Abstract In the current study, the physical and mechanical properties of polypropylene fiber-rein... more Abstract In the current study, the physical and mechanical properties of polypropylene fiber-reinforced lightweight geopolymer concretes are assessed. Geopolymer synthesis consists of rice husk ash (RHA) and nano-Al2O3 (NA) as solid precursors and 10 M sodium hydroxide (SH) and sodium silicate (SS) with a ratio of SS/SH = 2.5 as alkaline solution. NA amount is 20% of total volume of the binder for all mixtures. Scoria particles are used as lightweight aggregates (LWA) with replacement ratio of 0, 10 and 20% by volume of the total aggregates. Polypropylene (PP) fibers is added to the mixture with the amount of 0, 0.5 and 1% by the volume of the binder. Compressive and flexural strength, density, water absorption and rapid chloride permeability test (RCPT) were evaluated. Results indicated that PP fibers improves the mechanical properties (especially flexural strength) while incorporation of LWA reduced the compressive and flexural strength slightly. Water absorption of geopolymer samples decreased by the incorporation of PP fibers which can compensate significantly the negative impact of LWA replacement. Replacement of 10% LWA does not have significant impact on water absorption and chloride permeability of composites; however, 20% replacement reduced durability. Introduced lightweight geopolymer concrete would be suitable for structural applications due to its relatively low density, high compressive strength and good flexural strength, which is improved by adding PP fibers.
Journal of Research in Science, Engineering and Technology, 2019
In this paper, we evaluated seismic performance properties of steel plate shear wall (SPSW) using... more In this paper, we evaluated seismic performance properties of steel plate shear wall (SPSW) using Consecutive Modal Pushover Procedure (CMPP). This method is performed on 3, 6 and 9-story SPSW frames subjected to seven earthquake records which are scaled according to ASCE/SEI 7-05 provisions. We conducted nonlinear time history analysis (THA) to verify extracted outputs. The SPSW models indicate a relatively accurate estimation in nonlinear story drift and story displacement response of pushover procedures compared to that of the THA with respect to responses like shear story; while, in the high-rise model in specific, the deformation parameters are more accurate through an increase in the height of the models.
In this paper, the effects of different aluminum to silicon ratios in silicate chains of calcium ... more In this paper, the effects of different aluminum to silicon ratios in silicate chains of calcium silicate hydrates (C-S-H) are evaluated on the diffusion coefficient of chloride ions by molecular dynamics method. Tobermorite is a crystalline phase that is used for studying C-S-H properties in nano scale, because of its analogous chemical composition to C-S-H. Aluminum incorporation in C-S-H and the formation of calcium aluminosilicate hydrates (C-A-S-H) is due to both of hydration of tricalcium aluminate (C3A) in portland cement and aluminum oxides in pozzolans. There exist different Al/Si ratios in the tetrahedral chains of C-A-S-H depending on available aluminum oxides in cementitious raw materials. In order to compare the simulation results with previously-published experimental researches on cement pastes, a novel method is introduced here to calculate Al/Si ratio in tetrahedral chains of C-A-S-H using pozzolan replacement ratio in cementitious paste. MK (metakaolin) and FC3R (F...
In this paper, the behavior of three types of masonry walls is assessed subject to blast load as ... more In this paper, the behavior of three types of masonry walls is assessed subject to blast load as an out-of-plane impulse origin, and they are strengthened by the sandwich panel. The values of displacement and von Mises stress caused by blast loads are calculated using finite-element simulation. The modeled masonry walls are constructed using brick, grouted concrete masonry unit and ungrouted concrete masonry unit. Blast load is modeled by means of the CONWEP (conventional weapon) tool. A reliability analysis is conducted to evaluate outputs statistically and to calculate failure probabilities using Monte Carlo method. Plasticity properties of masonry and steel materials are simulated using concrete damage plasticity and Johnson-Cook (JK) models, respectively. Blast load is applied in three different levels of mild, moderate and severe. Results show that sandwich panel strengthening can efficiently reduce the stress and displacement values for all masonry wall types. Probabilities of failure in strengthened masonry walls are significantly decreased. Moreover, in non-strengthened cases, grouted blockwork wall has a lower stress and displacement comparing to the other masonry walls.
An experimental study was performed to assess the effect of metakaolin (MK) as supplementary ceme... more An experimental study was performed to assess the effect of metakaolin (MK) as supplementary cementitious material (SCM) and limestone powder (LP) and nano-titanium dioxide (nano-TiO2; NT) as mineral admixtures on the pore structure, mechanical and durability of self-compacting concrete (SCC). The fresh-state performance was evaluated by slump flow, T 50, V-funnel and L-box tests, and hardened-state parameters were analyzed through compressive strength, water absorption, density and electrical resistivity. Furthermore, permeability was analyzed by means of the rapid chloride permeability test and mercury intrusion porosimetry. Using additives resulted in improvement of rheological properties and compressive strength. Additionally, the density and electrical resistivity of SCC mixes containing SCMs and NT were higher than those of the control SCC mixes. Low absorption and permeability values were obtained for the mixes containing 5% NT. The results herein reported suggest that replac...
Diffusion is a particle transportation process beginning from one point of a system to another th... more Diffusion is a particle transportation process beginning from one point of a system to another through random molecular motion. This process depends on various parameters like temperature, concentration gradient, and particle size. The objective of this article is to assess the variation of diffusion coefficients of water molecules, chloride and sodium ions against different temperatures in calcium silicate hydrates (C-S-H) through molecular dynamics simulation. A uniform sodium chloride solution is modeled between cement hydrate layers with no concentration gradient. In such a solution, temperature could affect diffusion process in a significant manner. The two most important crystalline mineral analogues of C-S-H, tobermorite and jennite, are applied in this simulation. Diffusion coefficients of different ions and water molecules are found in different temperatures. It is revealed that diffusion coefficient is higher at high temperatures. Activation energies of chloride and sodium ions transport in cement hydrates are calculated through Arrhenius law. Output values of diffusion coefficients and activation energies are compared to previous experimental and simulation results in the related literature. A multi-scale analysis is run to estimate the penetration depth of Cl − ions in cement paste through Fick's second law.
Porous materials such as concrete could be subjected to aggressive ions transport. Durability of ... more Porous materials such as concrete could be subjected to aggressive ions transport. Durability of cement paste is extremely depended on water and ions penetration into its interior sections. These ions transport could lead different damages depending on reactivity of ions, their concentrations and diffusion coefficients. In this paper, chloride diffusion process in cement hydrates is simulated at atomistic scale using molecular dynamics. Most important phase of cement hydrates is calcium silicate hydrate (C-S-H). Tobermorite, one of the most famous crystal analogues of C-S-H, is used as substrate in the simulation model. To conduct simulation, a nanopore is considered in the middle of simulation cell to place water molecules and aggressive ions. Different chloride salts are considered in models to find out which one is better for calculation of the transport properties. Diffusion coefficients of water molecules and chloride ions are calculated and validated with existing analytical and experimental works. There are relatively good agreements among simulation outputs and experimental results.
In this paper, effects of natural pozzolan, called Chekneh, as a part of cement replacement and w... more In this paper, effects of natural pozzolan, called Chekneh, as a part of cement replacement and wood chips as a part of mixture aggregates on the mechanical and durability properties of concrete were studied. Nine concrete mixtures proportions within two categories were prepared. In the first category, the properties of concrete were evaluated by adding 10 and 15% of Chekneh pozzolan or wood chips and the second category containing combination of Chekneh pozzolan and wood chips was prepared. The results showed that adding optimal content of natural Chekneh, 10% of cement weight replacement to concrete improves the mechanical properties including flexural, compressive and tensile strength and durability properties of concrete including volumetric water absorption, electrical resistance and rapid chloride permeability. Also, the replacement of 10% wood chips as a part of aggregates causes improvement in mechanical properties of concrete. The combined effect of natural pozzolan and wood chips has the most positive effect on increasing the compressive, tensile and flexural strength in concrete, and the sample which contains 10% pozzolan and 10% wood chips has the most improvement compared to the control sample.
Corrosion of steel bars in concrete is a major problem reducing concrete structure lifetime that ... more Corrosion of steel bars in concrete is a major problem reducing concrete structure lifetime that must be considered in the design of structures. Many parameters involved in corrosion propagation contain different uncertainties; therefore, probabilistic analysis should be performed. In this paper, we proposed a reliability analysis method for RC frames subjected to simultaneous corrosion and static loads. It consists of the analysis of an arbitrary 2D frame at each time step to take into account the steel bars mass loss due to corrosion. We calculated instantaneous load-bearing capacity of elements. Analysis outputs would be extracted, and the probability of failure and reliability index could be calculated in each time step. Moreover, we conducted the sensitivity analysis for some parameters. It is shown that various parameters such as cover thickness, dimensions, strength of materials and reinforcements how could improve vulnerability of concrete structure subjected to corrosion. We obtained outputs based on various corrosion models proposed by different researchers. Obtained results were compared with one another, and they have good agreement with experimental results in the literature. Proposed method shows that corrosion process could decrease strength of structural elements significantly. Keywords Reliability • Corrosion • Chloride ion • Reinforced concrete • Monte Carlo method B Behnam Zehtab
In this article, based on a series of laboratory experiments, a new cubic energy-based damage ind... more In this article, based on a series of laboratory experiments, a new cubic energy-based damage index is introduced for identifying damage locations using acceleration measurements of strengthen-free and GFRP-strengthened reinforced concrete beams having different boundary conditions. For this purpose, wavelet-packet energy has been chosen as feature. Furthermore, a new damage localizing parameter is introduced to estimate damage location using proposed damage index data. In the framework of the laboratory results, potential damages could be detected and located correctly using introduced damage index and the results would be compared with some reference-based indexes. The proposed damage index would have minimum estimation error as compared with other indexes in the literature. Damaged beams are then strengthened with GFRP and the strengthening quality is evaluated using degree-of-strengthening index by comparing signals measured from strengthened and healthy beams.
در اين تحقيق، پاسخ ارتعاشي تير بتن آرمه¬ي ساده و نيز تير بتن آرمه مقاوم¬سازي شده با GFRP به روش آ... more در اين تحقيق، پاسخ ارتعاشي تير بتن آرمه¬ي ساده و نيز تير بتن آرمه مقاوم¬سازي شده با GFRP به روش آزمايشگاهي مورد بررسي قرار گرفته است. با استفاده از بررسي تغييرات انرژي سيگنال با تبديل پاکت-موجک و استفاده از شاخص آسيب و شاخص¬هاي ارزيابي انرژي، پاسخ تيرهاي سالم با پاسخ آن¬ها پس از آسيب در درجات آزادي مختلف، مقايسه شده¬اند و مکان و شدت آسيب به خوبي تخمين زده شده است. همچنين با مقاوم¬سازي تيرهاي بتني ساده¬ي آسيب ديده و مقايسه¬ي انرژي آن پيش از آسيب، پس از آسيب و پس از مقاوم¬سازي، کيفيت مقاوم¬سازي مورد ارزيابي قرار گرفته است.
AbstractIn the last decade nanomaterials due to their unique physical and chemical properties, ha... more AbstractIn the last decade nanomaterials due to their unique physical and chemical properties, have attracted the interest of researchers to fabricate new building materials with novel functions. One of the most referred to and used cementitious nanosized materials is nanosilica (nSiO2). Although the number of publications devoted to the influence of nanosilica on the properties of cementitious composites has increased over the course of the last decade, the field of polymer-cement composites (PCC) has remained under-studied. Therefore, this paper will deal with the potential application and the influence of nanosilica (nSiO2) on the mechanical properties of PCC.In this study the influence of diameter (100nm and 250nm) and quantity (1%, 3%, 5% by weight of cement) of nSiO2 on the consistency and mechanical properties of polymer-cement mortars (PCC) have been examined. Moreover, the hydration of cement compounds was followed by X-ray diffraction (XRD).Studies have shown that the addition of nanosilica has great potential to accelerate the pozzolanic reaction, thus reacting more with the CH and increasing conversion of C-S-H, and having the potential to improve mechanical properties of PCC. The obstacle overcome is the high water demand of nanosilica particles, leading to significant deterioration of consistency. Finer particles of nSiO2 seem to be more effective and cause fewer problems with the consistency of fresh mortars
Abstract In the current study, the physical and mechanical properties of polypropylene fiber-rein... more Abstract In the current study, the physical and mechanical properties of polypropylene fiber-reinforced lightweight geopolymer concretes are assessed. Geopolymer synthesis consists of rice husk ash (RHA) and nano-Al2O3 (NA) as solid precursors and 10 M sodium hydroxide (SH) and sodium silicate (SS) with a ratio of SS/SH = 2.5 as alkaline solution. NA amount is 20% of total volume of the binder for all mixtures. Scoria particles are used as lightweight aggregates (LWA) with replacement ratio of 0, 10 and 20% by volume of the total aggregates. Polypropylene (PP) fibers is added to the mixture with the amount of 0, 0.5 and 1% by the volume of the binder. Compressive and flexural strength, density, water absorption and rapid chloride permeability test (RCPT) were evaluated. Results indicated that PP fibers improves the mechanical properties (especially flexural strength) while incorporation of LWA reduced the compressive and flexural strength slightly. Water absorption of geopolymer samples decreased by the incorporation of PP fibers which can compensate significantly the negative impact of LWA replacement. Replacement of 10% LWA does not have significant impact on water absorption and chloride permeability of composites; however, 20% replacement reduced durability. Introduced lightweight geopolymer concrete would be suitable for structural applications due to its relatively low density, high compressive strength and good flexural strength, which is improved by adding PP fibers.
Journal of Research in Science, Engineering and Technology, 2019
In this paper, we evaluated seismic performance properties of steel plate shear wall (SPSW) using... more In this paper, we evaluated seismic performance properties of steel plate shear wall (SPSW) using Consecutive Modal Pushover Procedure (CMPP). This method is performed on 3, 6 and 9-story SPSW frames subjected to seven earthquake records which are scaled according to ASCE/SEI 7-05 provisions. We conducted nonlinear time history analysis (THA) to verify extracted outputs. The SPSW models indicate a relatively accurate estimation in nonlinear story drift and story displacement response of pushover procedures compared to that of the THA with respect to responses like shear story; while, in the high-rise model in specific, the deformation parameters are more accurate through an increase in the height of the models.
In this paper, the effects of different aluminum to silicon ratios in silicate chains of calcium ... more In this paper, the effects of different aluminum to silicon ratios in silicate chains of calcium silicate hydrates (C-S-H) are evaluated on the diffusion coefficient of chloride ions by molecular dynamics method. Tobermorite is a crystalline phase that is used for studying C-S-H properties in nano scale, because of its analogous chemical composition to C-S-H. Aluminum incorporation in C-S-H and the formation of calcium aluminosilicate hydrates (C-A-S-H) is due to both of hydration of tricalcium aluminate (C3A) in portland cement and aluminum oxides in pozzolans. There exist different Al/Si ratios in the tetrahedral chains of C-A-S-H depending on available aluminum oxides in cementitious raw materials. In order to compare the simulation results with previously-published experimental researches on cement pastes, a novel method is introduced here to calculate Al/Si ratio in tetrahedral chains of C-A-S-H using pozzolan replacement ratio in cementitious paste. MK (metakaolin) and FC3R (F...
In this paper, the behavior of three types of masonry walls is assessed subject to blast load as ... more In this paper, the behavior of three types of masonry walls is assessed subject to blast load as an out-of-plane impulse origin, and they are strengthened by the sandwich panel. The values of displacement and von Mises stress caused by blast loads are calculated using finite-element simulation. The modeled masonry walls are constructed using brick, grouted concrete masonry unit and ungrouted concrete masonry unit. Blast load is modeled by means of the CONWEP (conventional weapon) tool. A reliability analysis is conducted to evaluate outputs statistically and to calculate failure probabilities using Monte Carlo method. Plasticity properties of masonry and steel materials are simulated using concrete damage plasticity and Johnson-Cook (JK) models, respectively. Blast load is applied in three different levels of mild, moderate and severe. Results show that sandwich panel strengthening can efficiently reduce the stress and displacement values for all masonry wall types. Probabilities of failure in strengthened masonry walls are significantly decreased. Moreover, in non-strengthened cases, grouted blockwork wall has a lower stress and displacement comparing to the other masonry walls.
An experimental study was performed to assess the effect of metakaolin (MK) as supplementary ceme... more An experimental study was performed to assess the effect of metakaolin (MK) as supplementary cementitious material (SCM) and limestone powder (LP) and nano-titanium dioxide (nano-TiO2; NT) as mineral admixtures on the pore structure, mechanical and durability of self-compacting concrete (SCC). The fresh-state performance was evaluated by slump flow, T 50, V-funnel and L-box tests, and hardened-state parameters were analyzed through compressive strength, water absorption, density and electrical resistivity. Furthermore, permeability was analyzed by means of the rapid chloride permeability test and mercury intrusion porosimetry. Using additives resulted in improvement of rheological properties and compressive strength. Additionally, the density and electrical resistivity of SCC mixes containing SCMs and NT were higher than those of the control SCC mixes. Low absorption and permeability values were obtained for the mixes containing 5% NT. The results herein reported suggest that replac...
Diffusion is a particle transportation process beginning from one point of a system to another th... more Diffusion is a particle transportation process beginning from one point of a system to another through random molecular motion. This process depends on various parameters like temperature, concentration gradient, and particle size. The objective of this article is to assess the variation of diffusion coefficients of water molecules, chloride and sodium ions against different temperatures in calcium silicate hydrates (C-S-H) through molecular dynamics simulation. A uniform sodium chloride solution is modeled between cement hydrate layers with no concentration gradient. In such a solution, temperature could affect diffusion process in a significant manner. The two most important crystalline mineral analogues of C-S-H, tobermorite and jennite, are applied in this simulation. Diffusion coefficients of different ions and water molecules are found in different temperatures. It is revealed that diffusion coefficient is higher at high temperatures. Activation energies of chloride and sodium ions transport in cement hydrates are calculated through Arrhenius law. Output values of diffusion coefficients and activation energies are compared to previous experimental and simulation results in the related literature. A multi-scale analysis is run to estimate the penetration depth of Cl − ions in cement paste through Fick's second law.
Porous materials such as concrete could be subjected to aggressive ions transport. Durability of ... more Porous materials such as concrete could be subjected to aggressive ions transport. Durability of cement paste is extremely depended on water and ions penetration into its interior sections. These ions transport could lead different damages depending on reactivity of ions, their concentrations and diffusion coefficients. In this paper, chloride diffusion process in cement hydrates is simulated at atomistic scale using molecular dynamics. Most important phase of cement hydrates is calcium silicate hydrate (C-S-H). Tobermorite, one of the most famous crystal analogues of C-S-H, is used as substrate in the simulation model. To conduct simulation, a nanopore is considered in the middle of simulation cell to place water molecules and aggressive ions. Different chloride salts are considered in models to find out which one is better for calculation of the transport properties. Diffusion coefficients of water molecules and chloride ions are calculated and validated with existing analytical and experimental works. There are relatively good agreements among simulation outputs and experimental results.
In this paper, effects of natural pozzolan, called Chekneh, as a part of cement replacement and w... more In this paper, effects of natural pozzolan, called Chekneh, as a part of cement replacement and wood chips as a part of mixture aggregates on the mechanical and durability properties of concrete were studied. Nine concrete mixtures proportions within two categories were prepared. In the first category, the properties of concrete were evaluated by adding 10 and 15% of Chekneh pozzolan or wood chips and the second category containing combination of Chekneh pozzolan and wood chips was prepared. The results showed that adding optimal content of natural Chekneh, 10% of cement weight replacement to concrete improves the mechanical properties including flexural, compressive and tensile strength and durability properties of concrete including volumetric water absorption, electrical resistance and rapid chloride permeability. Also, the replacement of 10% wood chips as a part of aggregates causes improvement in mechanical properties of concrete. The combined effect of natural pozzolan and wood chips has the most positive effect on increasing the compressive, tensile and flexural strength in concrete, and the sample which contains 10% pozzolan and 10% wood chips has the most improvement compared to the control sample.
Corrosion of steel bars in concrete is a major problem reducing concrete structure lifetime that ... more Corrosion of steel bars in concrete is a major problem reducing concrete structure lifetime that must be considered in the design of structures. Many parameters involved in corrosion propagation contain different uncertainties; therefore, probabilistic analysis should be performed. In this paper, we proposed a reliability analysis method for RC frames subjected to simultaneous corrosion and static loads. It consists of the analysis of an arbitrary 2D frame at each time step to take into account the steel bars mass loss due to corrosion. We calculated instantaneous load-bearing capacity of elements. Analysis outputs would be extracted, and the probability of failure and reliability index could be calculated in each time step. Moreover, we conducted the sensitivity analysis for some parameters. It is shown that various parameters such as cover thickness, dimensions, strength of materials and reinforcements how could improve vulnerability of concrete structure subjected to corrosion. We obtained outputs based on various corrosion models proposed by different researchers. Obtained results were compared with one another, and they have good agreement with experimental results in the literature. Proposed method shows that corrosion process could decrease strength of structural elements significantly. Keywords Reliability • Corrosion • Chloride ion • Reinforced concrete • Monte Carlo method B Behnam Zehtab
In this article, based on a series of laboratory experiments, a new cubic energy-based damage ind... more In this article, based on a series of laboratory experiments, a new cubic energy-based damage index is introduced for identifying damage locations using acceleration measurements of strengthen-free and GFRP-strengthened reinforced concrete beams having different boundary conditions. For this purpose, wavelet-packet energy has been chosen as feature. Furthermore, a new damage localizing parameter is introduced to estimate damage location using proposed damage index data. In the framework of the laboratory results, potential damages could be detected and located correctly using introduced damage index and the results would be compared with some reference-based indexes. The proposed damage index would have minimum estimation error as compared with other indexes in the literature. Damaged beams are then strengthened with GFRP and the strengthening quality is evaluated using degree-of-strengthening index by comparing signals measured from strengthened and healthy beams.
در اين تحقيق، پاسخ ارتعاشي تير بتن آرمه¬ي ساده و نيز تير بتن آرمه مقاوم¬سازي شده با GFRP به روش آ... more در اين تحقيق، پاسخ ارتعاشي تير بتن آرمه¬ي ساده و نيز تير بتن آرمه مقاوم¬سازي شده با GFRP به روش آزمايشگاهي مورد بررسي قرار گرفته است. با استفاده از بررسي تغييرات انرژي سيگنال با تبديل پاکت-موجک و استفاده از شاخص آسيب و شاخص¬هاي ارزيابي انرژي، پاسخ تيرهاي سالم با پاسخ آن¬ها پس از آسيب در درجات آزادي مختلف، مقايسه شده¬اند و مکان و شدت آسيب به خوبي تخمين زده شده است. همچنين با مقاوم¬سازي تيرهاي بتني ساده¬ي آسيب ديده و مقايسه¬ي انرژي آن پيش از آسيب، پس از آسيب و پس از مقاوم¬سازي، کيفيت مقاوم¬سازي مورد ارزيابي قرار گرفته است.
AbstractIn the last decade nanomaterials due to their unique physical and chemical properties, ha... more AbstractIn the last decade nanomaterials due to their unique physical and chemical properties, have attracted the interest of researchers to fabricate new building materials with novel functions. One of the most referred to and used cementitious nanosized materials is nanosilica (nSiO2). Although the number of publications devoted to the influence of nanosilica on the properties of cementitious composites has increased over the course of the last decade, the field of polymer-cement composites (PCC) has remained under-studied. Therefore, this paper will deal with the potential application and the influence of nanosilica (nSiO2) on the mechanical properties of PCC.In this study the influence of diameter (100nm and 250nm) and quantity (1%, 3%, 5% by weight of cement) of nSiO2 on the consistency and mechanical properties of polymer-cement mortars (PCC) have been examined. Moreover, the hydration of cement compounds was followed by X-ray diffraction (XRD).Studies have shown that the addition of nanosilica has great potential to accelerate the pozzolanic reaction, thus reacting more with the CH and increasing conversion of C-S-H, and having the potential to improve mechanical properties of PCC. The obstacle overcome is the high water demand of nanosilica particles, leading to significant deterioration of consistency. Finer particles of nSiO2 seem to be more effective and cause fewer problems with the consistency of fresh mortars
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