JIMMA UNIVERSITY

JIMMA INSTITUTE OF TECHNOLOGY

FACULTY OF CIVIL AND ENVIRONMENTAL ENGINEERING

MSc. IN CIVIL ENGINEERING

CONSTRUCTION ENGINEERING AND MANAGEMENT CHAIR

ASSIGNMENT

SUBMITTED BY: EBSA BERHANU HATEU

ID NO. RM2815/12

SUBMITTED TO: MUGE MUKADDES DARWISH (Dr.)

December 16, 2019

Jimma, Ethiopi
 ASSIGNMENT

ETH- CONCRETE CONSTRUCTION Home works 1 and 2

1. What is the difference between cement and concrete?

ANSWER:

Concrete is a conglomerate, artificial stone like material obtained by hardening and curing a
mixture of mainly cement, water and aggregates and sometimes admixtures. Although the
terms cement and concrete often are used interchangeably, cement is actually an ingredient of
concrete. Concrete is basically a mixture of aggregates and paste.
2. List the condition that must be met to make satisfactory concrete mix?

ANSWER:

A satisfactory concrete mix is made of fresh cement; clean, well-graded aggregates; and clean
water. Admixtures are sometimes added to the mix to regulate its properties or the properties
of the finished concrete. The concrete must be thoroughly blended in the correct proportions,
with special attention given to avoiding excessive water content. To avoid segregation of its
constituents, it must be handled without moving or dropping it excessive distances and
compacted in the forms without excessive agitation.
3. What precaution must be taken to cure concrete properly? How does these changes
in very hot, very windy and very cold weather?

ANSWER:

It’s essential that concrete be kept moist until its required strength is achieved. The curing
reaction takes place over a very long period of time, but concrete is commonly designed on the
basis of the strength that it reaches after 28 days.

In very hot weather, the hydration reaction is greatly accelerated, and concrete may begin
curing before there’s time to place and finish it. This can be controlled by using cool
ingredients. Under extreme conditions, replacing some of the mixing water with an equal
quantity of crushed ice, making sure that the ice has melted fully and the concrete has been
thoroughly mixed before placing.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 1

 ASSIGNMENT

In very windy and very cold weather, the curing reaction occurs much more slowly. If it
reaches subfreezing temperatures while curing, the reaction stops completely until the
temperature of the concrete rises above the freezing mark. To achieve full strength, it’s
important that concrete be protected from low temperatures or freezing until it’s adequately
cured.
4. What problems likely occur if concrete has too low slump? Too low slump? How can
the slump be increased without increasing the water content of the concrete mixture?

ANSWER:

If concrete has too low a slump, it will be difficult to handle and place in the forms, and will
be likely to have voids. If the slump is too high, the concrete is likely to be weak and have
poor surface qualities. Water-reducing admixtures or air-entraining admixtures can be used to
increase the slump without increasing the water content.
5. Why precast concrete structural elements are usually cured with steam?

ANSWER:

Steam curing is suitable for pre-cast concrete products. Because of steam, the components are
heated homogeneously and the strength is achieved at a very rapid rate. Steam can pass and
infiltrate through small gaps of stacked pre-cast concrete products and strength is obtained
consistently from all sides.
6. What are the engineering property of fresh concrete?

ANSWER:

Properties of Fresh Concrete:

Fresh Concrete can be easily molded into any designed shape in construction. It can be
prepared on the spot and may give a wide range of properties from easily available raw
materials.
 The fresh concrete which may be expected to give the best results must possess the
property of workability. This is the most important property of fresh concrete.
 Fresh concrete should be capable of spreading uniformly without inducing any
segregation of the aggregates.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 2

 ASSIGNMENT

Generally engineering property of fresh concrete are:

 Workability
 Slump loss
 Temperature
 Bleeding/segregation
 Time of set
 Plastic shrinkage
7. What are the property of hardened concrete?

ANSWER:

Property of hardened concrete:

 Compressive strength: The main measure of the structural quality of concrete is its
compression strength.
 Tensile strength: Even though compression strength of concrete is best utilized, its
tensile strength is also important in a variety of items. It is used to design for shear,
torsion and crack width. This is much lower than compressive strength and general falls
between 8 and 15 percent of compressive strength.
 Creep: It is strain that occur under constant sustained compressive load. It is also defined
as deformation of a member under sustained load. It results in stress redistribution and
additional deformation and should be considered.
 Durability
 Porosity and density
 Fire resistance
 Thermal and acoustic insulation property
 Impact resistance
8. Why is concrete most widely used engineering material?

ANSWER:

Concrete has been the construction material used in the largest quantity for several decades.
The reason for its popularity can be found in the excellent technical properties of concrete as
well as in the economy of this material. Concrete’s continued popularity comes from the fact
that it is not only economical but it is very strong and durable. When compared to wood, asphalt
or other building materials, concrete outlasts them by decades and even gains strength over
Jimma Institute of Technology, Construction Engineering and Management Chair Page 3
 ASSIGNMENT

time. Concrete is an extremely versatile material that is used to construct buildings, bridges,
dams, tunnels, pavements, runways and roads. Additionally concrete is extremely fire
resistance so it is a safe material to use.

It is also characteristic that the properties of concrete ingredients have a major influence on the
fresh as well as hardened concrete. Therefore, the selection of concrete-making materials for a
given purpose is quite important. Generally the flexibility and versatility of the concrete make
concrete the most sought-after construction material in the world.
9. Comparing the steel, what are the engineering benefits of using concrete for
structures?

ANSWER:

Steel is one of the most important construction materials, which has high tensile strength and
much greater ductility and toughness. But it is susceptible to corrosion and has low fire
resistances. Whereas concrete has excellent formability, high fire and weather resistance, and
high compressive strength. On the other hand it is a relatively brittle material with less tensile
strength which prevents its economical use in structural members that are subjected bending,
shear and tension

The following are the benefits of concrete:

 It is monolithic. This gives it more rigidity.
 It is durable. It does not deteriorate with time.
 While it is plastic, it can be moldable into any desired shape.
 It is fire, weather and corrosion resistant.
 By proper proportioning of mix, concrete can be made water-tight.
 Its maintenance cost is practically nil.
10. Define the following terms: fine aggregate, coarse aggregate, gravel, grout, shotcrete,
hydraulic cement?

ANSWER:
 Fine aggregate: they are those aggregate which can pass through 4.75mmIS sieve. Fine
aggregates contribute towards reducing the number of voids, increase the workability
increase the volume, reduce the cost and proper density is provided.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 4

 ASSIGNMENT

 Coarse aggregate: these aggregates which are the residue of 4.75mm IS sieve and
passed through 75mm IS sieve. Coarse consists of crushed gravels. These aggregates
are firmed by natural disintegration of rocks or by artificial crushing of rocks or gravel.
 Grout: is a dense fluid which is used to fill gaps or used as reinforcement in existing
structures. Generally it is a mixture of water, cement, and sand and is employed in
pressure grouting, embedding rebar in masonry walls, connecting sections of pre-cast
concrete, filling voids, and sealing joints such as those between tiles.
 Shotcrete: is concrete or mortar conveyed through a hose and pneumatically projected
at high velocity onto a surface, as a construction technique, it is typically reinforced by
conventional steel rods, steel mesh, or fibers.
 Hydraulic Cement: is a product used to stop water and leaks in concrete and masonry
structures. It is a type of cement, similar to mortar, that sets extremely fast and hardens
after it has been mixed with water. Hydraulic cement can be used above or below grade,
however, it is extremely useful if used in:
 Swimming Pools
 Drainage systems
 Foundations
 Elevator pits
 Basement walls
11. What are the typical units of weights for normal weight, light weight, and heavy
weight concrete? How would you define high strength concrete?

ANSWER:

Units of weights
 Normal weight weighs 2000-2800 kg per cubic meter
 Light weight weighs up to 2000 kg per cubic meter
 Heavy weight weighs higher than 2800 kg per cubic meter

High-performance concrete: These types of concrete display a high level of performance.

They conform to specific standards such as rapid strength gain, easy placement, high
permeability, high durability, life term mechanical properties and addressing environmental
concerns. So high performance concrete shows better long time durability.
12. What is the significance of elastic limit in structural design?

Jimma Institute of Technology, Construction Engineering and Management Chair Page 5

 ASSIGNMENT

ANSWER:

Where is the elastic limit?

A method using energy dissipation as the yield criterion is employed to demonstrate that cyclic
stresses at levels considerably below the 0.01-percent yield strength cause significant changes
of the mechanical properties of some spring materials.

Elastic Modulus of concrete:

The modulus of elasticity or “Young’s Modulus” is defined as the slope of the stress-strain
curve within the proportional limit of a material. For a concrete material, the secant modulus
is defined as the slope of the straight line drawn from the origin of axes to the stress-strain
curve at some percentage of the ultimate strength. This is the value most commonly used in
structural design.
Since no portion of the stress-strain curve is a straight line, the usual method of determining the
Young’s Modulus is to measure the tangent modulus, which is defined as the slope of the
tangent to the stress-strain curve at some percentage of the ultimate strength of the concrete as
determined by compression tests.
13. What is the difference between strength and toughness? Why the 28-Day compressive
strength of concrete is generally specified?

ANSWER:
 Strength is Permanence by virtue of the power to resist stress or force or is a measure
of the maximum stress that a metal can support before starting to fracture.It refers to
resistance to deformation, and also to a large elastic range.
 Whereas Toughness is how well the material can resist fracturing when force is
applied. Toughness requires strength as well as ductility, which allows a material to
deform before fracturing. It is somewhat related to strength. Very strong materials will
have low toughness, i.e. low tolerance for flaws or defects, i.e. incipient cracks.
Toughness relates to the amount of energy absorbed in order to propagate a crack.
Materials with high toughness require greater energy (by virtue of force or stress) to
maintain crack propagation.

Why is the 28 -day compressive strength of concrete generally specified?

Jimma Institute of Technology, Construction Engineering and Management Chair Page 6

 ASSIGNMENT

Throughout the construction industry, the common belief is that concrete takes 28 days to cure
and reach 100% of its strength.

Specifying concrete strength is normally done with a minimum compressive strength (psi) at a
certain age (days). Specified concrete compressive strength is the minimum compressive
strength at which the concrete should fail in standard tests of 28-day-old concrete cylinders. A
typical concrete compressive strength specification requires 4,000 to 5,000 psi at 28 days. Some
go a step further and mandate that concrete products cannot be installed or used until 28 days
after the date of manufacture. This, mistakenly, has given concrete a reputation among some
specifiers as being weak or inferior if it has not cured for the full 28 days.
14. Discuss the significance of drying shrinkage, thermal shrinkage, and creep in
concrete.
ANSWER:

Drying shrinkage is defined as the contracting of a hardened concrete mixture due to the loss
of capillary water.

Significance of drying shrinkage

This shrinkage causes an increase in tensile stress, which may lead to cracking, internal
warping, and external deflection, before the concrete is subjected to any kind of loading.

Significance of thermal shrinkage

Due to increase in atmospheric temperature concrete tends to reduce its volume; the expansion
joints are therefore provided in concrete member of length more than certain length.

Significance of creep
 Creep does not necessarily cause concrete to fail or break apart. When a load is applied
to concrete, it experiences an instantaneous elastic strain which develops into creep
strain if the load is sustained.
 In reinforced concrete beams, creep increases the deflection with time and may be a
critical consideration in design.
 In eccentrically loaded columns, creep increases the deflection and can load to buckling.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 7

 ASSIGNMENT

 In case of statically indeterminate structures and column and beam junctions creep may
relieve the stress concentration induced by shrinkage, temperatures changes or
movement of support.

NB: Shrinkage of concrete is liable to cause cracking, but it has the beneficial effect of
strengthening the bond between the reinforcing steel and the surrounding concrete.
15. Define durability, in general what concrete types are expected to show better long
time durability?
ANSWER:

Durability is the ability to last a long time without significant deterioration. Durability of
concrete may be defined as the ability of concrete to resist weathering action, chemical attack,
and abrasion while maintaining its desired engineering properties.

High-performance concrete: These types of concrete display a high level of performance.

They conform to specific standards such as rapid strength gain, easy placement, high
permeability, high durability, life term mechanical properties and addressing environmental
concerns. So high performance concrete shows better long time durability.
16. What is significance of microstructure of a material? And provide definition for
microstructure.
ANSWER:

Microstructure is the very small scale structure of a material, defined as the structure of a
prepared surface of material as revealed by an optical microscope above 25X magnification.
The microstructure of a material (such as metals, polymers, ceramics or composites) can
strongly influence physical properties such as strength, toughness, ductility, hardness,
corrosion resistance, high/low temperature behaviour or wear resistance. A microstructure’s
influence on the mechanical and physical properties of a material is primarily governed by the
different defects present or absent of the structure.

Most importantly, microstructures affect the physical properties and behavior of a material, and
we can tailor the microstructure of a material to give it specific properties Although concrete
is the most widely used structural material, its microstructure is heterogeneous and highly
complex. Therefore, it is very difficult to constitute realistic models of its microstructure from
which the behavior of the material can be reliably predicted. However, knowledge of the

Jimma Institute of Technology, Construction Engineering and Management Chair Page 8

 ASSIGNMENT

microstructure and properties of the individual components of concrete and their relationship
to each other is useful for exercising control on the properties.
17. Describe some of the unique features of concrete microstructure that makes it difficult
to predict of behaviour of material from it is microstructure.
ANSWER:

The microstructure-property relationships in concrete are not yet fully developed; however,
some understanding of the essential elements of the microstructure would be helpful before
discussing the factors influencing the important engineering properties of concrete, such as
strength, elasticity, shrinkage, creep, and cracking, and durability.

The unique features of the concrete microstructure can be summarized as follows:

 There is the interfacial transition zone, which represents a thin shell small region next
to the particles of coarse aggregate, generally weaker than either of the two main

 Components: - the aggregate and the bulk hydrated cement paste; therefore, it exercises
a far greater influence on the mechanical behavior of concrete.

 Each of the three phases is itself a multiphase in character. For instance, each aggregate
particle may contain several minerals in addition to micro cracks and voids.

 Similarly, both the bulk hydrated cement paste and the interfacial transition zone
generally contain a heterogeneous distribution of different types and amounts of solid
phases, pores, and micro cracks

 Unlike other engineering materials, the microstructure of concrete is not an intrinsic

characteristic of the material because the two components of the microstructure, namely,
the hydrated cement paste and the interfacial transition zone, are subject to change with
time, environmental humidity, and temperature.
18. When cement paste is dried, the loss of water is not directly proportional to the drying
shrinkage. Explain why?
AMSWER:
 Shrinkage and shrinkage-induced cracking are increased by several factors,
including lack of curing, high W/C ratio, high cement content, low coarse aggregate
content, existence of steel reinforcement, and aging.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 9

 ASSIGNMENT

 How much drying shrinkage occurs depends on the size and shape of the concrete
structure.
 Also, non-uniform shrinkage could happen due to the non-uniform loss of water
such as in mass concrete structures, where more water is lost at the surface than at
the interior.
 In other cases, curling might develop due to the non-uniform curing throughout the
structure and, consequently, non-uniform shrinkage
 1st both the drying shrinkage and creep originate from the same source, that is, the
hydrated cement paste;
 2nd the strain-time curves are very similar;
 3rd the factors that influence the drying shrinkage also influence the creep generally
in the same way
19. In hydrating cement paste the relationship between porosity and impermeability is
exponential. Explain why?
ANSWER:

Paste permeability is directly related to the water/cement ratio and the degree of hydration or
length of moist-curing. Porosity is decrease with an increase in degree of hydration. A low
water/cement ratio and an adequate moist curing period result in concrete with low
permeability. High-strength concrete usually has very low permeability as a result of its low
water/cement ratio and the common use of silica fume. Concrete permeability is a function of
the permeability of the paste and aggregate. Decreased permeability improves concrete’s
resistance to saturation, sulfate attack, chemical attack and chloride penetration. Paste
permeability has the greatest influence on concrete permeability. Therefore the reason that the
relationship of porosity and impermeability is exponential is the water/cement ratio & other
additives being used in cement paste.
20. When concrete expose to fire, why elastic modulus shows a relatively higher drop than
the compressive strength?
ANSWER:
1. Cracking and micro cracking in the surface zone

This is usually sub-parallel to the external surface and leads to flaking and breaking away of
surface layers. Cracks also commonly develop along aggregate surfaces – presumably
reflecting the differences in coefficient of linear expansion between cement paste and

Jimma Institute of Technology, Construction Engineering and Management Chair Page 10

 ASSIGNMENT

aggregate. Larger cracks can occur, particularly where reinforcement is affected by the increase
in temperature.
2. Alteration of the phases in aggregate and paste

The main changes occurring in aggregate and paste relate to oxidation and dehydration. Loss
of moisture can be rapid and probably influences crack development. The paste generally
changes color and various color zones can develop. A change from buff or cream to pink tends
to occur at about 300°C and from pink to whitish grey at about 600°C. Certain types of
aggregate also show these color changes which can sometimes be seen within individual
aggregate particles. The change from a normal to light paste color to pink is most marked. It
occurs in some limestone’s and some siliceous rocks – particularly certain flints and cherty. It
can also be found in the feldspars of some granites and in various other rock types. It is likely
that the temperature at which the color changes occur varies somewhat from concrete to
concrete and if accurate temperature profiles are required, some calibrating experiments need
to be carried out.
3. Dehydration of the cement hydrates

This can take place within the concrete at temperatures a little above 100°C. It is often possible
to detect a broad zone of slightly porous light buff paste which represents the dehydrated zone
between 100°C and 300°C. It can be important, in reinforced or pre-stressed concrete, to
establish the maximum depth of the 100°C isotherm

• The presence of large quantities of evaporable water can cause one problem.

• If the rate of heating is high and the permeability of the cement paste is low, damage
to concrete may take place in the form of surface spalling.
Spalling occurs when the vapor pressure of steam inside the material increases at a rate faster
than the pressure relief by the release of steam into the atmosphere.
21. Why the strength is the property most valued in concrete by designers and quality
control engineers?
ANSWER:

Concrete strength is helpful in design of structural member. So, are should be given to the
strength of concrete. Because, as you know concrete is very good in compression and weak in
tension. Therefore we design concrete to withstand compression and provide steel to produce
ductility and carry the tensile loads.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 11

 ASSIGNMENT

22. In general, discuss how strength and porosity are related to each other?
ANSWER:

Porosity or permeability of aggregates and its absorption may affect the following factors:

 The bond between aggregate and cement paste

 Resistance to freezing & thawing of concrete

 Chemical stability

 Resistance to abrasion

 Specific gravity

 Yield of concrete for a given weight of aggregate.

So the strength of porous concrete is significantly affected by the porosity of its internal
structure. Strength and porosity of the paste-structure are dependent almost entirely upon the
water-cement ratio.
23. Explain how water cement ratio influence the strength of cement paste matrix and the
interfacial transition zone in concrete.
ANSWER:

The w/c ratio plays an important role in controlling the microstructure of the interfacial
transition zone and its thickness. In addition, at the same w/c ratio and age, reducing the
aggregate size tends to reduce the porosity and increase the content of unhydrated (UH)
particles in the region surrounding the aggregate. Moreover, at the same w/c ratio, they reported
that the interfacial transition zone is more porous compared to the bulk paste at 180 days than
at 7 days due to deficiency of UH content in the interfacial transition zone compared to bulk
paste at an early age.
24. Why does air entrainment reduce strength of moderate and high-strength concrete
but may increase the strength of low strength concrete mixtures.

ANSWER:

Air entrainment reduces the density of concrete and consequently reduces the strength. Air
entrainment is used to produce a number of effects in both the plastic and the hardened
concrete.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 12

 ASSIGNMENT

Air entraining admixtures not necessary or desirable in protected high-strength concrete. Air is
mandatory, where durability in a freeze-thaw environment is required (i.e. bridges, piers,
parking structures)

High compressive strength

Pursuing high compressive strength has been an important direction of concrete development

• It is defined as a concrete that can meet special performance and uniformity

requirements, which cannot always be achieved routinely by using only conventional
materials and normal mixing, placing, and curing practices.
• The requirements may involve enhancement of the characteristics of concrete, such as
placement and compaction without segregation, long-term mechanical properties,
higher early-age strength, better toughness, higher volume stability, or longer service
life in severe environments.
25. At a given water-cement ratio, either a change in the cement content or aggregate
grading can be made to increase the consistency of concrete mixture. Which one of
the two option would you recommend? Why is not desirable not to produce concrete
mixture of higher consistency than necessary?

ANSWER: Change in aggregate grading

Explanation:

Changing aggregate grading increases the quality of aggregate by having grading closer to the
fuller curve used in the concrete design and proportioning of various sizes of aggregates.
Normally, consistency is seen during pouring of concrete hence if concrete mix has high
consistency, it presents problem in workability hence flow is interfered with. The slump may
be too low leading to low flow.
26. Can we use recycled water from industrial operations as mixing water in concrete?
What about the use of sea water for this purpose?

ANSWER:

Jimma Institute of Technology, Construction Engineering and Management Chair Page 13

 ASSIGNMENT

There are no standards governing the quality of water for use in mixing concrete. In most cases,
water that is suitable for drinking and that has no pronounced taste and odour may be used. It
is generally thought that the PH of water should be between 6.0 and 8.0.
 Industrial cannot use potable water if recycled water is available. Recycled water is an
acceptable alternative to potable water. For some time now, the Standard Specifications
for Public Works Construction (SSPWC) has published the purity thresholds that
recycled water must meet under which public works concrete structures can be
constructed. The use of recycled water is strongly encouraged.
The use of seawater does not appear to have any adverse effect on the strength and
durability of Portland cement concrete but it is known to cause surface dampness,
efflorescence and staining. Seawater also increases the risk of corrosion of steel and its
use in reinforced concrete is not recommended.
27. In general how are compressive and tensile strengths of concrete related? Is this
relationship independent of concrete strength? If not why? Discuss how admixtures
and aggregate mineralogy can affect the relationship?

ANSWER:

Although the tensile strength of concrete increases with an increase in the compressive strength,
the ratio of tensile strength to compressive strength decreases as the compressive strength
increases. Thus the tensile strength is approximately proportional to square root of compressive
strength.

The tensile strength is affected by the same factor that affects compressive strength. The tensile
strength of a concrete develops more quickly than the compressive strength.

A number of factors affect the relation between two strengths. These are
 Aggregate
 Age
 Curing
 Air-Entrainment
 Light-weight concrete
 Method of Test

Jimma Institute of Technology, Construction Engineering and Management Chair Page 14

 ASSIGNMENT

28. What do you understand by the term CURING of concrete? What is the significance
of curing?
ANSWER:

Curing is the method in which freshly cast concrete is provided with wet conditions or moist
conditions for specific time once compaction is completed. Curing is accomplished to finish
the hydration reaction.

Significance of curing
1. Concrete strength gain: Concrete strength increase with age as moisture and a
favorable temperature is present for hydration of cement.
2. Improved durability of concrete: The durability of concrete is affected by a number
of factors including its permeability, porosity and absorptivity. Well cured concrete can
minimize thermal, plastic & drying shrinkage cracks, making concrete more water tight,
thus preventing moisture and water borne chemicals from entering into the concrete
and thereby increasing its durability.
3. Enhanced serviceability: Concrete that is allowed to dry out quickly undergoes
considerable early age shrinkage. Inadequate curing contributes to weak and dusty
surfaces having a poor abrasion resistance.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 15

 ASSIGNMENT

Homework 3
1. What test is suitable to measure the workability of flowing concrete mixes?
ANSWER:
 The suitable method to measure the workability of flowing concrete is flow test. It gives
an indication of quality of concrete with respect to consistency, cohesiveness and the
proneness to segregation. The spread of the flow of the concrete is measured and is
related to workability.
2. Which method is most suitable to measure the workability of dry concrete?
ANSWER:
 Vee bee consistometer test is a good laboratory test on fresh concrete to measure the
workability of dry concrete and it is not suitable for very wet concrete. Vee bee
consistometer test determines the mobility and to some extent compatibility of concrete.
In the vee bee consistometer test vibrator is used instead of jolting. Vee bee test
determines the time required for the transformation of concrete by the vibration.
3. What are the main causes of plastic shrinkage and plastic settlement crack?
ANSWER:
 Plastic Shrinkage cracks form while the concrete is still soft and finishable. These
cracks appear on horizontal exposed surface (top of slab / flooring / raft). Cracks may
form a random pattern or may appear parallel to one another. They range in length
from 25 mm to 2 meters, but are usually 300 to 600 mm long. They are spaced from a
few centimeters to as much as 3m apart. Plastic shrinkage cracks begin as shallow
cracks, but can become deeper if not attended in time.
Main causes of plastic shrinkage

Water from fresh concrete can be lost by evaporation, absorption by subgrade,

formwork and during hydration process. When the loss of water from surface of
concrete is faster than the migration of water from interior to the surface, the surface
dries up. This creates moisture gradient which results in surface cracking while
concrete is still in plastic condition. The magnitude of plastic shrinkage and plastic
shrinkage cracks are depending upon ambient temperature, relative humidity and
wind velocity. In other words, it depends upon the rate of evaporation of water from
the surface concrete. Rate of evaporation in excess of 1 kg/m2 per hour is considered
critical.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 16

 ASSIGNMENT

 Plastic settlement cracks: are so-called because they form while the concrete is still
plastic, i.e has not set. The settling concrete is restrained and cracks form at the surface.
They may become visible very early, i.e while finishing is proceeding, but are often not
noticed until some hours after placement.
What causes plastic settlement cracks?
 After it is placed, concrete bleeds, i.e the solids settle down and the mix water rises up
to the surface. If there is no restraint this merely produces a slight lowering of the
concrete surface. However, if the concrete is locally restrained from settling (eg. by a
reinforcing bar, duct or insert) while the adjacent concrete continues to settle, there is
the potential for a crack to form over the restraining element. It may also lead to a void
under the restraining element and where this is reinforcement it may affect the local
bond.
NB: Plastic settlement cracks are distinguished from Plastic shrinkage cracks by their distinct
pattern which typically mirrors the pattern of the restraining elements such as the
reinforcement.
4. How the tensile strength of concrete is determined?
ANSWER:
The tensile strength of concrete is measured by the units of Force per Cross Sectional area
(N/Sq. mm or MPa). The concrete is good in compression force and weak in tension force. So
the reinforcement has been provided in concrete to prevent the crack formation.
According to EBCS-2, 1995; in the absence of more accurate data, the characteristic tensile
strength of concrete can be determined from the characteristic cylinder compressive strength
by:
𝟐⁄
𝒇𝒄𝒕𝒌 =0.21*(𝒇𝒄𝒌 𝟑)

Where: fctk – tensile strength of concrete in MPa

fck – characteristic cylinder strength in MPa

5. If on-site slump fails, should engineers allow the contractor to continue the concrete
work?
ANSWER:
 No! If on-site slump or the workability test fails, it is strongly recommended to reject
that material or use it for some non-structural work for the same or lower the grade of
the concrete.
Jimma Institute of Technology, Construction Engineering and Management Chair Page 17
 ASSIGNMENT

6. In designing concrete structure, normally maximum aggregate sizes are adopted with
range from 10mm to 20mm. does an increase of maximum aggregate size benefit the
structure?
ANSWER:
 Consider an example of a cube. The surface area to volume ratio of a cube is 6/b
where b is the length of the cube. This implies that the surface area to volume ratio
decreases with an increase in volume. Therefore, when the size of maximum
aggregate is increased, the surface area to be wetted by water per unit volume is
reduced. Consequently, the water requirement of the concrete mixes is reduced
accordingly so that the water/cement ratio can be lowered, resulting in a rise in
concrete strength.
However, an increase of aggregate size is also accompanied by the effect of reduced contact
areas and discontinuities created by these larger sized particles. In general, for maximum
aggregate sizes below 40mm, the effect of lower water requirement can offset the
disadvantages brought about by discontinuities as suggested by Longman Scientific and
Technical(1887)
7. What are the major problems in using pumping for concreting works?
ANSWER:
 The main problems associated with pumping are the effect of segregation and bleeding.
To rectify these adverse effects, the proportion of cement is increased to enhance the
cohesion in order to reduce segregation and bleeding. On the other hand, a proper
selection of aggregate grading helps to improve the pump ability of concrete.
8. Is it desirable to use concrete of very high strength i.e. exceeding 60MPa? What are
the potential problems associated with such high strength concrete?
ANSWER:
 To increase the strength of concrete, say from 40MPa to 80MPa, it definitely helps in
improving the structural performance of the structure by producing a denser, more
durable and higher load capacity concrete. The size of concrete members can be
significantly reduced resulting in substantial cost savings. However, an increase of
concrete strength is also accompanied by the occurrence of thermal cracking. With an
increase in concrete strength, the cement content is increased and this leads to higher
thermal strains.
Consequently, additional reinforcement has to be introduced to control these additional
cracks caused by the increase in concrete strength. Moreover, the ductility of concrete
decreases with an increase in concrete strength. Attention should be paid during the
design of high strength concrete to increase the ductility of concrete. In addition, fire

Jimma Institute of Technology, Construction Engineering and Management Chair Page 18

 ASSIGNMENT

resistance of high strength concrete is found to be less than normal strength concrete as
suggested by Odd E. Gjorv(1994)
Though the tensile strength of high strength concrete is higher than that of normal
concrete, the rate of increase of compressive strength. For normal concrete, tensile
strength is about one-tenth of compressive strength. However, for high strength
concrete, it may only drop 5% of compressive strength.
Moreover, owing to a low aggregate content of high strength concrete, creep and
shrinkage increases.
9. What are the disadvantage of curing by ponding polythene sheet?
ANSWER:
 Ponding: This method of thermal curing is readily affected by weather condition (cold
wind). Moreover, a large amount of water used has to be disposed off the construction
sites after curing.
 Polythene sheet: This method of curing is based on the principle that there is no flow
of air over the concrete surface and thereby no evaporation can take place on top of the
freshly concreted surface by provision of polythene sheets. However, it suffers from the
demerit that polythene sheets can be easily blown off in windy condition and the
performance of curing would be affected. Moreover, for water lost due to self-
desiccation, this method cannot replenish these losses.
10. What is the indication of shear slump and collapse slump in slump test?
ANSWER:
 When one-half of the concrete mass slide down the other is called the shear slump.
This type of slump is obtained in a lean concrete mix. It is an indication of harsh mixes
with lack of cohesion.
 Collapse slump in slump test indication of test failure or poor proportion of the
aggregate, cement and water. In this case the test must be repeated.
11. In carrying out compression test for concrete, should test cubes or test cylinders be
adopted?
ANSWER:
 Basically, the results of compression test carried out by using cubes are higher than that
by cylinders. In compression test, the failure mode is in the form of tensile splitting
induced by uniaxial compression.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 19

 ASSIGNMENT

However, since the concrete samples tend to expand laterally under compression, the
friction developed at the concrete-machine interface generates forces which apparently
increase the compressive strength of concrete. However, when the ratio of height to
width of sample increases, the effect of shear on compressive strength becomes smaller.
This explains why the results of compression test by cylinders are lower than that of
cubes.
12. Which type of bar reinforcement is more corrosion resistance, epoxy-coated bar,
stainless steel bars or galvanized bars?
ANSWER: Stainless steel bars
 Based on the experiment conducted by the building Research Establishment, it was
shown that the corrosion resistance of galvanized steel was the worst among the three
types of bar reinforcement. For galvanized steel bars, corrosion started to occur when a
certain chloride content in concrete (i.e. 0.4% by cement weight) was exceeded.
However, for epoxy-coated bars, they extended the time taken for cracking to occur
when compared with galvanized steel bars.
The best corrosion resistant reinforcement among all is stainless steel. In particular,
austenitic stainless steel stayed uncorroded even there was chloride contamination in
concrete in the experiment.
13. Provide brief information on prefabricate concrete, high performance concrete.
ANSWER:
 Prefabricated concrete: is a construction product produced by casting concrete in a
reusable mold or “form” which is then cured in a controlled environment, transported
to the construction site and lifted into place. In contrast, standard concrete is poured
into site-specific forms and cured on site.
 High performance concrete: is a concrete mixture, which possess high durability and
high strength when compared to conventional concrete. This concrete contains one or
more of cementious materials such as fly ash, Silica fume or ground granulated blast
furnace slag and usually a super plasticizer. The use of some mineral and chemical
admixtures like Silica fume and Super plasticizer enhance the strength, durability and
workability qualities to a very high extent.
The high performance concrete does not require special ingredients or special
equipment’s except careful design and production. High performance concrete has

Jimma Institute of Technology, Construction Engineering and Management Chair Page 20

 ASSIGNMENT

several advantages like improved durability characteristics and much lesser micro
cracking than normal strength concrete.
High Performance concrete works out to be economical, even though its initial cost is
higher than that of conventional concrete because the use of High Performance concrete
in construction enhances the service life of the structure and the structure suffers less
damage which would reduce overall costs. It is also aesthetically satisfying.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 21

 ASSIGNMENT

CONSTRUCTION MATERIALS HOMEWORK

Set I (8) pts.
Question 1. What are the commonly used construction materials List and provide brief
information to each?
ANSWER:
1. Concrete
Concrete is a composite building material made from the combination of aggregate
(composite) and a binder such as cement. The most common form of concrete is Portland
cement concrete, which consists of mineral aggregate (generally gravel and sand), Portland
cement and water. After mixing, the cement hydrates and eventually hardens into a stone-like
material. When used in the generic sense, this is the material referred to by the term concrete.
2. Brick and Block
A brick is a block made of kiln-fired material, usually clay or shale, but also may be of lower
quality mud, etc. Clay bricks are formed in a moulding (the soft mud method), or in
commercial manufacture more frequently by extruding clay through a die and then wire-
cutting them to the proper size (the stiff mud process).
3. Metal
Metal is used as structural framework for larger buildings such as skyscrapers, or as an external
surface covering.
There are many types of metals used for building. Steel is a metal alloy whose major
component is iron, and is the usual choice for metal structural construction. It is strong,
flexible, and if refined well and/or treated lasts a long time. Corrosion is metal’s prime enemy
when it comes to longevity.
4. Glass
Clear windows have been used since the invention of glass to cover small openings in a
building. They provided humans with the ability to both let light into rooms while at the same
time keeping inclement weather outside. Glass is generally made from mixtures of sand and
silicates, and is very brittle.
5. Wood
Wood is a product of trees, and sometimes other fibrous plants, used for construction purposes
when cut or pressed into lumber and timber, such as boards, planks and similar materials. It is
a generic building material and is used in building just about any type of structure in most

Jimma Institute of Technology, Construction Engineering and Management Chair Page 22

 ASSIGNMENT

climates. Wood can be very flexible under loads, keeping strength while bending, and is
incredibly strong when compressed vertically.
There are many differing qualities to the different types of wood, even among same tree
species. This means specific species are better for various uses than others. And growing
conditions are important for deciding quality.
6. Ceramics
Ceramics are such things as tiles, fixtures, etc. Ceramics are mostly used as fixtures or
coverings in buildings. Ceramic floors, walls, counter-tops, even ceilings. Many countries use
ceramic roofing tiles to cover many buildings. Ceramics used to be just a specialized form of
clay-pottery firing in kilns, but it has evolved into more technical areas.
7. Plastic
The term plastics covers a range of synthetic or semi-synthetic organic condensation or
polymerization products that can be molded or extruded into objects or films or fibers. Their
name is derived from the fact that in their semi-liquid state they are malleable, or have the
property of plasticity.
8. Mud and clay
The amount of each material used leads to different styles of buildings. The deciding factor is
usually connected with the quality of the soil being used. Larger amounts of clay usually mean
using the cob/adobe style, while low clay soil is usually associated with sod building.
9. Rock
Rock is a very dense material so it gives a lot of protection too, its main draw-back as a material
is its weight and awkwardness. Its energy density is also considered a big draw-back, as stone
is hard to keep warm without using large amounts of heating resources.
10. Thatch
Thatch is one of the oldest of materials known; grass is a good insulator and easily harvested.
Many African tribes have lived in homes made completely of grasses year round. In Europe,
thatch roofs on homes were once prevalent but the material fell out of favour as
industrialization and improved transport increased the availability of other materials.
11. Brush
Brush structures are built entirely from plant parts and are generally found in tropical and
subtropical areas, such as rainforests, where very large leaves can be used in the building.
Native Americans often built brush structures for resting and living in, too.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 23

 ASSIGNMENT

Question 2. How can concrete and PVC be improved upon as building materials?
ANSWER:
As concluded by different scholars introducing a certain amount of PVC as an aggregate in a
concrete mix, improves the following property of the concrete:
 It increases the workability of concrete
 It increases the compressive strength of the concrete
 It increases the tensile strength of the concrete
 It increases the flexural strength of the concrete
Question 3. What are the alternative building materials that are equivalent to the
conventional building materials?
ANSWER:
 Bamboo
 Polyester Fiber
 Crumb Rubber
 Soil Conditioning Agents
 Straw Bale
 Bamboo
 Hemp Crete
 Rammed Earth
 Timber Crete
 Mycelium
Question 4. Which method is most suitable to measure the workability of a dry concrete
mix?
ANSWER:
 Vee bee consistometer test is a good laboratory test on fresh concrete to measure the
workability of dry concrete and it is not suitable for very wet concrete. Vee bee
consistometer test determines the mobility and to some extent compatibility of
concrete. In the vee bee consistometer test vibrator is used instead of jolting. Vee bee
test determines the time required for the transformation of concrete by the vibration.

Question 5. Briefly explain Building Materials selection criteria…

ANSWER:
• Strength.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 24

 ASSIGNMENT

• Availability.
• Durability.
• Workability.
• Ease of Transportation.
• Cost.
• Aesthetics.
• Resistance to Fire.
Question SET II (10 PTS)
Question 1) what are the major advantages and disadvantages (Limitations) of concrete?
ANSWER:
Advantages of Concrete
 Very durable
 Low maintenance
 Does not rust, rot, or burn
 Absorbs & retains heat
 Wind & water resistant
 Non-combustible (fire safe)
 Effective soundproofing material
Disadvantages of Concrete
 More expensive
 Heavy & difficult to transport (although lightweight concrete does exist)
 Limited versatility
 Slower to build with
 Susceptible to efflorescence
Question 2. How can be Concrete can be improved to be as a green material?
ANSWER:
Green concrete is defined as concrete that uses waste material for at least one of its
components, or concrete with a production process that does not cause environmental
destruction. Green concrete should also offer high performance and life cycle sustainability.
Concrete can be green material if the concrete industry become greener by:
 Reducing greenhouse gas emissions

Jimma Institute of Technology, Construction Engineering and Management Chair Page 25

 ASSIGNMENT

 Reducing the use of natural resources such as lime stone, shale ,clay natural sand and
rocks
 Reusing waste materials in concrete to reduce pollution i.e the concrete
industry, which uses vast amounts of energy and natural resources and contributes to
generation of CO2, can improve its record with an increased reliance on recycled
materials and in particular by replacing largest percentages of Portland cement by
byproducts of industrial processes.
Question 3. Provide detailed information on High performance concrete and possible
applications.
ANSWER:
High Performance Concrete: Is a concrete, which meets special performance and uniformity
requirements that cannot be always achieved by using only the conventional materials and
normal mixing, placing, and curing practices.
High performance concrete in which some or all of the following properties have been
enhanced.
(a) Ease of placement
(b) Long term mechanical properties
(c) Early age strength
(d) Toughness
Characteristics of High Performance Concrete
Concrete may be regarded as high performance for several different reasons.
 Very low porosity through a tight and refined pore structure of the cement paste.
 Very low permeability of the concrete.
 High resistance to chemical attack.
 Low heat of hydration.
 High early strength and continued strength development.
 Low water binder ratio.
 Low bleeding and plastic shrinkage.
Advantages of HPC
 Speed of construction
 Economical material in terms of time and money.
 Higher seismic resistance
 Improved durability

Jimma Institute of Technology, Construction Engineering and Management Chair Page 26

 ASSIGNMENT

 Abrasion resistance
 High tensile strength
 Reduced
 Maintenance cost
Disadvantages
 An extended quality control
 Cost
 Special constituents
 Manufactured and placed carefully.
Possible application of HPC
High strength concrete is required in engineering projects that have concrete components that
must resist high compressive loads. High strength concrete is typically used in the erection of
high rise structures. It has been used in components such as columns (especially on lower
floors where the loads will be greatest), shear walls, and foundations. High strengths are
occasionally used in bridge applications as well.
Question 4. List and explain advantages and disadvantages of metals in construction.
ANSWER:
Advantages:
 High strength/weight ratio
 Ductility
 Speed of erection.
 Quality of construction
 Ease of repair, modification & change
 Adaptation of prefabrication
 Repetitive use
 Expanding existing structures
Disadvantage:
 Corrosive unless
 The exploitation of metal ores to extract causes pollution uses up the Earth’s limited
resources.
 Metals are more expensive than other materials such as concrete.
Question 5. Define following terms:

Jimma Institute of Technology, Construction Engineering and Management Chair Page 27

 ASSIGNMENT

ANSWER:
a) Fine aggregate: they are those aggregate which can pass through 4.75mmIS sieve.
Fine aggregates contribute towards reducing the number of voids, increase the
workability increase the volume, reduce the cost and proper density is provided.
b) Coarse aggregate: these aggregates which are the residue of 4.75mm IS sieve and
passed through 75mm IS sieve. Coarse consists of crushed gravels. These
aggregates are firmed by natural disintegration of rocks or by artificial crushing of
rocks or gravel.
c) Cement: A cement is a binder, a substance used for construction that sets, hardens,
and adheres to other materials to bind them together. Cement is seldom used on its
own, but rather to bind sand and gravel together. Cement mixed with fine aggregate
produces mortar for masonry, or with sand and gravel, produces concrete.
d) Cement content in a mix: The cement content of concrete is important from the
aspect of durability, impermeability and strength. Too low a cement content may
cause inadequate structural capability or more frequently may not provide a durable
protective environment for the steel reinforcement, permitting rapid carbonation
and subsequent loss of the protective alkaline environment for the steel. Too high a
cement content may cause excessive shrinkage, particularly if inadequately cured,
thermal cracking from the heat of hydration if large pouring are involved, or the
risk of alkali silica reaction if a susceptible aggregate has been used and the cement
is not a low alkali type.
e) Cement content paste volume: is the method of optimization of concrete mixing
system to get quality mixture of concrete by minimizing the volume of cement paste
which, in turn means maximizing the volume of aggregate.
f) Mortar: Mortar is a workable paste which dries to bind building blocks such as
stones, bricks, and concrete masonry units, to fill and seal the irregular gaps
between them, and sometimes to add decorative colors or patterns to masonry walls.
In general the maximum size of the inert particles in mortar is less than 5mm, and
the cementing material is Portland cement and/or lime.
g) Grout: is a dense fluid which is used to fill gaps or used as reinforcement in existing
structures. Generally it is a mixture of water, cement, and sand and is employed in
pressure grouting, embedding rebar in masonry walls, connecting sections of pre-
cast concrete, filling voids, and sealing joints such as those between tiles.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 28

 ASSIGNMENT

h) Air-entrained concrete: is ordinary concrete that contains controlled amounts of

air in the form of microscopic bubbles. These intentionally entrained air bubbles
are extremely small.
Question SET III (12 pts.)
Question 1. Provide information on Glass, ceramics and Composites as a Construction
materials (use, functions, advantages and disadvantages).
ANSWER:
Glass:
What is glass?
It is an inorganic mixture that has been fused at a high temperature and cooled without
crystallization
Use: it is used to make delicate looking fenestrations on facades as well as conventional
windows. Solar power glass, switchable glass projection screens are a few of the newer uses.
Function: Glass is now being used in the building industry as insulation material, structural
component, external glazing material, cladding material;
Advantage:
 Weather and Rust Resistant
 Glass absorbs, refracts or transmits light.
 Transparency: The glass allows you to connect with the outer world visually.
 It is available in wide range of colors
 Aesthetically Appealing
 Glass is 100% recyclable
 Glass respects the environment. As it can recover itself many times, it is one of the
sustainable materials also.
 excellent abrasion resistant material
Disadvantage:
 It is an expensive material that ultimately adds to the cost of construction.
 The glass is very rigid and brittle material
 The Glass is less impact resistant
 The Glass is affected by alkalis ions.
 Glass offers superior transparency of heat
 Increasing the cost of security

Jimma Institute of Technology, Construction Engineering and Management Chair Page 29

 ASSIGNMENT

 Not suitable for Hot Climate Areas

Ceramic
Use: Ceramics are a material often used in construction, made from a mixture of minerals,
typically silica sand, with a clay binder and some impurities, and up to 30% water.
Advantage:
 Harder than conventional structure metals.
 Low coefficient of friction.
 Extremely high melting point.
 Corrosion resistance.
 Low density.
 Extreme hardness.
 Inexpensive.
 Easily available.
 Glazed ceramic does not stain.
Disadvantage:
 Dimensional tolerances difficult to control during processing.
 Weak in tension.
 Poor shock resistance.
 Can crack when hit with heavy items.
Composites:
Use: They are useful for their high stiffness-to-weight and strength-to-weight ratios in
comparison with conventional materials such as steel and reinforced concrete.
Function: Composites can be used in the construction of entire bridge structures, bridge decks
and bridge enclosures.
Advantage:
 Strong
 Light weight,
 Corrosion resistance,
 Design flexibility and
 Durability
Disadvantage:
 Composites have high recurring costs.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 30

 ASSIGNMENT

 Composites are higher nonrecurring costs.

 Composites have higher material costs.
 Composites have very expensive repairs and maintenance.
 Composites needed isolation to prevent adjacent aluminum part galvanic corrosion.
Question 2. Compare concrete versus timber as a building material.
ANSWER:
CONCRETE TIMBER
Man-made material Natural product of nature
Predominant building material Generic building material
Concrete is used in conjunction with
Timber can be very flexible and can keep
ironwork for strength and has low tensile
strength when compressed or bent.
strength.
Reinforced concrete is much cheaper than Timber needs more maintenance and care as
timber. compared to concrete.
Concrete has better insulation properties and
Timber is much lighter in weight as
has a high thermal storage capacity as
compared to concrete
compared to timber.
Concrete is environment friendly and has
Timber is largely used as a construction
high thermal efficiency as compared to
material in the earthquake zones.
timber.
Concrete has low tensile and hard in nature Timber is tensile and resists bending

Question 3. Provide brief information on Earth as a building material, and masonry

materials.
ANSWER:
Earth is regaining interest as a building material, not only in developing countries, where due
to its abundance and low cost it is a logic and interesting building material for constructing
superstructures, but also in modern societies where for reasons of sustainability and limiting
transport it has an important advantage opposed to the conventional building materials. In this
sense, a relatively new application of building with earth is the deep soil mixing process used
within the framework of geotechnical projects. An advantage of this method in comparison
with typical concrete solution is its independence from concrete supply on the field. Contrarily

Jimma Institute of Technology, Construction Engineering and Management Chair Page 31

 ASSIGNMENT

to concrete retaining walls, the execution of soil mix walls does not suffer from delayed supply
(e.g. due to traffic jams) of the fresh concrete.
With regard to this regaining interest for earth constructions, there is clearly a need for the
further development of specific testing techniques to allow further engineering development
of earth applications as well as the development of quality standards.
Question 4. Explain how the following factors affect construction material choice:
a) resource utilization in the choice of construction materials;
b) Social costs and shadow prices.
ANSWER:

The choice of materials for a project requires considerations of aesthetic appeal and initial and
ongoing costs, life cycle assessment considerations (such as material performance, availability
and impact on the environment) and the ability to reuse, recycle or dispose of the material at
the end of its life.

Materials must be used sustainably – this means the present use will not compromise future
use by running out or harming the environment at any time. Few materials fully meet this
criteria. The aim when selecting materials should therefore be to use:

1. materials from renewable or replaceable sources

2. recycled materials
3. materials that are in plentiful supply
4. materials with a lower environmental impact across their whole life cycle.

Life cycle assessment considerations include:

 extraction and manufacture

 sourcing
 construction/installation
 performance
 waste disposal/recycling/reuse

Extraction and manufacture

Jimma Institute of Technology, Construction Engineering and Management Chair Page 32

 ASSIGNMENT

Impact of extraction: The environmental impact of extraction such as large-scale mining, on

scarce, non-renewable resources is obvious, but even the extraction of renewable resources
will have some impact on the environment. The effects of extraction may be:

 noise
 visual pollution
 air pollution
 water pollution
 chemical emission
 release of CO2
 damage to ecosystems
 water use
 energy use.

Energy and resource use: The total energy used in the extraction, production, transportation
and construction of a building material is the embodied energy of that material. As high
consumers of energy, buildings have a significant impact on our environment. Understanding
embodied energy allows us to understand how much and where energy is used in the
construction of buildings and the benefits of recycling.

By products and emissions: The processes for the production of building materials can cause
pollution and emissions of CO2 and other greenhouse gases.

Sourcing

Material sources: The source of materials must be considered to keep transport costs and
resultant emissions to a minimum. The heavier or more bulky materials are, the greater the
transport costs will be – where possible, heavy and bulky materials in particular should be
sourced locally.

Availability: Availability may influence material selection decisions. Long delivery lead-in
times must be allowed for as delays may cause project hold-ups and cost and energy losses.

Cost: Cost considerations must include the initial cost of purchase and the life cycle costs of
materials. Life cycle costs include maintenance, replacement, demolition and disposal.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 33

 ASSIGNMENT

Maintenance cost considerations must also factor in additional environmental costs such as
the emission of volatile organic compounds (VOCs) when repainting.

Transport to site: The further materials must be transported, the greater the financial and
emissions costs will be. Heavy or bulky products will have greater transport costs than lighter
weight materials.

Construction/installation

Health and safety during construction/installation: Some materials such as solvents and
chemicals release VOCs, and materials that release dust and other airborne pollutants may be
harmful to people during installation or application. Limit harmful effects by

 using paints, adhesives and primers that contain fewer harmful solvents
 providing good ventilation in spaces where LOSP treated timber is being used
 Following the recommendations made by the manufacturer or supplier regarding
installation or application.

Ease of construction/installation: Select materials and systems for ease of construction and
installation. Complicated installations with close tolerances can result in greater wastage or
even rework being required.

Adaptability: The design of any building and the materials selection should consider the
future use or reuse of the building and use materials that facilitate adaptation or future
replacement. The more adaptable a material, the less waste will result from changing needs or
tastes.

Performance

Health and safety during the life of the building: Some materials give off emissions or
allow run-off or leaching of chemicals that can be harmful to the health of building occupants.
Adequate ventilation can mitigate some of the effects of gas emissions, but materials should
generally be selected to minimise adverse effects to occupants.

Structural capability: Materials must be selected or designed for their ability to support the
loads imposed by the building over the whole life of the building. An appropriate structural

Jimma Institute of Technology, Construction Engineering and Management Chair Page 34

 ASSIGNMENT

system and correct selection of structural materials can reduce excess material use and waste
and increase the building’s adaptability for other uses.

Durability and maintenance: The Building Code sets minimum required levels of durability
for different building elements, and this will be a primary driver for materials selection.
Beyond this, durability and maintenance requirements should be considered together across
the expected service life of the building. Some materials that do not appear to offer high levels
of durability may actually perform well over many decades with the right maintenance. Timber
weatherboards are a good example – where painted every 8–10 years, they can perform well
for 60 years or more.

Materials that require little maintenance are not necessarily a better choice from an
environmental point of view, particularly if their manufacture involves the release of large
quantities of greenhouse gases. Materials that require more maintenance may turn out to be
preferable if their original manufacture produced very few greenhouse gases.

Moisture resistance: Selected materials must be protected from moisture. Some materials
have a natural moisture resistance while others must be fully protected from moisture.

Material deterioration/decay: Some materials deteriorate rapidly, particularly in a moist

environment or if they are continuously wet, generally due to the growth of moulds or fungi,
or corrosion of some materials, so it is essential that materials selected have the durability
required for their area of use.

Thermal performance: Building design and material selection must contribute to good
thermal performance and reduced energy demand by including insulation and thermal mass in
the building. Building Code clause H1 Energy efficiency sets out minimum requirements for
thermal performance but BRANZ recommends that the minimum requirements are exceeded
wherever practicable.

Sound insulation: Building design and material selection must contribute to the sound
insulation of the building, both from exterior noise and sound transmission within the building.

Fire performance: Building design and material selection must be in accordance with the
requirements of Building Code clause C Protection from fire including fire compartment

Jimma Institute of Technology, Construction Engineering and Management Chair Page 35

 ASSIGNMENT

separations, allowing the occupants safe escape from the building and allowing fire service
personnel safe access to the building. Materials must be selected for ignitability, surface spread
of flame, fire loading, and fire resistance and stability.

Waste disposal/recycling and reuse

Reuse: Materials that can be reused after the useful life of the building will reduce the need
for new materials to be produced in the future. How materials are installed and fixed can have
an effect on the ability to reuse them, so the shorter the expected life of the building, the greater
should be the reliance on screw or bolt fixing rather than adhesive and other permanent fixings.

Recycling: Materials that can be recycled will reduce the need for new materials to be
produced, and the energy required to reconstitute materials is generally much less than
required for new production.

Waste disposal: Building design and site management should aim to minimise waste, thereby
reducing waste disposal and the release of pollutants. The impact of the disposal of materials
at the end of their serviceable life must be

Factors Influencing Economy of a Building Material

 Availability of Material
 Cost of Raw Materials (Cost of Unprocessed Material)
 Manufacturing Costs (Cost of Processed Material)
 Transportation Cost
 Cost of Placing
 Maintenance Cost

Question 5.
a) Define the following for cement: hydration; setting.
ANSWER:
 Cement: A cement is a binder, a substance used for construction that sets, hardens, and
adheres to other materials to bind them together. Cement is seldom used on its own, but
rather to bind sand and gravel together. Cement mixed with fine aggregate produces
mortar for masonry, or with sand and gravel, produces concrete.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 36

 ASSIGNMENT

 Hydration: Hydration is a chemical process by which cement reacts with water. It

forms a gel, which cements individual particles combine together.
 Setting: is the stiffening of cement paste after water is mixed. Broadly it refers to
change from fluid to rigid state.
b) Briefly describe the Pozzolana as a building material.
ANSWER:
Portland Pozzolan's Cement is a mixture of Pozzolan's panic material with Argillaceous and
Calcareous materials in powdered form. *Pozzolan's increases the strength of the cement but
initial setting time is more than OPC.
Pozzolan's should be in the range of 10–30%. If more than this range then strength will be
reduced. It is useful for most civil construction works like mass concreting etc. It is economical
for projects as less cost of cement than OPC. Gypsum is used for controlling of setting time.
ADVANTAGES OF PPC:
Higher durability of concrete structure due to less permeability of water.
More resistance towards the attack of alkalis, sulfates, chlorides, chemicals.
Better workability.
Low heat of hydration.
Due to high fineness, PPC has better cohesion with aggregates and makes more
dense concreteness.
Comparative lower Water-Cement ratio provides an added advantage for the
further increase of compressive strength of the concrete.
Better surface finish.
Question 6. Discuss modern energy efficient building materials and concept of
sustainability
ANSWER:
The most energy efficient building materials are the following:-
 Recycled steel
 Spray foam insulation
 Thermostat radiant barrier sheathing
 Bamboo plywood
 Insulating concrete forms
 Straw bales
 Plant- bassed polyurethane foam

Jimma Institute of Technology, Construction Engineering and Management Chair Page 37

 ASSIGNMENT

 Cool roof
 And others

Sustainability “…meeting the needs of the present generation without compromising the
ability of future generations to meet their needs.” The idea of sustainability involves enhancing
the quality of life, thus allowing people to live in a healthy environment, with improved social,
economic and environmental conditions, sustainable design is designed, built, renovated
,operated or reused in an ecological and recourse efficient manner.
Sustainable Design & Construction Actions
 Energy efficient buildings
 Re-use existing structures
 Efficient land use
 Use of renewable products / materials
 Protect soil and water resources
 Reduce / eliminate pollution
 Sustainability - addressed on a Life Cycle basis
 Origin & Manufacture of Building Materials

o Plentiful? Renewable? Recycled content? Energy expended to acquire?

Manufacturing pollutants & waste?

 Construction of the Building

o Energy expended to acquire & install? Pollutants generated? Waste generated

& can it be recycled?

 Building Maintenance

Energy use over its lifetime? Material impact on indoor air quality? Maintenance required?
Maintenance materials toxic? Recyclable? Fire & smoke properties.

Jimma Institute of Technology, Construction Engineering and Management Chair Page 38