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AGGREGATE MATERIALS. AGGREGATES (cont’d) Overview Definition: Usually refers to mineral particles but can relate to byproducts or waste materials. (i.e.

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Presentation on theme: "AGGREGATE MATERIALS. AGGREGATES (cont’d) Overview Definition: Usually refers to mineral particles but can relate to byproducts or waste materials. (i.e."— Presentation transcript:

1 AGGREGATE MATERIALS

2 AGGREGATES (cont’d) Overview Definition: Usually refers to mineral particles but can relate to byproducts or waste materials. (i.e. vitrified soils) Natural aggregates are formed from rocks or the decomposition and transport of rock (see fig 2-2) Natural sources include underwater, land ( stripping), Glacier Outwash.

3 Note: Disadvantage of natural aggregate deposits is: the content of impurities and dust. Rounded shapes and smooth surfaces are found with natural aggregates which is undesirable. However in some locations it may be more economical. AGGREGATES TESTING (cont’d)

4 Advantage of crushed stones: l Size of the particle can be manufactured as needed l Also angular shapes and rough surfaces are formed which is better suited for industry AGGREGATES TESTING (cont’d)

5 Rock Types Igneous Rock - Volcanic Rock which was molten at one time and then cooled i.e. Granites(CG), Basalt(FG) & Diabase Trap Rock is Basalt and Diabase Pumice and Scoria are rock filled with bubbles which are good for lightweight aggregate Trap Rock is an excellent aggregate AGGREGATES TESTING (cont’d)

6 Sedimentary Rock - Shows a lot of stratification from its natural deposition If it is a sand deposit formed rock it is known as sandstone or quartzite If it is a gravel deposit formed rock it is known as a conglomerate Note: Shale is not a great aggregate because of cleavage AGGREGATES TESTING (cont’d)

7 Metamorphic Rock - Formed from Sedimentary or Igneous under heat and pressure i.e Shale turns into slate i.e. Limestone turns into marble AGGREGATES TESTING (cont’d)

8 What qualities do we want in Aggregates? Weight- Prevents erosion of banks or for gabion retaining walls Resistance - For weathering and freeze/thaw To breaking and crushing To resistance to abrasion Ability- to transmit compressive forces as a mass to adhere to a cement agent Permeability- potential as a filtering or drainage system AGGREGATES TESTING (cont’d)

9 STRENGTH OF MATERIAL REVIEW COMPRESSIONTENSION TORSION THIRD POINT LOADING SPLIT TENSILE

10 ELASTIC LIMIT PROPORTIONAL LIMIT YIELD POINT ULTIMATE STRENGTH STRAIN STRESS STEEL VS CONCRETE Elastic Modulus(slope) or Young’s Modulus (E)

11 f’c:5700 psi f’c:4700 psi f’c:4100 psi f’c:3300 psi f’c:2600 psi strain(x10-4) Stress (psi) Stress - Strain Diagram of various concretes

12 Aggregates Usually refers to a soil that has in some way been processed or sorted.

13 Excavation

14 Crushing

15 Transportation

16 Sizing Stockpiling

17 Desired Aggregate Properties Toughness Soundness Deleterious Materials Gradation

18 Soundness Before After

19 l Aggregate Gradation –The distribution of particle sizes expressed as a percent of total weight. –Determined by sieve analysis Gradations

20 Mechanical Sieve Individual Sieve Stack of Sieves

21 Mechanical Sieve Stack in Mechanical Shaker

22 Book Notes –Chapt. 2 GRADATION CURVE: SP SW GP GW

23 Book Notes –Chapt. 2 SIEVE PANS : P.58 Gravel Clay and Silt Sand

24 * Uniformly graded - Few points of contact - Poor interlock (shape dependent) - High permeability * Well graded - Good interlock - Low permeability * Gap graded - Only limited sizes - Good interlock - Low permeability Types of Gradations

25 Aggregate Size Definitions l Nominal Maximum Aggregate Size –one size larger than the first sieve to retain more than 10% l Maximum Aggregate Size –one size larger than nominal maximum size

26 Questions - ?


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