Society is urging the public and private sectors to adopt sustainable measures to mitigate global warming. In response, the construction industry is exploring alternative binders to reduce its carbon footprint. Yet, durability concerns and regulatory gaps remain unresolved for this new generation of binders. In contrast, another potential path to decarbonization may lie in the built heritage. Standing the weathering of time, Egyptians, Phoenicians, and Romans relied on lime-based binders to create future-proof buildings before Portland cement was invented. However, as most lime applications were empirical and undocumented, the current bottleneck lies in the limited availability of scientific data—needed to establish lime as a sustainable and structurally viable material. Thus, this study investigated four mortar mixtures commonly used in masonry structures, monitoring key properties such as mechanical strength, permeability, and carbon capture capacity for six months. Results indicate that mixtures with higher air lime content exhibited lower strength, primarily governed by carbonation. Permeability tests confirmed air lime’s breathability, which favored carbon capture, as demonstrated through phenolphthalein and thermogravimetric analysis. Within the monitoring period, lime-cement groups absorbed more carbon dioxide earlier than others, likely due to interactions between hydration, carbonation, and water evaporation, which led to faster carbonation rates. Finally, an extended monitoring is recommended for future studies. ... Read more

Although air lime is a carbonatable binder with high carbon sink potential, reproducible research remains hindered by the limited availability of lime-oriented standards and openly accessible datasets. These limitations prevent the consolidation of fundamental knowledge and reinforce the perception of lime mortars as highly variable and empirical materials. This study addresses this gap by implementing a FAIR-aligned (Findable, Accessible, Interoperable, Reusable) and reproducible workflow for the characterization of air lime-containing mortars. Four mixtures were monitored for up to 364 days to assess fresh, physical, and mechanical properties under defined conditions. All experimental metadata and datasets are openly published in a structured repository. Results show that air lime-containing mixtures exhibited longer setting times, higher open porosity, greater carbonation depths, and lower compressive strength. Length change measurements indicate hydration-carbonation interactions, particularly in lime-cement systems. By combining experimental characterization with a FAIR-aligned and reproducible workflow, this work supports more transparent, resource-efficient research practices. ... Read more

Non-hydraulic lime (also known as air lime) is an ancient carbonatable binder that has regained attention due to its carbon sink potential. Besides lower CO2 emissions during production, air lime also absorbs carbon dioxide during its hardening process. Yet, the challenge with non-hydraulic lime (and alternative binders in general) lies in the absence of data, standards, and replicable studies. For instance, air lime is often used in masonry mortars, where volume stability (shrinkage and creep) is required to ensure structural safety, but research on this issue remains scarce. Therefore, the objective of this study was to apply existing frameworks to experimentally measure the total creep (EN 12390–17:2019) of non-hydraulic lime-containing mortars. Four groups were analyzed, with non-hydraulic lime contents of 100 %, 67 %, 50 %, and 0 % (binder volume). Specimens were subjected to three different curing conditions and then loaded and monitored for up to 240 days. The results showed that (i) unlike Portland cement, non-hydraulic lime mortars needed more time to develop strength under natural environmental conditions; (ii) the phenolphthalein test did not accurately monitor the carbonation depth of air lime-rich mortars; (iii) air lime-rich systems showed less shrinkage, possibly due to carbonation-induced expansion; and (iv) air lime-rich groups exhibited greater creep strains, confirming their high deformability. These findings demonstrate that air lime-containing mortars exhibit a distinct time-dependent behavior, highlighting the need to adapt existing standards for more accurate and reproducible long-term performance assessments. ... Read more

Recent studies have been focusing on the carbon sink potential of carbonatable binders as an attempt to reduce CO2 levels. Air lime is a carbonatable binder that fully relies on CO2 absorption to harden and, thus, offers great carbon sink potential. Yet, CO2 absorption is favoured only after the evaporation of the excess water. Therefore, this study investigated the behaviour of air lime-containing mortars regarding water retention and evaporation. Four groups (with different contents of air lime) were monitored for up to 91 days after curing. Results showed that higher contents of air lime yielded greater water retention capacity. Yet, water retention did not prevent the carbonation front from further advancing – especially within lime-cement groups. In this case, greater porosity proved to be an open door for the simultaneous evaporation and ingress of CO2. Thus, hero or villain? It depends on the mixture. ... Read more

Given the crucial role of carbonation in the hardening of lime-based binders, accurate measurements of carbonation depths are essential for analysing both carbonation kinetics and carbon sequestration capabilities. This study employed both the conventional phenolphthalein spray method and the profile-based method to determine carbonation depths in four types of binders. Unlike the distinct carbonation front observed in cementitious materials, lime-based binders displayed a transition zone between fully carbonated and uncarbonated areas. Meanwhile, the remaining portlandite content in some specimens did not necessarily increase with depth, and typical Liesegang patterns were observed. Compared to phenolphthalein spray method, profile-based methods provide more quantitative evidence for further analyses, but inevitable slice interval can also lead to errors in carbonation depth estimation. Therefore, developing a more precise and convenient method remains essential for a deeper understanding of the carbonation behaviour in lime-based binders. ... Read more

The service life of wastewater treatment plants is often impaired by the biogenic deterioration caused by sulfuric acid (H2SO4). This study used fly ash (as a Portland cement replacement) and different contents of neutral sodium silicate (0%-10%) as mitigating solutions. One group was immersed in lime-saturated water for 182 days, and the other was submitted to a 0.5% H2SO4 solution for the same interval. The microstructural analysis (SEM/XRD) confirmed the consumption of calcium-based compounds during the pozzolanic reaction, the Na2SiO3 hydration, and the H2SO4 attack. The neutralized depths measured after spraying phenolphthalein reiterated this trend. The H2SO4 front progressed inwards, promoting gradual peeling and the formation of gypsite. The slow diffusion of H2SO4 did not impair the early-age compressive strength, but the depletion of the alkaline reserve hindered the results in the long term. Therefore, Na2SiO3 was not a viable mitigating solution against the H2SO4 attack, contrary to fly ash. ... Read more

Internal sulfate attack (ISA) occurs in cement composites due to the presence of mineral sulfide in aggregates, such as pyrite (FeS2). The oxidation of the pyrite releases sulfate ions, which react with hydrated phases of Portland cement and produce expansive phases such as ettringite and gypsum. The objective of this article was to study the influence of crystalline admixture and polypropylene microfiber on the internal sulfate attack in Portland cement composites due to pyrite oxidation. Mortars with 10% pyrite content (by sand weight) were evaluated and compared with reference mortars (without pyrite). Pyrite oxidation was stimulated through wetting and drying cycles at 40 °C. Transport properties (water absorption by immersion, sorptivity, ultrasonic pulse velocity, and electrical resistivity), length change, flexural tensile strength, and microstructural properties were monitored for up to 24 weeks. Pyrite promoted degradation in all mortars over time. Mortars with microfibers had the lowest expansion due to the availability of voids for the consolidation of expansive phases. However, the high porosity and permeability of the material facilitated the entry of water and diffusion of oxygen. A large number of expansive phases and cracks were found in these mortars. The presence of soluble alkaline phases promoted the interaction between crystalline admixture and pyrite, accelerating the ISA. ... Read more

This article evaluated the effect of improved autogenous mortar self-healing in the alkali-aggregate reaction (AAR). Prismatic mortar specimens were cast with different contents of polypropylene microfiber and crystalline admixture. The crack-induction method (for subsequent self-healing) was the AAR accelerated mortar bar test itself. After AAR-testing, the specimens were submitted to wetting and drying cycles to stimulate the self-healing mechanism. These two approaches (AAR and self-healing steps) were alternately repeated four times. The results showed that the reference mortar and the mixture with 1% of polypropylene microfiber had the highest and lowest levels of expansion, respectively. The expansion rate was lower for the combined mixtures, although the initial values of length change were high. The visual inspection confirmed that improved autogenous self-healing could close cracks caused by AAR and promote microstructural densification. ... Read more