CMT MODULE 5-6 Flashcards
is a building material which solidifies and hardens after mixing
with water and placement due to chemical process known as hydration.
The water reacts with cement, which bonds the other components fine
aggregates (sand) and coarse aggregates (gravel) together; and eventually
produces a hard stone-like material.
Concrete
is used to make pavements, pipe, engineering structures,
foundations, roads, bridges, walls, footings, etc.
Concrete
A structural concrete with no reinforcement or with less
reinforcement than the minimum amount specified for reinforced
concrete.
Plain Concrete.
A structural concrete reinforced with no less than the minimum amounts of reinforcing bars, pre-stressing tendons or non-
pre-stressed reinforcement.
Reinforced Concrete.
A rich concrete mixture that can be used for columns of
reinforced concrete building and for construction where a very strong
and dense concrete is required.
Class AA.
A good concrete mixture that can be used for reinforced
concrete works of all kinds and best suited for general concrete works.
Class A.
A medium concrete mixture that can be used for plain concrete
foundations, walls, floors, etc. and for not much strength of
impermeability is required.
Class B.
A lean concrete mixture that can be used for heavy masses.
Class C.
The main ingredient is slaked lime and used as a binding
material.
Lime Concrete.
Produced to suit a variety of special requirements
of environmental condition.
Special Cement Concrete.
Obtained by embedding steel bars in tension
zones of the structural member to offset tension weakness of plain cement
concrete.
Reinforced Cement Concrete.
Obtained with high graded steel wires or
tendon wires.
Pre-Stressed Cement Concrete.
Manufactured from calcareous and siliceous materials.
Aerated Concrete.
Produced by using special heavy weight
aggregates and compacting well by mechanical means.
Heavy Weight Concrete.
Obtained by injecting cement sand mortar under
pressure to fill voids already packed and fully compact coarse aggregates.
Pre - packed Concrete.
Contains billions of microscopic cells per ft3 and
produced by the use of air entraining Portland cement.
Air Entrained Concrete.
Produced by using high-early strength cement.
High-Early Strength Concrete.
Made from light weight aggregates.
Light weight Concrete.
Fairly simple and quick for estimating mix proportion using
an assumed or known weight of concrete per unit volume.
Weight Method.
More accurate method involves used of specific
gravity values for all ingredients to calculate the absolute volume and each
will occupy in a unit volumes of concrete.
Absolute-Volume Method.
The term fineness modulus is used to indicate
an index number which is roughly proportional to the average size of the
particle in the entire quantity of aggregates.
Fineness Modulus Method.
Ratio of fine aggregates and coarse aggregates
to develop a dense mix that lies between 1:1/2 and 1:2 1/2.
Arbitrary Standard Method.
The quantity of fine aggregate used in the mixed
is about 10% more than the voids in the coarse aggregates and the quantity
of cement is kept about 15% more than the voids in the fine aggregates.
Minimum Voids Method.
In this method a box of fixed volume
is filled with varying proportion of fine and coarse aggregates.
Maximum Density Method.
The amount of water in mixing concrete is
the most important factor affecting the strength of a given
proportion.
Water Cement Ratio.
Properties of concrete are divided into two parts:
Properties of Fresh
Concrete or Plastic Stage and Properties of Hardened Concrete
is a measure of the stiffness or
sloppiness or fluidity of the mix. For effective handling, placing and
compacting the concrete; and consistency must be the same for each
batch. It is therefore necessary to measure consistency of concrete at
regular intervals.
Consistency.
Commonly used to measure consistency of concrete.
Slump Test.
From the time of mixing, fresh concrete gradually loses
consistency. This gives rise to the problems only if the concrete becomes
too stiff to handle, place and compact properly. Slump loss in concrete is
caused due to the following reasons: hydration of cement (generating
more heat), loss of water by evaporation, absorption of water by dry
aggregates and absorption of water by surfaces in contact with the
concrete.
Slump Loss.
The ease which concrete can be compacted fully without
segregation and bleeding. The workability of a concrete mix is the relative
ease with which concrete can be placed, compacted and finished without
separation or segregation of the individual materials. Workability is not the
same thing as consistency. Mixes with the same consistency can have
different workability’s, if they are made with different sizes of stone; the
smaller the stone the more workable the concrete. It is not possible to
measure workability but the slump test, together with an assessment of
properties like stone content, cohesiveness and plasticity; it gives a useful
indication.
Workability.
Implies the separation of the coarser particles from the mix
which results in non-homogeneity of the concrete mix.
Segregation.
The appearance of water along the cement particles on surface of
freshly laid concrete on compaction and finishing.
Bleeding.
Cement and aggregate particles have densities
about three times that of water. In fresh concrete they consequently tend
to settle and displace mixing water which migrates upward and may collect
on the top
Settlement and Bleeding.
The hardening of concrete before its hydration is known as setting
of concrete.
Setting.
Concrete derives its strength by the hydration of cement
particles. The hydration of cement is not a momentary action but a process
continuing for a long time.
Hydration.
reduces the density of concrete and
consequently reduces the strength.
Air entrainment.
The characteristics strength of concrete is defined as the
compressive strength of 150 mm size cubes after 28 days of curing below
which not more than 5 % of the test results are expected to fail. When we
refer to concrete strength; we generally talk about compressive strength of
concrete. Because concrete is strong in compression but relatively weak in
tension and bending.
Strength.
is measured in pounds per square inch (psi)
or newton per square millimeter (MPa).
Concrete compressive strength
mostly depends upon the amount and type of
cement used in concrete mix. It is also affected by the water-cement ratio,
mixing method, placing and curing.
Compressive strength
Both tensile strength and bending strength can be increased by adding
reinforcement.
Concrete tensile strength ranges from 7% to 12% of compressive strength.
Durability might be defined as the ability to maintain satisfactory
performance over and extended service life. The design service life of most
buildings is often
30 years
Environmental forces such as weathering, chemical attack, heat,
freezing and thawing mat deteriorate concrete. The period existence of
concrete without getting adversely affected by these forces is known as
Durability.
The resistance of concrete to the flow of water through its
pores. Excess water during concreting leaves a large number of continuous
pores leading to the permeability.
Impermeability.
Concrete shrinks with age and the total shrinkage
depends upon the constituents of concrete, size of the member and the
environmental conditions. Total shrinkage is approximately 0.0003 of
original dimension.
Dimensional changes.
The volume decrease of concrete caused by drying and chemical
changes. In another word, the reduction of volume for the setting and
hardening of concrete is defined as shrinkage.
Shrinkage.
Deformation of concrete structure under sustained load is defined
as. Long term pressure or stress on concrete can make
changes in shape. This deformation usually occurs in the direction the force
is applied. The permanent dimension change due to loading over a long
period is termed as creep.
Creep.
Ec = 33 γc sqrt fc
Modulus of Elasticity.
Sometimes it is called impermeability of concrete. Water tightness of
concrete is directly related to the durability of concrete. The lesser the
permeability; the more the durability of concrete.
Water Tightness.
Concrete has moderate thermal conductivity, much
lower than metals, but significantly higher than other building materials
such as wood, and it is a poor insulator. A layer of concrete is frequently
used for ‘fireproofing’ of steel structures. However, the term fireproof is
inappropriate, for high temperature fires can be hot enough to induce
chemical changes in concrete; which in the extreme can cause considerable
structural damage to the concrete.
Thermal Conductivity.
The unit weight of concrete depends on percentage of
reinforcement, type of aggregate and amount of voids.
Unit Weight.
