Development of rheological properties of sepiolte and production of sepiolite-fibre-reinforced concrete

Even though our country has the most important sepiolite reserves after Spain, most of our sepiolite beds are not at adequate quality. These types of ore beds contain dolomite as major impurity content, and varying amounts of illite, detritic quartz and volcanic glass depending on locations. Sepiolites with dolomite generally contain 50% or more sepiolite. In oreder to develop rheologic properties of these types requires enrichment process applications.In this thesis, first it is aimed to enrich white and brown sepiolites with purities of 60 ± 10% and 40 ± 10% from the Eskisehir-Sivrihisar region and develop rheological behavior, than produce sepiolite doped fiber reinforced concrete. Beneficiation processes with shaking table was carried out with -2 + 1 mm fraction of sepiolite samples and the white sepiolite suspensions viscosity of 151.04 cP was fed and a product obtained at 51% efficiency and viscosity of 320 cP, in case of brown sepiolite suspension of 815 cP viscosities, a product obtained at 43.1% efficiency and 1420 cP viscosity.Sepiolite samples enriched with shaking table, was subjected to a mechanical defibering process developed within this project and process parameters were optimized. A pre-mixing for 2 minutes at 1000 rpm agitation speed and final stirring at 16,000 rpm for 8 minutes were applied to brown sepiolite suspensions prepared at final solid to liquid ratio of 6% and a suspension with 20,000 cP viscosity obtained, and with same parameters were applied to white sepiolite samples prepared at solid to liquid ratio of 10% and a suspension 10,000 cP viscosity were obtained. The importance of producing stable suspensions in defibering technique is very well known, in order to produce much higher viscosity suspension, surface active reagents that alters-improves sepiolites physico-chemical properties and enhance the viscosity of white sepiolite to19,000 cP and brown sepiolite to 52,000 cP. SEM images of single fibers sampled from run of mine sepiolite suspensions and improved rheology suspensions indicated that the sepiolite fibers ellipsoid shape were developed in the suspension and a network structure constructed.In production of fiber reinforced concrete, both of these fiber types were added to concrete at solid rates of 0.5%, 1%, 2% and 3%. When brown sepiolite added at 0.5%-2% solid rates,the concrete samples compressive strength 7% increased after 28th day control measurements, whilst the concretes containing 1% and 3% white sepiolite fibers reassured similar strength behaviours at 28 days reference series. The brown and white sepiolite mixed at 2% solid rate concrete samples reproduced flexural strength value similar to strength of 28 days reference concretes. However, at the rates of 0.5%, 1% and 3% addition this flexural strength has decreased. Only when the brown sepiolite fiber addition at 0.5% and 3% increased splitting strength, in case of white sepiolite fiber addition at all rates increased the splitting strength. Especially with the addition of 3% rate of white sepiolite the splitting strength has increased by 29% depending on the increased durability of aggregate-cement matrix interface. On concrete characteristics, the brown sepiolite addition over the rate of 0.5% contribute the increase of compressive strength, in terms of splitting tensile strength white sepiolite addition over 2% represented more positive results. According to ultrasound trespassing speed measurements the concretes of 28 days with added both types of sepiolites represented quality concrete class values. According to freeze-thaw tests, the effect of brown sepiolites are better than white sepiolites, due to increase of fiber amount the resistance against freeze-thaw increased, while over 2% brown sepiolite addition degrades the homogeneity of concrete, therefore it decreases process ability of the slump and decrease the overall strength. At the rate of 3% sepiolite fiber addition arouse difficulties during stirring even when chemical additives are used, for this reason it is stated that the fiber addition up to 2% for both of the sepiolites would be appropriate