Status quo

"We produce more concrete than anything else, any other product, apart from clean water"

About three tons of cement are consumed for every person on Earth every year, for a total of about 22 billion tons. A useful yardstick to understand the extent of this data is that in the same way it has been estimated that the production of plastic is, in absolute terms, around 8.3 billion tons of plastic.

Ordinary Portland cement, the binder in the concrete production formula, is produced by cooking lime in special kilns in a process that emits about one ton of carbon dioxide for every ton of cement. Cement production is responsible for about 8% of global man-made CO2 emissions, according to the World Business Council for Sustainable Development. Some carbon dioxide released into the atmosphere is partially reabsorbed by the concrete: in 2016, it was estimated that between 1930 and 2013, about 43% of the CO2 released from lime during heating was then reabsorbed by concrete products worldwide. Unfortunately, this absorption comes at a price. When concrete is used in steel-reinforced structures, as CO2 moves through it, the pH of the surrounding environment changes: concrete loses its alkalinity and, when moisture and oxygen are present, it causes the reinforcement to rust.

Given these issues, concerns about the environmental impact and structural longevity of concrete, why do we continue to build with it? Concrete is economical, versatile, quick to make and does not require any special additional technical treatments. While still considered one of the most impacting materials on the biosphere, these intrinsic characteristics and some new developments towards "greener" formulas have confirmed concrete as a still viable option, even if radical changes to industry standards are likely to be met with caution. Furthermore, statistics show that reinforced concrete structures resist earthquakes much better than unreinforced brick buildings. Concrete's resilience to natural disasters contributes to its applicability.

Low-emissive concrete: applications in "INLEGNO" retrodesign

The exercise carried out in the INLEGNO volume involved the retro-design of a building currently under construction, from which it would be easy to extrapolate project data for objective comparison with a new innovative proposal. The idea was to compare the traditional construction technique, the one used in the reference case, with a hybrid concrete-wood construction, trying to understand how the aspects related to cutting emissions, increasing costs, solving technical problems, construction site management perceived architectural quality related to each other. The results obtained were encouraging and provided tools with which to defend, numbers in hand, an important choice such as that of focusing on timber structures for the construction of tomorrow's architecture.

Part of the maturity with which this research work was carried out also lies in the fact that, reasoning first and foremost on the actual feasibility of the proposed concept, it was decided to design a hybrid structure with the use of concrete as the predominant technology for the construction of foundations and lift shafts.

Today, one year after the publication of INLEGNO, we tried to find out how to work on the least sustainable component of the already formalised proposal: concrete. Proposing a hybrid structure does not necessarily mean that less noble and less innovative parts of the concept must remain so. Even a high-emissive industry such as the concrete one is moving towards options that allow the containment of the CO2 emissions associated with it. One of the main reasons behind reluctant attitudes towards more sustainable solutions, on paper, lies precisely in the fact that they are often not economically feasible. By anchoring part of the feasibility of a project to a technology that is known, tested, economically viable and made less impactful by a refurbishment, one can certainly increase the percentage of possibility that a proposal sees the light.

In light of these considerations, the cement-containing components of the project were revisited in collaboration with Italcementi.

The main objective was to calculate how many emissions attributable to the concrete structure could be cut if the raw material came from more innovative processing.

The lift shafts, ground floor structures and foundations were redesigned according to this criterion. Each characteristic strength of the concrete was coupled with its emissive contribution in order to understand whether and how, as the cross-section varies, the CO2 production may also vary. The design ideas were divided into different scenarios, from which data was then extrapolated to optimize the best mode. Again, the final choice was directed towards a hybrid option: a maximum characteristic resistance was not chosen, because although the quantity of CO2 emitted was greatly reduced, the construction costs would have increased, making it unaffordable. The project was rethought with structures that respect the ... characteristic resistance and integrate the emission reduction technologies related to the production of Portland cement, the material used as a binder in the concrete mix, proposed by Italcementi. The implementation of the ECO Low Carbon range in the structures described above has resulted in a reduction of approximately 65.4% of CO2 at a cost increase of approximately 2%.