This paper presents results regarding the phase composition, microstructure and textural properties of two types of aggregates, which were prepared via crushing or pelletization of alkali-activated Class F fly ash and cured under different conditions. The alkali activator was the same for aggregate products, containing an alkaline solution consisting of 8 M NaOH and Na-silicate (8 M NaOH/Na-silicate = 1:2.5 mass ratio). The aforementioned properties were influenced by two different preparation procedures combined with varying curing regimes (under normal conditions at 20 °C, RH 40–60% for 28 and 120 days and under an accelerated regime, at 65 °C for 5 days). Aggregates were characterized using X-ray diffraction (XRD), Fourier-transform transmission infrared spectroscopy (FTIR), back scattered electron microscopy with energy dispersive spectrometer (BSE-EDS) analyses and mercury intrusion porosimetry (MIP). The results showed noteworthy structural and textural diversities between the two types of aggregate. The method of preparation and curing regime affected the formation of the N-A-S-H structure and the texture of the alkali-activated fly ash product, with the crushing method giving an advantage.

This paper presents a circular business model (CBM) designed to promote the valorization of agricultural biomass ash for producing an alternative binder in construction, aiming to reduce CO₂ emissions and landfill waste. The circular economy framework emphasizes regeneration and restoration to minimize resource and energy use, waste generation, pollution, and other environmental impacts. Aligned with these principles of sustainability, the construction industry, energy sector and food processing industry can establish a shared interest through industrial symbiosis. In the proposed CBM, waste from one industry becomes an input for another. The model leverages industrial symbiosis by using sunflower husk ash (SHA) as an alternative hydroxide activator for alkali-activated materials. A case study of companies in the Republic of Serbia that produce SHA as waste forms the basis for this model, featuring promising results of experimental testing of three alkali-activated mortars produced by activating ground-granulated blast furnace slag (GGBFS) with different SHA contents (15, 25 and 35 wt% GGBFS), instead of commercially available hydroxide activators. The potential of SHA as an alternative activator was assessed by testing flow diameter and compressive strength at 7 and 28 days of curing. The highest 28-day compressive strength was attained for the addition of 25% SHA (28.44 MPa). The promising results provided a valid basis for CBM development. The proposed CBM is stream-based, resulting from merging and upgrading two existing industrial symbioses. This study highlights the benefits of the CBM while addressing the challenges and barriers to its implementation, offering insights into the possible integration of agricultural biomass ash into sustainable construction practices.

Building façade assessment could be performed in a more efficient way using a multidisciplinary approach and modern technologies. This study proposes the orthofaçade-based assisted inspection method (AIM), universal and applicable to different types of façade cladding and suitable for application in the condition assessment of inaccessible building façades or high-rise and large structures of all kinds. The AIM method offers a multidisciplinary approach by combining unmanned aerial vehicle (UAV) technology, electronic tachymetry, and digital image processing techniques (photogrammetry and open-source computer vision methods). The method was verified in a case study performed on a high-rise building façade. On-site data acquisition of high-resolution images of façade and control points was conducted by UAV and tachymetry. The data were further processed in photogrammetric software in order to generate a georeferenced orthofaçade. Crack detection was performed at pixel level via computer code using the OpenCV library methods. The established diagnostic model, defined by control points, enables precise determination of crack location. Crack length, width, or area could be calculated based on the coordinates of its points, by performing simple mathematical operations. The AIM method provides automation of crack detection and precise determination of location and geometrical parameters of detected crack.

The concept of circular economy has become an important topic nowadays. This paper provides a brief literature review that introduces sustainability and the circular economy by presenting their origins and their conceptual definitions. In accordance with the above-mentioned, the standards applied in Serbia are enumerated. In April 2020, the Roadmap for Circular Economy in Serbia, the first document that initiated a dialogue between decisionmakers, industry representatives, academia and civil society in order to define the goals, future steps and a time frame for the transition from a traditional linear model to the circular economy, was adopted. In November 2020, Serbia accepted the conditions of the European Union for linking the European Green Deal with the strategic development of the region by signing the Green Agenda for the Western Balkans. Furthermore, Serbia has a Digital Platform for the Circular Economy that provides support to companies through business models, examples of good practice and tools, in order to more easily apply the circular business model, and reduce the carbon footprint in production processes and products. Although the implementation of the circular economy is at the very beginning, there are already several examples of good practice in Serbia, in terms of sustainable building materials.

As the construction industry moves toward decarbonization, there is a growing focus on developing alternative binders with a lower carbon footprint to replace Portland cement. Alkali-activated materials (AAMs) have emerged as one of the promising solutions because of the lower CO₂ emissions from their production and comparable performance. The main components of AAMs are amorphous aluminosilicate-rich precursors that react with alkali activators to form a solid binding matrix. Raw materials generally used as precursors in AAMs are industrial by-products such as slag, coal combustion fly ash, or metakaolin. The most commonly used activators to reach the desired performance of the binder are alkali hydroxides and alkali silicates. However, conventional alkali activators are chemicals characterized by a negative environmental impact and high cost, which limits the wide-scale application of AAMs in the construction sector. Replacing conventional chemical activators with alternative ones derived from waste materials is a promising solution to enhance the sustainability of AAMs while promoting their broader application. This paper presents a targeted scoping review on the use of different biomass ashes instead of chemical activators in the AAMs technology. The results showed that different biomass ashes can be used not only as a source of alkalis and silicates but also as a partial replacement for commonly used precursors.

Previous studies have indicated that agricultural biomass ash is an important resource with great potential for the construction sector. To valorize agricultural waste (as a renewable energy source and as a supplementary cementitious material—SCM), the crucial steps in the integrated management system of the circular economy cycle are the establishment and maintenance of database on crop production, namely, on harvest residues amount and quantity and quality of available biomass ash. The purpose of the study was to establish a multi-level georeferenced interactive database (map) on the produced quantities of agricultural biomass ash and cement consumption in Vojvodina region (Republic of Serbia), based on the analysis of agricultural biomass ash stream through three sectors as potential actors of the supply chain: agriculture (biomass producers)—industry (biomass users)—construction industry (users of biomass ash). Conducted research indicates the annual potential of over 2.4 million tons of harvest residues from corn, wheat, soya and sunflower, available for energy purposes in Vojvodina region. The potentially available amount of ash that might be generated annually by harvest residues combustion is estimated at over 196 thousand tons. Identified available amount of biomass ash (4.2 thousand tons) indicates an extremely low utilization (~2%) of the biomass potential. On an annual basis, all current agricultural biomass ash production can be used for partial cement substitution up to 30% in six construction companies. However, the generated ash is mostly disposed of in municipal landfills, which represents the end of the waste stream.