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IMPACTS OF CHEMISTRY ON CEMENT ACQUISITION AND UTILIZATION

Conference Paper · March 2014

DOI: 10.13140/2.1.1543.9366

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U. A. Birnin-Yauri
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 IMPACTS OF CHEMISTRY ON CEMENT
ACQUISITION AND UTILIZATION.

U.A Birnin-Yauri

A Lead Paper Presented at the First National Conference Organized by the Faculty
of Science, Sokoto State University, Sokoto Themed " Impacts of Basic and
Applied Sciences on Resource Acquisition and Management". March 17th -22nd,
2014.

Abstract

Chemistry is such a science subject that no manufacturing industry can do without.

This paper discusses the roles of chemistry in production, quality control and
development of cements. The paper explains the use of chemistry right from
Environmental Impact Assessment for establishment of a cement industry,
quarrying of the raw material, grinding the raw materials and mixing them into
appropriate blend that would give good quality cement.
The paper further discusses the chemistry involved in the kiln reactions to
[produce good cement clinker..It also shades light on the chemistry of cement
hydration as well as how some environmental agents could affect the quality of
cement. In conclusion the asserts that chemistry is very vital and essential in any
manufacturing industry and whatever the industry manufactures.

Introduction
Cement is defined as a material with adhesive and cohesive properties which make
it capable of bonding mineral fragments into a compact whole (Neville, 2006)
However for constructional purposes, cement is restricted to bonding materials
used with stones, sand, bricks etc.

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There are two main classes of cement: hydraulic cements and non hydraulic
cements. The hydraulic cements include Portland, High Alumina and Expansive
cements. These cement have the ability of setting under water.
The non – hydraulic cements do not set under water. Such cements include plaster,
lime sorrels cement etc (Taylor, 1992)
For the purpose of this paper are will restrict ourselves to ordinary Portland cement
which is the only hydraulic cement being produced by all the ten cement industries
in Nigeria.
It may be interesting to note that in 2003, for every, woman and child in the world,
the consumption of cement was 320kg per annum, this was second only to the
consumption of water. (Neville, 2006)
Cement is used in building construction, such as houses, bridges, pavements, as
well as in oil wells.
The role of chemistry in cement industry start from the Environment Impact
Assessment (E.I.A) that is the assessment of possible effect on the environment in
which the cement industry is being planned to be sited.
There is need for the knowledge of environment chemistry in order to assess the
possible impact on the environment. Such as air, water and land pollutions. We as
well consider the social nuisance as well aesthetic effect such as the effect on
landscape.
Cement is manufacture from limestone or any calcareous material along with
argillaceous material such as clay.
These substances must contain 75% CaCO3 and 75% Al2O3 restricting for
production of good quality cement. Hence the need for good knowledge in
analytical chemistry.
In fact the burning of these calcareous and argillaceous materials is done in a
rotary kiln at the temperature of about 1500oC.
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There is need for good knowledge to know the best refractory material that can be
used for this high temperature operators and hence the need for chemical materials
science.
The fuel used to burn the finely ground cement raw materials is either black oil
(residual oil from petroleum refineries) or coal. We need to ascertain the chemical
composition of the fuels for efficient burning and also to ascertain the possible
environment pollutants in the oil as well as in the cement raw materials..
There is need for chemical knowledge in order to ameliorate the chemical reactions
taking place in the kiln.
In the kiln the formation of clinker involve the following reactions:
i. 2CaO + SiO2 2CaO + SiO2 Dicalcium silicate
ii. 3CaO + SiO2 3CaO + SiO2 Tricalcium silicate
iii. CaO + Al2O3 CaO + Al2O3 Tricalcium aluminate
iv. 4CaO + Al2O3 + FerO3 ------> 4CaO+Al2O3+Fe2O3 Tetra calcium
Aluminoferrite.
The combined products in reactions (i) to (iv) constitute the clinker which are
black noodles that are formed when the molten raw material is quenched with a
blast of cold air.
The composition of ordinate Portland cement is: CaO = 63% SiO 2 = 20%, Al2O3 =
6%' Fe2O3 = 3% alkali (K2O,Na2O) = 1% L.O.I = 2%, 3CaO.Al2O3 = 10.8%
3CaO.SiO2 = 54.1% 4CaO.Al2O3.Fe2O3 = 9.10 and 2CaO.SiO2 = 16.6%
The quantitative formation of these oxides depends on the proportion of calcareous
and argillaceous materials fed into the kiln.
The normal weight percent composition limits of Portland cement is:
CaO 60 - 67
SiO2 17 - 25
Al2O3 3-8
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Fe2O3 0.5 – 6.0
Alkalis 0.30 – 1.20
SO3 2 – 3.50
Below and above these ranges will cause the production of poor quality cement.
Hence we need to use our chemistry knowledge to get appropriate composition
right purity from the raw material.
For instance, if the argillaceous material (clay) has high iron content, if may
produce clinker that is hard to grind and hence will cause the wearing away
(corrosion) of the iron balls in the cement mill. The resultant cement may be
coloured (brownish). It is apparent that the significance of cement oxide
composition of cement cannot be over emphasized.

Hydration of cement
The entire hydration process of cement requires good understanding of physical
and analytical chemistry. The tricalcium aluminohydrates very quickly. Hence its
hydration has to be retarded using gypsum otherwise the cement will flash set.
That is to say that is will quickly loose plasticity (workability) within a few
minutes. Similarly the hydration of other phases are as follows:
i. 2C3S + 6H C3S2H3 + 3Ca(OH)2
ii. 2CaS + 4H C3S2H3 + Ca(OH)2
iii. C3A + 6H C3AH6
It is noteworthy that in the product of reactions i and iii which constitute of more
than 80% by weight of OPC, there is release of Ca(OH)2. Similarly we also have
the hydration of the alkalis.
M2O + H2O 2MOH (where M = K or Na)
This explains why pore fluid of cement paste is highly basic pH ≈ 13.5 (Birnin-
Yauri and Garba, 2006).
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It also explains the high susceptibility of cement to carbonation (Birnin-Yauri,
1998).
Knowledge of chemistry also explains the reaction and mode of action of gypsum
to retard the setting of cement and hence prevention of flash setting. On hydration
at temperatures below 20oC, C3A produces calcium aluminohydrates.
C4AH19 C3AH6 + CH +12H
In the presence of gypsum CaSO4 .2H,20, the C3A hydrates and reacts with gypsum
to form ettringite:
C3A + 3CaSO4 + 32H C3A.3CaSO4 .32H2O
The ettringite is semi-permeable. It is deposited on cement grain and hence retards
the reaction of the cement grain and water. Thereby retarding the hydration process
of the cement.
Sulphate Attack
From chemical knowledge we are able to understand that some cement are not
good enough for marine construction due to attack on the concrete by the sulphate
ion in the sea water (Birnin-Yauri and Glasser 1998).
We noted that hydration of cement produces a lot of (Ca(OH)2. in a set cement
structure the hardened calcium alumni can react with sulphate ions from the sea
water to form ettringite or monosulphate (3CaO.Al2O3.CaSO4.12H2O) with
consequences increase in volume of the frame with or the hydrated cement paste.
This can give 227% increase of volume of the solid phase (Birnin-Yauri, 1998).
Hence are modify the O.P.C to contain as low C3A as possible to avoid such
sulphate attack. Such modified Portland cement is called Sulphate – Resistant
Cement (RSC).

Chloride Attack
Reinforced concretes are required for construction of bridges, story buildings etc.
5
The iron rod used to re-enforce the concrete may be liable to corrosion usually
caused by chloride attack Damidot, Birnin-Yauri and Glasser 1994). Hence using
chemical knowledge we have been able to minimize chloride ingression and also
maximize the passivity of the iron rod within the concrete matrix (Birnin-Yauri
and Garba 2012). This calls for careful choice of mixing water for concrete. There
is also need for avoidance of sulphate-containing water such as that commonly
found in areas with abundant gypsum or salty water that is common in Bunza area
of Kebbi State.

Quality Controls
We need a lot of chemical knowledge of the cement in order to have proper quality
control of the product. For instant, Nigeria is a tropical nation. The rules of
concreting in Nigeria cannot be as that in cold countries like Europe. So there are
some qualitative standards set up by the Standard Organization of Nigeria (SON).
These standards are always controlled by the cement chemists so that the industry
is not found wanting by the regulatory body (SON).

ENVIRONMENT CONSEQUENCES OF CEMENT PRODUCTION

Cement production releases a lot of dust from the limestone quarry, raw materials
mill, cement will as well as the parking plant. Cement dust constitute of lime,
heavy metals and obnoxious gases from fuel burning Birnin-Yauri, 2002).
The lime – containing dust, when accumulated on farm lands may cause the soil to
be highly basic. Hence some crops may not grow well on such lands. Similarly
during raining season, the dust may settle on the leaves of the crops and become
encrusted on the leaves thereby preventing photosynthesis with consequence death
of the plants Anka, Birnin-Yauri and Chinoko 1995).

6
The dust nuisance could be felt several kilometers away from the cement industry.
In the locality, people cannot cook outside the kitchen. When they hang their
washed – clothes the clothes become soiled with the dust when it rains, the
deposited cement dust may be washed via run off into lakes and rivers thereby
causing eutrophication which in turn deflate the dissolved oxygen in the water.
Thereby causing the death of aquatic lives and affecting biodiversity of the local
habitant
It is therefore very important that the community withi9n which a cement industry
is sighted should be compensated. They may have free health care delivery, free
education as well as some other sited amenities in the community.

Conclusion
It is said that the only thing that is not chemistry is nothing. In another word, there
is chemistry in everything and in whatever we do. In fact no manufacturing
industry can exist without a chemist whatever their product is. Indeed bin cement
industry both the production and the quality control are the responsibility of
chemists. It is the chemists that direct the kiln operator on the ration of calcareous
and argillaceous materials that is need to produce a good quality cement.

REFERENCES
Anka R. M, Birnin-Yauri U A and Chinoko, J Y (1995) Analysis of Some
Environmental Pollutants within Sokoto Metropolis Proceedings of
Symposium on Chemistry and Biotechnology for National Development
Sheda Science and Technology Complex Abuja 17 – 18 th August 1995.

Birnin-Yauri U A and Glasser F P (1991) Chloride In Cement: Phase

Study of the Ca(OH)2-CaCl2-H2O System, Il Cemento 88 (3) 151-157

7
 Birnin-Yauri U A (1998) The Influence of Sulphate Admixtures on Some
Properties of High Alumina Cement. Nigerian Journal of Basic and Applied
Sciences. 7 1-8

Birnin-Yauri U A (2002) Public Enlightenment on Chemical Hazards: An

Ignored Responsibility of the Chemists. Presented as Guest Speech at the
Inauguration of Sokoto State Chapter of the Chemical Society of Nigeria.
Congregational Hall, City Campus Usmanu Danfodiyo University Sokoto. 20 th
July 2002

Birnin-Yauri U A and F. P. Glasser (1998) Friedel’s Salt,

Ca2Al(OH)6(Cl,OH).2H2O: Its Solid Solutions and Their Role in Chloride
Binding. . Cement and Concrete Research 25 (12) 1713-1723

Birnin-Yauri U. A. and S. Garba (2006) The Effect and Mechanism of Chloride

Ion Attack on Portland Cement Concrete and the Structural Steel
Reinforcement... Ife Journal of Science 8 (2) 131-135.

Damidot D, Birnin-Yauri U.A and Glasser F P (1994) Thermodynamic

Investigations of the CaO-Al2O3-CaCl2-H2O System at 25oC and the Effect of
Na2O and K2O. Il Cemento 91 (4) 243-254 .

Neville A M (2006) The Chemistry of cement and Concrete 4th Ed.

Pearson/Prenticehall London England pp.20-25

Taylor H F W (1996) Cement Chemistry Academic Press London pp60-75

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