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The authors would like to thank Jose Miguel Lao-Egea from “Promoción de Empleo Joven e Implantación de la Garantía Juvenil en I+D+I” of Spanish Ministry for Science Innovation and Universities, the Departments of Building Construction and Civil Engineering and Research Group TEP-968 “Tecnologías para la Economía Circular” (Technologies for Circular Economy) of Granada University for their contribution to this research., The environmental problems associated with the construction sector have promoted the worldwide scientific community to pay attention to the use of recycled aggregates from construction and demolition waste. SciMAT and VOSviewer bibliometric tools have been applied in order to analyse, quantify and visualise the conceptual and social aspects of this scientific field, as well as its evolution between 1973 and 2019. The study of 843 scientific papers in this field has shown that the most important thematic area has been Recycling. In general, the common objective of the published papers was to study the efficient use of resources contained in construction and demolition waste due to their treatment to produce recycled aggregates, particularly for use in concrete. Likewise, some lacks have been observed in other areas of the analysed field, e.g. the use recycled aggregates in applications subject to less demanding regulations (mortars, precast concrete products, or green roofs)., Los problemas medioambientales asociados al sector de la construcción han promovido que la comunidad científica mundial preste una mayor atención al uso de áridos reciclados procedentes de residuos de construcción y demolición. Para analizar, cuantificar y visualizar los aspectos más relevantes de este campo científico, así como su evolución entre 1973 y 2019, se han aplicado las herramientas bibliométricas SciMAT y VOSviewer. La revisión bibliométrica de 843 trabajos científicos publicados en este campo ha mostrado que el área temática más importante ha sido el Reciclaje. El objetivo común de los mismos ha sido el estudio del uso eficiente de los recursos contenidos en los residuos de construcción y demolición para producir áridos reciclados y ser usados en hormigón. Asimismo, se han observado algunas carencias en otros ámbitos del campo analizado, como el uso de áridos reciclados en aplicaciones sujetas a normativas menos exigentes (morteros, prefabricados no estructurales o cubiertas verdes)., Spanish Ministry for Science Innovation and Universities, Departments of Building Construction and Civil Engineering, Research Group TEP-968 “Tecnologías para la Economía Circular” (Technologies for Circular Economy) of Granada University

According to the recommendations of European Directive 2002/91/EC and its subsequent modifications in European Directives 2010/31/EU and 2012/27/EU, all of which refer to energy efficiency, consideration of the source of energy used to drive a heating system is essential when trying to optimise energy efficiency and also in reducing its cost and the environmental impact caused. In this context the use of biomass is an interesting alternative to fossil fuels. A study was made of 6,234 records of the thermal systems most frequently used in the province of Granada, classified according to the source of energy used. The energy study is focused on energy efficiency in building systems. The results show the predominance of fossil fuels: gasoil is the option most frequently chosen for heating (39%), while natural gas accounts for the highest percentage overall (49%), if we add together the power used for heating, cooling and domestic hot water. The replacement of fossil fuels by renewables would lead to a reduction in the environmental footprint, cutting CO2 emissions by 17% if 23% of equipment were replaced, this being the target set in the 2030 programme. The economic savings for consumers from using renewables according to 2030 targets could be as high as 6.24%. Keywords: Energy; Building; Renewables; Boiler; CO2 emissions; Energy efficiency.

In the last decades, several investigations have been developed on alkali-activated materials (AAM) with cementitious properties and for that reason also called binders, with a particular focus on the specific research areas of design and characterization of binders, mechanical behaviour and durability tests. Geopolymers consist of a polymeric framework of Si–O–Al, which is produced by condensation of tetrahedral aluminosilicate units, with alkali metal ions that balance the charge associated with tetrahedral aluminium. The geopolymers are usually synthesized from a two-part mixture, consisting of an alkaline solution (activator) and aluminosilicate solids (precursor), and the reactions occur at room temperature or slightly elevated. These materials can be used as cement and be applied in concrete and mortar. The excellent performance of cement and concrete with AAMs is attributed to the highly refined pore network, forming a denser structure phase of calcium aluminosilicate hydrate (CASH) or sodium aluminosilicate hydrate (NASH). In the last years, there was an intense development of studies focused on AAMs using traditional precursors such as waste-derived precursors such as blast furnace slag or coal fly ash, and synthetic ones as metakaolin. More recently, several research groups are testing different new waste as precursors and as activation reagents. The state of the art is focussed on precursors based on waste from urban, metallurgical, ceramic, construction and demolition and agro-industry activities. Regarding the activating solution, the state of the art also is focussed on waste derived reagents, differentiating between the cases in which the activating solution was prepared totally or partially from waste. Also recycled concrete aggregates (RCA) have been used with positive results in the manufacture of alkali-activated slag concrete (AASc).

Biomass comes from organic material such as trees, agricultural and urban waste, plants and shrubs, etc., and it can be used both for electricity production, for example, for heating, and as fuel for transport, and presents important advantages. The use of this resource promotes important economic and social development in rural areas, as well as having environmental benefits due to the elimination of waste and the reduction of CO2 emissions. Biomass energy is close to ‘carbon neutral’. The process of energy production through the combustion of biomass is considered to have important environmental advantages, but it also has the disadvantage of generating large amounts of ash that affect the efficiency in the conversion process of obtaining electrical energy or heating. Ash formed during biomass combustion can be divided into bottom ash and fly ash (FA). Biomass bottom ash is the fraction produced on the grate during primary combustion and is composed of the sand particles purged from the original bed, inorganic components of the feed and the unburned biomass fraction. Biomass FA is a finely divided residue that results from the combustion of biomass and that is transported by flue gasses. The use of ash from the combustion of biomass is conditioned by its physico-mechanical properties, but there is not much literature on the use of these ashes in construction materials.