Author
Dr Ron Casson
Sector
Technology
Date
6 March 2023
Since the Romans first developed hydraulic cements, concrete become the cornerstone of civilisation; after water, cement is the second most consumed material in the world today. Concrete has many sustainable benefits including its recyclability and durability. It also has a much smaller land footprint than timber and it’s resilient to natural disasters such as fire and flooding. As we continue to urbanise, the global cement market is expected to be worth USD 498.23 billion by 2028, yet cement still accounts for 7-8% of the world’s CO2 emissions. Can the future be green for concrete?
How to make concrete sustainable?
The industry has been working hard to reduce CO2 emissions and to promote biodiversity in several ways; the Global Cement and Concrete Association (GCCA) reports that the cement industry has reduced CO2 by 19.2% per tonne cementitious since 1990, and GCCA members have committed to the 2050 Net Zero Roadmap. There are many ways we can help reduce cement industry CO2 emissions, for example, using premanufactured waste materials, reducing raw materials, restoring quarries after extraction and using waste as fuel.
Although sand and stone make up 70% of concrete, by weight, Ordinary Portland Cement (OPC) — so called for its resemblance when hardened to Portland stone — is the most expensive and energy-hungry part of the mix. Ironically, we need to look back to Ancient Rome – where pozzolan-lime binders were first used to create a cementitious compound – before we can look to the future for sustainable concrete production. Named after their original Roman source Pozzuoli, these pozzolans, or volcanic ashes, had no cementitious value, although when mixed with calcium hydroxide (lime made from heated limestone) in the presence of water, the Romans were able to create a robust, cement-like compound.
What is the future for concrete technology?
The gain in popularity for OPC since it was first developed by Joseph Aspdin in the 19th century was due to its ability to gain strength quickly. This created a decline in demand for pozzolan-lime binders for almost 200 years, however, the more recent reintroduction of lime hydrates and other low carbon cement alternatives is likely to address many of today’s cement sustainability issues.
Pozzolan usage has been steadily growing during the 20th century, and most modern pozzolans are sourced from slag heaps and waste materials. These alternatives to cement tick several green boxes, although it’s important to remember that, while its long-term strength is often greater than that of OPC, using pozzolans as an alternative aggregate will reduce the rate at which it gains strength, therefore it’s not always possible to specify the strength at 28 days.
It seems sustainable concrete production gets a green light. Thanks to the engineers of Ancient Rome, the natural and waste materials that built the first harbours and aqueducts have become today’s sustainable alternatives to cement. These are widely available and less expensive to produce, they can be manufactured locally, and they provide the durability and resilience we need for civilisation today.