published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

This study is to compare the performance of recycled aggregate concrete and the impact of up to 50% cement replacement with fly ash on durability. Water content, sieve analysis, standard and modified compaction tests were performed to assess the physical properties of the recycled aggregate concrete. Accelerated aging tests were performed to predict the long term durability of the recycled aggregate concrete. Following Arrhenius modeling and TTS and SIM accelerated aging protocols, a time versus stiffness master curve was created. This allowed the prediction of equivalent age using experimental data and theoretical analysis. To account for environmental exposure, the specimens underwent 24 and 48 hours of wet-dry cycling and subjected. Overall there was an increase in stiffness and strength from the specimens containing fly ash. All tests performed predicted equivalent age beyond the testing period of 144 hrs. and up to 7 years. Specimens containing fly maintained a constant and higher density to environmental exposure. / by Lillian Gonzalez. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

The aim of this study was to assess the strength, durability properties and corrosion resistance of concrete samples using supplementary cementitious blended materials. In this investigation, three supplementary concrete materials (SCMs) were used together with ordinary Portland Cement (OPC) to form cementitious blends at different proportions. The supplementary materials are silica fume (SF), ground granulated blast furnace slag (GGBS) and fly ash (FA). Sixteen (16) different proportions of the cementitious blends were produced. Tests carried out on concrete samples include slump test, compressive strength, oxygen permeability, sorptivity, porosity, chloride conductivity test, resistance to chloride and sulphate attack. The electrode potentials of tested samples were also observed using electrochemical measurements. Concrete specimens prepared with 10%, 20%, 30%, 40%, up to 60% of blended cements replacement levels were evaluated for their compressive strength at, 7, 14, 28, 90 and 120 days while the specimens were evaluated for durability tests at 28, and 90 days respectively. The results were compared with ordinary Portland cement concrete without blended cement. Voltage, and temperature measurements were also carried out to understand the quality of concrete. The corrosion performance of steel in reinforced concrete was studied and evaluated by electrochemical half-cell potential technique in both sodium chloride, and magnesium sulphate solutions respectively. The reinforced concrete specimens with centrally embedded 12mm steel bar were exposed to chloride and sulphate solutions with the 0.5 M NaCl and MgSO4 concentrations respectively. An impressed voltage technique was carried out to evaluate the corrosion resistance of the combination of quaternary cementitious blended cement, so as to get the combination with optimum performance. Improvement of strength, durability, and corrosion resistance properties of blended concrete samples are observed at different optimum percentages for binary, ternary and quaternary samples. The effect of cementitious blends is recognized in limiting the corrosion potential of the tested SCM concrete samples. Generally, the cementitious blends with limited quantity of SF to 10% have the potential to produce satisfactory concrete. These should however be used for low cost construction, where high quality concrete is not required. / Civil and Chemical Engineering / M. Tech. (Chemical Engineering)

The eco-friendly alternatives use is increasing momentum in a conscious effort towards sustainability. In this regards, the relevance and the economic value of using copper slag as a concrete aggregate are explored in this study in order to contribute towards metallurgical waste recycling. Emphasis is placed on the evaluation of the concretes strengthening prepared with copper slag contents and produced under four curing methods: water immersion, water spraying, plastic sheet covering and air-drying. In each curing case excluding for water immersion, was duplicated in indoors (i.e. in the laboratory) and outdoor exposure (so was prone to varying environmental conditions). This was specifically aimed at capturing the effects of tropical weather conditions typical of the Lualaba province in the Democratic Republic of Congo. The control mix was designed to reach 25 MPa of compressive strength. Copper slag was successively incorporated as sand replacement at the following mass fractions: 20 %, 40 % and 60 %. Freshly mixed concrete samples were evaluated for workability. Cube specimens were cast accordingly, cured for 28 days and then tested for density and compressive strength. Results indicated an increase in strength up to 20 % of replacement rate for all the curing methods. Further additions resulted in reduction in the strength, but the rate of reduction depended on curing conditions. The increase in strength was mainly credited to the physical properties of copper slag that could have contributed to the cohesion of the concrete matrix. It has been found that appropriate ways of curing can still achieve greater results than that of the control mix since 80 % of humidity is ensure. The two-way ANOVA test performed on the 28-days compressive strength values confirmed the significant influence of the curing methods, of copper slag content and the interaction between them. It has been found that considerable influence is attributed to copper slag content and that warm environmental conditions further extend the concrete strengthening. / College of Engineering, Science and Technology / M. Tech. (Chemical Engineering)