Build a house - Concrete work

Tue, 06/21/2011 - 15:10 — Decknash

Concrete work

In the past buildings were made from mud and stones and slabs are carried by walls, These bearing walls are of large dimensions and thickness which take most of the space available.

reinforced Concrete

Later when new stronger construction materials became known, smaller cross-section for beam and column could safety carry loads and space is more efficiently used.

The most common construction materials are concrete, steel and wood. Every material has it’s own advantages and disadvantages. Among these three, Reinforced concrete is more commonly used in constructing buildings, bridges, tunnels and tanks.

Reinforced concrete is achieved by successful marriage of two materials namely concrete and steel and each of which has it’s duties and obligations to maintain a stable structures.

Plain Concrete

Plain Concrete : Concrete without reinforcement but often with light steel to reduce shrinkage and temperature cracking

Plain concrete = Cement + Water + Aggregate + Admixture

Plain Concrete is an artificial stone as a result of mixing cement, fine aggregates, coarse aggregates and water. The conglomentation of these materials producing a solid mass is called Plain Concrete.

The term plain concrete is used to describe any concrete mass used without any strengthening materials. The physical properties of plain concrete are very similar to stone and include the ability to withstand great pressure. Concrete is a combination construction material made of cement, ash, gravel, limestone, and granite. Some types of concrete include sand, chemical mixtures, and water.

Plain concrete is combined with water and then hardens in place after being poured. This process is known as hydration. The cement reacts with the water, creating a new chemical bond between the different materials in the concrete mix. As the water dries, the cement cured into a stone-like material.

fixing levelling bars for concrete level

or fix leveling rods

spread Nylon on ground (to keep water in concrete)

start casting concrete (plain concrete)

laying, spreading, leveling, vibrating and finishing concrete

helicopter

Pure concrete is the most commonly used man-made material in the world. The materials required to make plain concrete are taken from a series of mines located around the world. Special equipment and training is required to take the components that make concrete from the mines.

Transporting these materials is very expensive. As a result, most production facilities that create concrete are located next to the mine itself. The amount of water and staff required to create plain concrete are constant challenges for production facilities. There are significant costs associated with the production of this material.

When selecting a supplier for plain concrete, there are three items to compare: quality, price, and delivery terms. There are a small number of firms that produce concrete in the world. Take the time to review the different manufacture firms and their current quality ratings. It is important to think about what type of structure you plan to build with the concrete and review the assurance rating.

The price of plain concrete is tied to supply and demand, as well as commodity trading. People responsible for purchasing large quantities of concrete develop relationships with traders in the industry. There are cycles in any industry, and knowing the ebbs and flows of the supply cycle is critical to purchasing the commodity at the best possible price.

So after we cast plain cocrete , now our site clean and ready to start work in Reinforced Concrete

Reinforced Concrete

Reinforced Concrete on the other hand, is a concrete with reinforcement embedded in such a manner that the two materials act together in resisting forces.

Reinforced concrete = Steel + Cement + Water + Aggregate + Admixture

Reinforced concrete is concrete in which reinforcement bars ("rebars"), reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. It was invented by French gardener Joseph Monier in 1849 and patented in 1867.The term Ferro Concrete refers only to concrete that is reinforced with iron or steel. Other materials used to reinforce concrete can be organic and inorganic fibres as well as composites in different forms. Concrete is strong in compression, but weak in tension, thus adding reinforcement increases the strength in tension. In addition, the failure strain of concrete in tension is so low that the reinforcement has to hold the cracked sections together. For a strong, ductile and durable construction the reinforcement shall have the following properties:

High strength
High tensile strain
Good bond to the concrete
Thermal compatibility
Durability in the concrete environment

In most cases reinforced concrete uses steel rebars that have been inserted to add strength.

We need steel in reinforced concrete to help concrete in carrying tension force because concrete is weak in tension and it will crack .

Use in construction

Concrete is reinforced to give it extra tensile strength; without reinforcement, many concrete buildings would not have been possible.

Reinforced concrete can encompass many types of structures and components, including slabs, walls, beams, columns, foundations, frames and more.

Reinforced concrete can be classified as precast or cast in-situ concrete.

Much of the focus on reinforcing concrete is placed on floor systems. Designing and implementing the most efficient floor system is key to creating optimal building structures. Small changes in the design of a floor system can have significant impact on material costs, construction schedule, ultimate strength, operating costs, occupancy levels and end use of a building.

CONCRETE FORMWORK

Concrete Form Plywood

Scaffolding

DESIGN OF FORMWORK

1- Design, erect, support, brace, and maintain formwork so that it will safely support vertical and lateral loads that might be applied until such loads can be supported by the concrete structure.

2- Carry vertical and lateral loads to ground by formwork system until in-place construction has attained adequate strength for that purpose.

3- Construct formwork so that concrete members and structures are of correct size, shape, alignment, elevation, and position.

4- Design forms and false work to include assumed values of live load, dead load, weight of moving equipment operated on formwork, concrete mix, height of concrete drop, vibrator frequency, ambient temperature, foundation pressures, stresses, lateral stability, and other factors pertinent to safety or structure during construction.

5- Provide shores and struts with positive means of adjustment capable of taking up formwork settlement during concrete placing operations, using wedges or jacks or a combination thereof.

6- Provide trussed supports when adequate foundations for shores and struts cannot be secured.

7- Support form facing materials by structural members spaced sufficiently close to prevent objectionable deflection.

8- Fit forms placed in successive units for continuous surfaces to accurate alignment, free from irregularities, and within allowable tolerances.

9- Provide camber in formwork as required for anticipated deflections due to weight and pressures of fresh concrete and construction loads.

10- Provide formwork sufficiently tight to prevent leakage of cement paste during concrete placement. Solidly butt joints and provide backup material at joints as required to prevent leakage and finds.

REMOVAL OF FORMWORK, SHORING AND RESHORING

Striking and removal of formwork shall be carried out carefully and under competent direction to ensure that the concrete is not jarred or the surface damaged and the Contractor shall take particular care in striking and removal of formwork from surfaces to remain exposed in the finished work. Furthermore, formwork shall be left in place where, in the opinion of the Architect's Representative, it is advisable to protect the concrete against the effects of low temperatures or excessive evaporation. The Contractor shall notify the Architect's Representative of his intention 24 hours before removing formwork or de-propping.

CONCRETE REINFORCEMENT