-
حرية الوصول المقاله
1 - تعیین درصد بهینه اختلاط پسماند مقواسازی در تهیه بتن سبک غیر‌باربر
داریوش یوسفی کبریا سیده فاطمه سید علیپور مهدی دهستانیمقدمه و هدف: بیشتر صنایع کاغذ و مقواسازی برای دفع پسماندهای تولیدی خود، صرف نظر از هزینه های گزاف، از دو روش متداول سوزاندن و دفن در خاکچال استفاده می کنند. ترکیبات خطرناک موجود در این نوع پسماندها، سبب آلودگی های محیط زیست و به خطر افتادن سلامت بشر می شود. بسیاری از مط أکثرمقدمه و هدف: بیشتر صنایع کاغذ و مقواسازی برای دفع پسماندهای تولیدی خود، صرف نظر از هزینه های گزاف، از دو روش متداول سوزاندن و دفن در خاکچال استفاده می کنند. ترکیبات خطرناک موجود در این نوع پسماندها، سبب آلودگی های محیط زیست و به خطر افتادن سلامت بشر می شود. بسیاری از مطالعات سال های اخیر نشان می دهد که بعضی از ضایعات حاصل از صنایع کاغذ و مقوا می تواند به عنوان مواد اولیه در صنعت ساختمان به کار رود. این تحقیق با هدف تعیین درصد بهینه اختلاط پسماند مقواسازی در تهیه بتن سبک غیر باربر انجام شد. روش بررسی: در این تحقیق از دو نوع پسماند کارخانه مقواسازی (پسماند نوع1 حاوی مقوا و ماسه و پسماند نوع2 حاوی نایلون، یونولیت و مقوا) که بیشترین حجم پسماندها را تشکیل می دهند استفاده شد. مشخصات فیزیکی و میکروبی پسماندها مطابق ASTM اندازه گیری شد. همچنین ترکیب های مختلف شیمیایی پسماندها شامل عناصر مختلف با استفـاده از میکــروسکـوپ الکترونی اندازه گیری شد. پس از آماده سازی نمونه ها، آزمایش های مورد نظر برای تعیین درصد بهینه اختلاط پسماند در بتن در سنین 7، 14 و 28 روز انجام شد. یافته ها: از آنجاییکه pH نمونه بتن های تازه حاوی پسماند بزرگتر از 12 می باشد، می توان مطمئن شد که هیچ گونه مشکل میکروبی وجود نخواهد داشت. به طورکلی استفاده از پسماند در تولید بتن سبب کاهش مقاومت فشاری نمونه ها می شود. مقایسه مقاومت فشاری بتن های حاوی پسماند نوع1 و نمونه بتن های حاوی هر دو نوع پسماند، نشان می دهد با کاهش میزان پسماند نوع 2 نسبت به پسماند نوع1 مقاومت فشاری بتن بهبود می یابد. نتایج حاصل از آزمایش چگالی خشک، نشان دهنده کاهش چگالی نمونه های بتنی حاوی پسماند با افزایش درصد جایگزینی پسماند در بخش ماسه می باشد. همچنین استفاده از پسماند نوع2 باعث سبک تر شدن نمونه های بتنی نسبت به نوع1 می شود. مقادیر بهینه درصدهای جایگزینی پسماند بجای بخش ماسه بتن برای نمونه های حاوی پسماند نوع 1 و نوع 2، به ترتیب 70 و 75 و همچنین برای نمونه های حاوی هر دو نوع پسماند، 49 درصد پسماند نوع 1 و 21 درصد پسماند نوع 2 می باشد. بحث و نتیجه گیری: با توجه به نتایج به دست آمده، استفاده از پسماند نوع1 در تولید بتن به لحاظ اقتصادی و زیست محیطی به سبب استفاده از سیمان کمتر رضایت بخش تر می باشد. استفاده از پسماندهای کارخانه های مقواسازی در تولید بتن سبب صرفه های زیست محیطی و اقتصادی (سودآوری و تولید اشتغال، کاهش هزینه های انتقال پسماندها به محل دفن، کاهش وزن سازه، استفاده از پسماند به جای خرید ماسه و کاهش آلودگی های زیست محیطی ناشی از سوزاندن و دفن پسماندهـا در خاکچال) می شود. تفاصيل المقالة -
حرية الوصول المقاله
2 - Increasing of the cement strength and corrosion resistance of rebar inside it using silica nanoparticles
Fatemeh AbdiIn this work, silica nanoparticles were added to the mortar with one percent by weight of cement. To investigate the effect of these nanoparticles on the strength of cement, 7-day and 28-day strength according to ASTMC109 standard was obtained and compared with the resu أکثرIn this work, silica nanoparticles were added to the mortar with one percent by weight of cement. To investigate the effect of these nanoparticles on the strength of cement, 7-day and 28-day strength according to ASTMC109 standard was obtained and compared with the results of the control sample. the results showed that these nanoparticles increase the compressive and bending strengths. To investigate this nanoparticles effect on the corrosion resistance of the rebar inside the cement, polarization and EIS tests were performed in 3.5% salt solution.The results of the polarization test showed that the sample with silicon dioxide nanoparticles has more corrosion potential and less corrosion current, which indicates less corrosion rate and less corrosion tendency of this sample compared to the control sample. EIS analysis showed that samples with the presence of silicon dioxide nanoparticles have higher electrical impedance than the other. By simulating the equivalent circuit, the reason for the higher electrical impedance of the mortar in the presence of Sio2 nanoparticles was investigated.The results showed that the reason for the increase in corrosion resistance and electrical impedance is the increase in electrical resistance, increase in ion diffusion and the decrease in capacitance of mortar. تفاصيل المقالة -
حرية الوصول المقاله
3 - Synthesis of Environmentally Friendly Activated Alkali Concrete (Geopolymer) Based on Bentonite
A EsparhamGeopolymers can be mentioned as a new class of green cement adhesives. Geopolymers have recently been introduced as a greener alternative to conventional Portland cement (OPC) with the potential to minimize the negative environmental consequences of OPC such as carbon f أکثرGeopolymers can be mentioned as a new class of green cement adhesives. Geopolymers have recently been introduced as a greener alternative to conventional Portland cement (OPC) with the potential to minimize the negative environmental consequences of OPC such as carbon footprint and energy consumption. In this experimental study, the effects of different alkaline activating solutions on compressive, tensile, and indirect flexural strength, water absorption, and acid resistance of bentonite-based geopolymer concrete (GPC) were investigated. Also in this study, a new type of alkaline activator was used. In this study, GPC samples made from bentonite were produced and baked at 90 ° C. The results showed that the addition of NaOH to the mixture after 3 minutes of mixing KOH and Na2SiO3 with dry components (1/3 of the total mixing time) increases the compressive, tensile, and flexural strength and we also see that with this new method, water absorption capacity and the amount of weight loss of geopolymer concrete samples are reduced in acidic conditions. تفاصيل المقالة -
حرية الوصول المقاله
4 - Investigating the effect of nanosilica on the compressive strength of hard concrete by considering Atomic Force Microscopy (AFM) examinations
seyed mohammad mahdi shafiei mahboobeh pirizadeh Ebrahim ZolgharneinThis study investigated the compressive strength of hardened concrete and the formation of Calcium Silicate Hydrate (C-S-H) with the addition of nanosilica (SiO2). Compressive strength testing was performed using ASTM C496 to determine stress-strain curves and compressi أکثرThis study investigated the compressive strength of hardened concrete and the formation of Calcium Silicate Hydrate (C-S-H) with the addition of nanosilica (SiO2). Compressive strength testing was performed using ASTM C496 to determine stress-strain curves and compressive strength of the materials. The hydration process and formation of C-S-H and Calcium Hydroxide (CH) was examined using Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate an increase in compressive strength using 1, 3 and 5% of nanosilica to concrete replacement by volume in comparison to the control mix (without nanosilica). The optimum concrete replacement to yield maximum strength was of the 5% nanosilica content. Comparing the 56 day results for the 3 and 5% of nanosilica replacement samples, notice the same percentage of C-S-H formation of 83 and 85%, respectively تفاصيل المقالة -
حرية الوصول المقاله
5 - Effect of Basalt and Polypropylene Fibers on Unconfined Compressive Strength of Cement-Stabilized clay, an Experimental Approach
Seyed Hadi Sahlabadi Meysam Bayat Mohsen Mousivand Mohsen SaadatSo far, many studies have been done on the performance of conventional chemical stabilizers such as cement, lime, fly ash or other chemical additives. However, very limited researches were conducted on the mechanical behavior of cement-stabilized soil with fiber inclusi أکثرSo far, many studies have been done on the performance of conventional chemical stabilizers such as cement, lime, fly ash or other chemical additives. However, very limited researches were conducted on the mechanical behavior of cement-stabilized soil with fiber inclusion. Fiber-reinforcement of a stabilized soil offers new opportunities to improve ductility and strength characteristics of weak soils. The main objective of this research is considering the effects of curing time, initial moisture content, polypropylene fiber (PPF) or basalt fiber (BF) with or without addition of cement on the Unconfined Compressive Strength (UCS) of the clay soil. Different ratios of PPF or BF and/or cement were added to the soil to identify their influences on the UCS. The study finds that adding cement, PPF or BF to soil causes a remarkable increase in the strength. The strength of the PPF-reinforced specimens was observed significantly more than that of BF-reinforced ones. The strength of specimens increases gradually as the initial moisture content decreases and the cement content or curing time increases. However, the axial strain at failure for cement-stabilized specimens decreased with increasing cement content or curing time. Furthermore, it is concluded that the increase in UCS of combined PPF or BF and cement inclusions is more than the increase caused by each of them, individually. تفاصيل المقالة -
حرية الوصول المقاله
6 - Examining the Mixing Plan and the Results of the Plastic Concrete
Abolfazl Ostovarzijerdi Akbar Ghanbari Mohammad KarkonIn order to control seepage from the dam, various methods are used to reduce water seepage. One of the methods of reducing the permeability of the water according to its material is building cut-off walls and filling them with plastic concrete materials. In this study, أکثرIn order to control seepage from the dam, various methods are used to reduce water seepage. One of the methods of reducing the permeability of the water according to its material is building cut-off walls and filling them with plastic concrete materials. In this study, it has been tried to study the mixing plan of the plastic concrete in the main body of the Nargesi dam’s cutoff wall and to determine the results of compressive strength and elasticity modulus of 108 panels of cut-off wall in different ages in this project. Due to the individual concreting of each panel from the cutoff wall, the results of the plastic concrete panels at runtime are somewhat different. Due to the sensitivity of the plastic concrete to the dispersion of the results, considering that the cutoff wall should have a seamless function as well as the sensitivity of the concrete over time, it seems necessary to address this issue in an operational project. The results indicate that the growth rate of elastic modulus in a period of time is less than the growth rate of the compressive strength, and in other words, the plasticity of the concrete is changed less over time. تفاصيل المقالة -
حرية الوصول المقاله
7 - Compressive Strength and Ductility of Concrete Wrapped by CFRP
Seiyed Ali Haj Seiyed Taghia Behzad Saeedi Razavi Hamid Reza DarvishvandExisting reinforced concrete (RC) columns may be structurally deficient due to variety of reasons such as improper transverse reinforcement, flaws in structural design, insufficient load carrying capacity, etc. Fiber reinforced polymer (FRP) is a new generation of mater أکثرExisting reinforced concrete (RC) columns may be structurally deficient due to variety of reasons such as improper transverse reinforcement, flaws in structural design, insufficient load carrying capacity, etc. Fiber reinforced polymer (FRP) is a new generation of materials which illustrates in order to enhance concrete compressive strength and ductility. Among the FRP types, Carbon fiber reinforced polymer (CFRP) is more common. CFRP can be effectively used for strengthening and confinement the deficient RC columns. This research conducts to evaluate the behavior of this fiber in improvement of aforementioned quantities. In this investigation, three categories of compressive strength of concrete were selected. The samples were warped with 0, 1, 3, and 5 layers of CFRP were subjected under stress-strain tests. The results display that carbon fiber is more effective in enhancing the compressive strength and ductility. Fiber performance is more effective on low-strength concretes, and its effective role decreases with increasing the number of layers. تفاصيل المقالة -
حرية الوصول المقاله
8 - Mechanical Properties of Low Strength Concrete Incorporating Carbon Nanotubes
Meysam Morsali Reza FarokhzadNowadays, due to the increasing population and the expansion of urbanization, and consequently the need for high-rise and multi-storey buildings that , the safety and resistance of the load bearing members of the structures has become of interest to researchers. For thi أکثرNowadays, due to the increasing population and the expansion of urbanization, and consequently the need for high-rise and multi-storey buildings that , the safety and resistance of the load bearing members of the structures has become of interest to researchers. For this purpose, different approaches have been proposed, including nanomaterials as a suitable and optimal method. Using nanomaterials as a percentage of cement weight improves concrete performance and increases its strength. Since these materials should be used at the beginning of concrete construction, therefore, they cannot be used in constructed structures. But a protective coating containing these nanomaterials can enhance and improve the performance of the structures, which is applicable to the fabricated structures. The purpose of this study was to investigate the effect of protective coatings with Nano silica, carbon nanotube and graphene nanomaterials. For this purpose, four thicknesses different and 2% nanomaterials different, the effect of thickness and percentage of nanomaterials were investigated. The results show that the sample containing 15% of silica with 26.74 N/mm2 has the highest effect compared to other nanomaterials. However, due to the low percentages of carbon nanotube and graphene, these materials have a significant effect. تفاصيل المقالة -
حرية الوصول المقاله
9 - Investigating properties of fresh and hardened self-compacting concrete made of recycled aggregates
Pouria Javadi Ali DelnavazSelf-compacting concrete is a new high performance concrete with high ductility and segregation resistance. In recent years, construction material manufacturers have focused their attention on lightweight concrete and have strived to use lightweight concrete, if possibl أکثرSelf-compacting concrete is a new high performance concrete with high ductility and segregation resistance. In recent years, construction material manufacturers have focused their attention on lightweight concrete and have strived to use lightweight concrete, if possible, in load-bearing parts of buildings. Concrete with both self-compacting and lightweight properties is favourable in this context which is the so-called lightweight self-consolidating concrete. Given the novelty of self-compacting concrete industry and increased amount of construction materials resulting from earthquake (due to seismic hazards of Iran) and destruction of different buildings, in particular urban decay, on the other hand, feasibility study on production of self-compacting concrete with these materials is justifiable in terms of costs, environment protection and energy conservation. Accordingly, coordination between self-compacting factor and utilising these materials is important. So, in this research, the effect of recycled aggregates on mechanical properties of lightweight self-compacting concrete was investigated. Specimens were analysed using 2 mix designs with different contents (cement) by Slump, J-Ring and compressive strength tests. Results indicated that mix designs containing waste LECA have good consistency and stability. Also, mix designs containing waste scoria have high strength. Hence, in order to achieve self-compacting and lightweight properties, it seems logical to use those two waste materials. تفاصيل المقالة -
حرية الوصول المقاله
10 - Mix Design Selection For Old and New Generation of SuprePlasticizers
Navid Afshari Seiyed Ali Haj Seiyed TaghiaDetermination the optimal mix design plays an important role in order to gain the maximum characteristic strength. This research was conducted as a case study for Manjil tunnel project located in Qazvin-Rasht highway. For this purpose, 18 concrete mix designs were prepa أکثرDetermination the optimal mix design plays an important role in order to gain the maximum characteristic strength. This research was conducted as a case study for Manjil tunnel project located in Qazvin-Rasht highway. For this purpose, 18 concrete mix designs were prepared at the study phase of the project with specifications such as conventional water-to-cement ratios of 0.4, 0.5 and 0.6, the use of two generations of new and old conventional superplasticizer in Iran (naphthalene sulphonate and polycarboxylate ether types, respectively) with cement weight percentages of 0.2, 0.4 and 0.6. Superplasticizers are used to increase the fluidity of concrete without adding excess water. The naphthalene sulphonate is a polymeric molecule formed by condensation of naphthalene sulfonic acid and formaldehyde, in which the hydrophilic groups are mainly sulfonic groups. It has been demonstrated that polycarboxylate ether can mitigate plastic shrinkage of matrix because of the reduction of the build-up rate of capillary pressure by polycarboxylate ether. Finally, the optimal water-to-cement ratio and superplasticizer weight percentage were determined. Concrete mix designs with different ages of curing were made (0, 3, 7, 14 and 28 days). تفاصيل المقالة -
حرية الوصول المقاله
11 - The Effect of Compressive Strength Reduction of Column Section Expose due to Freezing-Thawing Cycles on the Seismic Performance of Bridges
Saeideh Alsadat Mousavi Mehran Seyed RazzaghiOne of the serious damages of tremendous earthquakes is the damage to bridges as the major components in an arterial road network, as relief operation is interrupted following cutting roads. Regardless of the magnitude and severity of an earthquake, other factors are al أکثرOne of the serious damages of tremendous earthquakes is the damage to bridges as the major components in an arterial road network, as relief operation is interrupted following cutting roads. Regardless of the magnitude and severity of an earthquake, other factors are also important in the strength and seismic performance of concrete bridges. Freezing-thawing cycles are among the factors, which erode the piers of concrete bridges over time. Therefore, it is necessary to evaluate the seismic vulnerability of bridges for future designs.This research aims at discussing the effect of freeze-thaw cycles on the seismic performance of concrete bridges using fragilitycurves. Fragility curves express the conditional probability to reach or exceed a level of damage as a function of ground motion parameters. The curves have been developed analytically using a probabilistic method. Ground motion parameter, peak ground acceleration, structural criterion, and relative displacement of piles were considered. The non-linear time history analysis in OpenSees was used for demand determination. The curves were drawn for the slight, moderate, and extensive damage levels in two modes of before and after damage caused by thawing and freezing, i.e. the mode in which the compressive strength of column section expose reduced. With respect to the fragility curves, the strength reduction increases bridge vulnerability, especially on slight damage levels. Comparing with the cyclic curves of the most vulnerable column in two modes of before and after the damage showed that energy absorption capacity lowered with the expose compressive strength reducing. تفاصيل المقالة -
حرية الوصول المقاله
12 - Investigation of mechanical and durability properties of lightweight concrete containing Pumice
Amirmohammad Soleimani Seyed Amir Hossein HashemiIn this research, the effect of the cement, sand, and pumice mixture on the durability of lightweight concrete is investigated. The intention of this paper is to replace a certain amount of the pumice percentage as an alternative option of the cement and pumice sand agg أکثرIn this research, the effect of the cement, sand, and pumice mixture on the durability of lightweight concrete is investigated. The intention of this paper is to replace a certain amount of the pumice percentage as an alternative option of the cement and pumice sand aggregate with conventional sand components. The experimental results include compressive strength, ion-chloride emission factor (RCPT and RCMT). The experiments are carried out at the concrete age of 28 and 90 days. The results indicate that pumice composition improves the durability of lightweight concrete. Furthermore, it was observed that the proposed mixing design have proper permeability resistance against the chloride ion attack. For 90 days aged concrete, it was notified that the samples had a chlorine ion penetration coefficient of 10% which is less than the concrete specimens of 28 days. Finally, the compressive strength of the new mixing design samples can beincreased by 1.5 to 2.5 Mpa after 90 days. تفاصيل المقالة -
حرية الوصول المقاله
13 - The possible use of Sewage Sludge Ash (SSA) in Self-Consolidating Concrete (SCC) for environmental sustainability
Mohamadreza Khanban Mahdi MahdikhaniNowadays, waste production is increased due to the growth of technology and excessive use of natural resources as well as production of new chemicals, among which the hazardous wastes are no exception of that stabilization and solidification method is one of the hazardo أکثرNowadays, waste production is increased due to the growth of technology and excessive use of natural resources as well as production of new chemicals, among which the hazardous wastes are no exception of that stabilization and solidification method is one of the hazardous waste management methods through which the waste materials are stabilized and confined. High flexibility for various pollutant compounds, ease of use, and being economical for large volumes of waste has led researchers to use this method to treat various wastes. In this research, sludge ash from sewage treatment plantsuses as waste in order to perform the stabilization and solidification process. Nine mix designs with a water to cement ratio of 0.46; and 0, 6, and 10 percent dried sludge residue of the Alborz Industrial City in Qazvin as the replacement of fine aggregate; 0, 2, and 4 percent of silica fume; and cement content of 600 kg/m3are produced. The mini slump flow, mini V-funnel, compressive strength, electrical resistancetests were carried out on the solidified samples to investigate the effect of waste on the performance of the mortar.The results show that the use of this waste as a substitute for fine aggregate could be taken into consideration. تفاصيل المقالة -
حرية الوصول المقاله
14 - A Study on the Quasi-static Compression Behavior of 5056 Aluminum Alloy Foams
Sadegh Soltani Hamed Deilami Azodi Seyed Hossein ElahiIn this paper, 5056 aluminum alloy foams with different percentages of calcium carbonate as foaming agents have been produced, and the physical and mechanical properties of the foams have been studied. Quasi-static compression tests have been carried out to determine th أکثرIn this paper, 5056 aluminum alloy foams with different percentages of calcium carbonate as foaming agents have been produced, and the physical and mechanical properties of the foams have been studied. Quasi-static compression tests have been carried out to determine the mechanical properties of foamed material. The effects of the amount of calcium carbonate on the size of the pores, the minimum thickness of the walls, density, compressive strength and energy absorption capacity of foams have been investigated. The uniform structure of the pores has been observed in foam specimens with 1.5, 1.8 and 2.1 wt% CaCO3. Increasing the amount of CaCO3 foaming agent from 1.5% to 2.1% has increased the average size of the pores by more than 180% and reduced the thickness of cell walls by 90%. So, the density and the relative density of the aluminum foams have been reduced by 28.6%. The results also show that increasing the amount of CaCO3 foaming agent decreases compressive strength, the absorbed energy and the elastic modulus of 5056 aluminum foams. By increasing the amount of foaming agent from 1.5% to 2.1%, the elastic modulus has reduced by about 16%, and a decrease of 21% has been seen in the energy absorbed by the foam at the strain of 0.4. تفاصيل المقالة -
حرية الوصول المقاله
15 - Effect of temperature and activator molar of Na2O to SiO2 in the process of synthesis and microstructure of cement geopolymer
M Asadi A Nemati R Naghizadeh K Arzani J FahimInorganic polymers were synthesized from dehydroxylated aluminosilicate clay (metakaolinite) condensed with sodium silicate in a highly alkaline environment. The thermal treatment of aluminosilicate materials causes changes in their structure with an increase in the amo أکثرInorganic polymers were synthesized from dehydroxylated aluminosilicate clay (metakaolinite) condensed with sodium silicate in a highly alkaline environment. The thermal treatment of aluminosilicate materials causes changes in their structure with an increase in the amorphous phase. For that kind of structural change XRD analysis is not appropriate, so those changes are currently assessed by infrared emission spectra analysis (FTIR). The most characteristic FTIR band in the geopolymeric systems appears in the wavenumbers region 990-1090cm-1 and is attributed to the asymmetric stretching vibration of T-O-Si, where T denotes Si or Al. The shift of this peak towards lower wavenumbers indicates the dissolution of the amorphous aluminosilicate phase of the raw material and the formation of a new amorphous gel in which the backbone consists of polymeric chains with smaller length in relation to the ones of the raw material. The SEM result showed that geopolymer paste was formed from quartz remaining particles and gel. The remaining particle size was reduced by increase of the curing temperature and Na2O/SiO2 molar ratio. The results indicated that samples with adequate strength are created compact and crack-free areas. تفاصيل المقالة -
حرية الوصول المقاله
16 - Prefabricated Concrete Elements for the facade Industry with Nano cement composites containing silica fume, nano-silica and TiO2
Raheleh Rostami Sayedeh Fatemeh Khoshkalam Soleimandarabi Mehdi NezhadnaderiUsing mineral admixtures in cement composites as a way to improve their mechanical and durability properties is a common practice in concrete technology. Among them silica fume and nano-silica effectively influence the composite's early and long-term properties. Due to أکثرUsing mineral admixtures in cement composites as a way to improve their mechanical and durability properties is a common practice in concrete technology. Among them silica fume and nano-silica effectively influence the composite's early and long-term properties. Due to the limited particle size distribution of nano and micro silica it is expected that the incorporation of some mineral additives with a size of greater than 500 nm may result in better mechanical and durability performance because of the filler effect. In this study, the effect of different percentages of TiO2 on mechanical properties of cement composites containing nano-silica and silica fume was investigated. Six designs were tested for compressive strength with respect to zero, 2.5 and 5 percent replacement of cement with TiO2. The addition of TiO2 has led to an increase in compressive strength. The best results from the sample with 2.5% TiO2 are obtained. This could be due to the effect of TiO2 particles filling. Comparison of SF3, SF2 and SF1 at 28 days of age showed that SF2 increased the compressive strength. This shows that TiO2 has a great potential for improving the mechanical properties of composite cement.The results showed that the addition of TiO2 had a positive effect on compressive strength. تفاصيل المقالة -
حرية الوصول المقاله
17 - Prefabricated Concrete Elements for the facade Industry with Nano cement composites containing silica fume, nano-silica, and TiO2
Sayedeh Fatemeh Khoshkalam Soleimandarabi Raheleh Rostami Mehdi NezhadnaderiUsing mineral admixtures in cement composites as a way to improve their mechanical and durability properties is a common practice in concrete technology. Among them, silica fume and nano-silica effectively influence the composite's early and long-term properties. Due to أکثرUsing mineral admixtures in cement composites as a way to improve their mechanical and durability properties is a common practice in concrete technology. Among them, silica fume and nano-silica effectively influence the composite's early and long-term properties. Due to the limited particle size distribution of nano and micro-silica, it is expected that the incorporation of some mineraladditives with a size greater than 500 nm may result in better mechanical and durability performance because of the filler effect. In this study, the effect of different percentages of TiO2 on the mechanical properties of cement composites containing nano-silica and silica fume was investigated. Six designs were tested for compressive strength with respect to zero, 2.5, and 5 percent replacementof cement with TiO2. The addition of TiO2 has led to an increase in compressive strength. The best results from the sample with 2.5% TiO2 are obtained. This could be due to the effect of TiO2 particles filling. Comparison of SF3, SF2, and SF1 at 28 days of age showed that SF2 increased the compressive strength. This shows that TiO2 has a great potential for improving the mechanical properties ofcomposite cement. The results showed that the addition of TiO2 had a positive effect on compressive strength. Increasing TiO2 nanoparticles content of more than 3 wt% is caused to reduce the compressive strength according to past studies. But in this study is shown that by adding 3% nanocillis or 20% silicified to increased TiO2 nanoparticles content of more than 3% wt, the results ofcompressive strength are not reduced. The use of 3% combined nano-silica or 20% silicafium will cover this defect of increased TiO2 nanoparticles content ofmore than 3% wt. تفاصيل المقالة -
حرية الوصول المقاله
18 - Mechanical Properties of Concrete Containing Tire Rubber Particles toward Constant Development
Hasan Sousani Amir MahmoudzadehWith many years of construction and application of common concrete, researchers have always been searching for a better composition. One of the notable ideas for achieving such a composition is using recycled materials. One of the materials which is suitable for environ أکثرWith many years of construction and application of common concrete, researchers have always been searching for a better composition. One of the notable ideas for achieving such a composition is using recycled materials. One of the materials which is suitable for environment and constant development is damaged tires .For studying mechanical properties of concrete containing tire particles, a series of experimental studies undertaken. In this study, a mix design with 28-day compressive strength of 40 MPa was considered. Then by replacing 10 percent (by weight) of sand with tire particles (without changing other parameters), the required test was done for determination of compressive and tensile strength of concrete samples. By application of microsilica, its effect on mechanical properties of concrete samples were studied. The obtained results from tests are demonstrated by graphs and tables. By considering the environment in this research ,it has been dealt with mechanical properties of concrete containing rubber particeles toward constant development. تفاصيل المقالة -
حرية الوصول المقاله
19 - بررسی پارامترهای موثر برمقاومت فشاری، مقاومت الکتریکی ویژه و جذب آب بتن متخلخل سبک
شهریار غلامین نوویرسر مرتضی جمشیدی رحمت مدندوستبتن متخلخل نوعی ویژه از بتن سبک با اسلامپ کم یا حتی صفر شناخته میشود که از سیمان، درشت دانه، درصد محدودی از ریز دانه (یا فاقد ریزدانه)، افزودنی‌های مختلف شیمیایی و پوزولانی تشکیل شده است. دراین مقاله از لیکای سازه‌ای با وزن‌حجمی m3kg/ 750 و نسبت آب به سیمان ثا أکثربتن متخلخل نوعی ویژه از بتن سبک با اسلامپ کم یا حتی صفر شناخته میشود که از سیمان، درشت دانه، درصد محدودی از ریز دانه (یا فاقد ریزدانه)، افزودنی‌های مختلف شیمیایی و پوزولانی تشکیل شده است. دراین مقاله از لیکای سازه‌ای با وزن‌حجمی m3kg/ 750 و نسبت آب به سیمان ثابت (3/0W / C =) ، برای ساخت بتن متخلخل سبک استفاده شد و اثر نسبتها‌ی مختلف سبکدانه به سیمان ( A/C ) شامل 3 ، 7/2 ، 4/2 ، 1/2 ، 8/1 ، 5/1 ، تخلخل کل و درصدحجمی خمیر سیمان بر روی مقاومت فشاری ، مقاومت الکتریکی ویژه و درصد جذب آب بتن متخلخل سبک درسن 28 روز مورد بررسی قرار گرفت. با افزایش نسبت A/C از 5/1 تا 3، حجم خمیر سیمان از 873/30 % به 436/15 % در نمونه‌ها کاهش و تخلخل کل از64/21 % به 08/38 % افزایش یافت که منجر به کاهش مقاومت الکتریکی ویژه از 45/11 به 841/6 ، کاهش مقاومت فشاری از Mpa 27/13 به MPa 37/4 و افزایش جذب آب از 185/11 % به 695/12 % در نمونه های بتن متخلخل سبک شد. نتایج این پژوهش بهبود ویژگیهای فیزیکی و افت ویژگیهای مکانیکی و دوام بتن متخلخل سبک حاوی لیکا را نشان دادند. تفاصيل المقالة -
حرية الوصول المقاله
20 - بررسی خواص مکانیکی بتن خاک اره‌ای
علی فروغی اصل سحر نوظهوربتن به‌عنوان پرمصرف‌ترین مصالح در احداث سازه‌های بتنی مختلف از اهمیت ویژه‌ای برخوردار است و با توجه به مقاوم‌سازی سازه‌ها در مقابل نیروهای جانبی مختلف جهت کاهش صدمات انسانی و اقتصادی، سبک‌سازی و تاثیر آن در رفتار بهینه سازه‌ها همواره مورد توجه بوده‌است و بتن‌های با چگال أکثربتن به‌عنوان پرمصرف‌ترین مصالح در احداث سازه‌های بتنی مختلف از اهمیت ویژه‌ای برخوردار است و با توجه به مقاوم‌سازی سازه‌ها در مقابل نیروهای جانبی مختلف جهت کاهش صدمات انسانی و اقتصادی، سبک‌سازی و تاثیر آن در رفتار بهینه سازه‌ها همواره مورد توجه بوده‌است و بتن‌های با چگالی کمتر می‌تواند به ساخت سازه‌های سبک‌تر منجر شود بطوری که استفاده از بتن‌های با وزن مخصوص کمتر از 1900کیلوگرم بر متر مکعب و مقاومت فشاری بیش از 17 مگاپاسکال در سازه‌های بتن مسلح، همواره مورد توجه بسیاری ازمهندسین طراح بوده‌است. یکی از روش‌های کاهش چگالی بتن استفاده از خاک اره در طرح اختلاط بتن‌هاست که نه تنها دارای مزایای اقتصادی است بلکه نقش چشمگیری در حفظ محیط‌زیست در مصرف مجدد ضایعات کارخانجات چوب‌بری دارد. در این پژوهش از خاک اره به‌عنوان جایگزین بخشی از ماسه بتن به میزان صفر (بتن بدون خاک اره به عنوان نمونه شاهد) ، 15%، 25 % و 35% استفاده شده است. نمونه‌های بتنی برای آزمایش مقاومت فشاری به ابعاد100×100×100 میلیمتر و برای آزمایش مقاومت کششی به ابعاد 200×100 میلیمتر تهیه و پس از عمل‌آوری‌های 7، 14 و 28 روزه تحت آزمایش‌های تعیین مقاومت فشاری، مقاومت کششی و چگالی قرار گرفتند. نتایج نشان می‌دهد که خاک اره 25% جایگزین ماسه با مقاومت فشاری 190 کیلو گرم بر سانتیمتر مربع و چگالی 1904کیلوگرم بر متر مکعب انتخاب بهینه‌ای است. تفاصيل المقالة -
حرية الوصول المقاله
21 - بررسی آثار حرارت بالا بر مقاومت فشاری، کششی و مدول‌الاستیسیته بتن قلیافعال
محمدحسین منصورقناعیدر سال های اخیر، بهبود خواص مکانیکی در بتن قلیافعال با هدف برتری نسبت به خواص مکانیکی بتن معمولی و کاهش مخاطرات زیست محیطی ناشی از کمبود منابع معدنی و انتشار گاز سمی دی اکسیدکربن در هوا (در راستای تولید سیمان)، مورد توجه محققین حوزه عمران قرار گرفت. در این پژوهش آزمایشگ أکثردر سال های اخیر، بهبود خواص مکانیکی در بتن قلیافعال با هدف برتری نسبت به خواص مکانیکی بتن معمولی و کاهش مخاطرات زیست محیطی ناشی از کمبود منابع معدنی و انتشار گاز سمی دی اکسیدکربن در هوا (در راستای تولید سیمان)، مورد توجه محققین حوزه عمران قرار گرفت. در این پژوهش آزمایشگاهی، یک طرح اختلاط از بتن معمولی حاوی سیمان پرتلند با عیار 500 کیلوگرم بر متر مکعب و یک طرح اختلاط از بتن قلیافعال بر پایه سرباره کوره آهنگدازی ساخته شد. به منظور بررسی خواص مکانیکی، آزمون های مقاومت فشاری، مقاومت کششی و مدول الاستیسیته بتن تحت دمای 21 و 600 درجه سلسیوس در سن عمل آوری 90 روزه انجام شد. در بخش نتایج، اعمال حرارت بالا (600 درجه سلسیوس) به نمونه های بتنی موجب افت 42 و 15 درصدی در مقاومت فشاری، افت 56 و 21 درصدی در مقاومت کششی و افت 63 و 49 درصدی در مدول الاستیسیته به ترتیب برای بتن معمولی و بتن قلیافعال گردید. مقاومت فشاری بتن قلیافعال نسبت به بتن معمولی در دمای 21 و 600 درجه سلسیوس به ترتیب 11 و 64 درصد برتری را نشان داد. مقاومت کششی بتن قلیافعال نسبت به بتن معمولی در دمای 21 و 600 درجه سلسیوس به ترتیب 9 درصد کاهش و 63 درصد برتری را نشان داد. مدول الاستیسیته بتن قلیافعال نسبت به بتن معمولی در دمای 21 و 600 درجه سلسیوس به ترتیب 16 و 62 درصد برتری را کسب کرد. نتایج حاصل از آزمون تصاویر میکروسکوپ الکترونی روبشی در هماهنگی و همپوشانی با سایر نتایج آزمون های این پژوهش قرار دارد. تفاصيل المقالة -
حرية الوصول المقاله
22 - بررسی خواص مکانیکی و تأثیرات سنگدانه‌های متداول در ساخت بتن متخلخل
مجید رستمی ایمان بهرامی چگنیبتن متخلخل، نوع خاصی از بتن با تخلخل بالا است که یکی از عمده‌ترین کاربردهای آن، استفاده در رویه‌ها می‌باشد. با توجه به اهمیت حمل و نقل در جهان امروز و استفاده از مصالح نوین در زیر ساخت‌های حمل و نقل جاده‌ای، دریایی، هوایی و ریلی، تحقیق در این زمینه مورد توجه قرار گرفته أکثربتن متخلخل، نوع خاصی از بتن با تخلخل بالا است که یکی از عمده‌ترین کاربردهای آن، استفاده در رویه‌ها می‌باشد. با توجه به اهمیت حمل و نقل در جهان امروز و استفاده از مصالح نوین در زیر ساخت‌های حمل و نقل جاده‌ای، دریایی، هوایی و ریلی، تحقیق در این زمینه مورد توجه قرار گرفته است. بتن متخلخل یکی از انواع روسازی‌های صلب می‌باشد، که مزایای فراوانی از قبیل نفوذپذیری بالا، هدایت هیدرولیکی مناسب، فیلتراسیون آب‌های سطحی و تزریق به سفره های آب زیرزمینی و... را دارا می باشد. اما با وجود مزیت‌های فراوان مقاومت فشاری پایین این نوع بتن یکی از معایب آن است، که این خود لزوم تحقیقات بیشتر در راستای بالا بردن مقاومت فشاری این نوع بتن‌ها را نشان می دهد. در تحقیق حاضر با انجام یک سری مطالعات آزمایشگاهی بر روی چند نمونه سنگدانه متداول با جنس و دانه بندی‌های مختلف، در گام نخست خواص فیزیکی و ظاهری آنها بررسی شده، و پس از تهیه طرح اختلاط‌های مختلف در ساخت نمونه های بتن متخلخل، خواص بتن‌های به دست آمده از جمله نفوذپذیری، تخلخل و مقاومت فشاری بررسی می شود و در ادامه پس از انجام آزمایش‌روی نمونه‌های مختلف، به بررسی و تحلیل نتایج پرداخته می شود. در نهایت براساس نتایج و تحلیل‌های بدست آمده از انجام آزمایشات، طرح اختلاط‌های بهینه بسته به نوع کاربرد آنها معرفی شده است. تفاصيل المقالة -
حرية الوصول المقاله
23 - بررسی خواص بتن ساخته‌شده با نخاله‌های بتنی وتاثیر اختلاط چند مرحله ای در آن
محمد خزایی عبدالکریم عباسی دزفولیاستفاده از مواد جانبی ساخت و تولید از موارد تقریبا جدید در ساخت بتن در تکنولوژی عالی بتن است. ّبتن حاصل از تستهای آزمایشگاهی را میتوان با خرد کردن و دانه بندی مناسب آنها در ساخت بتن تازه استفاده کرد. تحقیقات اخیر نشان دهنده آن است که استفاده از بتن خرد شده جایگزین قسمتی أکثراستفاده از مواد جانبی ساخت و تولید از موارد تقریبا جدید در ساخت بتن در تکنولوژی عالی بتن است. ّبتن حاصل از تستهای آزمایشگاهی را میتوان با خرد کردن و دانه بندی مناسب آنها در ساخت بتن تازه استفاده کرد. تحقیقات اخیر نشان دهنده آن است که استفاده از بتن خرد شده جایگزین قسمتی از سنگدانه منجر به کاهش مقاومت فشاری در بتن با روش معمول مخلوط کردن بتن میشود. در این تحقیق به روش خاص سه مرحله ایی طرح اختلاط و اثر آن بر پارامترهای مقاومتی پرداخته شده است. نمونه های بتنی مکعب 15 سانتیمتر شامل 0% ، 25% و 50% نخاله بتنی جایگذین قسمتی از سنگدانه استفاده شد. از فوق روان کننده بر اساس کربوکسیلات در طرحها استفاده شد. این طریق اختلاط باعث کارایی مناسب، پوشش مناسب روی سنگدانه و حفاظت از واکنش قلیایی سنگدانه می شود. روش اختلاط مواد که بایستی به ترتیب و پشت سر هم در سه مرحله انجام شد: درمرحله اول: کل شن + 50% آب + 50% سیمان: زمان اختلاط 30 ثانیه تا 1 دقیفه. مرحله 2: اضافه کردن 50% سیمان + 25% آب + فوق روان کننده + ماسه: زمان اختلاط 2 دقیقه. مرحله 3 اضافه کردن 25% آب: زمان اختلاط 3 دقیقه. کل زمان اختلاط حدود 6 دقیقه باید باشد. برای هر طرح 6 نمونه آماده گردید و در 7 روز و 28 روز تست های وزن مخصوص، جذب آب، مقاومت الکتریکی که (نشان دهنده نفوذ پذیری و دوام بتن است) و مقاومت فشاری انجام پذیرفت. نتایج نشانگر مقاومت فشاری و الکتریکی بالا در طرح 25% نسبت به سایر موارد بود. با توجه به مقاومت مناسب بدست آمده میتوان گفت با روش خاص اختلاط میتوان از نخاله های بتنی در ترکیب بتن با صرفه از نظر محیطی و مقاومتی استفاده کرد. تفاصيل المقالة -
حرية الوصول المقاله
24 - بررسی مقایسه ای رفتار مکانیکی بتن مسلح شده با الیاف فلزی صنعتی و براده‌ای بازیافتی
فرهاد جیره ضیاءالدین زمان زاده لیلا جلیلیدر سالهای اخیر اغلب تحقیقات آزمایشگاهی صورت گرفته در مورد رفتار مکانیکی بتن مسلح شده با الیاف فولادی بازیافتی و صنعتی در کشورهای خارجی بوده و لازم است مطالعه هایی در مورد بتن الیافی ساخته شده از مصالح موجود کشور انجام گیرد. در این مقاله تحقیق آزمایشگاهی و عددی در مورد ر أکثردر سالهای اخیر اغلب تحقیقات آزمایشگاهی صورت گرفته در مورد رفتار مکانیکی بتن مسلح شده با الیاف فولادی بازیافتی و صنعتی در کشورهای خارجی بوده و لازم است مطالعه هایی در مورد بتن الیافی ساخته شده از مصالح موجود کشور انجام گیرد. در این مقاله تحقیق آزمایشگاهی و عددی در مورد رفتار مکانیکی بتن الیافی انجام گرفته است. در قسمت آزمایشگاهی ابتدا با الگو برداری از طرح اختلاط ارائه شده در تحقیقات پیشین برای بتن الیافی بازیافتی دو طرح اختلاط متناسب با مصالح موجود کشور تعیین گردید به طوری که با افزودن دو مقدار متفاوت الیاف فولادی، اسلامپ روانی مطلوب را به ما بدهد. اثر الیاف صنعتی و براده‌ای بر روی رفتار فشاری و کششی بتن الیافی با انجام تستهای فشاری و کشش غیر مستقیم بررسی شد. افزودن الیاف صنعتی و براده ای باعث کاهش ناچیز مقاومت فشاری و کششی غیر مستقیم گردیده است. در شبیه سازی و مدلسازی اجزای محدود تستهای فشاری تشکیل ترک ها در المانهای بتنی اطراف عناصر فولادی، وقوع گرادیان تنش در این المانهای بتنی را تایید کرد که منجر به کاهش مقاومت فشاری بتن می شود. تفاصيل المقالة -
حرية الوصول المقاله
25 - ارزیابی رفتار مقاومت فشاری بتن سبک سازه‌ای متشکل از پرلیت، لیکا، الیاف فلزی و میکروسیلیس
حسین شاددل میلاد خیری قوجه بیگلو عبدالله عنایتی تکلهبا توجه به این که وزن سازه باعث افزایش نیروهای وارده به خصوص نیروهای جانبی مثل زلزله می‌باشد، پس به این دلیل هر قدر بتوانیم در مسیر سبک سازی ساختمان گام برداریم همان قدر توانسته‌ایم در برابر نیروی زلزله وارد بر سازه مقاوم باشیم. از آنجا که یکی از روش‌های تولید بتن سبک ا أکثربا توجه به این که وزن سازه باعث افزایش نیروهای وارده به خصوص نیروهای جانبی مثل زلزله می‌باشد، پس به این دلیل هر قدر بتوانیم در مسیر سبک سازی ساختمان گام برداریم همان قدر توانسته‌ایم در برابر نیروی زلزله وارد بر سازه مقاوم باشیم. از آنجا که یکی از روش‌های تولید بتن سبک استفاده از دانه‌های سبک می‌باشد و با توجه به نقش این دانه‌ها در مقاومت بتن، ارائه طرح اختلاط بهینه برای بتن‌های سبکدانه اهمیت دارد. نتایج حاصل از آزمایش‌ها بر روی 140 نمونه، نشان از دست‌یابی به بتن سبک سازه‌ای طبق استانداردASTM C330 که حداکثر وزن مخصوص بتن سبک سازه‌ای را بهkg/m3 1850 و حداقل مقاومت فشاری بتن سبک سازه‌ای را بهkg/cm3 170 محدود می‌کند نشان می‌دهد. میتوان با استفاده از پوزولان‌های با ذرات ریزتر و با تغییر در طرح اختلاط، وزن مخصوص و مقاومت فشاری نمونه‌ها را به طور صددرصد به حد تعریف شده طبق استانداردASTM C330 رساند. تفاصيل المقالة -
حرية الوصول المقاله
26 - بررسی آزمایشگاهی مقاومت فشاری بتن ژئوپلیمری براساس آزمون XRF و SEM
محمدحسین منصورقناعی مرتضی بیک لریان علیرضا مردوخ پوردر این مقاله، 3 طرح اختلاط از بتن ژئوپلیمری حاوی 92، 96 و 100 درصد سرباره کوره آهنگدازی، به ترتیب شامل 8، 4 و 0 درصد نانوسیلیس ساخته شد. پس از انجام آزمون مقاومت فشاری و انتخاب یک طرح از این سه طرح، بعنوان طرح بهینه به لحاظ برتری خواص مکانیکی، با افزودن 1 و 2 درصد الیاف أکثردر این مقاله، 3 طرح اختلاط از بتن ژئوپلیمری حاوی 92، 96 و 100 درصد سرباره کوره آهنگدازی، به ترتیب شامل 8، 4 و 0 درصد نانوسیلیس ساخته شد. پس از انجام آزمون مقاومت فشاری و انتخاب یک طرح از این سه طرح، بعنوان طرح بهینه به لحاظ برتری خواص مکانیکی، با افزودن 1 و 2 درصد الیاف پلی الفین به طرح بهینه، دو طرح دیگر از بتن ژئوپلیمری ساخته شد. نمونه های بتنی تحت آزمون های مقاومت فشاری در 7، 28 و90 روز عمل آوری، XRF در 7 روز عمل آوری و SEM در90 روز عمل آوری، قرار گرفتند. نتایج حاصله ضمن ارزیابی با یکدیگر، با نتایج حاصل از یک طرح اختلاط ساخته شده از بتن معمولی حاوی سیمان پرتلند، مورد مقایسه قرار گرفتند. نتایج حاصل از آزمون های این پژوهش نشان از برتری در خواص مکانیکی و ریزساختاری بتن ژئوپلیمری نسبت به بتن معمولی در تمام سنین عمل آوری داشت. در سن عمل آوری90 روزه بعنوان بهترین سن به لحاظ عملکرد، کمترین 4/62 مگاپاسکال و بیشترین 9/82 مگاپاسکال مقدار مقاومت فشاری به ترتیب در طرح 1 و 4 بدست آمد. در این سن، افزودن تا 8 درصد نانوسیلیس در بتن ژئوپلیمری موجب بهبود مقاومت فشاری تا میزان 9/21 درصد و افزودن تا 2 درصد الیاف موجب افت مقاومت فشاری تا میزان 5/22 درصد در این نوع از بتن گردید. نتایج حاصل از آزمون های XRF و SEM ضمن همپوشانی با یکدیگر، در هماهنگی با نتایج حاصل از آزمون مقاومت فشاری قرار داشتند. تفاصيل المقالة -
حرية الوصول المقاله
27 - تحلیل آماری تأثیر اتصال سرد بر مقاومت فشاری بتن ساخته شده به روش ملی طرح مخلوط بتن
آرش رفیعی احسان کریمیاز جمله مشکلات رایج در اجرای سازه های بتنی بروز درز یا اتصال سرد می‌باشد. ناپیوستگی به وجود آمده در جسم بتن درنتیجه اتصال سرد می‌تواند باعث ضعف سازه ای، افزایش نفوذ پذیری، کاهش دوام، خوردگی میلگردها و نمای بد در بتن شود. در تحقیق حاضر، به‌منظور بررسی تأثیر اتصال سرد بر أکثراز جمله مشکلات رایج در اجرای سازه های بتنی بروز درز یا اتصال سرد می‌باشد. ناپیوستگی به وجود آمده در جسم بتن درنتیجه اتصال سرد می‌تواند باعث ضعف سازه ای، افزایش نفوذ پذیری، کاهش دوام، خوردگی میلگردها و نمای بد در بتن شود. در تحقیق حاضر، به‌منظور بررسی تأثیر اتصال سرد بر روی مقاومت فشاری بتن، ۱۹۲ عدد نمونه مکعبی به روش طرح اختلاط ملی در ۴ حالت، به‌نحوی که ۴۸ عدد نمونه بدون اتصال سرد، ۴۸ عدد نمونه با اتصال سرد به صورت افقی، ۴۸ عدد نمونه بااتصال سرد به صورت عمودی و ۴۸ عدد نمونه بااتصال سرد به صورت مورب در بازه ی زمانی ۲۴ ساعته بتن ریزی شده و پس از طی ۲۸ روز عمل‌آوری با شرایط استاندارد با دستگاه جک فشاری، مقاومت فشاری نمونه ها مورد ارزیابی قرارگرفته است. پس از ارزیابی های به‌عمل‌آمده بر روی نتایج حاصل از آزمایش‌ها، مقادیر تأثیر اتصال سرد بر روی مقاومت فشاری نمونه ها، عدم قطعیت و احتمال شکست نمونه ها مورد بررسی قرارگرفته است. نتایج تحلیل ها حاکی از آن است که به‌طور کلی ایجاد اتصال سرد در بتن باعث کاهش مقاومت فشاری بتن می گردد؛ اما میزان کاهش مقاومت فشاری در اثر ایجاد اتصال سرد به زاویه آن بستگی دارد. همچنین اندازه زاویه سطح اتصال سرد بر روی میزان احتمال شکست آن نیز تأثیر دارد. تفاصيل المقالة -
حرية الوصول المقاله
28 - بررسی آزمایشگاهی مشخصات مهندسی بتن حاوی پوزولان معدنی محلی براساس آزمونXRD و SEM
مجتبی رنگرزیان رحمت مدندوست رضا محجوب مهدی رفتاریگرمایش کره زمین و تاثیرات ناشی از آن در محیط زیست، از بحرانهای پیش روی انسان است. یافتن راهی جهت کاهش عوامل تشدید کننده این گرمایش، در مدیریت و کنترل این بحران تاثیرگذار می‌باشد. از مهم‌ترین عوامل افزایش درجه حرارت اتمسفر، گازهای گلخانه‌ای هستند. کارخانجات تولید سیمان ب أکثرگرمایش کره زمین و تاثیرات ناشی از آن در محیط زیست، از بحرانهای پیش روی انسان است. یافتن راهی جهت کاهش عوامل تشدید کننده این گرمایش، در مدیریت و کنترل این بحران تاثیرگذار می‌باشد. از مهم‌ترین عوامل افزایش درجه حرارت اتمسفر، گازهای گلخانه‌ای هستند. کارخانجات تولید سیمان با انتشار مقادیر عمده CO2 نقش ویژه ای در افزودن این گاز در جوّ دارند. یافتن راهی جهت کاهش مصرف سیمان، می تواند گامی موثر در کنترل افزایش سالیانه دمای کره زمین باشد. دراین مطالعه بمنظور یافتن طرح بهینه جایگزینی پوزولان معدنی محلّی با بخشی از سیمان، دو طرح اختلاط با چهار گونه 5، 10، 15 و 20 درصد وزنی جایگزین بخشی از سیمان بتن گردید و آزمونهای مقاومت فشاری وکیفیت بتن درآنها مورد ارزیابی قرارگرفت. عناصر تشکیل دهنده بتن و تاثیر افزودن پوزولان معدنی محلی، توسط آزمون XRD و همچنین ریخت شناسی و رفتار ریزساختاری بتن توسط آزمایشSEM بررسی شد. نتایج نشان داد که بهترین میزان جایگزینی این پوزولان به سیمان دربتن، معادل 15درصد وزنی سیمان است و باعث افزایش 24 درصدی مقاومت فشاری نسبت به بتن سیمانی معمولی میشود. واکنش پوزولانی مطلوب باعث کاهش میزان Ca(OH)2 و CaCO3 در بتن شد. همچنین این پوزولان باعث کاهش منافذ، افزایش بهبود و یکپارچگی ناحیه انتقال سطحی (ITZ) در بتن در مقایسه با بتن سیمانی معمولی گردید. با توجه به اثرات این پوزولان در تقویت ساختار و کاهش مصرف سیمان در بتن، پوزولان معدنی محلی مورد مطالعه را میتوان به عنوان ماده‌ی کاهنده سیمان با افزایش مقاومت در بتن و دوستدار محیط‌زیست معرفی کرد. تفاصيل المقالة -
حرية الوصول المقاله
29 - Application of Artificial Neural Networks (ANN) to Predict Geomechanical Properties of Asmari Limestones
Mahdi Razifard Mashallah Khamechiyan Mohammad Reza Amin‐NaseriA number of common laboratory rock mechanics tests are carried out in all geotechnical projects such as dams, to determine parameters such as porosity, density, water absorption, sonic velocity, Brazilian tensile strength, uniaxial compressive strength, and triaxial com أکثرA number of common laboratory rock mechanics tests are carried out in all geotechnical projects such as dams, to determine parameters such as porosity, density, water absorption, sonic velocity, Brazilian tensile strength, uniaxial compressive strength, and triaxial compressive strength. In this paper, data obtained from two dams in Asmari Formation including Khersan 1 and Karun 4 - both located in Chahar-Mahal Va Bakhtiari Province, Iran - have been subjected to a series of statistical analyses. Then, using Multivariate Linear Regression (MLR) and Artificial Neural Networks values of UCS, E, C, and φ were predicted using the input parameters including depth, compression ultrasonic velocity, porosity, density, and Brazilian tensile strength. The designed ANN in this research was a feedforward backpropagation network which is powerful tool to solve prediction problems. Designed network had two hidden layer (hidden layer 1: 18 neurons and hidden layer 2: 20 neurons). Via comparing designed MLR and ANN models, it was revealed that ANNs (R2 UCS= 0.91, R2 = 0.87, R2 =0.78, R2 EC phi = 0.61) are more efficient than MLR models (R2 UCS= 0.69, R = 0.69, R = 0.66, and R2 22 EC phi = 0.50) in predicting strength and shear parameters of the intact rock. Also, to enhance the credibility of this study, some extra tests were carried out to evaluate the efficiency of network designed for prediction of strength parameters. The results obtained from this network were as: R2 UCS= 0.85, R2E = 0.81. تفاصيل المقالة -
حرية الوصول المقاله
30 - Effect of using nano-silicates in concrete strength properties (A laboratory study)
Hassan Heydari MofradThe presented study attempted to investigate mechanical properties of concrete containing nanosilicates based on experimental uniaxial compressive strength test (UCS). For this purpose, different nanosilica dosages including 0%, 2%, 4% and 6% with considering the cement أکثرThe presented study attempted to investigate mechanical properties of concrete containing nanosilicates based on experimental uniaxial compressive strength test (UCS). For this purpose, different nanosilica dosages including 0%, 2%, 4% and 6% with considering the cement/water ratio are used to preparing the totally 10 mixing scheme and 30 concrete laboratory samples (10×10×10 cm cubic specimens) which is tested under 7, 28 and 90 days age. According to the experimental results by increasing the amount of nanosilica in the samples, UCS is increased and mechanical properties of concrete improved under loading. But in 6% nanosilica specimens incremental slope is get smooth then 4% nanosilica specimens. This was also observed for the 28-day and 90-day samples. In the meantime, some samples containing 6% nanosilica under uniaxial pressure experienced a resistance drop in strength features, indicating a decreasing trend of durability improvement at values above 6% nanosilica. تفاصيل المقالة -
حرية الوصول المقاله
31 - Estimating of uniaxial compressive strength by using point load index for travertine rock of Mahallat
Saied Dehghan Ghasem SattariThe uniaxial compressive strength (UCS) is one of the most important parameters that is needed and determined for studying rock mechanics of intact rock in most rock engineering projects. In spite of simple appearance of this test, the careful performance is very diffic أکثرThe uniaxial compressive strength (UCS) is one of the most important parameters that is needed and determined for studying rock mechanics of intact rock in most rock engineering projects. In spite of simple appearance of this test, the careful performance is very difficult. Therefore, scientists have made many attempts for indirect estimation of this parameter using simple tests (such as point load index (Is)) and they generated some relations between these parameters. This paper presents the new relationship between UCS and Is by using laboratory tests on Travertine samples of Mahallat. To determine the relations between parameters, the mathematical modeling has been used. Statistical analyses show that the nonlinear equation has a higher correlation coefficient than the linear; also, by estimating another effective parameter, porosity, and by adding it to the last equation, the correlation coefficient between actual and predicted data was improved in multiple non-linear equations. The comparison between actual and predicted results has proved acceptably accurate. تفاصيل المقالة -
حرية الوصول المقاله
32 - Experimental Investigation of Strength and Water Absorption of Concrete Containing Desert Sand
Amir Hamzeh Keykha Jalal NajmaddiniThe purpose of this study is to investigate the effect of desert sand as a replacement on the tensile and compressive strength of concrete. To this end, a total of 180 cubic specimens (15×15×15 cm) and 90cylindricalspecimens (15×30 cm) were made with t أکثرThe purpose of this study is to investigate the effect of desert sand as a replacement on the tensile and compressive strength of concrete. To this end, a total of 180 cubic specimens (15×15×15 cm) and 90cylindricalspecimens (15×30 cm) were made with three concrete classes of C20, C25, and C30. Control samples (samples without desert sand) and samples containing 5%, 10%, 15%, and 25% sand were also produced. They were processed in mineral-free water at 7, 14, 21, and 28 days. They were then subjected to pressure and tension tests by a 200-ton digital concrete breaker jack. For the water absorption test, 15 cylindrical samples (7.5×15 cm) were made for C25 and 0%, 5%, 10%, 15%, and 20% desert sand. They were then tested after 28 days. The results showed that the compressive strength at the age of 28 days gradually increased by adding the sand. It reached the highest for C20 containing 10% sand. However, it reached the highest foe C25 and C30 containing 5% sand. Adding sand over 20% leads to decreasing compressive strength. The tensile strength of C25 and C30 concrete containing 5% sand and C20 concrete containing 10% sand was the highest compared to the control sample. Adding sand up to 10% leads to decreased water absorption, and then it increases after adding sand. تفاصيل المقالة -
حرية الوصول المقاله
33 - Laboratory evaluation on the effectiveness of polypropylene fibers on the strength behavior of CKD-stabilized Soil
Sadegh Ghavami Hamid Jahanbakhsh Fereidoon Moghadas NejadImproving the engineering properties of soils by chemical stabilization and using reinforcement material are means of complying with geotechnical design criteria. Nowadays, the use of chemical materials such as Portland cement and lime has been criticized despite the ac أکثرImproving the engineering properties of soils by chemical stabilization and using reinforcement material are means of complying with geotechnical design criteria. Nowadays, the use of chemical materials such as Portland cement and lime has been criticized despite the acceptable effect due to environmental pollution caused by their production as well as the contamination caused by these materials in the soil. One of the materials used to replace cement and lime is cement kiln dust (CKD), which has been used as filler in asphalt concrete, sewage sludge stabilization, and improving the physical and mechanical properties of soils in recent years. An experimental study was performed to evaluate strength behavior and microstructural characteristics of CKD-soil admixture reinforced by polypropylene fibers. The effect of content and length of fibers on mixture properties was investigated. The results indicated that CKD increases the strength of the soil, but its behavior is fragile. The use of fiber in combination with CKD, in addition to increasing the strength, makes the sample more ductile. The test results showed that the optimum content of polypropylene fibers is 0.5%. The failure pattern of fiber-reinforced specimens differed from that of fiberless specimens due to the bridge effect. The results of the UCS test agreed well with the results from the SEM analysis. تفاصيل المقالة -
حرية الوصول المقاله
34 - Investigation of nano-silica effects on Coarse-grained soil’s compressive strength: A case study for Aras Free Trade Zone (AFTZ)
Farhad Pirmohammadi AlishahBased on the increasing the usage of the resources and population growth, the soil with suitable properties for civil engineering project such as pavement construction is not available. Therefore, it is obligatory that the enhancement of local soils properties should be أکثرBased on the increasing the usage of the resources and population growth, the soil with suitable properties for civil engineering project such as pavement construction is not available. Therefore, it is obligatory that the enhancement of local soils properties should be appropriately deliberated. If for some reason it is not possible to relocate the project and replace the soil, or if the cost of soil replacement is not cost-effective, the soil remediation method should be considered so that if this method is economically and technically justifiable, it should be done. From this perspective, the effects of Nano-silica on soil compressive strength are important and necessary. In this study, a specific and different number of samples are prepared for comparison. The purpose of this study is to measure the uniaxial compressive strength of granular soils. It was concluded that Nano-silica filled pore space between Sand particles and a dense matrix were formed. This textural event caused an improvement in compressive strength of stabilized soils In this regard, the use of Nano-silica as a suitable and efficient additive in the thickening processes is recommended. تفاصيل المقالة -
حرية الوصول المقاله
35 - Experimental Study on Wastewater Application for Cement Mixing in Concrete
Mohammad Pordel Nezami Mohamad Aslalinezhad Fard Mahdi Aslalinezhad FardWater content is a very important part of concrete which has an important impact on strength of the concrete. The water condition in concrete is mostly located in drinking level which by shortcoming on the waters is required to reconsider the usage water in concrete. Th أکثرWater content is a very important part of concrete which has an important impact on strength of the concrete. The water condition in concrete is mostly located in drinking level which by shortcoming on the waters is required to reconsider the usage water in concrete. The presented study attempted to provide the experimental study on wastewater application for cement mixing in high-strength concrete. In this regard, the experimental assessment was conducted on 2 types of concrete mix named Mix 1 and Mix 2 (for 7 and 28 days) which is indicated of drinking water, and treated wastewater-based concrete. The main evaluation index is UCS which is performed on 10 samples. According to the results of the study, using treated wastewater provides the 12 to 18 MPa strength regarding UCS which is near to the freshwater (14 to 20 MPa). So, the application of treated wastewater can be considered as an alternative for fresh water in concrete. تفاصيل المقالة -
حرية الوصول المقاله
36 - Combined Porcelain Ceramic and Recycled Concrete Aggregates Used as Replacement for Coarse Aggregates in Concrete
Sayed Behzad Talaeitaba Maedeh DehghaniThe increasing production of construction waste on the one hand and the use of concrete as a widely used material in the construction industry, on the other hand, has always led researchers to reuse construction waste in concrete. Among the recycled materials that can b أکثرThe increasing production of construction waste on the one hand and the use of concrete as a widely used material in the construction industry, on the other hand, has always led researchers to reuse construction waste in concrete. Among the recycled materials that can be used in concrete, we can mention porcelain ceramic and recycled concrete. In the present study, these two types of recycled aggregates (recycled porcelain ceramics and recycled concrete) alone and together in different percentages of 20%, 40%, and 60% are used as the replacement of coarse aggregates in concrete with a strength of more than 50 MPa and high flowability. Slump test, compressive and flexural strength, water absorption, and water penetration tests have been performed on 150 samples made in 10 mixing designs along with an SEM test. The results showed that all the mixing designs had slumps of more than 180 mm. The compressive strength of the control sample averaged 60 MPa and the samples containing recycled aggregates averaged 68 MPa. Also, by combining two types of recycled aggregates, both the 7-day and 28-day strength increased with increasing replacement percentage with a linear trend. The highest increase was 28% for porcelain aggregates and 17% for combined recycled aggregates. In addition, the water penetration rate in the samples containing the combined recycled aggregates showed a significant decrease compared to the control sample. In the SEM test, it was observed that the samples containing the combined aggregates had a thicker and denser matrix. تفاصيل المقالة -
حرية الوصول المقاله
37 - Experimental investigation of Carbon, Glass and Steel fibers effect on failure strength and slump of standard concrete samples
Sohrab hosseini kheirabad Ehsan Kazeminezhad Soroush SafakhahFiber reinforced concretes due to their acceptable performance on structural members have been evaluated in many research. Planty of materials have been used in combination with the concrete and caused researcher focused on the concrete compressive strength. In this exp أکثرFiber reinforced concretes due to their acceptable performance on structural members have been evaluated in many research. Planty of materials have been used in combination with the concrete and caused researcher focused on the concrete compressive strength. In this experimental regard, effects of three types of fibers such as Glass, Carbon and double hook steel on tensile strength, compressive strength and slump of standard concrete samples have been investigated. Four various weight ratios for any of these fibers are used (0.5, 1.0, 1.5 and 2% of cement weight). Analysis is done on the 7 and 28 days of concrete age and a simple concrete sample is existing to compare with fiber concrete samples. Results showed that in all dosage of Glass and Steel, compressive strength is increased but in samples with carbon fibers in 1.5 and 2% is decreased. Tensile strength in all used dosage of fibers is increased. Slump values of all fiber samples are decreased and maximum decrease experienced in glass fiber samples. تفاصيل المقالة -
حرية الوصول المقاله
38 - Estimating an appropriate plastic concrete mixing design for cutoff walls to control leakage under the earth dam.
A Pashazadeh M Khosravi N GanjianMaking use of concrete materials in cut-off walls, because of their low permeability and standing high Hydraulic Gradient caused by underground drainage, has attracted great amount of attention. Using ordinary concrete with high elasticity modulus, compared to other mat أکثرMaking use of concrete materials in cut-off walls, because of their low permeability and standing high Hydraulic Gradient caused by underground drainage, has attracted great amount of attention. Using ordinary concrete with high elasticity modulus, compared to other materials may accompany with problems including brittleness of cutoffs due to dynamic stresses.To solve this problem, adding a certain percentage of clay (Bentonite) to plastic concrete materials reduces the concrete hardness as well as its elasticity coefficient, resulting in better ductility. Adding Ebonite (clay and excavation mud) decreases the possibility of hydraulic failure and cracking.In this article components of the plastic concrete and parameters which affect in properties and manners of its mixing design is analyzed. Based on the results that have been obtained from experiments on plastic concrete samples which have various mixing plans, diagrams have been presented to obtain a mixing plan of ideal plastic concrete with different characteristics which result in determining a key relationship in order to estimate mixing plan of an appropriate plastic concrete of cutoffs to control leakage under the dam. While under current situation, not using these relationships to estimate mixing plan of an appropriate plastic concrete of cutoffs in order to control leakage under the dam is costly and time consuming with considerable amount of errors. تفاصيل المقالة -
حرية الوصول المقاله
39 - The effect of physical and mechanical properties on the abrasion resistance of artificial stones produced with granite waste
Seyyed Mohammad Javad Mousavi Reza Abedinzadeh Mohammad ReisiThe recycling of mine stone waste has been interesting for the creation of employment opportunities and added value and the prevention of environmental pollution. The present study examined the effects of the physicomechanical properties on the abrasion resistance of ar أکثرThe recycling of mine stone waste has been interesting for the creation of employment opportunities and added value and the prevention of environmental pollution. The present study examined the effects of the physicomechanical properties on the abrasion resistance of artificial stones produced with granite cut waste. A total of four artificial specimens were produced under different compositions and methods. Their physicomechanical properties, such as density, porosity, water absorption, hardness, compressive strength, and abrasion resistance, were evaluated. Finally, the artificial stones were compared to natural granite and marble in abrasion resistance. It was found that an increase in the porosity and water absorption reduced hardness, compressive strength, and abrasion resistance. Furthermore, hardness, compressive strength, and abrasion resistance declined as the porosity and water absorption increased. The increased rotational speed and load in the Taber abrasion test diminished abrasion resistance. The epoxy resin-based artificial stone exhibited the highest performance among the artificial specimens. It had almost the same porosity and water absorption as natural granite and marble. However, the epoxy resin-based stone with lower Mohs hardness and compressive strength showed less abrasion resistance compared to the natural granite and marble. As a result, all four artificial stones showed satisfactory performance for the flooring of congested areas. تفاصيل المقالة -
حرية الوصول المقاله
40 - بررسی پارامترهای موثر برمقاومت فشاری، مقاومت الکتریکی ویژه و جذب آب بتن متخلخل سبک
شهریار غلامین نوویرسر مرتضی جمشیدی رحمت مدندوستبتن متخلخل نوعی ویژه از بتن سبک با اسلامپ کم یا حتی صفر شناخته می¬شود که از سیمان، درشت دانه، درصد محدودی از ریز دانه (یا فاقد ریزدانه)، افزودنی¬های مختلف شیمیایی و پوزولانی تشکیل شده است. در¬این مقاله ¬از لیکای ¬سازه¬ای ¬با¬ وزن¬حجمی m3¬¬¬kg/ 750¬ و نسبت آب به سیمان ثا أکثربتن متخلخل نوعی ویژه از بتن سبک با اسلامپ کم یا حتی صفر شناخته می¬شود که از سیمان، درشت دانه، درصد محدودی از ریز دانه (یا فاقد ریزدانه)، افزودنی¬های مختلف شیمیایی و پوزولانی تشکیل شده است. در¬این مقاله ¬از لیکای ¬سازه¬ای ¬با¬ وزن¬حجمی m3¬¬¬kg/ 750¬ و نسبت آب به سیمان ثابت (3/0W / C =) ، ¬برای ساخت بتن متخلخل سبک استفاده شد و ¬اثر ¬نسبتها¬ی مختلف سبکدانه به سیمان ( A/C ) شامل 3 ، 7/2 ، 4/2 ، 1/2 ، 8/1 ، 5/1 ، تخلخل کل ¬و درصدحجمی خمیر سیمان بر روی مقاومت فشاری ، مقاومت الکتریکی ویژه و درصد جذب آب بتن متخلخل سبک درسن 28 روز مورد بررسی قرار گرفت. با افزایش نسبت A/C از 5/1 تا 3¬، حجم خمیر سیمان از 873/30 % به 436/15 % در نمونه¬ها کاهش و تخلخل کل از64/21 % به 08/38 % افزایش یافت که منجر به کاهش مقاومت الکتریکی ویژه از 45/11 به 841/6 ، کاهش مقاومت فشاری از Mpa 27/13 به MPa 37/4 و افزایش جذب آب از 185/11 % به 695/12 % در نمونه‌های بتن متخلخل سبک شد. نتایج این پژوهش بهبود ویژگیهای فیزیکی و افت ویژگیهای مکانیکی و دوام بتن متخلخل سبک حاوی لیکا را نشان دادند. تفاصيل المقالة -
حرية الوصول المقاله
41 - Investigation of the Reduced Graphene Oxide Effect on the Concrete Strength, Impedance and Corrosion Resistance of Rebar Inside
fateme abdi Houdhyar Eimani KalesarIn this work, to investigate the effect of reduced Graphene Oxide nanoparticles on the strength of concrete and the corrosion resistance of rebar inside it, Graphene Oxide nanoparticles were added to the mortar with different weight percentages of cement. The strength أکثرIn this work, to investigate the effect of reduced Graphene Oxide nanoparticles on the strength of concrete and the corrosion resistance of rebar inside it, Graphene Oxide nanoparticles were added to the mortar with different weight percentages of cement. The strength of concrete was evaluated by measuring the compressive strength of 7 days and 28 days and comparing with the results of the control sample. To investigate the effect of reduced Graphene Oxide nanoparticles on the corrosion resistance of rebar inside it, polarization and EIS tests were performed in a 3.5% salt solution. The results showed that the addition of reduced Graphene Oxide nanoparticles increases the compressive strength and electrical impedance of the concrete. It was also found that there is an optimal value that the addition of Graphene Oxide nanoparticles more than that value causes a relative decrease in concrete strength and electrical impedance. Finally, by simulating the equivalent circuit, the reason for the decrease in impedance and as a result the corrosion resistance by adding more than the optimal value was investigated. تفاصيل المقالة -
حرية الوصول المقاله
42 - Prediction of compressive strength of concretes containing micro silica subject to carbonation using neural network
Ali DelnavazConcrete materials are exposed to special weather conditions, corrosion and significant damage. For this purpose, the effect of 28-day compressive strength changes on the samples studied in this study was investigated by considering the simultaneous effect of chloride i أکثرConcrete materials are exposed to special weather conditions, corrosion and significant damage. For this purpose, the effect of 28-day compressive strength changes on the samples studied in this study was investigated by considering the simultaneous effect of chloride ion penetration and carbonation phenomenon. For this reason, in the first case, the samples are exposed to carbon dioxide once and then to chloride ions. In the latter case, only samples under the influence of chloride infiltration are examined. To make the samples, which include 9 mixing designs, three water-to-cement ratios of 0.35, 0.4 and 0.5 and three percent of 0%, 7% and 10% silica fume have been used. Finally, an optimal model is introduced to predict the compressive strength of concrete containing micro silica exposed to carbonation using artificial neural network. Also, a relation for estimating compressive strength based on the ratio of water to cement and the amount of silica is presented. تفاصيل المقالة
سند
Sanad is a platform for managing Azad University publications
الروابط
المراكز ذات الصلة
دعامة
الصفحات الرسمية
حقوق هذا الموقع الإلكتروني مملوكة لنظام SANAD Press Management. © 1442-1445