Residual Compressive Strength of Recycled Aggregate Concretes after High Temperature Exposure

Abstract

Sustainability requirements are gaining importance in the construction industry, which needs to take specific measures in the design and construction of concrete structures. The use of recycled aggregates in concrete may be of special interest. Recycling a construction waste will close the life cycle of the original materials (e.g., concrete). Thus, environmental benefits would come from the lower waste generation, and from a lower necessity of raw materials for new structures. The current Spanish code for structural concrete considers the use of recycled aggregates in replacement rates up to 20% by aggregate mass, assimilating their properties with those of concretes without aggregate replacement. Higher substitution percentages would require further testing. In this work, substitution of coarse aggregate for recycled aggregates (with replacement percentages of 25%, 50% and 100%) has been studied, and the concrete’s residual properties after exposure to high temperatures (between 350 °C and 850 °C) have been assessed. Compressive strength and capillary water absorption tests were made after heating, and the experiments showed higher residual strength in concretes with the greatest content of recycled aggregates. However, a statistical analysis made with additional data available in the literature seemed to predict otherwise, and the recycled aggregate replacement would have a negative effect on the residual strength.

Residual Repeated Impact Strength of Concrete Exposed to Elevated Temperatures

“…The second stage, which is a semi-stabilization stage with a very small positive slope, is related to the strength recovery and low reduction between 300 and 500 • C, where the microstructure is still not very affected by the chemical and physical changes due to temperature exposure. Finally, the weight loss starts another high-slope reduction region after 500 • C, where the cement matrix was cracked owing to the chemical changes, and the bond between the cement and aggregate was almost lost due to the different thermal movements [78,79]. Excluding the initial strength gain at 100 • C and the strength recovery at 300 • C, it can be said that the strength loss can be related to the loss in weight.…”

FRP Confinement of Stone Samples after Real Fire Exposure

“…Although the alteration of the properties of rocks exposed to high temperatures has been widely studied during the last years, in most cases, the work is done under ideal laboratory conditions using electric furnaces, while investigations with exposure to real fire are scarce and usually limited to the analysis of historical buildings affected by fires [ 6 ]. It is clear that the use of electric furnaces in the laboratory allows the simplification and standardization of tests in order to facilitate the comparison of results with those of other investigations [ 7 ]. However, the atmosphere created inside the furnace does not reflect the real conditions of a building during the fire event, largely because the main mechanism of heat transmission is convection in the former case and radiation in the latter [ 8 ].…”

Evaluation of the mechanical response of calcarenite specimens confined with fiber reinforced polymers after high temperature exposure

“…Finally, sets 01, 04 and 07 were not heated at all in order to act as control samples. The target temperature was selected on the basis of previous studies [1,17], as it has been proven that this rock exhibits a dramatic loss of physical and mechanical properties at 600 • C. Several tests had been carried out previously, measuring with thermocouples the air temperature in the oven as well as inside some specimens, which allowed small corrections to be made with respect to the theoretical heating curve programmed in the device [28]. Regarding the behavior of the heated samples, it is important to highlight that no spalling or fractures were observed, as opposed to a previous work with real fire exposure [17], where some samples were severely damaged, especially in the quick water-cooled sets.…”