THE UNIVERSITY OF AZAD JAMMU AND KASHMIR

Aggregates

Prepared by: Zeeshan

Afzal

Introduction: Aggregates are defined as inert, granular, and inorganic

material that normally consist of stone or stone like solids.

Aggregates are used :

In road bases as Asphalt Aggregates.

With ordinary Portland cement(OPC) as normal aggregates as fills in foundations and as aggregate accordingly to project specific studies.

About three-fourth (75%) of the volume of Portland cement concrete is occupied by aggregates. Other 25% include cementing materials like cement, sand and synthetic admixtures.

Asphalt cement concrete occupy 90% or more of the total volume. The remaining portion is mainly sand and Bitumen which acts as cementing material in is Asphalt Aggregates.

Road Aggregate:

By volume, aggregate generally account for 92 to 96% of bituminous concrete.

Road aggregate are the non-active inert material used to provide mass to the base and sub-base courses.

Road aggregate should have high strength to bear the traffic load.

Road aggregates must have higher impact value to withstand the Tyre impact phenomenon.

ROAD AGGREGATES SHOULD HAVE RELATIVELY: HIGH STRENGTH HIGH RESISTANCE TO IMPACT & ABRASION IMPERMEABLE CHEMICALLY INERT LOW COEFFICIENT OF EXPANSION

THE MOST IMPORTANT PARAMETER FOR ROAD AGGREGATE IS POLISHED STONE VALUE:The polishing of road surface effect the skid-resistance.The rate of polish is proportional to the volume of traffic.

Straight stretches of road are less subjected to polishing than bends ( seven times more rapidly).

Polishing occur when fine detrital powder is introduced b/w tyre and surface.

Investigation shows that polishing is more in dry surface than wet.

The skid-resistance can be improved by blending aggregates.

POLISH STONE CHARACTERISTICS OF ROCKS:

Igneous & contact metamorphic rocks are good resistance to polish but depends on hardness b/w the minerals.

Coarse grained rocks with cracks in individual grains also improve resistance to polish.

Sandstones, Greywackes, gritty limestones offer good resistance to polish.

Pure limestone show a significant tendency to polish.

Road aggregate mainly cubic angular which help in better interlocking of the aggregate which in turn ultimately increases

the compressive strength.

Concrete Aggregate:

Portland cement concrete occupy volume of about 70-80% of aggregates.

Fine aggregates are used in making thin concrete slabs where a smooth surface is required. Fine aggregate is commonly known as Pan.

Coarse aggregate is used for more massive members.

SILICEOUS MATERIAL IN AGGREGATES THE SILICEOUS MATERIALS ARE OPAL, CHALCEDONY, FLINT &

VOLCANIC GLASS.

THESE SILICEOUS MATERIALS HAVE DELETERIOUS REACTION, IF HIGH ALKALI-CEMENT IS USED.

THIS CAN BE AVOIDED BY USING LOW ALKALI-CEMENT AND ALSO BY ADDING POZZOLANA TO THE MIX.

ALKALI-AGGREGATE REACTION CAN ALSO OCCUR WHEN GREYWACKES ARE USED IN AGGREGATE.

STRAINED QUARTZ:

The percentage of strained Quartz in the aggregate also have deleterious reaction.

If Percentage of Strained Quartz is >40%, were highly reative.

Between 30-35% were moderate reative.

ARGILLACEOUS DOLOSTONES

• Argillaceous dolostones ( containing clay minerals) may expand when used with high alkali-cement.

• The expansion is due to uptake moisture by the clay minerals.

SHRINKAGE EFFECT

Basalts, Gabbro, dolerite, greywackes are shrinkable, as they have large wetting and drying movements.

Clays and shale absorb water and likely to expand. On drying they show shrinkage, causing injury to the cement.

Therefore, clay minerals in aggregates should not exceed 3%.

Uses of aggregates: We need aggregate to meet our basic needs of construction as under:

Civil Engineering Structures

Public Sector

High Life Risk

Structures

Dams

Bridges

High Building Towers

Low Life Risk

Structures

Roads

Schools

Hospitals

Private Sector

High Life Risk

Structures

Skyscrapers

Plazas

Monuments

Low Life Risk

Structures

Houses

Pavements

Safety Structures (Parapets)

Sewerage storm water

drainage

Classification of Aggregates:

In Accordance with size: Course Aggregate: Retained on the No.4 (4.75mm) sieve. Fine Aggregate:

Aggregate passing No.4 sieve and predominantly retained on the No.200 sieve.

In Accordance with Source: Natural Aggregates: Aggregate is taken from natural

deposits. Some example are sand, crushed limestone, dolomite and gravels.

Manufactured Aggregates: Man-made materials produces as a main product or an industrial by-product. Some examples are blast furnace slag, lightweight aggregate and heavy weight aggregate.

In Accordance with Weight:Light weight aggregate:

Their unit weight is less than 1120kg/m3 and bulk density less than 1800kg/m3. Examples are Cinder, blast furnace slag,

volcanic pumice.

Normal weight aggregate: Their unit weight is 1520-1680kg/m3 and bulk density of 2300-24—kg/m3.

Heavy weight aggregate: Their unit weight is greater than 2100kg/m3

and the bulk density is greater than 3200kg/m3. A typical example is magnetite limonite, a heavy iron ore.

Types of aggregates:

Granite aggregates

Granite aggregates are crushed hard rock of granular structure, being the most common on Earth. It is the best aggregate for high-grade concrete

Gravel aggregates Gravel aggregates are aggregates acquired as the result of examining mined rock and by crushing natural stone rock. Gravel aggregates are used for foundations and concretes

Limestone aggregates Limestone is one of the main types of aggregates that besides the gravel and the granite types is used in road construction and in production of reinforced concrete objects.

Secondary aggregates:  Secondary aggregate comes from crushing construction

waste – concrete, bricks, and asphalt. These aggregates are used:

As a large-scale filler for concretes In road construction as a filler for roads and ramps

Slag aggregates  Slag aggregates are obtained by crushing of smelter slag

The cost of products from slag concretes is 20-30% lower than traditional ones.

Properties of Aggregate:

Strength

Hardness

Toughness Durability Shape of Aggregate

Specific Gravity Absorption, Porosity, Permeability

Properties of Aggregate:

Strength

• The aggregates should be sufficiently strong to bear the subjected load due to traffic wheel load, wear and tear, crushing, and structure load.

Hardness

• Hardness is the measure of resistance to crushing and abrasion of aggregate.

• Aggregate are subjected to crushing and abrasive wear during production, placing, compaction and also subjected to abrasion under traffic load

Toughness• Toughness is the ability of aggregate to resist

impact forces• Aggregates which lack adequate toughness and

abrasion resistance may cause construction and performance problems.

Durability• Aggregates must be resistant to breakdown, and

disintegration from weathering or they may break apart.

• Durability and soundness are terms typically given to aggregates weathering resistance characteristics

Specific Gravity

• The ratio of the mass of unit volume of material at a stated temperature to the mass of same volume of gas -free distilled water at a stated temperature

• Higher value of specific gravity indicates better aggregate, but the other properties should be necessary.

Absorption, Porosity, Permeability

• The size, number and continuity of pores through the aggregate particles may affect the strength of aggregate, abrasion resistance, surface texture, specific gravity, bonding capability and resistance to freeze and thaw action.

• Aggregates with low specific gravity and high water absorption are generally considered unsuitable unless they have acceptable hardness, toughness and strength properties.

Shape of Aggregate

• Particle shape and surface texture are important for proper compaction, deformation resistance and workability.

• In Hard Mix Asphalt (HMA), since aggregates are relied upon to provide stiffness and strength by interlocking with one another, cubic angular-shaped particles with a rough surface are best.

• However, in Plane Cement Concrete (PCC) rounded particles are better

Tests on Aggregate:

Specific Gravity And Water Absorption Test:Los Angeles Abrasion Test on coarse

aggregate:Soundness Test:Shape Test or Flakiness Index

Specific Gravity And Water Absorption Test:

Apparatus:

Oven Balance A wire mash basket not larger than

6.5mm A container in which basket may be

freely suspended. Two soft absorption cloths.

Procedure Sieving the sample through a No.4 sieve Wash the aggregate retained on No.4 sieve. Drying test sample. Immersion in the water. Placing the sample in wire mash basket and weigh in water

container at 23C. Using an absorbent cloth (towel) dry the surface of aggregate

by rolling up. Weigh the SSD (Saturated surface-dry condition) sample as

W2.

Dry the sample in oven at 110C for 1-3hrs.cool in air at room temperature, and then weigh as oven dry weight (W1).

Calculation:Bulk specific gravity:

Gsb= W2 /(W2 – W3)

W2 = SSD weight

W3 = Weigh in water

Apparent Specific gravity:Gsa = W1 /(W2– W3)

W1 = oven dry weight

Absorption:Abs% = [(W2 – W1) / W1] x 100

Important Points:The specific gravity of normally used in road construction ranges

from 2.5 to 3. High specific gravity of aggregate is indication of high strength.Water absorption value ranges from 0.1% to 2% for aggregates

used in road surfacing. Stone with absorption up to 4% have been used in base courses. Generally, less than 0.6% is considered desirable for surface

course.

LOS ANGELES ABRASION TEST ON COARSE AGGREGATE:

Apparatus: Los Angeles testing machine Test sieves Oven Balance 12-steel balls of 46.0-47.6mm

in diameter Sieve size Mass of indicated size(g)Passing Retained Grading    A B C D

37.5mm 25.0mm 1250      25mm 19mm 1250      19mm 12.5mm 1250 2500    

12.5mm 9.5mm 1250 2500    9.5mm 6.3     2500  6.3mm 4.74mm     2500  

4.75mm 2.36mm       5000Total   5000 5000 5000 5000

Principle: The Los Angeles test is a measure of degradation of mineral

aggregate Impact and grinding in a rotating steel drum containing a specified

number of steel balls. After the prescribed number of revolutions, and the aggregate

portion is sieved to measure the degradation as percentage loss.

Calculation:

Abrasion % = Wt. of initial sample – Wt. of retained of 1.7mm sieve x 100 Wt. of initial sample (total Wt.)

= Wt. of passing sieve (1.7mm) x 100 Wt. of initial sample

Important point: If it is less than 30% then this aggregate is suitable for all mixtures

if it is more than 50% then this aggregate is unusual for any mixture

Soundness TestSoundness is the resistance of aggregate to become worse by the

action of freeze and thaw.

Objective: the objective of test is to estimate the soundness of aggregates subjected to weathering action.

Apparatus Test sieve Oven Balance Perforated Container for immersion of aggregate in solution Basket made of wire mesh

Main Principle: The soundness test is accomplished by repeated

immersion of test sample in saturated solution of sodium sulfate followed by oven drying to partially or completely dehydrate the salt precipitation in permeable pore spaces.

Repeat the process of immersion and drying until the required no. of cycle is obtained.

Shape Test or Flakiness Index:

Objective: This test is used to determine the percentage of

flakiness and elongation of particles in aggregate.

The presence of flaky and elongated particles are considered undesirable as they may cause weakness or breaking down under load.

Main Principle: The flakiness index of aggregate sample is found

by separating the flaky particles and expressing their mass as a percentage of mass of Aggregate sample.

Apparatus: A thickness gauge Balance Metal trays Oven Sieves (flakiness measuring sieves) of size

related to the Thickness Gauge.

Problem Associated with Aggregates:

Cleanliness and Deleterious Materials. Aggregates must be relatively clean. Vegetation, soft particles, clay lumps and excess dust matter

may affect performance by quickly degrading, which causes a loss of structural support and/or prevents binder-aggregate bonding.

Clay The aggregate is carefully mixed with water in volumetric cylinder and

then let to settle. The clay particles will form layer with different color and structure on

the surface of aggregate.

Organic Impurities: Decaying vegetation may result in aggregates being contaminated

with organic matter. This material may have a retarding effect on the setting of

cementitious material and may result in lower strengths of the hardened material at all ages.

Organic impurities can be tested by colorimetric test. Tested aggregate is mixed with sodium hydroxide (NaOH) or potassium hydroxide (KOH) to prepare colored solution.

The color of solution is compared with color of standard solution, prepared according the standard. If the color of the test solution is darker than the standard solution, than aggregate have to be rejected.

Alkali-Reaction: One of the most important examples of reactive aggregates is

the Alkali-aggregate reaction in which alkali hydroxides react with the reactive silicates to form alkali silica gels which subsequently absorb water from their surroundings.

This leads to internal stresses in hardened concrete until its tensile strength is reached and it cracks.

The method to control the alkali-aggregate reaction is to limit the alkali content of the Portland cement to 0.6% or less.

BEST ROCK SOURCE AGGREGATE: • The best rock source aggregate is a debatable topic depending upon the

project specific studies..• Some materials used as aggregates have a higher specific gravity but

their impact values can be lesser as needed in the specific project• . For example, the specific gravity of Limestone is 2.69 gm/cm3 and of

basalt is 2.91gm/cm3 but their impact values are 20 and 13 respectively which indicates that Limestone having lesser specific gravity is more suitable in Asphalt aggregates whereas Basalts are more suitable to be used in high life risk structures like columns and foundations of bridges rather than to be used as Asphalt aggregate.

• However, the best aggregate sources with their workability are Limestone, Dolerite, Basalts whereas Quartizites, Hornfels, Microgranite are good but have less reserves.

SOURCE OF AGGREGATES IN PAKISTAN

• . Pakistan is country which is fully equipped with natural resources. There are various aggregates sources in Pakistan meeting the international engineering standards and comprise of compressive strengths which can be used in any project.

• The most extensively used aggregate source in most of the Pakistan is Margalla Hill Limestone, most of the quarrying activity is observed in the margalla hill source located at Hassanabdal and Taxila regions of Panjab.

• The sakesar limestone of Salt Range is also feeding most of the southern Punjab and vicinity.

• There is a lot of construction material sources situated in Azad Jammu and Kashmir. The Khwaja Seri area of Neelum valley has considerable reserves of Dolerite.

• Khurshidabad Distt. Haveli has massive exposure of Limestone. Similarly, the Bakot area near Kohala also of millions of tons of limestone.

• There is also a 10m thick bed of Margalla Hill Limestone in kamsar area Yadgar section. The aforementioned sources are usable for strengths up to 3000 Psi and structures with greater life risk structures.

• There are unlimited resources of Dolomite in Abbottabad formation which is exposed in most of Hazara, Muzaffarabad, Pir Panjal Range, District Kotli (Karjai Antlicline) and other parts of Pakistan. The SS1 of Murree Formation is a very considerable aggregate for marginal use if batch wise testing and project specific studies area considered accordingly.