D. Mostofinejad and M. Reisi,
Volume 24, Issue 1 (7-2005)
Abstract
Silica fume has been largely used in concrete in recent decades due to its effect on improvement of strength and
durability of concrete. On the other hand, attention has been recently paid to the use of limestone powder as a substitute for part of cement in concrete, basically because of its low price and its positive effect on the durability of concrete. The aim of the current study is the investigation of the interactive effect of silica fume and limestone powder on the compressive strength of concrete and the optimization of the mix design. To do so, 27 mix designs including 3 water-to-cementitious materials ratios (W/CM=0.25, 0.3 and 0.4) 3 silica fume-to-cementitious materials ratios (SF/CM=%0, %5 and %10) and 3 limestone powder-to-cement ratios (LP/C=%0, %15 and %30) were used and 28-day compressive strength of the cubic concrete specimens were determined. Then, the interactive effect of silica fume and limestone powder on compressive strength of concrete was investigated using isoresponse curves. Furthermore, the optimization of the mix design for concretes containing silica fume and limestone powder was carried out using “cost effective factor” (CEF) which is defined compressive strength divided by cost of concrete.
D. Mostofinejad and M. Hoseinian,
Volume 25, Issue 2 (1-2007)
Abstract
It is well known that the characteristics of concrete components greatly affect the durability of high strength/high performance (HS/HP) concrete against frost action. Undoubtedly, precise recognition of this relationship leads
to appropriate selection of the type and proportions of concrete components in any particular project. In the current study, the aim is to investigate the possibility of developing some mathematical-experimental models to explain the frost resistance of high-performance concrete, regarding the role of some of its main components. To do so, the effects of four key elements, i.e. water, silica fume, coarse aggregate, and number of freeze-thawing cycles, were studied on the frost resistance of HS/HP concrete were studied. 24 concrete mix designs including 3 ratios of water to cementitious materials, i. e. 0.4, 0.3, and 0.25 4 ratios of silica fume to cementitious materials, i.e. 0, 5, 10, and 15 percent and 2 types of coarse aggregates, i. e. Limestone and Quartzite were utilized for HS/HP concrete. Overall, about 432 concrete cubes were cast, cured and tested under freeeze-thaw cycles. Finally, some models were proposed for describing the frost resistance of high strength concrete.
A. R. Parvanian, H. R. Salimijazi, M. H. Fathi,
Volume 38, Issue 4 (1-2020)
Abstract
The concentrated solar power (CSP) is one of the renewable energy sources in which solar irradiation heat energy will be used in a steam turbine to generate electrical grid. Solar radiation is absorbed by a solar receiver reactor on the surface of a porous solar absorber. In this survey, synthesis and mechanical/thermal characterization of micro-porous silicon carbide (SiC) absorber to be used in solar reactor is carried out. SiC foams were synthesized and categorized based on three different pore sizes i.e. 5, 12 and 75 ppi. Mechanical behavior and thermal shock resistance of porous foams in the working temperature range for absorber (25-1200 °C) were evaluated. Results revealed that the specific compressive strength (σc/ρ) of foams increase exponentially by a decrement in the porosity percentage and the average pore size. Moreover, for foams with smaller pore size, a considerable decrease in mechanical strength due to thermal shock was observed. This could be due to increase in the number of struts per unit volume i.e. more weak struts to withstand the mechanical loading. So, porous foams with coarser pore sizes were distinguished to be more capable of tolerating thermal shock while serving as solar absorbers.
