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Showing 8 results for Allahverdi

A. Allahverdi, E. Najafi Kani,
Volume 7, Issue 3 (Sept. 2009)
Abstract

It has been shown that geopolymerization can transform a wide range of waste aluminosilicate materials into building materials with excellent chemical and physical properties such as fire and acid resistance. In this research work, geopolymerization of construction waste materials with different alkali-activators based on combinations of Na2SiO3 and NaOH has been investigated. A number of systems were designed and prepared with water-to-dry binder ratio, silica modulus, and sodium oxide concentration were adjusted at different levels and setting time and 28-day compressive strength were studied. The results obtained reveal that construction wastes can be activated using a proportioned mixture of Na2SiO3 and NaOH resulting in the formation of a geopolymer cement system exhibiting suitable workability and acceptable setting time and compressive strength. Laboratory techniques of Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were utilized for studying molecular and microstructure of the materials.
A. Allahverdi, B. Shaverdi, E. Najafi Kani,
Volume 8, Issue 4 (December 2010)
Abstract

:The aim of this work is to investigate the influence of sodium oxide on properties of fresh and hardened paste of alkali-activated blast furnace slag from Isfahan steel plant. The silica modulus (SiO2/Na2O) of activator was adjusted at 0.6 and a number of mixes were designed in such a way to contain different levels of sodium oxide including 1, 2, 3, 4, 5, and 6% by weight of dry slag. The most important physico-mechanical properties of the pastes including workability, initial and final setting times, 28-day compressive strength and efflorescence severity were measured. Suitable mixes were chosen for more studies including compressive strength at different ages, 90-day autogenous and drying shrinkages. According to the results, increasing the sodium oxide content of the mixes results in increased workability, reduced setting times, and higher compressive strength. The results confirm the possibility of achieving 28-day compressive strengths up to 27.5, 50.0 and 70.0 MPa for mixes with sodium oxide content of 1, 2 and 3 wt% respectively. The measured values for autogenous shrinkage were all less than 0.1% and SEM studies showed a significant decrease in pore sizes with increasing sodium oxide concentration from 1 to 2%.


A. Allahverdi, E. Najafi Kani,
Volume 8, Issue 4 (December 2010)
Abstract

Fast set and high early strength cements containing calcium fluoroaluminate phase (C11A7CaF2) are usually produced by sintering a proportioned raw mix from calcareous and argillaceous components as the main raw materials, at reduced temperatures about 1330 °C. In this work, the possibility of utilizing natural pozzolan as the argillaceous component in the cement raw mix and in order to decrease the sintering temperature of fast set and high early strength cement clinker containing C11A7CaF2 phase has been investigated. The results reveal that the sintering temperature can be reduced to temperatures as low as 1270 °C by utilizing a suitable natural pozzolan and improving the mix burnability. The experimental results confirm the possibility of achieving final setting times as low as 10 min and 3-day compressive strengths as high as 57 MPa


S. Bakhtiyari, A. Allahverdi, M. Rais-Ghasemi, A. A. Ramezanianpour, T. Parhizkar, B. A. Zarrabi,
Volume 9, Issue 3 (September 2011)
Abstract

Self Compacting Concrete (SCC) specimens with limestone (L) and quartz (Q) powders were formulated. The influence of the type

of the powder on the properties of fresh and hardened concrete was evaluated. Dense packing theories were used for mix design

of samples. The equation of Fuller and Thompson for particle size distribution (PSD) of aggregates was modified with considering

fine particles and a proper PSD curve was obtained for SCC. Experimental results showed that this method needs use of less

powder content and results in higher strength/cement ratio compared to traditional mixing methods. No significant difference was

observed between the compressive strengths of specimens containing limestone (L-specimens) and quartz (Q-specimens) powders,

with similar proportions of materials. The residual compressive strength of specimens was examined at 500°C and contradictory

behaviors were observed. One Q-specimen suffered from explosive spalling, while no spalling was occurred for L-specimens. On

the other hand, the residual strength of remained Q-specimens showed considerable increase compared to L-specimens. The results

show the necessity for more detailed investigations considering different effective parameters.


A. Allahverdi, M. Mahinroosta,
Volume 12, Issue 4 (Transaction A: Civil Engineering December 2014)
Abstract

It was found out that the logarithmic models fit the cement–slag blend systems well. In the present study, based on the experimental results, a logarithmic model has been developed to predict the compressive strength of chemically activated high phosphorous slag content cement. Mixes of phosphorous slag (80 wt.%), Portland cement (14 wt.%) and compound chemical activator (6 wt.%) were prepared at different Blaine finenesses using a laboratory ball mill. Compressive strengths of mortar specimens cured in lime-saturated water were measured at different curing times. Mathematical model was prepared in terms of curing time and water-to-cement ratio as independent variables and compressive strength as dependent variable. The comparisons between the model reproductions and the experimentally obtained results confirm the applicability of the presented model.
Hojjatollah Maghsoodloorad, Ali Allahverdi,
Volume 14, Issue 6 (Transaction A: Civil Engineering 2016)
Abstract

Efflorescence formation is an important soundness issue to be considered with alkali-activated cements. In this study, the impact of activator type on the efflorescence formation severity and methods of efflorescence reduction in alkali-activated phosphorus slag cement are investigated. Different alkaline activators including NaOH, KOH and liquid sodium silicate of different silica modules (Ms = SiO2/Na2O) were used for alkali-activation of phosphorus slag. Additions of high alumina cements (Secar 71 and 80) and application of hydrothermal curing condition at 85 °C for 7 h with different pre-curing times (1, 3 and 7 day) in humid environment (relative humidity of 95 %) and 25 °C were used for efflorescence control in alkali-activated phosphorus slag cement. Sodium containing activators resulted in more severe efflorescence formation compared with those of potassium containing activators. Also presence of liquid sodium silicate intensified efflorescence formation. Based on the results obtained, application of an optimum pre-curing stage in humid environment before hydrothermal curing regime stabilizes the cement matrix and improves the effectiveness of hydrothermal conditions.


Ali Allahverdi, Ebrahim Najafi Kani, Babak Shaverdi,
Volume 15, Issue 4 (Transaction A: Civil Engineering 2017)
Abstract

Present work is devoted to a better insight into the identification of carbonation versus efflorescence formation in alkali-activated blast-furnace slag and investigates the relation between the chemical composition of the alkali-activator and the extent of the occurrence of these two phenomena. Obtained results showed that mixes of relatively lower alkali contents suffers not only from weak compressive strength due microstructural defects, but also from carbonation during the first few days. On the other hand, mixes containing relatively higher alkali contents strongly suffers from efflorescence formation in spite of their interestingly high compressive strengths. Carbonation during the first few days can partially neutralize the alkali content of the surface layers of the material which in turn significantly affects the activation mechanism leading to the formation of binding compounds of lower degree of Si substitution with Al in the molecular structure.


Ali Allahverdi, Mostafa Mahinroosta, Shima Pilehvar,
Volume 15, Issue 5 (Transaction A: Civil Engineering 2017)
Abstract

Compressive strength is as one of the most important properties of concrete and mortar that its measurement may be necessary at both early and later ages. Prediction of compressive strength by a proper model is a fast and cost-effective way for evaluating cement quality under various curing conditions. In this paper, a logarithmic model based on the results of an experimental work conducted to investigate the effects of curing time and temperature on the compressive strength development of chemically activated high phosphorous slag content cement has been presented. This model is in terms of curing time and temperature as independent variables and compressive strength as dependent variable. For this purpose, mortar specimens were prepared from 80 wt.% phosphorous slag, 14 wt.% Portland cement, and 6 wt.% compound chemical activator at Blaine fineness of 303 m2/kg. The specimens were cured in lime-saturated water under temperatures of 25, 45, 65, 85 and 100 ºC in oven. The model has two adjustable parameters for various curing times and temperatures. Modeling has been done by applying dimensionless insight. The proposed model can efficiently predict the compressive strength of this type of high phosphorous slag cement with an average relative error of less than 4%.



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