Study on pervious recycled aggregate fibre reinforced concrete for airfield pavement

For the last several years, the attention has been devoted to the development of eco-friendly construction materials with the aim to reduce the environmental impact of construction. The integral part of this development is to find applications for which the recycled materials could be used efficiently. The presented study deals with the development of recycled aggregate fibre reinforced concrete which is going to be used for an innovative precast concrete pavement system. The system is being developed recently at Czech Technical University in Prague with the aim to provide a system for airfield pavement with rapid construction and recycled material utilization. The investigated material is going to be used for construction of a sub-base course which is underneath a surface course of precast concrete elements. Within the scope of the work, standard laboratory tests were conducted with the aim to observe mechanical properties of recycled aggregate fibre reinforced concrete. The obtained findings showed that the material exhibits ductile behaviour likely due to very long polypropylene fibres used for strengthening concrete matrix. On the contrary, the tested material has low modulus of elasticity in comparison with conventional concrete. Subsequently, the pilot construction of the sub-base course was carried out in order to examine both concrete mixture preparation and concrete course installation in practice. The obtained findings showed that a compaction ratio of the material is about 20 %. Moreover, a flat surface of the sub-base course was hard to achieve considering the used manufacturing technology

Impact of the self-healing agent composition on material characteristics of bio-based self-healing concrete

This paper investigates the composition of the biological self-healing agent based on its impact on material characteristics of concrete. A direct addition of the agent – a mixture of bacterial spores and nutrients – into concrete matrix has been investigated by many studies in recent decades. Under certain conditions, the applied microorganisms proved to be able to produce CaCO3, and researchers used this biocalcification process to autonomously seal microcracks in concrete. Thus, this bio-based material could potentially heal itself and lead to a more durable and economic structure. However, it has been shown that the self-healing agent, especially the indispensable nutrients, can positively or negatively influence the material characteristics. In this study, some of the most suitable and frequently proposed nutrients (calcium lactate, calcium nitrate, calcium formate, urea, and yeast extract) were directly added into cement mortar during the mixing process and their impact on material characteristics – compressive strength, flexural strength, and rheology – was evaluated and compared. Results show that calcium nitrate, calcium formate, calcium lactate, and urea have generally a potential to increase the compressive strength, especially in early ages. In contrast, the applied dose of yeast extract resulted in a drastic drop of compressive strength when compared to the control series, thus further optimization of the concentration is needed. The flexural strength was affected rather negligibly by the proposed nutritional admixtures