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A chemo-mechanical model is presented for the simulation of biogenic sulphide corrosion in concrete sewer pipes. The chemical model is formulated in terms of a system of coupled diffusion-reaction equations, which describe the processes of calcium hydroxide dissolution, calcium silicate hydrate dissolution and gypsum formation. The chemical problem is two-way coupled with a mechanical model that captures the damage processes caused by mechanical deformations, calcium silicate hydrate dissolution and gypsum formation. A set of numerical analyses illustrates that the model realistically simulates the growth of a gypsum corrosion layer and the consequent damage development in the concrete material. A validation experiment is performed that mimics the chemical process of biogenic sulphide corrosion, from which it is confirmed that the chemo-mechanical model adequately simulates both the shape of the experimental corrosion profile and the square root time development of the corrosion depth.

To sustain the decarbonization of the cement industry, identifying new sources of supplementary cementitious materials (SCMs) is crucial. This review paper examines recent scientific literature on the understanding, assessment, and processing of future and emerging SCM resources. Among the SCMs that have generated significant interest are calcined clays, natural pozzolans, reclaimed coal fly ashes, certain biomass ashes, concrete recycling fines, and recycled glass. These SCMs are gaining market access, and their processing and performance have been well-established in local contexts. A growing body of research is considering a much wider array of by-product and waste materials as potential future SCM sources. These materials are often available in high volumes, but they typically require beneficiation processing to enhance their performance and compatibility as SCM. While promising results have been achieved for many materials, future research and development efforts are necessary to better understand their impact on cement and concrete properties and establish or improve the viability of the proposed beneficiation processing. In conclusion, this review highlights the latest developments in testing and specifications that support the uptake of a wider range of SCMs in cement and concrete.

The gel compatibility in calcium contained geopolymers remains a controversial topic. This work aims to clarify the role of Ca availability in determining the geopolymerization of alkali-activated ladle slag/Class F fly ash blends. The results show that the product layer wrapping around slag particles largely governs the Ca diffusion into the environment, enabling the development of two separated gels, namely C-(N)-A-(S)-H and N-(C)-A-S-H type gel. A dense matrix consisting of geopolymer gel and Ca-enriched gel is achieved with 8 % of Na2O while increasing Ms. intensifies the incompatibility between two gels, leading to microcrack formation and lowered mechanical strength. The competition between different reaction mechanisms of the two gels predominates the initial properties and thermal performance of the hybrid binder. A thermal degradation model of hybrid geopolymer co-existing geopolymeric gel and Ca-enriched gel is proposed to describe the influence of gel compatibility on the thermal behavior of Ca incorporated geopolymer.

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Evaluation and quantification of the effects of the carbonation process on photocatalytic activity are essential for the long-term functional assurance of nano TiO2 modified photocatalytic concrete. This work focuses on the photocatalytic self-cleaning performance variation of mortar containing different dosages of nano TiO2 hydrosol at different carbonization duration. The colourimetric analysis is used to evaluate the self-cleaning performances of carbonated mortar samples. The distribution areas of anatase TiO2, hydrates, and carbonates in the mortar surface are characterized by the Confocal Raman Microscopy. The data recorded during the 28 days of carbonation show that the self-cleaning performance of mortar surfaces features a recovery phenomenon during carbonation. The correlations between photocatalytic self-cleaning performance and the possible parameters are analysed. A predictive model is suggested to evaluate the influence of carbonation degree on the photocatalytic self-cleaning ability of nano TiO2 hydrosol modified mortar.

Extrusion-based 3D Concrete Printing (3DCP) is rapidly gaining popularity in the construction industry. Trial projects are now being realized at an increasing rate around the world to test the viability of the technology against real-world requirements. This step, from the ‘simple’ deposition of filaments of self-stable concrete to its application in buildings and structures, with all associated requirements and interfaces, comes with challenges. These range from matching the design intent to the manufacturing capabilities (through structural analysis and approval, and reinforcement) to quality consistency (robustness) on large scale, and compatibility with other materials. In many of these areas, much simply remains unknown due to a lack of experimental data or information from projects where 3DCP has been applied. This paper aims at reducing this knowledge gap by presenting a systematic discussion, based on the analyses of eight realized 3DCP projects from around the world. It was found that the structural application of printed concrete is limited, due to a lack of regulatory framework for expedient approval, as well as limited reinforcement options which require to resort to unreinforced masonry analogies. The application of the technology features a host of practical issues that relate to the print process, material, site conditions, building integration and design – or to the 3DCP technology in general. Although some potential risks, such as shrinkage cracking and quality consistency are generally recognized, the measures taken to mitigate them vary considerably, and are largely based on individual expertise. The actual effectiveness is generally unknown. Finally, it was observed that, while the printing itself is fast, the preparation time is generally considerable. This is partially due to a lack of knowledge amongst professionals. In the practical production of a 3DCP project, three expertise areas are crucial: one for the digital part, one for the machine side, and one for the material side. Thus there is a strong need for educational institutions to develop dedicated training courses and incorporate relevant topics into their curricula.

The use of recycled aggregates (RCAs) could further enhance the sustainability of reactive magnesia cement (RMC) formulations, but the performances of RMC-RCA are still unknown to researchers. Therefore, in this study, the strength development of CO 2-cured RMC-RCA was explored for the first time, and the strength variation among groups was further interpreted by microstructural analyses. The initial results show that compared with samples with natural aggregates (NAs), a 28 d strength boost (i.e., 37 vs. 15 MPa) in RMC-RCA can be observed. The strength improved in RMC-RCA could be related to its refined microstructures, ITZs and larger carbonation depths, which resulted from the easiness of CO 2 penetration within samples. Then the presence of porous ITZs in RCA contributes to better CO 2 diffusion, as described in the proposed revised CO 2 diffusion model. Overall, while enabling a pronounced CO 2 capture potential of RMC concrete, this preliminary study could pave the path for the upcycling of RCAs in RMC concrete on a large scale.

Supplementary cementitious materials can affect the porosity of concrete, pore solution pH and chloride binding, all of which influence the type and magnitude of corrosion damage. Advanced corrosion monitoring techniques are needed to follow the development of corrosion on steel embedded in concrete across space and over time. In this study, coupled multi-electrode arrays (CMEAs) were used to characterise corrosion processes in OPC and three blended cements. Cyclic wetting with chlorides was undertaken to initiate corrosion. The results showed three distinct types of corrosion: localised corrosion (CEM I), localised corrosion that expanded over time (CEM II), and a combination of localised and general corrosion (CEM III and CEM IV). Cathodic locations were also monitored successfully, and the corrosion behaviour was related to total porosity and pH of the pore solution. MicroCT was used to quantify the volume of corroded material, which agreed well with results calculated from the CMEA measurements. Nasl. z nasl. zaslona. Opis vira z dne 7. 3. 2023. Bibliografija: str. 11-12. Abstract.

In this study, a protocol for synthesising beta-C2S using K2SO4 as a dopant has been reported. Quantitative X-Ray diffraction was used to characterise synthesised samples. It was observed that it is possible to synthesise beta-C2S with high purity (>96 wt%) and limit the formation of free lime to below 0.5 wt% using this protocol. Unreactive gamma-C2S was the main secondary phase present in the sintered samples. Isothermal calorimetry studies were conducted to understand the reaction kinetics which showed that beta-C2S reacts slowly but produces similar calorimetric curve profiles as that of C3S. The C-S-H formed from the hydration of C2S was observed to be morphologically and compositionally identical to the C-S-H produced from the hydration of C3S. The hydration kinetics of beta-C2S was seen to be affected by the presence of aluminosilicate pozzolan, such as calcined clay, which can have practical implications while producing blended cements with belitic clinkers., Cement and Concrete Research, 167, ISSN:0008-8846