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Showing 4 results for E. Najafi Kani

A. Allahverdi, E. Najafi Kani, S. Esmaeilpoor,
Volume 5, Issue 2 (spring 2008 2008)

Abstract: The use of alkali-activated cementitious materials especially over the past decades has significantly been increased. The goal of this research is to investigate the effects of silica modulus and alkali concentration on alkali-activation of blast-furnace slag. In this research, the most important physical characteristics of cementitious systems, i.e. the 28-day compressive strength and final setting time, were studied by changing influencing parameters such as silica modulus, i.e. SiO2/Na2O, (0.44, 0.52, 0.60, and 0.68) and Na2O concentration (4, 6, 8 and 10% by weight of dry binder) at a constant water-to-dry binder ratio of 0.25. Final setting time of the studied systems varies in the range between 55-386 minutes. The obtained results show that systems cured at an atmosphere of more than 95% relative humidity at room temperature exhibit relatively high 28-day compressive strengths up to 107 MPa.
A. Allahverdi, E. Najafi Kani,
Volume 6, Issue 2 (Spring 2009 2009)

geopolymer cement (inorganic polymeric binder) based on natural pozzolan are investigated. SiO

of activator and total molar ratios of Nacomposition exhibiting the highest 28-day compressive strength. Mixtures exhibiting the highest compressive strength were studied for their molecular structure using laboratory technique of Fourier transform infrared spectroscopy.Results obtained confirm that changes in chemical composition and curing condition can result in variations in degree of silicon substitution by aluminum in the second coordination sphere. Hydrothermal curing affects the molecular structure so that by increasing the hydrothermal curing temperatures, a lower degree of silicon substitution by aluminum in the second coordination sphere is observed. The molecular structure of the studied inorganic polymeric binde is composed of Si-O-Si chains bonded to Al-O and Si-O units creating two and three dimensional networks.

In this paper, the effects of chemical composition and curing conditions on molecular structure of2/Na2O molar ratio2O/Al2O3, and H2O/Al2O3 were changed to determine the optimum chemical
E. Najafi Kani, A. Allahverdi,
Volume 8, Issue 3 (september 2011 2011)

Shrinkage behavior of a geopolymer cement paste prepared from pumice-type natural pozzolan was studied
by changing parameters of chemical composition including SiO2/Na2O molar ratio of activator and total molar ratios
of Na2O/Al2O3, and H2O/Al2O3. For investigating the effect of curing conditions on shrinkage, hydrothermal curing
was also applied. The obtained results clearly revealed the governing effect of chemical composition on shrinkage.
Mixes with different Na2O/Al2O3 molar ratios exhibited different shrinkage behavior due to variations made in
SiO2/Na2O molar ratio. Application of hydrothermal curing after a 7-day period of precuring in humid atmosphere
also showed strong effect on shrinkage reduction.
A. Allahverdi, E. Najafi Kani, M. Fazlinejhad,
Volume 8, Issue 4 (december 2011)

Abstract: The linear expansion, early-age compressive strength and setting times of the binary mixtures of gypsum and Portland cement clinkers of relatively low C3A-contents were investigated. For this reason, type 1, 2, and 5 of Portland cement-clinkers were selected and a number of binary mixtures were designed. At relatively lower percentages of gypsum (about 5%), the early strength behavior is improved. Results obtained for compressive strength of mixtures with 5% gypsum confirm the possibility of achieving 28- and 90-day compressive strengths up to values higher than 100 MPa and 130 MPa, respectively. At relatively higher percentages of gypsum (more than 25%), excessive expansion caused by ettringite formation results in the formation of micro-cracks effectively weakening the strength behavior. The work suggests that type S expansive cements could be produced from Portland cement clinkers of relatively low C3Acontents.

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