The propagation of cracking in concrete is a mechanism governing many physical and mechanical properties of the material. The aim of this study was to experimentally investigate the crack propagation of new concrete compositions using image analysis. Several concrete mixes containing microsilica and nanosilica were made. For each composition, Compact Tension (CT) specimens were prepared with dimensions 150x150x12mm. Specimens were subjected to a tensile load. The formation and propagation of the tensile cracks was traced on the surface of the specimens using a high resolution digital camera with 60 mm focal length. Images were captured during testing with a time interval of one second. The compression strength and modulus of elasticity were also determined for reference. The results obtained with this method have shown that it is possible to monitor relatively small displacements on the specimen surface regardless of the scale of the representative area of interest and to evaluate the influence of filler on the cracking properties of concrete.

Geopolymer composites have been around only for 40 years. Nowadays, they are used in buildings and infrastructures of various kinds. A geopolymer’s main benefit is that it is a green material that is partially made by utilizing waste products. The carbon footprint from geopolymer matrix manufacturing is at least two times less than Portland cement manufacturing. Due to the nature of the geopolymer manufacturing process, there is a high risk of shrinkage that could develop unwanted micro-cracks that could reduce strength and create higher creep strains. Because of this concern, a common strategy to reduce long-term strains of the material, such as shrinkage and creep, is to add fiber reinforcement that would constrain crack development in the material. This article aims to determine how various kinds and amounts of different fiber reinforcement affect fly ash-based geopolymer composites’ creep strains in compression. Specimen mixes were produced with 1% steel fibers, 1% polypropylene fibers, 5% polypropylene fibers, and without fibers (plain geopolymer). For creep and shrinkage testing, cylindrical specimens Ø46 × 190 mm were used. The highest creep resistance was observed in 5% polypropylene fiber specimens, followed by 1% polypropylene fiber, plain, and 1% steel fiber specimens. The highest compressive strength was observed in 1% polypropylene fiber specimens, followed by plain specimens, 1% steel fiber specimens, and 5% polypropylene fiber-reinforced specimens. The only fiber-reinforced geopolymer mix with improved long-term properties was observed with 1% polypropylene fiber inclusion, whereas other fiber-introduced mixes showed significant decreases in long-term properties. The geopolymer composite mix with 1% polypropylene fiber reinforcement showed a reduction in creep strains of 31% compared to the plain geopolymer composite.

Global vibration-based methods in the field of structural health monitoring are intended to capture structural stiffness changes of buildings or other civil engineering structures. Natural frequencies of buildings or bridges are commonly used parameters to monitor these stiffness changes. Therefore, it is essential to clarify the limit at which this method is no longer sensitive enough to be useful for structural health monitoring purposes. This paper numerically investigates the effect of structural damage and soil–structure interaction on cellular-type reinforced concrete buildings’ natural frequencies. These buildings are a common housing stock of Eastern Europe but are rarely investigated in this context. Comparisons with a reinforced concrete frame and infill structure building are made. Finite element models representing three structural system types of nine-story reinforced concrete buildings were used for the numerical simulations. Furthermore, a five-story finite element model was used for a damage sensitivity comparison. It is established that, for cellular-type structure buildings to detect damage comparable to that investigated in the paper, structural health (fixed base model frequency) should be monitored directly. Then, a statistical significance level for frequency changes of no more than 0.1% should be adopted. Conversely, the rocking frequency is a very sensitive parameter to monitor building base condition changes. These changes are often a cause of the cracking of building elements.

With the growing importance of the principle of sustainability, there is an increasing interest in the use of timber–concrete composite for floors, especially for medium and large span buildings. Timber–concrete composite combines the better properties of both materials and reduces their disadvantages. The most common choice is to use a cross-laminated timber panel as a base for a timber–concrete composite. But a timber–concrete composite solution with plywood rib panels with an adhesive connection between the timber base and fibre reinforced concrete layer is offered as the more cost-effective constructive solution. An algorithm for determining the rational parameters of the panel cross-section has been developed. The software was written based on the proposed algorithm to compare timber–concrete composite panels with cross-laminated timber and plywood rib panel bases. The developed algorithm includes recommendations of forthcoming Eurocode 5 for timber–concrete composite design and an innovative approach to vibration calculations. The obtained data conclude that the proposed structural solution has up to 73% lower cost and up to 71% smaller self-weight. Thus, the proposed timber–concrete composite construction can meet the needs of society for cost-effective and sustainable innovative floor solutions.