CTC has presented an innovative computer vision system for the automatic classification of concrete waste from the construction and demolition sector. The solution makes it possible to assess the carbonation state of materials based on the chromatic contrast generated by a harmless pH indicator, which facilitates their characterisation and subsequent valorisation as recycled aggregate.
Validated under controlled laboratory conditions, the development is a tool that could help boost the recycling of these materials in Spain. According to Green Building Council España (GBCe) in its Circular Economy report, 54% of demolition waste materials are sent to landfill. This figure stands in contrast to the targets set by the European Union, which require 70% of these materials to be recovered or valorised.
Rafael Hidalgo-Gato García, CTC project manager, presented the research at the 1st Congress on Innovation in Construction, Building, Infrastructure and Concessions (IC2), recently held at the Palacio de la Magdalena in Santander. Mario González Martínez, Ruth García García and Alejandro López García (CTC); Daniela Eugenia Angulo Ramírez and Antonio Jesús Martínez-Espinosa (Construcciones Urdecon S.A.); and Francisco Javier Benito Saorín (University of Alicante) complete the list of researchers involved in the project.
He explained how the automated system offers an alternative to the conventional chemical indicator (phenolphthalein), which is associated with higher toxicological concerns and requires manual reading, by using a harmless turmeric-based pH indicator. The chromatic contrast generated by the indicator is captured through a multispectral system (RGB/NIR) with controlled lighting and is automatically analysed using a YOLO-based instance segmentation artificial intelligence model. This approach makes it possible to classify each fragment according to the predominance of carbonated or non-carbonated areas, generating a traceable output with a label and dominant percentage for each item.
The classification of carbonated concrete waste poses several technical challenges because the material is not homogeneous and is often mixed with other demolition waste. In addition, carbonation changes the surface alkalinity and alters both the behaviour and characteristics of the material. This makes it difficult to establish reproducible criteria for determining which fragments have the greatest potential for valorisation as recycled aggregate and which require additional treatment or testing.
In this context, the solution has been experimentally validated under controlled laboratory conditions, demonstrating stable classification and conservative behaviour in the presence of signals outside the training domain. The system includes an operating interface designed for process supervision and for future adaptation to semi-automated or industrial environments.
CO2MCHRETE project
This development is part of the CO2MCHRETE project (“Mineralised CO₂ in Cements and Concrete from Thermally Activated Waste and Slag”). The proposal is one of 49 projects funded under the “Science and Innovation Missions” programme of the Spanish Ministry of Science, Innovation and Universities in its 2024 call, specifically within MISSION 2, which promotes sustainable construction, sector digitalisation, circular economy and the reduction of carbon footprint in construction materials.
Técnicas Reunidas Internacional is leading the project, which involves Ferrovial Corporación, Construcciones Urdecon, Cementos La Cruz and Valoriza Servicios Medioambientales. Alongside CTC, the University of Castilla-La Mancha (UCLM), the LADICIM Laboratory (Materials Science and Engineering Division) of the University of Cantabria, Tecnalia Research & Innovation and the Polytechnic University of Cartagena (UPCT) complete the list of participating research organisations.
The system presented by CTC is part of one of the three lines of action planned within this research, which includes the development of the laboratory-scale prototype under controlled environmental conditions (temperature, humidity, lighting, concrete type, etc.).
To reach an industrial-scale prototype, it will be necessary to extend experimental validation to new concrete typologies, variable lighting conditions, different moisture states and representative plant-operation configurations. This evolution will need to be accompanied by calibration against reference tests and specific adaptation to the parameters of the operating environment.
