Aggregates for portland cement concrete (Lecture 2&3)

Question 1

What are the three major types of rock?

Answer 1

Igneous Rock- formed by cooling of magma. Ex. granite or trap rock
Sedimentary rock- Formed from disintegration of other rocks and deposited as sediments. ex limestone sandstone shale
Metamorphic rock- igneous or sedimentary rock that changed structure due to heat or pressure. usually harder and denser. ex marble or slate

Question 2

What are the differences between intrusive and extrusive igneous rock

Answer 2

Intrusive- formed by slow cooling beneath earths surface. Completely crystalline coarser grain. Ex granite & trap rock
Extrusive- formed by rapid cooling near earths surface. Finer grain materials with smaller crystals or glassy structure. Ex. Basalt or perlite.

Question 3

What are some examples of artificial aggregate

Answer 3

Blast furnace slag, expanded clay, expanded shale.

Question 4

What is coarse aggregate

Answer 4

Particles retained on No. 4 Sieve (3/16 in)

Question 5

What is fine aggregate

Answer 5

Particles passing No. 4 Sieve

Question 6

What are the functions of aggregate in concrete

Answer 6

1) Economy
2) Strength
3) Reduction in shrinkage and expansion

Question 7

What are the standard sieve sizes

Answer 7

3”, 1.5”, 3/4”, 3/8”, #4, #8, #16, #30, #50, #100, #200.

Question 8

What is the fineness modulus?

Answer 8

Fineness modulus is a number that quantifies the fineness of an aggregate.
Calculated by adding up cumulative percents retained on standard sieves to #100, then divided by 100.
ASTM C33 limis F.M. to 2.3-3.1. Lower number = finer aggregate.

Question 9

What is the Fuller’s max density curve? What is FHWA Max density curve?

Answer 9

percent passing =(size sieve/max aggregate size)^.5*100

FHWA is same as above except to .45 power.

Question 10

What is the max aggregate size?

Answer 10

Smallest sieve that 100% of aggregate must pass

Question 11

What is the nominal max size of an aggregate?

Answer 11

the smaller sieve which the major portion of the aggregate must pass. May retain 5% to 15%.

Question 12

What is uniform gradation

Answer 12

aggregates mostly one size

Question 13

What is gap graded

Answer 13

aggregate mixture that is missing a few sizes

Question 14

What is well graded

Answer 14

dense well graded with a distribution off sizes resulting in low air voids and high density when compacted

Question 15

What is dry bulk specific gravity

Answer 15

dry wt in air divided by the difference of SSD in air and wt in water.

Question 16

What is SSD bulk specific gravity

Answer 16

SSD wt in air divided by the displacement of water of SSD

Question 17

What is the absorption of an aggreate

Answer 17

SSD WT- Oven dry wt divided by oven dry wt

Question 18

What is the difference between bulk density and bulk unit weight

Answer 18

Bulk density is the mass of the aggregate divided by the volume of the solid and voids combined. Bulk unit weight is the wt of aggregate divided by bulk volume (ex container volume)

Question 19

What can be done to reduce segregation of aggregate in handling and storing

Answer 19

Do not stop in high cone shaped pile
Do not let aggregate run down slope
Avoid blowing wind when dumping

Question 20

What are the effects of particle shape and surface textures of aggregate on concrete?

Answer 20

Desire mix of rough and textured angular aggregate. To rough and textured though can require more water to reach better workability. Desire is to have mix of crushed and non crushed aggregate.

Question 21

What are the bulk unit weight of A) Normal natural aggregate B) Lightweight aggregate C) Heavyweight and D) Blast furnace slag

Answer 21

A) between 95 and 105pcf
B) less than 70 pcf
C) greater than 130
D) between 70 and 85pcf

Question 22

What are the properties of using recycled concrete as aggregate and the properties of concrete made with recycled concrete

Answer 22

Concrete can be crushed to proper gradation.
Strength and durability of new concrete will be limited by old concrete.
Has higher absorption, lower specific gravity, and lower natural strength.
LA abrasion max is 50%.