The investigation of the use of marble plant wastes in composite slab production

Drastic advances in civilization, and therefore developments in building industry have caused uncontrollable increase in the consumption of natural stones like marble and granite. Marble is generally consumed as countertops, floor tiles, wall tiles (panels), steps and table tops. Slab production for those application areas causes generation of huge volume of marble dust (~ -100 µm), which refers to about 20-40% of marble block depending on the thickness of used saw. Marble sludge contains significant environmental risks due to high surface area which is reasonably reactive. It may cause aridity in the region, reduces soil fertility, adversely affects the breathable air quality due to pollination, and affects negatively the ecosystem of disposed region. These potential environmental hazards could not be mitigated at acceptable rates due to insufficient waste recycling todays. Nowadays, high strength quartz composite slabs have taken great interest especially due to its high flexural strength and impact resistance in addition to its low water absorption rate compared to marble slabs. Engineered stones exhibit those appreciable properties due to usage of quartz both in aggregate and micronized sizes. Preparation of micronized quartz as filler component of composite slab production is an energy intensive process due to its high hardness. The underlying idea in defining the objective of this thesis was the possibility of marble dust usage over micronized quartz filler in composite slab production. Because marble dust has closer size distribution to that of micronized quartz filler. However, low hardness of CaCO3, the main mineralogical phase of marble dust, was thought to affect adversely the physical properties of composite slab. Therefore, aim of the thesis was stated as to determine potential usage rate of marble dust as filler material, to investigate the effect of sintering roasting on phase distribution of artificial filler mixture to overcome the hardness drawback of calcite, to clarify the phase distribution of sintered product, and to determine the different sinter phases on the physical properties of composite slab. Thesis works were held by supplying marble sludge from Yatağan Marble Processing Plant of Ermaş Mining Company. Micronized quartz filler was also supplied from the same company (Coante Quartz Surfaces Plant of Ermaş Mining Company). Characterization test of filler materials held by XRD, XRF, SEM-EDX and size analysis revealed that they were highly pure, and had closer size distribution. SEM imaging has shown that quartz filler contained sharp edged particles while marble dust particles were irregular, semi spherical, and needle like shaped ones. Slab production was performed by using marble dust as filler material at different rates in addition to micronized quartz. Filler mixtures were either used in its natural form and after roasting at 900ºC-1100ºC for 3 h and at 1200ºC for 1 h, 3 h, 5 h and 10 h to investigate the effect of hardness of phases present in filler material on the physical properties of slab. SEM imaging was applied to characterize filler mixture. SEM image analysis clarified that mixing by rod milling helped for accumulation of calcite on the sharp edges of quartz particle as centers for complex calcium silicate formation. Applied sintering roasting at different temperatures for different times and marble dust ratios caused the formation of xCaO.ySiO2 complex phases in those centers as spurrite, larnite, calcio olivine and wollastonite. Composite slabs produced by unroasted filler mixture exhibited appreciable physical properties at lower marble dust rate than 50%. On the other hand, roasting of 25% marble dust containing filler at 1200ºC for 10 h resulted in excellent mechanical data, even better than those of quartz composite slab. This finding was explained with the formation of hard-rounded larnite particles by roasting the filler. However, roasting was determined to reduce the product quality when marble dust rate is increased up to 50% due mainly to presence of free lime in the roasted filler mixture.