Mechanical behaviors of recycled agregate concete reinforced rebars

Wei Li

Doctoral thesis

Abstract:

To change the extensive production methods of the construction industry and achieve sustainable development, the durability of concrete structures needs to be improved. In addition, the circulation and regeneration of waste concrete are also conducive to environmental protection. Corrosion of reinforcing steel in concrete can cause rusting pressure, leading to cracking and even peeling off the concrete protective layer. This could seriously affect the bearing capacity and durability of the concrete structure. In the recycled aggregate concrete, the special microstructures such as the complex aggregate/mortar interface and the micro-cracks may have many effects on the rust cracking process. In this paper, the microstructure and rust cracking process of recycled aggregate concrete are studied. And the rust cracking mechanism of recycled aggregate concrete structure is analyzed deeply by means of experimental study and theoretical analysis. The rust cracking performance of recycled aggregate concrete was studied and discussed. The main research contents were as follows: (1) The mechanical properties and durability of recycled aggregate concrete at different ages under 5 different substitution rates were studied experimentally. The performance of different kinds of interfacial transition zone in recycled aggregate concrete was quantitatively tested by nanoindentation test technique. By revealing the characteristics of interface transition zone of recycled aggregate concrete and comparing with ordinary concrete, the paper explored the essential reason of the change regularity of macroscopic material properties of recycled aggregate concrete. In addition, this paper analyzed the mechanism of recycled aggregate concrete material performance inferior to ordinary concrete, and discussed the reference significance of test results for the engineering application of recycled aggregate concrete. (2) The corrosion of recycled aggregate concrete specimens with different regeneration rate was measured by wet-dry cycle accelerated method. In the experiment, the thickness of rust layer at crack initiation of recycled aggregate concrete protection layer was tested. In this paper, the filling behavior of corrosion products in the pores of recycled aggregate concrete and cracks were studied. The structure of the rust layer at the interface of steel/concrete and the filling of rust in concrete were observed by SEM and EDX analysis of the specimen. The distribution of the rust-filled area was quantitatively studied, and the filling condition of rust products in the cracks was observed and analyzed. (3) The theoretical prediction model of mechanical parameters of recycled aggregate concrete was established. Based on the meso-inclusion theory, the recycled aggregate concrete was regarded as a four-phase composite material composed of aggregates, mortar, interfacial layer and initial defect. The model of predicting the elastic modulus was established by two steps. Combined with elastic mechanics, the thickness of rust layer of recycled aggregate concrete was predicted. The corrosion-induced concrete cracking model in the complete cracking stage of protective layer was established, and the results were compared with the experimental results.

Abstract:

To change the extensive production methods of the construction industry and achieve sustainable development, the durability of concrete structures needs to be improved. In addition, the circulation and regeneration of waste concrete are also conducive to environmental protection. Corrosion of reinforcing steel in concrete can cause rusting pressure, leading to cracking and even peeling off the concrete protective layer. This could seriously affect the bearing capacity and durability of the concrete structure. In the recycled aggregate concrete, the special microstructures such as the complex aggregate/mortar interface and the micro-cracks may have many effects on the rust cracking process. In this paper, the microstructure and rust cracking process of recycled aggregate concrete are studied. And the rust cracking mechanism of recycled aggregate concrete structure is analyzed deeply by means of experimental study and theoretical analysis. The rust cracking performance of recycled aggregate concrete was studied and discussed. The main research contents were as follows: (1) The mechanical properties and durability of recycled aggregate concrete at different ages under 5 different substitution rates were studied experimentally. The performance of different kinds of interfacial transition zone in recycled aggregate concrete was quantitatively tested by nanoindentation test technique. By revealing the characteristics of interface transition zone of recycled aggregate concrete and comparing with ordinary concrete, the paper explored the essential reason of the change regularity of macroscopic material properties of recycled aggregate concrete. In addition, this paper analyzed the mechanism of recycled aggregate concrete material performance inferior to ordinary concrete, and discussed the reference significance of test results for the engineering application of recycled aggregate concrete. (2) The corrosion of recycled aggregate concrete specimens with different regeneration rate was measured by wet-dry cycle accelerated method. In the experiment, the thickness of rust layer at crack initiation of recycled aggregate concrete protection layer was tested. In this paper, the filling behavior of corrosion products in the pores of recycled aggregate concrete and cracks were studied. The structure of the rust layer at the interface of steel/concrete and the filling of rust in concrete were observed by SEM and EDX analysis of the specimen. The distribution of the rust-filled area was quantitatively studied, and the filling condition of rust products in the cracks was observed and analyzed. (3) The theoretical prediction model of mechanical parameters of recycled aggregate concrete was established. Based on the meso-inclusion theory, the recycled aggregate concrete was regarded as a four-phase composite material composed of aggregates, mortar, interfacial layer and initial defect. The model of predicting the elastic modulus was established by two steps. Combined with elastic mechanics, the thickness of rust layer of recycled aggregate concrete was predicted. The corrosion-induced concrete cracking model in the complete cracking stage of protective layer was established, and the results were compared with the experimental results.

Keywords

Recycled aggregate concrete, Corrosion layer, Corrosion product-filled paste, Cracking model, Interfacial transition zone

Keywords

Recycled aggregate concrete, Corrosion layer, Corrosion product-filled paste, Cracking model, Interfacial transition zone

Language used: English

Date on which the thesis was submitted / produced: 21. 5. 2018

Thesis defence

• Date of defence: 28. 6. 2018
• Supervisor: Miroslav Kursa
• Reader: Jaroslav Purmenský, Zdeněk Kuboň, Stanislav Lasek

VŠB - Technical University of Ostrava

Fakulta metalurgie a materiálového inženýrství

Doctoral programme:
Materiálové vědy a inženýrství