The purpose of the present work was to study the corrosion protection that relatively low-cost magnesium hydroxide coatings offer to concrete by stabilizing the surface pH. To facilitate the material’s adhesive ability, methyl-cellulose and carboxymethyl-cellulose were used as environmentally friendly additives in three different concentrations, 1, 0.4 and 0.1 wt.% of solids, respectively. The coatings were applied on the surface of concrete blocks, in two different coating thicknesses. A sulfuric acid solution was used to simulate the biologically produced acid in sewer pipes. Sulfuric acid was sprayed on the specimens, while the total amount of acid sprayed was calculated, in order to correspond to a specific reaction’s stoichiometry daily. The surface pH of coated specimens was monitored daily with a surface pH meter. The gypsum production was studied with X-ray diffraction, to evaluate the coatings’ protection. The experimental time period that coatings were consumed was compared with the theoretically consumption time.

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This paper presents the effect of adding nanoparticles SiO2 and Al2O3 in the cement with respect to mechanical, physical and structural properties. Nanoparticles were chosen for the development of nanocomposite building materials with high mechanical strength, durability and low permeability. Correspondingly, the cement used is Portland Cement CEMI42.5N. Five compositions have been prepared, a reference sample (OPC) and pastes with different nanoparticles. Nanoparticles of SiO2 and Al2O3 were added in 1.5% and 3% by weight of cement and the produced samples were tested after 7, 28, 90 and 120 days of curing. All the samples, in every hydration period, were tested for compressive strength, while their open porosity was measured and their microstructure was examined by means of infrared spectroscopy. Furthermore, for certain hydration periods, the chemical and elemental composition of the samples was evaluated by means of X-ray diffraction and scanning electron microscopy. The samples were also evaluated for capillary water absorption and shrinkage, while thermal analysis was performed for specific samples. The comprehensive analysis revealed a positive effect, in terms of structural properties, of nanoparticle admixture in cementitious systems. The addition of nanoparticles influence the workability of the composites and contributes to the formation of crystallization nuclei, which in turn enhance the durability of the material. Interestingly, it was found that high concentration of nanoAl2O3 in the admixure, results in high mechanical properties. Highlights: Different analytical techniques were combined in order to holistically test nanomodified cement pastes. nanoalumina is systematically tested as additive in cement pastes.

The self-healing mechanism of cementitious materials has been investigated by many researchers in the last two decades. In the journey of this quest, more and more advanced methods of analyzing the efficiency of healing have been employed. These methods are intended to clarify and quantify the healing mechanism. This paper presents five techniques, which are either common in the microstructure and nanostructure study or innovative in this field, which was used in order to identify the healing efficacy. Specifically, the application of scanning electron microscope (SEM) analysis, 3-D ultrasound tomography, nanoindentation, water absorption test (sorptivity), and software development in the Python programming environment for monitoring the crack closure have been used. The main objective of this study was to quantify several parameters, such as the geometry of the cracks, the properties of the healing products, as well as the healing depth. SEM analysis is a well-known technique that can contribute to identify the elements of the healing products and give the morphology of the surface. The methodology for nondestructive 3-D ultrasound tomography of healed specimens clarifies the ability of healing in depth.

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Stone has been a basic building material of different monuments and structural components such as foundations and masonry. At the same time, dif-ferent types of stones have been used for decorative architectural elements, such as cornices, reliefs, colonnettes, and corbels. The maintenance of stone ele-ments is essential for the continuity of these structures. Many studies have been performed to produce stones with artificial materials. This study aims to present a new approach to artificial stone with self-healing capability. Crystallines have been implied in two different dosages: 0.8 and 1.6% w./w, to achieve this goal. The addition of the crystalline admixtures affected the physical properties, de-creasing the porosity and the capillary absorption, proving the sealing properties of the admixtures. The self-healing efficiency has been tested with the sorption test, recovery of compressive strength, and 3D acoustic microscopy. The crys-talline admixtures accelerate the self-healing, increasing the sealing efficiency by 20% and recovering compressive strength by 15%. The analysis by 3D to-mography provided results that confirm the healing of the crack hasn't occurred only on the surface but extended to a certain depth.

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