CONSTRUCTION MATERIALS AND TESTING
GROUP 4 - AGGREGATES
I. WHAT ARE AGGREGATES?
● Aggregates are the natural or artificial inorganic granular materials used with a
cementing medium to form mortar or concrete.
● Aggregates occupy around 70% to 80% other volume of the concrete,reduce
shrinkage effects and minimize costs.
II. USES OF AGGREGATES
● Aggregates can be used in a number of ways in construction.
- As a Load Bearing Material
- As a Filling Material
- As an Infiltrating Material
● In roads and railway ballast the aggregates are used to resist the overall (static
as well as dynamic) load, to distribute the load properly to the supporting ground
and to drain the water off the surface.
● In concrete the aggregate is used for economy, reducing shrinkage and cracks
and to strengthen the structure. They are also used in water filtration and sewage
treatment processes.
III. METHODS OF EXTRACTING AND PROCESSING AGGREGATES
● Underwater sources:
- Dragline excavation
- Dredging
● Land Sources:
- Blasting bedrocks
- Track Drills
- Crushers and Screens
IV. GOOD QUALITIES OF AN IDEAL AGGREGATE
● An ideal aggregate used for the manufacturing of concrete and mortar, should
meet the following requirements:
- It should consist of natural stones,gravels and sand or in various
combinations of these materials.
- It should be hard, strong and durable.
- It should be dense, clear and free from any coating. It should be free from
injurious vegetable matters.
- It should not contain flaky (angular) and elongated pieces.
- It should not contain any material liable to attack steel reinforcement in
case of reinforced concrete
V. CLASSIFICATION OF AGGREGATES
● Classification Based on Shape
★ Rounded Aggregates
- Are naturally rounded aggregates that are formed by water or
weathering - Need less cement paste to make concrete
- Interlocking between particles is poor
- Not suitable for high strength concrete
★ Irregular Aggregates
- Partly shaped aggregates are called irregular aggregates
- No specific shape
★ Angular Aggregates
- These aggregates have sharp edges and rough surfaces.
- All types of crushed rocks are good examples for this type of
aggregate.
- They need more cement paste, since voids are more in the
aggregates
- Ideal for producing high strength concrete
★ Flaky Aggregates
- Flaky aggregates have thickness less than 0.6 times mean sieve
size to which particles belong.
- Flaky aggregates reduce the durability of concrete
★ Elongated Aggregates
- Individual particles are longer than they are wider or deeper and
due to this appear to be long and thin.
- This particle-type provides more surface area to a concrete mix
● Classification Based on Size
➔ Fine Aggregates
- Aggregates passing through 4.75mm sieve. Fine aggregates are
basically natural sand particles from the land through the mining
process, the fine aggregates consist of natural sand or any crushed
stone particles that are ¼” or smaller
➔ Coarse Aggregates
- The aggregates which are retained on IS 4.75mm sieve . Most
commonly used coarse aggregates are crushed stone, gravel,
broken pieces of burnt bricks, etc.
● Classification Based on Source
- Natural Aggregates- Are taken from native deposits with no change in
their natural state during production other than crushing, grading, or
washing. Examples: sand, gravel, crushed stone, pumice
- Natural sources for aggregates include gravel pits, river run deposits and
rock quarries.
- Artificial Aggregates- Are those materials obtained either as a
by-product of an unrelated industrial process or by a special
manufacturing process like heat treatment. Examples: blast-furnace slag,
expanded perlite, expanded vermiculite, burned clay
VI. GEOLOGICAL CLASSIFICATION
- All natural aggregates result from the breakdown of large rock masses.
Geologists classify rocks into three basic types: igneous, sedimentary, and
metamorphic.
- Igneous rocks are classified based on grain size and composition. Coarse grains
are larger than 2mm and fine grains are less than 0.2 mm.
- Sedimentary rocks coalesce from deposits of disintegrated existing rocks or
inorganic remains of marine animals
- Metamorphic rocks from igneous or sedimentary rocks that are drawn back into
the earth’s crust and exposed to heat and pressure, re-forming the grain
structure.
- All three classes of rocks are used successfully in civil engineering applications.
VII. SIEVE ANALYSIS OF AGGREGATES
● It is a process of dividing a sample of aggregate into various fractions, each
consisting of particles of the same nominal size. The resultant of particle size
distribution is called the gradation.
● Gradation
(a) Well Graded
- Well-graded aggregates have a gradation of particle size that fairly evenly
spans the size from the finest to the coarsest. A core of well-graded
aggregate concrete shows a packed field of many different particle sizes.
(b) Poorly Graded
- This aggregate is characterized by a small variation in size. It includes
aggregate particles that are near the same size. This means that the
particles of the aggregate pack together, leaving relatively large voids in
the concrete.
(c) Gap Graded
- Gap-graded aggregate consists of aggregate particles in which some
intermediate-size particles are missing. A core of gap-graded concrete
shows a field of small-seized aggregate interspersed with slightly large
aggregate pieces embedded in a small sized aggregate.
VIII. Properties of Aggregates
➢ Strength of Aggregate
- The coarse aggregates to be used in construction should be sufficiently
strong to withstand the loads because; it is the prime construction material
in the building as well as pavement.
- For a high-quality pavement, the aggregate should possess high
resistance to crushing, and to withstand the stresses due to traffic load.
➢ Hardness of Aggregate
- When the aggregates are used in the surface course, they are subjected
to constant rubbing or abrasion due to the constant movements of traffic
on the pavement.
- Hence, they must be hard enough to resist the wear and tear occurring
due to the abrasive action of traffic load.
➢ Toughness of Aggregate
- According to ‘M.S. Shetty’ (Author of Concrete Technology Theory and
Practice), toughness is the resistance of the aggregates to impact.
- Aggregates used in the construction of buildings and pavements are also
subjected to impact due to sudden load in buildings and moving wheel
loads on pavements. Hence, the resistance to impact is the desirable
property of aggregates.
➢ Durability of Aggregate
- The property of aggregate to withstand the adverse action of weather and
other chemical reactions can be termed as soundness.
- The aggregate used in the construction of buildings and pavements
should be durable i.e. it should have long life and should resist
disintegration due to the weather action.
- The aggregates are subjected to various physical and chemical reactions
of rain water, soil, water percolated in ground and many other impurities.
Hence, aggregate must be sound enough to withstand such reactions as
well as the weathering action.
➢ Shape of Aggregate
- According to ‘Zongjin Li’ (Author of Advanced Concrete Technology), the
shape of aggregate affects the workability of fresh concrete. Because the
differences in the surface area caused by different shapes, will determine
cement paste required to coat the aggregate, to provide lubrication and
increase workability.
- Apart from workability of concrete, the shape of aggregate is also an
essential property of aggregate because it also plays a significant role in
the strengthening, grading and interlocking of aggregate with each other,
which is ultimately responsible for toughness and firmness.
- Aggregates happen to fall in different shapes i.e. round, angular, cubical,
flaky or elongated. It is evident that aggregates with round, angular,
cubical shapes are more durable and sustainable as compared to flaky
and elongated ones.
➢ Specific Gravity of Aggregate
- The specific gravity and water absorption of aggregates are important
properties for designing concrete and bituminous mixes.
- Specific gravity of an aggregate is the ratio of the weight of a given volume
of aggregate to the weight of an equal volume of water. It is a quality
measure and determines the strength of aggregate.
➢ Adhesion with Bitumen
- The aggregates used in bituminous pavements must have less affection
for water as compared with bituminous material; otherwise, the bituminous
coating of the aggregates will get stripped off in presence of water. In
absence of water or moisture, there is no problem in bituminous
construction.
IX. TESTS TO BE CONDUCTED
● Crushing Test on Aggregates
- The aggregate crushing value gives the crushing strength of aggregate up
to which it can bear the load without fail.
● Abrasion Test on Aggregates
- Hardness property of aggregate is determined by conducting an abrasion
test. Los Angeles abrasion testing machine is used to conduct this test.
● Impact Test on Aggregates
- Impact value of aggregate will give aggregate capability against sudden
loads of forces.
● Soundness Test on Aggregates
- To determine the weathering resistance of aggregate, a soundness test is
conducted. If the resistance against weathering is good for aggregate,then
it will have high durability.
● Shape Test on Aggregates
- Shape of aggregate is also an important consideration for the construction
of pavement. Aggregate should not contain flaky and elongated particles
in it. If they contain this type of particles, they will affect the stability of the
mix.
● Bitumen Adhesion Test on Aggregates
- Bitumen adhesion test will give the stripping of bitumen from the
aggregate.
● Specific Gravity on Aggregates
- The specific gravity on aggregates measures strength or quality of the
aggregate. This property helps in general identification of aggregates.
PROPERTIES OF AGGREGATES
A Written Report
Presented to
Engr. Owiedah M. Malawani Jr.
Faculty of College of Information Technology and Engineering
Philippine Engineering and Agro-Industrial College Inc.
Marawi City
In Partial Fulfilment
of the Requirements for the Course
Construction Materials and Testing
A.Y. 2nd Trimester 2024-2025
ALIKHAN, ALIZEDNIEY B.
BAIMPAL, NOR-AINAH T.
HADJI ACMAD, JAMSHEED H.
MUSTAPHA, JAMSHIED U.
JANUARY 08, 2025