Recycled aggregate produced from concrete rubble has potential to be high-quality secondary raw material for use in concrete mixtures. As part of the thesis, I compared properties of reference concrete mixtures (OC) with natural aggregate and mixtures with different proportions of crushed concrete as recycled coarse aggregate. OC mixture was prescribed in the framework of round robin test (RRT) of the COST TU1404 Action. I first carried out tests in the framework of the RRT, on the OC, which was prepared from natural aggregate from France. Coarse aggregate particles of the French natural aggregate have higher porosity than Slovenian natural aggregates. For the French aggregate, all the necessary properties were given by the RRT coordinator, including grain density of particular fraction and its coefficient of water absorption. Recycled aggregate was obtained by crushing and sieving of concrete rubble. The grain density and the coefficient of water absorption of coarse fractions of recycled aggregates were determined in laboratory of UL FGG. I found out that the tested properties of the recycled concrete are very close to the same properties of natural coarse aggregate from France. Based on the composition of the OC I determined the composition of mixtures with recycled coarse aggregate. I replaced 30%, 50% and 100% of the coarse fraction volume of the OC with the recycled aggregate. On the recycled aggregate concrete mixtures I carried out the same tests in fresh and hardened state as for the OC. For all concrete compositions, I paid special attention to initial preparation of aggregate that should reach water-saturated surface dry condition of the grains. Obtained test results showed that compared to the OC the recycled aggregate concrete mixtures possess the same consistency and density in fresh state and slightly higher air content. The same is true also for the hardened state, since the compressive strength results were approximately the same for the reference and recycled aggregate concrete mixtures.
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