties and durability of marine concrete.When P and G,epoxy and rust inhibitor are added,the corrosion resistance of OAC columns is remarkable.Within 270 days of exposure,the stiffness and bearing capacity of OAC columns can be significantly strengthened,when specimens add the P+G+H or P+G+Z.The influence of concrete strength on the axial compression behavior of GOAC columns is significant.PVC pipe has a certain corrosion resistance effect on reinforced OAC columns,but has little effect on mechanical properties of GOAC columns.The compressive stress-strain constitutive curves of OAC and the confined OAC column are in good agreement with the experimental curves.The initial stiffness,peak load,ductility and energy consumption of GOAC specimens are generally increasing as the increase of longitudinal reinforcement ratio.The change of stirrup spacing has no significant effect on the bearing capacity of GOAC columns.As the increase of section size,the initial stiffness and peak load of GOAC columns increase,and the ductility fluctuates up and down.The influence law of exposure age(T<270d)on the mechanical properties of OAC specimens is not significant.Based on the flexural test of 20 beams specimens with GFRP bars,the effects of variable parameters on the flexural properties of the specimens were investigated,such as sea sand percentage,reinforcement ratio,shear span ratio and exposure age.The mechanical property index,initial crack width,failure mode,the longitudinal reinforcement strain,strain of concrete section and the load-deflection curve of specimens were obtained,and the influence law of variable parameters on the mechanical property index was analyzed.Influence degree of each influencing factor on the mechanical properties of the specimen was analyzed.The results show that the load-deflection curve of GOAC beams is bi-linear.The cross-section strain distribution of GOAC beams meets the plane section assumption.The effect of reinforcement ratio on the flexural behavior of GOAC beams is significant.The ABAQUS was used to establish the numerical model of GOAC members.The numerical results are in good agreement with the experimental results,which prove the validity and feasibility of the numerical model of GOAC members.The influence of concrete strength,the type of FRP bars and reinforcement ratio on the flexural behavior of OAC beams is analyzed.The range method was used to analyze the influence of various factors on the mechanical properties of the specimens.The results show that the concrete strength and the type of FRP bars have great influence on the peak load and deflection.With the increase of reinforcement ratio,the peak load of FRP reinforced marine concrete beam gradually increases,but the peak deflection in the middle of the span gradually decreases,and the change of ductility and energy consumption is not significant.Based on the test results of axial compression and bending,the peak stress and strain calculation models of OAC columns confined with GFRP bars are proposed.The calculation formulas of bearing capacity of OAC columns with GFRP bars and PVC pipes are modified.Based on the codes of China,the United States and Canada,the calculation formula of flexural capacity of GOAC beams is modified,and its calculated value of the modified formula is in good agreement with the test value.The research results enrich the experimental data and theoretical content of OAC and offshore concrete structures.It provides basic data and technical support for the further development of OAC structure.It can provide reference and basis for the construction of islands and reefs under the strategy of strengthening the sea.