Concrete

civil techniques

Railway Track Sleepers

abbu riyaz 1 May, 2023

Railway Track Sleepers are members which lay transverse to the rails on which the rail supports and fixes. Sleepers are concrete beds in the railway tracks. The sleepers are of concrete, timbers, steel, cast iron, RCC, and the Prestress concrete. The main role of sleepers is to transfer load from rails to the ballast. And the sub-grade below. It as a transverse member throughout the permanent way.

These sleepers fix vertical to each other. It fixes throughout the track. The main work of sleepers is to hold rails in a strong position. It receives the loads from rails and spread to ballast and sub-grades.

Functions of Railway Track Sleepers

Sleepers perform the following functions

It holds the rails at the proper gauge and at the proper level, flat curves, turnouts, and in diamond crossings.

Transfers load evenly from rails to ballasts to absorb vibrations of moving loads.
Provides a good stability of track.
The track circuiting is making easy with it.
Supports the rail tracks at proper super-elevation.
It acts as an elastic medium in between the ballast and the rails to absorb blows.
It maintains the horizontal and vertical alignments throughout the entire track for a long lifetime.
They provide a way to rectify track geometry during its use.

Requirements of Railway Track sleepers

For a long time period and for a good performance the sleepers need to some important requirements.

Sleepers must be economical.
Should have a low maintenance cost.
It should be easier to handle during the maintenance operations like lifting, packing, removal, and replacement.
The weight of sleepers should not be too heavy or too light. It should have a moderate weight for ease of access.
And capable to resist shocks of rails because of a fast-moving load with vibration.
It should have a proper spacing between two sleepers for ease of maintenance for removal and replacement.
Sleeper to design in a way that they should not push out easily due to moving loads.
A sleeper to provide with anti-theft qualities.

civil techniques

Concrete Proportioning and Properties

abbu riyaz 1 May, 2023

Concrete Proportioning and Properties are the two main fundamental things a civil engineer has to know about the construction. Concrete possess certain Proportioning and Properties. These Concrete Proportioning and Properties are as follows

Concrete Proportioning and Properties

Proportioning

The concrete in the construction field using for construction has many classifications. There are different grades of concrete in construction. These grades design according to the strength of concrete. It bases on the calculation of time period the concrete attains full strength. The grades of concrete are

M5, M7.5, M10, M15, M20, M25, M30, M35, M40.

The letter M denotes the mix. And the number indicates the compressive strength of concrete gain at 28 days in N/mm². M5 and M7.5 concrete grade of concrete use only for a simple foundation for masonry purposes. The grade of concrete below M15 not to use for Reinforce Cement Concrete. M20, M25, and M30 are the most common grade of concrete using in the modern construction field.

Some of the nominal mixes and mixing proportions are as follows

M5 Grade of concrete – 1:5:10
M7.5 Grade of concrete – 1:4:8
M10 Grade of concrete – 1:3:6
M15 Grade of concrete – 1:2:4
M20 Grade of concrete – 1:1½:3
M25 Grade of concrete – 1:1:2
M30 Grade of concrete – 1:1:3

Properties of Concrete

Some of the main and unique properties of concrete are its workability and water-cement ratios.

1. Workability

The ability of fresh mix concrete to fill the mold with proper vibration and poring method is workability. Workability depends on the water content, aggregate, binding materials, chemicals in concrete. Increasing water content and chemicals increase the strength and workability of concrete. Excessive water and chemicals lead to bleeding of the concrete/segregation. This leads to forming honeycomb in concrete structures. A good slump value to maintain in concreting for high strength.

2. Water-cement ratio

It is the weight of the mixing water divided by the weight of the cement. High-quality concrete produces by lowering the water-cement ratio without losing the workability of fresh concrete. And allowing it to properly place and cure.

A properly design mixture possesses desire workability for the fresh concrete and the long-life and strength of the concrete.

General properties of concrete

Some of the general properties of concrete are,

It possesses a high compressive strength and strength depends on the mix.

It hardens with age.

Free from corrosion and withstand chemical attacks

Bind strongly with steel as it is weak in tension

civil techniques

Concrete Manufacturing Process

abbu riyaz 1 May, 2023

Concrete Manufacturing Process consists of many stages. The Concrete mix for delivery from a plant instead of mixing on the job site. The concrete mixes, transports and delivers to a construction site to place in formworks for construction. And to form various structures, like a column, beam, slab, etc.

Concrete Manufacturing Process

The main Concrete Manufacturing Process is as follows

Batching
Mixing
Transporting
Placing
Compacting
Curing

1. Batching

It is the main thing in the Concrete Manufacturing Process. The measurement of materials like aggregates, cement, water necessary for preparing different grades of concrete is Batching. It is by two processes. One is volume and other is weight batching. The volume batching is by mixing materials with its volume. And weight batching is by the self-weight ratio of materials. It has ratios according to standard codes. Some of the different grades of concrete are M10, M20, M25, M30.

2. Mixing

Mixing is to produce uniform, high-quality concrete. The mixing equipment is capable of effective concrete material. Separate paste mix shows the mixing of cement and water into a paste before combines with aggregates. This increase the compressive strength of concrete. This paste mix in high-speed, shear-type mixer at a water-cement ratio of 0.30 to 0.45 by mass. The premix paste blends with aggregates. The remaining batch water and final mix complete in a rotating concrete mixing equipment.

3. Transporting

Transporting concrete require great care. After mixing, the concrete transports to site. The mixing carries near the construction site. A bucket, ropeway, belt conveyor use to transport concrete. Readymix conveyor trucks use mostly in the modern construction times. The concrete transporting by conveyor truck has time limits. The concrete transporting by trucks reach the construction plant early.

4. Placing

Concrete to place in a good manner. It places without segregation to reach maximum efficiency. The concrete not to pour over a height of 1.5m. As the height of pouring concrete increases, it leads to separation of aggregates and cement paste. It causes segregation of concrete and causes honeycomb. Many concrete placing equipment use in modern construction times. some of the equipment are concrete pumps and boom lifts. Concrete pumps are normal pumps with joints to connect and remove according to needs.

Boom lifts are concrete pumps with movable arms. With the help of movable arm, a concrete place easily at heights and corners which is difficult with the normal pump.

5. Curing

Curing is to provide best strength and hardness to concrete. It is the next step after placing of concrete. Curing helps concrete to gain strength early. The concrete requires a moist and wet environment to gain full strength. Proper curing of concrete leads to increase the strength of concrete. And prevent cracking at surface dries. Avoid freezing and overheating of concrete to gain its full strength.

civil techniques

Concrete in construction Field

abbu riyaz 1 May, 2023

Concrete in construction Field is a mixture of paste and aggregates. It composes of fly ash, fine and coarse aggregate, water and chemicals. The fine aggregates are sand and coarse aggregates are gravel. By hydration, the paste hardens and gains strength to form the concrete.

Concrete in construction Field

Concrete is soft in newly mix, strong at hardens. Hence concrete uses to build bridges, superhighways, houses, and dams.

There are some important factors involve in the manufacturing process of concrete. They are

Proportioning
water-cement ratio
Ingredients
Hydration
Placement
Curing and
Special techniques

1. Proportioning

Proportioning and mixing are the main things in making a strong concrete. so choose the materials carefully. The mixture that does not have enough paste to fill the gaps between the aggregates is difficult to place. And produce rough surfaces. A mixture of a high cement paste is easy to place. And produce a smooth surface.

2. water-cement ratio

The quality of the paste determines the character of the concrete. The strength of the paste depends on the ratio of water to cement. It is the weight of the mixing water divided by the weight of the cement. High-quality concrete produces by lowering the water-cement ratio without losing the workability of fresh concrete. And allowing it to properly place and cure.

A properly design mixture possesses desire workability for the fresh concrete and the long-life and strength of the concrete.

3. Ingredients

Natural water drinkable and has no bad taste or smell used as mixing water for concrete. Impurities in mixing water affect setting time and strength. It causes efflorescence, staining, corrosion of reinforcement, and reduce lifetime. Drinking water suitable for mixing concrete and aggregates are to choose properly.

The aggregates to be clean and free from matter that affects the quality of the concrete.

4. Hydration

Aggregates, water, and the cement combine, the mixture hardens. By hydration, the paste hardens and get the strength to form concrete. During this reaction, a node forms on the surface of each cement particle. The node grows and expands until it links up with nodes from other cement particles.

5. Placement

The concrete thoroughly mixes and workable is places in forms before the mixture becomes too stiff. At placement, the concrete compact within the forms to reduce honeycombs.

For slabs, concrete makes ideal to stand until the surface moisture film disappears. A wood or metal hand float uses to smooth off the concrete. Floating produces an even, but slightly rough, texture that has good slip resistance. And use as a final finish for exterior slabs. If smooth, hard, dense surface requires, floating follows by steel trowels.

6. Curing

The curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist damage. Curing ensures the continued hydration of the cement. So that the concrete continues to gain strength. Concrete surfaces cure by sprinkling with water fog. Other curing methods prevent evaporation of the water by sealing the surface with special sprays called curing compounds.

7. Special techniques

It uses for curing concrete during cold or hot weather to protect the concrete. The longer the concrete is wet, the stronger it becomes. The rate of hardening depends upon the composition, fineness of the cement, mix proportions, moisture, and temperature. Concrete continues to get stronger as it gets older. Most of the hydration and strength gain take place within the first month of concrete’s life cycle.

civil techniques

Soil Nailing

abbu riyaz 1 May, 2023

Soil nailing is a construction technique to reinforce soil to make it stable and strong. Soil nailing technique uses for slopes and excavations alongside highways, railway lines. It uses for, excavations, retaining walls slopes, to make it more strong and stable.

The soil reinforces with slender elements like reinforcing bars name as nails. These reinforcing bars install into pre-drill holes and grouts. The nails install at an inclination of ten to twenty degrees with vertical reinforcement.

Soil Nailing employes when requiring slopes for excavation cannot provide due to space constraints. And employes in the construction of retaining wall. It is an alternative to retaining wall structures.

At excavation, the shotcrete, concrete and grouting materials apply to the excavation face to grout the reinforcing steel and nails. It provides stability to the steep soil slope.

Types of Soil Nailing:

There are various types of soil nailing techniques:

Grouted Soil Nailing
Driven Nails
Self-drilling Soil Nail
Jet Grouted Soil Nail
Launched Soil Nail

1. Grouted Soil Nailing

In this type, the holes drills in walls or slope face and nails inserts in the pre-drill holes. These holes fill with grouting materials like concrete and shotcrete.

2. Driven Nails:

Driven nailing use for temporary stabilization of soil slopes. In this method, the nails drive in the slope face at the time of excavation. This method is very fast. It does not provide corrosion protection to the reinforcement steel and nails.

3. Self-drilling Soil Nail:

In this method, the hollow bars use. Hollow bars drills into the slope surface and grout inject simultaneously during the drilling process. This method of soil nailing is faster than grout nailing. This method provides more corrosion resistance to nails than driven nails.

4. Jet Grouted Soil Nail:

In this method, jets use for eroding the soil for creating holes in the slope surface. Steel bars install in this hole and grouts with concrete. It provides good corrosion protection for the steel bars and nails.

5. Launched Soil Nail:

In this method, the steel bars force into the soil with high speed using compressed air mechanism. The installation of soil nails is fast. And control over the length of bar penetrating the ground is difficult.

civil techniques

Footings

abbu riyaz 1 May, 2023

Footings designs to resist the shear force causes by imposing loads. Footings constructs in open space and known as open foundations. It provides with natural slopes on all sides. It employs for a depth up to 5 m. The base of the structure enlarges or spreads to provide individual supports. These type of foundations provides for the structure of moderate heights built on the dry ground.

Types of footings

Wall Footing
Isolated footing
Combined footing
Inverted footing
Continous footing
Cantilever footing
Grillage footing

1. Wall Footing

Footings are of simple or stepped on wall footing. The base course of the footings is of concrete or other material. These footings employ only for simple structures. It has one projection beyond the width of the wall on sides. The width of the concrete base is equal to twice the width of the wall. In single footings, the brick footing is widely employing.

2. Isolated or column footing

It uses to support individual columns. It is in step or has a projection in the concrete base. In heavy loads, steel reinforcement provides in both directions in concrete bed. An offset of 15 cm provides on all sides of the concrete bed. In brick masonry, offset is of 5 cm on all sides in regular layers.

3. Combined footing

A combined footing supports more columns in a row. The combined footing is of rectangular shape if both the column carry equal loads. In unequal loads it of trapezoidal shape. It is rigid and resisting on the homogeneous soil.

4. Inverted arch footing

Inverted arch footing use on the soft soil to reduce the depth of foundation. Loads above an opening transmit from supporting walls through inverter arches of soil. In this type of footing, the end columns are stable enough to resist the outward pressure causing by arch section.

5. Continuous footings

In this type of footing, a single continuous R.C. slab provides a foundation of more columns in a row. It is suitable for locations liable to earthquake activities. This prevents differential settlements in structure. To have a better stability deeper beam constructs in between columns.

6. strap or cantilever footing

It consists of more individual footings connects by a beam known as a strap and known as cantilever footing. This type of footing uses where the distance between the column is greater. It serves to transfer column loads on the soil with equal and uniform soil pressure.

7. Grillage footing

This type of footings uses to transmit heavy loads from steel columns to the soils having low bearing power. This type of arrangements avoids deep excavation. And provides a necessary area at the base to reduce the intensity of pressure. Grillage footings are of roll steel joists and name as grillage beams to providing in single or double tires.