| Composite concrete column is a novel type of composite concrete structure.The outer component of column is prefabricated with reinforced high-performance concrete,the inner component is directly cast poor-performance plain concrete.The mechanical properties,environmental friendly characteristics and economic benefit of components have been improved by optimizing the configuration of materials.A new design namely ECC/RC column,which comprising both inner plain concrete component and outer reinforced ECC component,has attracted interests of researchers and significantly enhances energy dissipation capacity.However,as the key material of preparing ECC,imported PVA fiber is expensive with refined quartz sand and fly ash are relatively in short supply.The use of domestic PVA fibers and replacement of fine aggregate to reduce ECC costs requires further research.Meanwhile,the composite concrete column is more suitable for the construction method of prefabricated assembly.However,the interface design and prefabricated construction method of the column needs further study.In order to relatively reduce the cost of composite concrete columns,enhance energy dissipation capacity,and simplify their interface design and prefabrication process,this paper proposes the use of PVC pipe as a one-time formwork to form an external ECC-PVC pipe concrete composite column.Firstly,research has been conducted on the mechanical properties of ECC using domestic PVA fibers and recycled glass as alternative activator or fine aggregates.Secondly,the interfacial bonding property of the PVC pipe-concrete and shear reinforcement measures were explored.Thirdly,the axial compression experiment research of external ECC-PVC pipe concrete composite column was carried out.The details are as follows:(1)The effect of using glass powder as supplementary cementious material or using glass sand as fine aggregates on the flexural/compressive strengths,flexural toughness and uniaxial tensile strength of engineered cementitious composites(ECC)was investigated.The test results indicate: replacing recycled glass as alternative activator or fine aggregate has less influence on flexural strength while increase the compressive strength;recycled glass fine aggregates improve capacity of multiple crack propagation;All ECCs containing recycled glass as alternative activator or fine aggregates present the multiple-crack and strain-hardening phenomena under bending load with excellent mixture design.Especially,the average ultimate tensile strain of ECC singly incorporating glass powder as alternative activator is close to 3%.(2)This paper adopted the "push-out test method" to study the interfacial bonding property of PVC pipe and concrete.Nine conventional PVC pipe bond test specimens and two additional 90-degree hooked bars bond test specimens were designed.The test results show that the interfacial bonding property of PVC pipe with the concrete is extremely small,which is recommended to consider it as the non-interfacial bonding property;with adding 90-degree hooked bars as shear connector,the shear-bond capacity of the interface between the PVC pipe and concrete is greatly improved.(3)In order to study the behaviour of composite columns under axial compression,ten ECC-PVC-RC composite columns,two reinforced ECC columns and two ordinary reinforced concrete columns were designed.The influences of different parameters on its failure mode,peak load,ductility coefficient,and energy dissipation coefficient were analyzed.The test results show that,before peak value,the ECC-PVC-RC series composite columns has many longitudinal fine cracks.After peak value,the fine cracks continue to differentiate and develop new cracks.The columns show excellent ductility,energy dissipation capacity and integrity.In addition,internal PVC pipe measures can simplify the prefabrication process and improve the ductility and energy dissipation capacity of the composite columns.The addition of 90-degree hooked bars can effectively improve the integrity of the component and increase its axial bearing capacity. |
