BS in Materials Engineering
Materials Engineering Department
Specific proportions of Portland cement, fly ash, and blast furnace slag cement mixtures where chosen by a ternary phase diagram to be investigated. By experimental testing and company data history fly ash was limited to not exceed 30% and contribution of Portland cement must be over 50%. Ten chosen mix designs were batched by following ASTM C305-94 and cured for twenty-eight and forty-two days, the extended cure length allows the reaction of pozzolanic material with calcium hydroxide to complete. Compressive strength testing at forty-two days yielded low strength for mix designs with 20% or less Portland cement compared to our 100% Portland cement control. The three mix designs with 30% Portland cement reached the greatest strength of all ternary designs and were averaged to be 1742 psi lower than the 7406 psi control, this is due to the more sufficient amount of calcium hydroxide produced for reacting with the fly ash, compared to the low, 10% and 20%, Portland cement mixes. The ternary design consisting of 30% Portland cement, 20% fly ash, and 50% slag exhibited the highest strength, 5879 psi, 1527 psi below the control. With the cementitious reactions being of greatest significance, SEM analysis was performed on selected mix designs. Images show cementitious reactions as hair like structures throughout the sample, additional observations of un-reacted spherical fly ash particles are present along the fracture area. Fly ash being a low strength contributor, it can be determined as a reason of low strength failure. With use of ternary mix designs environmental impacts are reduced; additionally meeting new California Air Resource board and California Department of Transportation pozzolanic regulations.