Fiber-reinforced concrete has a wide application in practice, and many fields of research are devoted to it. In most cases, this is a specific problem, i.e., the determination of the mechanical properties or the test method. However, wider knowledge of the effect of fiber in concrete is unavailable or insufficient for selected test series that cannot be compared. This article deals with the processing of a comprehensive test study and the impact of two types of fibers on the quantitative and qualitative parameters of concrete. Testing was performed for fiber dosages of 0, 40, 75, and 110 kg/m³. The fibers were hooked and straight. The influence of the fibers on the mechanical properties in fiber-reinforced concrete was analyzed by functional dependence. The selected mechanical properties were compressive strength, splitting tensile strength, bending tensile strength, and fracture energy. The results also include the resulting load–displacement diagrams and summary recommendations for the structural use and design of fiber-reinforced concrete structures. The shear resistance of reinforced concrete beams with hooked fibers was also verified by tests.

Sustainable development of concrete construction requires sustainable materials or sustainable binders. Specifically, alkali-activated materials (AAMs) are an interesting and wide group of materials. They have good strengths and are considered environmentally friendly materials because secondary materials are consumed during the preparation of AAMs. The durability of AAMs is also excellent. One of the most important parts of durability is frost resistance. The frost resistance of alkali-activated materials is usually very good. However, some studies showed opposite properties and poor frost resistance. The reason for this may be a different composition of the activator. The content of alkalis is often considered the main characteristic of alkali-activated materials. However, SiO₂ content can play an important role too. This paper discusses the different results for the mechanical properties and frost resistance of different compositions of alkali activators made of sodium water glass with a silicate modulus modified with potassium hydroxide. The role of the activator content and the water-to-cement ratio in this phenomenon is discussed. The results of this article show that the strengths of AAMs are significantly affected by the curing method. Water curing reduced some of the strength of the specimens compared to foil-covered specimens. Frost resistance depends on the method of curing and on the composition of the activator; some concretes with high strengths showed very low frost resistance.

One of the solutions for overheating the interior in the summer without increasing energy consumption is the integration of phase change material (PCM) into interior plasters. However, adding PCM to plasters deteriorates their properties and thus their usability. The aim of this paper is to determine how the microencapsulated PCM affects the mechanical, thermal, and fire properties of plasters and how much PCM can be added to the plaster. Two sets of samples were prepared: in set S, part of the aggregate was replaced by PCM; and in set R, only PCM was added. The bulk density, flexural strength, compressive strength, tensile strength perpendicular to the surface, thermal conductivity coefficient, specific heat capacity, melting, and solidification temperatures and enthalpy were measured. A single-flame source fire test and a gross heat of combustion fire test were performed to determine the reaction to the fire class. The results show that with an increasing proportion of PCM, the strength of the samples of set R decreased more significantly than it did with the samples of set S. It was found that only up to about 10% PCM could be added to set R, while up to 30% PCM could be added to set S.

The research presented in this article aimed to investigate the differences in mechanical properties between solid structural timber and the same reinforced element in three different ways. A three-point bending test was performed on wood elements reinforced with carbon-fiber-reinforced polymer (CFRP), 3D printed polycarbonate (3DPC) lamellas, and 3D printed polycarbonate with carbon fiber (3DPCCF) lamellas. In this comparison, the bending strength was large for CFRP samples, which have 8% higher performance than samples with 3DPCCF and 19% higher performance than samples with 3DPC. Conversely, when factoring in theoretical manufacturing costs, the performance of 3DPCCF is almost three times that of CFRP and 3DPC. In addition, 3D materials can be used for more complicated reinforcement shapes than those discussed in the paper.

Roman cement is the predecessor to modern Portland cement. Nowadays, it is a very promising product with lower CO2 emissions, frequently used to restore historical objects. However, there are still many practical problems as a setting that can be affected in several ways. One possibility is the multistage mixing of fresh mortar, a practical historical method that has not yet been scientifically investigated. This article presents an experimental study investigating the effect of multistage mixing on the properties of fresh and hardened mortar. The properties and structure of the mortar were compared with a reference mortar (retardened by citric acid). Multistage mixing affects fresh mortars with optimal consistency and a workability time of 120 minutes. The influence of mixing on the hydration process and structural formation is characterized by isothermal calorimetry and SEM. Comparison of reference and modified mixing mortars exhibits differences in hydration process, structure, and initial strength, but no significant effect at 90 days strength.

This article compares the results of numerical and experimental analysis of the mechanical properties of an optimized 3D-printed beam. The samples were subjected to a four-point bending test, and corresponding numerical models were created at the same time. The beams were printed using 3D printing and their weight was reduced by using an internal spatial grid with variable thickness that gradually increases towards the outer walls. This approach allows for effective optimization of material strength while minimizing raw material consumption during production. One of the key findings is the determination of the ultimate strength between fibers, the mode of failure, and the high agreement between the experimental results and the numerical model using the finite element method. The optimized beam achieved nearly 60% weight reduction while maintaining comparable load-bearing capacity. The knowledge gained opens up new possibilities in the field of materials engineering and also makes a significant contribution to the methodology of developing and optimizing these structures using 3D printing technology.