Bitumen is actually the liquid binder that holds asphalt together. The term bitumen is often mistakenly used to describe asphalt.

A bitumen-sealed road has a layer of bitumen sprayed and then covered with an aggregate. This is then repeated to give a two-coat seal.

Asphalt is produced in a plant that heats, dries and mixes aggregate, bitumen and sand into a composite mix. It is then applied through a paving machine on site as a solid material at a nominated or required thickness, relative to the end use. Asphalt results in a smoother and more durable surface than a bitumen-sealed road.  
                                   by:McAdam

Coarse Aggregates: 80 mm, 40 mm, 20 mm, 10 mm, IS Nos. 480

Fine Aggregates: IS No. 480, 240, 120, 60, 30 and 15.

All in aggregates: 80 mm, 40 mm, 20 mm, 10 mm, Nos: 480, 240, 120, 60, 30 and 15.

Permability ;

Figure shows some typical aggregate gradations and their associated permeabilities. This shows that even a small amount of particles passing the 0.075-mm sieve results in very low permeability. 

This is the best aggregate for high-grade concrete, and as it comes in a variety of shades, like grey, red and pink, it can also be used as a decorative feature. Granite itself is composed of feldspar, quartz and mica crystals, which dictate the colour of the stone. 

Bitumen is produced by fractional distillation of crude oil. Usually, distillation is done in two steps. First the crude oil is heated up to 300-350°C and introduced into an atmospheric distillation column. Lighter fractions like naphtha, kerosene and gas oil are separated from the crude oil at different heights in the column. The heaviest fractions left at the bottom of the column are called heavy residue.

The long residue is heated up to 350-400°C and introduced into a vacuum distillation column. By using reduced pressure it is possible to further distillate lighter products from the residue because the equivalent temperature (temperature under atmospheric conditions) is much higher. If second distillation were carried out under atmospheric conditions and by increasing the temperature above 400°C, thermal decomposition/cracking of the heavy residue would occur. The residue at the bottom of the column is called short residue and is the feedstock for the manufacture of bitumen. 



                                     by: McAdam

Limestone aggregates are creating through the crushing of sedimentary rock. This type of aggregate is one of the most commonly used in road construction and reinforced concrete aside from granite and gravel.

2. Size and shape - The size and shape of the aggregate particles greatly influence the quantity of cement required in concrete mix and hence ultimately economy of concrete. For the preparation of economical concrete mix on should use largest coarse aggregates feasible for the structure. IS-456 suggests following recommendation to decide the maximum size of coarse aggregate to be used in P.C.C & R.C.C mix.
 

3. Surface texture - The development of hard bond strength between aggregate particles and cement paste depends upon the surface texture, surface roughness and surface porosity of the aggregate particles.

If the surface is rough but porous, maximum bond strength develops. In porous surface aggregates, the bond strength increases due to setting of cement paste in the pores.

4. Specific gravity - The ratio of weight of oven dried aggregates maintained for 24 hours at a temperature of 100 to 1100C, to the weight of equal volume of water displaced by saturated dry surface aggregate is known as specific gravity of aggregates.

Specific gravities are primarily of two types.

Apparent specific gravity

Bulk specific gravity

Specific gravity is a mean to decide the suitability of the aggregate. Low specific gravity generally indicates porous, weak and absorptive materials, whereas high specific gravity indicates materials of good quality. Specific gravity of major aggregates falls within the range of 2.6 to 2.9.

Specific gravity values are also used while designing concrete mix.

5. Bulk density- It is defined as the weight of the aggregate required to fill a container of unit volume. It is generally expressed in kg/litre. 
 

6. Voids - The empty spaces between the aggregate particles are known as voids. The volume of void equals the difference between the gross volume of the aggregate mass and the volume occupied by the particles alone.

7. Porosity and absorption - The minute holes formed in rocks during solidification of the molten magma, due to air bubbles, are known as pores. Rocks containing pores are called porous rocks.

Water absorption may be defined as the difference between the weight of very dry aggregates and the weight of the saturated aggregates with surface dry conditions.

Depending upon the amount of moisture content in aggregates, it can exist in any of the 4 conditions.

Very dry aggregate ( having no moisture)

Dry aggregate (contain some moisture in its pores)

Saturated surface dry aggregate (pores completely filled with moisture but no moisture on surface)

Moist or wet aggregates (pores are filled with moisture and also having moisture on surface)

8. Bulking of sand - It can be defined as in increase in the bulk volume of the quantity of sand (i.e. fine aggregate) in a moist condition over the volume of the same quantity of dry or completely saturated sand. The ratio of the volume of moist sand due to the volume of sand when dry, is called bulking factor.

Fine sands bulk more than coarse sand

When water is added to dry and loose sand, a thin film of water is formed around the sand particles. Interlocking of air in between the sand particles and the film of water tends to push the particles apart due to surface tension and thus increase the volume. But in case of fully saturated sand the water films are broken and the volume becomes equal to that of dry sand.

9. Fineness modulus - Fineness modulus is an empirical factor obtained by adding the cumulative percentages of aggregate retained on each of the standard sieves ranging from 80 mm to 150 micron and dividing this sum by 100.

Fineness modulus is generally used to get an idea of how coarse or fine the aggregate is. More fineness modulus value indicates that the aggregate is coarser and small value of fineness modulus indicates that the aggregate is finer.

10. Specific surface - The surface area per unit weight of the material is termed as specific surface. This is an indirect measure of the aggregate grading. Specific surface increases with the reduction in the size of aggregate particle. The specific surface area of the fine aggregate is very much more than that of coarse aggregate.

11. Crushing value - The aggregates crushing value gives a relative measure of resistance of an aggregate to crushing under gradually applied compressive load. The aggregate crushing strength value is a useful factor to know the behavior of aggregates when subjected to compressive loads.

12. Impact value - The aggregate impact value gives a relative measure of the resistance of an aggregate to sudden shock or impact. The impact value of an aggregate is sometime used as an alternative to its crushing value.

13. Abrasion value - The abrasion value gives a relative measure of resistance of an aggregate to wear when it is rotated in a cylinder along with some abrasive charge. 

Gravel aggregates are sourced by sifting quarried rock and crushing natural stone. Gravel aggregates don’t possess as much strength as their granite counterparts, but they are often cheaper to purchase. Another, somewhat niche, but nevertheless positive quality is that it has a low radioactive content. Gravel aggregates are used for foundations and concretes, as well as products made of reinforced concrete and materials used in road construction. There are two types of gravel aggregates:

Bitumen is the binding material present in asphalt. Sometimes it is also known as mineral tar. Bitumen is produced by partial distillation of crude petroleum.

it is chemically a hydrocarbon and insoluble in water. But it totally dissolves in alkalies, alkaline carbonates, benzol, chloroform, bisulphide, naptha, coal tar, petroleum spirit and oil of turpentine.

It is obtained from 87% carbon, 11% hydrogen and 2% oxygen (By weight). The bitumen is produced in solid or semi-solid state and black or brown in color.

The general forms of bitumen are as following

It is a liquid compound which contains a large amount of bitumen in aqueous medium. It is suspended by some appropriate stabilizing agents in the aqueous medium.

This form of bitumen is produced by fluxing asphaltic bitumen in presence of some liquid distillates of petroleum or coal tar. Cut-back bitumen can be used as bitumen paint in cold.

It is a special form of bitumen produced by passing air under pressure at a higher temperature. This type of bitumen can be used as heat insulating material, roofing and damp-proofing felts, producing asphalt pipe and joint fillers etc.

It comprises of bitumen thinner and appropriate inert filler (40%-45%). Plastic bitumen can be used for filling cracks in masonry structures, stopping leakages etc.

This type of bitumen is obtained by distillation of the bitumen to a definite viscosity or penetration without further treatment:

Obtained by crushing construction waste (concrete, bricks and asphalt), secondary aggregates are designed as an effective, low cost option to other materials. It is approximately two times cheaper than granite, but it is not as strong as its costlier counterpart. However, secondary aggregates have a wide range of uses: a large scale filler for concretes with strengths of 5-20 MPa, road construction, maintenance works (used under asphalted areas and pavements) and for reinforcing weak soils. 

Sand is used to provide bulk and strength for materials like asphalt and concrete, as well as being used for decorative purposes. Sand combines with water and other aggregates to form the solid, durable concrete that is used in countless applications all over the world. It also plays a key role in the binding agent in asphalt, transporting it throughout the mix. 

Natural aggregates are found in our environment in different forms. They have different size and shape. They can resist the high compressive load. The different types of natural aggregates used in building purpose are mentioned below.

The main types of natural aggregates are sand, gravel, crushed rock such as granite, basalt etc..

You know that main origin of natural aggregates in from bedrocks. There are three classifications of bedrocks igneous rocks, sedimentary rocks and metamorphic rocks.
SAND
Sand is one of the main classifications of natural aggregate. You already know that sand is a finely divided granular material.

The sand is coarser than silt and finer than gravels. The major compound that consist is sand is silica. The silica is occupying in the sand in the form of quartz.

The diameter of the sand particles ranges from 0.075mm to 4,75mm. The sand is used as the fine aggregates for the purpose of concrete making.

GRAVEL
The gravel is another type of aggregates and is mainly used for as coarse aggregates in concrete. Bank gravel, bench gravel and crushed stone are the examples of gravel.

The size of gravel ranges from 4mm to 64 mm. The gravels are also classified into different namesbased on their size.

GRANITE
Granite is not widely used as much as sand and gravels. The granite comes under the category of igneous rocks that occupying below the surface of the earth.

The main compounds consist in the granites are feldspar, mica etc..The granite have light colored grains. The granite is mainly used for the purpose of tiles in the construction industry.

The other types of natural aggregates used for construction are basalt, crushed rock etc..