By Eng’r Werdi

REINFORCED CEMENT CONCRETE DEFECTS

Concrete defects are imperfections in concrete, such as cracks,

chips, holes, and spalls, that can occur at any point during the
process of mixing, placing, or curing, or after construction. These
defects can be caused by a number of factors, including:

 Poor materials or workmanship: Concrete defects can be caused

by poor-quality materials or workmanship, including poor structural
detailing and design.

 Temperature changes: Concrete can expand and contract as it

cures, and temperature changes in the environment can also cause
defects.

 Overloading: Concrete defects can occur over time due to

overloading.

 Poor maintenance: Concrete defects can occur over time due to

poor maintenance.
Most concrete surface defects occur due to problems
during surface smoothing and curing. Concrete surface
defects are listed as peeling, dusting, blistering, blooming,
plastic shrinkage cracks, hardened concrete cracks, joint
damage, but the list goes on.
Types of Concrete Defects - Causes, Prevention

1. Cracking

Various reasons for cracking are improper mix design, insufficient curing,
omission of expansion and contraction joints, use of high slump concrete
mix, unsuitable sub-grade etc. Prevention, use low water - cement ratio
maximize the coarse aggregate in concrete mix, admixtures containing
calcium chloride must be avoided.

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2. Crazing

Crazing also called as pattern cracking or map cracking is the formation of

closely spaced shallow cracks in an uneven manner. Crazing occurs due to
rapid hardening of top surface of concrete due to high temperatures or if
the mix contains excess water content or due to insufficient curing
Pattern cracking can be avoided by proper curing, by dampening the sub-
grade to resist absorption of water from concrete, by providing protection
to the surface from rapid temperature changes.

3. Blistering & Delamination

Blistering is the formation of hollow bumps of different sizes on concrete

surface due to entrapped air under the finished concrete surface. It may
cause due to excessive vibration of concrete mix or presence of excess
entrapped air in mix or due to improper finishing
Delamination is also similar to blistering. In this case also, top surface of
concrete gets separated from underlying concrete. Hardening of top layer
of concrete before the hardening of underlying concrete will lead to
delamination.
It can be prevented by using good proportion of ingredients in concrete
mix, by covering the top surface which reduces evaporation and using
appropriate techniques for placing and finishing.

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4. Dusting

Dusting, also called as chalking is the formation of fine and loose

powdered concrete on the hardened concrete by disintegration. This
happens due to the presence of excess amount of water in concrete

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To avoid dusting, use low slump concrete mix to obtain hard concrete
surface with good wear resistance.

5. Curling

When a concrete slab is distorted into curved shape by upward or

downward movement of edges or corners, it is called curling. It occurs
mainly due to the differences in moisture content or temperature between
slab surface (top) and slab base (bottom).
To prevent curling, use low shrink concrete mix, provide control joints,
provide heavy reinforcement at edges or provide edges with great
thickness.

6. Efflorescence

Efflorescence is the formation of deposits of salts on the concrete surface.

Formed salts generally white in color. It can be prevented by using clean
and pure water for mixing, using chemically ineffective aggregates etc.
And make sure that cement should not contain alkalis more than 1% of its
weight.

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7. Scaling and Spalling

Scaling and spalling, in both the cases concrete surface gets deteriorated
and flaking of concrete occurs. The main cause for this type of cases is
penetration of water through concrete surface. This makes steel gets

corroded and spalling or scaling may occurs.

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Cause of Building Cracking

Many construction professionals think that cracking is
only caused by incorrect mix design, but we have
explored the causes of cracking below.
1. Due to Low Quality Materials
If we use low-quality materials, cracking will occur, so
we must check the quality of the materials we use for
concrete (cement, sand, aggregate). If the concrete has
a steel structure, we must evaluate the quality of the
steel.
2. Due to Shrinkage
If we do not take proper care when mixing and watering
the concrete, shrinkage will cause cracking.
Shrinkage is very important for high concrete strength.
If we do not use the required water-cement ratio,
shrinkage cracking can occur.
3. Due to Low Quality Aggregate
Aggregate determines the overall strength of concrete.
If we use aggregate that is not good quality, our
construction may crack because it does not create the
desired bond with cement.
4. Due to Excessive Loads
Cracking occurs if the structure is subjected to a large
load before it has attained adequate strength. In
addition, if the stirrups and the arch (formwork) are
raised prematurely, it will expose our construction to
cracks.
5. Due to Improper curing

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This is one of the main causes of cracking in our

country - improper watering.
As soon as the concrete is set, it should be watered at
the appropriate time and rate.
6. Due to Inequality of stress distribution
When we fill a very large steel structure with a small
mix ratio of concrete, the stress distribution between
the steel and the concrete becomes non-linear, which
causes cracking.
7. Due to Improper Placing of Construction Materials
If proper care is not taken when casting on site and if a
suitable professional (including day laborer) is not
assigned to the job, cracking is likely to occur in the
concrete.

Sand Cone Test

The purpose of testing

 Measuring soil density, and checking blood quality.

Description of the device used

 The device is a vessel connected to a cone base and a tap to control

sand flow, and a metal board with a circular opening around the
cone base.
Steps of doing the test

1- Bring the device from the laboratory filled with calibrarian sand, and its
density is known.

2- We choose a random point in the site to conduct the test there.

3- Place the metal plate on the ground and the soil is unloaded with a
depth of 15 cm through the opening and the extracted soil is packed into
a bag and weight, and the weight of the extracted soil will be.

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4- Weigh the device filled with sand and then place the device so that the
base of the cone is on the hole of the metal plate and then let the sand
flow into the hole, by opening the tap.

5- After ensuring the hole is filled with sand, when you notice a stop of
sand leaking into the transparent bowl, the tap is closed.

6- The remaining sand is weighed by the machine and recorded.

7- By computational operations, the density of the soil on the site is

calculated as follows:

◾Wet soil density = Weight of soil extracted from the hole / Size of the
hole

◾The weight of the soil from the hole is known, which is the weight of the
soil extracted from the hole

◾Hole size = weight of sand that filled the hole / standard sand density

◾The weight of the sand that filled the hole = The weight of the machine
filled with sand - The weight of the sand remaining with suppression

◾The standard sand density is determined by the factory, and therefore

we find the density of the wet soil at the site

◾ Dry soil density on site = wet soil density / (moisture content + 1)

◾Site blood ratio = Dry soil density on site / Maximum dry density in
laboratory * 100

The Future of Ready Mix Concrete in Ethiopia

💫Ethiopia is a rapidly developing country with a growing economy.

⏺This has led to an increase in the demand for construction materials,

including ready mix concrete.

▶️Ready mix concrete is a pre-mixed concrete that is delivered to the

construction site ready to be used.

▶️It is a convenient and efficient option for construction projects, and it is

becoming increasingly popular in Ethiopia.

🏷There are a number of reasons why ready mix concrete is becoming the
future of construction in Ethiopia.

🚧First, it is a convenient and efficient option. Ready mix concrete is

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delivered to the construction site ready to be used, which saves time and
labor.

⏺It is also a consistent product, which means that the quality is

guaranteed. This is important for construction projects, as it ensures that
the project will be completed on time and within budget.

🚧Second, ready mix concrete is a sustainable option. It is made with

recycled materials, which helps to reduce the environmental impact of
construction projects.

⏺Ready mix concrete is also a durable material, which means that it can
last for many years with proper care and maintenance.

⏺This makes it a good investment for construction projects.

🚧Third, ready mix concrete is a cost-effective option.

⏺The cost of ready mix concrete is generally lower than the cost of other
construction materials, such as cement and sand.

⏺This is because ready mix concrete is produced in large quantities, which

reduces the cost per unit.

▶️The ready mix concrete industry in Ethiopia is growing rapidly.

▶️The construction industry is also expected to grow by an average of 10%

per year over the next five years.

⏺This growth is being driven by the increasing demand for construction

materials, the growing economy, and the government's commitment to
infrastructure development.

🔰The ready mix concrete industry in Ethiopia is facing a number of

challenges, including the lack of skilled workers and the high cost of raw
materials.

However, the industry is working to overcome these challenges and is

committed to providing high-quality concrete to its customers.

❇️The future of construction in Ethiopia is bright.

🎲The country is experiencing rapid economic growth, and the government

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is committed to infrastructure development.

⏺This is leading to an increase in the demand for construction materials,

including ready mix concrete.

⏺Ready mix concrete is a convenient, efficient, sustainable, and cost-

effective option for construction projects.

⏺It is becoming increasingly popular in Ethiopia, and it is the future of

construction in the country.

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