Date of Award

12-2006

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Civil Engineering

Advisor

Rangaraju, Prasada Rao

Abstract

The failure of concrete repairs is mainly due to improper selection of repair material based on individual repair material properties, without investigating the compatibility between repair material and substrate concrete. In this dissertation the compatibility between eight repair materials and substrate concrete was investigated in three stages. First, individual properties of the repair materials such as setting time, flow, compressive strength, flexural strength, split tensile strength, bond strength, drying shrinkage, freeze-thaw resistance, and permeability, were determined using standard ASTM test procedures. Second, the compatibility was investigated using a composite beam under third point loading. Third, the correlation of repair material properties with the compatibility was investigated to predict the durability of the concrete repair. Based on these studies, a test method is proposed to examine the compatibility between repair material and substrate concrete.
In the first stage, many variations in the material properties were observed among the eight repair materials. In the slant shear bond strength determination of the repair materials, it was observed that the failures of the composite cylinder did not occur on the slant surface for all repair materials as selected. Those types of failure lead to different values of the bond strength for the same repair materials. From the experimental and finite element method, it was observed that the bond strength of the repair materials and the mode of failures depended on (i) mechanical properties of the repair materials relative to the properties of substrate mortar (ii) surface texture of the slant surface, and (iii) type of curing methods used. Based on these findings, suggestions were made to improve the ASTM C928 specification.
In the second stage, the flexural strength, failure patterns, and load-deflection curves of the composite beam specimens were compared with the similar results of a control beam to assess the compatibility. It was observed that significant differences in compressive, flexural strength, and drying shrinkage between the repair material and substrate concrete caused incompatible failures.
In the third stage, it was observed that no significant correlation of the individual repair material properties exist with the compatibility and, hence, the durability of the concrete repair.

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