1. Aggregates
Chapter 4

2. Aggregates Granular mineral particles used
Various types of cementing material
Road bases
Backfill
Subbases
Railroad ballast
Fill under floor slabs
Concrete blocks
Water filtration beds
Drainage structures
Riprap
Gabion material

3. Sources Natural sand and gravel deposits Crushed rock
Slag and mine refuse
Rubble and refuse
Artificial and processed materials
Pulverized concrete and asphalt pavements
Other recycled and waste materials

4. Sources
Natural sand and gravel deposits – crushed rock – make up bulk of aggregates
Although the use of recycled materials is growing
Natural sand and gravel deposits are used for aggregates
Consist of sand or gravel soils

5. Natural sand and gravel deposits
Used for aggregate
Have been naturally sorted to eliminate most silt and clay
Mine in open pit mines –
May be crushed further to produce different sizes

6. Properties of aggregates
Three major classes of rock
Igneous rock
Original rock
Formed from the cooling of molten material
Coarse grained igneous rocks cool slowly
Fine grained igneous rocks cooled more quickly
Sedimentary rocks
Formed from the solidification of chemical or mineral sediments deposited
Metamorphic rocks
Igneous or sedimentary rocks that have been changed due to intense heat and presure

7. Best Types for aggregates
Igneous and metamorphic rocks are very hard
Excellent aggregates
Sedimentary rock is softer
But limestone and dolomite are acceptable for aggregate choices
Shale is not a good choice because it is made from clay
Slag is being used as well
Water cooled slag is a good choice for base courses and concrete
Air cooled slag is not a good choice because it could contain sulphur
Pulverized concrete is being used more and more
Asphalt pavements can be recycled as well
Limite to 30-50% of total for new installs
Use of other recycled materials is being investigated as well
Glass
Rubber pellets
Bricks
Building ruble

8. Aggregate terms and types
Fine aggregate (sand sizes) between no4 and no sieve
Course aggregate larger then no. 4
Pit run – aggregate from a sand or gravel pit no processing
Crushed gravel – aggregate from the crushing of bedrock – all particles are angular not rounded
Screenings – chips and dust or powder that are produced in the crushing of bedrock
Concrete sand – sand that has been washed
Fines – silt clay or dust smaller then no. 200 – usually not desirable
Aggregate and sieve sizes table 4-1 page 128

9. Nominal size Size determined by sieves
Not necessary that 100 percent be within the specified range
Small amount about 5 to 10% is allowed to be larger or smaller
Ex. 3/4in (19mm) 90 percent of sample must be smaller than 19 and 100 % must be smaller then next sieve size which is 1in (25mm)
Ex fine agg. Should pass through a no. 4 sieve (4.75mm) 100 percent passes through 9.5 (3/8) – 90 passes 4.75
Ex coarse aggregates – should pass 100 through 25 mm 90 passing the 19mm sieve and 10 passing the 4.75 sieve
Single coarse aggregate is called clear
Most particles are between the specified maximum size and minimum size
Ex 19mm – 100 smaller than 25mm 90 smaller than 19 and 10% smaller than 9.5mm

10. Aggregate Strength
Use to distribute imposed loads over surface of the soil
Or as economical filler material
The ability for aggregate particles to carry loads without moving is the most important factor
Loads come from both horizontal and vertical forces
The load is distributed over a large area
Crushed material is much better then rounded
Rough faces increase the friction between particles
Reduce the risk of sliding between particles
Densely graded also increase the strength
Particles are more easily lock together

11. Properties Gradation Grain size analysis
Specifications for highway bases, concrete and asphalt mixes require a grain size distribution that will provide a dense strong mix
Voids between larger particles are filled with medium particels – the remaining voids are filled with still smaller particles
Fuller maximum density curves
P=(d/D).5 where p is the percent passing sieve size d, and D represents the maximum sieve size (100% passing)
Revised maximum density relationship used by federal highway admin
4.5 is used in place of .5

12. The Problem with Fines Fines must be limited
Silt and clay particles (no. 200 sieve) are relatively weak
In concrete mixes to much cement is need to cover the fines – in addition they weaken the bond between the cement and those particles
Fines in highway bases may lead to drainage and frost heaving problems
Clay is more harmful the silt
Maximum values for liquid limit and index of plasticity are often specified for aggregates
Washed sieve analyses are required when the amount passing 75um is important (200 sieve)
Sample is dried and washed
Wash water is poured out over a 200 sieve
Material retained in the sieve is returned to the sample
It is then dried again and dry sieved
Total amount passing 200 sieve is the sum of the amounts lost in washing and passing the 75 um sieve
Example page 132 – 4-1

13. Relative density and absorption
Are important especially in concrete and asphalt mixtures
Necessary to measure accurately the volumes occupied by the aggregate and any water that might have seeped into the pores in the particles
Relative density rd=m/(V *pw)
Other formula exist for dealing with moisture in the agg. – page 133
Example 4-2 page 134
Example 4-3 page 134

14. Hardness Resistance to wear Important
Pavement surfaces – agg. Not get rounded or polished due to traffic
Floors – subject to heavy traffic
Roadbeds – subjected to innumerable cycles of lad application and removal
Most common test is the los Angeles abrasion test
Agg. Is placed in a drum with a number of steel balls
Drum is rotated a specified number of times
Loss of agg. Or amount ground down is measured
Example 4-4

15. Durability
Resistance to disintegration due to cycles of wetting and drying, heating and cooling and especially freezing and thawing
Especially dangerous with particles from sedimentary rocks
Soundness test is used
Sample of aggregate is saturated in a solution of magnesium sulphate or sodium sulphate and then removed and dried in a oven
Repeated five cycles
The percent lost or broken down is calculated
Example 4-5 page 137

16. Other properties Particle shape and surface texture
Affect the strength and bond with cementing materials
Resistance to sliding of one particle over another
Flat –thin or long needle shaped particles break more easily
Rough faces allow a higher friction strength
Deleterious substances
Harmful or injurious materials
Include weak or low quality particles and coatings that are found on the surface of aggregate particles
Include
Organic coating
Dust
Clay lumps
Shale
Coal particles
Friable particles easyt o crumble
Chert may break up when exposed to freezing and thawing
Badly weathered particles
Soft particles
Lightweight particles

17. Specifications For each of the properties of aggregates
Specification vary considerably
Requirements for road base differ from concrete and asphalt
Table 4-3 gives astm standard sizes of aggregates for highway work

18. Typical specifications for highway base
Passing 1in 100%
¾ 90 to 100%
3/8 50 to 75%
No %
No %
No to 22%
No %
Abrasion loss up to 40%
Soundness loss up to 18%
Example 4-6 page 140

19. Sampling and testing Csa standard A23.2-1a and astm standard d75
Give methods to follow in sampling aggregates
Page 143 list astm d75 standards
In conducting lab test – its critical that the sample tested be representative of the material being used in the field
Usually a sample splitter is used to obtain the test sample

20. Blending Aggregates
Meet the gradation requirement for asphalt or concrete it is often necessary to blend two or more aggregates together
Charts are available but normally done by trial and error
Example 4-8 page 147