CE165 – Midterm Review

CE165 – Midterm Review - This review covers...

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CE165 Midterm Review CE165 – Midterm Review Rosie Chae [email protected] March 18, 2008 This review covers: 1999 CE165 Midt E 1999 CE165 Midterm Exam The powerpoint will be posted on bspace N d t t k t No need to take notes BUT, jot down references as you see necessary Question 1 A tl d t h th f ll i A portland cement has the following composition: 60% C3S, 15% C2S, 13% C3A 12% C4AF 13% C3A, 12% C4AF Will the cement give early strength? Will the cement generate high heat of hydration? In what type of construction should you NOT use this type of cement? Start by analyzing the composition…. Reference: Table 6-6, p. 228
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PC Compounds “Standard” Our Composition Comment Standard composition (type 1) C3S 50-55% 60% HIGH 50 55% C2S 15-20% 15% LOW C3A 5-12% 13% HIGH C4AF 6-10% 12% HIGH ..then look into hydration reaction 2 C3S + 6 H CSH + 3 CH (120 cal/g) 2 C2S 4 H CSH CH (62 l/ ) 2 C2S + 4 H CSH + CH (62 cal/g) C3A + gypsum Ettringite (300 l/ ) M lf cal/g) Monosulfate Reference: p 213-220, table 6-4 The cement will generate high heat of hydration due to it’s high C3S and C3A content, and low C2S content. The cement will also produce more CH and Ettringite/Monosulfate, and less CSH. Compare the strength development… During concrete’s early ages, strength development is dominated by CH and ettringite formation. Since CSH is the best strength contributing hydration product, the cement will have high Reference: Figure 6-10, p 223 early strength, but low long term strength. Construction Application D i bl f i ld Desirable for: emergency repair, cold weather construction U d i bl f h t th Undesirable for: hot weather construction, mass construction (ex. dams) when sulfate resistance is dams), when sulfate resistance is required (ex. sewer)
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Question 1 Wh t d k b t th What do you know about the composition and principal characteristics of the following cement types: Type IS cement, calcium aluminate cement Type IS Cement Blended cement : Portland cement + blast furnace slag (weakly cemetitious & pozzolanic) Slow strength development Low heat of hydration Improved workability High long term strength Low porosity and permeability – good resistance to chemical attacks Good durability Reference: p. 230-239 Calcium Aluminate Cement Major composition: CA High early strength development High heat of hydration Hydrates/Hardens in cold temperatures Hydration product is unstable under high temperature/humidity conditions. It will undergo porosity increase and strength loss Reference: p. 243-246 Question 2 D fi l d i t i l Define pozzolan and give typical examples of both natural and by product pozzolans List the possible product pozzolans. advantages and disadvantages that can arise from the use of pozzolanic admixtures in concrete.
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Pozzolans C i t f ti ( h ) Consists of reactive (amorphous) silica P l i ti Pozzolanic reaction: CH + pozzolan CSH (slow reaction) It needs lime (calcium) to hydrate.
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