04: Aggregates Flashcards
Definition of Aggregate
• The term “aggregates” generally refers to mineral particles which have rocks as their origin unless otherwise specified.
• Aggregate; the inert filler materials, such as sand or gravel, used in making concrete
• Aggregates make up 60-75% of total volume of concrete (normal/ordinary concrete) 90% of asphalt pavements.
• Sand, gravel, boulders, stones or rocks that can be crushed into particles.
• By-product or waste material from industrial process or mining operation.
What are the Aggregate Sources
Natural Aggregate
• Sand and Gravel Mine (Pit)
• Quarry
Contrived Aggregate
• Recycled
Aggregates that come from
unconsolidated sand and gravel
deposits. Typically deposited by
streams (alluvium) or glaciers.
Sand and Gravel Mine (Pit) Aggregates
Aggregates that come from bedrock deposits. Bedrock, which is a consolidated rock includes: granite,
basalt, quartzite, gabbro, etc.
Quarry Aggregates
Products that include crushed concrete, bituminous or demolition debris and in some instances taconite tailings.
Recycled Aggregates
Methods of Extraction and Processing
Underwater Sources
• Dragline Extraction
• Dredging
Land Sources
• Track Drills
• Blasting Bedrock
• Crushers and Screens
Classification of Aggregates
Based on Shape
• Rounded aggregates
• Irregular or partly rounded aggregates
• Angular aggregates
• Flaky aggregates
• Elongated aggregate
• Flaky and elongated aggregates
These are completely shaped by attrition and available in the form of seashore gravel. These aggregates result the minimum percentage of voids (32-33%) hence gives more workability.
Rounded Aggregates
They require lesser amount of water-cement ratio. They are not considered for high strength concrete because of poor interlocking behavior and weak bond strength.
Rounded Aggregates
When the length of aggregate is larger than the other two dimensions then it is called _______ aggregate or the length of aggregate is greater than 180% of its mean dimension.
Elongated Aggregate
When the aggregate thickness is small when compared with width and
length of that aggregate, it is said to be?
Flaky Aggregate
When the least dimension of aggregate is less than the 60% of its mean dimension then it is
said to be?
Flaky Aggregate
This aggregates are partly shaped by attrition and these are available in the form of pit sands and gravel.
Irregular Aggregate
It may result 35-37% of voids. These will give lesser workability when compared to rounded aggregates. The bond strength is slightly higher than rounded aggregates but not as required for high strength concrete.
Irregular Aggregate
It consist well defined edges formed at the intersection of roughly planar surfaces and these are obtained by crushing the rocks.
Angular Aggregate
It result maximum percentage of voids (38-45%) hence gives less workability. They give 10-20% more compressive strength due to development of stronger aggregate-mortar bond. So, these are useful in high strength concrete manufacturing.
Angular Aggregate
Classification of Aggregates
Fine Aggregates
Coarse Aggregates
Define Fine Aggregates
• Sand and/or crushed stone
• <5 mm (0.2 in.)
• F.A. content usually 35% to 45% by
mass or volume of total aggregate
Define Course Aggregate
• Gravel and crushed stone
• ≥ 5 mm (0.2 in.)
• typically between 9.5 and 37.5 mm
Enumerate Aggregate Properties
• Strength
• Hardness
• Impact Value
• Resistance against Weathering (Weathering Resistance)
• Shape of Aggregate
• Bitumen Adhesion
• Specific Gravity/Relative Density
• Water Absorption
Aggregate crushing value gives the crushing strength of aggregate up to which it can bear the load without fail.
Crushing Strength Test
Hardness property of aggregate is determined by conducting what kind of test?
Abrasion Test
.
.
.
.
.
Los Angeles abrasion testing machine is used to conduct this test.
Shape of aggregate is also 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 mix.
Shape Test
This test will give the stripping of bitumen from the aggregate.
In case of bitumen pavement, the bitumen should be in pure contact with aggregate. To attain this aggregate should be clean and dry.
Bitumen Adhesion Test
To determine the stripping value of bitumen what kind of test is conducted on aggregates?
Static Immersion Test
Impact value of aggregate will give aggregate capability against sudden loads or forces.
Impact Test
To determine the weathering resistance of aggregate, this kind of test is conducted. If the resistance against weathering is good for aggregate, then it will have high durability.
Soundness Test
This property of an aggregate is the ratio of its mass to that of an equal volume of distilled water at specific temperature.
Specific Gravity (Test)
The specific gravity of aggregate is of two types, these are?
• Bulk specific gravity, in which total volume of aggregates along with their void space is considered.
• Apparent specific gravity, in which the volume of aggregates without considering void spaces is taken into account
This test helps to determine the water absorption value of aggregate.
Water Absorption Test
Kinds of Testing of Sand Quality in Construction Sites
• Organic Impurities Test
• Silt Content Test
• Particle Size Distribution
• Bulking of Sand
Sand shall not contain any harmful impurities such as iron, pyrites, alkalis, salts, coal or other organic impurities, mica, shale or similar laminated materials, soft fragments, sea shale in such form or in such quantities as to affect adversely the hardening, strength or durability of the mortar.
This test is conducted at the field, for every 20 cu m or part thereof.
Organic Impurities Test
.
.
.
.
.
The maximum quantities of clay, fine silt, fine dust and organic impurities in the sand/marble dust shall not exceed the following limit:
• Clay, fine silt and fine dust when determined in accordance within not more than 5% by mass in IS 2386 . natural sand or crushed gravel sand and crushed stone sand.
• Organic impurities when determined in color of the liquid shall be lighter in accordance with IS 2386
The maximum quantity of silt in sand shall not exceed 8%. Fine aggregate containing more than the allowable percentage of silt shall be washed so as to bring the silt content within allowable limits.
This is also a field test and to be conducted for every 20 cu m.
Silt Content Test
On the basis of particle size, fine aggregate is graded into four zones Where the grading falls outside the limits of any particular grading zone of sieves, other than 600 micron IS sieve, by a total amount not exceeding 5 percent, it shall be regarded as falling within that grading zone.
This test can be conducted at site or in laboratory for every 40 cum of sand
Particle Size Distribution
Fine aggregate, when dry or saturated, has almost the same volume but dampness causes increase in volume. In case fine aggregate is damp at the time of proportioning the ingredients for mortar or concrete, its quantity shall be increased suitably to allow for bulkage.
This test is conducted at site for every 20 cu m of sand. Based on bulking of sand, suitable water cement ratio is calculated for
concrete at site
Bulking of Sand
