Miles Hogg of Lignacite explores how concrete masonry has evolved to meet the demands of the 2050 net zero deadline.
Over the years, concrete masonry has evolved to meet many challenges, including carbon reduction targets for buildings and increasingly demanding acoustic standards. Now it is faced with a new challenge: to embrace and positively improve sustainability performance in its journey towards net zero.
Concrete masonry – a description for all types of concrete blocks and bricks – is the most widely used wall material in the UK. Masonry solutions in new housing account for around 80% of the housing market, but its use is not just confined to this sector. There is also strong demand in the commercial, educational, leisure and retail sectors.
CONCRETE & CEMENT EMISSIONS
According to the Mineral Products Association (MPA), concrete and cement currently account for around 1.5% of the UK’s carbon dioxide emissions. Thanks to early action by the industry, this is five times lower than the global average (7%), but there is still far more that can be done.
The MPA has also reported that the UK’s carbon dioxide emissions from concrete and cement stood at 7.3 million tonnes in 2018. This can be broken down into the following areas:
- Around 4.4 million tonnes of ‘process emissions’ from clinker production
- 2.2 million tonnes from fuel combustion
- 0.7 million tonnes from electricity use and transport.
From this, it is easy to see that clinker production is the main source of carbon emissions in the cement and concrete industry. Clinker is the principal ingredient in cement, which forms one of the main components in concrete. Clinker’s emissions arise from the combustion of fuels in the kiln and from process emissions, which are a by-product of the chemical reaction that produces clinker.
Compared with other industries, the masonry sector uses relatively little cement in its products. For example, the cement content of a common dense block is usually between 6% and 10% of the total mix by weight, depending on the manufacturer. However, for every tonne of cement produced, around 622 kilograms of CO2 is emitted, and it remains an important contributor to the masonry sector’s carbon footprint.
To address these emissions, the cement industry has an ambitious plan to go beyond net zero by 2050. This will result in a significant reduction in CO2 emissions, which will directly benefit all cement users, including the masonry sector. Below are just some of the initiatives planned or already underway for reduction in cement carbon emissions.
PROCESS IMPROVEMENTS
Process improvements include investment in new plant and manufacturing techniques, such as artificial intelligence (AI) and automation. This will help to reduce waste with more streamlined and carefully monitored production.
Alternative fuels, coupled with substantial investment in new technology, have already helped cement manufacturers to make significant reductions in their key emissions between 1990 and 2011.
More and more UK cement plants are now routinely using carbon-neutral fuels as a substitute for virgin fossil fuels, including treated household and commercial wastes, solvents, scrap tyres and pelletised sewage sludge. Each of these materials has a high caloric value and would otherwise go to landfill or incineration without energy recovery. Burning them in the extremely controlled settings of a cement kiln is safe and has a limited impact on the environment.
According to the MPA, decarbonising the electricity grid will encourage the electrification of the industry, reducing its reliance on fossil fuels. Using technologies such as plasma energy and CCUS (carbon capture, usage, and storage) could increase the industry’s electricity use by 80% to 130%.
THE BENEFITS OF CARBON CAPTURE, USAGE & STORAGE
UK investment in infrastructure and successful industry research has enabled the use of CCUS. This transformative technology represents the most significant and technically disruptive investment in the roadmap, creating the potential for a massive CO2 reduction of 61% by 2050. However, several hurdles need to be crossed first, including additional research, and the political issue of unfair carbon prices.
LOW CARBON CEMENTS
Traditionally, an effective way of reducing the carbon footprint of cement was to replace it with a proportion of supplementary cementitious materials (SCMs). These are primarily ground granulated blast furnace slag (GGBS) or pulverised fly ash (PFA). Used in abundance by the masonry industry, these industrial waste products are unfortunately declining in availability, which means that other SCMs need to be investigated.
REDUCING EMISSIONS IN CONCRETE MASONRY
The government’s ‘Net Zero Strategy: Build Back Greener’ set out policies and proposals for decarbonising all sectors of the UK economy to meet the nation’s net zero target by 2050.
The concrete masonry sector, part of the wider precast and concrete industry, has therefore adopted the UK Concrete and Cement Industry’s ‘Roadmap to Beyond Net Zero.’
Although roadmaps are vital in setting out the vision, it will be up to individual sectors and businesses to create their own micro strategies. With this in mind, what are some of the practical steps that can be taken by the concrete masonry sector to work towards net zero carbon targets?
AGGREGATES
Aggregates are the major component of concrete blocks and bricks by volume and are inherently low-carbon products. Most are naturally occurring materials requiring little processing and are usually locally sourced. In addition to primary aggregates, suitable materials for use in concrete products include air-cooled blast-furnace slag, crushed concrete aggregate (CCA), and manufactured and lightweight aggregates, as well as some by-products from the china clay industry, sometimes referred to as stent.
INCREASED EFFICIENCIES IN THE MANUFACTURING PROCESS
Carbon reduction will be supported by investment in more efficient production processes and projects to decarbonise the factories. The latter includes investing in renewable technology to reduce the demand for primary energy.
GREENER TRANSPORT
Generally, concrete blocks and bricks are delivered by road. Investment in new fleet vehicles and reduced road transport miles will help to lower carbon emissions. This endeavour will be aided by the government’s pledge to phase out new fossil-fuel powered heavy goods vehicles by 2035.
Key properties of masonry can also contribute to beyond net zero during the operational lifetime of buildings.
TAKING ADVANTAGE OF CARBONATION
Over time, CO2 in the atmosphere reacts with the calcium oxide in concrete to form calcium carbonate, a process called carbonation. This is recognised in UK accounting of greenhouse gases. In practical terms, this means that concrete products absorb CO2 from the atmosphere during their lifetime of 100-150 years.
Over this period, carbonation will result in the reabsorption of around a third of the CO2 emitted when making cement, significantly reducing the whole-life CO2 footprint of both the cement and the concrete for which it is used. In lower strength concrete, such as blocks and bricks, carbonation is more rapid during its service life, as CO2 permeates the material more easily.
Some masonry blocks (such as Lignacite) are also produced using a proportion of graded wood particles, which further increases its carbon sequestration over the course of its lifetime.
THERMAL INSULATION
The insulation properties of lightweight and aerated concrete products are not currently factored into lifecycle assessments. Once they are, they will enhance the net-negative potential.
THERMAL MASS
Thermal mass is a concept in building design that describes how the mass of the building can prevent internal temperature fluctuations. This is typically achieved through its ability to absorb unwanted heat during the day and then release it at night with the help of ventilation from cool night air.
Concrete masonry can provide a very useful level of thermal mass and, if appropriately designed, can help to eliminate the CO2 emissions that would otherwise be used in the mechanical heating and cooling of buildings.
POTENTIAL
Overall, there is much to consider in the pathway to net zero by 2050. However, the process for carbon reduction in the concrete masonry sector is well underway and there is huge carbon-saving potential, all of which bodes well for the future.
Miles Hogg is national specification manager at Lignacite