Effectiveness of high-strength composites as structural and protective coatings for structural elements

Fiber Composites made of carbon or glass fibers and organic polymers are being successfully used to strengthen plain, reinforced, and pre-stressed concrete structures. The advantages are high strength, lightweight, and resistance to corrosion. However, they are susceptible to fire and in some cases, degrade under UV radiation because the matrix consists of an organic polymer.; Organic polymers have also been used as protective coatings for more than thirty years. The impermeable membrane seals the concrete, preventing the ingress of salts, thus improving their long term durability. But the impermeability also results in delamination because trapped water accumulates at the interface.; The results presented in this dissertation deal with inorganic and polymer modified cement systems for coating and strengthening of concrete and steel structures. The coating system consisted of polymer modified cementitious materials or inorganic matrices. These matrices, reinforced with micro or discrete short fibers, were evaluated under wetting and drying, freezing and thawing, and scaling conditions. The potassium alumino silicate (inorganic) matrix that was studied is water based, has no toxins, and is fire resistant. It bonds well with concrete, steel, and wood. The results indicate that the matrices can be used as a protective coating against wetting and drying and scaling conditions. If the members are water saturated, the coatings do not provide protection against freezing and thawing.; The inorganic matrix was also evaluated for strengthening applications. Carbon fibers in the form of tows and sheets were used to obtain the strength increases. The strengthened samples were evaluated under wetting and drying and scaling conditions. The results indicate that inorganic matrix can be successfully used for strengthening plain and reinforced concrete members. The strengthening system is durable under the conditions tested. The matrix can also be used to coat steel beams.; Analytical procedures are presented for the analysis and design of plain and reinforced concrete members strengthened with high strength composites. The inorganic matrices provide a different failure pattern and low carbon strain at failure as compared to the organic matrices. These differences should be accounted for in the analysis.