The paper presents the results of the research identifying the hydration products present in hardened fly ash–slag pastes considered as alternative non-clinker binder. Thermal analysis (TG/DTG), infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used as complementary methods. The pastes contained the binder made of two components: fly ash from circular fluidized bed combustion of brown coal and ground granulated blast furnace slag. The components were mixed accordingly to five formulas differing in proportions, but with constant water/binder ratio (w/b = 0.5). No chemical activators were used to initiate the binding reaction of blast furnace slag. The results of thermal analysis, IR spectroscopy and scanning electron microscopy as well as the increase of compressive and flexural strength in time revealed the progression of hydration process in time and formation of products similar to ones present in hardened cement pastes. SEM observations of pastes after 90 days of curing showed fibrous (type I) and similar to honeycomb form of C–S–H phase, ettringite and calcium aluminates.

The production of concrete strongly influences the environment. It is a versatile and sustainable construction material capable of creating a wide range of structures. It has always been indispensable as a material for the engineering and construction industry, including applications in hydraulic structures (e.g., dams, underwater tunnels, sluices, and other concrete structures), where mass concrete is a fundamental material in the construction industry. Developing sustainable concrete as an alternative construction material to the traditional one provides a reduction in the carbon dioxide footprint with regard to cement use and waste material disposal in landfills. This paper provides a comprehensive review of current trends and opportunities in sustainable construction using mass concrete. It underscores the importance of incorporating eco-friendly practices to mitigate environmental impact by using by-products as green materials. The review highlights how optimizing clinker content, supplementary cementitious materials (SCMs), and aggregates can improve the strength, durability, and thermal stability of mass concrete. Strategic material selection helps minimize thermal cracking, extend service life, and reduce environmental impact. Future research should focus on developing advanced mix design strategies and standardized practices for sustainable infrastructure.

The article discusses the results of examining the impact of aggressive solutions on specimens of mortars with a slag-ash binder. Bar specimens were exposed to unidirectional diffusion of sodium chloride and sodium sulphate for 90 days. Next, the specimens were subjected to flexural and compressive strength tests, ion content tests, XRD phase composition tests, and microstructural SEM-EDS tests. The test results indicated that aggressive solution action resulted in decreased flexural strength, however, it did not impact the compressive strength of mortars. A minor impact of chloride ions on the pH of the pore liquid was recorded, while the tests did not show any influence of sulphate ions. Furthermore, aggressive ion concentration decreased in deeper specimen slices. Specimen phase composition testing after chloride ion action indicated the presence of a small amount of Friedel’s salt, while regular sodium chloride crystals were identified in the microscopic image. The performance properties of mortars exposed to the action of aggressive solutions were maintained.

The manuscript presents the condition of circular economy in Poland in diversified approach: subjective (waste streams, energy), sectoral (construction, wastewater treatment, coal energy), related to the resources (phosphorous and anthropogenic minerals) and considering proper energy management (almost zero energy buildings). The achievements reached in different sectors as well as the requirements towards implementation of CE are presented. The advancement of recycling technologies does not deviate from the global level, in terms of areas specific to Poland. Limiting the exploitation of natural resources and usage of new materials as well as producing more durable products are of CE concern. Also energy and heat recovery in buildings and technological processes (e.g. during wastewater treatment), ways of utilization of combustion by-products and water decarbonization waste are described. The implementation of CE in Poland needs not only research and technical activities, but also the modification of technological processes, the right policy, overcoming crosssectoral barriers, developing legal regulations and support schemes for CE.

Hardening slurries (water-bentonite-binder mixtures) constitute a well-established material used broadly, i.a., for cut-off walls in civil and water engineering. Although they usually contain Portland cement, similar to common concrete, their properties differ greatly, mostly due to a much higher water content. This characteristic of hardening slurries creates unique opportunities for the utilization of significant quantities of industrial by-products that are deemed problematic in the concrete industry. This article investigates the effect of the addition of by-products of fluidized-bed combustion of hard, brown coal and municipal sewage sludge, as well as ground granulated blast furnace slag, on the properties of slurries. Unconfined compressive strength tests, as well as mercury porosimetry, scanning electron microscopy, and X-ray diffraction analyses were performed. The results suggest that it is possible to design hardening slurry mixes of desired properties, both in liquid and solid state, containing at least 100–300 kg/m³ of industrial waste. This includes cement-free slurries based entirely on industrial by-products as binders. In addition, the analyzed slurries exhibited good chemical resistance to landfill eluates, at the same time effectively immobilizing heavy metals. It was concluded that hardening slurry technology can ensure the safe deposition of significant amounts of waste that would be otherwise difficult to manage, thus contributing to the circular economy concept.