Conclusions from the scientific-professional conference: "Current Trends in the Field of Materials and Structures"

held on 10/05/2024 at the IMS Institute Belgrade and on 10/10/2024 at the Faculty of Civil Engineering and Architecture in Niš

By adopting the Rulebook on technical requirements for concrete, full responsibility for placing concrete on the market is assumed by the concrete producer, who states in the declaration of performance the performance of the concrete with regard to its essential characteristics and thereby confirms its compliance with the prescribed requirements. The Rulebook introduces additional requirements for the producer in terms of implementing and documenting production control, as well as issuing documents (declaration of performance, delivery note, technical documentation, etc.). Also, adapting to the Rulebook requirements will, in addition to investments in material and human resources, require certain adjustments and a change in producer awareness regarding concrete production and control. In this regard, it is expected that producers will need assistance in the area of education and in preparing factory production control documentation. The increase in obligations and responsibilities of concrete producers in the process of assessment and verification of constancy of performance will bring significant improvements in this sector of construction products, in terms of improved quality and a higher level of safety of concrete made available on the market

Over the past few years, 3D concrete printing technology has significantly advanced as a response to the introduction of digitalization and process automation in construction, as well as to architectural demands for free-form shapes that have significantly increased the share of formwork costs in the total structure cost. Based on a large number of studies, appropriate methods for testing the properties of 3D printed concrete in both fresh and hardened states have been defined. Numerical models have been developed to simulate the printing process and serve to verify experimental research. There are only a small number of studies on finished elements and structures, and mostly only vertical loading tests have been performed. Further progress depends on resolving open issues such as standardization of the entire process—from testing mixture properties, design, to execution of these structures—and especially the incorporation of reinforcement. The main disadvantages are the large amount of cement required for preparing mixtures and the fact that the size of the printer itself dictates the dimensions of the object that can be produced. Practical application so far has been closely linked to cooperation between industry and the scientific community, in the sense that before every major practical application, both mixtures and finished elements were tested under laboratory conditions. In the Republic of Serbia, practical application of 3D printed concrete is not particularly widespread, and mixtures for 3D printing from the manufacturer SIKA can be found on the market. For the further development of this technology, greater interest from economic entities and initial investments in equipment, i.e., printers, are necessary. In general, 3D concrete printing technology is a reality worldwide, and with the elimination of the mentioned shortcomings and resolution of challenges, its application in modern construction will become increasingly broad. In any case, 3D printed concrete technology is not intended for mass construction of multi-story buildings, but should be adapted to prefabrication and achieving challenging architectural forms in structural and non-structural elements

Concrete masonry blocks made from lightweight aggregate and with the addition of waste powdered materials as a partial cement replacement represent innovative ecological products. Experimental research established that blocks with cavities filled with EPS-based thermal insulation material, in which three types of lightweight aggregate or recycled crushed concrete were used as aggregate for concrete preparation, and about 50% of cement was replaced with fly ash or bio-ash, have satisfactory compressive strength, so they can be used for constructing load-bearing façade walls or infill façade walls in frame structures. The thermal conductivity value of the analyzed blocks is such that, without additional thermal insulation, it enables their application in areas with mild, very moderate climates such as the Mediterranean, while in areas with colder climates, an additional layer of thermal insulation is required. The block dimensions were adopted to achieve, compared with conventional masonry blocks and brick, faster execution of works, and thanks to the fact that fewer blocks are needed per 1m2 of wall and that they interlock by tongue-and-groove principle, the number of thermal, i.e., cold bridges through which heat is lost from the building is reduced. The block surface is smooth, reducing the need for additional plastering, so only final wall surface finishing is possible. Based on all analyzed parameters, block D can be adopted as the most environmentally acceptable type. 

Advancing sustainable construction through the use of waste materials in porous concrete represents a good step toward building urban areas adaptable to pluvial flooding. Integrating circular economy principles into urban drainage and urban planning for the further development of modern cities contributes to reducing the quantity of waste materials that would otherwise end up unused in landfills, while also providing an efficient solution for adapting urban environments to changed climate conditions. The potential of porous concrete as a construction material is reflected in the possibility of using it for efficient on-site stormwater runoff management and water infiltration into the soil, while simultaneously reducing the risk of pluvial flooding in urban areas. Using waste materials as additives in porous concrete further strengthens the sustainability of applying CE principles in urban drainage by providing an alternative to traditional, resource-intensive materials. Implementation of this technology requires a multidisciplinary approach that includes cooperation between science and industry, engineers, urban planners, and local authorities. Through regulatory harmonization, research support, and education, an environment can be created that encourages innovation in sustainable construction and contributes to creating cities for future generations. In this sense, advancing sustainable construction through the use of waste materials in porous concrete represents a step forward toward achieving sustainable development goals, creating urban environments that are adaptable to changed climate conditions, while at the same time safe from the environmental protection standpoint.

With the aim of reducing the amount of waste, solutions were offered that would enable the integration of waste and recycled materials into new products, thereby providing them with new use value. Recycled cathode ray tube glass can be successfully used for making the finishing layer of concrete blocks and tiles, because it improves the properties of the wearing layer of these products, while on the other hand contributing to aesthetic value. Also, self-compacting concrete with the addition of recycled cathode ray tube glass can be considered suitable for manufacturing prefabricated concrete elements such as concrete curbs whose cross-section does not exceed 300 cm2. 

The use of waste glass enamel in concrete, as a partial cement replacement, on one hand contributes to a slight reduction in mechanical properties, while on the other hand does not jeopardize concrete durability. The physical and mechanical properties of concrete made with waste enamel in amounts up to 20% do not significantly differ from reference concrete, especially compressive strength as the most important concrete characteristic. By testing the impact of partial cement replacement with waste glass enamel in the amount of 15% by mass on the characteristics of concrete paving blocks, it was confirmed that these blocks can be used in practice without any restrictions.

Geopolymers are a relatively new type of material developed in recent decades. In developed countries they are widely applied, while in our country they are still at the level of scientific research, without serious practical participation. In general, geopolymer mortars and concretes can be an adequate substitute for traditional cement composites. Replacing part of electrofilter ash with other industrial by-products has a positive effect on certain mortar and concrete characteristics. Still, more important than all tested characteristics is the ecological aspect of geopolymers. The use of industrial by-products that form the basis for preparing geopolymer mixtures contributes to reducing local waste. Also, by implementing geopolymer mixtures prepared on the basis of electrofilter ash and with additions of granulated blast-furnace slag, converter slag, wood biomass ash, red mud, and waste glass, harmful environmental impact and CO2 emissions will be reduced. The subject concretes showed good resistance to sulfate action and abrasion, and could therefore be used as concretes for making concrete slabs, blocks, drainage channels, or underground parts of structures that will not be exposed to low temperatures. To practically confirm this possibility, it is first necessary to expand existing legal regulations and standards that would define their use. In order to solve this problem, it is necessary to carry out a series of same-type tests so that standardization of geopolymer composites can be performed.

The amount of waste (rejects) generated during the production of ceramic products in the construction industry is not negligible and amounts to between 15–30% of total production. The use of ceramic powder, obtained by grinding ceramic waste, as a replacement for part of cement stands out as particularly important from the aspect of the cement industry’s pursuit of sustainability through reducing clinker production by applying alternative materials. Experimental research was conducted on the possibility of applying ceramic powder generated by crushing waste from the ceramic industry of Vojvodina as a potential SCM material in modern masonry mortars. The results showed that replacing cement with ceramic powder reduces mortar workability, which is a consequence of the shape of ceramic waste particles after mechanical crushing and the higher absorption capacity of coarse construction ceramics. With increasing levels of cement replacement by ceramic powder, capillary porosity increased, resulting in greater capillary water absorption and lower mechanical properties of the mortar. Nevertheless, some mortars met the requirements for use in mortars for load-bearing masonry walls (class corresponding to an average mortar compressive strength of 5 MPa). From the aspect of mortar adhesion and vapor permeability, it was shown that replacing cement with ceramic powder does not have a major impact on the analyzed mortar properties. Replacing part of cement with locally available waste materials is, in this context of environmental protection, highly desirable. The analysis shows that by replacing part of cement with ceramic waste, significant reductions in CO2 emissions can be achieved (up to 40%). The general conclusion is that the application of ceramic powder in optimal quantities in masonry mortar production can not only provide important environmental benefits, but can also improve the mechanical and durability properties of these composites.

Analysis of the impact of products and processes on the environment must be integrated into different types of decisions in modern industry and legislation. When considering the environmental impacts of construction products and processes, it is of vital importance to study them in the form of the product life cycle, in order to avoid shifting problems from one part of the life cycle to another and/or from one geographical area to another. Product and process life cycle assessment (LCA) is directly linked to environmental product declarations (EPD) and product environmental footprint (PEF) in accordance with European Commission rules, then CO2 emission assessment, quantification of product carbon footprint (CFP), and issuance of greenhouse gas (GHG) emission permits. Current activities and updates regarding databases, quality assurance, consistency, and method harmonization contribute to the entire spectrum of previously mentioned activities. By 2026, the Republic of Serbia should have a functional system for monitoring, reporting, and verification of greenhouse gas emissions in order to fulfill its obligations under the Paris Agreement and prepare for the implementation of the cross-border CO2 tax (CBAM) introduced by the European Union from 2026. Accordingly, it can be concluded that assessing the environmental impacts of construction products and processes entails the necessity of communication between stakeholders (such as producers, EPD program operators, LCA practitioners, decision-makers, etc.) and the development of new bodies for certification and document verification with the aim of decarbonization, green production, lower GHG emissions, and sustainability in all sectors, especially in the construction sector.