Showing 19 results for Habibnejad Korayem
Moharam Habibnejad Korayem, Ali Shafei,
Volume 12, Issue 3 (8-2012)
Abstract
The equation of Motion by Gibbs - Appell formulation has been used the least for deriving the dynamic equations of manipulator robots. So, in this paper a new systematic method for deriving the equation of motion of n - rigid robotic manipulators with revolute - prismatic joints (R - P - J) is considered. The equation of motion for this robotic system is obtained based on (G - A) formulation. All the mathematical operations are done by only 3×3 and 3×1 matrices. Also, all dynamic characteristics of a link are expressed in the same link local coordinate system. Based on the developed formulation, an algorithm is proposed that recursively and systematically derives the equation of motion. Finally, a computational simulation for a manipulator with three (R - P - J) is presented to show the ability of this algorithm in deriving and solving high degree of freedom of robotic system.
Moharam Habibnejad Korayem, Ali Shafei,
Volume 12, Issue 5 (1-2013)
Abstract
The main purpose of this paper is to derive the inverse dynamic equation of motion of n-rigid robotic manipulator that mounted on a mobile platform, systematically. To avoid the Lagrange multipliers associated with the nonholonomic constraints the approach of Gibbs-Appell formulation in recursive form is adopted. For modeling the system completely and precisely the dynamic interactions between the manipulator and the mobile platform as well as both nonholonomic constraints associated with the no-slipping and the no-skidding conditions are also included. In order to reduce the computational complexity, all the mathematical operations are done by only 3×3 and 3×1 matrices. Also, all dynamic characteristics of a link are expressed in the same link local coordinate system. Finally, a computational simulation for a manipulator with five revolute joints that mounted on a mobile platform is presented to show the ability of this algorithm in generating the equation of motion of mobile robotic manipulators with high degree of freedom.
Moharam Habibnejad Korayem, Ali Shafei, Siavash Fathollahi Dehkordi,
Volume 13, Issue 1 (4-2013)
Abstract
The main goal of this paper is to present a mathematical model for inverse dynamic equation of elastic robotic manipulator with revolute-prismatic joints. Due to the fact that there is no limitation on the number of mechanical arms, the proposed model must be extracted based on a systematic and automotive algorithm. Also according to the high computational complexity, the equations should be formed by a recursive formulation. Hence, a recursive and systematic methodology for deriving the equation of motion of elastic robotic arm with revolute-prismatic joints is presented. The inverse dynamic equations for this robotic system are obtained based on Gibbs-Applle formulation. All dynamic expressions of a link are expressed in the same link local coordinate system. Finally, in order to show the ability of this formulation in deriving and solving the equation of motion of such systems, a computational simulation for a flexible single robotic arm with revolute-prismatic joint is presented.
Moharam Habibnejad Korayem, Ali Mohammad Shafei, Mahsa Doosthoseini, Behzad Kadkhodaei,
Volume 14, Issue 1 (4-2014)
Abstract
This paper presents a research into the progress of modeling of N-viscoelastic robotic manipulators. The governing equations of the system is obtained by using Gibbs-Appell (G-A) formulation and Assumed Mode Method (AMM). When the beam is short in length direction, shear deformation is a factor that may have substantial effects on the dynamics of the system. So, in modeling the assumption of Timoshenko Beam Theory (TBT) and its associated mode shapes has been considered. Although considering the effects of damping in continuous systems makes the formulations more complex, two important damping mechanisms, namely, Kelvin-Voigt damping as internal damping and the viscous air damping as external damping have been considered. Finally, to validate the proposed formulation a comparative assessment between the results achieved from experiment and simulation is presented in time domain.
Moharam Habibnejad Korayem, Hesam Khaksar, Rouzbeh Nouhihefz Abad, Moein Taheri,
Volume 14, Issue 14 (Second Special Issue 2015)
Abstract
In this paper we developed and modeled elastic - plastic contact theories for soft spherical nano - bacteria to be applied in manipulation of various micro/nanobio particles based on atomic force microscopy. First, we simulated elastic contact for three types of nano - bacteria: S. epidermidis, S. salivarius and S. aureus, using Hertz contact model and finite element. Comparing simulation results of elastic contact with experimental data showed that considering elastic contact for simulating the contact of nano - bio particles is not appropriate and will yield incorrect results. Therefore, in this research, we tried to develop and simulate Chang elastic - plastic contact theory to be applied in simulation of contact mechanics for application in simulating manipulation. Comparing simulation of Chang contact theory with available experimental data and the results from contact simulation of Chen et al showed that Chang’s complete elastic - plastic theory yields desirable results. Comparing the diagram of contact radius in terms of indentation in Hertz and Chang theories showed that the created contact radius in elastic - plastic state is larger than contact radius in elastic state.
Moharam Habibnejad Korayem, Ali Moahmmad Shafei, Nasibeh Karami, Saeed Rafee Nekoo,
Volume 14, Issue 15 (Third Special Issue 2015)
Abstract
This paper presents the investigation of general formulation and numerical solution of the dynamic load carrying capacity (DLCC) of flexible link manipulator. The proposed method is based on open loop optimal control problem. A two point boundary value problem (TPBVP) is provided, extracted from the Pontryagin's minimum principle. The indirect approach is employed to derive optimality conditions. The system’s dynamics equation of motion is obtained from Gibbs-Appell (G-A) formulation and assumed mode method (AMM). Elastic properties of the links are modeled according to the assumption of Timoshenko beam theory (TBT) and its associated mode shapes. As TBT is more accurate compared with the Euler-Bernoulli beam theory, it is exploited for mathematical modeling of flexible links. The main contribution of the paper is to calculate the maximum allowable load of a flexible link robot while an optimal trajectory is provided. Finally, the result of the simulation and experimental platform are compared for a two-link flexible arm to verify the introduced technique. The efficiency of the proposed method is illustrated by performing some simulation studies on the IUST flexible link manipulator. Simulation and experimental results confirm the validity of the claimed capability for controlling point-to-point motion of the proposed method and its application toward DLCC calculation.
Amin Habibnejad Korayem, Moein Taheri, Moharam Habibnejad Korayem,
Volume 15, Issue 1 (3-2015)
Abstract
Nowadays one of the arguments that have been raised in the world of nanotechnologies is moving or manipulation nanoparticles. This discussion is important because the displacement of nanoparticles can make structurally different than what is currently available. So to achieve this goal, the atomic force microscope probe is used as manipulator. In this way, the use of nanoparticles by pulling or pushing on the surface, are displaced and brought to the desired point. If you apply too much force is needed, Nanoparticle Continued movement (sliding or rolling) after standing atomic force microscopy probes and away from the desired final. On the other hand, if the force is low, so that it can’t overcome the static friction force, Nanoparticles will be no movement. So finding the optimal force is important in nanomanipulation. In this paper, with using nanoparticle dynamic simulation, the governing equations on nanoparticle are derived and simulated during manipulation happen that they can be used to obtain the critical force and time for gold, yeast and platelets nanoparticles, in gaseous, water, alcohol, and plasma environments. By comparing the results obtained in this paper, it is concluded that the movement of particles in different biological environments starts later and by a force of higher magnitude relative to the gaseous medium.
Moharam Habibnejad Korayem, Sepehr Dehghani Ghahnaviyeh, Mehdi Ghasemi, Moein Taheri,
Volume 15, Issue 1 (3-2015)
Abstract
In nanoparticles manipulation with atomic force microscope for modeling exact manipulation dynamics and prevent of damaging nanoparticles, it is necessary to compute critical force. For modeling dynamics and computing critical force that apply to nanoparticles it is necessary to modeling cantilever stiffness and determine sensitive geometrical parameters which are effect cantilever stiffness and critical force. In this paper at first it is investigated on two common different kinds of cantilevers which are V-shaped and dagger cantilevers. For modeling V-shaped cantilever stiffness this cantilever is divided into two parts a triangular head section and two slanted rectangular beams. After that the stiffness of each part is modeled separately and the total stiffness is computed. For modeling dagger cantilever stiffness it is used the same method and cantilever is divided into two parts a triangular head section and a rectangular beam and then the total stiffness is computed. Cantilevers stiffness and critical force in manipulation of biological particles and non-biological particles are very important because of that it is used EFAST sensitivity analyses for selecting suitable cantilever and its parameters. In this paper it has been shown that the dagger-shaped cantilever is more suitable for the manipulation of biological particles.
Moharam Habibnejad Korayem, Saeed Rafee Nako, Naim Yousefi Lademakhi,
Volume 16, Issue 8 (10-2016)
Abstract
Full feedback data is mostly essential in control design. The measurement of the variation of flexible joint robot (FJR) actuators is not easy as the measurement of the changes of FJR links’ angles. The measurement of the states is also affected by noise, and the disturbance in the workspace of the robot is not ignorable. Hence a state observer or a nonlinear estimator is necessary to improve the performance of the dynamic system. The state-dependent Riccati equation (SDRE) is one of the most promising nonlinear optimal control methods for estimating variables of systems. Systematic procedure, simple structure, and incorporating wide range of systems (under observability condition) are some advantages of SDRE method. The majority of nonlinear techniques linearize the model, but the SDRE directly uses the nonlinear state space; it is one of the reasons for its precision and flexibility in design with respect to other methods. The goal of this work is to merge the SDRE controller and estimator simultaneously to reduce the state error of the system in presence of external disturbance and measurement noise. So, first, the controller and the observer formulation has been stated. Then, the procedure has been applied to design and to simulate a 3 DOF robot arm with flexible joints. Next, the process has been tested experimentally using Scout robot and the simulation results have been verified. Finally, the proposed method of this paper has been compared with the optimal sliding mode.
Moharam Habibnejad Korayem, Hasan Aslani Payan, Ahmad Homayooni, Rouzbeh Nouhi Hefzabad,
Volume 16, Issue 9 (11-2016)
Abstract
In this paper, the modeling and simulation of manipulation of carbon nanoparticles have been investigated. The geometry plays a significant role in the dynamic behavior of nanoparticles manipulation and the evaluation of different geometric shapes of nanoparticles in this process is very important. To examine the geometry effects, the manipulation of a different kind of the nano-carbon allotropes has been studied. Furthermore, the manipulation of carbon nanotubes with different diameter has been simulated. For this purpose, the molecular dynamics method has been used to improve our knowledge and understanding about the nanomanipulation processes and dynamics. In the manipulation of carbon allotropes, the results indicated that more spherical allotrope Modes away, the easier manipulation process occurred and the forces on the probe have been reduced; this is due to the curvature of tip and nanoparticle. The results of nanotubes manipulation showed that increasing the diameter of the nanotube causes to increase the force on the probe. The indentation depth was extracted for each nanotube during the manipulation process. The results indicated that the indentation depth increases versus diameter increasing. According to the application of carbon-based structures and nanotubes as the drug carriers in medicine, such this simulation studies can reduce time and cost of experimental projects in this field.
Moharam Habibnejad Korayem, Amin Habibnejad Korayem, Moein Taheri, Saeed Rafee Nekoo,
Volume 16, Issue 11 (1-2017)
Abstract
Nowadays, movement of micro/nano particles has been attracted considerable attention to manufacturing different devices in micro/nano scale and medical and biological applications. Atomic Force Microscope Probe is widely being used for precise small scale movements. During nano-manipulation, micro/nano particles can be moved to a desired destination with high accuracy using Atomic Force Microscope while in contact mode with precise probe control. In this article, by selecting a proper amount of torque applied to the probe tip, deviation from the center and movement of probe have been investigated to assure the contact between the probe and micro/nano particle. Different liquid environments (water, alcohol, and plasma) with different micro/nano particles including biological and non-biological have been used for this investigation. In addition, using sliding mode control, Atomic Force Microscope Probe was used in different environments such as water, alcohol, and plasma. Obtained results showed that the time needed to control different micro/nano particles in plasma was shorter than that of in water; also the time needed in water was shorter than that of in alcohol.
Moharam Habibnejad Korayem, Mohsen Estaji, Ahmad Homayooni,
Volume 17, Issue 3 (5-2017)
Abstract
To investigate the effects of drugs on viruses, interactions between proteins and inserting desirable genetic changes on DNA, precise study of biological cells is a necessary demand for nowadays. In this way, exploring mechanical properties of these particles and their mechanical behavior in different situations is needed; manipulation of bioparticles in nano scale is an important process for investigating nanoparticles behavior; because the amount of exerted force, deformation and investigating the damage possibility can provide useful information. In this paper, a molecular dynamics modeling of bioparticles nanomanipulation based on AFM has been done. Bioparticles include virus, protein and ssDNA. The main goal of this study is investigating the substrate effect on exerted force on the bioparticles and exploring damage possibility. Three types of substrates have been used, including silicon, graphene sheet and golden substrate. Widespread usage and low level interactions with other materials are the reasons of choosing these substrates. Results show that on gold substrate, the maximum manipulation force occurs and damage possibility is high. Also on graphene substrate manipulation force and deformation of particle are more than the silicon substrate.
Ehsan Hosseini, Asghar Habibnejad Korayem,
Volume 17, Issue 11 (1-2018)
Abstract
The performance of cement paste as the reinforcing element in walls and transferring pipes in oil wells is of considerable importance. It is known that the mechanical properties of hardened cement can be altered under high pressure and temperature of oil well; the gravity of this change has an important role in the stability and service life of the well. This paper investigates the mechanical properties of hardened cement and GO-reinforced cementitious composites at molecular scale under the surrounding conditions similar to those of an oil well using molecular dynamics method. Results in nano scale revealed a decreasing pattern in mechanical properties of calcium silicate hydrate with increasing temperature of the oil well. However, pressure increment in the conventional range of the oil wells did not show any noticeable effect on hardened cement properties. Using GO proved to be beneficial to the calcium silicate hydrate, drastically improving its mechanical properties. Results concluded that GO nanoparticle can act as reinforcing elements in the cementitious matrix. The outcome of this research can provide more insights on the application of GO in the oil well cementitious matrix, in an ideal molecular conditions and thus passed over GO agglomeration, non-homogenous dispersion and impurities in the macro scale.
Volume 18, Issue 2 (7-2018)
Abstract
In the last decades, the development of nanotechnology has been rising and nanomaterials have been widely used in combination with many traditional materials. The prominent chemical and physical properties of nanomaterials enable them to play an important role in various applications such as modifying the structure of materials, improving the properties of composites, and manufacturing new multifunctional products. The building industry has not been exempted from this rule. Many studies have been carried out on the effect of nanoparticles on concrete performance and most of them demonstrated the improvement of concrete properties. There are a lot of studies on the effect of nanoclay on cement composites. However, there are little researches on the halloysite nanotube (HNT) effect, as subcategories of nanoclay, on the properties of cement composites. Halloysites are a kind of mineral clay which are often produced by air-induced erosion or by thermal transformation of ultramafic rocks, volcanic glasses, and pumice. They are chemically similar to kaolinite but, unit layers in halloysites are separated by a monolayer of water molecules. In general, halloysites have different shapes and exist in the plate, spherical, and tubular forms. The tubular structure is the dominant form of halloysite in nature. Chemically, the outer surface of the HNTs has properties similar to SiO2 while the inner cylinder core is related to Al2O3. Due to the tubular geometry, HNTs like carbon nanotubes could be classified as one-dimensional nanoparticles. Halloysite can grow into long multi-walled tubules, which morphologically resemble to multi-walled carbon nanotubes. In terms of dimensional characteristics, HNTs have an external diameter of about 30 to 190 nm, an inner diameter of about 10 to 100 nm and a length between 3 to 30 µm. Halloysite characteristics could be sum up as high length to diameter (L/D) ratio, high specific surface, large pore volume, low density in surface, and pozzolanic properties. Mechanical properties of HNTs could make them an ideal reinforcing additive to improve the mechanical properties of cement composites. In addition, due to the nano scale size of HNTs, they can play the role of filler and make a denser and stronger microstructure. Therefore, in this research, the effect of HNTs on the performance of cement mortar was evaluated and the workability and permeability of mortar samples containing 3% halloysite nanotubes were presented. The results indicated an increase of more than 28% of electrical resistance, a decrease of approximately 26% of water absorption rate, 23% reduction in water repellent, a decrease in the workability, and an increment in the rate of hydration of cement mortar due to the incorporation of 3% halloysite nanotube. These results indicate that halloysite nanotubes can be used as an appropriate nanoparticle to improve the properties of cementitious composites. The pozzolanic properties of HNTs enable them to decrease the permeability of cementitious matrices. Silicate of HNTs react with calcium ions of hydrated cement and increase the calcium silicate hydrate gel. This could lead to an enhancement in the durability of cementitious matrices. This paper can provide more insights on the application of nanoparticles with cementitious composites.
Volume 18, Issue 2 (7-2018)
Abstract
The surface protection materials have effective results to prevent concretes from corrosion. Reinforced concrete structures have the potential to be very durable and capable of withstanding a variety of adverse environmental conditions. However, failure in the structures does still occur as a result of premature reinforcement corrosion. There are corrosion protection systems and methods to extend the long-term durability of steel reinforced concrete. For example, application of zinc rich or cement based protective primers to reinforcement, surface protection systems of concrete, Cathodic protection using sacrificial zinc anodes, and conductive anode overlays within an impressed current cathodic protection system. In general, the main duty of surface protection is controlling both physical and chemical damages to concrete in order of preventing or reducing from steel bar corrosion and creating a coat of safekeeping against penetration of chloride ion, carbon dioxide, oxygen, and most importantly water. According to European Norm, three types of protection materials are existed based on function mechanism. Coating, hydrophobic impregnation, and impregnation materials are these systems, and two types of them used in this study. In this study, two materials of surface protection have used on the surface of three types of concrete. Two types of self compacting concrete with different w/c ratio and one ordinary concrete with similar mixture design to one of those SCC were used for estimating of durability of concrete. Epoxy resin and silane-siloxane were two types of surface treatment materials used in this study. SEM analysis and water contact angle test were done to study the function mechanism of surface protection material. The other tests are water vapor permeability, corrosion potential, and corrosion intensity. Some of the results of this study is that using this materials have effective impact on declining of corrosion potential, decreasing of corrosion intensity, and after all increasing durability of concrete. As shown in this paper, all of the protected samples except one, until 49th week did not have a sign of corrosion active phase. Increasing in ratio of W/C in the substrate makes weakness in function of this materials. In the other hand, results of half-cell potential of unprotected samples show SCC2 with 0.55 w/c ratio and NC with 0.45 w/c ratio shift from passive to active state in first days and SCC1 with 0.45 w/c ratio attained its active state in 5 weeks. However once corrosion has started in SCC2-EP in 8 weeks, corrosion rate was lower than unprotected samples. In the presence of surface protection systems, due to their ability to reduce water ingress in concrete, the corrosion intensity in all samples were lower than 0.23 µA/ cm^2. The results of water vapor permeability test showed that epoxy can decrease the water vapor permeability up to 65% instead of unprotected concrete. In the meantime, silane-siloxane doesn't have effective results in concrete breathability and have a similar performance to unprotected concrete. The results show using SCC don't have much different effect on quality of the materials function instead of ordinary concrete. Another important result is that protection materials which don't let to enough evaporate, are cause of much corrosion in compare of those that let concrete to breath.
A. Motahari, H. Zohoor, M. Habibnejad Korayem ,
Volume 20, Issue 3 (March 2020)
Abstract
In this paper, the design and construction of a new binary pneumatic actuated hyper-redundant manipulator is presented. The discretely actuated hyper-redundant manipulators have advantages such as wide workspace, the ability of obstacle avoidance and simple control. Despite of these advantages, few prototypes have been made so far, which each of them has some defects. These defects are small movement range, fairly high cost, and accelerated and impulsive motion. To solve these problems, the 3-revolute prismatic spherical parallel mechanisms (3-RPS) are used as modules in this paper. So the cost is reduced due to the lower number of legs. Also, the motion range has been increased by replacing the spherical joints with universal joints. The movements of the manipulator have been effectively more uniform and softer by using flow control valves on cylinders. Finally, several tests are conducted to determine how the manipulator moves and the results are presented.
Volume 21, Issue 1 (3-2021)
Abstract
Conventional construction cementitious composites typically contains cement, fine and gravel aggregate and additive in a specific ratio along with water. It is extensively used to bind the structural elements together like the bricks, stones, and concrete blocks, or end connection of the column and beam, and to develop a sufficient bond with the substrate as a repair cementitious composite, due to its several advantages, such as low cost, appropriate compressive strength, and easy access. However, some weaknesses of the cementitious mortar influence its performance under different conditions. For example, low tensile strength, brittle behavior, unacceptable performance against shrinkage cracks, and lack of resistance against stress concentration are some of these critical properties of the mortar, if not modified, the structures will be deteriorated in a short time. These deficiencies emerge from extravagance water, bleeding, plastic settlement, shrinkage stress and strain concentrations due to external limitations. When loads are applied and further increased, type of cracks grow and reach a critical condition, and catastrophic failure is precipitated. In this situation, the mortar will be exposed to severe damaging factors such as premature saturation, disadvantage of freeze-thaw, scaling, and corrosion of steel. In recent years, researchers in the field of concrete technology have focused on the using of a variety of fibers such as carbon, steel, glass, polypropylene and basalt fiber into the cementitious composites to improve their mechanical properties (especially their ductility behavior) and to some extent their durability. Accordingly, in the present study, the hybrid effect of different percentages of basalt and polypropylene fibers on the workability, mechanical behavior and durability properties of cementitious mortar was investigated. Polypropylene fibers are known in the field of reinforced concrete, but basalt fibers are a new potential additive in this field. In recent decades, researchers have studied more about basalt fibers because of their potential reinforcement properties in composite materials. The basalt fibers are an appropriate replacement for another fibers, including glass, steel, and carbon fibers in plenty of applications due to their excellent properties such as high mechanical properties specially tensile strength and flexural strength, good resistance to low and high temperature, low cost, durability, vibration resistance, high elasticity modules, great failure strain, acceptable persistence to chemical assault, impact load and fire with less toxic materials. Samples containing a hybrid composition of 0.05 and 0.125 percent (weight percent of total cement and aggregate) of the basalt and polypropylene fibers have been used in order to evaluate the effect of fibers so that a total of 4 types of mixed designs containing hybrids of basalt and polypropylene fibers were made and its results have been compared with a control sample. As expected, after analyzing the results, the fibers had no significant effect on the compressive strength of the cementitious composite, while the results of this study reported a favorable and remarkable performance of these fibers in increasing flexural and splitting tensile strength, as well as the water absorption of cementitious mortar is favorably decreased by the fiber. The sample containing 0.125% basalt and polypropylene fibers increased flexural and splitting tensile strengths by 28 and 23%, respectively. Also, the sample containing 0.125% basalt fiber and 0.05% polypropylene fibers resulted in 9.3% increase in compressive strength, 24% decrease in sorptivity and 15% water absorption. The results of the current study have shown that the simultaneous use of basalt and polypropylene fibers can improve significantly the mechanical behavior and durability properties of cementitious mortar, whereas according to the previous studies if each of these fibers is used separately, such a desirable result will not be obtained.
Volume 22, Issue 6 (11-2022)
Abstract
Cementitious composites are mainly used in the construction industry due to their good characteristics such as low cost, acceptable compressive strength, and easy access. However, there are many weaknesses in these materials, including low tensile strength, brittle behavior, and unacceptable durability (service life), which need to be improved to achieve more sustainable constructions. Nowadays, the using of nanotechnology have been growing and nanomaterials have been widely used in compound with a multitude of conventional materials. The outstanding chemical and physical properties of nanomaterials enable them to play a key role in various applications, such as modifying the material structure, ameliorating the properties of the material, and manufacturing modern multifunctional products. Recent advances in nanotechnology have led to produce nano-sized particles that can improve the durability performance of construction materials. Nanoparticles such as nano-silica, nano-Fe2O3, nano-clay, carbon nanotube (CNT), nano-Al2O3, nano-TiO2, and graphene oxide have been used to enhance the properties of cementitious composites. The performance of halloysite nanotube on the characteristics of cementitious composites has been studied less than other nanomaterials. Although the positive effects of nanomaterials such as halloysite nanotube (HNT) on the properties of cementitious composites have been proven, the very important issue of the correct and proper dispersion of nanomaterials in the cementitious environment has not been studied acceptably. The high surface energy and interparticle forces, including van der Waals, hydrogen bonding, and electrostatic interactions, make the nanomaterials highly susceptible to agglomeration. The aggregates of nanomaterials not only decrease their benefit but also act as potential weak spots in cementitious composites that can cause stress concentration, therewith diminishing the mechanical properties of cementitious composites. In this regard, the current paper investigated the effective factors on the agglomeration of halloysite nanotube (HNT) in the cementitious alkaline environment. Finally, this paper presented an approach for solving the problem of HNT agglomeration. Results showed that Ca2+, K+, and Na+ ions as alkaline agents of cement environment are the main factors to provide a state for HNT agglomeration. Among them, Ca2+ has more effect in agglomeration of halloysite nanotube due to the bridging effect between halloysite particles. From the results, the dispersion of HNT made better with increasing the alkalinity of cement environment until pH=11, while after this pH, the agglomeration of HNT started and the intense of agglomeration raised with the increase of pH, where it reached a maximum value at pH=13.5. Common approaches to nanoparticle dispersion are through physical methods (e.g., ultrasonic, high shear mixing, ball milling, etc.) and chemical methods (e.g., chemical modification of nanoparticle surfaces, use of dispersants such as surfactants, etc.). For the cementitious systems, a combination of ultrasonic and surfactant is mostly suggested. In this research, the effect of various surfactants on overcoming the agglomeration of halloysite nanotube in the cementitious environment was studied. The results indicated that the Polycarboxylate-based surfactant has better performance on improving the dispersion of HNT compared to that of other surfactants. Furthermore, incorporation of 3 wt% HNT enhanced the compressive, flexural and sorptivity of plain mortar up to 26, 22, and approximately 28%, respectively. The outcomes of the current paper display the fact that it is necessary to have special attention on the subject of the proper dispersion of nanomaterials in the cementitious environment for achieving the maximum efficiency of nanomaterials.
Volume 24, Issue 1 (4-2024)
Abstract
Portland cement is a crucial mineral chemical that is globally produced in large quantities. It has been reported that in 2011, approximately 3.6 billion tons of Portland cement were produced, and its demand continues to grow. However, this industry's expansion has resulted in increased environmental risks. Therefore, it is important to conduct research to enhance the sustainability of this product. The utilization of nanomaterials in cement and concrete materials has received significant attention in recent years. Employing nanotechnology to modify cement-based materials can significantly enhance the efficacy of this inorganic binder. Primarily, nanoparticles possess the capability to fill the porosity within the cement structure and exhibit pozzolanic properties that reinforce concrete. Additionally, the high specific surface area of nanomaterials facilitates increased reactivity at the nanoscale, thereby enhancing cement hydration and subsequently improving its mechanical properties.
Despite cement and concrete being known for their strength, they are also inherently brittle, which hinders their mechanical performance. In recent years, various nanomaterials have been utilized to address this weakness due to their high specific surface area and strengthening capability in different matrices, including cement. This study aims to evaluate the impact of incorporating a binary nanocomposite of titanium dioxide nanoparticles and graphene oxide to enhance the mechanical properties of the Portland cement.
For hybridization, electrostatic adsorption mechanism was used to connect TiO2 nanoparticles on graphene sheets and synthesize TiO2–GO nanocomposite. In this work, TiO2 powder was processed in nitric acid to accumulate protons in the form of H+ functional group on the surface of nanoparticles and make it positively charged. On the other hand, chemically produced GO suspension has an intrinsic negative charge due to the formation and presence of hydroxyl groups (OH–) on its surface. Therefore, the combination of these two charged substances with the opposite charge under several hours of stirring causes them to be connected and attracted to each other through electrostatics.
Cement paste with a water-to-cement ratio of 0.38 was prepared and hydrated for different durations (7, 14, and 28 days). Nanostructured reinforcement with a fixed concentration of 0.05 wt.% GO and varying concentrations of 0.5, 1, and 1.5 wt.% TiO2 were added to the cement. The resulting cement paste samples were analyzed for compressive strength, porosity, and microstructure. The study revealed that the sample containing 1 wt.% TiO2–0.05 wt.% GO exhibited the best mechanical behavior, with a 55% higher compressive strength compared to the unreinforced cement sample. Furthermore, this sample had the lowest porosity. Microstructural analyses indicated that the reinforced sample had a reduced porosity, improved hydration acceleration, and enhanced overall integrity of the structure, leading to the significant improvements in its mechanical properties.