Carrying the title for the sixth most populated metropolitan city in the world, Karachi also has to deal with the largest waste management crisis in the country. With an ever growing population, currently summing up to 22.8 Million and without a firm waste management system, the city streets seem to disappear under piles of debris. Furthermore, being the financial capital of Pakistan, leads to an increase in industry and labour growth, which eventually leads to residential and commercial development, increasing the demand for concrete. Cement manufacturing is responsible for 4.5 percent of the worlds CO2 emissions, replacing a small amount of it with plastic could reduce the Karachi's overall carbon footprint.
(Source: News Geography | MIT news)
Figure 1 - Plastic bottle waste in Karachi's Sultanabad district (Jang News)
In a year Pakistan produces 162.3 Million metric tons to CO2 out of which concrete production is responsible for 7%, which equals 11.36 Million metric tons per year. If 1.5 percent on cement is replaced with recycled plastic it could bring down CO2 emissions from 11.36 Million metric tons to 11.19 Million metric tons, which may seem like a fraction of the amount but over time up until 2030 Pakistan can achieve a total reduction in 2.04 Million metric tons of CO2.
(Source: World Bank | Book - Sustainability, Innovation and Entrepreneurship)
The process starts with recycled plastic flakes that are used to make water and soda disposable bottles, being put through gamma radiation(1), which is then crushed to form a fine powder, later mixed with Ordinary Portland cement, fly ash(2), limestone and clay and set to cure in cylindrical molds(3). When this specimen of concrete is put to the test, it shows a 15% increment in its strength carrying capacity compared to the ordinary cement mix and this strength can be varied with gamma radiation provided to the specimen, the more the plastic is irradiated, the more strength it can uphold.
(Source: MIT News)
Hence, going forward with this approach could really help tackle Karachi's waste crisis and help reduce the city's carbon emissions from cement production, also create awareness amongst citizens for the importance of recycling and help create more recycling plants eventually creating more employment opportunities.
 Gamma Radiation: A high frequency radiation in the electromagnetic radiation spectrum.
Figure 2 - Spectrum of Electromagnetic Radiation
 Fly Ash: Also known as Coal ash, it is a byproduct of coal burning at coal energy production plants.
 Cylindrical Molds: It is an object with two flat circular ends joint together to form a perfect cylinder, used to mold concrete into a desired cylindrical shape.