| Summary: | 碩士 === 國立臺灣海洋大學 === 河海工程學系 === 96 === In this study, the effects of fineness of slag in concrete are studied. Several mix proportions and two different water-reducing plasticizers were adopted. The water/binder ratios used are 0.45, the amount of paste is 350 kg/m3, the design compressive strength is 4,000 psi (27.46 MPa). Two fineness batches of slag are used (4,000 and 5,000 cm2/g). The replacement percentages of cement using slag are 25, 35 and 45 %. The amount of water-reducing plasticizer is 1%, the slump value is 18±2cm. Various tests were taken at age of 1, 3, 7, 14, 28 and 56 days.
Results showed that the activity of slag increased as the fineness increased. The early strength development is better for finer slag. In addition, for early age strength 25% replacement of cement using slag showed a higher value than 35% and 45% replacement due to the fact that the early strength of concrete mainly depends on the hydration of cement. Till the end, all specimens reached the designated strength. For fineness of 5,000 cm2/g group, the compressive strength reached 56.14 MPa. At age of 56 days, the compressive strength of higher fineness slag group is higher but difference is not so apparent and all values fall in the range of 50±6 MPa. For higher fineness slag, it can condense the pore structures more effectively such that concrete becomes denser. Due to the above-mentioned reason, adding higher fineness slag let the electrical resistivity of concrete enhance, the water absorption decrease and the penetration of chloride ions become harder. Under the same workability condition, naphthalene salt based water reducing plasticizer has positive contributions to workability, compactness, water absorption, durability and compressive strength. The SEM photos showed that after 28 days the CSH planar structures in concrete continuously grow and make concrete pore smaller such that concrete becomes denser.
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