Determination of Trace Amounts of Lead and Copper in Water Samples by Flame Atomic Absorption Spectrometry after Cloud Point Extraction

Shemirani, Farzaneh,Abkenar, Shiva Dehghan,Khatouni, Asieh Korean Chemical Society 2004 Bulletin of the Korean Chemical Society Vol.25 No.8

The need for highly reliable methods for the determination of trace metals is recognized in analytical chemistry and environmental science. A method based on the cloud-point extraction (CPE) technique for the trace analysis of Pb and Cu in water samples is described in this study. The analytes in the initial aqueous solution are complexed with pyrogallol, and 0.1%(w/v) Triton X-114 is added as surfactant. Following phase separation at $50^{\circ}C$, based on the cloud point of the mixture and dilution of the surfactant-rich phase with acidified methanolic solution, the enriched analytes are determined by flame atomic absorption spectrometry. After optimization of the complexation and extraction conditions, the enrichment factors of Pb and Cu were found to be 72 and 85, respectively. Under optimum conditions, the preconcentration of 60 mL of samples in the presence of 0.1%(w/v) Triton X-114 permitted the detection of 0.4 ${\mu}gL^{?1}$ of Pb and 0.05 ${\mu}gL^{?1}$ of Cu. The proposed method was applied successfully to the determination of Pb and Cu in water samples.

A review paper about experimental investigations on failure behaviour of non-persistent joint

Shemirani, Alireza Bagher,Haeri, Hadi,Sarfarazi, Vahab,Hedayat, Ahmadreza Techno-Press 2017 Geomechanics & engineering Vol.13 No.4

There are only few cases where cause and location of failure of a rock structure are limited to a single discontinuity. Usually several discontinuities of limited size interact and eventually form a combined shear plane where failure takes place. So, besides the discontinuities, the regions between adjacent discontinuities, which consist of strong rock and are called material or rock bridges, are of utmost importance for the shear strength of the compound failure plane. Shear behaviour of persistent and non-persistent joint are different from each other. Shear strength of rock mass containing non-persistent joints is highly affected by mechanical behavior and geometrical configuration of non-persistent joints located in a rock mass. Therefore investigation is essential to study the fundamental failures occurring in a rock bridge, for assessing anticipated and actual performances of the structures built on or in rock masses. The purpose of this review paper is to present techniques, progresses and the likely future development directions in experimental testing of non-persistent joint failure behaviour. Experimental results showed that the presence of rock bridges in not fully persistent natural discontinuity sets is a significant factor affecting the stability of rock structures. Compared with intact rocks, jointed rock masses are usually weaker, more deformable and highly anisotropic, depending upon the mechanical properties of each joint and the explicit joint positions. The joint spacing, joint persistency, number of rock joint, angle of rock joint, length of rock bridge, angle of rock bridge, normal load, scale effect and material mixture have important effect on the failure mechanism of a rock bridge.

The discrete element method simulation and experimental study of determining the mode I stress-intensity factor

Shemirani, Alireza Bagher,Haeri, Hadi,Sarfarazi, Vahab,Akbarpour, Abbas,Babanouri, Nima Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

The present study addresses the direct and indirect methods of determining the mode-I fracture toughness of concrete using experimental tests and particle flow code. The direct method used is compaction tensile test and the indirect methods are notched Brazilian disc test, semi-circular bend specimen test, and hollow center cracked disc. The experiments were carried out to determine which indirect method yields the fracture toughness closer to the one obtained by the direct method. In the numerical analysis, the PFC model was first calibrated with respect to the data obtained from the Brazilian laboratory test. The crack paths observed in the simulated tests were in reasonable accordance with experimental results. The discrete element simulations demonstrated that the macro fractures in the models are caused by microscopic tensile breakages on large numbers of bonded particles. The mode-I fracture toughness in the direct tensile test was smaller than the indirect testing results. The fracture toughness obtained from the SCB test was closer to the direct test results. Hence, the semi-circular bend test is recommended as a proper experiment for determination of mode-I fracture toughness of concrete in the absence of direct tests.

Determination of Trace Amounts of Lead and Copper in Water Samples by Flame Atomic Absorption Spectrometry after Cloud Point Extraction

Farzaneh Shemirani*,Shiva Dehghan Abkenar,Asieh Khatouni 대한화학회 2004 Bulletin of the Korean Chemical Society Vol.25 No.8

The discrete element method simulation and experimental study of determining the mode I stress-intensity factor

Alireza Bagher Shemirani,Hadi Haeri,Vahab Sarfarazi,Abbas Akbarpour,Nima Babanouri 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

The present study addresses the direct and indirect methods of determining the mode-I fracture toughness of concrete using experimental tests and particle flow code. The direct method used is compaction tensile test and the indirect methods are notched Brazilian disc test, semi-circular bend specimen test, and hollow center cracked disc. The experiments were carried out to determine which indirect method yields the fracture toughness closer to the one obtained by the direct method. In the numerical analysis, the PFC model was first calibrated with respect to the data obtained from the Brazilian laboratory test. The crack paths observed in the simulated tests were in reasonable accordance with experimental results. The discrete element simulations demonstrated that the macro fractures in the models are caused by microscopic tensile breakages on large numbers of bonded particles. The mode-I fracture toughness in the direct tensile test was smaller than the indirect testing results. The fracture toughness obtained from the SCB test was closer to the direct test results. Hence, the semi-circular bend test is recommended as a proper experiment for determination of mode-I fracture toughness of concrete in the absence of direct tests.

Experimental and numerical investigation of the effect of bridge area and its angularities on the failure mechanism of non-persistent crack in concrete-like materials

Alireza Bagher Shemirani,M.S. Amini,V. Sarfarazi,K. Shahriar,P. Moarefvand,Hadi Haeri 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.3

Experimental and discrete element methods were used to investigate the effects of distance between two preexisting cracks, bridge area (The length of the bridge area) and its angularities on the shear behaviour of bridge area. A punchthrough shear test was used to model the gypsum (concrete like) cracks under shear loading. Gypsum samples (concrete like) with dimension of 120 mm × 120 mm × 50 mm were prepared in the laboratory. Within the specimen model and near its four corners, four vertical notches were provided. Three different configuration systems were prepared for notches; i.e., paralell and in plane, inside echelon and outside echelon configuration systems, respectively. In these configurations, the length of cracks were taken as 2 cm, 4 cm and 6 cm based on the cracks configuration systems. Then, 9 specimens with different lengths of the bridge area and bridge area angles were prepared. Assuming a plane strain condition, special rectangular models were prepared with dimensions of 100 mm × 100 mm. similar to those for cracks configuration systems in the experimental tests i.e., 9 models with different lengths of the bridge area and bridge area angularities were prepared. The axial load was applied to the punch through the central portion of the model. This testing showed that the failure process was mostly governed by the lengths of the bridge area and bridge area angularities. The shear strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the lengths of the bridge area. The strength of samples decreases by increasing the crack length. Also, the outside echelon crack configuration system has the maximum value of strength while the inside echelon crack configuration system has the minimum value of specimen's tensile strength. The failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

A discrete element simulation of a punch-through shear test to investigate the confining pressure effects on the shear behaviour of concrete cracks

Alireza Bagher Shemirani,Vahab Sarfarazi,Hadi Haeri,Mohammad Fatehi Marji,Seyed shahin Hosseini 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.21 No.2

A discrete element approach is used to investigate the effects of confining stress on the shear behaviour of joint’s bridge area. A punch-through shear test is used to model the concrete cracks under different shear and confining stresses. Assuming a plane strain condition, special rectangular models are prepared with dimension of 75 mm×100 mm. Within the specimen model and near its four corners, four equally spaced vertical notches of the same depths are provided so that the central portion of the model remains intact. The lengths of notches are 35 mm. and these models are sequentially subjected to different confining pressures ranging from 2.5 to 15 MPa. The axial load is applied to the punch through the central portion of the model. This testing and models show that the failure process is mostly governed by the confining pressure. The shear strengths of the specimens are related to the fracture pattern and failure mechanism of the discontinuities. The shear behaviour of discontinuities is related to the number of induced shear bands which are increased by increasing the confining pressure while the cracks propagation lengths are decreased. The failure stress and the crack initiation stress both are increased due to confining pressure increase. As a whole, the mechanisms of brittle shear failure changes to that of the progressive failure by increasing the confining pressure.

The effect of compression load and rock bridge geometry on the shear mechanism of weak plane

Sarfarazi, Vahab,Haeri, Hadi,Shemirani, Alireza Bagher Techno-Press 2017 Geomechanics & engineering Vol.13 No.3

Rock bridges in rock masses would increase the bearing capacity of Non-persistent discontinuities. In this paper the effect of ratio of rock bridge surface to joint surface, rock bridge shape and normal load on failure behaviour of intermittent rock joint were investigated. A total of 42 various models with dimensions of $15cm{\times}15cm{\times}15cm$ of plaster specimens were fabricated simulating the open joints possessing rock bridge. The introduced rock bridges have various continuities in shear surface. The area of the rock bridge was $45cm^2$ and $90cm^2$ out of the total fixed area of $225cm^2$ respectively. The fabricated specimens were subjected to shear tests under normal loads of 0.5 MPa, 2 MPa and 4 MPa in order to investigate the shear mechanism of rock bridge. The results indicated that the failure pattern and the failure mechanism were affected by two parameters; i.e., the ratio of joint surface to rock bridge surface and normal load. So that increasing in joint area in front of the rock bridge changes the shear failure mode to tensile failure mode. Also the tensile failure change to shear failure by increasing the normal load.

A fracture mechanics simulation of the pre-holed concrete Brazilian discs

Sarfarazi, Vahab,Haeri, Hadi,Shemirani, Alireza Bagher,Nezamabadi, Maryam Firoozi Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.66 No.3

Brazilian disc test is one of the most widely used experiments in the literature of geo-mechanics. In this work, the pre-holed concrete Brazilian disc specimens are numerically modelled by a two-dimensional discrete element approach. The cracks initiations, propagations and coalescences in the numerically simulated Brazilian discs (each containing a single cylindrical hole and or multiple holes) are studied. The pre-holed Brazilian discs are numerically tested under Brazilian test conditions. The single-holed Brazilian discs with different ratios of the diameter of the holes to that of the disc radius are modelled first. The breakage load in the ring type disc specimens containing an internal hole with varying diameters is measured and the crack propagation mechanism around the wall of the ring is investigated. The crack propagation and coalescence mechanisms are also studied for the case of multi-holes' concrete Brazilian discs. The numerical and experimental results show that the breaking mechanism of the pre-holed disc specimens is mainly due to the initiation of the radially induced tensile cracks which are growth from the surface of the central hole. Radially cracks propagated toward the direction of diametrical loading. It has been observed that for the case of disc specimens with multiple holes under diametrical compressive loading, the breaking process of the modelled specimens may occur due to the simultaneous cracks propagation and cracks coalescence phenomena. These results also show that as the hole diameter and the number of the holes increases both the failure stress and the crack initiation stress decreases. The experimental results already exist in the literature are quit agree with the proposed numerical simulation results which validates this simulation procedure.

Experimental and numerical investigation of the effect of sample shapes on point load index

Haeri, Hadi,Sarfarazi, Vahab,Shemirani, Alireza Bagher,Hosseini, Seyed Shahin Techno-Press 2017 Geomechanics & engineering Vol.13 No.6

Tensile strength is considered key properties for characterizing rock material in engineering project. It is determined by direct and indirect methods. Point load test is a useful testing method to estimate the tensile strengths of rocks. In this paper, the effects of rock shape on the point load index of gypsum are investigated by PFC2D simulation. For PFC simulating, initially calibration of PFC was performed with respect to the Brazilian experimental data to ensure the conformity of the simulated numerical models response. In second step, nineteen models with different shape were prepared and tested under point load test. According to the obtained results, as the size of the models increases, the point load strength index increases. It is also found that the shape of particles has no major effect on its tensile strength. Our findings show that the dominant failure pattern for numerical models is breaking the model into two pieces. Also a criterion was rendered numerically for determination of tensile strength of gypsum. The proposed criteria were cross checked with the results of experimental point load test.