(15) In a freshly mixed concrete, which of the four cement minerals could be the
ID: 1732499 • Letter: #
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(15) In a freshly mixed concrete, which of the four cement minerals could be the most active one? How about in a 2-year old concrete? A. C3A, CaAF; of the following materials could be the best choice B. C3S, C2S; C. C3A, C2S D. C2S, C3A. want to re-open a concrete pavement under repair to public traffic in 3 hours, whiclh A. Sulfoaluminate cement; B. Magnesium phosphate cement; C. Type V Portland cement; D. Type IV Portland cement+ CaCl2; E. All of above; F. (A&B;). (17) Type V cement A. has higher weight percentage of C,S to improve the sulfate resistance; B. has lower weight percentage of C3A to improve the sulfate resistance; C. has higher weight percentage of C4AF to improve the sulfate resistance; D. is much finer to increase early age strength so that the sulfate resistance can be enhanced (18) Which of the descriptions about cement fineness is correct? A. Typical fineness of Type III Portland cement is 550 m/kg B. The finer the cement, the higher the long-term strength when keeping wic constrant; C. Finer cement can generate more heat when totally hydrated; D. none of above Which of the following supplementary cementitious materials is much finer than Portland cement? (19) A. Fly ash; B. Calcined clay; C. Silica fume; D. Natural pozzolan (20) Bleeding and segregation of fresh concrete A. can enhance strength of concrete as the effective w/c is reduced; B. can mitigate plastic shrinkage induced cracking; C. are phenomena of phase separation; D. can be avoided by using coarser aggregate.Explanation / Answer
15)C3A is most active mineral and liberates high heat in first few days of hydration.C2S is responsible for later gain of strength. Hence option C is correct.
16)option F is correct because both these cements give high early strength and rapid action which is desirable here.
17)option B is correct.
18)Finer cement has more specific area.Hence more heat of hydration will be liberated.
Hence option C is correct.
19) Silica fume is highly reactive cementitious material of neraly 85% smaller size than Ordinary cement.
Hence option C is correct.
20)Both are phase seperation.Hence option C is correct.
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