Figure 1. Variation of Compressive Strength of WPFRC produced from Conventional and Recycled Aggregates whensubjected to Acidic Attack
The addition of fibres into concrete has been found to improve several of its properties like tensile strength, cracking resistance, impact, wear and tear, ductility, fatigue resistance etc. Many types of fibres like steel fibres, carbon fibres, GI fibres, glass fibres, asbestos fibres etc., can be used in fibre reinforced concrete. Waste plastics can also be used as fibres. The disposal of waste plastic is resulting in environmental pollution. Plastic is a non-biodegradable material, and it neither decays nor degenerates in water or in soil. On the other hand it pollutes the water and soil. Plastic if burnt releases many toxic gases, which are very dangerous to health. Such plastics can be used in concrete in the form of fibres to impart some additional desirable qualities to the concrete. This paper presents the results of waste plastic fibre reinforced concrete (WPFRC) produced from recycled aggregates subjected to acid and alkali attack. The different percentages waste plastic fibre used in the experimentation are 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3% with an aspect ratio of 50. The results are compared with the waste plastic fibre reinforced concrete (WPFRC) produced from granite aggregates.
Fibres in cement based matrix act as cracks arresters, restricting the growth of flaws in the matrix, and preventing these from enlarging under load into cracks, which eventually cause failure. Prevention of propagation of cracks originating from internal flaws can result in improvements in static and dynamic properties of the matrix ( Amjad et al; Palanichamy; Parameshwaran ; Swamy ).
The idea that concrete can be strengthened by the inclusion of fibres was first put forward by Porter in 1910, but little progress was made in the development of this material until 1963 when Romualdi and Batson ( Parameshwaran; Rafat Siddique ) published their classic paper on the subject. Since then there has been considerable interest in fibre reinforced concrete and several kinds of fibres such as steel, fibrillated polypropylene, nylon, asbestos, coir, jute sisal, kenaf, glass, carbon have been used ( Kukreja; Rafat Siddique ).
Even though plastic is making wonders in many fields, it is also endangering the environment, causing environmental in many ways. Waste plastic is a health hazard, non-biodegradable/non-perishable material; it neither decays nor degenerates either in soil or in water. It cannot be burnt since it releases many toxic gases causing air pollution. When the waste plastic did not find any place for disposal in America and Europe they dumped million tones of waste plastics in the Atlantic and the Pacific Oceans, resulting in the death of many aquatic lives. Many researchers are trying to use plastic in a safer manner (Nabil Mustafa).
The conversion of large amount of available demolished waste into an alternate source of building material will contribute not only as a solution to the growing problem of waste disposal, but it will also conserve the resources of other building materials and thereby reduce the cost. The demolished waste reused as non-stabilized base or sub-base in highway construction ( Amjad et al; Di Niro et al; Mandal et al; Padmini A.K ).
Concrete is not fully resistant to acids. Most acid solutions will slowly or rapid ally disintegrate Portland cement concrete depending upon the type and concentration of acid. Certain acids, such as oxalic acid and phosphoric acids are harmless. The most vulnerable part of the cement hydrate is Ca (OH)2, but C-S-H gel can also be attacked. Siliceous aggregates are more resistant than calcareous aggregates.
Generally, naturally occurring acidic-ground waters are not common, being confined to marshy or peaty regions where extensive decomposition of organic matters occurs. Acidic waters may also occur in or adjacent to, land filled areas and in places where mining operations and stockpiling of mine tailings have occurred. Highly acidic conditions materials exist in agricultural and industrial wastes, particularly from the food-and animal-processing industries (Siddney Minddes).
Concrete will attack by liquids with pH value, less than 6.5. But the attack is severe only at a pH value below 5.5. At a pH value below 4.5, the attack is very severe. As the attack proceeds, all the cement compounds are eventually broken down and leached away, together with any carbonate aggregate material. With the sulphuric acid attack, calcium sulphate formed can proceed to react with calcium aluminate phase in cement to form calcium sulpoaluminate, which on crystallization can cause expansion and disruption of concrete.
If acids or salt solutions are able to reach the reinforcing steel through cracks or porosity of concrete, corrosion can occur which will cause cracking (Shetty 1974).
Concrete was prepared by using design mix proportion of 1: 1.435: 2.46 with a W/C ratio of 0.48 for conventional aggregates and recycled aggregates, which correspond to M20 grade of concrete. The different percentage of waste plastic fibres adopted in the experimental programme by volume fraction were 0%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3%. The aspect ratio adopted for the fibre was 50. The concrete cube specimens of dimensions 70.6 x 70.6 x 70.6 mm were cast and water cured for 28 days. After 28 days of water curing the specimens were washed thoroughly in running water and weighed in the sensitive balance. Then the specimens were transferred to the drums containing prepared acidic and alkali solution. The acidic solution was prepared using H2SO4 having a pH value of 2 to 3 and the alkali solution was prepared using NaOH having a pH value of 12 to 13. The pH of the solution was regularly monitored and maintained if necessary. After 60 days of immersion the specimens were taken out from the solution and thoroughly washed in running water. Then the specimens were left for drying. Then the specimens were accurately weighed to find the percentage loss of weight. The compressive strength was found for these specimens using a compression testing machine of capacity 2000 kN.
The Tables 1and 2 gives the loss of weight and percentage weight loss results of waste plastic fibre reinforced concrete produced from conventional and recycled aggregates when subjected to acidic and alkali attack for 60 days.
The Tables 3 and 4 gives the compressive strength results of waste plastic fibre reinforced concrete produced from conventional aggregates and recycled aggregates when subjected to acidic and alkali attack for 60 days.
Figure 1. Variation of Compressive Strength of WPFRC produced from Conventional and Recycled Aggregates whensubjected to Acidic Attack
Figure 2. Variation of Compressive Strength of WPFRC produced from Conventional and Recycled Aggregates when Subjected to Alkali Attack
Table 1. Percentage loss weight results of waste plastic fibre reinforced concrete produced from conventional and recycled aggregates when subjected to acidic attack
Table 2. Compressive strength test results of waste plastic fibre reinforced concrete produced from conventional and recycled aggregates when subjected to acidic attack
Table 3. Percentage loss weight results of waste plastic fibre reinforced concrete produced from conventional and recycled aggregates when subjected to alkali attack
Table 4. Compressive strength test results of waste plastic fibre reinforced concrete produced from conventional and recycled aggregates when subjected to alkali attack
Based on the experimental results the following observations were made.
Addition of waste plastic fibres by more than 2% may expose the fibres out of concrete and may come in contact with acidic media and deteriorate there by bringing down the compressive strength. Also it may be due to the fact that 2% addition of waste plastic fibres may interlock between the aggregates giving rise to higher compressive strength.
Thus it can be concluded that 2% addition of waste plastic fibres show more resistance to acidic attack both in conventional aggregate concrete and recycled aggregate concrete.
This is probably due to the reason that the recycled aggregates show less mechanical strength than the conventional aggregates. The recycled aggregates may develop micro-cracks inside their structure when they were previously loaded. Attached mortar to it may also bring down their strength.
Therefore it is suggested to use conventional aggregates in the production of waste plastic fibre reinforced concrete, when subjected to acidic attack. But since the percentage decrease in the strength is not much when recycled aggregates are used, they can be recommended in the areas where they are available easily. Use of little more amount of cement than the recommended is suggested in case of waste plastic fibre reinforced concrete with recycled aggregates. The use of recycled aggregates will save the natural quarries.
This may be due to the fact that, the adhered cement mortar may act as loose bond and may react with acidic media thus making the average loss of weight more in case of waste plastic fibre reinforced concrete produced from recycled aggregates.
Therefore it is suggested to use conventional aggregates in the production of waste plastic fibre reinforced concrete when subjected to acidic attack. But since the percentage decrease in the percentage loss of weight, is not much when recycled aggregates are used, they can be recommended.
Addition of waste plastic fibres by more than 2% may expose the fibres out of concrete and may come in contact with alkali media and deteriorate there by bringing down the compressive strength. Also it may be due to the fact that 2% addition of waste plastic fibres may interlock between the aggregates giving rise to higher compressive strength.
Thus it can be concluded that 2% addition of waste plastic fibres show more resistance to alkali attack both in conventional aggregate concrete and recycled aggregate concrete.
This is probably due to the reason that the recycled aggregates show less mechanical strength than the conventional aggregates. The recycled aggregates may develop micro-cracks inside their structure when they were previously loaded. Attached mortar to it may also bring down their strength.
Therefore it is suggested to use conventional aggregates in the production of waste plastic fibre reinforced concrete, when subjected to alkali attack. But since the percentage decrease in the strength is not much when recycled aggregates are used, they can be recommended in the areas where they are available easily. Use of little more amount of cement than the recommended is suggested in case of waste plastic fibre reinforced concrete with recycled aggregates. The use of recycled aggregates will save the natural quarries.
This may be due to the fact that, the adhered cement mortar may act as loose bond and may react with alkali media thus making the percentage loss of weight more in case of waste plastic fibre reinforced concrete produced from recycled aggregates.
Therefore it is suggested to use conventional aggregates in the production of waste plastic fibre reinforced concrete when subjected to alkali attack. But since the percentage decrease in the percentage loss of weight, is not much when recycled aggregates are used, they can be recommended.
The authors indebted to Vice-Chancellor, Christ University and Fr. Benny, Director of Christ University Faculty of Engineering, Bangalore-560074 for their constant encouragement.