Settlings in Structure, Early-age Cracking and Deformation, Neccesity of Aggregates, Classification, Tests for selection

1. 1
Hello!
I am Dr. Subash.T
Associate Professor
PhD (Civil Engg.), M.E(Env.Engg.), B.E (Civil Engg.)
Department of Civil Engineering
School of Civil and Environmental Engineering
Ambo University, Ambo, Ethiopia.
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+251 - 939722372

2. Construction Materials
Module- 3
Study on Aggregates for Concrete

3. Settling of structure – a View
• Settlement in a structure refers to the distortion or
disruption of parts of a building due to unequal
compression of its foundations; shrinkage after its
initial construction.
Types of Building Settlement
• Uniform Settlement:
During uniform settlement, the entire foundation
settles at a constant rate. ...
• Differential Settlement :
Differential settlement commonly occurs as a result
of the non-uniform movement of the underlying
soils (soil settlement at different rates).

5. Over time, foundations can settle because of shifts in the
earth or rock beneath them. Differential settlement occurs
when the ground beneath a building shifts or settles
unevenly, creating stresses on foundations and slabs.
Reasons for Differential Settlement
A number of different factors can contribute to differential
settlement issues. Some of the common reasons include the
following:
• “Trees, shrubs and other plants” can sometimes reduce the levels
of moisture in the area surrounding the structure. This can cause
soil to dry out and to provide less support for some areas of
building.
• The “wrong kind of soil” can also cause serious issues with settling
of the foundation or slab of your building. Over time, soils can
become compressed and incapable of providing adequate support
for larger structures. Clay soils are especially prone to excessive
compression.
• “Seismic activity” can create vibrations that can settle soil and
underlying layers of rock to cause serious issues for building.

6. Factors influencing Differential settling of Structure

7. Variations on Bearing Capacity

8. Problems with Differential Settlement in the
Construction Field
When different parts of a building settle at
significantly different rates because of changes in soil
conditions or seismic activity, this often causes a
number of unwanted side effects:
• Distortions or warping of the frame of the building
• Improper fit and function for doors and windows
• Cracks and deterioration of foundations and slabs
• Damage to walls and to flooring
• Structural instability that could result in building
being deemed unfit for occupation or habitation

9. Example for Differential settling of structure:
The most familiar example of differential settlements and their
consequences is the Leaning Tower of Pisa, which took two centuries
to build due to problems with differential settlements and inclination.

10. Because Pisa is built on wetlands, with the geological
profile of the soil consisting of clay and fine sand, and is
characterized by a high level of groundwater, conditions
for the construction of a tall structure have been
challenging since the very beginning.
The main cause of the differential settlement and
inclination of the Tower is the increased deformability
and compressibility of the foundation soil in the area
underneath the southern part of the Tower.
Note: Differential settlements can cause ‘significant
problems’ for other, lower structures as well, and it is
necessary to be familiar with the ‘potential measures’ in
order to eliminate them or at least reduce their effect to
an acceptable level.
ex. Selection of Suitable Aggregates,
Admixtures etc… for a Stable Foundation

11. Early – Age-Cracking
Early – Age - Deformation
• Early-age cracks are defined as ‘cracks’ that
generally develop within the first seven days
after the placement of concrete.
• Because of “temperature differences” and
“stress development during hardening of
concrete”.
• High-strength concrete is more prone to early-
age cracking due to autogenous shrinkage.
• Drying shrinkage hardly plays a role to cause the
early-age cracking in concrete.

12. • What is autogenous shrinkage?
It is “change in volume” due to the chemical
process of hydration of cement, exclusive of
effects of applied load and change in either
thermal condition or moisture content.

13. Autogenous Shrinkage and Drying Shrinkage
Autogenous shrinkage is caused by the “withdrawal of water from
the capillary pores in the hydrating paste”. The magnitude of
autogenous shrinkage increases as the water/cementitious ratio
decreases. Autogenous shrinkage is important in HSC, because
low water/cementitious ratios are used to obtain high strengths.
Note: The magnitude of autogenous shrinkage of concrete is also
proportional to paste content.
Drying shrinkage is the volumetric contraction of concrete by the
removal of water. Concrete with high water/cement ratios contain
more water that can be removed from the paste. Similarly
concrete with high paste content will also shrink more, due to the
overall higher water content. When the aggregate content is
increased from approximately 71% to 74%, drying shrinkage can
be reduced by as much as 20% (Neville 1995).

14. Early-age transverse cracks that occurred in a newly cast
reinforced concrete column; these cracks occurred within three
days after placing of concrete, the column was cured by wet
burlap

15. Early-age transverse crack in a concrete pavement slab
which widened over time; this crack started within 56 days
of concrete placement, the slab was cured using curing compound

16. Early-age corner crack in a concrete side-walk slab; this
crack appeared within 35 days after concrete
placement, the concrete slab was cured by curing compound

17. Early-age random cracks that occurred in a concrete
floor slab; most of these cracks appeared within 42 days
after placing of concrete, the slab was cured using
thermal curing blanket

18. Early-age map cracks that occurred in a newly cast concrete
floor slab; these cracks appeared within 14 days of concrete
placement; the floor slab was cured by spraying of water.

19. Restrained shrinkage cracking that occurred in a roadside concrete
curb; this crack initiated within 56 days of concrete placement; the
curb was cured with curing compound

20. Various Factors influencing Cracking on a Structure

21. Impact of Paste in Concrete
• Paste: “volumetrically unstable component of
concrete”.
“More Paste content Deformation
properties of concrete” are significantly
influenced.

22. Effect of paste content on the properties of
high-strength concrete pavements
Case study:
The paste content of the first set was varied from 23% to 37% by
mass, using multivariable analysis in conjunction with
superplasticiser (SP) dosage. The paste content of the second
set was varied from 25% to 60% by mass, only varying SP dosage
to control the workability.
The multivariable analysis revealed that, within the parameter
range tested, paste content influenced early-age properties, but
not long-term properties. Through variation of the paste content
over a wider range during the second set it was found that paste
content does influence both the early-age and long-term
properties of HSC. From the results it could be seen that
increasing the paste content of HSC generally has a detrimental
effect. The paste content of HSC used in UTCRCP should be
minimised, while maintaining a reasonable workability.

23. Note-1: Concrete undergoes a combination of load dependent
and load-independent deformation .throughout its lifetime.
Note-2: “Load-independent deformation” is a function of a
combination of ‘moisture and temperature effects’.
Fig: Load-independent and load-dependent deformation properties

24. Property-1: Fresh properties (Contour plot of
flow)

25. Hints from Figure-1
• Both “paste content” and “SP dosage”
influence the workability of HSC to the same
extent.
• When looking at the spacing between the
contour lines diagonally, it can be seen that
the flow increases faster at lower percentages
of the constituents.
• The improvement of flow flattens out towards
the higher paste content and SP dosage.

26. Property-2: Hydration properties

27. Hints from Figure-2
• The above Figure shows that the “maximum
temperature reached” under “semi-adiabatic
conditions has a positive correlation to the
paste content”.
• The SP dosage seemed to decrease the
maximum temperature reached at specific
paste content. This could be due to a
retardation effect, where the combination of
the retardation of heat generation and heat
dissipation impedes high maximum
temperatures

28. Property-3:Mechanicalproperties
The contour plot showed in Figure below shows that the
highest early-age strength can be achieved when the lowest paste
content and SP dosage is used. The workability of such a concrete
mix would be impractically low.

29. Introduction - Aggregate
• Aggregates make up 60-80% of the volume
of concrete and 70-85% of the mass
of concrete.
• Aggregate is also very important for strength,
thermal and elastic properties of concrete

30. Introduction - Aggregate
• Aggregate is a broad category of coarse- to
medium-grained particulate material - used in
construction, including sand, gravel, crushed
stone, slag, recycled concrete and geosynthetic
aggregates.
• Aggregates are a component of ”composite
materials” - such as concrete and asphalt
concrete; the aggregate serves as reinforcement
to add strength to the overall composite material.

31. Why do we use aggregates in
concrete?
• There are many reasons:
Reason-1: “Perhaps the biggest reason in cost”.
(Using aggregate as a filler can help concrete producers save a
lot of money. Cement usually costs seven or eight times what
stone and sand cost)
Reason-2: Aggregate is also very important for strength, thermal
and elastic properties of concrete, dimensional stability and
volume stability.
Reason-3: Cement is more likely to be affected by shrinkage.
Including aggregate in the mix can control the shrinkage level
and prevent cracking.

33. What type of rock is aggregate?
• Aggregates that are derived from natural
sources typically come from three different
rock types: igneous, sedimentary and
metamorphic.
• The mineral properties of the aggregate
determine the appearance of the rock and
also help determine its capabilities, including
if and how it can be used for paving.

34. Basic properties of aggregates
Basic properties of aggregates include:
i) Mineralogical composition
ii) surface texture and grain shape,
iii) Dustiness
iv) Porosity
v) Frost resistance
vi) Resistance to abrasion and polishing
vii)Asphalt absorption capacity

35. Mineral Compositions in Aggregate

36. Applications of Aggregates
• Foundation
• French drains
• Septic drain fields
• Retaining wall drains
• Roadside edge drains
• Base material under foundations, roads, and railroad
etc
In other words, aggregates are used as a stable
foundation or road/rail base with predictable, uniform
properties (e.g. to help prevent differential settling
under the road or building), or as a low-cost extender
that binds with more expensive cement or asphalt to
form concrete.

37. Classification of Aggregates
• Classification of aggregates based on: Grain
Size
• Classification of aggregates based on: Density
• Classification of aggregates based on:
Geographical Origin
• Classification of aggregates based on: Shape

38. Classification of aggregates based on: Grain Size
There are two overriding categories:
• Fine
• Coarse
• The size of fine aggregates is defined as 4.75mm or smaller. That is,
aggregates which can be passed through a number 4 sieve, with a
mesh size of 4.75mm. Fine aggregates include things such as sand,
silt and clay. Crushed stone and crushed gravel might also fall under
this category.
• Typically, fine aggregates are used to improve workability of a
concrete mix.
• Coarse aggregates measure above the 4.75mm limit. These are
more likely to be natural stone or gravel that has not been crushed
or processed. These aggregates will reduce the amount of water
needed for a concrete mix, which may also reduce workability but
improve its innate strength.

39. • Generally coarse aggregate is blended with
finer aggregates (such as sand) to fill in the
spaces left between the large pieces and to
“lock” the larger pieces together.
• This reduces the amount of cement paste
required and decreases the amount of
shrinkage that could occur.

40. Classification of aggregates based on: Density
There are three weight-based variations of aggregates:
• Lightweight
• Standard
• High density
• Different density aggregates will have much different applications.
Lightweight and ultra lightweight aggregates are more porous than
their heavier counterparts, so they can be put to great use in green
roof construction, for example. They are also used in mixes for
concrete blocks and pavements, as well as insulation and
fireproofing.
• High density aggregates are used to form heavyweight concrete.
They are used for when high strength, durable concrete structures
are required – building foundations or pipework ballasting, for
example.

43. Lightweight aggregate. Expanded clay
(left) and expanded shale
Coarse aggregate. Rounded gravel (left) and
crushed stone (right

44. Classification of aggregates based on: Geographical Origin
• Natural – Aggregates taken from natural sources,
such as riverbeds, quarries and mines. Sand,
gravel, stone and rock are the most common, and
these can be fine or coarse.
• Processed – Also called ‘artificial aggregates’, or
‘by-product’ aggregates, they are commonly
taken from industrial or engineering waste, then
treated to form construction aggregates for high
quality concrete. Common processed aggregates
include industrial slag, as well as burnt clay.
Processed aggregates are used for both
lightweight and high-density concrete mixes.

45. Classification of aggregates based on: Shape
Shape is one of the most effective ways of differentiating aggregates. The shape of your
chosen aggregates will have a significant effect on the workability of your concrete.
The different shapes of aggregates are:
• Rounded – Natural aggregates smoothed by weathering, erosion and
attrition. Rocks, stone, sand and gravel found in riverbeds are your most
common rounded aggregates. Rounded aggregates are the main factor
behind workability.
• Irregular – These are also shaped by attrition, but are not fully rounded.
These consist of small stones and gravel, and offer reduced workability to
rounded aggregates.
• Angular – Used for higher strength concrete, angular aggregates come in
the form of crushed rock and stone. Workability is low, but this can be
offset by filling voids with rounded or smaller aggregates.
• Flaky – Defined as aggregates that are thin in comparison to length and
width. Increases surface area in a concrete mix.
• Elongated – Also adds more surface area to a mix – meaning more cement
paste is needed. Elongated aggregates are longer than they are thick or
wide.
• Flaky and elongated – A mix of the previous two – and the least efficient
form of aggregate with regards to workability.

47. Unit weight classification
• Normal weight aggregates
They have a specific gravity between 2.5 to 2.7
produce concrete with unit weight ranging from 23 to
26 KN/m3 and crushing strength at 28 days between 15
to 40 MPa are termed normal weight concrete.
The commonly used aggregates. i.e. Sands and gravels:
crushing rocks such as granites, basalt, quartz,
sandstone and limestone, and brick ballast, etc.
• Light Weight aggregates
The lightweight aggregates having a unit weight up to
12 KN/m3 used to manufacture the structural concrete
and masonry blocks for the reduction of the self-
weight of the structure.

48. Following are the important properties of fine aggregates
1. Size: The size of fine aggregate should be equal to or less than 4.75 mm.
2. Shape: Sand of irregular nodular shape is preferable to completely round grained
sand. Shape of the aggregate plays a more important role in coarse aggregate rather
than fine aggregate.
3. Specific Gravity: It is the ratio of density of aggregate to the density to water.
4. Bulk density: It is the ratio of weight of aggregate (including voids) to its unit volume.
5. Moisture Content (% Water absorption): It is the ratio of weight of water absorbed to
weight of dry aggregate; measured in percentage.
6. Bulking: Bulking of sand means increase in volume of sand due to surface moisture.
7. Surface Texture: Surface texture is the property which defines whether a particular
surface is polished, dull, smooth or rough. Generally rough surface aggregate is
preferable to smooth aggregates.
8. Soundness: Soundness means the ability of aggregates to resist excessive change in
volume as a result of change in physical condition.
9. Durability: Some of the aggregate contain reactive silica, which reacts with alkalies
present in cement and hence reduce the durability. Durability is the ability to resist
against the weathering actions, chemical attack, etc.
10. Silt content: It is defined as the total quantity of fine particles of deleterious
materials having particle from 0.06 mm to 0.002 mm present in sand.

49. Porosity: Aggregation involves particulate adhesion
and higher resistance to compaction. Typical bulk
density of sandy soil is between 1.5 and 1.7 g/cm3.
This calculates to a porosity between 0.43 and 0.36.
Dustiness: Dustiness, defined as the tendency of a
powder material to generate airborne particles
under an external energy input.
Frost resistance is the property that a material can
withstand several freeze-thaw cycles without being
destroyed and its strength does not decrease
seriously when the material absorbs water to
saturation. It is expressed by frost-resistant level.

50. QUALITY REQUIREMENTS OF AGGREGATE
• Aggregates should be strong, hard, dense, durable, clear and free from
veins and adherent coating.
• Aggregates should be free from injurious amounts of disintegrated pieces,
alkalis, vegetable matter and other deleterious substances.
• Flaky and Elongated pieces should not be present in aggregate mass.
• Aggregate crushing value should not exceed 45 percent for aggregate used
for concrete other than for wearing surfaces, and 30 percent for concrete
for wearing surfaces, such as runways, roads and pavements.
• Aggregate impact value should not exceed 45 percent by weight for
aggregates used for concrete other than for wearing surfaces and 30
percent by weight for concrete for wearing surfaces, such as runways,
roads and pavements.
• Abrasion value of aggregate when tested using Los Angeles machine,
should not exceed 30 percent by weight for aggregates to be used in
concrete for wearing surfaces and 50 percent by weight for aggregates to
be used in other concrete.

51. Minerals and Rocks Types

52. CHARACTERISTICS OF AGGREGATES
Grading: Grading is the particle-size distribution of an aggregate
as determined by a sieve analysis.
Range of particle sizes found in aggregate for
use in concrete.
The grading and grading limits

53. Coarse aggregates are defined as any material greater
than 4.75 mm. A coarse aggregate is also identified as
any aggregate retained in a #4 sieve. Fine aggregates
are any material less than 4.75 mm that can pass
through a #4 sieve and is retained on a #200 sieve.

54. TESTS ON AGGREGATE
In order to decide the suitability of the
aggregate for use in pavement construction,
following tests are carried out:
• Crushing test
• Abrasion test
• Impact test
• Soundness test
• Shape test
• Specific gravity and water absorption test
• Bitumen adhesion test

56. Fig-1 Crushing Test Setup

57. 1.CRUSHING TEST
• The test consists of subjecting the specimen of aggregate in
standard mould to a compression test under standard load
conditions (See Fig-1). Dry aggregates passing through 12.5 mm
sieves and retained 10 mm sieves are filled in a cylindrical measure
of 11.5 mm diameter and 18 cm height in three layers. Each layer is
tamped 25 times with at standard tamping rod. The test sample is
weighed and placed in the test cylinder in three layers each layer
being tamped again. The specimen is subjected to a compressive
load of 40 tonnes gradually applied at the rate of 4 tonnes per
minute. Then crushed aggregates are then sieved through 2.36 mm
sieve and weight of passing material (W2) is expressed as
percentage of the weight of the total sample (W1) which is the
aggregate crushing value.
Aggregate crushing value = (W1/W2)*100
• A value less than 10 signifies an exceptionally strong
aggregate while above 35 would normally be regarded as weak
aggregates.

58. Los Angeles Abrasion Test Setup

59. 2.ABRASION TEST
• Abrasion test is carried out to test the
hardness property of aggregates and to decide
whether they are suitable for different
pavement construction works.
• The principle of Los Angeles abrasion test is to
find the percentage wear due to relative
rubbing action between the aggregate and
steel balls used as abrasive charge.

60. • Los Angeles machine consists of circular drum of internal diameter 700
mm and length 520 mm mounted on horizontal axis enabling it to be
rotated (see Fig-2). An abrasive charge consisting of cast iron spherical
balls of 48 mm diameters and weight 340-445 g is placed in the
cylinder along with the aggregates. The number of the abrasive
spheres varies according to the grading of the sample. The quantity of
aggregates to be used depends upon the gradation and usually ranges
from 5-10 kg. The cylinder is then locked and rotated at the speed of
30-33 rpm for a total of 500 -1000 revolutions depending upon the
gradation of aggregates.
• After specified revolutions, the material is sieved through 1.7 mm
sieve and passed fraction is expressed as percentage total weight of
the sample. This value is called Los Angeles abrasion value.
• A maximum value of 40 percent is allowed for Water Bound
Mechadam (WBM) base course in Indian conditions. For bituminous
concrete, a maximum value of 35 percent is specified.

61. Impact Test Setup

62. L.A. abrasion testing equipment
Steel spheres

65. Corresponding to the Selective Grades, Take the Abrasive
Charge
For Example, The “A” rating is for all natural sands. The “B” rating is for
manufactured fine aggregates.

68. After sieving through 1.7 mm Sieve

72. Test Concept
• The L.A. abrasion test measures the degradation
of a coarse aggregate sample that is placed in a
rotating drum with steel spheres. As the drum
rotates the aggregate degrades by abrasion and
impact with other aggregate particles and the
steel spheres (called the “charge”). Once the test
is complete, the calculated mass of aggregate
that has broken apart to smaller sizes is
expressed as a percentage of the total mass of
aggregate. Therefore, lower L.A. abrasion loss
values indicate aggregate that is tougher and
more resistant to abrasion.

73. Approximate Test Time
3 days from aggregate sampling to final weight determination.
A breakdown of testing time follows:
Reducing a sample to testing size 5 – 10 minutes
Washing the sample 5 – 10 minutes
Drying to a constant mass 8 – 12 hours (overnight)
Time in rotating drum 15 minutes
Sieving and rewashing 30 minutes
Drying to a constant mass 8 – 12 hours (overnight)
Final weighing 5 – 10 minutes

74. Figure shows typical before and after L.A. abrasion
aggregate samples

75. Determine the percent loss as a percentage of the
original sample mass.
Where:
Moriginal = original sample mass (g)
Mfinal = final sample mass (g)

76. • The aggregate impact test is carried out to evaluate the resistance
to impact of aggregates. Aggregates passing 12.5 mm sieve and
retained on 10 mm sieve is filled in a cylindrical steel cup of internal
dia 10.2 mm and depth 5 cm which is attached to a metal base of
impact testing machine. The material is filled in 3 layers where each
layer is tamped for 25 numbers of blows (see Fig-3). Metal hammer
of weight 13.5 to 14 Kg is arranged to drop with a free fall of 38.0
cm by vertical guides and the test specimen is subjected to 15
numbers of blows. The crushed aggregate is allowed to pass
through 2.36 mm IS sieve. And the impact value is measured as
percentage of aggregates passing sieve (W2) to the total weight of
the sample (W1).
• Aggregate impact value = (W1/W2)*100
• Aggregates to be used for wearing course, the impact
value shouldn’t exceed 30 percent. For bituminous
macadam the maximum permissible value is 35 percent. For Water
bound macadam base courses the maximum permissible value
defined by IRC is 40 percent.

77. Soundness test
• Soundness test is intended to study the resistance of aggregates to
weathering action, by conducting accelerated weathering test
cycles. The Porous aggregates subjected to freezing and thawing is
likely to disintegrate prematurely. To ascertain the durability of such
aggregates, they are subjected to an accelerated soundness test as
specified in IS: 2386 part-V.
• Aggregates of specified size are subjected to cycles of alternate
wetting in a saturated solution of either sodium sulphate or
magnesium sulphate for 16 – 18 hours and then dried in oven at
105 to 1100C to a constant weight. After five cycles, the loss in
weight of aggregates is determined by sieving out all undersized
particles and weighing.
• The loss in weight should not exceed 12 percent when tested
with sodium sulphate and 18 percent with magnesium
sulphate solution.

78. SHAPE TESTS
• The particle shape of the aggregate mass is determined
by the percentage of flaky and elongated particles in it.
Aggregates which are flaky or elongated are
detrimental to higher workability and stability of mixes.
• The flakiness index is defined as the percentage by
weight of aggregate particles whose least dimension
is less than 0.6 times their mean size.
• The elongation index of an aggregate is defined as the
percentage by weight of particles whose greatest
dimension (length) is 1.8 times their mean dimension.
This test is applicable to aggregates larger than 6.3
mm. Elongation gauge (see Fig-5) is used for this test.

79. Flakness Index Gauge

81. Elongation Gauge

82. Purpose : To determine the flakiness index of the coarse aggregate.
Significance : Coarse aggregate having flakier particles will adversely affect the strength of
concrete.
Definition : The flakiness index of the aggregate is the percentage by weight of particles in it,
whose least dimension (thickness) is less than three fifth of their mean dimension.
Apparatus : Balance, Metal guage, Sieve set.
Test procedure:
Take a sample of about 3 Kg.
Divide the sample into four quadrants.
Select two opposite quadrants and sieve them through the sieves arranges in the following order
63mm, 50mm, 40mm, 31.5mm, 25mm, 20mm, 16mm, 12.5mm, 10mm, 6.3mm.
Take the aggregate sample sieved through 63mm and retained on 50mm sieve. Find the weight
W1 gm.
Pass that sample through 63-50mm size of thickness gauge.
Find the weight of the aggregate passing through the respective slot (ie through 63-50mm) of
the gauge w1 gm.
Repeat the same procedure with 50-40mm, 40-25mm, 31.5-25mm, 25-20mm, 20-16mm, 16-
12.5mm and 10-6.3mm size of the thickness gauge.

84. References
• Roberts, F.L.; Kandhal, P.S.; Brown, E.R.; Lee, D.Y. and
Kennedy, T.W. (1996). Hot Mix Asphalt Materials, Mixture
Design, and Construction. National Asphalt Pavement
Association Education Foundation. Lanham, MD.↵
• Wu, Y.; Parker, F. and Kandhal, K. (1998). Aggregate
Toughness/Abrasion Resistance and Durability/Soundness
Tests Related to Asphalt Concrete Performance in
Pavements. NCAT Report 98-4. National Center for
Asphalt Technology. Auburn,
AL. http://www.eng.auburn.edu/center/ncat/reports/rep
98-4.pdf. Accessed 23 June 2004