Influence of recycled coarse aggregates characteristics on mechanical properties of structural concrete

This work studies with the influence of recycled coarse aggregates features on the mechanical properties of structural concrete. Recycled concrete is characterised by replacing different percentages of natural coarse aggregate with recycled coarse aggregate (0, 20, 50 and 100%) and two different water-to-cement ratios .50 and .65. The experimental program was carried out at the two laboratories: one at the University of A Coruña and another at the Università Politecnica delle Marche (Italy). For said purpose, two different recycled aggregates were used, with different water absorptions and compositions. Results obtained allowed the authors to establish different mechanical behaviour of recycled concrete (compressive strength, tensile splitting strength and modulus of elasticity) due to different replacement percentages and characteristics of the recycled aggregates

Internally cured high performance concrete with magnesium based expansive agent using coal bottom ash particles as water reservoirs

Shrinkage is one of the main concerns related to high performance concrete (HPC) durability. Its high density paste, consequence of a low water to binder ratio, can be unprofitable if cracks appear due to excessive tension when volume changes are restrained. Therefore, volume stability is a priority. In this work, three different strategies have been studied with that purpose: integration of fly ash as a low reactive supplementary cementitious material, internal curing via coal bottom ash particles as water reservoirs and the use of an expansive agent based on magnesium oxide (MEA). Many research works address the three shrinkage reduction strategies individually. However, studies regarding their simultaneous use are not prevalent so this work proposes its combined application. Results indicate that internal curing and MEA have a synergistic effect in HPC. Internal curing enhances MEA expansion due to the lack of water in this kind of concrete, contributing to autogenous shrinkage compensation. When concrete is affected by air-drying conditions, the use of MEA, internal curing, or both together make shrinkage to increase. MEA effectively expands in wet cured HPC although internal curing is not effective in this condition due to the absence of self-desiccation and limited porous aggregate water desorption. Taking into account the effects of each shrinkage reduction strategy and curing condition, it has been concluded that the use of fly ash as supplementary cementitious material, internal curing and MEA is recommended together with prevention of water evaporation from HPC surface. © 2020 Elsevier Lt