Calculation of the effective diffusion coefficient during the drying of clay samples

Cilj ovog rada je da se na primeru dve opekarske gline sa različitih lokaliteta odredi efektivni koeficijenat difuzije na osnovu eksperimentalno snimljenih krivih sušenja. Razvijen je metod i napravljena su dva kompjuterska programa za određivanje ovog koeficijenta, koji se zasnivaju na matematičkom rešavanju Fikove, odnosno Krankove difuzione jednačine. Po prvi put uzeto je u razmatranje i skupljanje opekarskih proizvoda u toku sušenja a odgovarajuća korekcija je uneta u proračun. Rezultati pokazuju da su vrednosti efektivnog koeficijenta difuzije određeni kompjuterskim programima (sa korekcijom i bez korekcije na skupljanje opekarskih proizvoda) reda veličine koje su navedene u literaturi za druge vrste opekarskih glina. Na osnovu matematičkim putem prognoziranih vrednosti efektivnog koeficijenta difuzije konstatovano je, da bez obzira na polazni mineraloški sastav opekarske sirovine, postoji 90 % slaganja prognoziranih krivih sušenja sa eksperimentalno snimljenim krivima sušenja. Za slučaj kada je uvedena u proračune i korekcija na skupljanje opekarskih proizvoda ovo slaganje je još veće.The aim of this study was to calculate the effective diffusion coefficient based on experimentally recorded drying curves for two masonry clays obtained from different localities. The calculation method and two computer programs based on the mathematical calculation of the Second Fick Law and the Cranck Diffusion Equation were developed. Masonry product shrinkage during drying was taken into consideration for the first time and the appropriate correction was entered into the calculation. The results presented in this paper show that the values of the effective diffusion coefficient determined by the designed computer programs (with and without the correction for shrinkage) have similar values to those available in the literature for the same coefficient for different clays. Based on the mathematically determined prognostic value of the effective diffusion coefficient, it was concluded that, whatever the initial mineralogical composition of the clay, there is 90 % agreement of the calculated prognostic drying curves with the experimentally recorded ones. When a shrinkage correction of the masonry products is introduced into the calculation step, this agreement is even better

The standard reaction Gibbs energy of the cation exchange reaction of the biionic (Mg, Na)-form of montmorillonite

The aim of this paper is to contribute to the knowledge of the quantitative formulation of the ion exchange reaction in clays. The equilibrium was studied at 11 °C in a system of solutions of NaCl and MgCl2, the concentrations of which never exceeded 0.1 mol dm-3, and the "Jelenkovac" montmorillonite, the particle size of which was below 2 mm. The standard reaction Gibbs energy of the Mg-Na exchange determined by applying the Gapon equation (DrGoNaMg = 11.9 kJ mol-1) and that obtained according to Levy-Shainberg (DrGoNaMg = 10.5 kJ mol-1) showed a large degree of concordance. The latter method also includes the exchangeable ion activity coefficient obtained from ion-clay interaction data which includes data on the thickness of the interlayer space in the montmorillonite structure, as well as the thickness of the basis montmorillonite layer itself

Cavitation Properties of Rendering Mortars with Micro Silica Addition

Micro-silica is a highly efficient mineral additive whose role is reflected in improvements of microstructure packing, strength and durability of non-shaped composite building materials such as concrete and mortar. A comparative study of performances of rendering mortars with different quantities of micro silica was conducted. The experimental program included production of reference mortar based on Portland cement and quartz sand (CM) and three mortars with 5, 10, and 15 % addition of micro silica (SCM-5, SCM-10, and SCM-15). The effect that micro silica addition has on the thermal behavior and mechanical properties of mortars was discussed. Hydration mechanisms and thermally induced reactions were studied at temperatures ranging from ambient to 1100 degrees C by differential thermal analysis. The results were supported by X-ray diffraction analysis. The cementing efficiency of micro silica was assessed by cavitation erosion test. The changes in the morphology of mortar samples prior and upon cavitation testing were monitored by means of the scanning electron microscope imagining. It was found that 5 % of superfine micro silica (SCM-5 mortar) has positive effects on mechanical strengths (15 % increase in compressive strength) due to microstructure densification arising from the successive filling of voids by the micro silica. Addition of micro silica also improved the cavitation erosion resistance in comparison with reference cement mortar (SCM-5 showed cavitation velocity as low as 0.09 mg/min). This qualifies mortars with micro silica addition as building materials which can be safely employed in potential hydro-demolition environment