Influence of temperature in the evolution of compressive strength and in its correlations with UPV in eco-concretes with recycled materials

• Eco-concretes with fine and coarse recycled concrete aggregates and biomass ashes.
• Impact of the curing temperature on the correlation between compressive strength and UPV.
• Effect of recycled materials on the correlation between compressive strength and UPV.
• The influence of biomass ash on concrete compressive strength depends on temperature.
• Neglecting curing temperature on strength estimates based UPV may render inaccuracies.

This research studies the influence of temperature on the evolution of compressive strength and on its correlations with the ultrasonic pulse velocity in concretes and eco-concretes, with a focus on the ages between 1 and 28 days. To that end, 9 concrete mixtures are studied, with parametric variations in the following components: (i) the type of aggregate, including several replacement ratios of recycled aggregate; (ii) water/cement ratio; (iii) cement content, as well as its partial replacement with biomass ashes. These 9 mixtures can be further divided in two major groups: 6 vibrated concretes and 3 self-compacting concretes. The 6 mixtures of vibrated concretes are: a mixture of reference, three mixtures with partial replacement of fine and coarse recycled concrete aggregates (8%, 20% and 31% replacement), and two mixtures with partial replacement of cement with biomass ashes from the paper industry (15% and 30% replacement). The 3 remaining mixtures corresponding to self-compacting concretes are: one reference mixture of self-compacting concrete and two additional mixtures with partial replacement of fine and coarse recycled concrete aggregates from precast elements (20% and 50% replacement). The influence of temperature on the evolution of strength in each of the mixtures is determined for curing temperatures of 5 °C, 20 °C and 45 °C. The study further includes the evaluation of the influence that temperature and mixture parameters (particularly those of eco-concretes) have on the relationship between compressive strength and ultrasonic pulse velocity.