The construction industry is one of the most demanding in terms of natural resources, and of the most polluting in terms of emissions to the atmosphere. Concrete is one of the most used materials in engineering and is a paradigm of the consumption of rocks for aggregates, used in polluting industries such as cement production. In trying to reduce the consumption of natural resources, efforts are being made to use waste as recycled aggregates. This fact has evident economic and environmental advantages, but it has a drawback. The concrete prepared with recycled aggregates has lower mechanical strength than ordinary concrete. This decrease of resistance is mainly due to a higher porosity exhibited by the materials from recycled aggregates. But the increase of porosity can be a great advantage in terms of sound absorption. In this work several types of recycled aggregates have been tested, paying special attention to their acoustic behaviour and pore structure. The results show that concrete made with recycled waste are effective in absorbing sound. It might become an alternative to traditional concrete, since recycling samples behave similarly or better in terms of sound absorption, using recycled materials, and increasing their life-cycle. The measurement of acoustic properties, as well as density, has already been undertaken in previous works. This work presents an image analysis methodology that is completely novel, and that helps to understand the acoustic behaviour of concrete elements.
A study of the mechanical behavior of self-compacting concrete mixtures under sand replacement (as fine aggregate) by iron slag (residue from industrial machining) from 0.0% to 50.0% of mass, variations of water/cementitious material ratio between 0.3 and 0.5 and nano SiO2 incorporation between 0.0% and 2.0% by mass of cementitious materials is presented. Fresh state tests of slump flow were performed, and the main rheological parameters: static yield stress and plastic viscosity were determined from a rheometer. For the hardened state, compressive strength tests were performed. The study of iron slag incorporation and water/cementitious materials ratio variation was developed based on a statistical methodology of central composite design from axial points based on a 2k factorial with central points, besides a posterior analysis of variance and Tukey’s multiple comparison tests. The optimization of these variables was developed using response surface methodology on 7 days compressive strength results, from the statistical design, besides the posterior determination of nano SiO2 effects on the optimized proportions. Among the most relevant results regarding the presence of iron slag, an increase in the early age compressive strength was found, with the optimized mixture strength being more than 100% higher than mixtures without iron slag at 7 days of curing. Regarding the effect of nano SiO2 addition to the optimized mixture, a detriment of the rheological parameters and a consequent reduction of the workability were the most remarkable findings. With the obtained results, iron slag proves to be a feasible sand replacement in self-compacting concrete mixtures.
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