The Global Cement and Concrete Association (GCCA) shows “20 Ways Concrete Is Sustainable”:
Concrete is the most used man-made material on earth. It forms the foundations of cities and connects communities. Without it, many of the elements of modern life we take for granted today wouldn’t be possible. Concrete will play a vital role in providing solutions to the challenges of the future and in building a sustainable world of tomorrow.
Concrete in Sustainable Communities:
Concrete has amazing sustainability benefits and we are working hard to make it even more sustainable, especially with concrete roads:
Concrete Roads:
Roads are a key enabler of development in both cities and rural areas. Concrete roads:
• Offer durable road construction
• Help lower vehicle emissions
• Reflect more solar radiation than alternatives such as asphalt
• Could enable in-transport charging of electric vehicles
• Offer solutions to the challenges of delivering best performance—enabling safety, traffic intensity and durability, and possible additional duties such as drainage—as efficiently as possible in terms of resource consumption, cost of construction, and vehicle interaction.
Typical construction methods include:
• Roller compacted concrete – RCC
• Jointed plain concrete pavement – JPCP
• Continuously reinforced concrete pavement – CRCP
• Hybrid Pavment – Visible surface is usually concrete, but a thin asphalt wearing surface can also be added—hybrid pavement. Hybrid solutions are also available with a concrete sublayer and asphalt top layer acting together to form the road structure. Cementitious solutions for soil stabilization beneath the road structure are also used. The use of concrete for soil stabilization at initial build reduces energy and material consumption, as it avoids the need to remove poor soil and replace with alternative materials.
According to MIT and others’ research on pavement vehicle interaction, stiffer and smoother roads reduce vehicle emissions. Concrete roads:
• Stiffer
• Durable—less maintenance, therefore smoother
• Help minimize vehicle emissions
• Potential to charge electric vehicles while driving, as certain concrete mixes to conduct electricity.
Albedo
Albedo is the fraction of solar radiation reflected from a materials’ surface. Concrete has an albedo of 0.4, while asphalt has an albedo of just 0.1—the higher the value, the higher the reflectivity. Concrete roads have the benefit of a higher albedo, therefore concrete has surface temperatures lower than darker solutions.
As a lighter material, CONCRETE:
• Reflects more of the sun’s radiation than other construction materials
• Reduces warming, particularly in urban areas.
• Reflect a higher proportion of solar radiation than darker materials, such as asphalt
• Mitigate the consequences of warming from CO2 emissions
• Reduce the urban heat island effect
• Reducing demand for street lighting
Geoengineering (climate engineering) aims to alleviate the impact of climate changes.
… highly-reflective surfaces—CONCRETE—
fall within the class of geoengineering “solar radiation
management (SRM)”, which focuses on increasing
the whiteness, therefore reflectivity, of urban areas
Finally, the use of concrete helps to reduce the temperature increase experienced in urban heat islands (UHI), mitigating the impacts of climate warming. Reducing UHI lowers the risk of smog, which forms in higher temperature environments, with subsequent benefits to public health.
Abundant, Local & Cost-Effective:
A key tenet of sustainable construction is the responsible use of virgin raw materials, which includes protecting availability of such materials for future generations. This is easily achieved for materials that are abundant, available, and fully recyclable—as is the case for concrete and its constituents. Concrete’s widespread availability allows local sourcing of concrete and its constituents, making it an affordable and cost-effective construction material, means the sustainability of concrete. Its durability, flexibility, resilience, etc., can be enjoyed in both developed and emerging economies.
Local sourcing benefits:
• Ensures security and availability of supply—versus materials sourced from further afield or from regions of political risk
• Minimizes the distance of transport to the construction site—limits global emissions, saves on fuel, and employee expenses
• Maximizes the scope for responsible sourcing of the concrete and its constituents—ensures environmental and social impacts of construction are well managed and minimal
• Local standards and regulations are adhered
• Imposed enhanced standards are achievable
• Economic and social benefit to the local and regional community in construction region:
—employment of local people
—paying of taxes to the local and regional governments
—patronage to local restaurants and establishments
• Stays affordable in contrast to other raw materials that face supply constraints and disruption (either practical or political) which enables the sustainability values of concrete (durability, versatility, resilience, and many more) to be enjoyed in emerging economies, where a need for the basic infrastructure of health, education, housing and transport is amplified by often significant vulnerability to the effects of climate change.
Balancing the Energy Grid
The ability of concrete to store heat could make it an important energy storage solution, helping to balance electricity grids by flexibly using renewable energy at times of peak generation.
Thermal mass is the ability of heavyweight building materials like concrete to store energy, which is later released. In summer this avoids overheating and keeps temperatures comfortable by both absorbing energy from the air and providing cool radiative surfaces. In winter, the thermal mass can absorb heat gains during the day and reradiate them in the evening. A benefit is to use the thermal storage capacity offered by the structure to provide flexibility in energy grids, thereby facilitating the uptake of renewable energy.
One of the challenges of renewable energy is the mismatch between when this energy is generated and when it is needed. In order to make the most of the energy generated by renewables, such as wind and solar, flexibility is needed in the electricity grid. Concrete buildings can shift consumer demand in time through structural thermal energy storage.
One form this can take is known as active demand response (ADR), where smart controls and energy storage help balance the electricity grid. The structural thermal energy storage capacity of a heavyweight building has huge potential—requires no additional investment costs as other storage systems. By actively preheating or precooling during off-peak times, energy is absorbed and stored within the fabric of a building, then released over the course of the next few hours. This offers several benefits for the environment. Higher use of renewable energy reduces:
• Use of fossil fuels
• CO2 emissions
• Energy bills for consumers—energy is used during off-peak times, when electricity prices are lower
• Energy grids lower peak demand, reducing the need for additional investment in power generation capacity
Carbon Uptake
It is well known that making cement produces CO2 primarily as a result of the carbon-intensive process by which its key ingredient, cement, is manufactured. BUT! What is less well known is that concrete absorbs CO2 throughout its lifecycle—known as concrete carbonation/cement recarbonation—CARBON UPTAKE!
Recarbonation is a natural process over the concrete’s lifetime that occurs when concrete reacts with CO2 in the air. The exact amount of CO2 that concrete can reabsorb has a maximum of 100% of that emitted during the calcination of limestone in the cement manufacturing process. (Process CO2 emissions; cause of about 60% embodied CO2 of concrete).
The AMOUNT of CARBON UPTAKE will depend on a range of parameters:
• Resistance class
• Exposure conditions
• Thickness of the concrete element
• Recycling scenario
• Secondary use
CARBON UPTAKE occurs:
• At different speeds:
—Relatively QUICKLY in non-reinforced products or thin/porous applications (renders, mortars, concrete blocks and mineral foams)
—More SLOWLY in reinforced concrete and thicker elements. Non-reinforced porous applications, such as masonry, that are exposed to air, can fully recarbonate within a few years, and it is estimated that such applications account for about 2/3s of the concrete global carbon sink
• When reinforced concrete structures are demolished—increased surface area and exposure to air accelerates the process.
• When stockpiles of crushed concrete are left exposed to the air before reuse and is faster—great attribute for recycled concrete pavements
Several carbonation-based binders have emerged that are produced with lower CO2 emissions (burnt at lower temperature), but use a significant amount of CO2 to harden—currently limited to niche markets.
Photocatalytic Concrete
The use of photocatalytic concrete can help remove air pollutants, providing clean air in our cities and towns. Air pollution continues to pose a significant threat to health worldwide. According to the World Health Organization (WHO), in 2016, 4.2 million premature deaths worldwide were attributed to ambient air pollution, with more than 1 in 4 deaths of children under 5 years directly or indirectly related to environmental risks—both ambient air pollution and household air pollution.
One solution to this challenge is heterogeneous photocatalysis (solid catalytic processes caused by light irradiation) by semiconductor particles or coatings. The application of such photocatalysts in concrete is well-established, but despite this, photocatalytic concretes are still not in mainstream application. Ideal places for utilising photocatalytic concrete:
—busy streets
—high traffic lanes
—parking lots
—intersections
—squares
—gas stations
—toll roads
Good photocatalytic effectiveness has to have the following conditions:
• Presence of relatively high concentrations of NOX (and other polluting agents)
• Daylight or an acceptable amount of UV light
• Regular rinsing either with rain or cleaning water to wash away the reaction products
Circular Economy
The concrete and cement industry is a key link in the CIRCULAR ECONOMY, utilizing recycled/secondary aggregates and cementitious industrial byproducts in concrete and alternative fuels/raw materials in cement kilns. Circular economy and industrial ecology principals have been applied by the cement and concrete industry for decades, utilizing the by-products of other industries and various other secondary materials, including municipal refuse and concrete demolition waste:
• Durable: can be reused and repurposed long after original design life has expired, maximizing use of resources and slowing the circular economy loop
• Ideal for design for disassembly—for recovery and reused in new projects
• Demolition waste can be recycled as an aggregate, reducing both the extraction of new raw materials and the amount of waste sent to landfill
SUPPLEMENTARY CEMENTITIOUS MATERIALS (SCMs)—often by-products from other industries—fly ash from coal fired power stations and ground granulated blast furnace slag (GGBS) from iron ore production, to partially replace clinker in cement or directly in concrete.
ALTERNATIVE FUELS/RAW MATERIALS—derived from industrial by-products and waste materials, including municipal refuse—can be used as a partial substitute for traditional fossil fuels, such as coal and petcoke, in the cement kiln. Co-processing reduces the use of more carbon-intensive fuels, as well as contributes to the circular economy, making use of materials otherwise destined for landfill. In addition, some alternative fuels, such as used tyres, contain elements required in clinker production, helping to reduce raw material consumption.
DESIGN for DISASSEMBLY (DfD)—aim is to aid deconstruction (demolition) through planning and design. It allows components and materials to be removed more easily, facilitating their subsequent reuse. DfD:
• Economic benefits to builders, occupants, and communities
• Environmental benefits to builders, occupants, and communities
• Helps to reduce the consumption of raw materials
• Lowers waste during construction, renovation, and demolition
Concrete’s durability, mechanical and fire resistance, global availability, variety of type and form, and flexibility in design and application, give it significant potential for disassembly and reuse.
RECYCLED AGGREGATES—availability of naturally occurring virgin aggregates varies from country to country and region to region:
• With adequate planning by government authority, available resources will be accessible
• Use of recycled material should be considered when possible
• Many areas with mature infrastructure are faced with an increasing amount of construction and demolition waste. There is therefore increased interest in recycled aggregates with concrete demolition waste a major source of such materials.
Recycling rates for crushed concrete vary significantly, depending on:
• Local laws/regulations for landfilling demolition waste
• Accessing natural aggregates
• Incentives and/or penalties affect the aggregates industry adaptation to increased use of recycled concrete as a source of aggregates
• Policies that require the segregation of good-quality concrete waste during demolition processes
• Maintaining its traceability helps to maximize the re-use of recycled concrete aggregate
High re-use rates are reported in Netherlands, UK and Japan.
Recycled concrete is primarily used for road construction, with smaller amounts also used in new concrete production. Concrete production may also require slightly higher cement contents when recycled aggregates are used.
The use of recycled concrete aggregates is a clear and obvious example of the circular economy at play and has benefits that include reducing the use of natural resources and reducing landfilling. It provides significant opportunity for the concrete industry to contribute to the sustainability of the modern built environment.
Porous Concrete
POROUS CONCRETE helps to reduce the risk of flooding in urban areas, draining and filtering rain away from the surface, with benefits to human health and safety. Sustainable urban drainage systems (SUDS) are an increasingly important component of climate adaptation in urban areas, as more frequent and more severe rainfall events occur because of climate change. Porous concrete offers a solution to challenges of surface flooding, flash floods, and water runoff—allowing designers to incorporate SUDS into developments.
The use of porous concrete:
• Reduces the risk of flash flooding
• Minimizes stormwater runoff to surrounding waterways
• Allows natural filtration to recharge local groundwater suppliers
• Helps to treat pollutants from vehicles and other sources (in the form of hydrocarbons and heavy metals, and sediment accumulate on the surface)
• Allows clean water to pass through the pavement into the native soil beneath
• Certain regions, dry and clean surfaces minimize the risk of mosquito breeding
• Open pore structure absorbs less heat from solar radiation—lowers heat island effects in urban areas
• Light color absorbs less heat from solar radiation than darker pavements—lowers heat island effects in urban areas
There are concrete solutions to the climate change risk of increased surface flooding—positive for concrete and demonstrates concrete’s sustainable value.
Self-healing Concrete
Concrete’s ability to heal reduces the need to detect and repair cracks that may otherwise lead to corrosion of reinforcement and deterioration of the concrete. This reduces costs, while boosting durability. Self-healing concretes reduce the need to detect and repair cracks and are one strategy to address corrosion risk—social, economic, and environmental benefits. Self-healing concretes reduce the need for maintenance and/or increasing longevity reduces disruption, as well as the cost and use of materials.
Many concrete elements crack without any concern; some are designed to crack; and for some elements, the avoidance, repair, or self-healing of cracks is of benefit. Recent research has aimed at furthering concrete’s self-healing properties. This includes the use of:
• Superabsorbent polymers (SAP), or hydrogels
• Micro-organisms that precipitate calcium carbonate—embedded in the concrete matrix after immobilization on diatomaceous earth in microcapsules or in SAP; bacterial cell will be coated with a layer of calcium carbonate, resulting in crack filling
• Encapsulated polymers that break open during cracking, releasing their content; agent flows into the crack causing reaction; crack faces bond together, healing the crack
Concrete is a unique material, which is why the GCCA takes the challenge of sustainability seriously as a sector. The GCCA vision sees a world where concrete supports global sustainable economic, social and environmental development priorities; and where it is valued as an essential material to deliver a sustainable future for generations to come.
For the Global Cement and Concrete Association (GCCA) “20 Ways Concrete is Sustainable” website PLUS VIDEO, please go to: https://gccassociation.org/concrete-and-sustainability/
For the video on the ISCP website, please go to: https://www.concretepavements.org/2020/09/13/gcca-video-sustainability-of-concrete/