2. Soil Composition
Soils are made of four main components:
mineral matter (40 - 60 %)
soil water (20 - 50 %)
soil air (0 - 40 %) The soil pore space is filled
either by soil water or soil air
Mostly nitrogen, oxygen and carbon dioxide
organic material (small percentage).
3. Forensic Soil Tests
Soil Density (measured as bulk density)
Soil Texture
Soil characterization: soil presence of
carbonates, soil color, relative amount of living
material, structure type, general appearance of
the soil, soil structure
Amount of nutrients (nitrogen, potassium,
phosphorous)
Microscopic examination of soil
4. Soil Forensics
The transfer of soil trace evidence is governed by
what has become known as the Locard Exchange
Principle
When two surfaces come into physical contact
there is a mutual exchange of trace evidence
between them
5. Soil Forensics
The United States Department of Agriculture,
which collects soil data at many different scales,
state there were more than 21,000 soil series
identified in the United States alone
6. Soil Forensics
Soil evidence must be recognized on questioned
items and subsequently at known proposed crime
scenes and alibi localities
Evidence must be well documented.
Meticulous collection and preservation of soil
samples must be maintained so as to ensure the
integrity of the soil evidence
Soil characterization is done
7. What makes soil a useful item for trace
evidence?
Soil is highly individualistic in that there are an almost
infinite number of different soil types
Soils may change rapidly over very short distances both
horizontally and vertically
Ability to distinguish between soil samples
Soil materials are easily described and characterized by
color and by using various analytical methods such as
XRD (mineralogy) and spectroscopy (chemistry)
8. What makes soil a useful item for trace
evidence?
Soil has a strong capacity to transfer and stick, especially
the fine clay- and silt-size fractions
Soil materials are easily located and collected using hand
lenses or light microscopes
National and international computerized databases of
soil profile data and maps can be readily accessed by
police or soil scientists through the Internet
10. Soil Color
Is affected by the mineral content, amount of
decayed material, parent material.
As rocks containing iron or manganese weather,
the elements oxidize forming small crystals with a
yellow or red color
Organic matter decomposes into black humus
Using a soil color chart, you are looking at hue
(color), intensity and value (lightness or
darkness)
15. Soil Texture
Texture is determined according to the relative
proportions of sand, silt, and clay in the soil
-Sand, the larger size of particles, feels gritty
-Silt, moderate in size, has a smooth or floury
texture
-Clay, the smaller size of particles, feels sticky.
Use soil texture chart to name soil texture
16. Relative Size of Particles
Table of Size of Sand, Silt and Clay
Name Particle Diameter
Clay below 0.002 millimeters
Silt 0.002 to 0.05 millimeters
Very fine sand
Fine sand
Medium sand
Coarse sand
Very coarse sand
0.05 to 0.10 millimeters
0.10 to 0.25 millimeters
0.25 to 0.5 millimeters
0.5 to 1.0 millimeters
1.0 to 2.0 millimeters
Gravel 2.0 to 75.0 millimeters
18. Soil pH
Soil pH is a measure of soil acidity or alkalinity.
It is an important indicator of soil health
Natural soil pH reflects the combined effects of
soil-forming factors:
parent material,
Time
relief or topography
climate
organisms
19. Soil pH
pH is potential hydrogen in
water solution
Acidity – Soil pH is less than
7.
Alkalinity – Soil pH is
greater than 7.
Soil pH level is highly variable
depending on field location
and time of year
20. Inherent Factors Affecting Soil pH
Inherent factors affecting soil pH such as
climate, mineral content and soil texture
cannot be changed.
Natural soil pH reflects the combined
effects of soil-forming factors (parent
material, time, relief or topography, climate
,and organisms).
The pH of newly formed soils is
determined by Minerals in the soil’s parent
material.
21. Temperature and rainfall control leaching
intensity and soil mineral weathering. In
warm, humid environments, soil pH
decreases over time in a process called
soil acidification, due to leaching from
high amounts of rainfall.
In dry climates, however, soil weathering
and leaching are less intense and pH can
be neutral or alkaline.
22. Soils with high clay and organic matter content are more able
to resist a drop or rise in pH (have a greater buffering
capacity) than sandy soils.
Although clay content cannot be modified, organic matter
content can be changed by management. Sandy soils
commonly have low organic matter content, resulting in a
low buffering capacity, high rates of water percolation and
infiltration making them more vulnerable to acidification
23. Soil pH is Affected by Land Use and
Management.
Soils with high clay and organic matter content
are more able to resist a drop or rise in pH (have
a greater buffering capacity) than sandy soils.
Areas of forestland tend to be more acidic than
areas of grassland
24. Forensics and pH
pH can be affected by the oils on your skin
You must wear gloves when performing pH tests
When testing for pH it is wise to do several tests
for accuracy
pH is measured using litmus paper, pH paper or
pH meter
25. Soil Profile
A soil profile is a
vertical view of the
layers of soil from the
surface down to the
unaltered parent
material, and is used
in classifying soils.
26. Soil Profile- Names of Layers
O Horizon - The top, organic layer of soil, mostly of leaf litter and humus
(decomposed organic matter).
A Horizon - topsoil; it is found below the O horizon and above the E
horizon. Seeds germinate and plant roots grow in this dark-colored layer. It
is made up of humus mixed with mineral particles.
E Horizon - This eluviation (leaching) layer is light in color; this layer is
beneath the A Horizon and above the B Horizon. It is made up mostly of
sand and silt, having lost most of its minerals and clay as water drips through
the soil (in the process of eluviation).
B Horizon - Also called the subsoil - this layer is beneath the E Horizon and
above the C Horizon. It contains clay and mineral deposits (like iron,
aluminum oxides, and calcium carbonate) that it receives from layers above
it when mineralized water drips from the soil above.
C Horizon - Also called regolith: the layer beneath the B Horizon and
above the R Horizon. It consists of slightly broken-up bedrock. Plant roots
do not penetrate into this layer; very little organic material is found in this
layer.
R Horizon - The unweathered rock (bedrock) layer that is beneath all the
other layers (not shown in soil profile to the left
27. Soil Classification
Soils are classified based on the climate where
found as have similar materials
Climate factors, type of biome will affect the
characteristic of the soil (dry versus rainy;
temperate forest versus desert)
28. Soil Order Characterisitics
Alfisols develop in humid and subhumid climates, frequently under forest vegetation, slightly to
moderately acid
Andisols over 60 % volcanic (ash, cinder, pumice, basalt), low density, Dark A horizon, very
high cation exchange capacity
Aridisols exist in dry climates, salty layers
Entisols no profile development, river floodplains, volcanic ash deposits and sands
Histosols organic soils (peat and mucks) from swamps, bogs and marshes
Inceptisols have weak to moderated horizon development due to cold, water loged soils
Mollisols frequently under grassland, Deep, dark A horizons, lime accumulation
Oxisols excessively weathered, are in tropical and subtropical climates, low fertility
Spodosols Coniferous forest soils, sandy, leached soils strongly acid profiles, well-leached E
horizons
Ultisols extensively weathered soils of tropical and subtropical climates, strongly acid, Thick A
horizon
Vertisols Found in temperate to tropical climate with distinct wet and dry seasons, high content
of clays that swell when wetted and show cracks when dry
29. Bulk Density
Bulk density is an indicator of soil compaction
The dry bulk density of a soil is inversely related
to the porosity of the same soil
The more pore space, the lower the bulk density
soils rich in organic matter have lower bulk
density
Test is performed by extracting a large soil
sample in a standard size can.
30. Bulk density is calculated as dry weight of soil
divided by its volume .
This volume includes the volume of soil particles
and the volume of pores among soil particles.
Bulk density is typically expressed in g/ cm3.
31. Soil Fertility
Plants require macronutrients of nitrogen,
phosphorous, and potassium to grow
Soils can become depleted by leaching of
minerals due to water or large uptake of a certain
mineral by plants
32. Density-Gradient Tube
Some forensic laboratories utilize the densitygradient
tube technique to compare soil specimens.
Typically, glass tubes 6–10 millimeters in diameter and 25–40
centimeters long are filled with layers of two liquids mixed in
varying proportions so that each layer has a different
density value.
For example, tetrabromoethane (density 2.96 g/mL)
and ethanol (density 0.789 g/mL) may be mixed so that each
successive layer has a lower density than the preceding one, from
the bottom to the top of the tube.
33. The simplest gradient tube may have from six to ten layers,
in which the bottom layer is pure tetrabromoethane and the top
layer is pure ethanol, with corresponding variations of
concentration in the layers between these two extremes.
When soil is added to the density-gradient tube, its particles sink
to the portion of the tube that has a density of equal value; the
particles remain suspended in the liquid at this point. In this way,
a density distribution pattern of soil particles can be obtained and
compared to other specimens treated in a similar manner
34. Only a few crime laboratories
use this procedure to compare
soil evidence.
There is evidence that the test
is far from definitive, because
many soils collected from
different locations yield
similar density distribution
patterns. At best, the density-
gradient test is useful for
comparing soils when it is
used in combination with
other tests.
35. Color
Color is one of the most important identifying characteristics of
minerals and soils.
Minerals form a mosaic of grays, yellows, browns, reds, blacks,
and even greens and brilliant purples.
Virtually all possible colors of the visible light spectrum are
represented. With most geologic materials and soils, the native
minerals contribute directly to the soil color.
This is particularly true with stream deposits, windblown silts, and
other recent formations that have been in place a comparatively
short period of
time.
36. If sands along a river channel are examined, the color of each
sand grain can generally be recognized individually; however,
after a deposit has weathered for a long period of time, there is a
degree of leaching, accumulation, and/or movement of
substances within the soil.
Soil particles become stained, coated, and impregnated with
mineral and organic substances, giving the soil an appearance
different from its original one.
The mineral grains, especially the larger ones, are generally
coated. In most situations the coatings on the soil particles consist
of iron, aluminum, organic matter, clay, and other substances.
The coloring of the coatings alone can give some indication as to
the history of the sample.
37. The “redness” of a soil depends not only on the amount of
iron present but also on its state of oxidation, with a
highly oxidized condition tending to have a more
reddish color.
The iron on the coatings of the particles probably is in the
form of hematite, limonite, goethite, lepidocrocite, and
other iron-rich mineral forms.
Black mineral colors in the soil are generally related to
manganese or various iron and manganese combinations.
38. Green colors are generally due to concentrations
of specific minerals rather than of the mineral
coatings.
For example, some copper minerals, chlorite, and
glauconite are usually green. Deep blue to purple
coloration in the soil is generally due to the
mineral vivianite, an iron phosphate.
39. To have some uniformity in descriptions of the
color of geologic materials and soils, certain
standards have been established.
The color standards most frequently used in the
United States are those of the Munsell Color
Company.
40. The color standards are established on three
factors: hue, value, and chroma.
Hue is the dominant spectral color, value is the
lightness color, and chroma is the relative
purity of the spectral color.
42. Soil and rock colors are generally recorded as, for
example, 7.5YR5/2 (brown). The 7.5YR refers to the
hue, 5 the value, and 2 the chroma.
This standardization of colors offers some degree of
uniformity, but moisture content will also affect the
color of the soil, as will light intensity and wavelength.
Soil color is different in natural light than in fluorescent
and different still in incandescent light.
43. If a soil is air dry, it may be recorded as yellow, but
if moist the recording may be yellowish brown.
Moisture added to a dry soil will usually result in a
more brilliant appearance.
It is therefore important to record not only the color of
the soil but also an estimate of the “wetness factor” at
the time of the recording.
44. In studying soil samples for forensic purposes, the sample is
normally dried at approximately 100◦C and viewed with natural
light, preferably coming from a northerly direction.
A north-facing window is a good location for such observations.
Such studies should be made on samples that have the same
general size distribution of particles.
The color of samples prepared from the individual sieved-out
particle size ranges gives important additional data. Two or more
samples, collected for study, can be compared directly by the
observer
45. Particle-Size Distribution
The determination of the distribution of particle sizes in a sample
can often provide significant evidence.
This determination is often produced for a variety of reasons:
(1)to produce samples for comparison studies that are similar, in
which case the control sample may contain some larger or
smaller particles that are not present in the sample being
questioned or an associated sample, and they must be removed;
46. (2) the samples may be broken down into
subsamples in which all the particles
are in the same size range for mineral or color
studies; or
(3) a determination of the distribution of particle
sizes may be produced as a method of comparison.
47. The basic methods used for the separation of sizes are
(1) passing the sample through a nest of wire sieves, with
the size of the openings decreasing from top to bottom;
(2) determining the rate of settling of the grains in a fluid,
which is a measure of the size of the particles; and
(3) instruments that measure the size of particles in a
microscopic view and record the number of particles of
each size.
The distribution of particle sizes is then plotted on a
diagram.
48. Before making a mechanical analysis to determine the size
distribution of particles, it is necessary to disperse the soil.
Individual soil particles tend to stick together in the form of
aggregates. Cementing agents of the aggregates must be
removed; otherwise, a cluster of silt and clay particles
would have the physical dimensions of sand or gravel.
Cementing agents consist of organic matter, accumulated
carbonates, and iron oxide coatings, and in some situations
there is a mutual attraction of particles by physicochemical
forces.
49. If carbonates have cemented the particles together, it is desirable to
pretreat the sample with dilute hydrochloric acid to remove the
carbonates.
The sample is then treated with hydrogen peroxide to remove the
organic cementing agents.
All samples must be treated in the same way, and it must be
determined before treatment that important information will not be
lost, such as dissolving carbonate cement from grains that should be
treated as single grains.
50. A number of methods can then be used to determine the size
distribution of the finer particles in a dispersed suspension.
The hydrometer method is a rapid method
for determining the percentage of sand, silt, and clay in a sample.
It is based on the principle of a decreasing density of the
suspension as the solid particles settle out.
This method, although rapid and accurate, is unsatisfactory if we
want to make a subsequent examination of the various size ranges,
because there is actually no physical separation of the various-
sized particles.
51. One of the most accurate and satisfactory procedures
for fractionating soil samples is by the pipette method.
This consists of pretreating the sample as is done
in the hydrometer method, dispersing the soil in water,
and calculating the time required for various-sized
particles to settle out from the suspension.
The principle is based on the fact that the rate of
settling depends on the size of the mineral
matter, with larger particles settling at a more rapid
rate.
52. Petrographic Microscope
A petrographic microscope differs in detail from an ordinary
compound microscope . However, its primary function is the same:
to produce an enlarged image of an object placed on the stage. The
magnification is produced by a combination of two sets of lenses, the
objective and the ocular. The function of the
objective lens, at the lower end of the microscope tube, is to produce
an image that is sharp and clear. The ocular lens merely enlarges this
image.
For mineralogical work, three objectives—low, medium, and high
power—are normally used. The magnification produced by
objectives is usually 2× (low), 10× (medium), and 50×
(high).
54. The petrographic microscope is an important tool in many
aspects of forensic work and is the best method for a study of the
optical properties of rocks and minerals.
A study of individual mineral grains or thin sections of rocks and
related material is easily accomplished by anyone trained in the
use of the instrument.
A thin section is a thin slice of rock mounted on a glass slide. The
slice is normally 30 μm in thickness and may be prepared from a
solid rock or loose material impregnated with plastic.
55. Cathodoluminescence
The instrument used for cathodoluminescence is a
luminoscope that is attached as a stage on a microscope or a
scanning electron microscope.
The specimen—for example, mineral grains or a thin section—
is bombarded with a beam of electrons generated by the
instrument.
When the electrons strike the surface of the specimen,
an optical luminescence is produced, which is seen as a display
of colors.
57. The colors and their intensity depend in large part on
very small changes in the concentration of trace
impurities, the minerals present, and where the trace
impurities are located in the structure of the minerals.
Thus, the method has wide application in determining
or observing a variety of differences in mineral grains
that otherwise appear similar.
58. X-Ray Diffraction
X-ray diffraction is one of the most important and reliable methods of
identifying
the composition of geologic, soil, and other crystalline substances .
The method is based on the arrangement of atoms, ions, and molecules within
the specimen. The sample is analyzed by passing x-rays through a crystal and
measuring the angle of the diffracted x-rays.
Each crystalline material has its own distinctive x-ray pattern. The x-ray
diffraction pattern of a sample is controlled by the internal structure of the
specimen.
The diffraction pattern can be collected on film, on an image plate, or by using
an electronic detector.
60. Methods of examination
Microscopic Examination:
Observe the colour of the soil as such and after drying in
oven at 105oC. Observe its nature particularly size and
shape.
Sort out the foreign element (if it is there) as; paper
pieces, leaves, grass, seed, brick fragments, glasses,
animal and wooden matters etc.
61. Sample Preparation
Set of sieves( ranging in size from ASTM No.5 to 200), Motor-
driven sieve shaker.
Method
Arrange the set of sieves in numerical order with smallest number
(largest mesh size) at the
top and the largest number (smallest mesh size) at the bottom e.g. 5-
10-18-25-35-60-80-90-100-120-200 and so on. Place the sieves on
the shaker and pour the soil sample into the top sieve.
Place the cover on the upper sieve, fasten the binding straps.
Switch on the shaker and allow the shake to operate for 5 minutes.
Then, switch off the shaker and release the binding
straps.
62. Note- If power shaker is not available, shaking of the sieves can
be done manually.
Remove the sieve cover and separate the sieves. Collect the soil
retained in each sieve separately and mark them. The only portion
of sample to be used in the analysis is one taken
from a sieve of middle range size.
Note-For a blood stained soil, blood should be removed from soil
first before sample preparation.
63. Removal of Blood from Blood Stained Soil
Prepare a saline water of about 0.85% i.e. dissolve 85mg of NaCl
in100 ml of distilled water.
Pour the blood stained soil sample in saline water and stir for
separation of blood.
After few hours, decant the water and wash with distilled water.
After then, dry the sample in hot oven or on a hot plate at 105oC and
keep it in a desiccator.
64. Observations
Apparatus: Stereo-microscope capable with high magnification
range.
Method: Simple observations
Take some soil sample on a clean microscopic slide/ glass plate and
make its thin layer.
Place the slide/plate with soil on viewing stage of stereo-microscope
and using different magnifications take the microscopic observations
of soil sample retained in each sieve during the sample preparation
separately in the following manner:
a. Observe the colour of soil particles after drying at 105oC.
65. b. Observe the nature of particles as- geometrical shape, black
particles (coal dust, black minerals), red particles (brick dust,
red ash, iron oxide or metal oxide), colourless particles
(quarts grains, colourless mineral fragments), green minerals,
particles of vegetation (grass, leaf fragments, seeds, moulds,
fungi, micro-organism etc.
c. Find out the traces of foreign materials as -dung cloth fibres,
glass fragments, hair, wooden particles etc.
d. Note every observation and compare with control soil sample.
66. Microscopical Observation with Chemical Reagents
Place the soil sample on the stage of microscope in
the same manner as described above and examine.
Moisten a small portion of soil with water and then
add a small drop of concentrated hydrochloric acid
(HCl) on it.
Observe the nature of reaction as- bubbles and
colour.
67. Bubbles arising from solid particles indicate insoluble
carbonates such as chalk, dolomite or lime stone.
Similarly yellowing colour indicates the presence of
soluble iron it can be confirmed by appearance of green
colour on adding a few drops of potassium ferrocyanide
solution to the sample.
68. Observation of Particle Size Distributions
Apparatus: Set of sieves (ranging in size from ASTM No.5 to
200), Motor-driven sieve shaker, Analytical balance with an
accuracy of ± 0.0002 gm, Standard Weights.
Methods:
a.Take an accurately weighed quantity (50g) of soil sample.
b. Arrange the set of sieve in numerical order and shake the soil.
69. C. Collect the soil retained in the each sieve separately and
reweigh accurately.
Calculate its percentage as given below:
Percentage of soil retained on sieve No.(..)= (Weight of
soil retained on sieve)x100 / (Total weight of soil taken)
71. Ignition Test
Apparatus: Analytical balance with an accuracy ± 0.0002 gm,
Standard Weights, Alumina crucible (porcelain dish may be used),
Muffle furnace of high temperature range (1000oC).
Method:
Take an exactly weighed quantity (one gm) of soil sample from
sieve fractions dried at 105oC in a alumina crucible and keep it in a
muffle furnace.
Heat it at temperature between 750-800oC for 1 hr. And then, cool it
to room temperature. Reweigh accurately and record the loss in
weight and change in colour on ignition.
72. Calculate the percentage of loss on ignition to the nearest
0.1 and compare it with a control soil sample.
Calculation:
Initial weight of soil sample taken = Wo g
Weight of soil sample after ignition = W1 g
Weight loss on ignition = (Wo- W1) g
Percent weight loss =(Wo- W1)/ (W0) * 100
73. Observation of Density Distributions of Soil Particles
This analysis depends upon the principle that an object will be
suspended in a liquid of same density. It will sink in a liquid that is less
dense and float in a liquid that is more dense.
When two different liquids of different density are mixed together, they
will diffuse into one another and its density will be as :
D1= [(V1d1) + (V2d2)]/ (V1) + (V2 )
Where:
d1 = density of liquid I (more dense; bromoform)
d2 = density of liquid II ( less dense; xylene)
V1 = volume of liquid I (bromoform) in ml
V2 = volume of density II (xylene) in ml
When the liquids of different densities are successively filled by equal
volume in a narrow tube, a density gradient within the tube will be
formed.
74. On the basis of this principle, density distributions of soil particles are observed as
the following:
Apparatus: Glass tubes of size 30cm x 5-10mm (closed at one end and fitted with
corks), Bromoform (sp.gr. 2.89), Xylene (sp.gr.0.88) or bromobenzene (sp.gr.
1.52), Graduated cylinder -10ml, Analytical balance capable of measuring ±0.01 g,
Sample bottles.
Method:
Prepare the solution of mixture of bromoform and xylene in seven
sample bottles (marked 1 to 7) separately in the following
proportions (6 ml of each solution):
I. Bottle No.1: Pure bromoform (sp.gr. 2.89)
I. Bottle No.2: 5 parts bromoform and 1 part xylene.
II. Bottle No.3: 4 parts bromoform and 2 parts xylene.
III. Bottle No.4: 3 parts bromoform and 3 parts xylene.
IV. Bottle No.5: 2 parts bromoform and 4 parts xylene.
V. Bottle No.6: 1 parts bromoform and 5 parts xylene.
VI. Bottle No.7: Pure xylene(sp.gr. 0.88)
75. pH Measurement of Soil Sample
In order to observe the acid-alkali behavior of the soil, pH value of
soil sample can be determined as follow:
Apparatus: a pH-meter with standard electrolytes (buffers) solution
of pH 7 and 4.
Dissolve weighed quantity ( one gm of soil sample in 100 ml
distilled water and stir thoroughly. Filter it. Take the filtrate and
measure the pH value. Adding 10 ml, 20ml, 30ml, 40ml, and so on
successively in solution, measure the pH values after each dilution
and observe their variations.
Similarly, measure the pH values for control soil sample in the same
conditions and compare with suspect soil sample
76. EXAMINATION OF CEMENT SAMPLES
Scope
i.To detect adulteration in cement samples.
ii. To check the quality of cement samples.
iii. To identify the nature of adulterants used in cement
samples.
77. Portland cement may be defined as a product
obtained by intimately mixing together calcareous
or other silica, alumina, and iron oxide-bearing
materials, burning them at a clinkering temperature
(1450 ) and grinding the resulting clinker.℃
In 1824 Joseph Aspdin gave the name Portland
cement because this product resembled the colour of
the stones from Portland, England. Cements are
mainly mono silicates of calcium, soluble in dilute
acids and alkali.
79. COMPOSITION OF PORTLAND CEMENT:
Lime CaO 60-67%
Silica SiO2 17-25%
Alumina Al2O3 03-08%
Iron Oxide Fe2O3 0.5-06%
Magnesia MgO 0.1-04%
Soda & Potash Na2O & K2O 0.2-01%
Sulfur Trioxide SO3 01-2.75%
Free Lime CaO 00-01%
80. Types of Cements : -
There are many types of cements available, but few of
them are discussed here.
1.Rapid Hardening Portland Cement- is similar to that of
ordinary Portland cement, but is grounded finer and
slightly altered in composition. Its setting time is similar,
but it develops its strength more rapidly.
81. 2.Quick setting Portland Cement –
it differs from normal Portland cement in its
setting time, which is less , compared to Portland
cement. Its rate of hardening may be similar to
that of ordinary or rapid hardening Portland
Cement.
82. 3.White Portland Cement - is an ordinary Portland cement
containing a low proportion of iron oxide, so that its colour is white
instead of grey.
4.Water proof Portland Cement- is ordinary Portland Cement in
which at grinding stage small proportion of calcium stearate or
non-saponifiable oil is added.
5.Hydrophobic Cement - is a material obtained by grinding Portland
Cement clinker with a water repellent film forming substance such
as fatty acid in order to reduce the rate of deterioration under
favourable storage or transport conditions.
83. 6.Low-heat Portland Cement - is a material in which
chemical composition has been so adjusted as to reduce
the heat of hydration.
7. Portland Pozzolona Cement – in ordinary Portland
cement, a pozzolonic material like brick powder, fly
ash etc. are added in the range of 20-40%. This cement
is called Portland Pozzolona Cement and is generally
used in the preparation of plaster materials.
84. OTHER BUILDING MATERIALS
1.Stone powder, is poly silicates of calcium, magnesium and
iron etc. and is practically insoluble in dilute acids.
2.Concret, is the hard mass obtained by solidification of the
inert material like sand, coarse stone, water and cement.
3.Mortar, is the mixture of sand and cement for plastering the
brickwork.
4. Sand , is mostly silica in defined form and insoluble in dilute
mineral acids, should be clean, strong, durable uncoated well-
graded particles. The particles should be free from alkali,
organic matter, loam or other substances. The diameter of the
sand particles should not be above 6 mm.
85. Sampling
Mix thoroughly each sample of cement separately and collect about
100 gm of each sample in porcelain dish/ watch glass. Dry for 30
minute in oven at 105oC and, then, cool it to room temperature.
Place it in a desiccator and marked as ‘representative sample.
Note: 1. If any solid lumps of cement, which are usually formed due
to absorption of moisture, are observed in sample, note it, prior any
testing because the presence of lumps will affect the results of
testing. Some times, it may confuse to form opinion. This type of
cement is known as ‘Expired Cement’.
2. All exhibits/samples containing cement should be kept in a dry
(moisture free) atmosphere i.e. at 30-35oC
86. Procedures
Bromoform Test
Apparatus: Test tube/ gradient tube, Bromoform (sp. gr.=2.89)
Method: Take 200-300 mg of each of representative sample (2)
into separate test tube/ gradient tube containing 5 ml bromoform
(sp. Gr.= 2.89). Shake vigorously the tube and keep it for setting
for 1 hr.
88. Fineness Test
Apparatus: Sieve of 90μm size (IS: 460(I)-1985), Analytical
balance with an accuracy of ± 0.0002 gm, Standard Weights, a
Nylon or Bristle Brush.
Method: Collect about 50 g of representative sample of cement
(1.2) and weigh accurately to the nearest 0.01 g. Place it on a clean
and dry 90μm IS sieve with pan attached.
Holding the sieve in both hands and sieve with a gentle wrist
motion more or less continuous rotation of sieve should be carried
out through out the sieving. (Washers, slots and slugs etc. should
not be used on the sieve). The underside of the sieve should be
slightly brushed using a nylon or pure bristle brush after every five
minutes of sieving.
89. Weigh the mass of cement sample retained on 90μm IS sieve and
calculate its percentage as below:
Calculation:
Initial weight of cement sample taken = Wo g
Weight of cement sample retained on sieve = W1 g
Percent cement sample retained on sieve; x = W1/ W0 * 100
Percent cement sample passed through 90μm = (100-x)
90. Ignition Test
Apparatus
Analytical balance with an accuracy of ± 0.0002gm, Standard
Weights, Alumina crucible or Platinum crucibles, Muffle furnace
of high temperature range (1000oC).
Method
Take an exactly weighed quantity (one gm) of sample (2) in
alumina/ platinum crucible and keep in a muffle furnace. Ignite it
at temperature between 900-1000oC for 1 hr. and then,
cool it to room temperature.
Weigh accurately and record the loss in weight as the loss on
ignition and calculate the percentage of loss on ignition to the
nearest 0.1.
Observe the colour on ignition and compare it with colour of
initial (prior ignition sample).
91. Calculation of ignition loss:
Weight of sample before ignition = xo gm
Weight of sample after ignition = x1 gm
Weight loss on ignition = (xo - x1) gm
Percentage loss of ignition =(xo - x1)/ xo * 100
94. Examination of Cement Sample by Using X-Ray Diffraction
Technique
cement is made by mixing together calcareous and argillaceous
materials at high temperature and its property depend on various
phase compositions of clinker and on the structure of individual
crystal phase.
Cement has, thus, an unique structural/phase characteristics and
any changes in its structure clearly reveals the alteration of its
quality.
Keeping in view, x-ray diffraction technique- ‘a tool of structure
determination can frequently be used in forensic context to analyse
the quality of cement sample.
96. In some case,
(i.) When a specific or two more adulterants are blended in such
way that the values of the basic constituents remain within the
limits of prescribed in the specifications, conventional physical
and chemical methods are not of much helpful and in addition,
(ii) Identification of nature of adulterant is also very difficult by
conventional methods since both the cement adulterant usually
have same ingredient, x-ray diffraction method is more useful.
97. Identification of Adulterated Cement
Compare the XRD patterns so observed for sample with
XRD patterns of pure/standard cement carefully and on
the basis of comparison only, adulteration in cement can
be detected easily.
Remarks: Presence of any extra new XRD peak/line in
XRD patterns of sample clearly reveals the adulterated
or poor quality cement.
98. EXAMINATION OF MORTAR
Scope
To find out the cement content in mortar (mixture of cement and
sand) i.e. the ratio of cement and sand in mortar.
Sample preparation
Collect about 500 g of sample of mortar (mixture of cement and
sand) from different portions of whole sample. Pulverise it and mix
thoroughly.
Take 50-100 g as representative sample and pass it through 90
micron sieve. Dry it at 150oC for 1 hr. and keep in desiccator.