Marijana Serdar

This study examines alkali-activated concrete (AAC) containing 15 wt.% wood biomass ash (WBA) as a partial precursor replacement for precast street furniture. The bench was produced using ground granulated blast furnace slag (GGBFS), WBA, and graded aggregates, activated with sodium hydroxide and sodium silicate solution. Fresh properties, including workability and density, were assessed, while hardened concrete was evaluated for compressive and tensile strength, modulus of elasticity, water absorption, and freeze–thaw resistance. The results indicate that the AAC demonstrates high workability, long-term strength development, and adequate durability, confirming its potential as a sustainable, high-performance alternative to conventional concrete for outdoor urban applications.

Stray current in urban railway systems presents a significant challenge, including localized corrosion of rails, fastening systems, and adjacent metal structures, which compromises infrastructure safety. This study focuses on enhancing the resistance of rail fastening systems to mitigate stray current. Laboratory tests were conducted on samples where rails were fixed using two different fastening systems. During testing, the samples were subjected to 26 VDC, and electrical resistance and potential distribution were measured under controlled conditions. The results indicated that both systems were inadequately insulated, resulting in stray current, although in one system the anchor bolts were insulated primarily to prevent current leakage into the track substructure. Material analysis showed that the elastomeric elements in this system were not specified for high electrical resistance, so stray current was not prevented. Modifications for both systems were proposed to improve stray current prevention and were analyzed using numerical models in COMSOL Multiphysics software. The study highlights the importance of establishing precise requirements for the electrical resistance of fastening systems and developing a standardized methodology for measuring resistance.

This study presents the optimisation of an alkali-activated binder produced from ground granulated blast furnace slag (GGBFS) and potassium-rich sunflower husk ash (SHA), by varying SHA content, curing regime, and mixing procedure. Both materials are locally available in the Republic of Serbia. The influence of SHA content (15%, 25%, and 35% by mass of GGBFS) and curing conditions (ambient and 65 °C) on hydration products, workability, and compressive strength was examined. The water-to-binder ratio and GGBFS content were kept constant, and a one-part alkali activation approach was employed using untreated SHA. Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were performed on paste samples, after 2, 7 and 28 days of curing, while workability and compressive strength of mortars were measured after 7 and 28 days. Increasing SHA content enhanced the formation of C-S-H and C-A-S-H gels, resulting in a consistent rise in compressive strength, from 26.6 MPa to 36.2 MPa after 7 days and from 46.2 MPa to 55.1 MPa after 28 days of ambient curing. Workability was slightly reduced with increasing SHA content, resulting in flow diameters of 156.04 mm (15% SHA), 154.10 mm (25% SHA) and 152.76 mm (35% SHA). Curing at 65 °C accelerated early strength gain for 33% to 39% but produced lower 28-day strengths than ambient curing. Additionally, for the optimal mix, SHA was also pre-immersed in water for varying durations to assess its effect on workability, compressive strength, and potassium ion leaching. This pretreatment increased compressive strength by up to 14.7%, depending on immersion time, but reduced workability by up to 15.5%. The novelty of the research is reflected in attaining the highest 28-day compressive strength of 55 MPa (for 25% SHA by mass of GGBFS), under ambient curing, without SHA pretreatment or immersion, highlighting the potential for low-energy, sustainable binder systems using agricultural and industrial by-products.

Calcined clays are a promising route to lower-carbon binders, but widescale adoption of limestone calcined clay cements (LC³) requires using low-kaolinitic resources due to the limited availability and pricing of high-grade sources. This study evaluates the long-term hydration of two locally available kaolinite–illite composite clays (kaolinite contents 18% and 13%) in binary (30% SCM) and ternary LC³-type (30% SCM + 15% limestone) binders, benchmarked against OPC and fly ash systems. Over 1 year, thermogravimetric analysis showed lower portlandite (CH) and increasing bound water in SCM systems relative to OPC, reflecting ongoing secondary hydration reactions of the SCMs. XRD/Rietveld confirmed formation of hemi- and monocarboaluminate, enhanced in LC³ versus the corresponding binaries. The degree of hydration (DoH) for clay blends exceeded OPC from 7 days onward and reached comparable hydration levels after 1 year, indicating a beneficial later-age contribution from illite. Mortar tests showed that binary clay mixes approximated the 42.5 N class target at 28 days, while all LC³ mixes exhibited lower early strength but additional strength gain from 28 to 90 days. Overall, low-grade kaolinite–illite clays combined with limestone deliver LC³ systems with hydration development and mechanical performance comparable to commonly used fly ash-based cements, supporting their feasibility as regionally sourced, low-carbon binders.

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.

S obzirom na značajan utjecaj građevinskog sektora i potrebu za zelenom transformacijom, obrazovanje ima ključnu ulogu. Ovaj rad opisuje ulogu obrazovanja u promicanju održivosti. Kolegij Zelena gradnja, uspostavljen unutar EU projekta GREENCO, predstavljen je kao primjer dobre prakse. Projekt GREENCO usklađuje obrazovne programe s tržišnim potrebama (održivost, digitalizacija). Rad detaljno prikazuje sadržaj i metodologiju kolegija, uključujući projektno učenje i rezultate ankete studenata. Anketa je potvrdila interes za održivost unatoč nedostatku adekvatne pripreme kroz kurikulum. Kolegij Zelena gradnja uspješno integrira održivost u visoko obrazovanje, fokusirajući se na razvoj zelenih vještina.

Due to the impact on the environment, the construction industry is striving to comply with the EU Green Deal in terms of reducing the natural resources used to produce cement. One of the strategies is the use of industrial by-products such as cement substitutes. In this work, the autogenous shrinkage of cement pastes with red mud (RM), limestone (LS), silica fume (SF), and calcined clay (CC) was investigated. The materials used originate from the same region in South-Eastern Europe. Five different mixtures were tested, in which the replacement level for cement varies up to 20% for RM and up to 10% for SF, LS, and CC. In addition, the behavior in the fresh state was evaluated by testing the workability and setting time and in the hardened state by testing the compressive and flexural strength. The results show that as the amount of supplementary cementitious material (SCM) increases, the deformation of autogenous shrinkage gradually increases. Normalized to the amount of cement, the compressive strength showed higher efficiency of the cement when SCMs were added. The results suggest that the SCMs used, with their fine particle size, provide additional nucleation sites for hydration products, resulting in higher efficiency of the cement in achieving compressive strength and higher autogenous shrinkage when SCMs are present.

Alkali-activated materials (AAMs) are alternative binders with no cement in their composition. They are synthesized from aluminosilicate-rich precursors and alkaline activators – usually hydroxides and silicates. They significantly contribute to the overall CO2 footprint of AAMs, leading to efforts to replace them with alternative alkali-rich waste materials such as agricultural biomass ashes. The paper presents the comparison of slag-based mortars activated with sunflower husk ash (SHA) – a locally available waste material in the Autonomous Province of Vojvodina, Serbia, and KOH and NaOH. The influence of SHA on the mortars was assessed by comparing the 7- and 28-day compressive strength.