Investigation of engineering properties of micronized colemanite added ultra high performance concrete

Due to the fact that Turkey has the largest share in the world's boron reserves and the usage areas of boron minerals are increasing day by day, studies are carried out in our country to develop boron products and new production technologies, to commercialize the developed products and methods, and to ensure sustainable development. Colemanite, which is one of the boron minerals containing boron oxide in different proportions and showing natural compound characteristics, has a great commercial importance, but is among the main boron minerals that are converted into high value-added products. With the studies carried out, the use of boron minerals in the cement sector is gaining importance. In this study, it was aimed to produce colemanite added ultra-high performance concrete (UHPC) with improved mechanical, physical and durability properties. In order to determine the most suitable colemanite additive ratio to be used in Ultra High Performance Concrete mixtures, the cement tests were carried out as a preliminary study with 0.50, 1.00, 1.50, 2.00% colemanite substitution. UHPC mixtures were prepared with 0.25, 0.50, 1.00% colemanite additive determined according to the preliminary study results. Some experiments were carried out on the UHPC samples in the fresh and hardened concrete phase. In addition, colemanite added cement pastes were prepared and hydration developments were investigated by XRD, FT-IR, DTA-TG and SEM analyses. Flow diameter, density, air content, shrinkage and hydration temperatures were measured to determine the fresh concrete properties of the prepared UYPB mixtures. In the hardened concrete phase, on the 2nd, 7th, 28th and 56th days, density, compressive and flexural strength, schmidt hammer, ultrasonic pulse velocity and on the 56th day impact resistance, electrical resistivity, carbonation resistance, capillary water absorption, abrasion resistance, sulfate resistance, freeze-thaw resistance tests were carried out. According to the results obtained within the scope of the study, it has been determined that a more impermeable concrete with improved physical, mechanical and durability properties of UHPC can be obtained with colemanite additive and 1% colemanite additive provides the best performance for UHPC.