Strength and durability studies of waste nylon cable ties concrete

Of late, concrete technology is changing at a fast phase. Concrete is a flexible material and several attempts are being made to incorporate different materials specially industrial wastes as substitutes to the existing ingredients to enhance the quality of concrete. On the other hand environmentally sustainable concrete is in great demand. As plastic waste disposal has become a major problem for the modern day society, concrete has played a vital role as a dumping material. Plastic can either be used in concrete either as a partial substitute for fine aggregate or as an additive.Plastic wastes are present in different forms. This study focuses on use of waste Nylon Cable Ties (NCT) as a partial replacement of fine aggregates (1%, 2%, 4%) and as addition (0.5%, 1%, 1.5%) for M40 grade of concrete. Different tests like flexural, split tension, compression,effects of temperature and permeability test are being carried out. It was observed that 2% replacement of M-sand by waste NCT gives better results compared to 1% and 4% replacement of waste NCT. Addition of 1% NCT gives maximum compression, spilt tensile strength and flexural strength in concrete. When compared to replacement of fine aggregates by waste NCT, addition of waste NCT is found to give better strength.The permeability of the specimens was reduced for both replacement and addition of NCT ties. However permeability was found to be lesser for addition of NCT ties. But the performance of these specimens was not very satisfactory for either replacement or addition of NCT ties.


Introduction
Plastic is one of the most commonly used wonder material worldwide. This has become boon to the people and bane to the environment in terms of quantum of non-biodegradable waste generation. According to newspaper article India is generating 9.46 Mtonnes of plastic waste annually and in that 43 % remains uncollected [1]. Also, about 60 % of global plastic produced dumped in landfills or in other natural environment causing further damage [1]. One of the areas where the plastic waste can be utilized effectively is its use in concrete. Concrete is the most important man-made construction material widely used all over the world. It proves to be an excellent waste disposal means for fly ash, ground granulated blast furnace slag, silica fume, powdered marble, plastic wastes like PET bottles, rubber tire, electronic waste which are not easily recycled and reused for different purposes by partial and complete replacement of aggregates and also as addition of materials. Use of plastic waste in concrete is not new. Different types of plastic waste are used in different forms in concrete to enhance its properties. One of commonly used plastic waste used in concrete is use of PET waste [2,3,4]. With addition of rubber tire mix is beneficial for improving thermal It was  [2,3]. Also, the pellets made from PET or other forms of plastic can be used beneficially as partial replacement of fine aggregates [5] and coarse aggregates [6,7] or as shredded ties [4,8]. When replaced as a fine aggregate, up to 2 % replacement, the compressive strength, split tensile and flexural strength increases [5]. When replaced as coarse aggregates, 20 % replacement showed acceptable strength [7]. Slump of fresh concrete increases with addition of pellet shaped PET aggregates and decreases with flakier plastic aggregates. With the addition of plasticizers, the workability increases by 10 % to 15 % and compressive strength by 5 % [9].
In this study, waste nylon cable ties, a form of plastic wastes are being used. Nylon cable ties are generally used for wrapping and tight packing of plastic bags in malls, aerospace, automotive, in electronics systems and military applications. Nylon Cable Ties (NCT) is a class of polymeric materials which are also known as polyamides i.e. Nylon 6/6. NCT is light weight, possesses high tensile strength and is more sustainable. In this study, replacement of fine aggregates and addition of waste NCT both are studied. fine aggregates (M-Sand) are replaced with 1%, 2%, and 4% of waste NCT by weight and the waste NCT is added by 0.5%, 1%, 1.5% of total weight of fine aggregates in concrete. The grade of concrete considered in the study is M40.

Materials used
Ordinary Portland cement of 53 grade was used for this study. The results of the basic tests conducted on cement like normal consistency, initial and final setting times, and specific gravity are tabulated in Table 1. Aggregates smaller than 4.75mm and up to 0.075mm are considered as fine aggregate. M-Sand conforming to Zone-II was used as fine aggregate. Various tests were conducted to ascertain the basic properties of the materials such as cement and aggregates. The results are tabulated in Tables 1  and 2. Aggregates greater than 4.75 mm are considered as coarse aggregates. 20mm and 10mm size aggregates were used in the ratio of 3:2. Nylon cable ties were used in varying lengths of 0.3mm-50mm and 2.5mm thickness.

Methodology
The main aim of conducting this study is to find the effectiveness of waste nylon plastic ties both as a replacement and addition to concrete in place of fine aggregate. The experimental investigation is planned as follows: 1. To evaluate the relevant properties of the materials such as cement, sand, coarse aggregate 2. To obtain mix proportions of OPC concrete for M40 using IS Code:10262-2009. The waste NCT are used for replacement of fine aggregates (M-Sand) in varying percentages 1%, 2%, and 4% of waste NCT by weight. Also calculate the mix proportion with waste NCT in concrete for addition by 0.5%, 1%, 1.5% of total weight of fine aggregates. 3. To prepare the concrete specimens such as cubes for compressive strength, cylinders for split tensile test, prisms for flexural strength and also cubes for durability studies in laboratory. 4. To evaluate the mechanical properties of concrete such as compressive strength, split tensile test and the flexural strength. 5. To conduct the durability studies such as water permeability, porosity and water absorption on the specimens. 6. To compare the results for addition and replacement.

Mix design
The mix design for M40 grade of concrete was carried out as per IS 10262:2009. The proportions of the materials used in the present study are given in Table 3.  In this study, the mix proportions of waste NCT is carried out both for partial replacement of fine aggregate by its weight and also for the addition by the total weight of the fine aggregates. The various proportions of the components used for carrying out the experimental studies has been tabulated in Table 3.

Test Results of Hardened Concrete
The tests conducted on hardened concrete were compression, flexure and split-tension. Figures 6 to 8 indicate the compression, split tension and flexure tests on specimen. The graphs for the test results related to compressive, split tensile and flexural strengths for varying percentages of waste NCT dosages are shown in Figures 9 to 14 for both addition and replacement. The results of compressive, split tensile and flexural strength for varying percentages of waste NCT ties for replacement of M-sand are as given in Table 4 and for addition are given in Table 5.

Compressive Strength
Cube specimens of 150 mm x150 mm x150mm size were casted and tested on a digital compressiontesting machine in accordance with IS 516-1959 for the compressive strength. The compressive strengths of cubes were varied from 39.52MPa to 40.52 MPa for waste NCT ties varying from 0% to 4% replacement of fine aggregates and the peak strength of 43.65 MPa was obtained at 2% replacement. In case of addition of waste NCT ties, the compressive strengths were varied from 39.52 MPa to 40.86 MPa and the maximum strength of 46.43 MPa was obtained at 1% addition. When compared with the results of replacement and addition, better results were obtained for 1% addition of waste NCT ties Table 3. Proportion of NCT by replacement of fine aggregate and addition for one m 3 of concrete  Table 5. Compressive, split tensile and flexural strength test results for addition of NCT Note: NCTA 1% indicates addition of waste nylon ties by 1% by weight of fine aggregates.

Split-Tensile Strength
Cylindrical specimens 200mm long and 100mm in diameter were casted and tested for tensile strength on a digital compression testing machine in accordance with IS 516-1959. The split tensile strength of the cylinders increased from 4.25MPa for control specimens to 4.82MPa and a peak strength of 5.08 MPa was obtained for a replacement of 2% waste NCT ties. In case of addition of waste NCT ties, the strength increased from 4.25MPa and peaked to 5.84MPa at 1% addition and decreased further. When the test results of replacement and addition were compared, better results were obtained for 1% addition of waste NCT ties.

Flexural Strength
Beam specimens of dimension 100 mm x100 mm x500mm were casted and tested on a flexural testing machine in accordance with IS 516-1959.The flexural strength of the beams increased from 7.5 MPa to 7.92 MPa for waste NCT ties varying from 0% to 4% replacement of fine aggregates. The maximum flexural strength of 11.5 MPa was obtained for 2% of replacement of waste NCT ties. In case of addition of waste NCT ties, the strength increased from 7.5MPa and peaked to 10.95MPa at 1.5% . When the test results of replacement and addition of waste NCT were compared, better results were obtained for 1.5% addition of waste NCT ties. The percentage increase in mechanical strength properties of concrete specimens for replacement and addition of waste NCT are presented in Table 6.

Durability Tests
Durability of concrete is a major concern in the life cycle of concrete. Concrete is structurally strong enough to sustain the external loads but concrete structures may fail due to external environmental effects. Durable concrete will be always retain its original form, stability, quality serviceability when exposed to environment. Therefore, it necessary to conduct durability tests on concrete to test its sustainability. In this study different durability tests like water permeability and effect of temperature on cube specimens of size 150mm x150mm x150 mm after 28days of curing were carried out.

Water Permeability
Water permeability test is conducted for to understand the ability of concrete to allow the movement water or fluids. Cylindrical specimens of 150mm height and diameter were casted to carry out the tests as per IS 3085:1965. An air pressure of 10 kg/cm 2 was applied. The test results of permeability obtained for 7, 14, 28, 56 and 90 days are presented in Table 7.

Temperature Test:
The test was conducted to determine the effect of temperature on strength of concrete. Cube specimens of dimensions 150mm x 150mm x 150mm were used to find out the compressive strength affected by temperature. After demoulding the cubes from moulds, it was cured for 28 days. After curing, the cubes were kept in oven for a period of one hour at 100 0 C maintaining a constant temperature as shown in Figure 15. After one hour the cubes were taken out from the oven, and allowed to be cooled. The compressive strength was tested and value was recorded [10]. The reduction in the compressive strengths of the specimens after conducting the temperature test are presented in Table 8. As observed from the test results there is a reduction of compressive strength for both replacement and addition of waste NCT ties. The reduction in compressive strength is more in case of replacement of NCT ties. Figures 18 and 19 depict the reduction in compressive strengths in the temperature test.