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.

The article handles potential approaches to design and determination of total load capacity of foundation slabs and floors. The research is focused on punching shear failure of reinforced ground...

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.

The current findings on concrete with fibers show that research has focused primarily on individual aspects, especially in terms of mechanical properties and structural uses. However, no broader view of the problems solved has been provided. In this study, we present a conceptual overview of a new, comprehensive experimental program for the assessment of fiber-reinforced concrete, which includes the analysis of microstructural and structural elements, as well as specific features such as shrinkage and resistance to pressurized water. The proposed experimental program included several variants of schemes for the dosing of fibers into concrete, using steel fibers that were short and straight. Fiber dosing was performed up to 110 kg/m³. The basic tests performed included tests of the compressive strength of concrete, and of the split and flexural tensile strength for different dosing amounts. Within the structural tests of reinforced concrete beams without shear reinforcement, two variants of spans with different degrees of reinforcement were implemented. Herein, the test results are evaluated graphically with a detailed analysis of the positive effect of fibers, and we also provide general recommendations for the structural uses of the fibers used and the design of fiber-reinforced concrete structures. Among the important results of this experimental program was the observation of a significant increase (of the order of tens) of the percentage of the split tensile strength and an increase of the overall load-bearing capacity of the reinforced concrete beams without shear reinforcement. Among the important aspects of our findings is the fact that a fine-grained concrete mixture was used, which increased resistance to pressure water seepage, and therefore, the effect of shrinkage can be influenced by the method of production and the treatment of the concrete used. We also provide detailed figures of the microstructure.

The study of new and innovative quasi-brittle materials offers new possibilities for use in construction, but detailed knowledge of their behavior and mechanical properties is required. The use of new materials in the design solution of a structure is usually associated with numerical methods, which has a number of both advantages and disadvantages. Sophisticated numerical methods, without a sufficiently detailed input knowledge, can provide highly variable results with little informative value. The main goal of this article is to present the procedure for the identification of fracture mechanical parameters for a specific concrete with the use of developed inverse analysis combining multi-criteria decision analysis, stochastic modelling and nonlinear analysis. Subsequently, the identified mechanical parameters of concrete are used for the parametric study of shear resistance of structural beams without shear reinforcement, as an alternative or generalized approach to the study of damage to concrete and concrete structures. This research includes an experimental program using 24 reinforced concrete beams and a detailed determination of basic and specific mechanical properties during laboratory tests. The process of inverse analysis is illustrated in detail for the solved task. The use of nonlinear analysis for detailed failure modelling is based on a 3D computational model and a fracture plastic material model for concrete. Finally, the results of the experimental program and numerical modelling are discussed, leading to a number of conclusions.