Rock Types: Igneous, Sedimentary and Metamorphic

• Rocks are classified by geologists into three types: metamorphic, sedimentary, and igneous.

Rock Types

• Sedimentary rocks form through the accumulation and cementation of mineral or organic particles in water bodies.
• Metamorphic rocks originate from other rock types that have changed due to high heat, pressure, and mineral-rich fluids.
• Igneous rocks, also known as magmatic rocks, form from the cooling and solidification of magma or lava.

Predominant Rock Minerals

• Feldspar includes Orthoclase (potassium feldspar) and Plagioclase (calcium/sodium feldspar).
• Quartz is silicon dioxide.
• Micas include Biotite and Muscovite.
• Calcium Carbonate includes calcite and dolomite.
• Iron Oxide is a predominant rock mineral.

Aggregates

• Aggregates are granular materials used in concrete and bituminous mixes.
• Fine aggregates consist of washed sand.
• Coarse aggregates consist of gravel and crushed rock.

Laboratory Tests for Aggregates

• Laboratory tests evaluate the physical characteristics of aggregates.
• Unit Weight Test
• Specific Gravity Test
• Absorption Test
• Washing in sieve
• Sieve Analysis
• Organic and Mortar Strength
• Soundness
• Abrasion Test

Mineral Aggregates

• Aggregates are a crucial component of concrete.
• Aggregates are classified into fine, coarse, and slag.
• Natural aggregates come from natural deposits.
• Manufactured aggregates come from manufacturing industries like blast furnace slag and clay.

Processing of Aggregates

• Good aggregate processing aims to obtain high-quality aggregates at the lowest cost.
• Excavation and Quarrying involves removing overburden like clay and silt.
• Transportation moves the aggregates.
• Washing removes deleterious materials like clay, mud, and leaves.
• Crushing reduces the size of materials.
• Sieving sizes materials.

Gradation and Aggregate Blending

• Gradual gradation in size from coarse to fine is a key property.
• Gradation affects the workability of concrete mixes, the stability and durability of bituminous concrete mixes, and the drainage and frost resistance of base courses.
• Aggregates can be dense, gap graded, uniform, well graded, or open graded.

Methods of Expressing Size Distribution

• Fuller Thompson Method: P=100(d/D)n
• P = percentage finer than the sieve
• d = sieve size in question
• D = maximum size of aggregate to be used
• N = coefficient of adjustment
• Aggregate gradation affects structural capacity, drainage, and frost susceptibility.

Fineness Modulus

• Fineness Modulus denotes the relative fineness of sand and is defined as one hundredth of the sum of the cumulative percentage held on the standard sieve test of sand.
• Fineness Modulus Value ranges from 2.25 to 2.35.

Sources of Aggregates

• Depletion of aggregates from sources with known satisfactory performance leads to the following major possibilities:
  • Production of synthetic aggregates
  • Beneficiation of unsuitable aggregates
  • The use of manufactured and waste materials as supplements and replacements for conventional aggregates in construction.

Distress Classifications

• Unsound aggregates result in three distress classifications:
  • Pitting and popouts
  • D-line cracking Deterioration, caused by the change in volume of coarse aggregates particles breaking the bond with mortar mix
  • Map cracking, disintegration in which random cracks developed in a well-distributed pattern

Aggregate Issues

• Pitting is the disintegration of weak, friable pieces of aggregates due to frost action.
• Popouts are caused by rapid disruption of harder but saturated pieces of rocks or aggregates.
• Gradation refers to the amount of each size of particles used in the mixture.
  • Too much proportion of coarse aggregates leaves voids that require more cement-paste to fill.

Aggregate Beneficiation

• Several processes have been developed in the beneficiation of aggregates:
  • Washing
  • Heavy-media separation
  • Elastic fractionation
  • Jigging

Beneficiation Methods

• Washing removes particles coatings or to change the gradation.
• Stokes’s law determines velocity of settlement, where V = velocity of settlement and D = particle diameter.
• Heavy Media Separation uses the principle that the specific gravity of much deleterious materials is lighter than the specific gravity of the sound aggregates.
• Elastic Fractionation measures aggregate quality by the distance they bounced from a surface.
• Jigging is a specific-gravity method of removing light particles such as coal, lignite, or sticks.

ASTM Tests Concerning Aggregates

• ASTM Tests fall into three categories:
  • Tests concerning the quality of aggregates
  • Tests concerning deleterious particles in aggregates
  • Tests used in the design of concrete mix and bituminous concrete mix

Tests Concerning Quality

• ASTM C131 tests resistance to degradation of small size coarse aggregate by abrasion and impact in the Los Angeles machine.
• ASTM C88 tests the soundness of aggregates by use of sodium sulfate or magnesium sulfate.
• ASTM C666 tests the resistance of concrete to rapid freezing and thawing.
• ASTM C215 tests fundamental transverse, longitudinal, and torsional frequencies of concrete specimens.
• ASTM C597 tests pulse velocity through concrete.
• ASTM C671 tests critical dilation of concrete specimens subjected to freezing.
• ASTM C682 evaluates frost resistance of coarse aggregates in air-entrained concrete by critical dilation procedure.
• ASTM C672 tests scaling resistance of concrete surfaces exposed to deicing chemicals.
• ASTM C295 details petrographic examination of aggregates for concrete.

Specific Purposes of the Test

• Used for preliminary determination of quality.
• Used for establishing properties and probable performance.
• Used for correlating samples with aggregates previously tested and used.
• Used for selecting and interpreting other tests.
• Used for detecting contamination.
• Used for determining effects of processing.
• Used for determining physical and chemical properties.
• Used for describing and classifying constituents.
• ASTM D1075 tests the effect of water on cohesion of compacted bituminous mixtures.

Tests Concerning Deleterious Materials in Aggregates

• ASTM C33 concerns aggregate specifications, where P = percent of clay lumps or friable particles, W = weight of the test sample passing the layer of sieves but coarser than the No. 16 sieve, and R = the weight of particles retained on the designated sieve.
• ASTM C142 tests clay lumps and friable particles in aggregates.
• ASTM C117 tests materials finer than No. 200 sieve in mineral aggregates by washing.
• ASTM C123 tests lightweight pieces in aggregates.
• ASTM C40 tests organic impurities in sands for concrete.
• ASTM C227 tests the potential alkali reactivity of cement-aggregate combinations (mortar-bar method).
• ASTM C289 tests the potential reactivity of aggregates.
• ASTM D75 pertains to sampling of aggregates, used for preliminary investigation of the potential source of supply, control of the product at the source of supply, control of the operations at site of use, and acceptance or rejection of the materials.

Tests Used in Design

• ASTM C136 is for sieve or screen analysis of fine and coarse aggregates.
• ASTM C127 tests specific gravity and absorption of coarse aggregates.
• ASTM C128 tests specific gravity and absorption of fine aggregates.
• ASTM C29 tests unit weight of aggregates.