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Nikbin I.M.,Islamic Azad University at Rasht | Davoodi M.R.,Babol Noshirvani University of Technology | Fallahnejad H.,Babol Noshirvani University of Technology | Rahimi S.,Lamei Gorgani Institute of Higher Education | Farahbod F.,Housing and Urban Development Research Center
Journal of Materials in Civil Engineering | Year: 2016

This paper describes and discusses an experimental study on the effect of mineral filler on the fracture behavior and ductility of self-compacting concrete (SCC). Based on an experimental program, a series of three-point bending tests was carried out on 118 notched beams. SCC was prepared with various contents of mineral filler with water-to-cement (w/c) ratios of 0.47 and 0.6. For all mixes, the fracture parameters were analyzed using the work-of-fracture method (WFM) and the size-effect method (SEM) to obtain a suitable correlation between these methods that is used to calibrate fracture numerical models. Given an increase in mineral filler content and a decrease in the w/c ratio in SCC, the results yielded the following conclusions: (1) fracture energies, GF in WFM and Gf in SEM, increase slightly; (2) the brittleness number increases; (3) the characteristic length (Lch) in WFM and the fracture process zone length (Cf) in SEM decrease, which may be due to an increase in the packing density and changes in the pore size distribution; and (4) the behavior of SCC specimens, based on the size-effect curve, approaches the linear elastic fracture mechanics criterion. In addition, the results showed that there is a significant correlation between GF and Gf values (GF/Gf=3.0). © 2015 American Society of Civil Engineers.

Ahmadi B.,Amirkabir University of Technology | Ramezanianpour A.A.,Amirkabir University of Technology | Sobhani J.,Housing and Urban Development Research Center
Magazine of Concrete Research | Year: 2014

The aim of this paper is to evaluate the corrosion activity of cracked flexural reinforced concrete elements in a marine environment. Some non-destructive test results of a comprehensive research project are presented and discussed. Corrosion activity of 24 cracked reinforced concrete prisms under sustained loading and 12 uncracked reinforced concrete prisms are assessed using three non-destructive testing methods. The specimens are located in the tidal zone of a field exposure station on the south coast of Iran. The results obtained during 14 months of exposure are presented and discussed in this study. It is found that the corrosion of rebar in the cracked zone initiates shortly after exposure to sea water and declines over the exposure period. Also, the corrosion of steel reinforcement in the cracked zone becomes more severe by increasing crack width/cover ratio. Furthermore, the corrosion current density and electrical resistivity results are more sensitive to the distance between testing point and crack point compared to the half-cell potential results.

Ghafoori N.,University of Nevada, Las Vegas | Najimi M.,University of Nevada, Las Vegas | Sobhani J.,Housing and Urban Development Research Center | Aqel M.A.,University of Toronto
Construction and Building Materials | Year: 2013

This paper is intended to compare robustness of linear and nonlinear regressions, and neural network prediction models in estimating rapid chloride permeability of self-consolidating concretes based on their mixture proportions. Several models were developed by varying number of independent variables and samples (mixtures) allotted to training and testing. The results of this study showed the superior performance of neural network models in comparison with the prediction models obtained by linear and nonlinear regressions, particularly when testing evaluations were chosen from the boundaries of mixture proportions. Within the linear and nonlinear prediction models, power relationships produced the most consistent performance. © 2013 Elsevier Ltd. All rights reserved.

Karami M.,University of Tehran | Akhavan-Behabadi M.A.,University of Tehran | Raisee Dehkordi M.,University of Tehran | Delfani S.,Housing and Urban Development Research Center
Solar Energy Materials and Solar Cells | Year: 2016

In this paper, the optical and thermophysical properties of CuO nanofluid as the working fluid of low temperature direct absorption solar collector which is prepared by dispersing the CuO nanoparticles into mixture of distilled water and ethylene glycol (70%:30% in volume) as the base fluid is investigated at the different temperatures for different volume fractions. The results showed that the nanofluids had higher absorption coefficient compared to the base fluid in the whole wavelengths for solar energy, ranging from 200 to 2500 nm. The absorbed energy fraction of CuO nanofluid with only 100 ppm (volume fraction 0.01%) nanoparticle volume fraction is 4 times more than that of the base fluid at solar collector depth of 1 cm. The viscosity increased with the increasing volume fraction and decreased exponentially with the increasing temperature. The thermal conductivity of CuO nanofluids increased with the increase of CuO volume fraction in the base fluid and temperature. At the investigated volume fractions, the thermal conductivity of the nanofluids was found to increase with respect to the base fluid up to about 13.7% for the 100 ppm CuO nanoparticle volume fraction. Higher thermal conductivity and lower viscosity of CuO nanofluids by increasing temperature, together with the appropriate optical properties, introduce this kind of nanofluids as an appropriate candidate to effectively enhance the direct absorption solar collector efficiency. © 2015 Elsevier B.V. All rights reserved.

Khorami M.,Islamic Azad University at Eslamshahr | Sobhani J.,Housing and Urban Development Research Center
International Journal of Civil Engineering | Year: 2013

Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2% and 4% of waste agricultural fibers in combination with and without 5% replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.

Sadrmomtazi A.,Guilan University | Rasmi Atigh H.,Guilan University | Sobhani J.,Housing and Urban Development Research Center
Asian Journal of Civil Engineering | Year: 2014

Externally bonding of fiber reinforced (FRP) sheet to reinforced concrete (RC) beams has become a popular flexural strengthening method in recent years. The ultimate flexural strength of those strengthened beams can be improved efficiently, but it is often prevented by premature failure modes, such as sheets end interfacial debonding. This paper proposes an effective method to prevent sheets end interfacial debonding. Hence, an experimental and analytical study conducted to verify the efficiency of the proposed method. Therefore, nine concrete beams with dimensions of 100 mm width, 160 mm height and 1200 mm length were manufactured and tested. Eight specimens were strengthened in flexure with various numbers of CFRP layers and different sheets end strengthening methods. From the test results of this study it is conducted that the design guidance of ACI 440.2R-02 and ISIS Canada overestimates and the developed method by Toutanji et al. underestimates the flexural strength of CFRP strengthened RC beams at yielding. Also, applying the proposed method to sheets end strengthening, prevented sheets end interfacial debonding and increased load carrying capacity of those strengthened beams by 26% and 32%. The ductility (i.e. δ_u/δ_y) of those strengthened beams increased by 77% and 90%.

Hesami S.,Babol Noshirvani University of Technology | Ahmadi S.,Babol Noshirvani University of Technology | Sadeghi V.,Babol Noshirvani University of Technology | Hassanabadi M.E.,Housing and Urban Development Research Center
International Journal of Pavement Research and Technology | Year: 2014

Strength is the primary concern for Portland cement pervious concrete (PCPC) designs. Since PCPC has a high void ratio (often without fine aggregate due to the permeability requirement), compressive and tensile strengths tend to be lower than thoseofconventional concrete pavements. In this experimental study, PCPC mixes made with steel fibers and polyphenylene sulfide(PPS) fibers and various amounts of sand were evaluated. Mechanical properties, porosity, and permeability of the PCPC were tested. The results pointed out adding fibers to the mixes increased the concrete strength as well as void content. It is noteworthyto mention that PPS fibers performed better thansteel fibers. Addition of a small amount of fine sand (approximate 7 % by weight of total aggregate) to the mixes with PPS fibers significantly improved the concrete strength. © Chinese Society of Pavement Engineering.

Abbasi O.,Housing and Urban Development Research Center | Ghanbari A.,Housing and Urban Development Research Center | Asghar Hosseini S.A.,Housing and Urban Development Research Center | Beitollahi A.,Housing and Urban Development Research Center
International Journal of Geotechnical Engineering | Year: 2016

Predominant natural frequency is a basic parameter in the design of seismic structures, including retaining walls. Knowing the frequency of free vibration aids understanding of the actual seismic behavior of structures. Soil and wall interaction also plays an important role in the seismic analysis of retaining walls. In this study, the analytical method was used to obtain a precise formulation for the predominant natural frequency of retaining walls with fixed and variable cross sections using the beam theory for an elastic foundation and the energy method. Using the suggested formula, the interaction of the soil and wall at the predominant natural frequency was easily considered. The predominant natural frequency of flexible modes for the wall was compared using the suggested formulation with modal analysis using ANSYS. © 2016 Taylor & Francis.

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