Rapid urbanisation, and infrastructure development and maintenance, are ‘eating’ up a huge amount of natural resources, such as limestone, sand, aggregates and water.
Cement production, used in concrete making, is globally the most energy intensive process. It is estimated that for every tonne of Portland Cement produced 1.6 tonnes of limestone are removed from the ecosphere (Sant, 2020). The processing of limestone to cement requires a vast amount of energy. According to the Intergovernmental Panel on Climate Change, for every tonne of cement produced there is a one and a quarter tonnes equivalent of CO2 released, (Fischedick M, 2014). In 2015, cement production is estimated to have contributed to 2.8 billion tonnes of CO2, equivalent to 8% of global CO2 consumption, R. Andrew, 2018). As a result the use of cementitious materials to replace cement and lower the negative environmental impacts of the concrete industry is increasingly sought after. Pulverised Fly Ash (PFA), from the burning of coal in power plants has traditionally been used to replace cement in the UK. However, transition to renewable sources of energy and the use of biomass to substitute a portion of coal in power plants has brought a change in the quality of PFA less of it is now being used to replace cement. (Millward-Hopkins et al., 2018) Alternative solutions are increasingly being investigated (Benghida, 2017).
Residual fractions of Municipal Solid Waste (MSW), comprises of household waste collected by local authorities or commercial companies that contain a diverse range of materials; such as packaging, food waste and general refuse. Incineration with energy recovery, is a well-established and widely implemented residual MSW management approach in the UK, reducing the residual MSW mass by 80-85% (Zeng et al., 2020). The process burns waste and produces unstable by-products, namely bottom and fly ash. Fly ash presents a challenge for waste contractors as it contains leachable heavy metals, chlorides and organic contaminants. However, the majority of fly ash components are rich mineral sources of silica and lime, making it a suitable alternative as a raw feed material for cement production (Tosti et al., 2018).
The physio-chemical and mineralogical characteristics of incinerated fly ash, is identified by coarser and wider sized grading than that of typical cement, containing high soluble fractions of chlorides and sulphates. The high fractions within the fly ash yield higher water reductions. When fly ash substitutes 20% of cement by mass in the total cementitious volume, water demand is reduced by approximately 10% (Zeng et al., 2020). A study sound that the performance characteristics of mortars produced with cement that has a 10-20% weight (wt.) incineration fly ash content, can increase mortar setting times and meet the minimum strength requirements. (Zeng et al., 2020). Moreover, efforts have been made to produce environmentally friendly cementitious material from blends containing partial amounts of incineration fly ash. It was shown that its use in replacing cement can reduce the carbon footprint of concrete up to 40%, thus minimising the global warming effects (Zeng et al., 2020).
The incorporation of waste by-products, such as incineration fly ash, in the manufacture of Portland Cement can create synergies between the concrete production and waste management industry, delivering a sustainable solution to the efficiency problems faced by both industries. However, further investigation concerning raw mix parameters and conditions adjustments are needed in order to; enhance the feasibility of the process, can relieve the pressure of landfills, reduce the CO2 production during cement processes, produce electricity during waste incineration and achieve the concept of zero waste production.
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References
Benghida, D., 2017. Concrete as a Sustainable Construction Material. Key Engineering Materials, 744, pp.196-200.
Fischedick M., J. Roy, A. Abdel-Aziz, A. Acquaye, J.M. Allwood, J.-P. Ceron, Y. Geng, H. Kheshgi, A. Lanza, D. Perczyk, L. Price, E. Santalla, C. Sheinbaum, and K. Tanaka, 2014: Industry. In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlömer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA
Millward-Hopkins, J., Zwirner, O., Purnell, P., Velis, C., Iacovidou, E. and Brown, A., 2018. Resource recovery and low carbon transitions: The hidden impacts of substituting cement with imported ‘waste’ materials from coal and steel production. Global Environmental Change, 53, pp.146-156.
M. Andrew 2018: Global CO2 emissions from cement production ()
Sant, G., 2020. New Technique Could Make Cement Manufacturing Carbon-Neutral. [online] Phys.org
Tosti, L., van Zomeren, A., Pels, J. and Comans, R., 2018. Technical and environmental performance of lower carbon footprint cement mortars containing biomass fly ash as a secondary cementitious material. Resources, Conservation and Recycling, 134, pp.25-33.
Zeng, C., Lyu, Y., Wang, D., Ju, Y., Shang, X. and Li, L., 2020. Application of Fly Ash and Slag Generated by Incineration of Municipal Solid Waste in Concrete. Advances in Materials Science and Engineering, 2020, pp.1-7.
I’m Sajni a third year BSc Environmental Sciences student at Brunel and am passionate about providing long-term value to the construction industry on sustainable solutions that lead to change and influence policy.
As 小湿妹视频’s Environmental and Ethics Officer, I am the student representative and voice on tackling environmental issues, opening up relevant dialogues and debates relating to sustainability, discussing ideas and managing campaigns. I eventually became the student advocate on fossil-fuel divestments during an Environmental, Social and Governance (ESG) campaign, producing a report and highlighting the relative importance for the university to consider its interactions with institutions.
As an advocate of the sustainability agenda, I believe it is becoming increasingly important in the current climate crisis and will continue to do so both during the pandemic and the years following it.