Aggregates

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 . 200 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 – 19 -4.75 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. 4 35-55% • No. 16 15-40% • No. 50 5 to 22% • No. 200 2-8% • 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