CMT Lesson 4

Aggregates

Coarse particulate rock-like material derived from igneous, sedimentary, and metamorphic rocks or manufactured from blast furnace slag, used in concrete production.

Primary Aggregates

Naturally occurring deposits of minerals like crushed rocks, sand, and gravel, used in construction projects.

Secondary Aggregates

By-products of processes like quarrying or mining, produced through industrial processes.

Recycled Aggregates

Previously used materials collected through deconstruction, crushed, and processed for reuse.

Normal-Density Aggregates

Natural materials like gravels, basalt, granite, limestone, and sandstone used in concrete with relative densities of 2.55–2.75.

Lightweight Aggregates

Porous materials like dolomite, pumice, and perlite used to reduce density in concrete.

Heavyweight Aggregates

High-density materials like barytes and haematite used for radiation shielding in concrete.

Coarse Aggregate

Larger aggregates above 4.75mm used in concrete production.

Fine Aggregate

Smaller aggregates below 4.75mm like river sand or crushed stone sand used in concrete.

Rounded Aggregate

Smooth aggregates from rivers or seashores, unsuitable for high-strength concrete due to weak bond strength.

Irregular Aggregates

Good bond strength aggregates suitable for ordinary concrete, with some voids.

Angular Aggregates

Sharp, angular particles providing good bond strength, suitable for high-strength concrete.

Flaky Aggregate

Aggregates with small thickness compared to width and length, affecting workability.

Elongated Aggregate

Aggregates longer than they are thick, adding surface area to the mix.

Natural Aggregates

obtained by crushing from quarries of igneous, sedimentary or metamorphic rocks

Artificial Aggregates

broken bricks, furnace slag, and synthetic aggregates

All-in Aggregate

Naturally available aggregates of different fractions of fine and coarse sizes

Graded Aggregate

• Aggregate most of which passes through a particular size of sieve

Flaky and Elongated

A mix of the previous two– and the least efficient form of aggregate with regards to workability.

Strength

• Should be at least equal to that of the concrete

Stiffness

modulus of elasticity of concrete is approximately equal to the weighted average of the moduli of the cement paste ad the aggregate

Bond Strength

State of internal stress even if no external forces are present

Shape and Texture

Influences the properties of fresh concrete more than when it has hardened

Specific Gravity

Greatly influence the strength and absorption of the concrete

Bulk Density

Depending upon their packing, the particles shape and size.

Void

If it is more in the concrete, the strength will  be low

Pores

entrapped bubbles in the rocks during their formation lead to a minute holes or cavities

Moisture content

Expressed as a percentage of the weight of the saturated surface dry aggregate

Bulking

Increase in the volume of given mass of fine aggregate caused by the presence of water

Fineness Modulus

It is the numerical index of fineness, giving some ideas about the mean size of the particles in the aggregates

Soundness

Is defined as the ability of aggregate to resist changes in volume as a result of changes in physical conditions

• Specific heat

• Thermal conductivity

• Coefficient of expansion

Thermal Properties of Aggregate

• Igneous

• Sedimentary 

• Metamorphic

Aggregates are Derived from (3)

• Coarse aggregate

• Fine aggregate

2 types of Aggregates

1. Primary Aggregates

2. Secondary Aggregates

3. Recycled Aggregates

3 Group of Aggregates

1. Normal - Density Aggregates

2. Lightweight Aggregates

3. Heavyweight Aggregates

Classification of Aggregates (Based on Density)

• Natural Aggregates

• Artificial Aggregates

Classification of  Aggregate (Geological Origin)

• Coarse Aggregate

• All-in Aggregate

• Graded Aggregate

• Fine Aggregate

Classification of Aggregate (Based on Size)

• Rounded Aggregate

• Irregular Aggregates

• Angular Aggregates

• Flaky Aggregate

• Elongated

• Flaky and Elongated

Classification of Aggregate (Based on Shape)

• Strength

• Stiffness

• Bond Strength

• Shape and Texture

• Specific Gravity 

• Bulk Density

• Void

• Porosity

• Moisture content 

• Bulking

• Fineness Modulus

• Soundness

• Thermal Properties of Aggregates

CHARACTERISTICS OF AGGREGATES

• Specific Gravity

• Water Absorption

• Abrasion

• Density

• Uniformity

TEST CARRIED OUT ON AGGREGATES:

1. Degree of compaction

2. Grading of aggregates

3. Shape of aggregate particles

Bulk Density of Aggregates Depends Upon 3 Factors

Water Absorption

• gives an idea on the internal structure of aggregate 

• aggregates having more absorption are more porous in nature & considered unsuitable

1. Absorption Capacity (AC)

2. Effective Absorption (EA)

3. Surface Moisture (SM)

3 Quantities Used in Water Absorption

Absorption Capacity (AC)

maximum amount of water the aggregate will absorb. The range for most normal-weight aggregates is 1 - 2%.

Effective Absorption (EA)

amount of water required to bring an aggregate from the air dry state to the saturated-surface-dry state.

Surface Moisture (SM)

• amount of water in excess of SSD.

• represents water in excess of the SSD state,

Bulk Density

• UNIT WEIGHT of an aggregate is the mass or weight of the aggregate that is required to fill a container of a specified unit volume.

• Mass of the aggregate over the volume of aggregate particles with voids.

Relative Density

• or SPECIFIC GRAVITY of an aggregate is the ratio of its mass to the mass of an equal volume of water.

• Most aggregates have a relative density between 2.4-2.9 with a corresponding particle (mass) density of 2400-2900 kg/m3 (150-181 lb/ft3).

• Wire Mesh Bucket

• Setup of Water Absorption Test

Apparatus Required in Water Absorption

Hardness Property

determined by conducting abrasion test

Los Angeles Abrasion Test

• to find the percentage wear due to relative rubbing action between the aggregate and steel balls used engineering play a

• pivotal role in assessing the durability and wear resistance of materials used in construction, as abrasive charge

• Los Angeles abrasion machine.

• Abrasive charge balls: These are made of cast iron or steel, with a diameter of approximately 48mm, and each ball weighs between 390 to 445 grams; six to twelve balls are necessary.

• Sieves: Including IS Sieves with the following mesh sizes - 1.70mm, 2.36mm, 4.75mm, 6.3mm, 10mm, 12.5mm, 20mm, 25mm, 40mm, 50mm, 63mm, and 80mm.

• A balance with a capacity of 5 kg or 10 kg.

• Oven for drying.

• Miscellaneous elements such as a tray.

Apparatus for Los Angeles Abrasion Test

• Balance

• Sieves

• Los Angeles Testing

• Abrasive Charges

Apparatus Required in Abrasion Test

Density

• ratio of the mass of aggregate to the mass of an equal absolute volume of water (the measure of the compactness)

• inversely proportional to void content

• directly proportional to strength

Uniformity

the consistency in size, shape, and gradation of aggregate particles

Fineness Modulus (FM)

• used in determining the degree of uniformity of the aggregate gradation.

• defined as the sum of the cumulative percentages retained on specified sieves divided by 100.

• describes the average size of particles in a sample of aggregate.

• Wire Mesh Bucket

• Setup of Water Absorption Test

• Pycnometer

Apparatus Required in Density and Uniformity

Duff Abrams

material research who defined fineness modulus in 1918