3 geological materials for construction

Geological Materials
Used in Construction
MSc Course
R. R. Gadgil, Dept. of Earth Science, Goa University

1. Building or Dimension stone
 Stone has been used as a construction
material for thousands of years. One of the
reasons for this was its ready availability
locally. Furthermore, stone requires little
energy for extraction and processing.
 Indeed, stone is used more or less as it is
found except for the seasoning, shaping
and dressing that is necessary before it is
used for building purposes.R. R. Gadgil, Dept. of Earth Science, Goa University 2

Building or Dimension stone-Terminology
 Quarries are places where rock is separated from its natural
beds and processed for its use in construction.
 There are open and underground quarries.
 Open quarries may be shelf quarries where the rock is
extracted from hillside or pit quarries where rock is excavated
from certain depth in ground.
 Quarry products are dimension stone, crushed stone and
broken stone.
 Dimension stones are blocks with more or less even surfaces of
specified shape and usually of specified size.
 Dimension stones are rapidly being replaced in building
construction by reinforced concrete or baked clay products.R. R. Gadgil, Dept. of Earth Science, Goa University 3

 Crushed stone industry is survived by lime and
cement industry.
 Most of the crushed stone comes from limestone and
remaining from basalt, granite, sandstone and
quartzite.
 Riprap is broken stone or boulders used as a protective
layer on the upstream face of an earth embankment to
protect it from wave action and general erosion by
water.
Building or Dimension stone-Terminology
R. R. Gadgil, Dept. of Earth Science, Goa University 4

Building or Dimension stone
 A number of factors determine whether a rock will be worked as a
building stone.
 These include the volume of material that can be
quarried; the ease with which it can be quarried; the
wastage consequent upon quarrying; and the cost of
transportation; as well as its appearance and physical
properties (Yavuz et al., 2005).
 As far as volume is concerned, the life of the quarry should be at
least 20 years.
 The amount of overburden that has to be removed also affects the
economics of quarrying.

 Obviously, there comes a point when removal of overburden makes
operations uneconomic. However, at that point, stone may be
mined if conditions are favourable.
 Weathered rock normally represents waste therefore the ratio of
fresh to weathered rock is another factor of economic importance.
 The ease with which a rock can be quarried depends to a large
extent on geological structures, notably the geometry of joints and
bedding planes, where present.
 Ideally, rock for building stone should be massive, certainly it
must be free from closely spaced joints or other discontinuities as
these control block size.
 The stone should be free of fractures and other flaws.

 In the case of sedimentary rocks, where beds dip
steeply, rocks can give rise to problems of slope
stability when excavated.
 On the other hand, if beds of rock dip gently, it is
advantageous to develop the quarry floor along the
bedding planes.
 The massive nature of igneous rocks such as granite
means that a quarry can be developed in any direction,
within the constraints of planning permission.

 A uniform appearance is generally desirable in building stone.
 The appearance of a stone largely depends on its colour, which
is determined by its mineral composition.
 Texture also affects the appearance of a stone, as does the way
in which it weathers.
 The texture and porosity of a rock affect its ease of
dressing, and the amount of expansion, freezing and
dissolution it may undergo.
 For example, fine-grained rocks are more easily dressed than
coarse varieties. The retention of water in a rock with small
pores is greater than in one with large pores and so they are
more prone to frost attack.R. R. Gadgil, Dept. of Earth Science, Goa University 8

 For usual building purposes, a compressive strength of 35 MPa is
satisfactory, and the strength of most rocks used for building
stone is well in excess of this figure.
 In certain instances, tensile strength is important, for example,
tensile stresses may be generated in a stone subjected to
ground movements.
 However, the tensile strength of a rock, or more particularly its
resistance to bending, is a fraction of its compressive
strength.
 As far as building stone is concerned, hardness is a factor of
small consequence, except where a stone is subjected to
continual wear, such as in steps or pavings.R. R. Gadgil, Dept. of Earth Science, Goa University 9

 The durability of a stone is a measure of its ability to
resist weathering and so to retain its original size,
shape, strength and appearance over an extensive
period of time.
 The amount of weathering undergone by a rock in field
exposures or quarries affords some indication of its
qualities of resistance.
 However, there is no guarantee that the durability is
the same throughout a rock mass and, if it changes, it
is far more difficult to detect, for example, than a
change in colour.R. R. Gadgil, Dept. of Earth Science, Goa University 10

 According to Leary (1986), one of the tests that is frequently
used in Britain to make an initial assessment of the durability of
sandstone as a building material is the acid immersion test.
 This involves immersing specimens for 10 days in sulphuric acid
of density 1.145 Mg m-3.
 Stones that are unaffected by the test are regarded as being
resistant to attack by acidic rainwater.
 Those stones that fail are not recommended for external use in
polluted environments.
 A more severe test consists of immersing specimens in sulphuric
acid with a density of 1.306 Mg m-3.
 Experience has shown that this test is of particular value when
the design life of a proposed building is exceptionally long.

Factors affecting engineering service
of rock-Frost action
 Damage can occur to stone by alternate wetting and drying.
 What is more, water in the pores of a stone of low tensile strength
can expand enough when warmed to cause its disruption.
 For example, when the temperature of water is raised from 0
to 60°C, it expands some 1.5%, and this can exert a pressure
of up to 52 MPa in the pores of a rock.
 Indeed, water can cause expansion within granite ranging from
0.004 to 0.009%, in marble from 0.001 to 0.0025% and in quartz
arenites (sandstones) from 0.01 to 0.044%.
 The stresses imposed on masonry by expansion and contraction,
brought about by changes in temperature and moisture content,
can result in masonry between abutments spalling at the joints,
blocks may even be shattered and fall out of place.

 Frost damage is one of the major factors causing
deterioration in a building stone (Ingham, 2005).
 Sometimes, small fragments are separated from the
surface of a stone due to frost action but the major
effect is gross fracture.
 Damage to susceptible stone may be reduced if it is
placed in a sheltered location.
 Most igneous rocks, and the better quality sandstones
and limestones, are immune. As far as frost
susceptibility is concerned, the porosity, pore size and
degree of saturation all play an important role.R. R. Gadgil, Dept. of Earth Science, Goa University 13

 If a rock is saturated, freezing of water induces tensile stresses
in the rock and cracking may result.
 However, the degree of saturation of rocks is generally less than
100%. Frost action therefore, will cause cracking only when
there is not enough space within the pores to permit the
freezing water to expand (about 9% by volume of water)
 Also, frost action depends as much on the diameter of the pores
as on the degree of saturation.
 Rock with wide pores that give up water readily (i.e by
evaporation) is not particularly susceptible to frost damage
even in cold climates.

 Once ice has formed, the ice pressure rapidly increases with
decreasing temperature, so that at approximately -22°C, ice can
exert a pressure of 200 Mpa (Winkler, 1973).
 Usually, coarse-grained rocks withstand freezing better than the
fine-grained types.
 Indeed, the critical pore size for freeze–thaw durability appears
to be about 0.005 mm.
 In other words, rocks with larger mean pore diameters allow
outward drainage and escape of moisture from the frontal advance
of the ice line and, therefore, are less frost susceptible.
 Fine-grained rocks that have over 5% sorbed water are often very
susceptible to frost damage, whereas those containing less than 1%
are very durable.

 When stone is won from a quarry, it contains a certain amount of
pore water referred to as quarry sap. As this dries out, it causes
the stone to harden.
 Since laminated rock may scale badly if water freezes in open
bedding planes, it is particularly inadvisable to place it with the
cleavage or bedding planes vertical.
 Limestones with shaly layers or any rock with seams that sorb
water readily are not recommended to use in cold climates.
 Careless operation of dressing machines or tooling of the stone may
produce bruising.
 Subsequently, scaling may develop at points where the stone was
bruised, spoiling its appearance.R. R. Gadgil, Dept. of Earth Science, Goa University 16

of rock-Salts
 Some of the world’s most important historic monuments, such as
the Nabatean rock-hewn temples at Petra in Jordan, the Harappan
remains at Mohenjo-Daro in Pakistan, the Alhambra in Granada,
Spain, and the Sphinx in Egypt, are seriously affected by salt
crystallisation.
 Indeed, the problem affects buildings and monuments
around the world, from hyper-arid desert environments
to Mediterranean climates and the cooler and wetter
conditions found in the UK.
 The reason salts pose a problem to masonry is
because they are soluble and can dissolve and
recrystallise, often within the pores of the stone at
the point of evaporation.R. R. Gadgil, Dept. of Earth Science, Goa University 17

of rock-Salts
 Each salt has different solubility characteristics,
and some are more problematic than others.
 Some are able to take up water from the air, and
some can change structure as a consequence of
their hydration and dehydration.
 Some salts can dissolve in the water they have
taken up from the air, through deliquescence
(as is the case for halite).
 In many situations salts are present in complex
mixtures and their behaviour in damp masonry is,
as a result, quite complicated.R. R. Gadgil, Dept. of Earth Science, Goa University 18

of rock-Salts
 Salts can be transported onto and
into masonry in many ways, such
as by capillary rise from
groundwater and soil water,
splashed from run-off on nearby
roads and other impermeable
surfaces, in rainfall and driving
rain, in fog and dew, and as sea
spray.
 Many buildings will receive salts
from multiple sources. Whether or
not these salts pose a problem will
depend upon the aggressiveness of
the environmental conditions and
the vulnerability of the masonry.R. R. Gadgil, Dept. of Earth Science, Goa University 19

of rock-Salts
 The nature of the environmental conditions
surrounding a building or monument, and those
inside a building, are crucial to influencing how far
moisture and salts penetrate and how often
dissolution/crystallisation and hydration/
dehydration reactions take place.
 Relative humidity and temperature, and variations
in these over daily and annual timescales, are
particularly key environmental factors.

of rock-Salts
 Deleterious salts, when present in a building stone,
are generally derived from the ground or the
atmosphere, although soluble salts may occur in the
pores of the parental rock.
 Their presence in a stone gives rise to different
effects. They may cause efflorescence (white
spots) by crystallizing on the surface of a stone.

of rock-Salts
 In subflorescence, crystallization takes
place just below the surface and may be
responsible for surface scabbing.
 Crystallization caused by freely soluble
salts such as sodium chloride, sodium
sulphate or sodium hydroxide can lead to
the surface of a stone crumbling or
powdering.
 Deep cavities may be formed in magnesian
limestone when it is attacked by
magnesium sulphate.

of rock-Salts
 Salt action can give rise to honeycomb weathering in
some sandstones and porous limestones.
 Disruption in stone also may take place due to the
considerable contrasts in thermal expansion of salts in
the pores. For instance, halite expands by some 0.5%
from 0 to 60°C, and this may aid the decay of stone.
 Conversely, surface induration of a stone by the
precipitation of salts may give rise to a protective hard
crust, that is, case hardening.

of rock-Atmospheric gases
 Building stones derived from sedimentary rocks may undergo a
varying amount of decay in urban atmospheres, where weathering
is accelerated due to the presence of aggressive impurities such as
SO2, SO3, NO3, Cl2 and CO2 in the air, which produce corrosive
acids.
 Limestones are the most suspect. For instance, weak sulphuric acid
reacts with the calcium carbonate of limestones to produce
calcium sulphate.
 The latter often forms just below the surface of a stone and the
expansion that takes place upon crystallization causes slight
disruption.
 If this reaction continues, then the outer surface of the limestone
begins to flake off.

of rock
 The degree of resistance that sandstone offers to weathering
depends on its mineralogical composition, texture, porosity,
amount and type of cement/matrix, and the presence of any
planes of weakness.
 Accordingly, the best type of sandstone for external use for
building purposes is a quartz arenite that is well bonded with
siliceous cement, has a low porosity and is free from visible
laminations. The tougher the stone, however, the more expensive
it is to dress.
 Sandstones are chiefly composed of quartz grains that are highly
resistant to weathering but other minerals present in lesser
amounts may be suspect, for example, feldspars may be
kaolinized.R. R. Gadgil, Dept. of Earth Science, Goa University 25

of rock
 Calcareous cements react with weak acids in urban
atmospheres, as do iron oxides that produce rusty surface
stains.
 The reactions caused by acid attack may lead
occasionally to the surface of a stone flaking off
irregularly or, in extreme cases, to it crumbling.
 Laminated sandstone usually weathers badly when it is
used in the exposed parts of buildings, it decaying in
patches.R. R. Gadgil, Dept. of Earth Science, Goa University 26

of rock
 Exposure of a stone to intense heating causes expansion of
its component minerals with subsequent exfoliation at its
surface.
 The most suspect rocks in this respect appear to be those
that contain high proportions of quartz and alkali feldspars,
such as granites and sandstones.
 Indeed, quartz is one of the most expansive minerals,
expanding by 3.76% between normal temperatures and
570°C.
 Generally speaking, finely textured rocks offer a higher
degree of heat resistance than do coarse-grained varieties.

of rock
 Stone preservation involves the use of chemical treatments
that prolong the life of a stone, either by preventing or
retarding the progress of stone decay or by restoring the
physical integrity of the decayed stone (Bell and Coulthard,
1990).
 A stone preservative, therefore, may be defined as a
material that, when applied, will avert or compensate
for the harmful effects of time and the environment.
 When applied, the preservative must not change the
natural appearance or architectural value of the stone to
any appreciable extent.

Cutting methods of rock
 In some cases, stone may be obtained by splitting along
the bedding and/or joint surfaces by using a wedge and
feathers.
 Another method of quarrying rock for building stone
consists of drilling a series of closely spaced holes (often
with as little as 25 mm between them) in line in order to
split a large block from the face.
 Stone also may be cut from the quarry face by using a
wire saw or diamond-impregnated wire.
 Flame cutting has been used primarily for winning
granitic rocks. It is claimed that this technique is the only
way of cutting stone in areas of high stress relief.

Durability of rock
 Granite is ideally suited for building, engineering and monumental
purposes.
 Its crushing strength varies between 160 and 240 MPa. It has
exceptional weathering properties, and most granites are virtually
indestructible under normal climatic conditions.
 There are examples of granite polished over 100 years ago on
which the polish has not deteriorated to any significant extent.
Indeed, it is accepted that the polish on granite is such that it is
only after exposure to very heavily polluted atmospheres, for a
considerable length of time, that any sign of deterioration becomes
apparent.
 The maintenance cost of granite as compared with other materials
is therefore very much less and, in most cases, there is no
maintenance cost at all for a considerable number of years.

 Rocks used for roofing purposes must possess a
sufficient degree of fissility to allow them to split
into thin slabs, in addition to being durable and
impermeable.
 Consequently, slate is one of the best roofing
materials available and has been used extensively.
 Today, however, more and more tiles are being
used for roofing, these being cheaper than stone,
which has to be quarried and cut to size.
2. Roofing and facing materials

 The specific gravity of a slate is about 2.7 to 2.9, with an
approximate density of 2.59 Mg m-3.
 The maximum permissible water absorption of a slate is
0.37%.
 Calcium carbonate may be present in some slates of
inferior quality that may result in them flaking and
eventually crumbling upon weathering.
 Accordingly, a sulphuric acid test is used to test their
quality.
 Top quality slates, which can be used under moderate to
severe atmospheric pollution conditions, reveal no signs of
flaking, lamination or swelling after the test.
2. Roofing and facing materials

 Armourstone refers to large blocks of rock that are used
to protect civil engineering structures.
 Large blocks of rock, which may be single-size or, more
frequently, widely graded (rip-rap), are used to protect
the upstream face of dams against wave action.
 They are also used in the construction of river training
schemes, in river bank and bed protection and
stabilization, as well as in the prevention of scour around
bridge piers.
 Armourstone is used in coastal engineering for the
construction of rubble mound breakwaters, for revetment
covering embankments, for the protection of sea walls,
and for rubble rock groines.
3. Armourstone

 Indeed, breakwaters and sea defences represent a
major use of armourstone.
 As the marine environment is one of the most aggressive in which
construction occurs, armourstone must afford stability against
wave action, accordingly block size and density are all important.
 Shape is also important since this affects how blocks interlock
together.
 In addition, armourstone must be able to withstand rapid and
severe changes in hydraulic pressure, alternate wetting and drying,
thermal changes, wave and sand/gravel impact and abrasion, as
well as salt and solution damage.
3. Armourstone

 Crushed rock is produced for a number of purposes, the chief of
which are for concrete and road aggregate.
 Approximately 75% of the volume of concrete consists
of aggregate, therefore its properties have a
significant influence on the engineering behaviour of
concrete.
 Aggregate is divided into coarse and fine types, the former
usually consisting of rock material that is less than 40 mm and
larger than 4 mm in size.
 The latter is obviously less than 4 mm.
4. Crushed rock: Concrete Aggregate

 High explosives are used in drillholes when
quarrying crushed rocks.
 The holes are drilled at an angle of about 10–20°
from vertical for safety reasons, and are usually
located 3–6 m from the working face and a similar
distance apart.
 Generally one, but sometimes two, rows of holes
are drilled. The explosive does not occupy the
whole length of a drillhole.

 A single detonation fires a cordex instantaneous fuse (or the
like), which has been fed into each hole.
 It is common practice to have millisecond delay intervals between
firing individual holes, in this way the explosions are
complementary.
 The object of blasting is to produce a stone of workable size.
 Large stones must be further reduced by using secondary blasting.
 The height of the face largely depends on the stability of the rock
mass concerned.
 After quarrying, the rock is fed into a crusher and then screened to
separate the broken rock material into different grade sizes.

 The shape of aggregate particles is an important property
and is governed mainly by the fracture pattern within a
rock mass.
 Rocks such as basalts, dolerites, andesites, granites,
quartzites and limestones tend to produce angular
fragments when crushed.
 However, argillaceous limestones, when crushed, produce
an excessive amount of fines.
 Angular particles are said to produce a denser concrete.

 The less workable the mix, the more sand, water and cement must be added to
produce a satisfactory concrete.
 Fissile rocks such as those that are strongly cleaved, schistose, foliated or
laminated have a tendency to split and, unless crushed to a fine size, give rise to
tabular- or planar-shaped particles.
 Planar and tabular fragments not only make concrete more difficult to work, but
they also pack poorly and so reduce its compressive strength and bulk weight.
 Furthermore, they tend to lie horizontally in the cement, allowing water to
collect beneath them, which inhibits the development of a strong bond on their
under surfaces.
 The surface texture of aggregate particles largely determines
the strength of the bond between the cement and themselves. A
rough surface creates a good bond, whereas a smooth surface
does not.

 As concrete sets, hydration takes place, and alkalies (Na2O and
K2O) are released.
 These react with siliceous material such as opal, chalcedony, flint,
chert and volcanic glass.
 If any of these materials are used as aggregate in concrete made
with high-alkali cement, then the concrete is liable to expand and
crack, thereby losing strength.
 ASR is a simple acid-base reaction between calcium hydroxide, also
known as Portlandite, or (Ca(OH)2), and silicic acid (H4SiO4, or
Si(OH)4). For the sake of simplicity, this reaction can be
schematically represented as following:
Ca(OH)2 + H4SiO4 → Ca2
+ + H2SiO4
2− + 2 H2O → CaH2SiO4 · 2 H2O

 The mechanism of ASR causing the deterioration of concrete can be
described in four steps as follows:
1. The alkaline solution attacks the siliceous aggregate, converting it
to viscous alkali silicate gel.
2. Consumption of alkali by the reaction induces the dissolution of
Ca2+ ions into the cement pore water. Calcium ions then react with
the gel to convert it to hard C-S-H (Calcium-Silicate-Hydrate).
3. The penetrated alkaline solution converts the remaining siliceous
minerals into bulky alkali silicate gel. The resultant expansive
pressure is stored in the aggregate.
4. The accumulated pressure cracks the aggregate and the
surrounding cement paste when the pressure exceeds the tolerance
of the aggregate.

 These troubles can be avoided if a preliminary
petrological examination is made of the aggregate.
 In other words, material that contains over 0.25% opal,
over 5% chalcedony, or over 3% glass or cryptocrystalline
acidic to intermediate volcanic rock, by weight, will be
sufficient to produce an alkali reaction in concrete,
unless low-alkali cement is used.
 This contains less than 0.6% of Na2O and K2O.
 If aggregate contains reactive material surrounded by or
mixed with inert matter, a deleterious reaction may be
avoided.

 Certain argillaceous dolostones have been found to expand when used
as aggregates in high-alkali cements, thereby causing failure in
concrete.
 This phenomenon has been referred to as alkali–carbonate rock
reaction, and its explanation has been attempted by Gillott and
Swenson (1969).
 CaMg(CO3)2 + 2 NaOH → CaCO3 + Na2CO3 + Mg(OH)2 (Brucite)
 They proposed that the expansion of such argillaceous dolostones
(brucite) in high-alkali cements was due to the uptake of moisture by
the clay minerals.
 This was made possible by dedolomitization that provided access for
moisture.

 Aggregate constitutes the basic material for road construction
and is quarried in the same way as aggregate for concrete.
 Because it forms the greater part of a road surface, aggregate
has to bear the main stresses imposed by traffic, such as
slow-crushing loads and rapid-impact loads, and has to resist
wear.
 Therefore, the rock material used should be fresh and have
high strength. In addition, the aggregate used in the wearing
course should be able to resist the polishing action of traffic.
 The aggregate in blacktop should possess good adhesion
properties with bituminous binders.
5. Road aggregate

 Aggregate used as road metal must, in addition to having high
strength, have high resistance to impact and abrasion, polishing and
skidding, and frost action.
 It must also be impermeable, chemically inert and possess a low
coefficient of expansion.
 The properties of an aggregate are related to the texture and
mineralogical composition of the rock from which it was derived.
 Most igneous and contact metamorphic rocks meet the requirements
demanded of good roadstone.
 On the other hand, many rocks of regional metamorphic origin are
either cleaved or schistose and are therefore unsuitable for
roadstone.
5. Road aggregate

 This is because they tend to produce flaky particles when
crushed.
 Such particles do not achieve good interlock and,
consequently, impair the development of dense mixtures
for surface dressing.
 The amount and type of cement and/or matrix material
that bind grains together in a sedimentary rock influence
roadstone performance.
5. Road aggregate

 One of the most important parameters of road aggregate is the
polished stone value, which influences skid resistance.
 A skid-resistant surface is one that is able to retain a high degree of
roughness while in service.
 At low speeds, the influence of the roadstone is predominant,
whereas at high speeds, the influence of surface tension on skidding
mainly depends on aggregate grading and the aggregate–binder
relationship.
 The rate of polish is initially proportional to the volume of the traffic.
 Straight stretches of road are less subject to polishing than bends,
which may polish up to seven times more rapidly.
5. Road aggregate

 Stones are polished when fine detrital powder
is introduced between the tyre and surface.
 Investigations have shown that detrital
powder on a road surface tends to be coarser
during wet than dry periods.
 This suggests that polishing is more significant
when the road surface is dry than wet, the
coarser detritus tending to roughen the
surface of stone chippings.
5. Road aggregate

 Igneous rocks with a high silica content resist abrasion better than those in
which the proportion of ferromagnesian minerals is high, in other words, acid
rocks such as rhyolites are harder than basic rocks such as basalts.
 Some rocks that are the products of thermal metamorphism, such as hornfels
and quartzite, because of their high strength and resistance to wear, make good
roadstones.
 In contrast, many rocks of regional metamorphic origin, because of their
cleavage and schistosity, are unsuitable.
 Coarse-grained gneisses offer a similar performance to that of granites.
 Of the sedimentary rocks, limestone and greywacke frequently are used as
roadstone. Greywacke, in particular, has high strength, resists wear and
develops a good skid resistance. Some quartz arenites are used, as are gravels.
5. Road aggregate

Gravel deposits usually represent local
accumulations, for example, channel fillings.
In such instances, they are restricted in width and
thickness but may have considerable length.
Fan-shaped deposits of gravels or aprons may
accumulate at the snouts of ice masses, or blanket
deposits may develop on beaches.
6. Gravels & Sands - Gravels

 A gravel deposit consists of a framework of pebbles between
which are voids.
 The voids are rarely empty, being occupied by sand, silt or clay
material.
 River and fluvio-glacial gravels are notably bimodal, the
principal mode being in the gravel grade, the secondary in the
sand grade.
 Marine gravels, however, are often unimodal and tend to be more
uniformly sorted than fluvial types of similar grade size.

 The shape and surface texture of the pebbles in a gravel deposit
are influenced by the agent responsible for its transportation and
the length of time taken in transport, although shape is also
dependent on the initial shape of the fragment, which in turn is
controlled by the fracture pattern within the parental rock.
 Gravel particles can be classified as rounded, irregular, angular,
flaky and elongated in shape.

 Gravel particles generally possess surface coatings that may be the result of
weathering or may represent mineral precipitates derived from circulating
groundwater.
 The latter type of coating may be calcareous, ferruginous, siliceous or,
occasionally, gypsiferous.
 Clay also may form a coating about pebbles.
 Surface coatings generally reduce the value of gravels for use as concrete
aggregate.
 Clay and gypsum coatings, however, can often be removed by screening
and washing.
 Siliceous coatings tend to react with the alkalies in high-alkali cements and
are, therefore, detrimental to concrete.

 The textural maturity of sand varies appreciably.
 A high degree of sorting, coupled with a high degree of
rounding, characterizes mature sand.
 The shape of sand grains, however, is not greatly influenced by
the length of transport.
 Maturity is reflected in the particle composition of sand, and it
has been argued that the ultimate sand is a concentration of pure
quartz.
 This is because the less-stable minerals disappear due to
mechanical or chemical breakdown during erosion and
transportation or even after sand has been deposited.
6. Gravels & Sands - Sands

 Sands used for building purposes are usually siliceous in
composition and should be as free from impurities as possible.
 Ideally they should contain less than 3%, by weight, of silt or
clay, since they need a high water content to produce a workable
concrete mix.
 A high water content leads to shrinkage and cracking in concrete
on drying.
 Furthermore, clay and shaly material tend to retard setting and
hardening, or they may spoil the appearance of concrete.

 If sand particles are coated with clay, they form a poor bond with
cement and produce a weaker and less durable concrete.
 The presence of feldspars in sands used in concrete has
sometimes given rise to hair cracking, and mica and particles of
shale adversely affect the strength of concrete.
 Organic impurities may affect the setting and hardening
properties of cement adversely by retarding hydration and,
thereby, reduce its strength and durability.
 If iron pyrite occurs in sand, then it gives rise to unsightly rust
stains when used in concrete.

 The salt content of marine sands is unlikely to produce any
serious adverse effects in good-quality concrete, although it
probably will give rise to efflorescence however, Salt can be
removed by washing sand.
 High-grade quartz sands are used for making silica bricks used
for refractory purposes.
 Glass sands must have a silica content of over 95%.
 Uniformity of grain size is another important property, as this
means that the individual grains melt in the furnace at
approximately the same temperature.

 Lime is made by heating limestone, including chalk, to a
temperature between 1100°C and 1200°C in a current of air, at
which point carbon dioxide is driven off to produce quicklime
(CaO).
 Approximately 56 kg of lime can be obtained from 100 kg of
pure limestone.
 Slaking and hydration of quicklime take place when water is
added, giving calcium hydroxide.
 Carbonate rocks vary from place to place both in chemical
composition and physical properties so that the lime produced in
different districts varies somewhat in its behaviour.
7. Lime, Cement and Plaster

 Portland cement is manufactured by burning pure limestone or
chalk with suitable argillaceous material (clay, mud or shale) in
the proportion 3:1.
 The raw materials are crushed and ground to a powder, and then
blended.
 They are then fed into a rotary kiln and heated to a temperature
of over 1800°C.
 Carbon dioxide and water vapour are driven off, and the lime
fuses with the aluminium silicate in the clay to form a clinker.
 This is ground to a fine powder, and less than 3% gypsum is
added to retard setting (hardening).

 When gypsum (CaSO4.nH2O) is heated to a temperature
of 170°C, it loses three quarters of its water of
crystallization, becoming calcium sulphate hemi-
hydrate, or plaster of Paris.
 Anhydrous calcium sulphate forms at higher
temperatures.
 These two substances are the chief materials used in
plasters.

 ---Granite - How Its Made – YouTube
 ---How its Made Paving Asphalt – YouTube
 ---From the Quarry to the Countertop – YouTube
 ---From the Roads to the Rock Quarry – YouTube

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