Urban areas are critical for resource efficiency and circular construction. With half of all extracted materials and energy, and one third of the total waste generated, the construction sector is one of the greatest stake in the European Union’s (EU) efforts to make its economy circular. The European Commission has undertaken specific initiatives to promote a more efficient use of resources in the construction sector through a better management of construction and demolition waste. The Circular Economy Package has impulsed measures requiring construction sector stakeholders to mainstream the re-use, recycling and recovery of construction and demolition waste. In the short and medium term, the management of raw materials and waste in construction should be improved by intensifying the necessary actions for saving non-renewable natural resources and for recovering waste not merely in volume but in value as well.
The climate and biodiversity topics are currently at the forefront of the international sustainability agenda and the 17 UN Sustainability Development Goals (SDGs) provide an underlying and more broad-based set of targets and communication framework for countries, cities and companies. In September 2019 the UN hosted their Climate Action Summit to boost ambition and accelerate actions to implement the Paris Agreement on Climate Change. In September 2020 alongside the UN General Assembly there will be the Biodiversity Leaders’ Summit ahead of the UN Convention on Biological Diversity event to finalise a post-2020 Global Biodiversity Framework. And as for the UN SDGs, signed in 2015, these are goals for 2030 so with a decade to go, 2020 is the year for many “a decade to go” events. At the Global Cement and Concrete Association (GCCA), we are acting together with members and affiliates, on all these issues as would be expected of an organisation that has been founded by members from around the globe, to speak on behalf of the industry to global audiences. For example, GCCA was at the September 2019 UN Climate Action Summit hosting an industry event explaining commitments from the cement and concrete industry to reduce greenhouse gas emissions; we are gearing up to be part of international biodiversity events in 2020; and, and at our annual conference in USA in October 2020 we are addressing the theme of SDGs.
2020 marks the first anniversary of the publication of the book “New Trends in Eco-Efficient and Recycled Concrete”. It is a technical book that describes the new possibilities available today to manufacture concrete with different wastes and by products. Although recycled aggregate concrete is not currently applied using specific wastes, by-products, or treated rubbers for example, its use will allow to substantially reduce the carbon footprint that is produced when cement-based and quarried materials are applied in construction applications, and that will also allow the reincorporation of all these wastes in a viable way in a large number of uses. More than 30 researchers from all over the world have collaborated in this book, contributing with technical and experimental contents, comprising 21 chapters, which include ideas for the future that can be applied in new structures, buildings, infrastructures, and urban constructions.
Aluminium cannot be used to reinforce regular concrete since the high pH will attack the metal and evolve hydrogen gas. However, Al/5%Mg alloy is stable in concrete where 55% cement is replaced with calcined clay in the concrete mix. Replacing high fraction of clinker burnt at 1450ºC, and with high CO2emission from limestone decomposition in the raw meal, with a clay calcined at 850ºC obtainable by biofuel give obvious savings in energy and CO2 emissions. Furthermore, since aluminium can withstand carbonation and chlorides a cover of only 20 mm for mechanical interaction with reinforcement is needed resulting in a smaller concrete volume. Binder with 55% calcined clay is sulphate resistant and do not induce AAR due to lower pH and no remaining calcium hydroxide in the system. The only degradation mechanism left is freeze-thaw avoidable by proper air entrainment. Thus, in theory an infinite service life without maintenance may be at hand for aluminium metal reinforced concrete.
The paper examines the potential of Metakaolin (MK) and Silica Fume (SF) blended with Portland Cement (PC) and Fly Ash (FA) in improving the flexural fatigue performance of concrete in which 100% Coarse Natural Aggregates (NA) has been replaced by Coarse Recycled Concrete Aggregates (RCA). The fatigue life data of different concrete mixes was obtained by performing flexural fatigue tests on approximately 128 beam specimens under four-point loading. In total, 96 static flexural tests were also conducted to facilitate fatigue testing. The fatigue performance of concrete containing RCA was assessed by estimating the variation in the fatigue tests data using Weibull distribution, design fatigue lives, theoretic fatigue lives etc. It has been seen that there is considerable reduction in the fatigue performance of concrete made with RCA compared to concrete containing NA. The use of blended cements such as MK and SF in combination with PC and FA has been found to significantly enhance the fatigue performance of concrete containing RCA. Also to predict the flexural fatigue strength of concrete made with RCA, the materials coefficients of fatigue strength prediction models have been estimated. The S–N–Pf curves have also been generated from the fatigue test data for all the concrete mixes. These models can be used to predict the flexural fatigue strength of concrete made with RCA and MK and SF. Further, the two million cycles endurance limits have been estimated for all the concrete mixes.
The prodigious demand for aggregates in the construction industry leads paucity of natural aggregates, which commands to look after somealternatives. Also aiming to solve the problems caused by the construction and demolition waste, this paper presents the development of sustainable concrete by replacing 100% of natural coarse aggregate (NA) with recycled concrete coarse aggregate (RA). The performance and suitability of recycled aggregate concrete were studied. Both RA concrete and NA concrete were prepared for various W/C ratios of 0.75, 0.65, 0.55, 0.45. Experimental tests were conducted to find out mechanical properties by means of compressive strength, split tensile strength, flexural strength, and elastic modulus, whereas durability performance was checked using RCP test (Rapid Chloride penetration test), sorptivity test, water permeabilitytest and surface resistivity test. Finally, a comparison was made between the recycled aggregate concrete and conventional concrete. In this study, it was observed that although there was a reduction in the performance of RAC compared to NAC, the RAC can be useful in producing low to medium strength concretes if designed appropriately.
In the present study, concrete is made with replacing sand by recycled fine aggregate in different water cement ratios (0.45, 0.50, and 0.55). Mechanical and durability properties of fine recycled aggregate concrete have been evaluated. The results showed that, reduction of compressive and tensile strength while using fine recycled concrete aggregate (FRCA) as fine aggregate when compared to natural aggregate concrete. The percentage of water absorption for FRCA based concrete mixes is higher when compared to conventional mixes. And also, it is observed that depth of penetration of water and rapid chloride permeability of FRAC were higher when compared with concrete having river sand as fine aggregate.
As recycled aggregate has a high water absorption rate, the traditional mixing process (TMP) is likely to create an area where cement hydration is inadequate near recycled aggregate, thus affecting the performance of recycled aggregate concrete. In this paper, to improve the performance of recycled aggregate concrete, a pre-mixing thick cement paste (PTCP) method is proposed via theoretical analysis and experimental verification. The PTCP method and TMP are compared to investigate the statistical distribution patterns of the 28-d compressive strength of recycled aggregate concrete. The results show that compared with the TMP, the PTCP method improves the 28-d compressive strength of recycled aggregate concrete by 7.8 - 15%. In addition, the PTCP method significantly improves the frost resistance of recycled aggregate concrete without changing the mixture ratio. This study provides technical reference for the recycled aggregate concrete mixing process.
Concrete is globally available and the material of choice for the majority of buildings and infrastructure. It is relatively inexpensive, readily available and in many ways sustainable and as a result will continue to be used for the foreseeable future. However, it is not without challenges from alternative materials and design concepts, but also from aesthetic, durability and environmental concerns. These trends and issues were addressed previously [1] in order to identify and determine priorities at a national and international level for research, development and best practice. This paper revisits the predictions made in order to judge to what extent progress has been made.
