MODIFICATION OF CEMENTITIOUS MATRIX OF RAPID-HARDENING HIGH-PERFORMANCE CONCRETES

The paper presents the results of research concerning the peculiarities of modern High Performance Concretes based on cementitious systems "Portland cement – active mineral additives – micro fillers – superplasticizers – accelerators of hardening". Physico-chemical regularities of structure formation of super plasticized cementitious systems are established. It is shown that the formation of secondary fine ettringite due to the interaction of active alumina with calcium hydroxide and gypsum in the non-clinker part of the binder because of the effect of "self-reinforcement" compensates for shrinkage and increases the strength of the cementitious system. The modification of the cementitious matrix makes it possible to obtain Rapid Hardening High Performance Concretes that provide early loading and turnover of the formwork of monolithic constructions.

Effect of the pore structure of an active alumina catalyst on isobutene production by dehydration of isobutanol

An alumina catalyst was prepared by mixing and pinching with pseudo-boehmite, and the catalyst was reamed with polyethylene glycol.

Effect study of an amount of active alumina addition on the properties of alumina refractories with a complex additive of chromium oxide and zirconium dioxide

An effect of active alumina amount introduced into a batch (7.5 - 22.0 %) on the properties of alumina samples containing a complex additive of chromium oxide (10 %) and zirconium dioxide (3 %) was studied. The optimal amount of introduced active alumina (12.5 %) was established, which ensures the production of samples fired at a temperature of 1580 ºС, with the lowest open porosity (18.2 %), the highest apparent density (3.25 g/cm3) and the highest cold crushing strength (117 N/mm2), refractoriness under a load of 0.2 N/mm2 > 1700 ºС, thermal shock resistance (in the mode of 1300 ºС — water) not less than 7 thermal cycles.The results of carried out studies were used in the development of production technology of domestic refractory products based on fused corundum, α-form alumina, active alumina, containing the complex addition of chromium oxide and zirconium dioxide, by semi-dry pressing method. These refractory products characterized by high properties and intended for service at a temperature of 1850 ºС in the combustion chamber of carbon black production reactors.The use of these refractories in the lining of above mentioned high-temperature industrial units will allow to increase a duration of their operation due to an increase in the refractory durability in service, as well as to save material and energy resources associated with a relining of the reactors.

Effect investigation of a complex additive of chromium oxide, zirconia and a technological binder type on the properties of corundum refractories

The effect of a complex additive of chromium oxide and zirconium dioxide, as well as a temporary technological binder type on the properties of corundum refractories was studied. The optimal complex additive containing chromium oxide and zirconium dioxide in certain quantities, and the type of temporary technological binder have been determined. The use of these complex additive and technological binder provides to receive following properties of samples after firing at 1580 C open porosity 17.4 %, apparent density 3.29 g/cm3, cold crushing strength 138 N/mm2, refractoriness under a load of 0.2 N/mm2 > 1700 C thermal shock resistance (1300 C — water) of at least 8 heat cycles. Based on the research results, the required regulatory documentation has been developed. As a result of the studies, a technology for the semi­dry pressing of domestic corundum refractories based on fused corundum, α­alumina and active alumina with the complex addition of chromium oxide and zirconium dioxide was developed. This technology provides refractory products with high properties. The use of these products in the combustion chamber of production reactors of carbon black will provide their higher durability in service, and, consequently, the operation duration of high­temperature units.

A green approach of preparation of fine active alumina with high specific surface area from sodium aluminate solution

A green preparation of fine active alumina from saturated sodium aluminate solution by phase evolution is presented. High capillary pressure, numerous mesopores, and the inhibition of aggregation produced FAA with an extremely high specific surface area.

Effect of Aluminum Hydroxide Addition on Properties of Fired Refractory Clay Brick

The pottery of Ratchaburi is very famous especially dragon jar which was fired by using dragon kiln. The kiln was made of unfired clay bricks, which its properties including high refractoriness, low thermal shrinkage and durable are desired. Aluminum hydroxide is an interesting material for improving brick’s properties, providing high active alumina (gamma-alumina) content after decomposition, high melting point and also reasonable cost. The study evaluated the effect of an additive, Al (OH)3, on the fried properties of refractory clay brick. In this study, four difference proportions of Al (OH)3 to clay , including 0:100, 25:75, 49:51 and 76:24 were studied. The specimens of 5x5x5 cm3 were formed by hand molding, then were fired at 1200, 1300 and 1400°C. The properties including refractoriness, volume shrinkage, strength, bulk density, water absorption, and slaking time were investigated. The samples of 25:75 ratio of Al (OH)3 to clay, which was fired at 1300°C exhibited high in refractoriness, low volume shrinkage of 5% and relatively low density of 1.69 g/cm3 as compared to those of 1400°C fired. Moreover, the moderate water adsorption of 15 % and useable compressive strength of 12.4 MPa was also observed. As a result, these properties suitable for using in firebox of dragon kiln of Ratchaburi province.