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Showing 25 results for Mechanical Properties

Mazloom M., Ramezanian Pour A.a.,
Volume 2, Issue 1 (3-2004)
Abstract

This paper presents the long-term deformations of reinforced high-strength concrete columns subjected to constant sustained axial forces. The objective of the study was to investigate the effects of binder systems containing different levels of silica fume on time-dependent behaviour of high-strength concrete columns. The experimental part of the work focused on concrete mixes having a fixed water/binder ratio of 0.35 and a constant total binder content of 500 kg/m3. The percentages of silica fume that replaced cement in this research were: 0%, 6%, 8%, 10% and 15%. The mechanical properties evaluated in the laboratory were: compressive strength secant modulus of elasticity strain due to creep and shrinkage. The theoretical part of the work is about stress redistribution between concrete and steel reinforcement as a result of time-dependent behaviour of concrete. The technique used for including creep in the analysis of reinforced concrete columns was age-adjusted effective modulus method. The results of this research indicate that as the proportion of silica fume increased, the short-term mechanical properties of concrete such as 28-day compressive strength and secant modulus improved. Also the percentages of silica fume replacement did not have a significant influence on total shrinkage however, the autogenous shrinkage of concrete increased as the amount of silica fume increased. Moreover, the basic creep of concrete decreased at higher silica fume replacement levels. Drying creep (total creep - basic creep) was negligible in this investigation. The results of the theoretical part of this researchindicate that as the proportion of silica fume increased, the gradual transfer of load from the concrete to the reinforcement decreased and also the effect of steel bars in lowering the concrete deformation reduced. Moreover, the total strain of concrete columns decreased at higher silicafume replacement levels.
S. Eshghi, V. Zanjanizadeh,
Volume 5, Issue 3 (9-2007)
Abstract

This paper presents an experimental study on seismic repair of damaged square reinforced concrete columns with poor lap splices, 90-degree hooks and widely spaced transverse bars in plastic hinge regions according to ACI detailing (pre.1971) and (318-02) using GFRP wraps. Three specimens were tested in “as built” condition and retested after they were repaired by glass fiberreinforced plastic sheets. They were tested under numerous reversed lateral cyclic loading with a constant axial load ratio. FRP composite wraps were used for repairing of concrete columns in critically stressed areas near the column footings. Physical and mechanical properties of composite wraps are described. Seismic performance and ductility of the repaired columns in terms of the hysteretic response are evaluated and compared with those of the original columns. The results indicated that GFRP wraps can be an effective repair measure for poorly confined R/C columns due to short splice length and widely spaced ties with 90-degree anchorage hooks. Both flexural strength and ductility of repaired columns were improved by increasing the existing confinement in critical regions of them.
A.a. Ramezanianpour, M. Mahdi Khani, Gh. Ahmadibeni,
Volume 7, Issue 2 (6-2009)
Abstract

Rice Husk Ash (RHA) is a by-product of the agricultural industry which contains high amount of silicon dioxide (SiO2). In this research, for the first time in the Middle East, in order to supply typical RHA, a special furnace was designed and constructed in Amirkabir University of Technology. Afterwards, XRD and XRF techniques were used to determine the amorphous silica content of the burnt rice husk. Attempts were made to determine the optimum temperature and duration of burning. Results show that temperature of 650 degrees centigrade and 60 minutes burning time are the best combination. Then various experiments were carried out to determine properties of concretes incorporating optimum RHA. Tests include compressive strength, splitting tensile strength, modules of elasticity, water permeability and rapid chloride permeability test. Results show that concrete incorporating RHA had higher compressive strength, splitting tensile strength and modulus of elasticity at various ages compared with that of the control concrete. In addition, results show that RHA as an artificial pozzolanic material has enhanced the durability of RHA concretes and reduced the chloride diffusion.
M. Bastami, F. Aslani, M. Esmaeilnia Omran,
Volume 8, Issue 4 (12-2010)
Abstract

Structural fire safety capacity of concrete is very complicated because concrete materials have considerable variations. In this paper, constitutive models and relationships for concrete subjected to fire are developed, which are intended to provide efficient modeling and to specific fire-performance criteria of the behavior of concrete structures exposed to fire. They are developed for unconfined concrete specimens that include residual compressive and tensile strengths, compressive elastic modulus, compressive and tensile stress-strain relationships at elevated temperatures. In this paper, the proposed relationships at elevated temperatures are compared with experimental result tests and pervious existing models. It affords to find several advantages and drawbacks of present stress-strain relationships and using these results to establish more accurate and general compressive and tensile stress-strain relationships. Additional experimental test results are needed in tension and the other main parameters at elevated temperatures to establish well-founded models and to improve the proposed relationships. The developed models and relationships are general, rational, and have good agreement with experimental data.


A. Allahverdi, B. Shaverdi, E. Najafi Kani,
Volume 8, Issue 4 (12-2010)
Abstract

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


Nader Shariatmadari , Marzieh Salami, Mehran Karimpour Fard,
Volume 9, Issue 2 (6-2011)
Abstract

The main task in the design and construction of impermeable liners in landfills is to block the migration of pollutants to the groundwater

systems or to reduce its rate to a reasonable amount. That is why environmental regulations force governments to construct engineered

waste dumps for waste management purposes. These liners are exposed to various types of chemical, biological, and physical processes

and are affected by the leachate which is produced from decomposition of waste materials accompanying methane gas. The leachate

includes a lot of components such as water and different types of salts. For this reason, the geotechnical characteristics of clay liners

which are evaluated in laboratories using distilled water or tap water might be far different from the representative sample of the in-situ

conditions. There are some evidences regarding the effect of these salts on the physical and mechanical properties of clay barriers which

could affect the long-term performance of these liners. Since the main criterion for impermeable bottom liners in landfills is their

hydraulics conductivity, the increase of this parameter could have a considerable environmental impact. This paper embraces the results

of a recent study on the effect of three inorganic salts, NaCl, CaCl2 and MgCl2 on some geotechnical properties of a common used clay

soil in impermeable bottom barrier in Kahrizak landfill, the main waste disposal center of the Tehran Metropolitan. Also the effect of

bentonite content by adding different percentage of this special clay mineral, 10 and 20 percent, on these properties was investigated.

Laboratory tests like liquid limit, compaction, 1D consolidation and free swell tests were performed for this purpose. Results indicated

that all of these salts could have a considerable effect on the geotechnical properties of the mixtures. The main reason of such effects is

the changes which occur in diffuse double layer of clay particles.


A.a. Maghsoudi, Sh. Amohamadpour, M. Maghsoudi,
Volume 9, Issue 3 (9-2011)
Abstract

Considering normal concrete (NC) the type of concrete need to be vibrated after placing in the formwork, Lightweight

concretes have been successfully applied in the building constructions for decades because of their low specific weight in

connection with a high strength, a high capacity of thermal insulation and a high durability. The development leading to a self

compacting light weight concrete (SCLWC) represents an important innovative step in the recent years. This concrete combines

the favorable properties of a lightweight concrete with those of a self compacting concrete (i.e., the type of concrete need no

vibration after placing in the formwork). Research work is aimed on development of (SCLWC) with the use of light weight

aggregates " Light expand clay aggregate (Leca)". In this investigation, by trial and error procedure, different mix design of

SCLWC were caste and tested to reach a so called standard self compacting concrete in fresh matrix phase such as values of

slump flow, L-box, V-funnel and in hardened phase, the 28 day compressive strength. Based on the results obtained, for two best

so-called standard mix design of SCLWC the stress-strain diagrams are drawn and discussed. Also by three different methods,

the modulus of elasticity of SCLWC are obtained and discussed here. It was found that a brittle mode of failure is governed in

SCLWC.


M. Biglari, I. Ashayeri,
Volume 11, Issue 2 (11-2013)
Abstract

Seismic ground motion is profoundly affected by geometrical and mechanical properties of soil deposits overlaying bedrock.

Local seismic ground response of saturated soil deposits was studied in literature by applying the effects of soil stress state

and index properties on the strain-dependent normalized shear modulus reduction, G/G0, and damping ratio, D, curves in an

equivalent linear analysis. However, experimental investigations revealed that, G0, G/G0, and D of unsaturated soils are

influenced by stress state as well as suction. This study presents the results of linear and equivalent linear seismic ground response

analysis of unsaturated soil deposits incorporating suction effects on G/G0 and D curves. Seismic ground response analyses were

done with the computer program EERA for three sets of soil profiles, which are included in saturated, constant and linearly

variable suction unsaturated soil deposits. The results of current study present the magnitude of variation in natural frequency,

amplification ratio and spectral acceleration of unsaturated soil deposits.


M. Khorami, J. Sobhani,
Volume 11, Issue 4 (12-2013)
Abstract

Worldwide, asbestos fibers utilized in fiber cement boards, have been recognized as harmful materials regarding the public health and environmental pollutions. These concerns motivate the researchers to find the appropriate alternatives to substitute the asbestos material towards the sustainability policies. In this paper, the applicability of asbestos replacement with three types of agricultural waste fibers, including bagasse, wheat and eucalyptus fibers were experimentally investigated. To this end, the flexural behaviour and microstructure of cement composite boards made by addition of 2 % and 4 % of waste agricultural fibers in combination with and without 5 % replacement of silica fume by mass of cement were evaluated. The results of this study attested the applicability of utilized waste agricultural fibers in production of cement composite boards by improving the flexural and energy absorption characteristics, more or less, depending on the type of fibers. Moreover, it is found that application of silica fume in production of cement composite boards led to an increase in flexural strength.
P. Ramadoss,
Volume 12, Issue 1 (3-2014)
Abstract

Abstract: This paper presents the influence of adding steel fibers and incorporation of silica fume on the mechanical properties of high-strength concrete. The variables investigated were steel fiber volume fraction (0 to 1.5%), silica fume replacement (5, 10 and 15%) and water-to-binder ratio (0.25, 0.30, 0.35 and 0.40). The influence of fiber content in terms of fiber reinforcing index on the compressive and splitting tensile strengths of high-strength steel fiber reinforce concrete (HSFRC) is presented. The use of silica fume increased both the compressive and splitting tensile strengths of concrete at 28 days. On the other hand, the addition of crimped steel fiber into high-strength concrete improves splitting tensile strength significantly. Based on the test data, using regression analysis, empirical expression to predict 28-day tensile strength of HSFRC in terms of fiber reinforcing index was developed and the absolute variation and integral absolute error (IAE) obtained was 3.1% and 3.3, respectively. The relationship between splitting tensile and compressive strength of SFRC was reported with regression coefficient (r) = 0.9. The experimental values of previous researchers were compared with the values predicted by the model and found to predict the values quite accurately.
M. Zargaran, N. K. A. Attari, P. Teymouri,
Volume 12, Issue 1 (3-2014)
Abstract

Polymeric yarns for reinforcing cement composites have got great interest in all over the world. In this research the performance of bonding between Nylon tire cord grad yarns, and one kind of cement composite called fine grained concrete was studied. Two kinds of Nylon cord yarns, nylon 6 and 66, with different finesse were selected. The durability of yarns with time in alkaline media was investigated. Meanwhile the effect of usual tire cord coating on bonding performance and alkaline durability of yarns were studied by mechanical testing and SEM images. Then the bonding of these yarns to cement paste and the effects of finesse on bonding performance were investigated by pull out tests. The results show that coating could enhance alkaline durability. Results also show that yarns with higher finesse are more sensitive to alkaline media and their mechanical properties reduced more. SEM images show that in general, alkali damage of Nylon tire cord yarns was not deep and no significant changes were observed on the surface of filaments after exposed to alkali. The bonding of Nylon tire cord to cement composite was suitable and no slippage was observed. The pull out behavior of finer yarns is better than coarse yarns. Meanwhile tire cord coating could enhance bonding of yarns to cement paste.
A. H. Eghbali, K. Fakharian,
Volume 12, Issue 1 (1-2014)
Abstract

Portland cement can be mixed with sand to improve its mechanical characteristics. Many studies are reported in literature on this topic, but the effect of principal stress rotation has not been investigated yet. Considering the inherent anisotropy of most sands, it is not clear whether the added cement shall contribute to equal increase in strength and stiffness at vertical and horizontal directions or not. Furthermore, it is not well understood how the cement as an additive in non-compacted (loose) sand compared to compacted (dense) sand without cement, contribute to improving the material behavior in undrained condition such as limiting the deformations and the liquefaction potential. In this research, undrained triaxial and simple shear tests under different stress paths are carried out on different mixtures of Portland cement (by adding 1.5, 3 and 5 percent) with clean sand to investigate the effect of principal stress rotations. The triaxial test results revealed that the cement mixture reduces the anisotropy, while it improves the mixture mechanical properties compared to compacted sand without cement. The results of the simple shear tests validated the triaxial test results and further clarified the effect of the  parameter or rotation of principal stresses on the behavior of cemented sand mixtures.
M. B. Esfandiari Sowmehsaraei, R. Jamshidi Chenari,
Volume 12, Issue 1 (1-2014)
Abstract

Soil reinforced with fiber shows characteristics of a composite material, in which fiber inclusion has a significant effect on soil permeability. Concerning to the higher void ratio of carpet fibers, at first stages it may be expected that an increase in fiber content of the reinforced soil would result in an increase in permeability of the mixture. However, the present article demonstrates that fiber inclusion will decrease the permeability of sand-fiber composite.A series of constant head permeability tests have been carried out to show the effects and consequently, a new system of phase relationships was introduced to calculate the dry mass for the sand portion of the composite. Monte Carlo simulation technique adopted with finite element theory was employed to back calculate the hydraulic conductivity of individual porous fibers from the laboratory test results. It was observed that the permeability coefficient of the porous fibers are orders of magnitude less than the skeletal sand portion due to the fine sand particle entrapment and also the fiber volume change characteristics.
E. Lotfi, S. Delfan, A. Hamidi, H. Shahir, Gh. Fardi,
Volume 12, Issue 1 (1-2014)
Abstract

In saturated soils, heating induces thermal expansion of both grains and the pore fluid. Lower thermal expansion coefficient of aggregates results in the increase of pore pressure and reduction of the effective stress besides subsequent volume changes due to the dissipation of pore pressure and heat transfer. Dissipation of thermally induced pore pressure with time is a coupled thermo-hydro-mechanical (THM) phenomenon, involving gradients of pore pressure and temperature, hydraulic and thermal flows within the mass of soil and changes in the mechanical properties with temperature. The objective of this paper is presentation of a numerical method to determine the effect of temperature on consolidation of clays. In this regard, the finite element code, PISA is used for one dimensional THM analysis of porous media. The analysis performed using both linear elastic and elastoplastic Cam clay models. Modified Cam clay model was applied in elastoplastic analysis. Variation of temperature, displacements and pore pressure determined with time and compared with numerical solutions of other researchers. Also it was indicated that implementation of coupled THM analysis yields better results for displacements compared to the hydro mechanical (HM) one. Application of elastoplastic constitutive model instead of linear elastic one indicated that preconsolidation pressure has an important effect on results of analysis.
M. L. Li, Q. Chun-Xiang, Z. Yong-Hao,
Volume 12, Issue 2 (4-2014)
Abstract

It introduced an innovative bioengineering method of consolidating incompact sand by urea-hydrolysis producing calcite cementation under the inducement of urease producing microbe. In the paper it discussed the effects of cementation methods and time on porosity and mechanical properties of microbe-inspired cementing sand columns. Method A adopted reaction fluid gravitational permeating and external pressing and method B adopted reaction fluid gravitational permeating and outlet intermittent plugging method. 28-day sand columns prepared by method A exhibited stronger mechanical properties than those prepared by method B, considering of the compressive strengths and three-point flexural strength as well. Pore volume fractions of sand columns prepared by method A reduced with an increase in cementation time which represented the bulk densities of sand columns were improved positively with time. The compressive strengths and the flexural strengths of sand columns prepared by method A increased with time. All these improved mechanical properties were attributed to the fact that the increasing amount of microbe inspired calcite precipitation with time consolidated sand columns by filling or bridging in sand gaps.
R. Perumal, K. Nagamani,
Volume 12, Issue 4 (12-2014)
Abstract

An experimental study on the impact performance of silica fume concrete and steel fiber reinforced concrete at 28 days and 56 days under the action of repeated dynamic loading was carried out. In this experimental investigation, w/cm ratios of 0.4 and 0.3, silica fume replacement at 10% and 15% and crimped steel fibers with an aspect ratio of 80 were used. Results indicated that addition of fibers in high-performance concrete (HPC) can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths, toughness and ductility of HPC. Pulse velocity test was carried out for quality measurements of high-performance steel fiber reinforced concrete. Steel fibers were observed to have significant effect on flexural strength of concrete. The maximum first crack strength and ultimate failure strength at 28 days were 1.51 times and 1.78 times, respectively at 1.5% volume fraction to that of HPC. Based on the experimental data, failure resistance prediction model was developed with correlation coefficient (R) = 0.96 and absolute variation determined is 1.82%.
B.a. Mir,
Volume 13, Issue 3 (12-2015)
Abstract

Fly ash is one of the most plentiful and versatile of the industrial by-products. At present, nearly 150 million tonnes of fly ash is being generated annually in India posing dual problem of environmental pollution and difficulty in disposal. This calls for establishing strategies to use the same effectively and efficiently. However, it is only in geotechnical engineering applications such as the construction of embankments/dykes, as back fill material, as a sub-base material etc., its large-scale utilization is possible either alone or with soil. Soil stabilization can be achieved by various means such as compaction, soil replacement, chemical improvement, earth reinforcement etc. Usually, in the case of clay soils, chemical improvement is commonly most effective since it can strengthen the soil, to remove its sensitivity both to water and its subsequent stress history. Among chemical means or additives, fly ash/lime provides an economic and powerful means of improvement, as demonstrated by the significant transformation that is evident on mixing with heavy clay. In the present investigation, different percent fly ashes (10%, 20%, 40%, 60% & 80%) were added to a highly expansive soil from India by dry weight of the natural soil, and subjected to various tests. The important properties that are necessary for using fly ash in many geotechnical applications are index properties, compaction characteristics, compressibility characteristics, permeability and strength. Based on test results, it has been found that using fly ash for improvement of soils has a two-fold advantage. First, to avoid the tremendous environmental problems caused by large scale dumping of fly ash and second, to reduce the cost of stabilization of problematic/marginal soils and improving their engineering properties for safe construction of Engineering Structures. 


A.r. Hariharan, A.s. Santhi , G. Mohan Ganesh ,
Volume 13, Issue 3 (9-2015)
Abstract

This research paper presents the use of wasteful supplementary cementitious materials like fly ash and silica fume to conserve the cement used in concrete. The cement industry is one of the major producers of greenhouse gases and an energy user. In this study, Portland cement was used as a basic cementitious material. Fly ash and silica fume were used as the cement replacements by weight. The replacement levels of fly ash were 30%, 40% and 50%, and silica fume were 6% and 10%. The water binder ratio was kept constant as 0.4 and super plasticizer was added based on the required workability. Results of the binary and ternary concrete mixtures compressive strength, split tensile strength and flexural tensile strength were taken for studyup to 90 days. Based on the experimental results of compressive strength, prediction models were developed using regression analysis and coefficients were proposed to find the split tensile strength and flexural strength of binary-ternary concrete mixtures at 28 and 90 days.
M.m. Kamal, M.a. Safan, Z.a. Etman, M.a. Abd-Elbaki,
Volume 13, Issue 4 (12-2015)
Abstract

The current research intends to study the possibility of producing fiber recycled self-compacting concrete (FRSCC) using demolitions as a coarse aggregate (crushed red brick and crushed ceramic). Steel fibers were used in recycled self-compacting concrete (RSCC) to improve fresh and hardened properties of this type of concrete. Thirty nine concrete mixes were prepared to achieve the aim proposed in this paper. Steel fiber volume fraction varied from 0 to 2.0% by the volume of concrete with aspect ratio 65. The fresh properties of FRSCC were evaluated using slump flow, J-ring and V-funnel tests. Compressive strength, tensile strength, flexural strength and density tests were performed in order to investigate mechanical properties. The optimum volume fraction of steel fibers was 0.25% and 1.0% for the mixes contained crushed red brick and ceramic as a coarse aggregate respectively. At optimum content of steel fibers, the compressive strength for the RSCC mixes with steel fibers improved by 11.3% and 31.8% for the mixes with crushed ceramic and crushed red brick, respectively with respect to control mix. Also the tensile strength and the flexural strength for the mixes were improved


Nader Shariatmadari, Behnam Askari Lasaki, Hasan Eshghinezhad, Behzad Askari,
Volume 14, Issue 7 (10-2016)
Abstract

The main purpose of this study is to investigate the influence of urban solid waste leachate on the mechanical properties of the soil. Order to provide a more accurate identification of the contaminated soils, Cylindrical specimens of the soil, according to the density curves with different initial conditions (different initial contamination levels) were prepared, then the soil specimens were loaded at different load levels using a direct shear testing equipment and a universal testing machine to apply axial compression on the specimens. By analyzing the results, the stress-strain and failure behavior of the soil specimens containing different percentages of the solid waste leachate was evaluated. The most important result was reducing the mechanical properties of the soil contaminated with different percentages of solid waste. The results of adding lower quantities of leachate, is far more significant compared to the received results from adding higher amounts of leachate.



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