The current work is intended to explain the role of some organic admixtures on the hardened structure of refractory concretes with aluminous cement. The influences on the mechanical-structural properties in the normal hardening but in the heating conditions at different temperatures are emphasized, also. These are due to the influence on the hydration process (i.e. the kind of the neoformations and degree of hydration) and implicitly on the size and distribution of structural pores.
R eferences 1. B. Ranjith Babu, R. Thenmozhi, “An investigation of the mechanical properties of sintered fly ash lightweight aggregate concrete (SFLWAC) with steel fibers”, Archives of Civil Engineering LXIV(1): 73–85, 2018. 2. M. Collepardi, “Admixtures used to enhance placing characteristics of concrete”, Cement and Concrete Composites 20(2–3): 103–112, 1998. 3. Dr.K.V.S. Gopala Krishna Sastry, A. Ravitheja, Dr.T. Chandra Sekhara Reddy, “Effect of foundry sand and mineral admixtures on mechanical properties of concrete”, Archives of Civil Engineering LXIV(1
The paper deals with the mechanics of sand with some admixtures of fines. The basic question is whether such admixtures are liquefiable or not. Experimental results show that admixtures of fines do not essentially influence the liquefaction susceptibility of granular soils. The original experimental investigations support this conclusion.
and Technology of Concrete Admixtures , pp. 257–278, 2016. https://doi.org/10.1016/b978-0-08-100693-1.00011-4  G. Gelardi, S. Mantellato, D. Marchon, M. Palacios, A. B. Eberhardt, and R. J. Flatt, “Chemistry of chemical admixtures,” Science and Technology of Concrete Admixtures , pp. 149–218, 2016. https://doi.org/10.1016/b978-0-08-100693-1.00009-6  T. M. Vickers, S. A. Farrington, J. R. Bury, and L. E. Brower, “Influence of dispersant structure and mixing speed on concrete slump retention,” Cement and Concrete Research , vol. 35, no. 10, pp. 1882
The influence of admixtures on the course of hydrolysis of titanyl sulfate
The study focused on the question how admixtures, such as iron(II), iron(III), magnesium and aluminium salts influence the degree of TiOSO4 conversion to hydrated titanium dioxide (HTD). Titanyl sulfate solution, an intermediate product in the industrial preparation of titanium dioxide pigments by sulfate route was used. The admixtures were added to the solution and their concentration was gradually changed. It was found that hydrolysis clearly depended on Fe(II) and Fe(III) concentrations. The higher the concentration of iron(II) (up to 5 wt %) in the solution was, the higher conversion degree was achieved. A reverse relationship was observed concerning the influence of iron(III) introduced up to 1.5 wt %. The constant rates of both phases of titanyl sulfate hydrolysis (including the formation of an intermediate colloidal TiO2 and final products) depended on iron(II) and iron(III) content in the solution. The concentration of other constituents did not influence hydrolysis in the investigated part of the process (up to 2.6 wt % of Mg and up to 0.3 wt % of Al). However, the size of primary particles of the obtained TiO2·nH2O did not depend on the content of the above-mentioned constituents in the solution.
A catalytic combustion of organic admixtures of air belongs to the basic technologies of gas purification. A macrokinetics of admixtures combustion over the porous catalysts was described. The theoretical approach is in agreement with standard description of macrokinetics of the catalytic processes. The relationship between the fundamental magnitudes: observed process rate r*, reaction rate r in the kinetic zone, and a coefficient of the surface utilization η in the form r*= r · η have been described. These magnitudes combines the Thiele module φ. A kinetics equation for the isothermal and non-isothermal conditions was provided. The influence of mass and heat transfer in the catalyst grain on the course of the process was described by means of the surface utilization coefficient η. An equation describing this coefficient for both isothermal and non-isothermal conditions was given. The second part of this work concerns the application of theory. When the composition of purified gas is continuously varied, a quantitative approach is rather impossible. The theory was used for the qualitative analysis of process on the basis of the experimental results. A fulfillment of the first-order kinetics means that the degree of admixtures conversion does not depend on their initial concentrations. A non-isothermicity of the catalyst grain is expressed in such a way that the process rate observed over the large porous grains of the catalyst can be higher than the reaction rate in the kinetic zone. A temperature deference between the catalyst grains and flowing gas causes that the reactor can be stably operated at varied concentrations of admixtures and temperature over a relatively wide range. It was also demonstrated that the flammable admixtures may advantageously influence the conversion of hardly combustible admixtures
; Imparting Lasting, Effective Moisture Resistance”. 27. US-Patent 7381252. 2003. “Anti-Corrosion Admixture Composition for Concrete Compositions for Use in Reinforced Concrete Structures”. 28. US-Patent 7407535. 2006. “Compositions Containing a Disodium or Dipotassium C9-15 Branched Alken-1-Ylsuccinate for Treating Formed Concrete Structures; Despite Being Water Soluble the Treatments Deliver Improved Moisture Resistance”. 29. US-Patent 7498090. 2003. “A Material Such as Reinforced or Unreinforced Concrete Coated with a Disodium or Dipotassium Salt of an Unsaturated
REFERENCES Thomas M D A: “Optimizing the use of fly ash in concrete”. PCA IS548, Portland Cement Association, Skokie, IL, 2007, pp. 1-24. 2. Du L, Folliard KJ: “Mechanisms of air entrainment in concrete”. Cement and Concrete Research, Vol. 35, No. 8, 2005, pp. 1463–1471. 3. Pedersen K H, Jensen A D, Skjøth-Rasmussen M S et al.: “A review of the interference of carbon containing fly ash with air entrainment in concrete”. Progress in Energy and Combustion Science , Vol. 34, No. 2, 2008, pp. 135–154. 4. Justnes H, Ng S: “Future Challenges for Concrete Admixtures
the Chemistry of Cement (ICCC 2015), Beijing, China, Oct. 13-16, 2015. [Online] https://www.researchgate.net/publication/290392716 [Accessed on 3.10.2018] 7. Kubens S: “Interaction of cement and admixtures and its influence on rheological properties”. Cuvillier Verlag, Inhaberin Annette Jentzsch-Cuvillier, Nonnenstieg 8, 37075 Göttingen, Germany, 2010. [Online] https://cuvillier.de/de/shop/publications/752 [Accessed on 29.1.2019] 8. Rath S & Ouchi M:. “Effective Mixing Method for Stability of Air Content in Fresh Mortar of Self-Compacting Concrete in Terms of
Cement industry has a huge environmental impact - it is responsible for a considerable part of man-made CO2 emissions. The prospective scenario to solve this problem is to substitute part of the cement clinker with industrial by-products or waste materials. In the present study coal ash and wood ash were used as a partial substitution of cement at 3 levels (20%; 30% and 40%) in concrete mixes. Ash was used in two ways - with no additional grinding and additionally ground for 30 minutes. Compressive strength of the hardened concrete samples was determined at the age of 7, 28, 56, 84 and 112 days. Ecological and economical characteristics of the materials were calculated.