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The fire spalling of concrete is a complex phenomenon, which can affect the integrity of the structures during a fire. This thermal instability is associated with a complex coupled chemo-thermohydro- mechanical mechanism and it can be influenced by many factors, related to material (e.g. permeability, porosity and water content), geometry (e.g. shape and size) and environmental parameters (e.g. mechanical load and heating rate). Concrete made with recycled concrete aggregates presents higher porosity, higher water content and different interfaces between aggregates and mortar. All these aspects can lead to a different behaviour under fire exposure, including the spalling risk of these sustainable concretes. The main objective of this paper is to analyse the influence of the use of recycled concrete aggregates on the spalling risk of concrete. In this paper, concrete prisms with different replacement rates of recycled coarse aggregates (0 up to 100%) were exposed to a standard fire curve (ISO 834-1) with a constant uniaxial compression load. After heating, samples surfaces were evaluated by means of digital photogrammetry. Results showed that concrete with RCA is sensitive to explosive spalling. All replacement rates presented higher degree of spalling than concrete made with natural aggregates. [ABSTRACT FROM AUTHOR]

In civil engineering, the behavior of a cracked concrete is a major challenge with regard to the management of a structure's durability. The purpose of this experimental work is to better understand the behavior of a quasi-brittle cracked material at macro-scale, and to provide new data for numerical models. Cyclic compression/tension tests were performed on a notched concrete specimen. The effects of cracks' closure opening were investigated by classical measurements (displacement sensors) and digital image correlation. Damage and inelastic strains were exhibited when cracks propagate during the tensile phase. When the load is reversed to induce compressive stress, the effect of damage on the concrete stiffness was progressively reduced. A relation between the inelastic strains and the damage variable emerges, and it is proved that these two variables are not thermodynamically independent. The study on the crack lips' displacement shows that at least a part of the inelastic strain is due to the friction between the crack lips. The evolution of the damage and the dissipated energy during a loading cycle were also calculated, and results showed that the dissipated energy grows hyperbolically with the crack propagation. [ABSTRACT FROM AUTHOR]

Concrete made with recycled concrete aggregates (RCA) presents particular properties that may lead to a specific behaviour under fire conditions, including the spalling risk. The spalling sensitivity of concrete made with RCA was evaluated through a campaign conducted in three concrete series: reference, direct replacement, and strength-based replacement. The last was designed to have the same performance as concrete made with natural aggregates (NA). Samples with different replacement rates of recycled coarse aggregates (0 %, 10 %, 20 %, 40 %, and 100 %) were exposed to the standard fire curve (ISO 834-1) with constant uniaxial loading (2.5 and 5 MPa). During the tests, the furnace temperature and spalling events were recorded. After the tests, digital photogrammetry was used to observe the spalling damage (volume and depth). Fire tests indicated that concrete made with RCA exhibited a higher spalling degree than concrete made with NA. Results also show that the replacement rate acts in different ways: in concrete with RCA replacement rates up to 40 %, the spalling damage increases, but a further increase does not lead to higher spalling. In addition, RCA changes the physical properties of concrete, which may trigger spalling, particularly water content. • The spalling sensitivity of concrete made with RCA was investigated. • Digital photogrammetry was used to evaluate the damage degree of spalled specimens. • For the given conditions, concrete made with RCA showed more spalling damage than concrete made with NA. • The higher water content of concrete made with RCA was one of the triggering parameters for spalling. [ABSTRACT FROM AUTHOR]