Initial setting times of three (3) concrete mixes, which have identical proporti
ID: 1711247 • Letter: I
Question
Initial setting times of three (3) concrete mixes, which have identical proportions of coarse aggregate, fine aggregate, cement and water, are measured. The only difference among these three (3) concrete mixes is the type of cement used. The original concrete mix that contained 100% Portland cement (Mix A) was modified to include 25% fly ash and 75% Portland cement (Mix B) and 10% silica fume and 90% Portland cement (Mix C). What would be the expected initial setting times of these three (3) concrete mixes? a. Setting time of Mix C > setting time of Mix B > setting time of Mix A b. Setting time of Mix B > setting time of Mix A > setting time of Mix C C. Setting time of Mix A = setting time of Mix B = setting time of Mix C d. Setting time of Mix A > setting time of Mix B > setting time of Mix C What factor(s) affect the long-term deflection of a reinforced concrete beam? a. Temperature of the concrete b. Vibratory loads C. Creep and drying shrinkage strains d. Strength of the concrete Concrete tensile strength can be assessed by a bend test (flexural strength), or indirectly assessed by the indirect tensile strength or directly assessed by the tensile strength test. For a given concrete mix, what would be the order of these strength values? a. Flexural strength > indirect tensile strength > direct tensile strength b. Flexural strength > indirect tensile strength = direct tensile strength C. Indirect tensile strength > direct tensile strength > flexural strength d. Flexural strength = indirect tensile strength > direct tensile strengthExplanation / Answer
Answer 8:
(C) as addition of pozzolana such as fly ash or silica fume does not significantly affect the setting time so for all there mix setting time will be same.
Answer 9:
(C) long term deflection of concrete is caused by the creep deflection due to sustained load and drying shrinkage in concrete.
Answer 10:
(a) flexural strength of concrete is higher than indirect tensile strength measured by split cylinder test which is higher than the direct tensile strength.