New techniques for the rehabilitation of concrete and steel structures

The results presented in this dissertation focus on the development of a durable repair system for concrete structures and an enhanced protocol for durability and corrosion resistance testing of concrete repair materials and coatings for steel structures. The primary characteristics of the repair material are: rapid strength gain, low shrinkage, flowable and develop good bond with aged concrete. The objective was to obtain a matrix composition with shrinkage strains less than the tensile cracking strain capacity. Tensile strain capacity of the matrix was increased using discrete fibers. In the area of accelerated testing, a new test protocol was developed for accelerated testing of coatings and thin repair layers. The objective was to develop response variables that provide clear quantitative measures. This was achieved by incorporating direct tensile pull-off strength of the virgin and deteriorated coatings as the main response variable for determining the durability of coating. Review of the current state of the art indicated that there is a need for durable repair systems and a protocol for accelerated testing. A rapid-set composite formulation that has minimum shrinkage was chosen based on extensive review of all the products that are currently available. The chosen commercial product performance was further improved in the areas of shrinkage strain reduction and improvement of mechanical properties, with specific focus on increasing the tensile strain capacity. Use of admixtures and fibers were found to provide substantial improvements for both areas. The new formulation was used for both horizontal and non-horizontal patch repairs. For accelerated testing, a new response variable, namely, direct tensile (adhesion) strength of coating at various levels of exposures was found to be an excellent quantitative measure. For the exposure itself, deep freezing was added in addition to the current practice of exposure to ultraviolet and salt water spray. Tests were conducted on five commercially available coatings to establish the viability of the proposed protocol. Based on the experimental results and analysis presented in this dissertation, it is possible to formulate long lasting rapid repairs for both horizontal and non-horizontal patches. The system identified gains more than 6500 psi in compressive strength in 3 hours, an ultimate shrinkage strain of 0.000230 in/in has a modulus of rupture of 1198 psi at 28 days with a tensile strain capacity of 0.000457 in/in. The combination of the tensile strain capacity and ultimate shrinkage strain makes it possible to produce durable crack free repairs. The proposed test protocol for accelerated durability test provides a distinct quantitatively measurable response variable. In the current practice corrosion growth measured after long exposure durations are typically less than a few millimeters. The measurement is also difficult because of fuzzy corrosion growth. In the proposed method, growth up to 6 millimeters of corrosion was established using pull-off tests. Pull test values decreased from 1018 psi to 158 psi. The method can also be used for thin repair systems.Ph.D.Includes bibliographical referencesby David P. Caroni