Multi-Scale Design for Durable Repair of Concrete Structures.

Abstract

The huge flow of material and energy driven by concrete global production and consumption, and by the rapid deterioration of concrete infrastructure systems, have created great economic, social and environmental impacts worldwide. Presently it is difficult to meet the challenge of sustainable infrastructure development with traditional brittle concrete. Additionally, the limitations of current concrete repair technologies and materials are evidenced by the fact that about half of all concrete repairs fail. Furthermore, disconnect between material engineering, system durability assessment, and structural application often causes breakdowns within the overall durability design.

This dissertation fundamentally addresses this technology bottleneck by developing and demonstrating a new multi-scale design framework for durable repair of concrete structures. This is accomplished through the establishment of links between the development, assessment, and implementation of an innovative ductile repair technology that tackles major concrete deterioration problems at different length scales.

More specifically, critical repair material properties that influence each deterioration stage are determined and engineered into an innovative High Early Strength Engineered Cementitious Composites (HES-ECC) with high tensile ductility and self-controlled tight crack width. The ECC design is achieved through micromechanical tailoring of matrix and fiber/matrix interfacial properties. A quality control technique is also developed for minimizing material variability and optimizing robustness.

In order to implement ECC material in complex field environments, a comprehensive understanding of its mechanical properties, durability, and interaction with existing concrete under various environmental exposure and mechanical loading conditions is obtained. First, the age-dependent mechanical and shrinkage properties are experimentally characterized. Simulated ECC repaired systems subjected to various loading and environmental exposure conditions are then investigated for damage behavior. ECC repair is discovered to effectively suppress the three major deterioration mechanisms in concrete repairs: (a) cracking and interfacial delamination due to restrained volume change, (b) reflective cracking due to stress concentration from pre-existing concrete cracks, and (c) chloride penetration that initiates corrosion of embedded steel. Furthermore, it is elucidated that ECC remains durable under combined mechanical loading and aggressive chloride exposure. Finally, the applicability and durability of the newly developed ductile repair technology is field demonstrated in a bridge repair project in Southern Michigan.