Properties of reinforced concrete 2
Slump testing of concrete 3
Curing of concrete 5
Curing process: 5
Concrete is a composite material which mostly comprises of water, cement and aggregates. However, in order to achieve desired physical properties and in order to improve various forms of strength of the concrete, they are mixed with additives and reinforcements while preparing their mixture (Mehta, 1986). Reinforced concrete can be termed as a composite material where the low tensile strength and ductility is enhanced by the reinforcement of materials in its mixture that possess higher tensile strength and ductility. This type of reinforcements can be done using steel, fibres and polymers. We are going to carry research on the various properties of reinforced concrete along with few tests to enhance and measure its quality. I am going to design a reinforced concrete beam in this work.
Properties of reinforced concrete
Reinforcement of concrete improves its properties and makes it suitable for desired applications which require high tensile strength and ductility. Properties of reinforced concrete are as under (Mehta, 1986):
• High tolerance of tensile strain, that is, high tensile strength,
• High relative strength,
• Strengthens the bonding ability of concrete without considering the pH and moisture content,
• High anti-corrosive strength and ability to withstand water effectively
• High thermal compatibility is achieved which helps to resists changes at different temperatures.
• High durability that allows it to be designed in desired shapes,
• High ductility that helps it to get moulded easily.
Slump testing of concrete
Slump test is carried out on concrete to measure the workability of fresh concrete. It helps to ensure the consistency of a particular batch of concrete which measures the ease with which the concrete flows. It also helps to estimate the degree of wetness. The slump test measures the nature of the concrete in the shape of inverted cone facing the gravity. It helps to obtain the suitability of the concrete for specific applications with specific strengths. It is carried out as follows (Khayat, 1999):
This test involves taking a fresh concrete that is just prepared and is taken in its wet state.
This test is carried with the help of a mould which is in the shape of an inverted cone and is called as the slump cone. This cone has a handle on its outer side and is kept on a hard, moist, smooth and non-absorbent surface as shown in the figure below.
The cone should be firmly held in its place. The fresh concrete is filled in the cone in three successive stages with the quantity gradually increasing by 30 % every time. It is then tamped by a steel rod at each stage of slumping as shown below. The tamping is carried by immersing the rod till the last level of the concrete.
After the third stage where the concrete overflows the cone and rises up to the top, the cone is very slowly carried above vertically without shaking or moving the mixture in it. The concrete layer inside remains undisturbed. After removing this, the concrete tilts which is known as slumps and is shown in the figure below. Measure the distance between the upper end of the slump and the straight edge of the cone. This distance is termed as the slump and it is measured for the reinforced concrete to measure its workability. The height of the slump helps to estimate the strength and wetness of the concrete and helps to determine its use in the specific field as per the desired application.
Slump test procedure of reinforced concrete
There are four types of slump that are obtained in the slumping test. They are:
• True slump: In this type of slump, retains the shape and subsides or tilts gradually without creating major slopes.
• Zero slump: In this type of slump, the concrete does not slump at all and there are hardly any changes in the level of concrete.
• Collapsed slump: In this type of slump, the concrete subsides completely, that is, it collapses completely.
• Shear slump. In this type of slump, the upper portion of the concrete subsides along the sides slipping in the side direction, thereby, leaving a sloppy surface.
On the basis of this slumps that are determined, the workability and suitability of the concrete for different purposes is obtained.
Slumps in the range of 0 – 25 mm are very dry and are used in the construction of roads. Slumps in the range of 10 – 40 mm are used in the foundations that require light reinforcement and workability of medium quality is required. Slumps in the range of 50 -90 mm are used in the applications which require high workability and wetness to withstand vibrations and other stresses that come in its way.
Curing of concrete
Curing of concrete is termed as the process which helps the concrete from losing the moisture and helps to maintain it in a desired temperature range. Through the curing process, we can increase the strength of the concrete and reduce the permeability comparatively. It also helps to delay the drying shrinkage until the concrete has gained the strength to withstand cracking due to shrinkage (Bairagi, 2013).
When mixture of cement and water ids made, hydration takes place. When this mixture is prepared, it has sufficient amount of water. But gradually, it goes ion decreasing rapidly due to the evaporation and loss of moisture from the surface of the concrete. But it is necessary to retain this water in this stage, so as to ensure that the concrete gains adequate strength and is durable enough to be used for the desired purpose. There are various ways by which curing can be achieved and they are (Aoyama, 2001):
• Water cure: In this type of cure, the concrete is sprinkled and mist sprayed so that it gets fully filled and flooded. It is one of the most effective method of curing that helps reduce the evaporation of water from the surface.
• Water retaining methods: In this type of cure, there are various coverings that are used on the surface to avoid the evaporation of water from the surface. This coverings consists of canvas, sand, burlap or straw. This makes sure that the surface of the concrete mixture stays wet and the moisture is not lost from it.
• Waterproof paper or plastic film seal: In this type of cure, various film seals made of water proof paper or plastic are applied when the concrete becomes moist enough that it does not get damaged. However, application of plastic seal is not desirable where the appearance of concrete is of great importance because it removes the upper colour and smooth surface of the concrete.
• Chemical Membranes: In this type of cure, there is a construction of membrane made up of chemicals that provides adherence to the surface of concrete and protects it from consistent evaporation. However, special care needs to be taken while selecting the chemical and the application of the concrete is to be considered before using the chemical.
In this way, curing of concrete helps to withstand the structural loading, high tensile stresses, fatigue, weathering, corrosion, abrasion, low permeability and chemical attack.
Aoyama, H. (2001). Design of modern highrise reinforced concrete structures. . London:: Imperial College Press.
Bairagi, N. (2013). Reinforced concrete design.,. Journal Of The Indian Institute Of Science, 83(5 \& 6).
Khayat, K. (1999). Workability, testing, and performance of self-consolidating concrete. . ACI Materials Journal,, 96(3).
Mehta, P. (1986). Concrete. Structure, properties and materials.