Journal of Engineering Geology

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The main objective of this research is to provide information about the effects of mineralogical characteristics of aggregates on concrete properties. Crushed aggregates were selected with different petrographics from different resources. Aggregates such as, Marble, Dolomite, Tuff, Granite, Genasis, Basalt, Andesite, Lumashele, Sand Stone and Diorite which have different chemical, physical and mechanical properties were used in this study. The results of the study showed that physical and mechanical properties of minerals control properties of concrete and undesirable properties of concrete influenced with which of mineral. Also, the results indicated that aggregates with flaky and elongated minerals subjected to weathering have a great effect on undesirable properties of concretes. The highest uniaxial compressive strength (33 MPa) at 28 curing days was measured in the specimens prepared with dolomite aggregates while the lowest strength (13 MPa) was measured in the specimen prepared with lumashele aggregates at the same age.

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 In this research, prediction of concrete strength containing different aggregates using Non-destructive (Ultrasonic) testing through Artificial Neural Networks was carried out. For this purpose, aggregates with different properties were selected from the quarries, and then their destructive and nondestructive properties were obtained in laboratory. The significance of this research, using different aggregates with physical, mechanical and chemical properties also used two different test methods, such as Non-destructive static and dynamic testing, which are respectively uniaxial compressive strength and compressive wave velocity. Thus, this model includes various types of samples and the prediction model includes static and dynamic tests. The results showed that the use of artificial neural networks not only increases the accuracy, but also it reduces costs and time.

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The use of heavy concrete as a protective shield against high-energy gamma rays is very common. It is also an effective, versatile and economical material. The heavy concrete production can use lead slag as raw materials. The use of lead slag in the production of concrete blocks saves natural resources and reduces the environmental problems caused by the accumulation of industrial waste. However, concrete production, due to the presence of heavy metals with high atomic number can be used as an effective shield against gamma radiation. This study examines the use of lead slag produced in the battery recycling process as concrete aggregates. For this purpose, strength and gamma-ray attenuation coefficient for concrete samples prepared by replacing 40 to 60 percent lead slag instead of natural aggregate. The effect of 1 to 5 percent lead powder in setting time of concrete was measured. The results showed that by increasing the amount of lead slag, density, mechanical strength and gamma-ray attenuation coefficient for concrete samples increased significantly, but lead powder delays setting time of cement paste. In general, appropriate lead slag concrete construction with minimal thickness, reduce the cost of protection and provides the highest level of attenuation

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Introduction
Pressure tunnels in hydroelectric plants are used to convey water to powerhouses. These tunnels are the sources of seepage flow to the rock formation, thus, during the water filling, they will have a low resistance to seepage and, by increasing the internal water pressure of the tunnel, the inflow force will be transferred to the rock mass. In these conditions, the cracks, pores and all other elements of the rock mass are affected by the seepage forces in all directions. This hydro-mechanical interaction affects changing the stresses and displacements of the rock mass around the tunnel and causes modifications in the permeability of rock elements during the water filling. Therefore, changes in stress distribution lead to alterations in the permeability coefficient and redistribution of the seepage field. In these conditions, since the analytical solution of the problem is not possible, the numerical analysis based on the finite element method has been used in this study.
Material and methods
In this approach, the rock mass is considered as an equivalent continuum in which the effects of discontinuities are taken into account in its material behavior. High-pressure tunnels under internal water pressure requires reinforced concrete lining to prevent hydro-fracturing. The ABAQUS software is capable of analyzing such as seepage from the tunnel, modeling of the steel bars in concrete, and taking into account hydro-mechanical interaction. Thus, the software is used for numerical analysis.
The pressure tunnel of the Gotvand dam and hydroelectric power plant (HPP) scheme is taken as a case study for the numerical simulation. Pressure tunnel of the Gotvand dam located in the southwest of Iran is taken as a case study for the numerical simulation. Among behavioral models in the software, Mohr-Coulomb failure criterion is considered to describe the rock mass, but the principle of effective stress determines the rock mass behavior. Since the concrete lining of the pressure tunnel will undergo two mechanisms of the cracking due to tension and the crushing due to compression, concrete damaged plasticity model is used to predict the response of the concrete elements. The evolution of the yield surface of the concrete lining is also controlled with tensile and compressive equivalent plastic strains, correspondingly.
In this study, the hydro-mechanical interaction is implemented based on the analysis of the pore fluid/deformation analysis, and the direct-coupled method is used to solve the governing equations of the problem. To verify the proposed model, the elastic behavior of the media is simulated to compare the numerical and the analytical solutions and good agreement is obtained. The numerical analyses are carried out the hydro-mechanical interaction with constant permeability coefficient. When cracks develop in the concrete lining at high water pressure, the properties of the concrete lining change and as a result, the stress dependent permeability of the lining and surrounding rock mass in pressure tunnels should be considered. The coefficient of permeability controls the rate of seepage flow in porous and fractured media. Although permeability represents an original property of the porous media, it can be modified when subjected to the stress variations. Instead of changing aperture, the change in the void space or volume is the typical consequence that results to change the permeability coefficient. In order to bring the model closer to the real conditions and in the validation of the new model, the influence of the permeability coefficient variations of the concrete and rock mass on the deformations and stresses of the model has been added to nonlinear analysis by USDFLD code. Increasing the water head in the tunnel during water filling is also considered with the combination of DLOAD and DISP codes in the model.
Results and discussion
Since the lining and rock mass have nonlinear properties and complex behavior, for verification of the model in ABAQUS software, the model is simulated with homogeneous, isotropic and elastic behavior. The results of seepage flow on the interface of the concrete lining and rock mass obtained by analytical and numerical solutions indicate that there is a ±5 % difference between them. Then, the results of the elastic behavior of the model show a good agreement with the results of analytical solutions. Therefore, this numerical model has been employed for the nonlinear analyses.
Finally, the optimal thickness of the concrete lining with the appropriate arrangement of the reinforcement in the reinforced concrete linings is utilized to minimize water losses from the tunnel based on the new model. Thus, the results of the analysis with the aim of reducing the water losses from the tunnel indicate that the suitable arrangement of the steel bars in the concrete lining leads to the distribution of micro cracks in the lining, and the reinforcement stress stays at a lower value with high internal water pressure. Based on the new numerical model, it is suggested that the lining should be designed with the thickness of 40 cm and the reinforcement with the diameter of 16 mm and the spacing of 20 cm.
 Conclusion
The results of the numerical model indicate that to control the seepage outflow from concrete-lined pressure tunnels, the thickness of the lining and the suitable arrangement of the steel bars in the concrete lining play a significant role in preventing excessive seepage from the tunnel./files/site1/files/124/3dadashi%DA%86%DA%A9%DB%8C%D8%AF%D9%87.pdf

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Introduction
Nanostructured materials have gained increasing attention of industry and the academia in recent decades, due to their prominent behaviors. In this regard, the building industry is considered to be the major consumer of nanostructured materials in terms of its needs, including strength, resistance, durability and high performance. Studies on nanoscale behavior of cement and concrete to develop new building materials and their applications are of high importance. A typical method for the development of high performance concrete (HPC) often contains various parameters, including the mix of conventional concrete with different types of additives. Nano-Calcium carbonate (Nano-Precipitated Calcium Carbonate) is a nano-sized filler which is used in this research. The results indicate that the higher the optimal content of nano-precipitated calcium carbonate powder, the higher the initial heat of the roller-compacted concrete; also, the resistance of the samples significantly increases over time. However, the level of permeability of roller-compacted concrete decreases by optimal increase of nano-calcium carbonate powder due to its fine grains, filling properties, and high specific level. The results of this study show that the adequate use of this material improves some properties of roller-compacted concrete.
Material and methods
In this study, the content of Nano-calcium carbonate used was selected at 0, 1, 2, 3 and 4 percent replacing a volume of cement consumed in concrete. Type II Portland cement, crushed fluvial sand, and crushed coarse aggregates with a maximum size of 19 mm were used. The aggregates’ grading range in the mix has been selected according to the ACI325-10R. The chemical formula of Nano-calcium carbonate powder is CaCo₃ and the average particle size is between 15-40 nm
According to the roller-compacted concrete specifications, 5 mix designs have been used with different proportions of stone materials in preparing of concrete. The samples were made on a vibrating table and in the cylindrical molds of 15 × 30 cm according to ASTM C1176 standard.
By increasing the cement grade, the slope of the Vebe curve increases, which means an increase in speed and reduction in efficiency over time in higher grades. Increasing the cement grade from 275 to 300 kg/m³ leads to increased Vebe time. In other words, it can be said that the efficiency is reduced at a lower rate in lower grades of new roller-compacted concrete mix. The Vebe time of the roller-compacted concrete pavement should be between 30-40 s to achieve optimal efficiency. According to the results of Vebe time, the efficiency of the roller-compacted concrete with the grade of 300 kg/m³ has a better functionality than other mixtures and lasted more than others in the 30 to 40 second range. Accordingly, concrete with a grade of 300 kg/m³, is the compressive strength according to this design.
Determining the compressive strength of cylindrical concrete samples of different ages is done according to the ASTM C39/C39M standard. For permeability test, the BS EN 12390-8: 2009 was used in which the sample should be put under pressure of  (0.5±)5 for 72 hours immediately after molding. Determining the tensile strength of concrete cylindrical samples at different ages is done according to the ASTM C496 standard. The peak is obtained using the XRD analysis of the crystallite size by determining the width of the peaks. In interpreting the XRD data, a list of peak resolution and their intensities is observed. To determine the elemental composition of materials, a non-destructive analytical technique is used by X-ray which is so-called XRF (X-ray fluorescence). A scanning electron microscope is a powerful magnification tool and is used to distinguish elements.
Results and discussion
The results indicate that the increased Vebe time occurs by an increase in the percentage of nano-calcium carbonate. In terms of the compressive strength of cylindrical roller-compacted concrete samples, 2% of nano-calcium carbonate at the ages of 7, 28, and 90 days has been effective in increasing compressive strength in higher ages. Such that, at the ages of 28 and 90 days, it is increased by 12% and 15 % compared to the control sample, respectively. The nano content increases over 15% causes decreased compressive strength and thus had negative effects on the rheological properties of the roller-compacted concrete. In terms of tensile strength of the cylindrical roller-compacted concrete samples, 2% of nano-calcium carbonate at the ages of 7, 28 and 90 days has been effective in increasing compressive strength in higher ages, such that at the ages of 7, 28 and 90 days, it has been increased by 25%, 30% and 30 % compared to the control sample, respectively. However, it can also be concluded that the excessive increase has partly reduced the tensile strength.
The variation of the permeability coefficient is a function of concrete porosity and water penetration in the roller-compacted concrete. Also, there are significant changes in the concrete permeability coefficient by adding different percentages of nano-calcium carbonate to concrete.
Adding nano-calcium carbonate up to 2% of cement weight to the roller-compacted concrete reduces the permeability coefficient of the roller-compacted concrete. One of the reasons for this phenomenon is capillary interstice filling in the roller-compacted concrete. Moreover, the nano-calcium carbonate increase of over 2% of cement weight raises the permeability of the roller-compacted concrete.
Adding 4% of nano-calcium carbonate to the roller-compacted concrete pattern increases the intensity of the peaks in the XRD test. Given that the average crystallite size is obtained from full width at half height of the peaks, by increasing the peaks’ intensity and their width at half height of the peaks, we get smaller crystallite size. Also, by adding 4% of nano-calcium carbonate, the widths of the peaks are increased, which means smaller crystals and increased crystallite inner tension.
Conclusion
Nano-calcium carbonate, due to its special features, including a high specific surface area, has a good performance in improving the mechanical properties and durability of the roller-compacted concrete, if it is used at a certain and optimal amount. The roller-compacted concrete with the grade of 300 kg / m3 has better functionality than other mixtures, and lasted more in the 30 to 40 second range.
The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest compressive strength at the age of 7 days and shows 4% increase in resistance compared to a control sample at the age of 7 days. The mix design containing 2% nano-calcium carbonate has the highest compressive strength at the age of 28 days and shows 12% increase in resistance compared to a control sample at this age and improved the compressive strength. The mix design containing 2% nano-calcium carbonate has the highest compressive strength at the age of 90 days and shows 15% increase in resistance compared to a control sample at this age. The mix design including 3% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 7 days, and shows 25% increase in resistance compared to a control sample at the same age. The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 28 days and shows 30% increase in resistance compared to a control sample at the same age. The mix design containing 2% of nano-calcium carbonate replacing cement, has the highest tensile strength at the age of 90 days and shows 30% increase in resistance compared to a control sample at the same age. ./files/site1/files/131/3Extended_Abstract.pdf
 

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Introduction
Concrete faced rockfill dams have been considered in recent years more than other types of dams due to their low dependency on the bed and the shape of the valley, as well as the simpler construction technology. In this regard, rockfill dams are a suitable substitute for embankment dams because of higher stability of the body and the availability of rock aggregates. On the other hand, because the permeability of rock aggregates is much higher than other materials, different methods are used to seal these types of dams. One of these methods is the use of non-impermeable concrete facing in the upstream of these dams. This particular type of gravel dams is called Concrete-Faced Rockfill Dams (CRFD). In this study, a contact element with a definition of elastic-plastic failure in the modeling process is proposed to simulate the surface separation and re-contact of the concrete face with the rockfill surface of the dam.
Method
In this paper, behavior of a concrete faced rockfill dam under earthquake loads is investigated. For this purpose, near-field earthquake records with focal depth lower than 15 km (for example Tabas earthquake 1978, M=7.4, and San Fernando earthquake 1970, M=6.6) are used. Moreover, to study the dam behavior under dynamic loads, interaction between concrete face and rockfill part of the dam is investigated and finally, some parameters including displacement, absorbed energy and base shear are evaluated. So, finite element method and Abaqus software is used for the study. Verification of the models is carried out using the results of previous researches by conducting modal analysis and determining natural vibration period. Then, the interaction between the concrete face and rockfill part as well as the effect of water level changes in stability of dam under dynamic load is investigated. Concrete behavior is simulated using concrete damaged plasticity. Therefore, concrete density, compressive strength and tensile strength and elasticity modulus are 2350 kg/m³, 25 MPa, 3 MPa and 29 GPa, respectively. Poisson’s ratio is assumed to be 0.2. Furthermore, 4-node shell elements are used to simulate concrete face and Drucker-Prager constitutive model is used to define rockfill material behavior.
The density and Poisson’s ratio for 2B, 3C and 3B layers are 2150 kg/m³ and 0.35, respectively. The shear modulus values for these layers are respectively 8.93, 2.89, and 3.85 GPa. In order to perform the simulation, the part of the dam structure beside the bed rock and the surrounding rock is considered as fixed bearing, and only the rockfill part and concrete face of the dam is simulated. Based on this assumption that the bed is rigid, there is no need to consider the dam foundation. This method is frequently used in literature review.
All the surfaces of the dam and bed rock are considered as fixed bearing to simulate the real condition where the dam is attached to bed rock and the surrounding rock. The interaction between dam layers is defined as tie. For defining the interaction between rockfill body and concrete face, tangential and normal contacts are defined using penalty method with friction coefficient equal to 0.5. In the next step, the model is meshed using 4-node shell elements for concrete face, 8-node brick and 4-node pyramid solid elements for rockfill body. Rayleigh damping is used to simulate the structure damping. The effective length of the dam reservoir has been determined by conducting several analyzes, so that the minimum required length for reservoir is reached in order to decrease the number of elements of the model.
Results and discussion
1. Interaction between concrete face and rockfill body
The results show that the increase of friction coefficient between concrete face and rockfill part from 0.5 to 0.7 has not affect the displacement of dam crown along the earthquake direction. However, when the concrete face is fixed to the rockfill part, significant changes are induced in dam crown displacement time history. In all cases, the deflection due to the dam weight is increased when the concrete face is attached to the rockfill body. The reason can be attributed to the tied interaction between these layers which results in similar deflection of concrete face with rockfill body and higher deflection of concrete dam crown. However, after the application of earthquake load, the displacement of the dam crown decreased in both analyses when tie interaction is defined between concrete face and rockfill body. In this study, due to the very high volume of analysis and its timeliness, it was not possible to examine the dam behavior in the free vibration regime, and therefore, it is not possible to assume the last displacement values at the end of analyses as the permanent displacement of dam. Figure 1 shows the relative displacement of the dam for the two selected earthquakes with a friction coefficient equal to 0.5 between the concrete face and the gravel body. According to Figure 1, the maximum displacement induced by the earthquake is related to Tabas and then, San Francisco earthquake. Furthermore, the high energy content of the Tabas record has been more effective in inducing greater displacement than the other record.
 
Figure 1. Lateral displacement of dam crown relative to the dam base for the selected earthquakes; Tabas and San Fernando.
The results also indicate that when the friction coefficient between concrete face and rockfill body is 0.5, the lowest damage occurs in the dam compared to that happens when friction coefficient is 0.7 or when the surfaces are tied. When the tied surfaces are used, the most damages takes place in concrete face, since all rockfill body displacement transmits to concrete face which results in much more concrete damages compared to the other interaction cases.
2. Effect of water level in reservoir on dam behavior
In this section, the effect of water level on seismic behavior of dam is investigated. For this purpose, the dam reservoir is analyzed in three cases including empty, half full and full (90% of dam height). Each study cases are examined under San Fernando and Tabas earthquakes. Figure 2 shows the relative displacement of dam crown in the three water level case for San Fernando and Tabas earthquakes.
 
Figure 2. Relative displacement of dam crown in three water level cases of empty, half and full for (a) Tabas and (b) San Fernando earthquakes
According to Figure 2, for both earthquakes, the dam crown displacement along the earthquake direction is significantly increased by increasing the water level, so that the maximum displacement in full case is 50% higher than empty case.
Conclusion
In this study, using the finite element method and simulation by Abaqus, the seismic behavior of concrete face rockfill dams has been investigated. For this purpose, the verification is firstly carried out using previous research results in literature. In the next step, nonlinear dynamical analysis is carried out, taking into account large displacements for the models under the earthquake record acceleration. The results illustrate that increasing the friction coefficient between the concrete face and the rockfill body from 0.5 to 0.7 has no significant effect on the displacement of the dam crown under earthquake load. Moreover, by using tie interaction between the concrete layer and the rockfill body, there is a substantial difference in the history of the relative displacement of the dam, and the displacement of the dam due to its weight has been increased. Furthermore, the results of this study exhibit that, with increasing the water level in dam reservoir, the deformation of the crown of the dam along the earthquake application direction has had a relatively significant increase, such that in the full state, the maximum displacement is increased by about 50% compared to that of the empty case. This is while the most damage of concrete is observed in the case when half height of dam in filled by water. Due to the more destructive power of near-field earthquakes and their impact nature, only near-fault earthquakes have been used in this research. Therefore, the results of this study are valid only for the behavior of dam under near-field earthquakes.
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