Aggregates for portland cement concrete (Lecture 2&3) Flashcards
What are the three major types of rock?
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
What are the differences between intrusive and extrusive igneous rock
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.
What are some examples of artificial aggregate
Blast furnace slag, expanded clay, expanded shale.
What is coarse aggregate
Particles retained on No. 4 Sieve (3/16 in)
What is fine aggregate
Particles passing No. 4 Sieve
What are the functions of aggregate in concrete
1) Economy
2) Strength
3) Reduction in shrinkage and expansion
What are the standard sieve sizes
3”, 1.5”, 3/4”, 3/8”, #4, #8, #16, #30, #50, #100, #200.
What is the fineness modulus?
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.
What is the Fuller’s max density curve? What is FHWA Max density curve?
percent passing =(size sieve/max aggregate size)^.5*100
FHWA is same as above except to .45 power.
What is the max aggregate size?
Smallest sieve that 100% of aggregate must pass
What is the nominal max size of an aggregate?
the smaller sieve which the major portion of the aggregate must pass. May retain 5% to 15%.
What is uniform gradation
aggregates mostly one size
What is gap graded
aggregate mixture that is missing a few sizes
What is well graded
dense well graded with a distribution off sizes resulting in low air voids and high density when compacted
What is dry bulk specific gravity
dry wt in air divided by the difference of SSD in air and wt in water.
What is SSD bulk specific gravity
SSD wt in air divided by the displacement of water of SSD
What is the absorption of an aggreate
SSD WT- Oven dry wt divided by oven dry wt
What is the difference between bulk density and bulk unit weight
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)
What can be done to reduce segregation of aggregate in handling and storing
Do not stop in high cone shaped pile
Do not let aggregate run down slope
Avoid blowing wind when dumping
What are the effects of particle shape and surface textures of aggregate on concrete?
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.
What are the bulk unit weight of A) Normal natural aggregate B) Lightweight aggregate C) Heavyweight and D) Blast furnace slag
A) between 95 and 105pcf
B) less than 70 pcf
C) greater than 130
D) between 70 and 85pcf
What are the properties of using recycled concrete as aggregate and the properties of concrete made with recycled concrete
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%.
