Plain concrete is known as concrete without steel reinforcement. It is an intimate mixture of cement, fine aggregates, coarse aggregates and water. It can be easily molded to desired shape and size before it hardens. Plain concrete is strong in compression but weak in tension.

Major ingredients of plain concrete are;

• Binding materials such as cement, lime, polymer.
• Fine aggregate material such as sand.
• Coarse aggregate materials like crushed stone, gravel, and granite.
• Clean water.

Common cement, sand and coarse aggregate ratios are;

1:1:2, 1:2:4, 1:3:6, 1:4:8

Constituents of plain concrete.

Cement:

Cement is the binding material. It binds and hardens when water is added. Generally a concrete mix with more cement gives more strength.

Coarse aggregate:

Coarse aggregates consists of crushed stones of igneous origin. They should be clean, hard, angular and sharp. They give mass to the concrete and prevent shrinkage of cement.

Fine aggregates:

River sand is the common fine aggregate for plain concrete. Its gives mass to concrete and fills voids created by coarse aggregates.it adds density to concrete. A denser concrete is higher in strength.

Water:

Water used for making concrete should be clean. It hydrates the cement to form a plastic mass which hardens gradually. Water makes it possible to mix the concrete with ease and place it in final position. The more water the better, however, excess water reduces the strength of concrete. A water – cement ratio of 0.5-0.6 is used to achieve desired concrete strength when hand mixed.

Preparing and placing of concrete.

Batching:

Batching by volume or weight are the 2 common methods of measurement.

Mixing: 

Thorough mixing to produce good quality concrete. Cement, sand and coarse aggregates is mixed in dry condition, then in wet condition after adding water. Hand and machine mixing are 2 common methods of mixing of concrete mixing

Transport and placing:

Fresh concrete is transported on site using head pans, wheel barrow on small scale work while concreting chutes, bell conveyors or pumps are used in large scale construction.

Compaction:

Compaction of concrete is necessary to remove entrapped air during placement of concrete. Compaction can be carried out by hand or with help of  concrete vibrators

Cement mortar is an intimate mixture of cement , sand and water. Cement is the binding material, and sand is the fine aggregrate. The binding material (cement) develops when water is added to the mixture. Sand suitable for cement mortar include, river sand, gutter or pit sand.

Sand used for cement mortar must have the following properties;

• should be chemically inert.
• It should be free from organic or vegetable matter.
• Should not contain salt.
• Should contain sharp, angular, coarse grain that is well graded and hard.

Preparing cement mortar.

Cement and sand in the required ratio is first thoroughly mixed in dry condition then water gradually added and mixed until required consistency is achieved.

Cement to sand ratio for various works;

• Masonry Works :   1:6 to 1: 8
• Plastering:    1:3 to 1:6

Mortar Curing.

Curing is the process of ensuring sufficient moisture during hardening of mortar. Curing is ensured by spraying of water. It starts 6 – 24 hours after mortar has been applied

Characteristics of Cement Mortar;

• Cement sand ratio mix richer than 1:3 is prone to shrinkage.
• Mortar with well-proportioned mix gives an impervious surface.
• Mortar with leaner mix may become porous.
• Strength of mortar depends on the cement sand ratio.

Compressive Strength of various cement sand ratios;

• 1:3 –   10N/mm2
• 1:4 –  7.5N/mm2
• 1:5 –   5.0 N/mm2
• 1:6 –   3.0 N/mm2
• 1:8 –    0.7 N/mm2

Uses of cement mortar.

• To bind masonry units like blocks and bricks.
• Plaster walls and slab.
• Give neat finishes to walls and concrete works.
• Fill joints and cracks in walls.
• As filler material in stone masonry.

Timber is wood used for building/construction works. Timber means ‘to build’. A felled tree is first cut into sizes of suitable lengths called rough timber that are transported to timber yard. By sawing rough timber, it is converted into various commercial sizes like planks, battens, posts, beams etc. Such form of timber is known as converted timber.

Properties of timber suitable for building construction.

• Should be uniform in colour.
• Should have pleasant  odour when freshly cut.
• Clear ringing sound when struck indicates the timber is good.
• Good timber should have good texture
• The timber should be of high density
• Timbers should be strong and durable.
• Good timber do not warp under changing environmental conditions.
• Timber should be capable of resisting shock loads.
• Good timber do not deteriorate due to wear. This property should be looked into, if Timber is to be used for flooring.
• Timber should have high strength in bending, shear and direct compression.
• Timber should have high modulus of elasticity.
• Good fire resistance.
• Low water permeability.
• Good workability, should not clog the saw.
• Capable of resisting the action of fungi and insects attack.
• Timber should be free from defects like dead knots, shakes and cracks.

How timber Can be Preserved

Timber is preserved by protection from fungi and insects attack. Timber should be well seasoned before preservatives are applied. The following are the widely used preservatives:

Tar: Hot coal tar is applied to timber with brush. Tar coating protects the timber from attack of insects and fungi.

Paints: Paint improves the appearance of the timber. Solignum paint is a special paint which protects the timber from the attack of termites.

Chemical salt: These are the preservatives made by dissolving salts in water. The salts used are copper sulphate, masonry chloride, zinc chloride and sodium fluoride.

Creosote: Creosote oil is obtained by distillation of coal tar.

Uses of Timber in construction

•  Construction of columns, trusses, piles.
•  Making of doors, windows, flooring and roofing.
• Construction of railway sleepers, fencing poles, electric poles and gates.
•  For temporary works such as scaffolding, centering, shoring and strutting, packing of materials.

Structural analysis which involves strenuous mathematical calculations is a core skill required for civil and structural engineers. Almost every project handled by a civil/ structural engineer will involve structural analysis.

Structural analysis can be very tedious and when there are many projects to be done, moving from one mathematical calculation to the other may eventually lead to frustration and then errors.

There are many structural analysis/ design software available that make analysis and design very easy, however , there are free structural analysis software available which can ease analysis and design, one of them is the RC 21 Sub-frame analysis excel program (RC 21) developed by reinforced concrete council UK.

RC 21 analyses reinforced concrete frame structures to BS 8110. While the United Kingdom no longer uses the BS 8110 and adopted the Euro code, BS 8110 is still being used in many African countries, and also other countries outside Africa.

RC 21 analyses reinforced concrete elements based on input parameters to determine design moments and shear forces necessary to further calculate amount of reinforcement required.

You can watch the video on how RC21 works, by clicking the my youtube video link below.

https://www.youtube.com/watch?v=kkTyB3cFkn4

RC 21 can analyze slab, beams and columns. It can analyze up to six spans and seven supports.

Input parameters required for analysis to complete include;

Dead and live loads.

Span (slab/beam length)

Beam/slab/column section dimensions (size)

End conditions

Load factor

Colum height above/below beam level.

Results calculated include design slab, beam and column moments and shear forces. RC 21 considers 3 load cases and calculates design moments based on worse case loading. RC 21 is a free excel program, to down load, you can visit the following URL; REINFORCED CONCRETE FRAME ANALYSIS TO BS 8110.

You can also directly view and download RC 21 by clicking HERE

The excel program will open in your browser, to download finally, click the download icon at top right of your screen.