Ways Of Improving Concrete Durability And Resistance: Importance And Techniques

Research Hypothesis

Concrete material’s durability and resistance are very important since in most cases, the products of the concrete are basically employed where resistance and durability are key. In some basic cases where such are employed includes the construction of Reinforced concrete (RCC), the building of slabs and columns in house construction, building of bridges as well as other sites. The research questions in this research are what some ways of archiving concrete durability and resistance and why are that important (Dyer, 2014). This report will hence address the above research questions and this will hence make the report to be well understood.

In this paper also addresses some of the hypothesis of the research paper.  These are;

• All types of concrete treatments are very appropriate in enhancing resistance and durability of concrete.
• Improving resistance and durability of concrete are cost-effective (cheap in long run).
• Improving concrete durability and resistance has highly promoted the safety of the people in the society (reduces the chances of accidents).

Selection of the material plays a very important role in improving the resistance as well as the durability of the concrete materials employed in the building and construction (Wei, 2010). The mixing ratio of cement to water (w/cm) will also help in realizing a strong material which will ensure the concrete material is both durable and resistant to breakage.  The selection of the chemical admixture, w/cm, cementitious material (like silica fumes, GGBFS, Portland cement and natural pozzolans) will depend on the amount of strength needed, exposure of the structure constructed (whether the structure will be covered or left bare), need to reduce the thermal gradient (Engineers, 2016). Chemical admixture will enhance resistant and durability of the materials (concrete). Air-entraining admixture will offer resistance to thawing and freezing will lower the w/cm.  The W/Cm can be reduced also through using high range water reducing admixtures. All these will lower the chances of shrinkage cracking and this reduces the permeability of the concrete hence high resistance of the concrete material (King Wong, 2014). Concrete´s resistance and durability can be improved through several ways some of the most common ways which can be employed to help realized this is discussed below;

Most of the concrete materials are designed by the structural engineer to last for a period of 50-100 years.  The difference in years will thus depend on the treatment done to ensure that the concrete is more resistance and durable (Kropp, 2014). But in this period of time is contrary to what is happening in most constructions since there is no or inadequate treatment to ensure the improvement of the durability and resistance of the materials.  It is very true to say that everything which occurs to the concrete happens due to water, Water conveys chemical contaminant into the concrete materials, therefore, water is capable to erode the surface, contributes to the disruptive and expansive reactions,  corrosion of the steel reinforcement (Chengula, 2018).

These joints are unavoided in any construction structure, they are also the common points in a concrete structure where through which water will always find its way through. If water penetrates through these construction joints, it can deteriorate the structure in several ways. But the most common one is water moving and reaching the reinforcing steels which lead to their corrosion, therefore, lowering the durability and resistance (Shi, 2010). These construction joints will highly help in directing the movement of water in a structure since when water is not directed it can move anyway in the structure which will result in corrosion of the reinforcing steels.  And when these joints are not there, there will be unplanned joints known as cracks. The construction joints should use a waterproof system to help to avoid water into the structure.  Such construction joints in a building or any other structure are illustrated using the diagram below;

Ways of improving the durability and resistance of the concrete materials

Fig 1: Showing construction joints  (Shi, 2010).

Concrete durability and resistance as aforementioned begin with mixing design of the concrete which is appropriately matched to the service conditions which concrete materials will be exposed to.  There is no mix design can be durable in every condition (Siddique, 2012). For instance, when concrete is subjected to soil contaminated with sulphate then the mix design must consider employing using a cement which is resistant to sulphate. Nevertheless, the mix design is not suitable when there is exposure of the concrete to a series of thawing and freezing in a wet environment. If by any means the mix design needs to include an air-entrain admixture because air entrained will aid to guard the concrete in such conditions. Some companies like Portland cement publishes control and design of mixing concrete which has a perfect guide in the concrete mix design. 

The concrete mix ratio for this design is illustrated using the table below where M stands for “mix“;

From the above table, the ratio of sand is always half that of the aggregate and this is a standard design mix. And water also plays a very important role in determining the durability and resistance of the concrete structure (béton, 2012).  The greater amount of water will reduce the durability as well as the resistance of the concrete but if the water is too low, the workability of the concrete will also reduce. This is because when there is low water it becomes very difficult to place concrete, therefore, the structure becomes less resistant as well as less durable ( since the concrete will not stick).

Albeit mix design should vary to match the situations in the concrete, but there is one factor which common to all perfect concrete materials and that factor is to ensure that the permeability is kept as low as possible (Nawy, 2012). It is very vital that water should be kept out of the concrete structure (Ludwig, 2012). When lowering the permeability is done through a perfect mix proportioning as well as lowering quantity of free water in the concrete mix through using the plasticizers or through using water reducing admixtures.  Concrete material which is subjected to water must use a waterproofing system (Huang, 2014).  When the permeability is highly reduced, the durability and residence of the concrete are highly increased. 

Due to the increasing demand to attain high resistance and durability of a concrete material, new techniques to achieve this has also landed on the addition of the steel fiber on the cement to make a very strong concrete due to the strength qualities of the steel. The steel fiber can be illustrated using the following diagram;

Fig 3: Showing the steel fiber  (Caldarone, 2014).

The application of steel fiber has resulted in the improvement of some key mechanical properties in a concrete. Some of these properties include durability and toughness in tension which results in the high resistance of a concrete. The irregular fibers which are distributed in the concrete help in filling the cracks which are in the composite (Caldarone, 2014). The steel fiber in the concrete material allows the steal fiber reinforcing material to withstand significant stresses in the post-cracking point in a concrete.  The reinforced steel concrete will remain in its fresh conditions from the point the steel is mixed to a point its set. At this point, the concrete is handled, conveyed, put and compacted (Nikolov, 2015). The nature of the concrete at this point is at a fresh condition are very vital since it influences the quality of the reinforced concrete. 

1. Construction Joints

There are several tests which can be employed to obtain the strength of the concrete after its treatments (Setzer, 2014). But the most important test is the Reinforced concrete compressive strength test since it provides the idea about all the characteristics of the concrete. This type of test is based on several factors like cement strength, water-cement ratio, and quality control during the time of production of concrete.  This type of test is done either in a cylinder or in a cube. And this type of test should be as per the International Standard (IS516:1959).  This type of test can be given by the following equation;

f_CK=   . . . . . . . . . . . . . . . . . . . . . . . . . . . .  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Where A is a shear area, P is the compressive load at failure and f_CK is the compressive strength of concrete.

Suitably the most common overlooked way to realize the durability and resistance of the concrete is through having a proper curing of the concrete material. Proper curing of the concrete, therefore, means maintaining conditions which enable the concrete to strengthen and attain optimal durability (Wesche, 2016).  Proper humidity and temperature are the most important parameter in proper curing of the concrete.  Therefore the temperature should be above 10⁰ C for the resistance of the concrete to proceed at a suitable pace (James, 2013). The humidity of the concrete must as well be maintained more so in first few days to help boost the hydration of the cement and this help in keeping the concrete from drying, shrinking and finally cracking ( this will lower the resistance and durability of the concrete) (Mihashi, 2018). Proper curing of the concrete will efficacy reduce the permeability, therefore, increasing resistance and durability, therefore, the concrete´s life expectancy will be really more.

Concrete proper curing can be done using the following steps

1. Formwork applied in making the concrete is left.    The formwork is left in place or around the column of the concrete or in some cases under the suspended slabs. This will help in preventing the concrete from drying out so quickly. This step one can be illustrated by the below diagram;

Fig 4: Showing concrete left on a formwork as a way of concrete curing  (Mindess, 2014). 

2. Sprinkle water on the formation after the formwork has been removed. An easier way is to keep water sprinkled on the formation, this can be done by hands held pipes or in some cases, it can be done by using a garden sprinkler. Some of the disadvantages of using this method of curing include the following;

i. This method of proper curing is used a lot of water (wasteful of water).

2. Mix Design

ii. The concrete should not be kept dry at any time, this is almost not possible.

And it can be illustrated using the following diagram;

Fig 5: Showing water sprinkled on the concrete as a way of concrete curing  (Mindess, 2014). 

3. Curing through the use of the plastic shield. Actually, this is the most effective way of concrete curing. In this method, a spray from horse pipe is applied in to make the surface wet and then a plastic is laid on the concrete (Mindess, 2014).  The plastic is kept in position by the use of the cement block or a timber.  This is more efficient since it does not stop other work. When it is laid other work in the construction will just go on. The diagram below illustrates how the film of plastic is sprayed over the concrete surface.

Fig 6: Showing plastic sprinkled on the concrete as a way of concrete curing  (Mindess, 2014). 

The curing of concrete can be done on large scale on the slab during the construction of a building, this can be illustrated by the following diagram;

Fig 7: Showing proper curing in action  (Mindess, 2014). 

Another important way to realize resistance and durability is through having a proper concrete placing the consistency and the workability of the mix of the concrete should be sufficient to consolidate and place the concrete into mass solids which are not having any rock or void pockets (Bentur, 2013).  A commitment to perfect vibration activities is vital to success here.  Placement of concrete will hence help in removing the gaps (voids ) formed in the concrete resulting in a high resistance of the concrete hence the material becomes more durable.  This concrete placement is very vital since during the formation of the concrete there are some voids which are created within the concrete therefore when a concrete is done the voids are highly reduced, basically concrete placement reduces the permeability, therefore, increasing the resistance as well as the durability of the concrete.  The practice of the concrete placement is illustrated in the following diagram;

Fig 5: Showing the process of doing the concrete placement  (Bentur, 2013). 

During placement of concrete more water needs to be added in the concrete used in the placement of the concrete. This will make the floody concrete to move down into the voids hence resulting to reduction of voids. This reduces the permeability and increases the durability and resistance of the concrete (Henderson, 2013).

Concrete material is treated and other activities can be carried out to the concrete to ensure that the durability and resistance of the concrete are achieved. Therefore by realizing these, there are some advantages which come with such activities. And such are listed below;

• This activity of improving the durability and resistance will help in reducing the concrete slab thickness and this makes the construction to appear very descent.
• When the concrete is more resistant and more durable, the maintenance  cost will be highly reduced
• This activity will reduce the absorption of water and chemical which can react with reinforced steel which may cause the corrosion of the steel hence reduction in maintenance cost.
• It helps in reducing the site labour for controlling the steel reinforcement.
• It results to a stronger surface having very few bleed holes.
• This will aid in easy and faster placement of the joints.
• There will be an equal distribution of the steel fiber in the concrete material during construction.

The overall elastic strain of the concrete which determines the resistance of the concrete can be obtained from the Matarov´s Formula. The formula is illustrated in the equation 2 below;

Log ?y =a+blog N . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

3. Lowering Permeability

Where N is the loading level of the concrete, ?y is the elastic deformation value while a and b are the coefficient of deformation.

Conclusion

In summary, there are several ways in which the durability and resistance of a concrete material can be achieved, these methods enable the concrete to last for long, reduces the cost of maintenance, results to the strong surface with fewer bleed holes. Some of these methods which are commonly employed are discussed above includes lowering the permeability of the concrete, placing the concrete within the voids formed during the construction, curing the concrete through using some common methods as discussed above.  From the hypothesis above, some hypothesis could not be proved, for instance, not all types of concrete treatment were effective, and some were just used because they are very affordable (like the use of water in concrete treatment).  But others could be easily proved, for example, improving the concrete resistance and durability is cheap in long run, this was proved since improvement of durability of concrete reduces the chances of doing the repair ( it reduces the maintenance cost) hence it is cheap in the long run.  It will also highly promotes the safety of the people in the society (reduces the chances of accidents).  This is because accidents which might occur due to the low resistance of the concrete used in the construction of the building can result in the collapse of buildings and this can result in loss of people life. 

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