Development of epoxy-organoclay nanocomposite as high performance coating and as matrix material of durable GFRP composite for civil engineering applications.

摘要

The degradation of concrete structures is a major issue faced by many countries around the world. Available data on polymer-organoclay nanocomposites indicates the potential of this kind of material to be employed as high performance coating to enhance the durability of concrete structures, or as matrix of fiber reinforced polymers (FRP) to enhance the durability of FRP-retrofitted structures or structures with FRP components. To perform an in-depth assessment of the applicability of nanocomposites in civil engineering, the present thesis will focus on the synthesis, testing and characterization of epoxy-organoclay nanocomposite as well as GFRP made with epoxy-organoclay nanocomposite matrix. Direct comparisons with neat epoxy and normal GFRP composite will be performed.;Epoxy-organoclay nanocomposites were fabricated using the in-situ polymerization method. The prepared epoxy nanocomposites were found to exhibit intercalated structure with some exfoliated silicate layers. The results from various tests show that organoclay introduction increases the flexural and tensile modulus of epoxy at the expense of reduced strength and failure strain, but has little effects on the Vickers hardness. Both the thermo-mechanical property and thermal stability of epoxy are enhanced by the incorporated organoclay. However, the wear resistance of epoxy becomes worse with the introduction of organoclay.;The water/solution absorption behaviors of epoxy nanocomposite at different temperatures were studied through the moisture absorption test. At room temperature, the diffusion of water and salt solution in neat epoxy and 3wt% epoxy nanocomposite slightly deviates from the Fickian diffusion; while at 60°C, the diffusion of water and alkaline solution in both materials significantly deviates from the Fickian diffusion. In each case, the weight gain rate of epoxy nanocomposite is lower at the initial stage but becomes higher at the subsequent stage, and the equilibrium weight gain of nanocomposite is higher than that of neat epoxy. To examine the barrier performance of epoxy nanocomposite coating for concrete, water vapor transmission test and salt water spray test were conducted for thin concrete specimens with and without coating. When epoxy nanocomposite coating is applied in place of neat epoxy coating, resistance of concrete to both moisture transmission and chloride penetration are significantly improved. This is because the traveling path of water or solution in epoxy is significantly increased due to the presence of silicate layers with large aspect ratio.;GFRP nanocomposite was fabricated using the vacuum assisted hand lay-up method. The durability of GFRP nanocomposite was studied by tensile testing after samples were aged under three different environmental conditions, including elevated temperature, alkaline immersion and freeze-thaw cycling. The tensile properties of both GFRP composite and nanocomposite degrade significantly with increasing temperature or increasing immersion time in alkaline solution. Interestingly, the degradation rate of GFRP composite under these two conditions is reduced when epoxy-organoclay nanocomposite is used as the matrix material. This can be attributed to the improved barrier property and thermal stability of the nanocomposite. When exposed to freeze-thaw cycling, the tensile properties of both materials degrade first and then level off with increasing aging time. However, in this case, organoclay introduction has little effects on the degradation rate of GFRP composites.;To further understand the degradation mechanisms of GFRP composite and to study how epoxy nanocomposite matrix delay the degradation of GFRP composite, material characterization analysis were conducted for GFRP composite and nanocomposite samples aged in alkaline solution at 60°C. After aging, hydrolysis, chain scission and dehydration are found to occur in both epoxy and nanocomposite matrices, leading to reduction in the Vickers hardness of matrix materials and storage modulus of GFRP samples. The fiber-matrix interface of GFRP sample is found to be weakened and thickened with the entrance and residual of alkaline solution. Moreover, glass fibers embedded in GFRP samples are corroded after alkaline aging. All these changes contribute to the tensile property degradation of aged GFRP. The effects of organoclay introduction on the degradation of matrix, fiber-matrix interface and fiber reinforcements of GFRP samples are complicated.;Epoxy coatings are commonly used for the surface protection of reinforced concrete structures and GFRP composites have been used in the construction industry as structural components or for the rehabilitation of concrete structures. The greatly improved moisture barrier performance of epoxy-organoclay nanocomposite coating and the improved alkaline resistance of GFRP nanocomposite are therefore important findings of practical significance.