Engineering Materials

This research paper discusses various aspects of engineering materials, including the setting and hardening of concrete, the use of cement replacement materials, and the influence of aggregates on the workability of concrete. It also explores the challenges of concreting in hot climates and provides precautions to minimize adverse effects. The paper provides references to relevant sources for further reading.

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ENGINEERING MATERIALS
A Research Paper on Materials By
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Engineering Materials 2
1. (a)
The term setting is used when describing the process of stiffening of the cement paste. Setting
process involves the change of cement paste to a state that is rigid from fluid and it is a
phenomenon which normally occurs after 2 hours of mixing the concrete mix. The concrete
achieves stiffness to retain its shape. The setting time is the duration that the concrete mix
requires to support a specific quantity of weight without denting1.
Hardening process which is also referred to as stiffening process normally takes place after the
setting process. It is a process by which there is occurrence of hydration of silicate compounds in
concrete.
(b)
Hydration involves the reaction of the concrete with water. The paste of cement should be fully
saturated with water in order to cure the concrete properly. Concrete must be kept moist during
the process of curing so as to attain the optimal durability and strength. The concrete should be
covered with damp fabric or plastic to keep young and fresh concrete moist so as to prevent
evaporation.
After the concrete have been positioned and consolidated, it should be permitted to properly cure
so as to attain good characteristics. As the concrete gains strength and hardens, it becomes less
vulnerable, therefore, the critical time duration is the initial days and hours after being placed.
1 Chandigarh T, Civil Engineering Materials (4th edn, Tata McGraw-Hill Education 2011)
Gambhir M, Concrete Technology: Theory and Practice (2nd edn, Tata McGraw-Hill Education 2013)

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Proper curing of concrete is normally significant since it helps in keeping it supported and also
keeping it moist2.
(c)
Some of the particular problems of concreting in hot climates as opposed to the temperature in
UK include:
Thermal cracking: Concrete can experience thermal cracking when the concrete is originally
positioned and the concrete interior is exposed to heat of hydration and heat rising from the
settlement of the concrete.
Plastic shrinkage: Hot weather conditions promotes loss of moisture and evaporation from the
surface. Plastic shrinkage takes place when the stress of shrinkage surpasses tensile strength of
the concrete hence resulting in cracks until the stress is reduced.
Poor appearance of the surface: Increase evaporation rate results in stiffening and drying of the
surface which may cause colour differences on the surface because of the different rates of
cooling and hydration.
Compressive strength: higher water requirement and high concrete temperature in hot dry
climates may result in lower strength. This also increases drying shrinkage of the concrete
hardened3.
2 Gan J, 2009. Cement and Concrete (2nd edc, CRC Press 2009)
Illston M. & Domone P, Construction Materials: Their Nature and Behaviour (3rd edn, CRC Press 2011)
3 Lamond J. & Pielert H, Significance of Tests and Properties of Concrete and Concrete-making Materials
(1st edc, ASTM International 2013)
Michael G. & Carmelo M, Concrete Solutions (2nd edc, CRC Press 2009)

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Precautions
Precautions can be taken to minimize the potential adverse effects of hot weather on the features
of the hardened and fresh concrete. Shading and sprinkling of water on the aggregates before
mixing can also assist in lowering the concrete temperature. The reinforcement, forms, and sub-
grades should be moistened before being placed to reduce the concrete temperature. There are
also numerous types of admixtures which can help in lowering the temperature also reducing the
evaporation rate from the surface4.
2. (a)
Cement replacement material is a distinct category of naturally occurring material or industrial
waste product which can be used in replacing most of the Portland cement partially in concrete
mixes. Some of the materials used for cement replacement that are regularly used include ground
granulated blast-furnace slag, condensed silica fume, and flu ash.
Pozzolan are materials which reacts chemically in the presence of moisture with the calcium
hydroxide to produce hydration of Portland cement to form calcium hydrate. These materials
differently react with different cement. Two or more of the pozzolan can be joined to maximize
the properties of concrete.
Some of the examples of pozzolan materials include:
 Ground granulated blast-furnace slag
 Fly ash5
4 Ramezanianpour A, Cement Replacement Materials: Properties, Durability, Sustainability (3rd edc,
Springer Science & Business Media 2013)
5 Reinhardt H. & Grosse C, Advanced Testing of Cement-Based Materials during Setting and Hardening -
Report of RILEM Technical Committee 185-ATC (2nd edc, RILEM Publications 2011)

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(b) Why may the use a pozzolanic cement replacement be beneficial in increasing the resistance
of concrete to sulphate attack?
The use a pozzolanic cement replacement be beneficial in increasing a resistance to sulphate
attack of concrete since the properties of hardened blended cements are greatly attributed to the
development of binder microstructures, majorly dimension, shape, type, and distribution of both
pores and binder microstructure. The resistance to sulphate attack is attributed to the pozzolanic
reaction in which calcium hydroxide is used to generate extra C-A-H and C-S-H reaction
products. This reaction products fill pores and result in a refining of the pore structure or pore
size distribution.
3. Briefly describe the following, with references:
(i) Influence of aggregates on the workability of a concrete mix;
Concrete is a mixture of water, aggregate, and cementious material. Aggregate is a significant
component that defines the dimensional stability and thermal and elastic properties of concrete.
The compression strength of the concrete is an important factor in the aggregate selection. When
evaluating the concrete strength, majority of concrete aggregates have greater strength compared
to the other concrete components and hence not a factor in the strength of normal strength of
concrete. The bulk unit weight, soundness, reactivity, specific gravity, moisture content, size
gradation, texture and shape must be known before mixing concrete to attain the mixture desired.
The shape and texture of aggregate affect the properties of fresh concrete compared to the
concrete that have already hardened. Concrete is more workable when rounded and smooth
aggregate is applied and not elongated or round angular aggregate6.
6 Swamy R, Cement Replacement Materials (3rd edc, Surrey University Press 2008)
Tattersall G, Workability and Quality Control of Concrete (4th edc, CRC Press 2009)

Engineering Materials 6
The size and grading distribution of aggregate in a significant feature since it determines the
paste requirement for concrete that is workable. The content of moisture of the aggregate is a
significant factor when determining the correct cementitious/water material ratio. Aggregate can
be found different states of moisture, namely oven-dry, air-dry, saturated surface, and wet.
(ii) Segregation and bleeding in fresh concrete;
Segregation is the separation of the components of the concrete. A perfect of concrete should
have ingredients which are homogenously distributed. There are three types of segregation,
namely, separation of coarse aggregate from the mixture, paste separation from the coarse
aggregate, and then the separation of water from the rest of the material since water has the
lowest specific gravity.
Concrete bleeding can be defined as a form of segregation in which some quantity of water
comes out of the concrete surface since water has a low specific gravity compared to the other
concrete ingredients. Bleeding is observed predominantly in an insufficiently mixed, badly
proportioned, and highly wet mix concrete. Water comes up and accumulates at the surface due
to bleeding. The channels of bleeding are normally responsible for causing concrete
permeability. The water accumulated creates water voids and minimizes the bond between the
paste and aggregates. The poor bond between the paste and the reinforcement or the paste and
aggregate can be remedied through concrete re-vibration7.
(iii) Setting and hardening of concrete;
7 Taylor P, Curing Concrete (2nd edc, CRC Press 2013)
Tynes W, Investigation of Cement-replacement Materials: Report 13 : Use of Water-reducing and Water-
reducing Retarding Admixtures in Mass Concrete (1st edc, Waterways Experiment Station 2015)

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Concrete setting is the concrete stiffening after it has been positioned. After a concrete has been
set, it is no longer in fluid state, however, it may still be weak. Setting involves the change of
concrete paste to rigid state from fluid state.
Hardening is the process of growth of strength of concrete and may processed for months or
weeks after the concrete has been placed and mixed. Hardening is as a result of the formation of
calcium silicate hydrates. Hardening and setting result from the continuing reaction between
water and cementitious material.
(iv) The heterogeneous nature of hardened concrete.
A hardened concrete is a heterogeneous material since it is composed of coarse aggregates, fine
aggregates, water, and cement. The property of concrete depends on the individual
characteristics of the coarse aggregates, sand, and cement. A material is said to be homogeneous
when its characteristics are similar in all directions such as in the case of cement8.
BIBLIOGRAPHY
Chandigarh T, Civil Engineering Materials (4th edn, Tata McGraw-Hill Education 2011)
8 Tattersall G, Workability and Quality Control of Concrete (4th edc, CRC Press 2009)

Engineering Materials 8
Gambhir M, Concrete Technology: Theory and Practice (2nd edn, Tata McGraw-Hill Education 2013)
Gan J, 2009. Cement and Concrete (2nd edc, CRC Press 2009)
Illston M. & Domone P, Construction Materials: Their Nature and Behaviour (3rd edn, CRC Press 2011)
Lamond J. & Pielert H, Significance of Tests and Properties of Concrete and Concrete-making Materials
(1st edc, ASTM International 2013)
Michael G. & Carmelo M, Concrete Solutions (2nd edc, CRC Press 2009)
Ramezanianpour A, Cement Replacement Materials: Properties, Durability, Sustainability (3rd edc,
Springer Science & Business Media 2013)
Reinhardt H. & Grosse C, Advanced Testing of Cement-Based Materials during Setting and Hardening -
Report of RILEM Technical Committee 185-ATC (2nd edc, RILEM Publications 2011)
Swamy R, Cement Replacement Materials (3rd edc, Surrey University Press 2008)
Tattersall G, Workability and Quality Control of Concrete (4th edc, CRC Press 2009)
Taylor P, Curing Concrete (2nd edc, CRC Press 2013)
Tynes W, Investigation of Cement-replacement Materials: Report 13 : Use of Water-reducing and Water-
reducing Retarding Admixtures in Mass Concrete (1st edc, Waterways Experiment Station 2015)