No abstract

Estimation of concrete strength is an important issue in ready-mixed concrete industry, especially, in proportioning new mixtures and for the quality assurance of the concrete produced. In this article, on the basis of the existing experimental data of compressive strength of normal and recycled aggregate concrete and equation for compressive strength calculating given in Technical regulation are compared. The accuracies of prediction by experimental data obtained in laboratory as well as by EN 1992-1-1, ACI 209 and SRPS U.M1.048 are compared on the basis of the coefficient of determination. The determination of the compressive strengths by the equation described here relies on determination of type of cement and age of concrete with the constant curing temperature

Crystallization kinetics of 22.5Li2O?10Al2O3?30GeO2?37.5P2O5 (mol%) glass was studied under non-isothermal condition using the differential thermal analysis (DTA). The study was performed by using the first crystallization peak temperature (Tp1) which belongs to the precipitation of LiGe2(PO4)3 phase in the glass. The activation energy of glass crystallization (Ea) was determined using different isokinetic methods. The dependence of Ea on the degree of glass-crystal transformation (?) was studied using model-free isoconversional linear integral KAS (Kissinger-Akahira-Sunose) and FWO (Flynn-Wall-Ozawa) methods. It was shown that the Ea varies with ? and hence with temperature and consequently the glass/crystal transformation can be described as a complex process involving different mechanisms of nucleation and growth. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 34001 and Grant no. 172004]

The investigation included concrete made by using recycled brick as aggregate. Experimental work included several types of concrete made with the same cement content (385 kg/m3), and same consistency (slump about 1 cm). Recycled brick and combination of natural river aggregate and recycled brick were used as aggregates. The influence of percentage and grain size of crushed brick aggregate on concrete compressive strength, water absorption and frost resistance were observed. On the basis of the results obtained during experimental research, a general conclusion can be drawn that the application of recycled concrete as aggregate can lead to new composites with satisfactory physical-mechanical properties

The results of preparation and structural characterization of glass-ceramics from the system Li2O-Al2O3-GeO2-P2O5 are shown in this paper. The crystallization behaviour of the selected glass was examined under non-isothermal and isothermal crystallization conditions. DTA, XRD and SEM methods were employed for analyses. It was confirmed that this glass crystallizes by the volume crystallization mechanism. The results also showed that the glass crystallize by primary crystallization. As a primary phase the LiGe2(PO4)3 is formed and the traces of GeO2 as a secondary one is present. The crystallization process occurred at a high homogeneous nucleation rate and the spherical morphology of crystal growth. By applying the Kissinger relation the activation energy of crystal growth Ea = 462 kJ/mol was determined. [Projekat Ministarstva nauke Republike Srbije, br. 34001 i br. 172004]