Periodic Reporting for period 2 - TRAC (Tailor-made Recycled Aggregate Concretes)
Reporting period: 2020-07-01 to 2024-04-30
This project is intended to overcome current barriers of using RCA in concrete for structural applications and to bridge the knowledge gap between scientists and engineers.The novelty of the proposed research exchange is to develop common approaches which can be used for a wide range of recycled aggregate concrete products. By developing collaborative multi- and inter-disciplinary research we can improve our knowledge, skills, and experiences more effectively and more efficiently. Not only can this reduce the cost of the research but can also speed it up and disseminate the research findings more quickly and more widely, thus to achieve a multi-win scenario. In many cities, particularly in many developing countries, old buildings are being demolished and new ones are being constructed. From an environmental and cost savings standpoint, it is logical to take waste from on site and reuse it in a new project. The proposed research is extremely timely and important to advance innovation in sustainable construction materials to be applied in infrastructure development, providing a robust scientific underpinning for the design of recycled aggregate concrete mix based on its applications, considering the current shortage of virgin aggregate in many countries. The research will also contribute to the development of the modelling tools required to resolve uncertainties in the parameters influencing the long-term performance of recycled aggregate concrete structures, enabling the safe and confident utilisation of RCA in infrastructure applications in the Europe and worldwide.
The research findings have been reported by 27 peer-reviewed journal papers. The main findings are:
• Adding extra water or alkaline solution for a similar workability will decrease the mechanical strength of the mortar, and thus this is not a good way to application of RFA in concrete.
• The weakest ITZ is the one between the new paste and RLWA covered with old paste and the strongest ITZ is the one between new paste and RLWA without old paste.
• The addition of 1-2% Chinese RA or 20% Chinese RFA in the cementitious mortar does not impair the compressive strength, and the addition of 30% RLWA in concrete can keep the similar or even higher compressive strength compared with the reference concrete.
• The addition of up to 20% Chinese RFA in the cementitious mortar does not increase the dry shrinkage.
• The RAC specimens have shown similar failure characteristics regardless of monotonic or cyclic loading.
• To achieve the targeted flow slump of SCC, the FDW replacement of up to 50%wt increases the superplasticizer requirement more than the control SCC and SCC mixed with RHA while decreasing the fresh density compared to the control SCC.
• For a given type of RCA, the relative effective diffusion coefficient of chlorides in the concrete increases almost linearly with the replacement ratio of NA in the concrete. The rate of the increase, however, is dependent on the properties of the mixture of the concrete such as w/c or w/b ratio. The higher the w/c or w/b ratio is, the smaller the rate of the increase is.
• The effective diffusion coefficient decreases with the increase of the total volume fraction of NA and RCA regardless the NA replacement ratio used. However, the rates of the decrease are significantly different when different NA replacement ratios are used. The concrete with higher replacement ratio of NA decreases much slowly than the concrete with lower replacement ratio of NA.
• Chloring binding in concrete involves both physical and chemical reactions of chlorides with cementitious materials near the pore surface of concrete. Chloride binding can reduce the penetration speed of chlorides in concrete and thus improve the service life of concrete structures. Therefore, it is important to consider the chloride binding in the chloride diffusion model.
• Adding extra water or alkaline solution for a similar workability will decrease the mechanical strength of the mortar, and thus this is not a good way to application of RFA in concrete.
• The weakest ITZ is the one between the new paste and RLWA covered with old paste and the strongest ITZ is the one between new paste and RLWA without old paste.
• The addition of 1-2% Chinese RA or 20% Chinese RFA in the cementitious mortar does not impair the compressive strength, and the addition of 30% RLWA in concrete can keep the similar or even higher compressive strength compared with the reference concrete.
• The addition of up to 20% Chinese RFA in the cementitious mortar does not increase the dry shrinkage.
• The RAC specimens have shown similar failure characteristics regardless of monotonic or cyclic loading.
• To achieve the targeted flow slump of SCC, the FDW replacement of up to 50%wt increases the superplasticizer requirement more than the control SCC and SCC mixed with RHA while decreasing the fresh density compared to the control SCC.
• For a given type of RCA, the relative effective diffusion coefficient of chlorides in the concrete increases almost linearly with the replacement ratio of NA in the concrete. The rate of the increase, however, is dependent on the properties of the mixture of the concrete such as w/c or w/b ratio. The higher the w/c or w/b ratio is, the smaller the rate of the increase is.
• The effective diffusion coefficient decreases with the increase of the total volume fraction of NA and RCA regardless the NA replacement ratio used. However, the rates of the decrease are significantly different when different NA replacement ratios are used. The concrete with higher replacement ratio of NA decreases much slowly than the concrete with lower replacement ratio of NA.
• Chloring binding in concrete involves both physical and chemical reactions of chlorides with cementitious materials near the pore surface of concrete. Chloride binding can reduce the penetration speed of chlorides in concrete and thus improve the service life of concrete structures. Therefore, it is important to consider the chloride binding in the chloride diffusion model.
The exchange programme provided by this RISE project has offered a great opportunity for researchers, particularly young researchers, to develop their skills and gain experience in the fields that are likely to drive concrete research over the next decade. It helped them to develop the international contacts necessary for a successful long-term career, and prepare them for making use of new facilities and new tools available in the world. The program also allowed individual partners to take advantage of the skills of talented researchers from highly respected research institutions both inside and outside Europe and to learn from their experiences. The workshops have been open to undergraduate and postgraduate students in the host institutes, which help to attract more young people into this engineering field.
Within the project we have made 116.6 secondment months in total where 100 PMs were funded by EU, delivered five workshops and 15 seminars, published 27 journal papers, and presented 4 papers in international conferences. The project has involved 33 researchers, and most of them are PhD research students or early career researchers. As the outcomes of this project, 7 funded research projects have been secured (with a total value of over €800k) to further advance low carbon concrete technologies in practice.
Within the project we have made 116.6 secondment months in total where 100 PMs were funded by EU, delivered five workshops and 15 seminars, published 27 journal papers, and presented 4 papers in international conferences. The project has involved 33 researchers, and most of them are PhD research students or early career researchers. As the outcomes of this project, 7 funded research projects have been secured (with a total value of over €800k) to further advance low carbon concrete technologies in practice.