LECTURE 1: SOIL AND
ENGINEERING STONES
SOIL
AGGREGATES
&
SOIL AND SOIL AGGREGATES
WHAT IS SOIL?
The term Soil used by engineers, refers to the
unconsolidated mineral materials at or near the earth's
surface, including the air, moisture, organic matter, and
other substances that may be incorporated therein,
which may result from natural processes, such as
weathering, decay, and chemical reaction.
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Granular soils which include sand and gravel;
Fine-grained soil which include silts and clay;
Organic soils which include muck peat or organic
silts.
PARTICLE SIZE OF SOIL
THE THREE MAJOR DIVISIONS OF SOIL
A. GRANULAR SOIL
o Good load-bearing qualities
o Permeable, hence they drain readily
o Comparatively incompressible when
subjected to static loads
o Not subject to changes in strength or
volume due to variation in water
content. However, loose granular
materials will undergo a considerable
reduction in volume if subjected to
vibratory loads
B. FINE-GRAINED SOIL
o Poor load - sustaining qualities
o Highly impermeable
o Compressible under sustained load
o Subject to change in volume and
strength due to variation in water
content
C. ORGANIC SOIL
o Has low shear strength, which can be
prone to instability under load
o Has a low bearing capacity, meaning it
has insufficient support for structures
o Sensitive to moisture changes
o Inferior to fine-grained soil with respect
to the properties stated under the latter
THE FIVE GROUP CLASSIFICATIONS OF SOIL
A. GRAVEL - Rounded or water-worn pebbles. No
cohesion or plasticity.
B. SAND - Gritty and loose grains. Individual grains
are readily seen and felt. No plasticity or
cohesion. If dry, a cast formed in the hand will
fall apart; if moist, a cast will crumble when
touched.
C. SILT - Fine and barely visible grains. When in a dry
pulverized condition, it feels soft and floury. Can
hardly be made plastic. Exhibits little or no
strength when air-dried. A dried cast is easily
crushed in the hands.
D. CLAY - Can be made plastic by adjusting its water
content. Exhibits considerable strength when
air-dried; difficult or impossible to crush in
hands. Clay can be molded and rolled into thin
threads without breaking or crumbling within a
moderate to wide range in water content, and
threads of considerable length will support their
weight when held by one hand.
E. ORGANIC SOILS - Gray to black color. Fibrous
structure due to the presence of undecomposed
plant matter. Unhealthy sewage sludge odor. It
is found as deposits in swamps and peat bogs.
WHAT IS AN AGGREGATE?
Aggregates are the most mined material in the world.
Aggregate is a broad-encompassing boulder, cobbles,
crushed stone, gravel, air-cooled blast furnace slag,
native and manufactured sands, and manufactured and
natural lightweight aggregates. Aggregates may be
further described by their respective sizes.
THE TWO TYPES OF AGGREGATES
A. NORMAL WEIGHT AGGREGATE
traditional aggregates, radiation attenuation for use in
nuclear and medical facilities, higher compressive
strength, options of natural materials like magnetite or
manufactured materials with high specific gravity, and
often a higher cost compared to lightweight aggregates
due to the materials used.
Heavyweight aggregates include magnetite, with a
specific gravity of 4.3; barite 4.2; limonite 3.8;
ferrophosphorus 6.3; and steel shot or punching 7.6.
Such heavyweight aggregates may be used instead of
gravel or crushed stone to produce a dense concrete for
example, for shielding of nuclear reactions.
These typically have specific gravities between 2.0 and
3.0. They are usually distinguished by size as follows:
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Boulders - Larger than 6 in.
Cobbles - 6 to 3 in.
Coarse aggregate - 3 in. to No. 4 sieve
Fine aggregate - No. 4 sieve to No. 200 sieve
Mineral filler - Material passing No. 200 sieve 2
Used in most concrete construction, normal-weight
aggregates are obtained by draining riverbeds or mining
and crunching formational material. Concrete made with
normal-weight fine and coarse aggregates generally
weights about 144 lb. / ft3. Boulders and cobbles are
generally not used in their as-mined size but are crushed
to make various sizes of coarse aggregate and
manufactured sand and mineral filler.
Aggregates comprise the greatest volume percentage in
portland-cement concrete, mortar, or asphaltic
concrete. In a Portland-cement concrete mix, the coarse
and fine aggregates occupy about 60 to 75% of the total
mix volume. For asphaltic concrete, the aggregates
represent 75 to 85% of the mix volume.
B. LIGHTWEIGHT AND HEAVYWEIGHT AGGREGATE
Lightweight aggregates, materials with low density used
in construction and derived from natural resources or
industrial by-products, exhibit characteristics such as
significantly lower density than traditional aggregates,
high porosity contributing to their lightweight nature,
thermal insulation properties, generally lower
compressive strength, and options like expanded shale,
clay, or industrial by-products.
In contrast, heavyweight aggregates, chosen for
enhanced density and radiation shielding in construction,
have characteristics including much higher density than
GRADATION OF AGGREGATES
The distribution of aggregate sizes in a concrete mix is
important because it directly influences the amount of
cement required for a given strength, workability of the
mix (and amount of effort to place the mix in the forms),
in-place durability, and overall economy. ASTM C33
provides ranges of fine- and coarse-aggregate grading
limits.
WHAT IS ASTM?
American Society for Testing and Materials
THE SEVEN PROPERTIES OF AGGREGATES
A. HARDNESS – Coarse–aggregate hardness is
measured by the Los Angeles Abrasion Test,
ASTM C131 or C595. These tests break the
aggregate down by impacting it with steel balls
in a steel tumbler. The resulting breakdown is
not directly related to the abrasion an aggregate
receives in service, but the results can be
empirically related to concretes exhibiting
service lives.
B. SOUNDNESS – Aggregate soundness is measured
by ASTM C88, "Test Method for Soundness of
Aggregates by Use of Sodium Sulfate or
Magnesium Sulfate." This test measures the
amount of aggregate degradation when exposed
to alternating cycles of wetting and drying in a
sulfate solution.
C. PARTICLE SHAPE – Natural sand and gravel have
a round, smooth particle shape. Crushed
aggregate (coarse and fine) may have shapes
that are flat and elongated, angular, cubical, disk,
or rodlike. These shapes result from the crushing
equipment employed and the aggregate
mineralogy. Extreme angularity and elongation
increase the amount of cement required to give
strength, difficulty in finishing, and effort
required to pump the concrete. Flat and
elongated particles also increase the amount of
required mixing water. The bond between
angular particles is greater than that between
smooth particles.
D. POTENTIAL ALKALI REACTIVITY – Aggregates that
contain forms of silicas or carbonates may react
with the alkalines present in Portland cement
(sodium oxide and potassium oxide). The
reaction product cracks the concrete or may
create pop-outs at the concrete surface.
E. RESISTANCE TO FREEZING AND THAWING – The
pore structure, absorption, porosity and
permeability of aggregates are especially
important if they are used to make concrete
exposed to repeated cycles of freezing and
thawing. Aggregates that become critically
saturated and then freeze cannot accommodate
the expansion of the frozen water.
F. IMPURITIES IN AGGREGATES – Erratic setting
times and rates of hardening may be caused by
organic impurities in the aggregates, primarily
the sand. Pop-outs and reduced durability can be
caused by soft particles, chert, clay lumps and
other friable particles, coal, lignite, or other
lightweight materials in the aggregates.
G. VOLUME STABILITY – It refers to susceptibility of
aggregates to expansion when heated or to
cyclic expansion and contraction when saturated
and dried. Aggregates that are susceptible to
volume change due to moisture should be
avoided.
CLASSIFICATION OF AGGREGATES BASED ON UNIT
WEIGHT
ENGINEERING STONES
THE FIVE PARAMETERS CONSIDERED IN SELECTING A
GOOD CONSTRUCTION STONE
A. CHEMICAL COMPOSITION – Using/selecting a
stone for construction, its chemical properties
and composition must be tested and verified
because different elements and compounds in
stones have different properties.
B. STRONGNESS AND HARDNESS – The more
compact grained and heavier a stone, the
stronger it is. The specific gravity of good stone
should be above 2.7. Stones used for road metal,
paving blocks, floor slabs and railway ballast
have to withstand mainly abrasion or wear and
tear.
C. RESISTANCE TO HEAT – Resistance to heat means
that the stone must have a very low amount of
expansion due to large increase in temperature.
D. BIO-DETERIORATION – Certain trees and
creepers thrust their roots in the joints of stones
and have both mechanical and chemical adverse
effects. Special microbes can grow on the surface
and in minute fissures, their by-products cause
flaking and discoloration.
E. APPEARANCE – The aesthetic aspect that is color,
appearance, and show of stones must also be
considered when being used in a project.
Appearance depends on the color and the ease
with which the stone can be dressed, rubbed or
polished.
THE THREE GEOLOGICAL CLASSIFICATION OF STONES
A. SEDIMENTARY
Characteristics:
o Sandstone,
limestone,
dolomite
originally formed mainly in sea water, or
lakes, from the remains of animals and
plants, also from transportation and
deposition of rock products. Rounded
and Angular in shape.
Classifications:
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Detrital is made from disintegrated preexisting rock.
Biogenetic is made from shells and other
fossilized fragments.
Chemical is made from chemical
precipitation.
B. METAMORPHIC
Characteristics:
Marble, serpentine, onyx, slate, quartzite, gneiss
are produced from sedimentary or igneous rocks
by the action of heat and pressure.
o No pressure - fossils survive
o Low pressure - fossils distorted or
destroyed
o Moderate pressure - Grains form
moderately
o High pressure - Active fluids may
circulate
o Heat alone, Metamorphic Aureole
surrounding a deep plutonic intrusions,
possibly with active fluids
o Dynamic Meta - Large scale movement
phenomena
o Crushing actions produce Xylonite Meta
rock from powder
o Low angle thrust fault: Plate pressure
coupled with subsidence
o Thrust movement, plate movement
Classifications:
According to Structure
o Contact type is crystalline
o Regional type is usually foliated
According to Grain size
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+0 Big grain, High pressure
00 Med grain, Med pressure
-0 Small grain, Low pressure
C. IGNEOUS
Characteristics:
o Intrusive - subsurface crystallization
o Extrusive- above surface crystallization
o Mineral content
o Grain size, Plutonic >3/16" coarse.
Extrusive 1/64" - 3/16" Medium and <
1/64" fine
o Crystal shape
o Texture % A, %B, crystal angle
o Color
Classifications:
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Acid rocks > 65% Si + > 10% Modal
Quartz
Intermediate rocks 55% - 65% Si
Basic rocks 45% - 55% Si < 10% Modal
Quartz
Ultra-Basic < 45% Si
TEST OF STONES
Once a stone has been selected on aesthetic basis, it is
important than to ensure whether it exhibits the
necessary physical properties and durability to remain in
working condition for a long time. Fixing method
adopted for the construction of stones also affects the
type of stones selected. Physical properties such as
density, compressive strength and porosity are
measured in order to determine its durability.
APPLICATIONS AND USES OF STONES
APPLICATIONS AND USES OF AGGREGATES
USES OF STONES
USES OF AGGREGATES – The uses of aggregates can be
summarized in to the following three categories:
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Sandstone is a popular stone with sculptors.
Good and durable construction material
Thresholds and steps in manor houses
War memorials in the 19th and 20th centuries
Limestone for burning lime and also for
manufacture of cement
Limestone as a flux in blast furnaces
Insulators in electrical appliances
BUILDING STONES
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Millions of tons of crushed rock are needed
annually for road base, paving, ready-mixed
concrete and asphalt.
Sandstone which is not so hard-wearing or
beautifully patterned is used for garden walls
and paths in landscaping.
Basalt: It is quarried and crushed as "Blue Metal"
which is used as a road-base, and in reinforced
concrete as aggregate.
Although wood, straw and mud is used for
houses in some parts of the world, most
buildings are preferred to be built of stones.
Building wells.
Material for foundation and walling of buildings,
dams, bridges, etc.
Aggregate
Stone walls
Roof tile in the form of slates
Murram for covering and flooring of road surface
Limestone for burning lime and for the
manufacture of Portland cement
Shale is a component of bricks and may also be
used in manufacturing of cement.
Nite, another stone type is used for architectural
construction,
ornamental
stones
and
monuments.
Marble is widely used in construction industry,
for aesthetic purposes, beautification and
strength
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As a Load Bearing Material
As a Filling Material
As an Infiltrating Material
USES OF AGGREGATES IN CONCRETE – The purpose of
aggregates in concrete is:
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To provide a rigid structure
To reduce the shrinkage and cracking
Concrete aggregate is used in many structures
and substructures e.g. different elements of a
Building, bridges, foundations
The smaller the aggregate size the greater its
surface area and the more binding material
(cement) will be required, resulting in a higher
cost
The greater the aggregate size the larger will be
the voids, resulting in wastage of binding
material (cement)
USES OF AGGREGATES IN RAILWAY BALLAST
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A fully loaded train weighs in thousands of tons.
To avoid damage to the rails, ground and other
nearby structures a very tough aggregate is
needed not only to support this high weight but
also to distribute and transfer it properly to the
ground.
Railway ballast generally consists of a tough
igneous rock (crushed), such as granite, with a
larger diameter varying between 30mm to
50mm. Particles finer than this diameter in
higher proportion will reduce its drainage
properties. While a higher proportion of larger
particles result in the load on the ties being
distributed improperly.