3. (a) Using DOE method to design a theoretical concrete mix, needed for the construction of reinforced concrete columns in marine environment. The following materials are available for use: Ordinary Portland cement (CEM I); 20 mm maximum size crushed granite and (uncrushed) river sand as coarse and fine aggregates, respectively. Specific requirements for the concrete are as follows: Concrete grade C40; maximum water-to-cement ratio of 0.45 and minimum cement content of 360 kg/m3 (BS 8500.1:2006); and slump of 100 mm. The tests on concrete making materials gave the following results: • Specific gravity values for granite and river sand are 2.65 and 2.60, respectively; • Specific gravity of cement is 3.5; • Fine aggregate grading showed 40% passing 600 mm sieve; and • Assume 5% defective level (k = 1.64) and standard deviation based on 50 results = 3 MPa. [Ans: C = 455 kg/m3, W = 205 kg/m3, FA = 760 kg/m3, W = 930 kg/m3] (b) Redesign the concrete mix if superplasticiser is used to achieve 20% reduction in water content. Comment on the advantages and disadvantages of using superplasticiser in concrete mixes. [Ans: C = 365 kg/m3, W = 164 kg/m3, FA = 840 kg/m3, W = 1026 kg/m3] (c) Redesign the first mix if 20% cement is replaced with fly ash (having cement efficiency factor of 0.30 and specific gravity of 2.40) for the same water to cement ratio. A 30 kg/m3 water reduction is achieved due to the combined use of fly ash and water-reducer. [Ans: C = 360 kg/m3, F = 90 kg/m3, W = 175 kg/m3, FA = 783 kg/m3, W = 957 kg/m3] (d) Compare the three mix compositions and comment on the workability, strength development, durability, and economical and environmental impact of the three mix design.
3. (a) Using DOE method to design a theoretical concrete mix, needed for the construction of reinforced concrete columns in marine environment. The following materials are available for use: Ordinary Portland cement (CEM I); 20 mm maximum size crushed granite and (uncrushed) river sand as coarse and fine aggregates, respectively. Specific requirements for the concrete are as follows: Concrete grade C40; maximum water-to-cement ratio of 0.45 and minimum cement content of 360 kg/m3 (BS 8500.1:2006); and slump of 100 mm. The tests on concrete making materials gave the following results: • Specific gravity values for granite and river sand are 2.65 and 2.60, respectively; • Specific gravity of cement is 3.5; • Fine aggregate grading showed 40% passing 600 mm sieve; and • Assume 5% defective level (k = 1.64) and standard deviation based on 50 results = 3 MPa. [Ans: C = 455 kg/m3, W = 205 kg/m3, FA = 760 kg/m3, W = 930 kg/m3]
(b) Redesign the concrete mix if superplasticiser is used to achieve 20% reduction in water content. Comment on the advantages and disadvantages of using superplasticiser in concrete mixes. [Ans: C = 365 kg/m3, W = 164 kg/m3, FA = 840 kg/m3, W = 1026 kg/m3]
(c) Redesign the first mix if 20% cement is replaced with fly ash (having cement efficiency factor of 0.30 and specific gravity of 2.40) for the same water to cement ratio. A 30 kg/m3 water reduction is achieved due to the combined use of fly ash and water-reducer. [Ans: C = 360 kg/m3, F = 90 kg/m3, W = 175 kg/m3, FA = 783 kg/m3, W = 957 kg/m3]
(d) Compare the three mix compositions and comment on the workability, strength development, durability, and economical and environmental impact of the three mix design.
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