CO2-Mineralised Nesquehonite: A New “Green” Building Material

Synthetic nesquehonite with a Mg(HCO3)OH·2H2O chemical formula is a solid product of CO2 mineralization with cementitious properties. It constitutes an “MHCH” (magnesium hydroxy-carbonate hydrate) phase and, along with dypingite and hydromagnesite, is considered to be a promising permanent and safe solution for CO2 storage with potential utilization as a supplementary material in “green” building materials. In this work, synthetic nesquehonite-based mortars were evaluated in terms of their compressive strengths. Nesquehonite was synthesized by CO2 mineralization under ambient conditions (25 °C and 1 atm). A saturated Mg2+ solution was used at a pH of 9.3. The synthesized nesquehonite was subsequently studied by means of optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Impurity-free nesquehonite formed elongated fibers, often around a centerpiece, creating a rosette-like structure. The synthesized nesquehonite was mixed with reactive magnesia, natural pozzolan, standard aggregate sand and water to create a mortar. The mortar was cast into 5 × 5 × 5 silicone mold and cured in water for 28 days. A compressive strength of up to 22 MPa was achieved. An X-ray diffraction study of the cured mortars revealed the formation of brucite as the main hydration crystalline phase. Carbon dioxide mineralized nesquehonite is a very promising “green” building material with competitive properties that might prove to be an essential part of the circular economy industrial approach.

A Life-Cycle Approach to Integrate Environmental and Mechanical Properties of Blended Cements Containing Seashell Powder

The adverse consequences of producing ordinary Portland cement (OPC) on the environment have introduced cement production as the fourth largest source of anthropogenic carbon emissions after petroleum, coal, and natural gas. Managing and reducing the environmental concerns regarding the impacts of cement production on the environment, namely the depletion of non-renewable fuel resources, consumption of natural raw materials, and releasing huge amounts of CO2 into the atmosphere should be, therefore, one of the key priorities of the cement industry. Application of locally available minerals and wastes that can be blended with OPC as a substitute could considerably reduce the environmental impact. The present study evaluates the potentiality of waste seashell to be used as an additive in the production of blended cement through a modified life cycle approach integrating environmental and mechanical performances. In this regard, 34 cements consisting of different blends of OPC, seashell powder (within the range of 4–30% by OPC mass), and natural pozzolan (up to 30% by OPC mass) were tested to identify the optimal dosage of OPC substitution. Environmental impacts of the cements were assessed through life-cycle analysis. The possibility of mitigating the carbon dioxide emissions in the production of cements, with similar mechanical performance compared to that of OPC, was evaluated by considering both the mechanical and environmental results. The outcome of this study introduced more environment-friendly and sustainable options for future cements.

Effects of the Variety and Content of Natural Pozzolan Coarse Aggregate on the Thermo-Mechanical Properties of Concrete

The present study investigated the effects of the variety and content of three natural pozzolan coarse aggregates on concrete. Natural pozzolan aggregates have been obtained from three volcanoes (Boutagrouine, Timahdite, and Jbel Hebri) located in the Middle Atlas region in Morocco. The three pozzolans studied were characterized, and then a comparison was made by replacing the natural aggregate with the pozzolan aggregate in the concrete in different percentages, namely 25, 50, and 100 % in volume. The results showed that the variety and content of pozzolan aggregate have a significant impact on the properties of concrete, primarily caused by the characterization of pozzolan aggregate. The density of concrete decreases with the addition of pozzolan aggregate, which decreases depending on the type of pozzolan aggregate used. The highest compressive strength was measured in the concrete specimens prepared with aggregate BP while the lowest compressive strength was noted in the concrete specimens prepared with aggregate RP. On the other hand, the substitution of NA at 100% by BP, GP, and RP aggregates leads to a decrease in the thermal conductivity of about 67%, 62%, and 55% respectively.

Experimental analysis of lime putty and pozzolan-based mortar for interventions in archaeological sites

The study aims at defining and characterizing a specific restoration mortar for archaeological masonry structures made with traditional materials and to assess the suitability of the mixture compared to other mortars; such a goal is crucial to develop and define interventions in the archaeological sites. The mixture was defined to ensure compatibility with ancient materials and following frequently adopted recommendations at the site, specifically by using: (1) raw materials as similar as possible to the ancient ones; (2) traditional mix design. Therefore, the mixture was made with commercial lime putty CL 90-S type and natural Phlegrean pozzolan, i.e. volcanoclastic material collected from the volcanic area located in the West of Naples in Italy. The precious and limitedly available natural pozzolan used in the experiments resulted in an exclusive mortar which is very similar to the archaeological ones. The mortar has a binder to aggregate ratio 1:3 by volume, according to traditional techniques typically encountered in the ancient Roman city of Pompeii and Vesuvius surrounding area. The evolution of the flexural and compressive strength, elastic modulus, bulk density, open porosity and ultrasonic pulse velocity has been monitored for up to 200 days, based on standard procedures. Moreover, the hardening process was monitored with Differential Thermal Analysis up to 90 days, through the evaluation of phase transitions associated with dehydroxylation and decarboxylation, considering different depths from the external surface of the mortar. The achieved mechanical properties were compatible with those of lime-based mixtures for repair interventions of ancient masonry structures. Moreover, the mortar was found to be well-suited to mitigate cracking, showing a low ratio between its stiffness and load capacity compared to other typologies of mortars used for masonry restoration. Ultrasonic pulse velocity test proved to be a reasonable complementary method to monitor the evolution of the hardened properties of the mortar. Carbonation was found to be still progressing at 90 days. The data presented provide useful and reliable information to approach the complex process of restoration in archeological sites.