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The synthesis of N-A-S-H gel with high Si/Al ratios (>2) has been rarely reported in the literature, leaving the establishment of a reliable synthesis route as an open challenge. This paper aims to synthesize N-A-S-H gels with Si/Al ratios ranging from 1 to 3 and establish their thermodynamic database. The effects of reaction temperature, reaction time, initial Si/Al, concentration of reactants and pH of the matrix on the Si/Al ratios of the synthesized N-A-S-H gel were investigated. Results showed that N-A-S-H gels with target Si/Al ratios can be synthesized by controlling the concentration of reactants, pH and initial Si/Al ratios. The solubility products of the obtained N-A-S-H gels were determined via dissolution tests at different temperatures, to determine thermodynamic data. The development of this experimentally derived thermodynamic database of N-A-S-H gels constitutes a crucial step in the advancement of thermodynamic modeling of geopolymer, providing valuable insight into geopolymer reactions and phase assemblages., Materials and Environment

Many (inter)national standards exist to evaluate the resistance of mortar and concrete to carbonation. When a carbonation coefficient is used for performance comparison of mixtures or service life prediction, the applied boundary conditions during curing, preconditioning and carbonation play a crucial role, specifically when using latent hydraulic or pozzolanic supplementary cementitious materials (SCMs). An extensive interlaboratory test (ILT) with twenty two participating laboratories was set up in the framework of RILEM TC 281-CCC ‘Carbonation of Concrete with SCMs’. The carbonation depths and coefficients determined by following several (inter)national standards for three cement types (CEM I, CEM II/B-V, CEM III/B) both on mortar and concrete scale were statistically compared. The outcomes of this study showed that the carbonation rate based on the carbonation depths after 91 days exposure, compared to 56 days or less exposure duration, best approximates the slope of the linear regression and those 91 days carbonation depths can therefore be considered as a good estimate of the potential resistance to carbonation. All standards evaluated in this study ranked the three cement types in the same order of carbonation resistance. Unfortunately, large variations within and between laboratories complicate to draw clear conclusions regarding the effect of sample pre-conditioning and carbonation exposure conditions on the carbonation performance of the specimens tested. Nevertheless, it was identified that fresh and hardened state properties alone cannot be used to infer carbonation resistance of the mortars or concretes tested. It was also found that sealed curing results in larger carbonation depths compared to water curing. However, when water curing was reduced from 28 to 3 or 7 days, higher carbonation depths compared to sealed curing were observed. This increase is more pronounced for CEM I compared to CEM III mixes. The variation between laboratories is larger, Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Using Al-rich supplementary cementitious materials to partially replace Portland cement is a well-established empirical approach to mitigate expansion of concrete caused by alkali-silica reaction (ASR). However, the mechanisms behind it are still not completely understood. Synthesis of ASR products in the laboratory provides a unique opportunity to better understand the conditions and mitigation mechanism of ASR. This study focusses on the synthesis of an 10.8 Å ASR product, which is structurally identical to the ASR product formed in concrete. The effect of Al and Li on formation of the 10.8 Å ASR product is studied. The results show that Al does not prevent the formation of the 10.8 Å ASR product, whereas the formation of the 10.8 Å ASR product is supressed in presence of Li. At low initial Li/Si an amorphous product is formed and a crystalline lithium silicate at high initial Li/Si ratio.

New self-healing agents that can chemically bind seawater ions invading cracked cementitious materials were proposed. The potential of self-healing and binding of seawater ions were investigated by thermodynamic modeling. It was found that CaO-NaAlO2 and CaO-metakaolin agents can have Cl−, SO42− and Mg2+ chemically bound by reacting with sea water to form Friedel's salt, Kuzel's salt, ettringite and hydrotalcite. The removal of Cl− from seawater firstly increased and then decreased with the increase of Ca/Al molar ratio in both agents, while the removal of Mg2+ and SO42− were hardly influenced and approximated 100%. Because NaAlO2 dissolves and releases Al(OH)4− rapidly, precipitates binding Cl−, SO42− and Mg2+ were formed fast. In comparison, the reaction of metakaolin binding aggressive ions occurred after 3 days. Because of the faster reaction and the capacity to make [Cl−]/[OH−] lower in the solution, CaO-NaAlO2 would be more efficient for self-healing and mitigating reinforcement corrossion than CaO-metakaolin., Accepted Author Manuscript, Materials and Environment

Using Al-rich supplementary cementitious materials to partially replace Portland cement is a well-established empirical approach to mitigate expansion of concrete caused by alkali-silica reaction (ASR). However, the mechanisms behind it are still not completely understood. Synthesis of ASR products in the laboratory provides a unique opportunity to better understand the conditions and mitigation mechanism of ASR. This study focusses on the synthesis of an 10.8 Å ASR product, which is structurally identical to the ASR product formed in concrete. The effect of Al and Li on formation of the 10.8 Å ASR product is studied. The results show that Al does not prevent the formation of the 10.8 Å ASR product, whereas the formation of the 10.8 Å ASR product is supressed in presence of Li. At low initial Li/Si an amorphous product is formed and a crystalline lithium silicate at high initial Li/Si ratio.

Blended cements, where Portland cement clinker is partially replaced by supplementary cementitious materials (SCMs), provide the most feasible route for reducing carbon dioxide emissions associated with concrete production. However, lowering the clinker content can lead to an increasing risk of neutralisation of the concrete pore solution and potential reinforcement corrosion due to carbonation. carbonation of concrete with SCMs differs from carbonation of concrete solely based on Portland cement (PC). This is a consequence of the differences in the hydrate phase assemblage and pore solution chemistry, as well as the pore structure and transport properties, when varying the binder composition, age and curing conditions of the concretes. The carbonation mechanism and kinetics also depend on the saturation degree of the concrete and CO2 partial pressure which in turn depends on exposure conditions (e.g. relative humidity, volume, and duration of water in contact with the concrete surface and temperature conditions). This in turn influence the microstructural changes identified upon carbonation. This literature review, prepared by members of RILEM technical committee 281-CCC carbonation of concrete with supplementary cementitious materials, working groups 1 and 2, elucidates the effect of numerous SCM characteristics, exposure environments and curing conditions on the carbonation mechanism, kinetics and structural alterations in cementitious systems containing SCMs., Accepted author manuscript, Corrigenda DOI: 10.1617/s11527-020-01599-1 and DOI:10.1617/s11527-021-01658-1, Materials and Environment

Blended cements, where Portland cement clinker is partially replaced by supplementary cementitious materials (SCMs), provide the most feasible route for reducing carbon dioxide emissions associated with concrete production. However, lowering the clinker content can lead to an increasing risk of neutralisation of the concrete pore solution and potential reinforcement corrosion due to carbonation. carbonation of concrete with SCMs differs from carbonation of concrete solely based on Portland cement (PC). This is a consequence of the differences in the hydrate phase assemblage and pore solution chemistry, as well as the pore structure and transport properties, when varying the binder composition, age and curing conditions of the concretes. The carbonation mechanism and kinetics also depend on the saturation degree of the concrete and CO2 partial pressure which in turn depends on exposure conditions (e.g. relative humidity, volume, and duration of water in contact with the concrete surface and temperature conditions). This in turn influence the microstructural changes identified upon carbonation. This literature review, prepared by members of RILEM technical committee 281-CCC carbonation of concrete with supplementary cementitious materials, working groups 1 and 2, elucidates the effect of numerous SCM characteristics, exposure environments and curing conditions on the carbonation mechanism, kinetics and structural alterations in cementitious systems containing SCMs., Accepted author manuscript, Corrigenda DOI: 10.1617/s11527-020-01599-1 and DOI:10.1617/s11527-021-01658-1, Materials and Environment