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Povzetek: The impact of oxic and thermal transient phases on corrosion of carbon steel in cementitious environment was studied through three in situ experiments (Tournemire URL, France). For two years, heated metallic samples (80 °C) were placed in direct or indirect contact with two different cementitious materials: a low-pH Bentonitic Cement Grout (BCG) and a Portland cement paste material (CEM I). Mineralogical and microstructural analyses were carried out in an attempt to identify the combined effects of pH, chemistry and microstructure properties associated with such specific cementitious media on steel corrosion mechanisms. Additionally, in situ Electrical Resistance (ER) corrosion sensors allowed to continuously monitor the corrosion rates corresponding to each of the three field experiments. Post-mortem characterisation indicated that metallic samples embedded in low-pH BCG were heavily damaged and exhibited high corrosion rate. Conversely, steel samples in contact with highly alkaline CEM I environment appeared to be much less impacted by corrosion processes and revealed extremely low corrosion rate values. A comparison between these field experiments observations and results previously obtained through complementary laboratory mock-up tests finally enabled the evaluation of the impact that variations in geometrical/design aspect existing between in situ and laboratory tests can induce on material degradation.
Ključne besede: bentonitic cement-based grout, deep geological disposal of nuclear waste, anoxic environment, electrical resistance corrosion sensors, groundwater, low-pH cement
Objavljeno v DiRROS: 27.01.2026; Ogledov: 155; Prenosov: 32
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Povzetek: The phase assemblage evolution of binders with novel supplementary cementitious materials (SCMS) during exposure to adverse environments needs to be quantified to accelerate their adoption, and further optimize binder formulation. As such, the interaction between chloride and cementitious matrices with novel SCMs needs to be quantified. The goal of workgroup 2 of RILEM TC EBD-298 is to assess the methods used to quantify chloride binding. This state-of-the-art report reviews the standardized and novel methods to measure chloride binding through an average content (acid/water soluble) or a specific bound content per phase (XRD, TGA, SEM–EDS, …). Each method is presented with respect to our current understanding of chloride binding and speciation in cementitious materials. The discussion around the purpose, use and reporting of each method highlights the gaps limiting the comparison between studies, in particular the lack of standard protocol, and complementary characterization. This review is the groundwork for a “cookbook” of experimental workflows to investigate chloride binding in modern cementitious binders.
Ključne besede: cement, chloride, supplementary cementitious materials, CSMs
Objavljeno v DiRROS: 12.01.2026; Ogledov: 214; Prenosov: 87
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Povzetek: The content of leftover cement paste is a crucial parameter for determining recycled aggregates quality. Various methods assess this, including wet techniques (acid dissolution, chemical degradation, water absorption), physical approaches (freeze-thaw cycles, mechanical shredding, oven-dried density, thermal disaggregation), and spectroscopic or microscopy analyses. However, these methods often lack accuracy, are time-consuming, or depend on operator skill. A novel X-ray Powder Diffraction and Rietveld quantitative phase analysis approach is introduced to improve measurements precision. Results are compared with multi-scale analyses (microscopy, Xray computed tomography, mechanical testing) on recycled aggregate concrete specimens. Findings highlight a strong correlation between leftover cement paste content and key concrete properties, including microstructure, hydration products, and mechanical performance. This study confirms that leftover cement paste content is a decisive factor in recycled concrete aggregate properties, and that the proposed method offers a rapid and reliable approach to control this parameter.
Ključne besede: recycled concrete aggregate, leftover cement paste, CDW, X-ray diffraction, microstructure
Objavljeno v DiRROS: 27.08.2025; Ogledov: 523; Prenosov: 304
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Povzetek: The precise and accurate determination of sulphate levels in cement is of utmost importance due to the potential occurrence of internal sulphate attack in concrete, which affects the latter’s durability, and thus, also the safety of concrete constructions. The estimated measurement uncertainty provides a level of confidence in the experimental results, and enables the comparison of data, both between different laboratories and between different methods. This paper presents an alternative approach to the estimation of measurement uncertainty in the determination of sulphate in cement, based on the use of proficiency testing data. The calculations used in this procedure refer to the estimation of reproducibility within-laboratory component of the analysis of control samples, as well as of the bias component of sulphate content data for different types of Portland cement derived from several proficiency testing trials.
Ključne besede: cement, sulphate, measurement uncertainty, alternative approach
Objavljeno v DiRROS: 03.03.2025; Ogledov: 612; Prenosov: 481
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Povzetek: This study focuses on the kinetics of hydration, phase assemblage, microstructure and mechanical properties after various hydration times of two different BCSA cements at 5, 20, 40 and 60 ◦C and compares experimental data with thermodynamic modelling. Different curing temperatures change the type of hydrates and their amounts. Ye’elimite and gypsum in belite-ye’elimite-ferrite cements are almost fully reacted after 24 h of hydration at 20, 40 and 60 ◦C, while not at 5 ◦C. The hydration of belite is slower than the one of ye’elimite, but reaches a high degree of hydration after 150 days which is increasing with temperature. Less ettringite is present at elevated temperatures due to its increasing solubility, while more monosulfate is observed. Furthermore, with increasing temperature siliceous hydrogarnet forms at the expenses of strätlingite as well as more C S H is found as more belite reacts resulting in higher compressive strength. Dense and homogenous microstructure is observed at 5 ◦C, while it is more heterogeneous at higher temperatures. The presence of more ye’elimite resulted in higher ettringite and str¨atlingite formation and a higher compressive strength, while more belite yields more C S H in the hydrates and lower compressive strength.
Ključne besede: belite-ye’elimite-ferrite cement, temperature, hydration, thermodynamic modelling
Objavljeno v DiRROS: 11.12.2023; Ogledov: 1351; Prenosov: 1115
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