Cement Works: Reducing Air Pollution, Saving Our Skies

The cement industry is a significant contributor to air pollution, releasing large volumes of greenhouse gases and other atmospheric pollutants. The production of cement requires substantial energy consumption, with the burning of fossil fuels and the chemical process of converting calcium carbonate lime into calcium oxide lime being the main sources of CO2 emissions. Other harmful emissions from cement works include nitrogen oxides, sulphur dioxide, carbon monoxide, methane, and particulate matter. These emissions have severe effects on human health and the environment, causing respiratory issues, ecological imbalances, and climate change.

To reduce atmospheric pollution from cement works, several strategies can be employed. These include adopting cleaner production technologies, improving energy efficiency, using alternative fuels and raw materials, and implementing stringent emission controls. For example, the use of cleaner-burning kiln fuel and renewable energy sources can help reduce air pollution and greenhouse gas emissions. Additionally, replacing a portion of the cement used in production with lower-carbon alternative materials, such as fly ash, bottom ash, and slag, can also reduce emissions. Implementing carbon capture, utilisation, and storage technologies can significantly mitigate CO2 emissions, but only if powered by clean energy.

Using industrial waste as a cement substitute

Cement manufacturing is a major source of pollution, contributing to around 8% of annual global carbon dioxide emissions. The process involves heating limestone to extremely high temperatures, releasing carbon dioxide and consuming large amounts of energy. As such, there is a growing interest in reducing carbon emissions related to concrete. One approach is to use industrial waste as a substitute for cement.

Industrial waste can be utilised as a supplementary cementitious material or in cement-free concrete to reduce the demand for cement. Two types of industrial waste, in particular, have been identified as effective substitutes for limestone in cement production: residual materials from kaolin production and residual materials from aluminium production. These materials contain no carbon dioxide, meaning they can be used to produce large quantities of high-quality, climate-friendly cement without releasing additional carbon dioxide.

Other industrial by-products such as fly ash, metakaolin, silica fume, and ground granulated blast furnace slag can also serve as cement substitutes in pervious concrete. By substituting up to 20% of cement with these materials, we can reduce cement consumption, carbon footprint, energy usage, and air pollution associated with conventional cement production.

In addition to industrial waste, agricultural waste and construction waste can also be incorporated into concrete production. For example, sugarcane bagasse ash and nano eggshell powder have been used as cementitious materials to reduce cement content in the concrete industry. Furthermore, concrete recycling is becoming increasingly common, with old concrete rubble being used as aggregate in new concrete mixtures.

Reducing dependency on cement demand

Reducing the dependency on cement demand is a crucial aspect of mitigating the environmental impact of the cement industry. Here are some strategies and measures to achieve this:

Enhancing Manufacturing Technology for Cleaner Production

The cement industry can adopt cleaner production techniques to reduce pollution. This includes improving the manufacturing technology in cement plants to minimise dust, noise, and greenhouse gas emissions, especially carbon dioxide. Using industrial waste as a supplementary cementitious material or exploring cement-free concrete alternatives can also help reduce the demand for cement.

Alternative Materials and Binders

One way to reduce cement demand is by utilising alternative materials that are economically viable and have a lower environmental impact. For instance, the use of industrial waste or alternative binders, such as fly ash, bottom ash, or slag, can reduce the amount of cement needed while also enhancing the strength and durability of concrete. These by-products from other industries would otherwise end up in landfills, so incorporating them into concrete mixtures is a more sustainable option.

Optimising Cement Usage and Material Efficiency

Optimising cement usage and adopting material efficiency strategies can significantly reduce cement demand. This can be achieved by minimising over-design, maximising the lifetimes of buildings and infrastructure, and promoting resource-efficient manufacturing. Additionally, adopting precast concrete components and performance-based concrete design can also help reduce the amount of cement required.

Carbon Capture and Storage (CCS)

While not directly reducing cement demand, implementing CCS technology plays a crucial role in decarbonising the cement industry. Capturing and storing carbon dioxide emissions can help balance out the carbon footprint associated with cement production. This strategy is particularly important when used in conjunction with other demand-side interventions to achieve net-zero emissions.

Policy Interventions and Standards

Policy interventions and revisions of standards can greatly influence cement demand. Governments can implement regulations, financial incentives, and building codes that promote the use of low-clinker cements and alternative binders. Additionally, policies that encourage material efficiency, circular economy principles, and the development of net-zero cement and concrete are essential.

Research and Innovation

Continued research and innovation are vital to reducing the dependency on cement demand. This includes exploring new technologies, such as electric kilns, alternative fuels, and novel cement recycling methods. By investing in research and development, the industry can identify more sustainable alternatives and improve existing processes to minimise the environmental impact of cement production.

Using alternative materials with lower environmental impact

The cement industry is one of the largest producers of carbon dioxide, a greenhouse gas, and is responsible for up to 8% of worldwide CO2 emissions. The production of cement involves firing materials such as limestone and clay in a kiln, which releases carbon dioxide from the energy used and the chemical reaction of the mixture.

To reduce the environmental impact of cement works, alternative materials with lower environmental footprints can be used. Here are some examples:

Green Concrete

Green concrete, developed in Denmark in 1998, uses waste material from power plants, mining, quarrying, and incinerator residue as a substitute for cement. It requires less energy for production, resulting in lower carbon dioxide emissions and reduced environmental damage. It is also more durable, requires less maintenance, and is more cost-effective.

Ashcrete

Ashcrete is a greener alternative that utilizes fly ash, a waste product from coal combustion, as a replacement for cement. It increases the strength, resilience, and durability of the mixture while being cost-effective. However, it takes longer to set and develop strength compared to traditional concrete.

Micro Silica/Silica Fume

Micro silica, also known as silica fume, is an ultra-fine powder byproduct from silicon metal industries. It offers strength enhancement and corrosion resistance by reducing the permeability of the concrete mixture. It can replace between 7-12% of the cement found in traditional mixes, but it makes the construction process more complex as the resulting substance is less workable.

Blast Furnace Slag

Blast furnace slag is obtained from steel manufacturing and refined into ground granulated blast furnace slag (GGBFS). Its fine nature makes it highly workable and reduces permeability. However, it has low initial strength and a longer setting time, making it unsuitable for emergency works.

Recycled Concrete

Instead of leaving concrete debris as rubble during demolition, it can be deconstructed and recycled for new building projects. This reduces CO2 emissions and offers benefits such as greater stability and enhanced production turnaround.

Grasscrete

Grasscrete is a sustainable alternative for paving that involves laying concrete with patterns for grass and flora, creating a natural element to walkways and flooring. It improves rainwater absorption and drainage, and the incorporation of flora means less concrete is needed.

Recycled Plastic Waste

Incorporating recycled plastic waste as an aggregate in concrete can help reduce CO2 production and transportation costs. However, it can potentially weaken the strength of the material as plastic doesn't mix well with sand.

Mycelium

Mycelium, sourced from miniscule threads in mushrooms, forms a dense, durable, and naturally fire-resistant material when mixed with organic matter. While it is less strong than standard concrete, it is significantly lighter and more environmentally friendly.

Hempcrete

Hempcrete is made from hemp fibres, which are easy to grow and produce, making it an accessible and sustainable option. It is lighter than traditional concrete and has superior thermal properties.

Reducing fugitive emissions

Fugitive dust emissions are a major source of environmental pollution during cement manufacturing. Dust is generated during transportation, loading, and unloading of the clinker to be deposited outside the silo.

• Use of dry processes instead of wet processes for making cement.
• Collection and recovery of dust from grinding raw materials.
• Use of electrostatic precipitators (ESPs) to capture fugitive dust emissions. ESPs should remove more than 98% of particulates, so the amount of particulate emissions of fugitive dust into the atmosphere will be in a range of 1% to 2% only.
• Use of wetting the source material or installing barriers to prevent dust from leaving the source area.
• Use of ventilation systems in conjunction with hoods and enclosures covering transfer points and conveyors.
• Minimising drop distances by using adjustable conveyors.
• Wetting down dusty areas such as roads to reduce dust generation.
• Providing appropriate stormwater and runoff control systems to minimise the quantities of suspended material carried off-site.
• Use of dust collectors - a dust collector (bag house) is a typically low-strength enclosure that separates dust from a gas stream by passing the gas through a media filter.
• Use of cyclones - dust-laden gas enters the chamber and forms a vortex, with larger particulates pushed outward and forced against the chamber wall, while cleaned air swirls upward and exits through an outlet at the top.
• Use of electrostatic precipitators - in an electrostatic precipitator, particles suspended in the air stream are given an electric charge and then removed by the influence of an electric field.

Implementing carbon capture and sequestration technologies

• Select an appropriate carbon capture technology: Different carbon capture technologies such as amine scrubbing, calcium looping, oxy-combustion capture, and direct separation can be considered. The selection should be based on factors such as technology readiness, compatibility with existing cement plant infrastructure, and cost-effectiveness.
• Retrofit existing cement plants: Retrofitting involves modifying existing cement plants to accommodate carbon capture technology. This may include changes to preheaters, precalciners, kilns, and coolers to make them "carbon-capture ready." It is essential to conduct a thorough assessment and select the most suitable technology for retrofitting.
• Pilot testing: Before implementing carbon capture technology on a large scale, it is crucial to conduct pilot tests to evaluate the technology's performance and feasibility. This involves setting up a small-scale demonstration project to gather data and optimize the technology for the specific cement plant conditions.
• Address technical challenges: Carbon capture technologies may face technical challenges, such as energy requirements, process integration, and by-product management. It is important to thoroughly understand these challenges and develop strategies to overcome them.
• Collaborate with experts: Collaborating with experts in carbon capture and sequestration can help cement works access the necessary technical knowledge and expertise. Partnering with research institutions, technology providers, and experienced consultants can facilitate a smoother implementation process.
• Invest in research and development: Investing in research and development can help cement works stay abreast of emerging technologies and innovations in carbon capture and sequestration. This includes exploring advancements in areas such as carbon capture readiness, process integration, and energy efficiency.
• Engage with policy and regulations: Staying informed about relevant policies, regulations, and incentives related to carbon capture and sequestration can help cement works make strategic decisions. Engaging with policymakers and industry associations can also influence the development of supportive frameworks.
• Explore commercial opportunities: Implementing carbon capture and sequestration technologies may open up commercial opportunities for cement works. For example, captured carbon dioxide can be utilized for enhanced oil recovery or sold to other industries for utilization or storage.
• Monitor and optimize performance: Continuous monitoring and performance optimization are crucial for the successful operation of carbon capture and sequestration technologies. This includes regular maintenance, data analysis, and process adjustments to ensure the technology functions efficiently and effectively.
• Promote knowledge sharing and best practices: Sharing knowledge and best practices within the cement industry can accelerate the adoption of carbon capture and sequestration technologies. Cement works can collaborate and learn from each other's experiences to improve the implementation process.
• Address financial considerations: Implementing carbon capture and sequestration technologies may involve significant financial investments. Cement works should carefully evaluate the economic viability, considering capital costs, operational expenses, and potential revenue streams associated with carbon capture and utilization.

Frequently asked questions