Completely recyclable concrete

(Mieke De Schepper, J. Schoon, Eleni C. Arvaniti, for more information contact prof. dr. ir. Nele De Belie)

As the construction sector uses 50% of the earth’s raw material and produces 50% of its waste, the development of more durable and sustainable building products is crucial. Looking at the life cycle of products, one can see that closing the loop, recycling waste materials is of great importance. Within this project completely recyclable concrete (CRC) is designed for reincarnation within the cement production, following the ‘Cradle-to-Cradle’ concept (C2C). By adequately adding limestone aggregates and industrial by-products, the chemical composition of CRC is similar to that of cement raw materials. In this way, the concrete rubble of a demolished CRC-construction can start a new life as raw material for cement production without any modification. If CRC is used on a regular basis, a closed concrete-cement-concrete material cycle will arise, which is completely different from the current life cycle of traditional concrete. (Mieke De Schepper)

Life cycle: closed concrete-cement-concrete cycle  - Overview regeneration process  

Regenerated clinker – Optical microscopy image – SEM image

Concrete constructions that are exposed to aggressive environments (e.g. industrial and seaside buildings, de-icing salts and sewage), could carry elements such as chlorides, sulphur and alkalis after demolition, which will end up in the recycled material. Degradation of a CRC structure can influence the future burnability of the CRC rubble. Moreover, these compounds could affect strength and durability of the concrete that will be made with regenerated cement. In an industrial scale, the presence of the sulphur, alkali or chlorine in the CRC raw material can cause coating formation in the kiln and as a consequence a less stable kiln operation. Therefore, the role of chloride and sulphate ions in the regenerated clinker of CRC is investigated. This study focuses on the alterations of the main mineralogical phases in CRC clinker in the presence of chloride or sulphur in the clinkering process. Thermodynamic models will be applied to study the effect of different concentrations, for instance, chlorides and sulphates in the clinker composition. (Eleni C. Arvaniti)

Another research project with regard to completely recyclable concrete aims to examine the use of building and demolition waste or non-marketable by-products of the production of natural and recycled aggregates as alternative raw materials for clinker kilns with enumeration of all possible limitations. Numerical simulations are carried out to maximise their use as raw materials, taking into account their chemical variation, their behaviour within a clinker kiln, and their impact on cement properties. Furthermore, clinkers are produced and analysed according to the above described simulations and in function of realistic dosages before they will be used in fully characterized Portland cements. The ultimate aim is to reduce the ecological impact of the produced alternative clinker as well as the production process of the recuperated material compared to the current situation. The first results show promising influences on the Life Cycle Assessment and the CO2 impact. (J. Schoon).

Recycling of (cementitious) roofing and façade products

View on a cement factory