Assessment of the self-healing capacity of cementitious materials through active thin sections.

Since self-healing of cementitious materials can theoretically improve the service-life of concrete structures, it has gathered significant attention from both researchers and industry during the last two decades. Many researchers have proposed different methods to assess and quantify the self-healing capacity (i.e. the ability of cementitious materials to heal cracks) that is generated in concrete autogenously as well as autonomously. Even though many methodologies can be found in the literature, a way to accurately quantify the healing products produced by any self-healing mechanism has not been yet achieved. In this study, a methodology is proposed to observe and to quantify in-time formation of healing products based on active thin sections. Thin sections of Portland cement paste have been prepared with no epoxy impregnation to facilitate reactions between the cement matrix and the surrounding environment. Artificial cracks (260 µm wide) were induced at 28 days of age and the crystal growth was continuously monitored up to 28 days of self-healing. Through image analysis of the micrographs, it was calculated that the autogenous self-healing capacity of paste (triggered by portlandite carbonation in uncontrolled indoor conditions) was around 55% after 28 days of self-healing. Healing products were further characterised through Environmental Scanning Electron Microscope analysis. Based on the results obtained in this study, the proposed methodology seems to be promising to compare the self-healing mechanisms triggered by different healing agents.

Plutonic Rocks as Protection Layers to Concrete Exposed to Ultra-High Temperature.

Concrete structures perform poorly when withstanding thermal shock events, usually requiring repair or replacement after one single instance. In certain industries (such as petrol, metallurgic and ceramics), these events are not only likely but frequent, which represents a considerable financial burden. One option to solve this issue would be to decrease the heating rate imposed onto the concrete material through the use of a protective surface layer. In this work, the suitability of dunite and microgabbro as protective materials is explored through X-ray diffraction, thermal dilation, optical microscopy, X-ray microtomography, thermo-gravimetric analysis and a compressive test. Further, the thermal dilation was used as an input to simulate a composite concrete-rock wall and the respective stresses caused by a thermal shock event. The dehydration of chrysotile in dunite and the decomposition of analcime, chamosite and pumpellyite in microgabbro were both favourable for the performance of the stones in the desired application. The thermal stability and deformation were found in the range of what can be applied directly on concrete; however, it was clear that pre-heating treatment results in a far more durable system in a cyclic thermal load situation.

Mechanical Behavior of Printed Strain Hardening Cementitious Composites.

Extrusion based additive manufacturing of cementitious materials has demonstrated strong potential to become widely used in the construction industry. However, the use of this technique in practice is conditioned by a feasible solution to implement reinforcement in such automated process. One of the most successful ductile materials in civil engineering, strain hardening cementitious composites (SHCC) have a high potential to be employed for three-dimensional printing. The match between the tailored brittle matrix and ductility of the fibres enables these composites to develop multiple cracks when loaded under tension. Using previously developed mixtures, this study investigates the physical and mechanical performance of printed SHCC. The anisotropic behavior of the materials is explored by means of mechanical tests in several directions and micro computed tomography tests. The results demonstrated a composite showing strain hardening behavior in two directions explained by the fibre orientation found in the printed elements. Moreover, the printing technique used also has guaranteed an enhanced bond in between the printed layers.