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                                                             CHAPTER ONE

                                                              INTRODUCTION    
1.1 WHAT IS CONCRETE 

Concrete is an artificial engineering material made from a mixture of Portland cement, water, fine and course aggregates, and a small amount of air. It is the most widely used construction material in the world.
Concrete is the only major building material that can be delivered to the job site in a plastic state. this unique quality makes concrete desirable as a building material because it can be molded to virtually any form or shape. Concrete provides a wide latitude in surface textures and colours and can be used to construct a wide variety of structures, such as highways, and streets, bridges, dams, barge buildings, airport runways, irrigation structures, breakwaters, piers and docks, sidewalks, soles and farm buildings, homes and even barges and ships.
Other desirable qualities of concrete as a building material are its strength, economy, and durability. Depending on the mixture of material used, concrete will support, in compression, 700 or more kg/sq cm (10,000 or more 1b/sq in). the ensile strength of concrete is much lower, but by using properly designed still reinforcing, structural members can be made that are as strong in tension as they are in compression. The durability of concrete is evidenced by the fact that concrete columns built by the Egyptians more than 3000 years ago are still standing. 
There are however, many different types of concrete, the names of some are distinguished by the types, sizes and densities of aggregates e.g. eight weight, normal weight or heavy weight. Concrete are similar in composition to mortar, which are used to bond unit masonry. Mortars however, are normally made with sand as a hole aggregates.
Whereas, concrete contain much larger aggregates and this usually have greater strength. As a result, concrete have a much wider range of structural application, including pavements, footings, pipes, unit majoring, walls, dams and tanks. Because ordinary concrete is much weaker in tension than in compression, it is usually prestressed or reinforced with a much stronger material, such as steel, to resort tension.
There are various methods employed for carting ordering concrete. For very small projects, sacks of prepared mixes may be purchased and mixed on the site with water, usually a drem-type, portable, mechanical mixer.
For large projects, mix ingredient are weighed separately and deposited in a stationary batch mixer or a continuous mixer. Concrete mixed or agitated in a truck is called ready mixed concrete. In general, concrete is placed and consolidation is forms by hand tamping or pudding around reinforcing steel or by spreading at or near vertical surface. Another technique vibration or mechanical pudding, which is the most satisfactory one for achieving proper consolidation. 
CONSTITUENT OF CONCRETE 
The two major components of concretes are cement parts and inert materials. The cement parts consists of Portland cement, water, and some air either in the form of naturally entrapped air voids or minute, intentionally entrained air bubbles. The inert materials are usually composed of fire aggregate, which is a material such as sand, and course aggregate, which is a material such as gravel, crushed stone, or slag. In general, fire aggregate particular are smaller than 6.4mm (.25mm) in size, and course aggregates a particles are large than 6.4mm (.025mm). Depending on the thickness of structure to be built, the size is used, when Portland cement is mixed with water, the components of the cement react to form a cementing medium. In properly mixed concrete, each particles of sand and course aggregates is completely surrounded and coated by this paste, and all spaces between the particular are filled with it. As the cement part sets and hardens, it binds the aggregates into a solid mass.
Under normal conditions, concrete grows stronger as it grows older. The chemical reactions between cement and water that cause the parts to harden and bind the aggregates together require time. The reactions take place very rapidly at first and then slowly over a long period of time.

1.2 SALT WATER (SEA WATER)
Sea water has a salinity of about 3.5%. in that about 78% is sodium chloride and 15% is chloride and sulphate of magnesium. Sea water also contain small quantities of sodium and potassium salts. This can react with reactive aggregates in the same manner as alkalizes in cement. Therefore, sea water should not be used even for Pcc if aggregates are known to be potentially alkalie reactive. It is reported that the use of sea water for mixing concrete does not appreciately reduce the strength of concrete although it may lead to corrosion of reinforcement in certain cases. Research workers are unanimous in their opinion, that sea water can be used in un-reinforced concrete or mass concrete sea water slightly accelerates the early strength of concrete. But it reduces the 28day strength of concrete by about 10 to 15percent.
However, this loss of strength could be made up by redesigning the mix. Water containing large quantities of chlorides in sea water may cause efflorescence and persistent dampness. When the appearance of concrete is important, sea water may be avoided. 
Granite, limestone, sand stone, or basaltic rock are crushed for use principally as concrete aggregate or road stone.
ADVANTAGES OF CONCRETE
Under normal conditions, concrete grows stronger as it grows older. It is the most widely used material (construction) in the world, because it is the only major building material that can be delivered to the job site in a plastic state.
Concrete can be molded into different form or shape due to its unique quality. Other qualities of concrete as a building material are its strength, durability, and economy, depending on the mixture of material used.
Concrete provides a wide latitude in surface texture and colours and can be used to construct a wide variety of structures, such as highways and street bridges, dams, large buildings, airport runways, irrigation structures, breakwaters, piers and docks, sidewalks, silos and farm buildings, home and even barges and ships.
DISADVANTAGES OF CONCRETE 
• Ordinary concrete are much weaker in tension, than in compression.
• Concrete is a bottle material and presses very low tensile strength, limiting ductility and little resistance to cracking
• Internal micro cracks as inherent present in the concrete and its poor tensile strength propagates such micro cracks and eventually leading to bottle failure of concrete.
• Concrete containing micro silica is vulnerable to plastic shrinkage, cracking and therefore, sheet or mat curing should be considered.

1.3 OBJECTIVES AND PURPOSE OF STUDY
The purpose of the study is to know the adverse negative effect the water (salt) may have on concrete. 
Water is an important ingredient of concrete as it actively participates in the chemical reaction with cement. Since it helps to form the strength giving cement gal, the quantity and quality of water is required to be looked into very carefully. Sea water has a salinity of about 3.5percent, in that , about 78% is sodium chloride and 15% is chloride and sulphate of magnesium. It is said that the use of salt water (sea) for mixing concrete does not appreciably reduce the strength of concrete through it may lead to corrosion of reinforcement in certain cases. The aim of the experiment is to prove whether or not, if the sea water can reduce the strength of concrete.

1.4 SCOPE AND LIMITATION OF STUDY 
A popular yard-stick to the suitability of water for mixing concrete is that, if water is fit for drinking, it is fit for making concrete. This does not appear to be a true statement for all conditions. Some water containing imparities may be suitable for other purpose, but not for the mixture of concrete.
Some specification requires that if the water is not obtained from source that has proven satisfactory, the strength of concrete or mortar made with questionable water should be compared with similar concrete or mortar made with pure water. Sea water has a salinity of about 3.5percent, in that, about 78% is sodium chloride and 15% is chloride and sulphate of magnesium. It is reported that the use of sea water for mixing concrete does not appreciably reduce the strength of concrete although it may lead to corrosion of reinforcement in certain cases.
The purpose of the experiment is to prove the doubt of people whether or not if salt water has an effect on concrete.

About 80 percent of the surface of the earth are covered by oceans; therefore, a large number of structures are exposed to Salt water with high salinity either directly, or indirectly when winds carries Salt water spray up to a few miles inland from the coast. As a result, several coastal and offshore sea structures are exposed to the continuous action of physical and chemical deterioration processes. This challenge of building and maintaining durable concrete structures in coastal environs have long become a serious issue to the people living in this areas and this provides an excellent opportunity to understand the complexity of concrete durability problems in these areas.

Concrete is one of the major building materials use in modern day construction. It is a composite construction material composed of cement and other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate made of gravels or crushed rocks such as limestone, or granite, plus a fine aggregate such as sand), water, and chemical admixtures (Akinkurolere et al, 2007; Neville and Brook, 2008; Matthias, 2010). Concrete is used for numerous purposes in construction such as construction of buildings, dams, foundations, highways, parking structures, pipes, poles among others (Matthias, 2010). Also, the use of concrete offshore drilling platforms and oil storage tanks is already on the increase. Concrete piers, decks, break-water, and retaining walls are widely used in the construction of harbours and docks. Floating offshore platforms made of concrete are also being considered for location of airports, power plants, and waste disposal facilities in order to relieve land from pressures of urban congestion and pollution (Gopal, 2010).Seawater is water gotten from sea, which is salty in taste. Salt water can be said to have a solution containing a great number of elements in different proportions. Primarily Salt water contains some chemical constituent such ions of chloride, magnesium, calcium and potassium (Akinkurolere et al, 2007; Gopal, 2010). Most seawater is fairly uniform in chemical composition, which is characterized by the presence of about 3.5 percent soluble salts by weight. The ionic concentrations of Na+ and Cl- are the highest, in Atlantic Ocean typically 11000 and 20000mg/litre respectively. Table 1 shows the concentration of major ions present in the world sea.


Table 1:          Concentration of Major Ions in Some of the World Seas

Major

Concentration (mg/l)

Ions

Black

Marmara

Mediterranean

North

Atlantic

Baltic

Arabian

BRE**

Red

Sea

Sea

Sea

Sea

Ocean

Sea

Gulf

Exposure

Sea


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