Polyurethane foam (PUF) is an exceptionally adaptable product that has a variety of applications—it can be found almost everywhere. Due to such high utilization, the amount of polyurethane foam waste generated each year is growing over time. Rebonding polyurethane foam waste is a suitable way to progress towards a circular economy. In this paper, the prospect of using rebonded polyurethane foam (RPUF) in noise control applications is examined. An experimental study was carried out on RPUFs with various thicknesses and densities. The sound absorption coefficients at normal incidence and air resistivity were measured. The five-parameter Johnson-Champoux-Allard (JCA) model was adopted for the simulation of the porous layer. The remaining unknown parameters of the JCA model were estimated by inverse acoustic characterization based on fitting the transfer matrix method (TMM) model of an unbounded porous layer with rigid backing to the experimentally obtained sound absorption coefficients. Furthermore, sound absorption coefficients were calculated for a wide range of sample thicknesses, as well as for different air gap thicknesses between the wall and the porous layer. For some of the considered RPUFs, a sound absorption coefficient above 0.8 was achieved over a wide frequency range.

The textile industry is one of the oldest industries and the third most important industry branch in Macedonia. It has had a steady increase in production over the years. Growing production line proportionally generates textile waste. Although it is terminologically categorized as waste, textile waste can be a valuable resource and is one of the textile industry’s main challenges. Textile waste, appropriately treated with the possibilities offered by the recycling process or used as a clean waste, can find multi-faced application in different construction areas. This paper covers research that examines the possibilities of applying textile waste in the field of thermal insulations in buildings. The focus is on developing thermal insulation solutions applied in sustainable and ecologic buildings. Applied thermal insulation has a primary impact on reducing electricity consumption and greenhouse gas emissions associated with indoor air conditioning. That would mean that buildings incorporating appropriate thermal insulation offer greater comfort, directly increasing the quality of life. This is an additional economic-environmental dimension. According to the experimental testing, the thermal conductivity coefficient of the textile waste is obtained at 0.039 W/m·K. Its value defines a thermal insulation material suitable for the purpose and has approximate values to the other materials usually used for thermal insulation in buildings. Implementing a product made of textile waste with appropriate performance would bring economic benefits to the industry and open new job opportunities.

Urbanization and increased traffic across Europe are leading to increased exposure of the population to harmful levels of noise, primarily caused by road traffic. Over 30% of the population is exposed to levels exceeding the limits recommended by the World Health Organization (WHO). Among the various noise reduction strategies, reinforced concrete noise barriers stand out as one of the most effective passive measures. This research analyses the geometric optimization of reinforced concrete noise barriers with different top-edge designs (flat, T-shape, symmetric and asymmetric V-shape) using the Bound Optimization by Quadratic Approximation (BOBYQA) method. The analysis was conducted using COMSOL Multiphysics software, where a coupled solid mechanics and pressure acoustics model was developed. The simulations were performed in a frequency range from 50 to 3150 Hz. The results show that geometry has a significant impact on acoustic efficiency, with the asymmetric V-shape demonstrating the greatest noise reduction. These findings highlight the key role of geometric optimization in the design of cost-effective and sustainable noise protection solutions.

Buildings account for a significant share of final energy consumption, with space heating representing one of the major energy uses in residential buildings. Therefore, improving the thermal performance of building envelopes is an important strategy for reducing energy demand. Green roofs can contribute to this objective by modifying roof thermal properties and reducing heat losses through the building envelope. This study investigates the use of machine learning to predict annual heating demand and potential heating energy savings associated with replacing conventional roof configurations with a selected green roof assembly in a representative stock of Macedonian buildings. A representative dataset comprising 2934 building cases based on post-2013 buildings designed in accordance with the national energy-performance regulations was assembled. The dataset covers a wide range of building typologies, envelope thermal properties, climatic conditions and heating schedules. Three supervised learning models, Random Forest, Artificial Neural Network and Extreme Gradient Boosting (XGBoost), were developed and compared. The results show that XGBoost achieved the highest predictive accuracy and the best computational efficiency, with test coefficients of determination of 0.9901 for the heating demand of conventional roof buildings and 0.9956 for green-roof-related heating energy savings. Most simulated buildings showed heating energy savings of up to 10% following green roof implementation, while only a limited number of cases exhibited increases in heating demand of up to 3%. The feature importance analysis identified heated floor area, heating duration and wall area as the major drivers of heating demand in conventional roof buildings, whereas roof thermal transmittance was the most influential factor governing green-roof-related heating energy savings. The findings demonstrate that machine learning can reliably reproduce the results of the established energy performance assessment methodology and provide rapid estimates of the potential heating energy savings associated with replacing conventional roofs with a selected green roof system across a representative building stock. The proposed approach can support engineers, urban planners and architects in the early-stage assessment of green roofs as an energy-efficient measure.

The global environmental problems facing the world today largely stem from the excessive exploitation of natural resources. An increasing number of world studies aim to find ways to replace natural resources, introducing new building materials that utilize plants, polymers, and industrial or municipal waste. On the other hand, approximately 90% of waste tyres end up in landfills, meaning there is no designated plan for their further utilization. One of the various solutions for reducing tyres waste and protecting the environment involves using waste tyres in green building materials. This study investigates the properties of concrete mixtures in which a portion of the fine aggregate is replaced by waste rubber particles, with the aim of reducing existing waste and the need for natural aggregate. For the purposes of this paper, 4 different mixtures were tested that differ in the percentage of rubber: replacements of 0, 15%, 30% and 50% of the aggregate with waste tyre by volume. Consistency of the fresh concrete decreased as the percentage of waste rubber increases, as well as the bulk density of hardened concrete, resulting in lightweight building materials. The strength properties and water resistance of the tested samples also decreased with the increase of the rubber waste percentage. The results indicate that increasing the waste rubber in concrete mixtures has a significantly more adverse effect on compressive strength and water impermeability than on flexural strength. However, despite the reduction in strength caused by the use of rubber in the concrete, concrete with a high content of rubber particles (50%) would be suitable for non-load-bearing elements, whereas lower contents (15% and 30%) remain viable for structural applications. The positive properties of concrete with waste rubber are highlighted, their application is suggested.

The transition toward a circular economy in the construction sector promotes the reuse of materials, the development of bio-based composites, and the recycling of industrial waste streams. While these strategies significantly reduce resource consumption and environmental impacts, they also introduce new challenges related to fire safety, material performance, and regulatory compliance. Circular construction increasingly incorporates combustible bio-based materials, recycled polymers, and waste-derived composites, which may alter fire behavior and increase fire loads in buildings. This paper reviews recent developments in circular construction materials, including bio-based composites, recycled tire rubber concrete, wood-based insulation foam, and agricultural waste reinforced polymers. Furthermore, the study discusses the role of bio-based flame retardants, and the emerging regulatory challenges related to hazardous substances and waste reuse. The findings highlight the need for integrated design approaches that combine sustainability, fire safety engineering, and risk management frameworks. Achieving safe circular construction requires collaboration between researchers, industry, and policymakers to ensure that environmental benefits do not compromise building safety.