Axial Compression Behavior of Square Steel Tube Recycled Aggregate Concrete under Acid Rain Corrosion

Literature Overview

This paper by Chen Mengcheng, Wang Chao, Huang Hong, and Liu Jingjian from East China Jiaotong University investigates the axial compression behavior of square steel tube recycled aggregate concrete (CFST) members subjected to acid rain corrosion. The study combines experimental testing of 11 corroded specimens with finite element analysis (FEA) using ABAQUS, employing two different approaches to model the effects of acid rain corrosion on the structural response. The research addresses an important sustainability and durability issue, as recycled aggregate concrete is increasingly used to reduce construction waste, but its performance under corrosive environmental conditions requires thorough evaluation.

Material and Environmental Context

Recycled Aggregate Concrete

Recycled aggregate concrete (RAC) is produced by replacing a portion or all of the natural aggregate with crushed waste concrete. This practice reduces the demand for natural resources and diverts construction waste from landfills, contributing to sustainable construction. However, RAC typically exhibits lower mechanical properties than conventional concrete due to the presence of adhered old mortar on the recycled aggregate, which reduces the aggregate-paste bond strength and increases the porosity of the concrete.

Acid Rain Corrosion

Acid rain, caused by atmospheric pollution with sulfur dioxide and nitrogen oxides, has a pH below 5.6 and is increasingly prevalent in industrial and urban areas. The acidic environment attacks the cement paste in concrete through acid-base reactions, dissolving calcium hydroxide and calcium silicate hydrate, leading to increased porosity, reduced strength, and degraded durability. For steel tube components, acid rain causes corrosion of the steel surface, leading to wall thickness reduction and degradation of material properties.

Experimental Program

Specimen Configuration

The study tests 11 square steel tube RAC short column specimens subjected to acid rain corrosion. The specimens are designed to represent typical CFST columns in building structures, with square cross-sections and short span-to-depth ratios to ensure axial compression behavior. The acid rain exposure is applied for a controlled duration to achieve a representative level of corrosion damage.

Loading Protocol

The specimens are loaded in axial compression until failure, with load and displacement recorded throughout the test. The load-displacement curves are used to determine the peak load, displacement at peak load, and post-peak behavior of the specimens. The failure mode and damage pattern are documented for each specimen.

Finite Element Analysis

Modeling Approach 1: Wall Thickness Reduction

The first FEA approach models the effect of acid rain corrosion by reducing the wall thickness of the steel tube to account for the material loss due to corrosion. The reduction in wall thickness is determined from experimental measurements of the corroded specimens and is applied uniformly to the steel tube in the FEA model. The concrete properties are kept at their original values, assuming that the corrosion primarily affects the steel tube.

Modeling Approach 2: Material Property Degradation

The second FEA approach models the effect of acid rain corrosion by degrading the material properties of the steel tube, specifically the yield strength and elastic modulus. The degradation factors are determined from experimental testing of corroded steel coupons and are applied to the steel tube in the FEA model. The wall thickness is kept at its original value, assuming that the corrosion primarily affects the material properties rather than the geometry.

Comparison of Results