Aggregates Flashcards
How much % does the agg. represents in concrete volume?
60%-75%
How much % does the agg represents in concrete mass?
70%-85%
Why do we use agg. in concrete?
- Economical benefits
- Volume stability
What are the 2 size of aggregates?
Fine and coarse
What are the fine agg.?
Sand and/or crushed stones
What are the coarse agg.?
Gravel and crushed stone
What are the typical size of fine agg. in mm?
<5mm (>5mm for coarse agg.)
What are the 4 types of weight of agg.?
- normal weight
- light weight
- structural light weight
- Heavy weight
What is the density of light weight?
250 to 1450 kg/m3
What is the density of normal weight?
2200 to 2400 kg/m3
What is the density of stru. light weight?
1450 to 1850 kg/m3
What is the density of heavy weight?
up to 6400 kg/m3 (high density)
What are the 4 sources of agg.?
Natural gravel and sand
Rocks and minerals
Crushed blast-furnace slag
Recycled waste concrete
How can we determine the distribution of agg. (grading)?
Sieve analysis with mesh sieve
What are the 7 sieves for fine agg.?
9.5mm
4.75mm
2.36mm
1.18mm
600 micromm
300 micromm
150 micromm
(pan)
What are the 13 sieves for coarse agg.?
100mm
90 mm
75 mm
63mm
50 mm
37.5 mm
25 mm
19 mm
12.5 mm
9.5 mm
4.75 mm
2.36 mm
1.18 mm
(pan)
What is the purpose of distribution curve?
To see if the grading of agg is good or bad
What is max size of agg. (SIEVE)?
smallest sieve that all the agg. passes throught.
What is the nominal maximum size?
Standard sieve opening immediately after the max. size of agg.?
Note: must not exceed–> 1/5 of narrowest dimension between sides of forms, 3/4 of clear spacing between rebars and between rebars and the form and 1/3 depth slabs
What is FM?
Sum of the cumulative percentages by mass of a sample of agg. retained in each of standard sieves and dividing the sum by 100. (EXCLUDING PAN)
What is the FM of Coarse agg.?
2.8-3.1
What is the FM of fine agg.?
2.3-2.5
What are the ideal moisture conditions for fine and coarse aggregates?
Saturated surface dry (SSD)
Larger coarser agg. =?
lower S.A. –> Lower cement and water required –> less workability and more strength (less w/c ration)
What is D-Cracking?
Cracking of concrete caused by freeze-thaw deterioration of the agg. within concrete.
What is ASR? (alkali silica reaction)
Alkali hydroxide + Reactive silica = Alkali silica gel
Alkali silica gel + moisture (H2O) = EXPANSION
How to control ASR?
Non -reactive agg.
Limit alkali loading
Lithium based admx.
SCM’s (fly ash; slag; silica fume)
Limestone sweetening
How does the agg. should be stored?
avoid contamination
avoid segregation
