The paper presents the obtention and characterization of Portland cement mortars with limestone filler and nano-calcite additions. The nano-calcite was obtained by the injection of CO2 in a nano-Ca(OH)2 suspension. The resulted nano-CaCO3 presents different morphologies, i.e., polyhedral and needle like crystals, depending on the initial Ca(OH)2 concentration of the suspension. The formation of calcium carbonate in suspensions was confirmed by X-ray diffraction (XRD), complex thermal analysis (DTA-TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM and HRTEM). This demonstrates the viability of this method to successfully sequestrate CO2 in cement-based materials. The use of this type of nano-CaCO3 in mortar formulations based on PC does not adversely modify the initial and final setting time of cements; for all studied pastes, the setting time decreases with increase of calcium carbonate content (irrespective of the particle size). Specific hydrated phases formed by Portland cement hydration were observed in all mortars, with limestone filler additions or nano-CaCO3, irrespective of curing time. The hardened mortars with calcium carbonate additions (in adequate amounts) can reach the same mechanical strengths as reference (Portland cement mortar). The addition of nano-CaCO3 in the raw mix increases the mechanical strengths, especially at shorter hardening periods (3 days).
HIGHLIGHTS
-Carbon black (CB) particles in nanometric domain can be successfully incorporated in cement matrices in order to obtain special concretes/mortars with self-sensing properties.
-Piezorezistivity monitoring of mortars is a non-destructive method used to assess the structural characteristics of composite materials.
-The presence of CB in studied mortars provides a specific electrical sensitivity which may change when curing time increases.
The paper presents the manufacture and characterization of special mortars based on Portland cement (PC) and a nanopowder with electrical properties (carbon black - CB). These materials were characterized from the point of view of mechanical strengths as well as properties specific for self-sensing materials i.e. variation of electrical signal when applying a mechanical strain. The electrical signal and mechanical strength values are strongly dependent on the composition and microstructure of mortars.The values of electrical resistance are strongly correlated with the composition, morphology and curing time of the mortars. In this study significant changes of the electrical behaviour (piezoresistivity) of the mortars vs. curing time (90 or 180 days) were noticed, so this must be considered in practical applications. The best results were obtained for the mortars with 0.5-3 wt.% CB cured for 180 days.
This research work assesses the influence of a chromium-rich waste (from potassium dichromate manufacture) on the hydration and hardening processes of two types of Portland cements with limestone filler and slag additions. Therefore, mixtures of Portland cement and chromium-rich waste, corresponding to 0.5% wt. and 1% wt. Cr, were prepared and tested. The analyses performed on cement pastes with chromium waste content, showed that chromium immobilization is mainly due to the formation of Ca6Al2Cr3O18�32H2O (CrEt); this compound results by the substitution of [SO4]2- groups from ettringite lattice of with [CrO4]2-. CrEt crystals growth on the surface of clinker particles forms a diffusion barrier which explains longer setting times for cements with chromium content. The increase of chromium content in the studied systems decreases the compressive strength values but these remain above the lower limits imposed for this type of materials. The chromium content in leachates prepared according to the method described in SR EN 12457-2, was well below the legal limit of 70 mg/Kg established by Romanian legislation. A better chromium immobilisation was achieved in the cement with slag content, in good correlation with the nature and amount of formed hydrates.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.