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Abstract The recycling bio-waste shells problem has grown more and more serious in recent years and many efforts have been made to solve this problem. One possible solution is to put these bio-shells into concrete and recycle them as building materials using the aggregate matrix concrete approach. To verify the engineering feasibility, the mechanical properties of bio-shells aggregated concrete were invested via gradient substitution rates at 10%, 30%, and 50% with a total of 78 groups of specimens in this paper. Our results show that the mechanical properties of the concrete were enhanced in maximum flexural strength and maximum compressive. Economic performance was also analyzed and found that the costs of frame-shear structure, frame structure, and tube-in-tube structure were reduced by 10.2%, 10%, and 10.3%. The carbon environmental assessment also shows superiority in the carbon reduction of a single specimen with various rates of the shell. In summary, compared with ordinary concrete materials, it is very possible to use waste bio-shells as a substitute for aggregates to develop the sustainable recycling development of concrete materials.

The recycling bio-waste shells problem has grown more and more serious in recent years and many efforts have been made to solve this problem. One possible solution is to put these bio-shells into concrete and recycle them as building materials using the aggregate matrix concrete approach. To verify the engineering feasibility, the mechanical properties of bio-shells aggregated concrete were invested via gradient substitution rates at 10%, 30%, and 50% with a total of 78 groups of specimens in this paper. Our results show that the mechanical properties of the concrete were enhanced in maximum flexural strength and maximum compressive. Economic performance was also analyzed and found that the costs of frame-shear structure, frame structure, and tube-in-tube structure were reduced by 10.2%, 10%, and 10.3%. The carbon environmental assessment also shows superiority in the carbon reduction of a single specimen with various rates of the shell. In summary, compared with ordinary concrete materials, it is very possible to use waste bio-shells as a substitute for aggregates to develop the sustainable recycling development of concrete materials. [ABSTRACT FROM AUTHOR]

The demolishing waste generated due to demolishing of the structures has proved difficult to handle due to scarcity of the dumping space particularly in urban areas. It's use in new concrete solves the problem to some extent but developed product differ in properties both at fresh and hardened state. To overcome the deficiency nylon fibers are proposed in this work. The compressive and tensile strength of proposed concrete at hardened state and workability as fresh property of concrete are studied. Conventional and recycled aggregates were used in equal proportion. Nylon fibers of 1 mm diameter and 25 mm length were used from 0.25% to 2% with 0.25% increment in each successive batch were used. Using 1:2:4 mix with water cement ratio equal to 0.5, total of 10 mixes were designed. Workability of each mix was evaluated by slump cone test. Water curing for 28-days was used for five samples in each batch. Compressive and tensile strength were computed from crushing load determined in universal testing machine. Comparison of the results with those of control concrete revealed that 1.5% of nylon fibers along with 50% recycled aggregates produce maximum compressive strength 930.16 (MPa) with 24% more than conventional concrete (24.16 MPa) and 56% more than recycled aggregate concrete (19.27 MPa) without nylon fibers. The tensile strength of the proposed concrete (3.66 MPa) was noticed 22% and 55% higher than the conventional concrete (3.0 MPa) and recycled aggregate concrete (2.36 MPa) at optimum dosage. Hence the impact of optimized doze of the nylon fiber shows improved strength properties of the concrete. [ABSTRACT FROM AUTHOR]

In this study, 18 short-column lightweight ceramsite concrete samples were prepared in rectangular stainless steel pipes, which were used for axial pressure performance tests that took the cross-sectional length–width ratio of the rectangular stainless steel pipe (1.0, 1.5 and 2.0), the wall thickness of the steel pipe (3 mm, 4 mm and 5 mm), and the strength grade of the filled concrete (C20 and C30) as the main parameters. Then, the failure patterns, axial load–displacement curve, axial load–strain curve, ultimate bearing capacity and the interaction between the steel pipe and concrete in the specimens were measured. The test results revealed that the short-column concrete specimens in the steel pipes exhibited typical shear failure and "waist-bulging" failure under axial compressive loads. In the elastic stage, the bearing capacity of the specimens was able to reach 65–85% of the ultimate bearing capacity, with the residual bearing capacity essentially reaching 70% of the ultimate bearing capacity. Furthermore, the ultimate bearing capacity of the specimens demonstrated an increase with the rise in the strength grade of the filled concrete, with the thickness of the stainless steel pipe and with the decrease in the length–width ratio of the steel pipe cross-section. The specimens exhibited a distinct hoop effect. As the length–width ratio decreased and the hoop coefficient increased, the ductility coefficient and the strength enhancement coefficient basically displayed an increasing tendency, while the concrete contribution ratio exhibited a decreasing trend. [ABSTRACT FROM AUTHOR]

In this study, 18 short-column lightweight ceramsite concrete samples were prepared in rectangular stainless steel pipes, which were used for axial pressure performance tests that took the cross-sectional length–width ratio of the rectangular stainless steel pipe (1.0, 1.5 and 2.0), the wall thickness of the steel pipe (3 mm, 4 mm and 5 mm), and the strength grade of the filled concrete (C20 and C30) as the main parameters. Then, the failure patterns, axial load–displacement curve, axial load–strain curve, ultimate bearing capacity and the interaction between the steel pipe and concrete in the specimens were measured. The test results revealed that the short-column concrete specimens in the steel pipes exhibited typical shear failure and “waist-bulging” failure under axial compressive loads. In the elastic stage, the bearing capacity of the specimens was able to reach 65–85% of the ultimate bearing capacity, with the residual bearing capacity essentially reaching 70% of the ultimate bearing capacity. Furthermore, the ultimate bearing capacity of the specimens demonstrated an increase with the rise in the strength grade of the filled concrete, with the thickness of the stainless steel pipe and with the decrease in the length–width ratio of the steel pipe cross-section. The specimens exhibited a distinct hoop effect. As the length–width ratio decreased and the hoop coefficient increased, the ductility coefficient and the strength enhancement coefficient basically displayed an increasing tendency, while the concrete contribution ratio exhibited a decreasing trend.

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Based on the coupling algorithm of smoothed particle hydrodynamics and finite element method, numerical simulation of high-velocity water jet impacting heterogeneous concrete containing aggregates according to the real concrete CT slices was conducted to study the damage evolutions and fracture characteristics of concrete with real structure. The damage evolution and fragmentation process of heterogeneous concrete were obtained, and the fracture characteristic was compared with homogeneous concrete. The internal energy change laws and the damage and stress evolutions in homogeneous and heterogeneous concretes at different time were investigated. And the failure mechanisms of water jet crushing heterogeneous concrete were revealed. The results show that the concrete elements mainly suffer multi-stage plastic damage accumulation failure induced by water jet impact due to stress wave effect, pressured water wedge effect, water flow scouring effect, squeezing effect of aggregate, and stress concentrations. The failures of upper and deep concrete elements are mainly caused by compressive shear stress, which is combined with tensile stress. In homogeneous concrete, the bowl-shaped broken pit with smooth sidewall and the symmetrically distributed cracks are formed. In heterogeneous concrete, the aggregate will prolong the damage accumulation process and lead to the formation of the abnormal broken pit with irregular and rough contour. Cracks prefer to propagate at interface between aggregate and mortar, and concrete elements at interfaces will suffer the sudden brittle failure caused by stress concentration when the damage accumulates to a certain extent. Overall, the internal energy in concrete first rapidly and then slowly increases, and there is a poorer absorption efficiency of jet kinetic energy for heterogeneous concrete, in which the internal energy of aggregates and mortar is closely related to the specific impact object of water jet. The research results would lay the theoretical foundation for water jet efficiently crushing concrete. [Display omitted] • Water jet impacting concrete with actual aggregates was simulated and verified. • Damage evolution and fragmentation process were investigated. • Energy changes and damage-stress evolutions were compared. • Failure mechanisms of heterogeneous concrete were revealed. [ABSTRACT FROM AUTHOR]