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CIVL3725 - Construction Materials and Methods > Lecture #2 - Concrete Ingredients - Part 2 > Flashcards

Lecture #2 - Concrete Ingredients - Part 2 Flashcards

1
Q

Name the three different types of failure for a poor mix.

A

Aggregate, paste, bond

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2
Q

What is the ideal failure mode?

A

Combined failure (aggregates, paste, and bond all fail a bit)

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3
Q

Where do normal weight natural aggregates come from?

A

Natural gravel and sand, weathering and erosion of rocks, sometimes requires a bit of processing

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4
Q

What are sound sources of natural aggregates? (rock type)

A

metamorphic and igenous

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5
Q

Define metamorphic.

A

Recrystallization and reorganization of minerals due to pressure, volume, and termperature changes.

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6
Q

Define igneous.

A

Solidifcation of magma and lava

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7
Q

What are unsound sources of natural aggregate? (rock type)

A

shale and siltstone (sedimentary)

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8
Q

Define sedimentary.

A

consolidation and compaction of sediments

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9
Q

What is a sound transport mechanism for natural aggregate?

A

materials at higher elevations than glacier and are untouched

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10
Q

What is a questionable transport mechanism for natural aggregates? Explain.

A

water transport, smoothed by prolonged agitation in water, harder than less abraded sand and gravel but smooth surface can reduce bond with cement paste

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11
Q

How is manufactured aggregate produced?

A

crushing sound parent rocks or crushing air-cooled blast-furnace slag

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12
Q

What are some features of manufactured aggregate?

A

customizable in terms of grading and higher quality as particle elongatoin and layered flakes can be reduced and less likely to be contaminated by clay minerals and organic material

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13
Q

Which has a rougher texture, manufactured or natural aggregate?

A

Manufactured

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14
Q

Which is more uniformly graded: manufactured or natural aggregate?

A

manufactured

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15
Q

How is recyled concrete aggregate made?

A

Demolishing and removing existing concrete, crushing it in crushers, removing embedded items and reinforcement and dirt, wood, etc., grading and washing

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15
Q

What is recycled-concrete-aggregate?

A

Recycled concrete from buildings, pavements, and other structures used as aggregate to be more sustainable

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16
Q

What are the features of recycled concrete aggregate?

A

higher absorption because the hardened cement paste is more porous, lower specific gravity

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16
Q

What do you need to do if absorption is high in your aggregate?

A

add more water for workability, adjust water for concrete mix

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16
Q

Which is less angular, cubical or long: manufactured or natural aggregate?

A

Natural

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17
Q

What is recycled concrete aggregate mostly used for?

A

pavement reconstruction

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18
Q

What might marine-dredged aggregate contain that is not good?

A

seashells (weak), and salt (ruins)

19
Q

What are the sources of marine-dredged aggregate?

A

estuaries, seabed

19
Q

What weight of aggregate needs to be prewetted or kept moist?

A

lightweight

19
Q

Why do we need grading limits?

A

affects proportions, workability, pumpability, economy, porosity, durability, shrinkage

20
Q

Why would you use marine-dredged aggregate even though it sucks?

A

if other resources are not available in your region, as you need to use whatever’s close by for sustainability and cost

20
Q

What is grading?

A

particle size distribution of aggregate

21
Q

What kind of curve does single-sized aggregate grading have?

A

single sharp curve

22
Q

What kind of grading curve does poorly graded aggregate have?

A

two sharp cruves

23
Q

What kind of grading curve does well graded aggregate have?

A

two smooth curves

24
Q

What does the ideal grading curve distribution look like?

A

like a parabola of different sizes

25
Q

Is the volume of paste greater than the voids between aggregates? Why?

A

yes, to provide workability, cohesiveness of the paste matters

26
Q

What is the fineness modulus?

A

sum of percent retained on each sieve (except pan)/100

27
Q

Why can’t we only have very fine sand as aggregate?

A

too expensive

28
Q

Why can’t we only have very coarse gravel as aggregate?

A

mix is harsh and unworkable

29
Q

What is the maximum aggregate size?

A

Smallest sieve that all aggregates pass through (100% passing)

30
Q
A
31
Q
A
32
Q

What is the nominal maximum aggregate size?

A

smallest sieve that majority of aggregate passes through (85 to 95% passing), first sieve that retains aggregate

33
Q
A
34
Q
A
35
Q
A
36
Q

What does maximum aggregate size depend on?

A

Shape and size of concrete member, amount and distribution of reinforcing steel, need to have enough workability so that the concrete can be placed properly without honeycomb or voids

37
Q

Explain why low maximum aggregate size is not economical.

A

Surface covered by paste increases which causes required water and cement to increase so more cement paste is required to provide enough bond which is expensive.

38
Q

What is air-entrainment?

A

Microscopic air bubbles in concrete.

39
Q

What are the features of air entrainment?

A

Increased resistance to freeze and thaw durability, increased resistance to scaling caused by de-icing chemical, improved workability, reduced segregation and bleeding

40
Q

How does air entrainment help vs no air entrainment in concrete?

A

Water in capillary pores freezes which expands and creates stress in concrete which then tends to crack. Entrained air allows water to expand which relieves stress and prevents cracking

41
Q

What is water content in concrete?

A

Water in cement paste and water absorbed by aggregates

42
Q

How much moisture is in oven dry aggregate?

A

none

43
Q

How much moisture is in air dry aggregate?

A

less than potential absorption

44
Q

How much moisture is in saturated surface dry (ssd) aggregate?

A

equal to potential absorption

45
Q

How much moisture is in damp or wet aggregate?

A

greater than absorption, has free water

46
Q

What needs to adjusted to account for the moisture condition of aggregates?

A

water content

CIVL3725 - Construction Materials and Methods (4 decks)

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