The production and use of cements with low CO2 emissions is an extremely topical issue for environmental protection and for the well-being of the planet. Recently a RILEM international conference dedicated to innovative technologies for sustainable development in construction was held in 2020 (3rd International Conference on Innovative Technologies for Clean and Sustainable Development – ITCSD 2020) where this theme was addressed and from which a paper signed by Indian authors is taken. I believe it is interesting to report the essential contents of this paper for a diffusion at the Italian level and for a better knowledge of those who operates in the construction market.
La produzione e l’impiego di cementi a bassa emissione di CO2 è un tema estremamente attuale per la salvaguardia ambientale e per il benessere del pianeta. Recentemente si è svolta nel 2020 una conferenza internazionale RILEM dedicata alle tecnologie innovative per lo sviluppo sostenibile nelle costruzioni (3rd International Conference on Innovative Technologies for Clean and Sustainable Development – ITCSD 2020) dove è stato affrontato proprio questo tema e da cui è tratto un articolo a firma di autori indiani di cui ritengo interessante riportare i contenuti essenziali per una diffusione a livello italiano e per una maggiore conoscenza di chi opera nel mercato delle costruzioni.
The new cements based on calcined clay as an alternative to traditional cements
After a brief introduction on the need to contain CO2 emissions in the cement industry as much as possible, the authors underline the availability of a new type of cement called with the acronym LC3 (Limestone Calcined Clay Cement) whose technology, based on the combined and synergistic action of three main components, clinker, calcined clay and ground limestone, it is developing all over the world. This new type of cement therefore contains a much lower clinker content (even less than 50%) than today's type I and type II portland cement and type IV pozzolanic cement (see the European cement standard EN197), reducing CO2 emissions by up to 30%. There could be many technical advantages related to the use of LC3 cement in concrete, such as:
Faster development of mechanical strengths (faster formwork removal times);
Shorter duration of the seasoning of the castings (less influence of manpower);
Better cohesiveness and resistance to segregation of mixtures (greater tolerance on any changes in water content in concrete)
Increased resistance to chemical attack (increased durability);
Less water permeability (greater use in concretes intended for foundation works in contact with groundwater);
A lower heat of hydration (massive casting).
Among the commercial advantages is highlighted the greater availability of raw materials, in particular the clay used for the production of LC3 cement, available also from the waste of various mining activities. Even the limestone used can be more easily found, having a lower degree of purity than that one used for the production of Portland cement clinker. In fact, any impurities such as quartz and clay minerals do not adversely affect the quality of LC3 cement. In addition to these factors, the authors state that an additional important property of LC3 cement is to reduce the amount of clinker at production sites where materials such as fly ash or ground granulated slag are not available or are very expensive and this affects, of course, also to the production of concrete.
However, there are both technical and commercial critical issues on the use of LC3 cement. The authors pointed out some fundamental aspects, such as:
The lack of sufficient field experience with respect to the more than centennial history of traditional cements;
The development of new specific standards;
Laboratory tests are still few in number to verify the technical requirements and technical expectations of users in the market (ready mix manufacturers, prefabricators, designers);
A more demand for water and consequently a greater consumption of superplasticiser additives compared to traditional cements;
A potential increased risk of corrosion of rebars induced by carbonation of concrete in reinforced concrete structures;