Katalin Kopecskó

Forensic investigation of concrete deterioration requires transforming macroscopic symptoms into testable hypotheses and combining complementary analytical methods. Two diagnostic case studies are presented. In pre-stressed railway sleepers, pop-out spalling occurred around large yellowish-brown aggregate particles. Thermal analysis and SEM/EDS identified dolomitic limestone and revealed dedolomitization-related microstructural changes, microcracking, and increased local porosity. In a reinforced-concrete silo used for corn gluten feed, carbonation mapping, XRD, thermal analysis, and wet-chemical testing revealed spatially non-uniform degradation, locally deep carbonation, portlandite loss, interaction with acidic organic material, and elevated chloride and sulfate-related indicators. Both cases demonstrate that reliable diagnosis requires a staged methodology linking damage morphology, alternative hypotheses, targeted sampling, and complementary analytical techniques, while recognizing limitations where available samples cannot discriminate between all competing deterioration mechanisms.

Cellulose nanocrystals (CNCs), increasingly utilized in cement‐bound materials, offer improved material properties and enhanced sustainability due to their bio‐based origin. Nanosilica (NS), known for its high reactivity and refinement of cement microstructure, also significantly impacts cement performance. Although CNC and NS differ markedly in composition, morphology, and interaction mechanisms with cement matrices, CNCs being organic rod‐shaped nanoparticles that modulate hydration kinetics, and NS being inorganic spherical nanoparticles promoting early hydration, their comparative investigation can yield deeper insights into optimizing cement‐based composites. This study comparatively investigates the effects of CNC and NS incorporation (0.25%, 0.50%, and 0.75% by cement weight) on the rheological, mechanical, and microstructural properties of cement pastes and mortars. Results revealed that both CNC and NS additions reduced flow diameters; however, CNC was acting as a setting retarder and NS as a setting accelerator. Rheological measurements showed increased yield stress and plastic viscosity with increasing concentrations of CNC and NS. Compressive strength was notably enhanced with CNC incorporation, achieving peak strength at 28 days with 0.50% CNC, whereas at 90 days, 0.75% CNC exhibited the greatest strength improvement. In comparison, NS significantly improved early‐age mechanical strength due to its high pozzolanic activity, achieving rapid hydration and a denser microstructure at earlier curing periods. Microstructural analyses validated these outcomes, linking CNC and NS incorporation to improved hydration products and densified pore structures. This comprehensive study addresses the current knowledge gap concerning the rheological impacts of CNC and NS in cementitious systems, presenting CNC integration compared to NS incorporation as a sustainable approach to enhance cement performance through environmentally advantageous bio‐based materials.

The radioactive waste cementation technology at the Paks Nuclear Power Plant solidifies low- and intermediate-level liquid radioactive wastes using cementitious materials. Such cement paste is mixed and poured into steel containers containing solid radioactive waste, and the cemented containers undergo a verification process before final deposition. The composition of the cement pastes may need to be altered for each type of liquid radioactive waste, and the mixtures are sensitive to the quality of the binders. Therefore, the types of cement must be tested prior to being identified for each shipment. As the product standards can only serve to verify the basic properties of the given type of cement, and the measurement process is time-consuming, it was necessary to develop a simple and rapid additional identification method to check the application properties relevant to the application field before the cementing process begins. This study evaluates various types of cement produced by the Beremend Cement Plant of Duna-Dráva Cement Ltd. (DDC), Holcim Hungary Ltd. and Danucem Ltd. Through semi-adiabatic calorimetry, combined boric acid and acidic dissolution testing, the CEM I 42.5 N cement from Beremend Cement Plant was identified as the most suitable for ensuring the continuous and reliable operation of the cementation process. Additionally, the applicability of this method in the construction industry was also investigated for other commonly used types of cement.

This study investigates the effects of incorporating metakaolin (MK) and silica fume (SF) on the fresh and hardened properties of 3D printed concrete (3DPC). Five mix designs were prepared with MK replacement levels of 0%, 10%, 12.5%, and 15%, along with one mix containing 10% MK and 5% SF. Key performance metrics include flowability, green strength, pumpability, shape retention, buildability, extrudability, compressive strength, and interlayer bond strength. The results showed that increasing MK content generally enhanced early strength gain, shape retention, and buildability; however, a high MK dosage (15%) negatively affected extrudability and caused visible cracking. The mix with 10% MK and 5% SF (MK10SF5) demonstrated the best overall performance, achieving excellent shape retention ( S ₁ = 0.99), the highest buildability (72 printed layers), and the highest compressive strengths: 85.4 MPa for cast specimens and 78.8, 64.4, and 73.0 MPa in the X , Y , and Z directions, respectively, for 3D printed specimens. It also recorded the highest interlayer bond strength of 2.14 MPa. The superior performance of MK10SF5 is attributed to the synergistic effects of MK and SF, which enhance particle packing, cohesion, and pozzolanic reactivity. These findings highlight the potential of MK and SF in optimizing 3DPC for improved printability and mechanical performance.

This experimental study examines the effects of landfill leachate contamination on soil hydraulic conductivity over a 12-month period, addressing the current lack of long-term experimental data in this field. Laboratory permeability tests were performed on sandy clayey silt samples contaminated with leachate at concentrations ranging from 5% to 25%. Microstructural and mineralogical analyses were conducted using SEM and XRD to identify the mechanisms behind observed changes. The results identify a critical threshold at 15% contamination, where soil behavior transitions from granular to cohesive characteristics. Hydraulic conductivity increases at low contamination levels (5–10%, up to 1.2 × 10⁻⁷ m/s) but decreases significantly at higher levels (4.172 × 10⁻⁸ m/s at 15%, 8.545 × 10⁻⁹ m/s at 20%). These changes are controlled by contamination level rather than exposure time, with values remaining stable throughout the 12-month period. The study provides essential parameters for landfill design and contamination assessment, demonstrating how leachate concentration affects long-term soil hydraulic properties through mineral formation and structural modification.

Collapsible soils, such as loess, are a kind of problematic soil that is naturally unsaturated and withstands high loads at their natural moisture content, but unexpectedly collapses when wet and saturated, creating a risk to buildings constructed on it. This study highlights the effect of chemical stabilizers, including perlite and metakaolin, on the physicochemical behavior of collapsible soils, especially Zeta potential measurement, and the soil’s morphology. The properties of natural soil were compared to those of treated soil using a set of Zeta potential measurement tests. Furthermore, scanning electron microscopy (SEM) analysis was used to validate the results. According to the results, perlite and metakaolin changed the loess soil properties. The results showed that the absolute Zeta potential of soils increased after adding perlite and metakaolin, which indicated a higher dispersity of soils mixed with perlite or metakaolin. The scanning electron microscope (SEM) indicated that untreated samples had a loose structure with extensive pores, whereas treated samples had a dense and uniform structure with particle rearrangement. The flocculation and agglomerations in the soil matrix, which are a significant contributing factor to the mechanical property enhancement of the metakaolin-stabilized samples, were confirmed by SEM images. According to the microstructure and product composition analyses, the calcium-aluminate-silicate hydrate (CASH) generated by the metakaolin enhanced cementation between the flake units of the plain soil, and the soil structure of the plain soil stabilized by the metakaolin was denser.