Using Post-Use Plastics As Partial Aggregates In Construction

The Growing Environmental Problem of Plastics

One of the enduring environmental problems of modern times is the increasing production and use of plastics, which are then difficult to recycle because they take a very long term to decompose, straining fragile ecosystems. Research shows that the world buys a million plastic bottles each minute  and the global plastic consumption is envisaged to reach half a trillion bottles by the year 2021; this will outstrip all efforts aimed at recycling and poses a big danger to ecosystems, particulalry coastlines, oceans, and other environments, according to Laville and Taylor (2017). the production of plastics has grown tremendously over the years, from 50 million metric tons in 1976 to a high of 311 million metric tons in 2014, according to DW (Deutsche Welle) (2017). Further, most products made from plastics are disposal products instead of being used to make lasting products. On average, each person uses about 45 kilograms of plastic yearly, although the use varies from region to region. For instance, China produces 26% of plastic in the world, but japan is the largest consumer per capita. The demand for cement is also rising and this is placing a major strain on the environment as sand must be harvested for use with cement in construction. As a consequence, some governments have enacted laws to regulate or ban sand dredging because of its adverse environmental effects. India for instance, is facing a major problem in environmental degradation due to sand dredging from riverine and other ecosystems led by a ‘sand mafia’ fueling the $ 120 million building boom (Hawley, 2017), (Romig, 2017)and this has led to bans being imposed on sand dredging (Jha 2017). Because of the twin challenge of sand dredging that damages ecosystems, especially riverine and coastlines, and the environmental disaster that is plastics, new sustainable approaches are needed to solve the twin environmental challenges. Further, the world is facing a shortage of sand (Greene, 2017), (Torres, Liu, Brandt & Lear 2017)even as the construction boom continues unabated in some regions, especially fast growing economies like India and China. Among the proposals that have been put forth is to use plastics in construction; however, before this can go mainstream, a better understanding of how plastics perform in concrete when used in construction, especially because most of this plastic will be recycled and not originally intended for use with concrete. This paper will start with a detailed literature review of the topic, followed by a description of the project aims and objectives as well as a research question(s). A brief description of the research methodology and experimental set up will be discussed an evaluation done before drawing conclusions.  A project plan to undertake the research will then be outlined.

The Sand Shortage and its Environmental Impacts

Sand is among the major components used in building construction that has supported civilizations from ancient times to the present. With the increased construction boom, such as mega cities in China and much of the world, one would be forgiven for thinking they are looking at sand castles. However, sand is finite and it is already a cause for major conflict. Sand resources are getting depleted with annual demands hovering around 40 billion metric tons (Campbell 2015). the most common sand type is quartz and although one would assume deserts have limitless amounts of sand, the sand is not applicable in construction because wind has eroded it and not water, making the particles round and difficult to stick together, leaving only beach and river sand as the remaining viable alternative sand sources (Campbell 2015). The world is facing a plastic glut, that is everywhere, from the food table to the ocean floor and in water bodies, with numerous plastic gyros. A new problem is that some gut bacteria survive treatment to destroy them by attaching to plastics and ending up in water bodies (Montgomery 2017). The cost of construction is increasing daily as the sand shortage continues to bite; Thosar and Husain (2017) have proposed a solution to reduce construction costs by replacing sand with plastic waste. The use of plastic waste will solve several problems, including using recycled plastic to create a new product that can be used as an alternative to sand aggregate. Apart from lowering construction costs and helping solve the plastc problem by recycling it, the approach will also save fragile ecosystems and fauna, given that only beach and riverine systems sand is the most utilized and most suitable sand for use in building applications (Thosar & Husain, 2017).

Ismail and Al-hashimi (2008) undertook an experimental test to test if plastic can safely be used in concrete as an aggregate replacement. Using 254 tests in 86 experiments, the researchers tested the fresh density, slump, compressive strength, dry density, and toughness indices at room temperature by partially replacing sand in concrete at amounts of 0, 10, 15, 20% of sand with 800 kg concrete mixture. The mixtures were cured for between 3 an 28 days and the results showed that r3cycle plastic can safely be used to substitute sand in concrete aggregates; plastic reduced micro cracking and offers a huge promise in reducing materials cost and help solve some of the waste problems due to plastic. Marzouk, Dheilly and Queneudec (2017) investigated the value that recycled/ used plastic waste wold have when used in cement concrete composites using an experimental design. The researchers investigated the mechanical characteristics and densities of composites produced by adding various percentages ranging from 0 to 100% of post consumer plastic to concrete composites. Using electron microscopy, the relationship between composite micro-structure and mechanical properties were evaluated. The results show that substituting sand with plastic at levels below 50% (volume) did not affect the flexural and compressive strength of composites. Shredded used plastic can be successfully used to substitute sand in cement concrete composites without affecting the properties of the concrete composite. Hama and Hilal (2017) investigated the effect of fresh properties for self compacting concrete ( SCC) when plastic waste was used as replacement. Using different mixes of SCC with constant water to binder ratio of 0.32 to 520 kg per square meter  and 30% weight fly ash was used to replace cement. Different plastic contents or varying coarseness was added to the SCC and the V funnel flow time, L-box T40 and T20 flow times, slump flow diameter, L-box height ratio, 20 day SCC compressive strength, and the T50 slump flow times workability properties were tested.  The results show that plastic waste can be used as a substitute fine aggregate in SCC. Vanitha, Natarajan and Praba (2015) explored if waste plastics can be utilized partially to replace coarse aggregates in concrete blocks on the backdrop of rapid urbanization and industrialization. The rapid development in infrastructure, the researchers reasoned, results in several adverse effects such as construction materials shortages and increased waste production, including plastics while sand resources are increasingly exploited to provide the sand needed for use n concrete construction. The authors researched the use of plastics to replace sand in construction materials, researching on the M20 concrete aggregate. The researchers used between 0 and 10% plastic as replacement for aggregate with varying degrees of aggregate coarseness. The researchers casted various solid blocks and paver blocks and their physical characteristics tested using plastic to replace designated amounts of aggregates in M20 concrete. The compressive strength tests on the blocks was 2% for solid blocks and 4% for paver bocks, showing that plastic can be safely used as an aggregate replacement in concrete and used in construction.

Recent Studies on the use of Plastics in Concrete

This proposed research aims at determining the suitability of using plastic, specifically post use plastic such as used plastic bottles as a replacement for sand aggregates in concrete. In particular, the objective is to determine the amounts of plastics that can safely be used as sand aggregate replacements in construction concrete

• What is the compressive strength of concrete in which varying amounts of post-use plastic has been added to replace sand aggregates?
• What is the safe limit of plastics that can be added to concrete for application sin the building industry?
• How does plastic particle size affect the compressive strength of concrete when used as an aggregate?
• Can plastics be used to replace sand aggregates in concrete mixes or it should be used as a partial replacement?

This proposed research is motivated by present events relating to costs, environmental degradation and what to do with the enormous volumes of plastics being produced that will soon overtake recycling efforts, as discussed in the introduction. The successful use of plastic as a replacement for sand, either fully or partially will greatly reduce pressure on the environment, especially on riverine and water bodies that suffer adverse effects of sand dredging, affecting communities and ecosystems adversely. This proposed research hopes to solve two problems using a ‘single stone’ by enhancing plastic recycling efforts, easing their adverse environmental effects while helping lower the cost of building houses, a critical aspect of helping ensure more people in the world can afford decent housing. This research has the goal of determining, through an experimental research, the safe limits of plastic quantities that can be used to replace sand in concrete mixes; this paper hopes to fully and satisfactorily answer the research questions listed above.

plastics take thousand s of years to decompose naturally, making them tough substances that can last for a long time. Further, plastics are light, being lighter than sand aggregates by 70%. this means that sand can effectively be used in construction as a concrete aggregate to achieve reduced weight per volume of the concrete. Tests have shown that the compressive, flexural, modules rupture, and indirect tensile strength of concrete decreases as the amount of plastic used as aggregates in the concrete increases, however, the fresh weigh of the concrete decreases and also leads to changes in module failure to more ductile than brittle failure (Jibrael and Peter 2016).  This research will therefore be conducted with the following hypothesis;

Post-use Plastic can Safely be used in Construction as a partial Aggregate Replacement in Non-Structural Applications; it Will Improve Failure to be More Ductile rather than Brittle.

This proposed research will make use of an experimental research design where variables will be tightly controlled, with a control variable also being used. The experimental research design is the most suitable for this kind of experiment because it allows for randomization to ensure the outcomes are valid and reliable and to reliably create homogeneous groups of treatment and eliminate possible biases and judgments. The randomization concept also enables objects to be assigned randomly using only the criteria of chance to experimental groups (Glennerster & Takavarasha 2013).   

Experimental Findings on the Use of Plastics as Aggregates in Construction

This proposed research will use concrete in the ratio of cement to sand to gravel as 1:1.67:2.5 with the ratio of water being 0.46 as shown below;

Material	Specifications
Cement	Portland cement
Sand	Fine aggregate sand having an sg (specific gravity) of 2.7
Water	Fresh water
Grave	Gravel with sg of 2.72 and maximum sizes of 12.5 mm

To this mixture, post use plastic will be added in different quantities and mechanical properties of the concrete mix done. The plastic to be used is recycled ones added in the percentages of 0% (control), 1%, 5%, 10%, 25% and 100% from the sand used in the concrete. The plastics will be washed and ground to give articles with an sg of 1.04. The gravel and sand will be mixed first in an electrical mixer for a minute and cement added with water added gradually and mixed until a homogeneous concrete mixture is formed. Molds will be used for casting after cleaning and oiling and placed on a level location. Concrete will be poured onto the molds and the surfaced levelled using a trowel and marked for reference. The molds will be placed on a flat level place for 24 hours. The molds will then be placed in a curing tank for between 7 and 28 days. The following tests will then be done on the concrete at different plastic percentages as replacement (partial for sand).

Test	Description
Slump test	This is a test designed to determine concrete consistency/ stiffness. This test shows how much water is in a mix and should match the desired value for finished products of between 7 and 9 mm (Klieger & Lamong 2011)
Concrete hardness test	This will be done after having the samples dry for half an hour.
Compressive strength test	Is a common test for hardened (cured) concrete and is the most significant test for structural purposes. Compressive tests will be undertaken based on the BS EN 12390>3 when the concrete is 7 days old and at 28 days old (Choo & Newman 2003)
Flexural strength test	This will be used for testing rupturing modulus of the concrete using a central point load (Choo & Newman 2003)
Indirect tensile strength	This will be based on the ASTM C496-62T standard where a cylinder is compressed along 2 diametrically opposite axial lines through plywood bearing strips. Compressive load is distributed over a small width by the plywood cushion, sufficient enough to eliminate undue stress concentration while compensating for irregularities on the surface. A transverse tensile stress is produced by the compressive force which remains constant along the sample vertical diameter (Richardson 2003)

The results of the compressive strength tests for hardened concrete will be obtained using the relation f cu =P/A to obtain compressive stress in MPa. The compressive stress will be obtained at 7 days and at 28 days for varying percentages of added used plastic to the concrete mix. The indirect tensile strength of the concrete samples will also be obtained at different percentages of plastic at 7 and 28 days using the relation  f ct = 2 P/π DL. Finally, the Flexural strength will also be obtained at the same quantities of plastic at 7 and 28 days intervals using the relation ft = MC/I. In this set up, the plastic used is the independent variable while the compression stress, the flexural strength, and the indirect tensile strength of the concrete mixture is the independent variable. The tests will show if plastic can be used to substitute sand in concrete mixes safely without a significant degradation in the desired mechanical properties of concrete for compression stress, flexural strength, and the indirect tensile strength and the different percentages of plastic that can be used. 

Conclusion

This research proposal is aimed at determining if post use plastic can be used as a replacement, either partially or in full for sand aggregates for concrete used in construction. The research is important because plastic wastes has become a crisis with consumption projected to continue increasing yet biodegradability of plastic takes far too long, up to thousands of years. This has created a pollution crisis (of plastic), from land fill to sea beds. Further, increased construction has seen increased dredging for sand, usually from beaches and riverine systems, disturbing fragile ecosystems and creating a new environmental menace. Proposal have been made for use of plastic as an aggregate in construction concrete to help reduce plastic waste menace by recycling it and ease pressure on beaches and riverine systems sand dredging. Using an experimental research design, the compression stress, the flexural strength, and the indirect tensile strength of concrete with varied amounts of plastic used as aggregate to replace sand will be tested and used to either accept or reject the hypothesis that Post-use Plastic can Safely be used in Construction as a partial Aggregate Replacement in Non-Structural Applications; it Will Improve Failure to be More Ductile rather than Brittle.

Research Aim, Objectives, and Hypothesis

References

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