An investigation of the beneficial effects of adding carbon nanotubes to standard injection grout

Mortar grouting is often used in masonry constructions to mitigate structural decay and repair damage by filling cracks and voids, resulting in an improvement in mechanical properties. This paper presents an original experimental investigation on grout with added carbon nanotubes (CNTs). The samples were prepared with different percentages of CNTs, up to 1.2 wt% with respect to the binder, and underwent three‐point bending tests in crack mouth opening displacement mode and compressive tests. The results showed that very small additions (up to 0.12 wt% of CNTs) increased not only flexural and compressive strengths (+73% and 35%, respectively, in comparison with plain mortar) but also fracture energy (+80%). These results can be explained on the basis of a reduction in porosity, as evidenced by mercury intrusion porosimetry, as well as by a crack bridging mechanism and by the probable formation of nucleation sites for hydration products, as observed through scanning electron microscopy

Evaluation of Methodologies for Assessing Self-Healing Performance of Concrete with Mineral Expansive Agents: An Interlaboratory Study

Self-healing concrete has the potential to optimise traditional design approaches; however, commercial uptake requires the ability to harmonize against standardized frameworks. Within EU SARCOS COST Action, different interlaboratory tests were executed on different self-healing techniques. This paper reports on the evaluation of the effectiveness of proposed experimental methodologies suited for self-healing concrete with expansive mineral additions. Concrete prisms and discs with MgO-based healing agents were produced and precracked. Water absorption and water flow tests were executed over a healing period spanning 6 months to assess the sealing efficiency, and the crack width reduction with time was monitored. High variability was reported for both reference (REF) and healing-addition (ADD) series affecting the reproducibility of cracking. However, within each lab, the crack width creation was repeatable. ADD reported larger crack widths. The latter influenced the observed healing making direct comparisons across labs prone to errors. Water absorption tests highlighted were susceptible to application errors. Concurrently, the potential of water flow tests as a facile method for assessment of healing performance was shown across all labs. Overall, the importance of repeatability and reproducibility of testing methods is highlighted in providing a sound basis for incorporation of self-healing concepts in practical applications

A review on aqueous gelcasting: A versatile and low-toxic technique to shape ceramics

This review aims to provide a comprehensive survey of recent low-toxic approaches used in the gelcasting process. In recent years, several natural gelling agents have been developed as possible alternatives to acrylamide systems, which were previously used extensively but are now rarely employed owing to their neurotoxicity. This work collects some successful case studies on aqueous gelcasting based on low-toxic or non-toxic gel-formers that have been applied to produce both dense and porous ceramics. Major innovations in the development of nanocomposite materials, transparent ceramics and microstructurally graded materials are discussed as well

Microstructural study of aged ferrite powders for sensing layers

Nanosized powders of La0.80Sr0.20Fe0.95Cu0..05O3-w were investigated in terms of structural, morphological, chemical and surface properties by using several characterization techniques. The XPS and IR measurements showed the presence of surface hydroxide and carbonates species. After calcination of the powders at 900 degrees C the amount of carbonates decreased but was still significant. The sensing activity of thick film based on La0.80Sr0.20Fe0.95Cu0.05O3-w was tested as a function of relative humidity and the results indicate that (i) after one year of ambient storage the sensing material lost quite completely its sensitivity to humidity, (ii) the sensing activity of the film was mostly re-activated after a thermal treatment at 900 degrees C for 2 h, and (iii) the huge shift of the detection limit to low RH caused by the presence of 5 mol% Cu is also restored

Impermeabilization of carbon black-based smart coatings for strain-sensing purposes

This study explores self-sensing properties in carbon black (CB)-based cementitious coatings, focusing on the influence of internal moisture on electrical measurements. Various saturation levels were examined by gradually drying the coatings and encapsulating them with epoxy resin to shield them from external humidity. Results show that inner water impacts the strain-sensing response of the coating, reaching an optimal moisture saturation of 25% where an equilibrium between carbon black particles, water, and free ions was attained. For coatings on tension surfaces of concrete beams under flexural loads, 230.7 ± 25.8 was the obtained gauge factor for 3 wt% added carbon black. Epoxy-sealing reduced the bonding strength between the coating and the substrate by 27%. Nonetheless, epoxy-encapsulated coatings with 3 wt% carbon black achieved a gauge factor of 110.9 ± 35.5, indicating a promising path for the production and application of self-sensing coatings that remain unaffected by external humidity conditions.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 860006

Preparation and mechanical characterization of dense and porous zirconia produced by gel casting with gelatin as a gelling agent

A modified gel casting procedure based on a natural gelatin for food industry and commercial polyethylene spheres as pore formers was successfully exploited to produce dense and porous ceramic bodies made of yttria stabilized tetragonal zirconia polycrystal (Y-TZP). Vickers and Knoop microhardness, elastic modulus and fracture toughness measurements on dense samples obtained by experimental investigation closely matched results found in the literature for similar materials. However, after a careful analysis of obtained results, no indentation size effect and a lower scattering of experimental data from low load indentations were observed, in comparison with literature. Mechanical testing of porous samples (with reproducible values of porosity of about 40%) evidenced a high scattering of compressive strength values, suggesting that the uneven distribution of cavities in the material or the presence of defects from the agglomeration of pore forming agents could have a more direct influence on the mechanical properties of such materials than the absolute value of porosity. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Preparation and characterization of Ce-ZrO2/Al2O3 composites by DLP-based stereolithography

This work investigates the printability of Ce-ZrO2/Al2O3 composites through a Digital Light Processing (DLP) technology. Commercially available 10 mol% CeO2 and 12 mol% CeO2-stabilized zirconia were mixed with alumina powders, to provide 11 mol% CeO2-stabilized ZrO2/16 vol% Al2O3 (Ce-ZA16) composite materials. The powders were dispersed under wet conditions, and the homogeneous nanometric dispersion was maintained once added into the liquid monomer. Slurries at several solid loadings were explored, with and without dispersant addition. First, the key role of the dispersant to significantly enhance the solid loading and thus the sintered density was demonstrated. Second, among different dispersant-added slurries at various solid loadings, ranging from 65 to 80 wt%, the best compromise between rheological behavior and curing depth was estab-lished. The best formulations, comprised between 70 and 80 wt%, successfully provided fully dense and completely homogeneous composites