introduction to civil engineering lecture 5

Introduction to Civil

Engineering

Lecture 5

1

Out lines

Materials of Construction.

1. Steel.

2. Concrete.

3. Bituminous Materials.

4. Bricks and Blocks.

2

3

1. Steel.

2. Concrete.

3. Bituminous Materials.

4. Bricks and Blocks.

Materials of Construction

4

2. Concrete.

Concrete is a man-made composite the major

constituent of which is natural aggregate, such

as gravel and sand. The other principal

constituent of concrete is the binding medium

used to bind the aggregate particles together to

form a hard composite material. This binding

medium is the product formed by a chemical

reaction between cement and water.

Materials of Construction

5Materials of Construction

Concrete.

In its hardened state concrete is a rock-like material with a high compressive strength.

By virtue of the ease with which fresh concrete in its plastic state may be molded into

any shape it may be used to advantage architecturally. Normal concrete has a low tensile

strength. For structural applications it is normal practice to incorporate steel bars to

resist any tensile forces (reinforced concrete). Concrete is also used in conjunction with

steel sections. Concrete forming the compression flange (composite construction).


Concrete.

Concrete is used structurally in

• Buildings for foundations, columns, beams and slabs.

• Shell structures.

• Bridges.

• Sewage-treatment works.

• Railway sleepers.

• Roads and highways.


Concrete

• Cooling towers

• Dams

• Chimneys

• Harbors

• Off-shore structures

and so on…

Concrete requires little maintenance and has good fire resistance.


Concrete.

Constituent materials of concrete

Concrete is composed mainly of three materials, namely, cement, water and aggregate. An

additional material, known as an admixture, is sometimes added to modify certain of its

properties.

Cement, on mixing with water, is the chemically active constituent.

The aggregate is an economical filler material with good resistance to volume changes

which take place within the concrete after mixing. It plays no part in chemical reactions.

Proportions of the constituent materials encountered in concrete mixes are ranged as (60-

75%) aggregates, (25-40%) cement paste and (1-2%) voids.


Concrete.

Cement

The most widely used is Portland cement. The basic raw materials used in its manufacture are

calcium carbonate (from limestone rocks) and silica, alumina and iron oxide (from clay rocks).

Cement is prepared by first intimately grinding and mixing the raw constituents in certain

proportions, burning this mixture at a very high temperature to produce clinker and then grinding it

into powder form.

Cement has the important property that when mixed with water a chemical reaction (hydration)

takes place which produces a very hard and strong binding medium for the aggregate particles. In

the early stages of hydration, while in its plastic stage, cement mortar gives to the fresh concrete its

cohesive properties.


Concrete.

Chemical composition.

Four compounds are formed during the production of cement;

1. Tricalcium silicate 3CaO.SiO2 abbr. C3S

2. Dicalcium silicate 2CaO.SiO2 C2S

3. Tricalcium aluminate 3CaO.Al2O3 C3A

4. Tetracalcium aluminoferrite 4CaO.Al2O3. Fe2O3 C4AF

Typical chemical composition of ordinary Portland cement OPC;

Lime, CaO 65%, Silica, SiO2 21%, Alumina, Al2O3 5%, Iron oxide, Fe2O3 3%

Others 6%


Concrete.

Setting and hardening

Initial set is the beginning of noticeable stiffening in the cement paste.

Further stiffening occurs and the stage at which this is complete is known as final set.

The setting times are affected by cement composition, water/cement ratio and by the ambient temperature.

British standard requires for OPC initial setting time to be not less than 45min and final setting time not more

than 10h.

Strength

The strength of hardened cement is its most important property.

British standard requires for OPC minimum compressive strength using mortar cubes to be not less than

23N/mm2 at age of 3 days and not less than 41N/mm2 at age of 28 days.


Concrete.

Aggregate

1. Aggregate is usually stronger than concrete. Normally concrete strength is between 30-50 N/mm2, and aggregate strength is

generally between 70-350 N/mm2.

2. Aggregate porosity affects the strength of concrete, water absorption and permeability of concrete.

3. Relative density of aggregate falls within the range 2.5-3.0

4. Shape of aggregates:

-Rounded: Fully water-worn

-Irregular: Naturally irregular

-Angular: Well-defined edges

-Flaky: Thickness is small relative to the other two dimensions

-Elongated: Length is large relative to the other two dimensions

5. Coarse Aggregates and Fine Aggregates


Concrete.

Aggregate

Normally aggregate particles size used in concrete varies from 40mm to 0.15mm.

Coarse Aggregates: Particles larger than 5mm.

Fine Aggregates (sand): Particles less than 5mm.

6. Grading of Aggregates

Aggregates should be used in concrete such that the particles of different sizes are proportioned carefully.

Grading of Aggregates affects the stability of concrete mix.

5. Types of Aggregates

- Heavyweight Aggregates: Produces concrete with density of 4000-8000kg/m3 (Heavyweight Concrete). This concrete is used for radiation

shielding.

- Normal Aggregates: (Produces concrete with density of 2300-2500kg/m3 (Normal Concrete). This concrete is used for most purposes.

- Lightweight Aggregates: Produces concrete with density of 750-1100kg/m3 (Lightweight Concrete). This concrete is used for insulation, and

for blocks production.


Concrete.

Basic Requirements for Concrete

In its hardened state (in the completed structure) the concrete shall have adequate

durability, the required strength and the desired surface finish.

In its plastic state, or the state during which it is to be handled, placed and

compacted in its final form, it should be sufficiently workable for the required

properties in its hardened state to be achieved.

This means that:

1. The concrete should be sufficiently fluid for it to be able to flow into and fill

all parts of the formwork, or mold, into which it is placed.


Concrete.

2. It should do so without any segregation (or separation) of the constituent materials while

being handled from the mixer or during placing.

3. It must be possible to fully compact the concrete when placed in position.

4. It must be possible to obtain the required surface finish.

If does not have the required workability in its plastic state, it will not be possible to

produce concrete with the required properties in its hardened state.


3. Bituminous Materials

A term (Bituminous Materials) is generally taken to include all materials

consisting of aggregate bound with either bitumen or tar. Materials of this

kind are used almost exclusively in road construction. Other uses are

mainly as a waterproofing material in roofing and coating.

Bitumen mastics were used in Mesopotamia in the waterproofing of

reservoirs about 3000 B.C. These materials were naturally occurring

bitumen. Most of today’s bituminous materials are the products of

industrial refining process.


Bituminous Materials

Terms used in any discussion of bituminous materials

Binder: a material used for the purpose of holding solid particles together.

Bitumen: a viscous liquid or a solid, consisting essentially of hydrocarbons and their derivatives. It is

non-volatile and softens gradually when heated. It is black or brown in color and possesses

waterproofing and adhesive properties. It is obtained by refining processes from Petroleum.

Asphaltic cement: Bitumen, a mixture of lake asphalt and bitumen, with cementing qualities,

suitable for the manufacture of asphalt pavements.

Asphalt: a term for certain mixtures of asphaltic cement and mineral matter.

Tar: a viscous liquid, black in color with adhesive properties obtained by the destructive distillation

of coal.



The bituminous mixtures contain varying proportions of four materials:

1. Coarse aggregates: crushed stone or gravel with grain size exceeding

that of sand ( > 2.36 mm)

2. Fine aggregates: mineral material sand ( < 2.36 mm)

3. Filler: fine-grained mineral material, often Portland cement(< 0.075

mm)

4. Binder: tar, bitumen, etc.



Use of Bituminous Materials

The wide use of bituminous materials arises from

1. Their relative cheapness and availability in large quantities.

2. Their durability.

3. Their adhesive and waterproofing qualities.

4. The ease with which they can be handled at elevated temperatures, but

quickly become stiff and resistant to deformation at normal temperatures.

All these make bituminous mixtures widely used for road construction.



Bituminous Road Materials

The total pavement is made up of a number of elements as

shown in figure

- The Subgrade: the soil on which the road is supported.

- The Subbase: layer of granular material.

- The Base: the main structural layer which helps to spread the

concentrated loads from traffic over large area.

- The Surfacing: consists of two layers; to supply the desired

riding and nonskid properties:

1-The base course: of lower quality asphaltic mixture.

2-The wearing course: of higher quality asphaltic mixture.



Bituminous Waterproofing Materials

Common use is the mastic asphalt in tanking and flat roofs.

Thin coatings of bitumen paints or emulsions applied to

absorptive materials have the effect of sealing capillaries so that

both water and water vapor are prevented from moving through a

material.

22End of Lecture 5

Next Lecture :Blocks.

introduction to civil engineering lecture 5

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