The application of tube-filled concrete composite columns is becoming more and more popular. The traditional tube-filled column is easy to rust and expensive to maintain, which leads to the practical need of replacing high-strength aluminum alloy. 7A04 aluminum alloy has high strength and strong corrosion resistance, which is more in line with the material requirements of modern building structures. In view of this, four groups of 7A04 aluminum alloy tube concrete short columns were tested under axial compression, and the corresponding ABAQUS finite element simulation was established. The influence of tube thickness and concrete strength grade on compressive strength, ductility, transverse deformation coefficient, and improvement coefficient of strong concrete strength of composite column is considered in this paper. The results show that the failure mode of composite short columns is central uplift or shear failure. The tube thickness of high-strength aluminum tube has a great influence on the strength of specimens, and the ductility of composite columns decreases with the decrease of the collar coefficient. The finite element model can well reflect the development trend of the load-strain curve, and the formula of composite column bearing capacity proposed by regression analysis can well predict the strength of 7A04 aluminum alloy tubular concrete short column. The research results have a certain reference significance for the structural design of high strength aluminum concrete-filled columns.

The influence of four factors (water-binder ratio, recycled coarse aggregate replacement rate, fly ash substitution rate, and superplasticizer content) on the workabilities and mechanical properties of recycled coarse aggregate self-compacting concrete (RCASCC) was studied using the orthogonal test method. Based on the orthogonal test design and range analysis method of the fresh and hardened properties of RCASCC, the optimal mix is as follows: water-binder ratio of 0.269, recycled coarse aggregate replacement rate of 30%, fly ash substitution rate of 40%, and superplasticizer content of 0.50%. Then, the porosity and aperture size distribution of nine groups of RCASCC were tested by mercury intrusion porosimetry (MIP) at the microlevel. The macroscopic and microscopic relationship was established by combining the results of mechanical property tests and MIP. Fractal dimension D of the B.B. Mandelbrot model was used to study the fractal characteristics of pore volume of RCASCC. Results showed that porosity and strengths are negatively correlated, and the relative strength can be roughly judged according to the porosity. The pore structure of nine groups of RCASCC materials has evident fractal characteristics of irregular shape. The complex pore structure adversely affects strength.

7A04 aluminum alloy has high strength and strong corrosion resistance, and its quality is only 1/3 of steel. Using 7A04 aluminum alloy to replace ordinary steel tube to confined concrete, it can effectively reduce the member section, reduce the weight of the structure, and more in line with the material requirements of large span materials and high-rise buildings. In this paper, nine groups of 7A04 aluminum alloy tube confined high strength concrete long column were tested under axial compression and eccentric compression with aspect ratio and eccentricity as variables. And the corresponding ABAQUS finite element model was established. The results show that the failure phenomena of the nine groups are basically the same, and the specimen deflection curve shape is similar to the sine half-wave curve. The ultimate bearing capacity of the specimen decreases with the increase of aspect ratio and eccentricity. When the axial compression or eccentricity of the specimen is small, the variation of the longitudinal and transverse strain at the midspan is similar in the elastic stage. When the eccentricity is large, the longitudinal and transverse strain at the midspan of the specimen is obviously tensile at one side and compressive at one side at the beginning. Finally, based on the test and simulation results, a formula for calculating the bearing capacity of 7A04 aluminum alloy tube high strength concrete long columns is proposed. This formula can better predict the stable bearing capacity of the specimen, which has certain reference significance for the structural design of 7A04 aluminum alloy tube high strength concrete long columns.

Finding a method to optimize the design of the polyethylene fiber-engineered cementitious composite (PE-ECC) mix proportion is an urgent endeavor. The analytic hierarchy process (AHP) is an efficient decision-making tool for complicated problems with multiple variables and uncertainties. In this study, initial cracking strength, ultimate tensile strength, tensile displacement, and test age, as influencing factors of the PE-ECC optimum mix design were considered. The weightings of the factors were quantified through the AHP method according to the tensile test results of 14 groups of specimens with different mix proportions. The water to binder ratios (0.25, 0.27, 0.29, 0.31), the mineral admixtures (30%, 40%, 50%, and 60%), and the PE ratio (2%) were the three main test parameters for the factors of the PE-ECC tensile properties. The weight of each influence factor was calculated by constructing a matrix, which confirmed that the judgment matrix satisfies the consistency test. The optimum mixture ratio of 30% fly ash and 0.27 water-binder ratio were obtained. The results demonstrate the applicability and rationality of the AHP theory. The findings from this study can be used as a guideline for the optimized design of PE-ECC mix proportions.