Test Review from Notes

Question 1

Water of questionable origin can be tested and used to make concrete if ___________.

Answer 1

It produces a 28 day strength equal to at least 90% of those obtained from mortar made with known acceptable water.

Question 2

What are chloride ions and how are they formed?

Answer 2

Chloride ions are electrically charged atoms of chlorine which form when salt dissolves in water. They cause problems in reinforced steel by speeding up the deterioration of reinforcing steel embedded in concrete.

Question 3

What forms on the steel in a high (above 11) pH level?

Answer 3

A protective oxide forms on the steel preventing normal oxidation (rusting) of the steel.

Question 4

What do chloride ions do to the protective coating?

Answer 4

The chloride ion disrupt the protective steel and rusting can proceed even in a high pH.

Question 5

Controlling the chloride content in concrete is difficult because ___________.

Answer 5

Chloride ions can get into the concrete from many sources.

Question 6

How can chloride ions get into the concrete?

Answer 6

From the aggregates, the admixtures, the cementing materials, and the environment (deicing salt, sea water, sal-laden air).

Question 7

What does excess water cause? (6 points)

Answer 7

1) lower strength
2) less durability
3) higher permeability (less watertight)
4) increased shrinkage
5) less volume stability (more volume change from wetting and drying)
6) poorer bond to the reinforcing steel and successive layers of concrete

Question 8

How much of the concrete is aggregate?

Answer 8

60%-70% of the volume, which is 70%-80% of the mass.

Question 9

What does the aggregate influence? (4 points)

Answer 9

It influences:

1) properties of freshly mixed concrete
2) properties of hardened concrete
3) mix properties
4) economy (cost)

Question 10

What does fine aggregate consist of?

Answer 10

Natural or crushed stone in which most particles are below 5mm.

Question 11

What does coarse aggregate consist of?

Answer 11

River gravel and crushed stone and/or air cooled blast furnace slag. The largest particles are between 10mm and 40mm. Most concrete has a max. size of 20mm.

Question 12

What is the gravel in southern ontario like?

Answer 12

It’s generally clean, durable, and rounded from the glacial process.

Question 13

What are the different types of rocks and how are they formed? (3 types)

Answer 13

igneous-from molten rock
sedimentary-from deposits or sediments
metamorphic-igneous or sedimentary rocks changed by heat or pressure

Question 14

Aggregates classified by size (chart).

Answer 14

boulders ->200mm
cobbles -60mm-200mm
gravel -coarse -20mm-60mm
gravel -medium -6mm-20mm
gravel -fine -2mm-6mm
sand -coarse -0.6mm-2mm
sand -medium -0.2mm-0.6mm
sand -fine -0.06mm-0.2mm
silt -0.002mm-0.06mm
clay -0.002mm

Question 15

What properties do aggregates need? (5 points)

Answer 15

1) strong-wear resistant
2) hard-wear resistant
3) clean-free from coatings in clay
4) durable-chemically and mechanically stable
5) free of absorbed chemicals (sulphates and chlorides)

Question 16

Mohs Hardness Scale

Answer 16

1) talc
2) gypsum
3) calcite
4) fluorite
5) apatite
6) feldspar
7) quartz
8) topaz
9) corundum
10) diamond

Question 17

How to choose a max aggregate size?

Answer 17

1/5 narrowest dimension between the sides between the sides of the forms (wall)
1/3 of the slab depth

Question 18

The moisture content affects the requirement for adding additional water to the mix. What are the mixed proportions based on in regard to the aggregates?

Answer 18

The aggregates need to be dry on the surface but fully saturated.

Question 19

What should batching be based on?

Answer 19

Batching should be based on mass and not volume.

Question 20

What kinds of aggregates should be avoided for freeze and thaw resistance?

Answer 20

Moderately porous aggregate like chert should be avoided to avoid pop outs.

Question 21

What is aggregate beneficiation?

Answer 21

It is the process used to improve the quality of available aggregates. This may include crushing, screening, and washing to obtain the proper gradation and cleanliness,

Question 22

In marine areas what do they use for aggregate?

Answer 22

They use seashells which are made acceptable by crushing. This improves their shape. Washing them in fresh water reduces salt levels and removes organic materials.

Question 23

Why is proper handling and storage of aggregates necessary?

Answer 23

To prevent segregation of the aggregates. Stockpiles should be built in layers of uniform thickness, not just a big pile.
Round aggregate segregate more than crushed or angular aggregates.
Large aggregate separates more than fine aggregates.
Dry aggregate separates more than moist/wet aggregates.

Question 24

The aggregate must have a dry sample more than _______________.

Answer 24

nominal maximum aggregate size (mm)/minimum mass of sample (kg)
10/1
14/3
20/5
28/10
40/15
56/20
80/60

Question 25

Portland cement is created by burning several types of cement together. A chemical conversion takes place at temps. of 1450°C to 1650°C yielding ________________.

Answer 25

tricalcium silicate C3S
dicalcium silicate C2S
tricalcium aluminate C3A
tetracalcium aluminoferrite C4AF - for lower temp`

Question 26

The fine aggregate grading is intended to do what?

Answer 26

Maximize the void space around the coarse aggregate and maximize the workability of the concrete while minimizing the need for additional mix water.

Question 27

Name the types of portland cement.
Type GU
Type MS
Type MH
Type HE
Type LH
Type HS

Answer 27

GU - General Use
MS - Moderate Sulphate Resistance
MH - Moderate Heat of Hydration
HE - High Early Strength
LH - Low Heat of Hydration
HS - High Sulphate Resistance

Question 28

What are qualities of the ingredient C3S in portland cement?

Answer 28

harden rapidly

responsible for initial set and early strength

Question 29

What are qualities of the ingredient C2S in portland cement?

Answer 29

hardens slowly

responsible for strength after one week

Question 30

What are qualities of the ingredient C3A in portland cement?

Answer 30

produces large heat and fast set and some early strength
gypsum slows down this reaction
attacked by sulphates

Question 31

What are qualities of the ingredient C4AF in portland cement?

Answer 31

reduces temperature required to make cement
acts as a flux in burning clinker
hydrates quickly with little strength
produces colour (grey)

Question 32

What are the types of pozzolans?

Answer 32

type N - natural pozzolans from volcanic glass, diatomaceous earth, opaline chert, shales, tuffs, pumicite, and calcined clays
type F - fly ash from burning anthracite or bituminous coal
type C - fly ash from burning lignite or sub-bituminous coal