José Luis García Calvo

Study of the Microstructure Evolution of Low-pH Cements Based on Ordinary Portland Cement (OPC) by Mid- and Near-Infrared Spectroscopy, and Their Influence on Corrosion of Steel Reinforcement

Low-pH cements are designed to be used in underground repositories for high level waste. When they are based on Ordinary Portland Cements (OPC), high mineral admixture contents must be used which significantly modify their microstructure properties and performance. This paper evaluates the microstructure evolution of low-pH cement pastes based on OPC plus silica fume and/or fly ashes, using Mid-Infrared and Near-Infrared spectroscopy to detect cement pastes mainly composed of high polymerized C-A-S-H gels with low C/S ratios. In addition, the lower pore solution pH of these special cementitious materials have been monitored with embedded metallic sensors. Besides, as the use of reinforced concrete can be required in underground repositories, the influence of low-pH cementitious materials on steel reinforcement corrosion was analysed. Due to their lower pore solution pH and their different pore solution chemical composition a clear influence on steel reinforcement corrosion was detected.

An Innovative Self-Healing System in Ultra-high Strength Concrete Under Freeze-Thaw Cycles

The development of cementitious materials with self-healing properties is currently a very active research line in order to increase the service life of structures and reduce the costs associated to maintenance and repair. A combination of silica microcapsules containing an epoxy sealing compound and nanosilica particles functionalized with amine groups has been developed to confer self-healing properties to an ultra-high performance concrete. The durability of the self-healing system under severe climatic conditions is considered in this work. Cylindrical concrete specimens were made with and without the self-healing additions. After a curing time of 28 days, micro-cracks with a controlled width were created in the specimens that were subsequently subjected to a freeze-thaw test consisting of four cycles per day between −20 and +20 °C. The results from capillary water absorption test after 150 cycles confirm the efficiency of the sealing system even under the aggressive conditions considered in this study.