3D concrete printing (3DCP) technology holds significant potential to revolutionise traditional concrete production methods, offering designers and architects greater flexibility in creating intricate and innovative structures. Beyond structural applications, 3D printed concrete products encompass decorative elements, customised design solutions, and even artistic installations. The 3DCP process is highly automated, often integrating building information modelling (BIM) systems, minimising the need for manual labour and generating minimal material waste. 3DCP is regarded as one of the most advanced and efficient methods for fabricating concrete components in the future. This paper examines 3DCP technology and equipment, focusing on the selection of binder types, aggregates, and chemical admixtures, suitable for printable concrete mixes. Particular attention is given to the consistency and workability of 3DCP mixtures. Furthermore, the study evaluates the influence of 3D printing parameters on the mechanical properties of hardened concrete. The insights presented in this review contribute to a deeper understanding of 3D concrete printing technologies, equipment, and materials, benefiting researchers, structural engineers, and designers in the pursuit of enhanced durability and performance of 3D printed concrete structures.

The utilisation of Portland cement has aroused tremendous concerns owing to its production exerting a lot of pressure on the environment. Alternative eco-binders have been developed to replace it, among which alkali-activated materials (AAMs) have drawn great attention, especially due to the possibility of encompassing industrial and agricultural waste, which significantly improves the sustainability and cost-efficiency of the material. Biomass wood ash (BWA) is a by-product generated from power plants and, along with the advocation for biomass fuel as a renewable energy resource, there have been increasing applications of BWA in building and construction materials. This review examines the use of BWA as a precursor source in AAMs. Due to its low chemical and hydraulic reactivity, more active binary precursors are usually introduced to guarantee mechanical properties. Whereas the increment of BWA content can have a negative influence on material strength development, it is still a promising and feasible material, and new approaches should be developed to improve the effectiveness of its utilisation. Currently, study of BWA-based AAMs is still in the beginning stages and more research is needed to investigate the effects of BWA characteristics on the property evolution of AAMs, focusing on the durability and analysis of eco-efficiency. Overall, this review provides a comprehensive overview of the characterisation of BWA and its potential applications in AAMs, and meanwhile, based on the analysis of present research trends, proposes some prospective directions for future research.

This study explored unprocessed high-carbon biomass fly ash (BFA) in alkali-activated materials (AAM) with less alkaline Na₂CO₃ as the activator. In this paper, the effects of the Na₂CO₃/Na₂SiO₃ (C/S) ratio and curing temperature (40 °C and 20 °C) on the setting time, structure formation, product synthesis, and physical-mechanical properties of alkali-activated BFA pastes were systematically investigated. Regardless of curing temperature, increasing the C/S ratio increased the density and compressive strength of the sample while a decrease in water absorption. The higher the curing temperature, the faster the structure evolution during the BFA-based alkaline activation synthesis process and the higher the sample’s compressive strength. According to XRD and TG/DTA analyses, the synthesis of gaylussite and C-S-H were observed in the sample with an increasing C/S ratio. The formation of the mentioned minerals contributes to the compressive strength growth of alkali-activated BFA pastes with higher C/S ratios. The findings of this study contribute to the applicability of difficult-to-recycle waste materials such as BFA and the development of sustainable BFA-based AAM.

The increased early hydration rate of high early strength cement has economic advantages in many civil engineering fields (faster formwork removal or earlier demoulding of precast elements). Styrene–butadiene rubber (SBR) latex is the most common polymer in aqueous dispersions suitable for admixing in cement-based materials. It allows the designing of structures with specific properties for a variety of applications. The analysis of literature sources has shown that different properties of SBR latex-modified cement-based material samples reported were usually measured at 3, 7, 14, and 28 days of hardening. In this research, the authors decided to investigate a combined effect of high early strength Portland cement, characterized by an increased hydration rate, and SBR latex able to retard this process for a prolonged hardening period—up to 90 days in modified mortar samples. This study covers the results of the effect of different amounts of SBR latex (5%, 10%, 15%, and 20%) on the properties of modified mortar samples with a constant water-to-cement ratio prepared with high early strength Portland cement 42.5 R. The mortar samples were prepared from local raw materials produced by the Lithuanian companies. The properties, such as dry bulk density, ultrasonic pulse velocity, capillary water absorption, compressive and flexural strengths, and toughness, after three different hardening periods (7, 28, and 90 days) of the mortar samples were investigated. The applied mathematical–statistical methods allowed a detailed prognosis of the dependence between the dry bulk density and the strength properties of modified mortar samples. The combination of 42.5 R strength class Portland cement with the SBR latex in amounts ranging from 5% to 20% seems to be suitable for designing durable structures with specific properties.

In case of a fire, the flame can spread from the building through the outer openings to the outside. In such cases, the fire temperature thermal effect determines the façade fibrocement tile thermal destruction, while the flammable thermo-insulating systems used for building energy effectiveness ensures it sets on fire. The spread of such a fire becomes uncontrollable and raises an immediate danger to the people inside the building, while such event dynamics delay and make it harder to put out the fire. Extra additive usage in façade fibrocement tiles can raise its resistance to fire temperature effect. Carbon fiber is widely known as a material resistant to the high temperature destructive effect. An investigation was conducted on the influence that carbon fiber has on the properties of autoclaved fiber cement samples. The autoclaved fiber cement samples were made from the raw materials, typical for façade fiber cement plates, produced in an industrial way (using the same proportions). In the samples, carbon fiber was used instead of mix cellulose fiber in 0.5%, 0.75%, 1% proportions. After completing the density research, it was determined that the carbon fiber effect had no general effect on the sample density. Ultrasound speed spreading research showed that the carbon fiber insignificantly makes sample structure denser; however, after the fire temperature effect, sample structure is less dense when using carbon fiber. The results of both these investigations could be within the margin of error. Insignificant sample structure density rise was confirmed with water absorption research, which during the 1% carbon fiber usage case was lower by 4.3%. It was found that up to 1% carbon fiber usage instead of mix cellulose fiber creates a dense structure of autoclaved fiber cement samples, and the carbon fiber in the microstructure influences the mechanical properties of the autoclaved fiber cement samples. After using carbon fiber in ambient temperature, the sample compressive strength and bending strength increased. However, the results of mechanical properties were completely different after experiencing fire temperature effect. Scanning electron microscopy research showed that the bond between the carbon fiber and the cement matrix was not resistant to high temperature effect, due to which the structure of the samples with carbon fiber weakened. Research showed that carbon fiber lowers the mechanical properties of the autoclaved fiber cement samples after high temperature effect. After analyzing the density, ultrasound speed spreading, water absorption, microstructure and macrostructure, compressive strength, and bending strength, the authors determined the main CF usage for AFK dependencies: 1. CF usage up to 1% replacing MCF makes the AFK structure more dense up to 1.5%, and lowers the water absorption up to 4.3%; 2. CF incorporates itself densely into the AFC microstructure; 3. CF usage up to replacing MCF improves the AFK strength properties up to until the fire temperature effect. Compression strength increases up 7.3% while bending strength increases up to 14.9%. 4. AFK hydrate amount on CF surface is lower than on MCF; 5. Fire temperature effect on AFK with CF causes dehydration by removing water vapor from the microstructure, resulting in a lot of microcracks due to stress; 6. The CF and cement matrix contact zone is not resistant to fire temperature effect. SEM experiments were used to determine the CF “self-removing” effect; 7. Due to complex changes happening in the AFK during fire temperature effect, CF usage does not improve strength properties in the microstructure. Compression strength decreases to 66.7% while bending strength decreases to 20% when compared with E samples.

Drinking water treatment sludge (DWTS) is a typical by-product of drinking water treatment plants. Concerns are growing about how to deal with big amounts of this sludge generated globally. One of the ways is to reuse DWTS as a supplementary material in cementitious systems and thus reduce landfill disposals. For our studies, we used DWTS containing more than 52% Fe₂O₃. The DWTS was taken from a water treatment plant in Vilnius, Lithuania. This work aimed to find potential applications of unprocessed DWTS in cementitious systems as a supplementary material that changes the physical and mechanical properties of the final product. Tests were performed with cementitious mortars where the binder was replaced with DWTS (from 0% to 12.5%). Local raw materials such as Portland cement CEM I 42.5R and sand 0/4 were used in the tests. Water absorption, absorption kinetics, and mechanical strength tests were conducted, and predictive freeze–thaw resistance was estimated. The heat release rate and open–closed porosity were also measured. The results showed that DWTS impacts the hydration of cementitious mortars, lowers their density (from 2122 kg/m³ to 1954 kg/m³), as well as compressive strength (from 41.78 MPa to 24.76 MPa) and flexural strength (from 6.24 MPa to 4.07 MPa), and increases total porosity (from 28.1% to 34.6%) and closed porosity (from 9.1% to 14.9%). The lowest toughness value of 6.08 was recorded in the 12.5% DWTS sample. From our conducted research, it could be observed that raw DWTS potentially changed the porosity parameters of cementitious mortars. This resulted in an incremental improvement in durability and an improvement in the hardness of cementitious mortars. A higher content of raw DWTS changed the colour (to reddish) of cementitious mortars, due to its higher Fe₂O₃ content (up to 53%). All of the above-mentioned properties allowed the designing of cementitious landscape products with a wider range of colours.