This informal CPD article, ‘What are AACMs and How Can They be Used in Building Restoration?’ was provided by C-Probe Systems, who offer low-carbon, sustainable corrosion protection and monitoring products for the restoration and new-build markets.
Concrete plays a significant role in society – it makes up vital infrastructure which we use daily, such as buildings, roads, bridges and tunnels. It is evident that in modern society we are highly reliant on this essential industry. Although it is relatively cheap, easy to source and durable, producing Portland cements (PCs) which are used in the production of concrete is unsustainable without active carbon reduction planning.
The production consumes vast amounts of raw materials, with over 3 tonnes of material being required to produce a tonne of PC, alongside large amounts of heat energy to convert limestone generating high volumes of CO2 emissions and harmful greenhouse gases. Currently, the cement industry accounts for 8-10% of the worldwide carbon dioxide emissions total, meaning that the industry is becoming increasingly interested in researching and utilising alternatives to PCs.
Alkali activated cementitious materials (AACMs), in some formulations also known as geopolymers, are created from a range of materials (usually industrial waste by-products), known as precursors. These produce a cementitious powder material that can be used instead of PCs but harden on the addition of an alkali liquid activator to create an aluminosilicate rheology.
Sustainability
AACMs are an environmentally sustainable material which could reduce resource depletion, construction waste, and harmful emissions which accelerate climate change. They are a positive source of change to the cement industry as AACMs are produced with no heat (ambient blending) from waste streams arising from fossil fuel, steel, and mining, and when incorporated in mix designs to form a hardened material they required a reduced water content.
There is a consensus that alkali-activated cements can offer cradle-to-grave greenhouse emissions savings ranging from 40–80% depending on sources compared to PC, presenting them as a ‘greener’ alternative to traditional materials.
Durability
In other studies, AACMs have shown to have comparable compressive strength and workability with improve flexural strengths compared to Portland concretes and mortars. Other characteristics include no shrinkage, high resistance to fire (>1200 °C for over 5 hours), and chemical resistance, showing that they are a highly resilient repair material that can be utilised within a wide range of structures and environmental exposure conditions without affecting performance.
Furthermore, the stable nature of the material, conductivity and its controllability mean it can be used as an Impressed Current Cathodic Protection (ICCP) anode. ICCP is considered as one of the most reliable methods for protecting steel frame structures from corrosion – the electrochemical process of cathodic protection means the steel is turned into a cathode (via the use of an anode and electrical current) and corrosion cannot take place on the steel.
ICCP has also been found as the best method to preserve embodied carbon in buildings, as it requires minimal intrusive works, and the aim is to protect as much as the reinforced concrete with the throwing power of the anode material.
AACMs being able to act as ICCP anodes means that they can be applied as a mortar, grout, or concrete conventionally placed by cast in-place or cut and grouted into decks to incorporate into existing reinforced concrete structures, as well as gunned into joints for transitional steel frame masonry-clad buildings. Once electrical current is passed through the embedded steel of these structures, whether it be bridges, heritage buildings or a parking structure, is protected continuously for the long-term.
The use of AACMs in restoration eliminates disruption and costly repairs as they can, and should be, used as a preventative measure before the structure falls beyond repair and demolition. The use of sustainable build materials, like AACMs, which can double as corrosion protection is highly beneficial for the sector, as it means vital embodied carbon is preserved for the structure’s whole life, and it has provided sustainability with structural future proofing.
It is clear that the restoration of our existing concrete infrastructure is a main component of building a low carbon built environment and reaching climate goals. Forming cathodic protection anodes from sustainable materials is key in achieving this also builds a positive legacy for future generations.
We hope this article was helpful. For more information from C-Probe Systems, please visit their CPD Member Directory page. Alternatively, you can go to the CPD Industry Hubs for more articles, courses and events relevant to your Continuing Professional Development requirements.
References
1: G. Jones, P. Lambert, “Characterisation of Low-Carbon AACM Concrete and Mortar,” Concrete 50, 9 (2016): pp. 50-52.
