vub wapenschild

Interreg project 'Concrete to concrete', master thesis, Recovery of sand fraction

01.09.2019 - 01.02.2020

Concrete is used worldwide and its production needs tremendous amounts of sand. The recycling of end-of-life concrete becomes more and more interesting economically and environmentally. Application for particles larger than 4 mm are already existing, however, the fine fraction below 4 mm caused some issues, namely the separation of the hardened cement paste glued on others particles. In this report is investigated how different treatments influence the properties of this fraction. Thus this report presents the characterization of mortars made from CEM I were the sand has been replaced by the product of different treatment. Coming from a batch where the size distribution the recycled concrete was first sieved (with sieve openings of : 4mm, 2mm, 1mm, 0.5mm, 0.212mm, 0.125mm, 0.063mm) before being dehydrated at 550°C. or 750°C, then some of the material was softly milled in planetary ball mill in order to break hardened cement paste. To look at the impact of temperature and milling, XRD and XRF and sieving analysis were carried out. XRD pointed out different changes in microstructure depending of the temperature of treatment. XRF and PSD analysis showed how the different milling parameters influenced size and composition. Finally mortars were casted with dehydrated fines or milled material as sand replacement to compare with mortar with fresh sand. Compression tests and resoanalysis showed that after 28 days the sample with dehydrated fines had strength 10% smaller comparing to the reference, on the other hand the compressive strength of mortars with milled material was 2.5 times smaller than the reference. Concerning Young’s modulus, both sets where fresh sand was replaced have a modulus about two times smaller than the reference. These results give good hopes and many paths to explore so that one day sand could be replaced by some cheap recycled cement material without great mechanical properties losses and thus making concrete industry more environmentally sustainable. (Hugo Keller, Master thesis)