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Research subject: This study demonstrates a synthetic strategy for the preparation of porous SiO₂ for adsorption applications using natural and waste materials from rice husks which are functionalized with polymer dendrimer molecules and surface amino groups as the source of biosilica and were investigated to remove divalent cadmium ions from aqueous solutions.
Research approach: Porous silica nanoparticles with a mean diameter of 45 nm were successfully fabricated from rice husk (RH) biomass via a multistep method. During the first step, sodium silicate is extracted from rice husks. Then, cetyltrimethylammonium bromide, HCl, and acetic acid were added to the sodium silicate solution, and the resulting mixture was sonicated. After the hydrothermal reaction, the collected samples were calcinated to obtain silica nanoparticles. These synthetic nanoparticles were identified using various techniques such as Fourier-transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, field emission scanning electron microscopy, nitrogen adsorption-desorption analysis and dynamic light scattering analysis. Then, the adsorption kinetics and the effects of synthetic nanoadsorbents dosage on the removal of divalent cadmium ions were investigated. The effect of contact time on cadmium adsorption and recyclability of adsorbent was also investigated.
Main results: The results show that there is no significant reduction in the performance and activity of this nanosorbent in the adsorption of metal ions after 6 times of recycling and reuse. The excellent performance of this nanosorbent in the removal of metal ions is due to its high porosity, active surface amine groups and high surface-to-volume ratio.

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Abstract:Self-consolidating concrete (SCC) has been used increasingly over the last two decades, especially in the pre-cast concrete industry because of its ability to consolidate without vibration even in congested areas. The development of SCC mixture design has been driven mostly by private companies who desired to utilize advantages of SCC. Consequently, there exists limited public information regarding the performance of SCC mixtures. In addition, SCC can be characterized as flowing concrete without segregation and bleeding, capable of filling spaces and dense reinforcement. Further it should be able to flow through, and completely fill the form without vibration. Due to the technical and economic advantages that can be accrued by the use of pozzolans, they play an important role when added to Portland cement by usually increasing the mechanical strength and durability of concrete structures. This paper present, an experimental study on the properties of different self-consolidating concrete mixes containing three types of pozzolanic materials in comparison with SCC mixtures without any pozzolanic materials and conventionally vibrated concrete mixtures. Silica fume, pumice powder and rice husk ash were used for both cement and filler replacements. Various experiments such as slump-flow, J-ring, L-box, V-funnel and sieve segregation resistance were investigated for fresh concrete. Further, compressive strength, water and chloride-ion permeability and capillary water absorption at various days were carried out to determine the properties of self-consolidating concretes. The test results indicated that pozzolanic materials such as RHA and VP can be used to produce SCCs. Regarding the strength properties, the test results showed that the 270-day compressive strength of ordinary SCC is about 70 MPa, while SCC mixtures containing SF, RHA and VP have strengths more than 90, 77 and 76 MPa, respectively. In addition, the results proved that artificial and natural pozzolans enhanced the durability of SCC and reduced the penetration, significantly. For instance, adding 15% pumice and 7% silica fume in the SCC specimen reduced the water depth at 90 days by 19% and 54%, respectively.

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Every year, more than 600,000 tons of rice husk are produced in rice mills in Iran, which are left in nature without proper use or burned. But, with biotechnological methods, it is possible to convert these agricultural wastes into compost with high content of nitrogen and minerals. Accelerating the production of high quality organic fertilizer and reducing the process time requires determining and studying the factors affecting the composting process. In this research, rotten wood waste in the presence of whey was used as an inoculum and the process was studied for one hundred days. The results showed that the process of rice husk composting decreased the ratio of carbon to nitrogen from 161.2 to 21.1 and also increased the nitrogen content from 0.28 to 1.33 percent. By studying temperature changes during the process, it was determined that the degradation of easily biodegradable compounds at the beginning of the process caused an increase in the population of microorganisms and an increase in temperature, and as the process continued, the temperature of the composting environment gradually decreased. On the other hand, the results indicated that the addition of tree bark fertilizer does not affect the quality of the compost content, but it changed the color of the product. The results of the evaluation of the produced compost showed that adding 10 percent by weight of compost to the soil had a significant effect on the length and weight of cowpea.
 

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Due to the increasing use of concrete and the use of additives in it , research in this direction is very important . Resistance is one of the effective values in the design and control of concrete quality that numerous factors and parameters affect it . Perhaps increasing in concrete mixing time is one of the parameters that are considered less attention and in this research ; the effect of mixing time on compressive strength of Nano - silica concrete with pozzolan rice husk was studied and were compared with concrete without Nano - silica and pozzolan rice husk .Therefore the effect of sulfate to reduce the resistance of this type of concrete was studied and compared . So , a number of pieces of concrete cube with sides of 15 cm contains %1 Nano - silica and 20% pozzolan husk Rice with a time of mixing varies between 10 to 40 minutes , that every 5 minutes , 3 samples of concrete were taken and made in the days 3 , 7 and 28 under the stress test and ultimately the results of mixing different compressive strength by the time was drawn and reported . Rice husk also tested and its components determined and compared with the standard . Nano - silica concrete and concrete pozzolan rice husk and without Nano – silica and pozzolan was also photographed to compare the density of particles , and at the end testing plan was written by Taguchi testing of concrete . The results show that for the most compressive strength of concrete pozzolan Nano comes with rice husk , the right time (optimal) 25 minutes with a Taguchi test results differ by about 9 percent lower than the margin of error is permitted , that at this time the concrete maximum compressive strength shows the maximum compressive strength at 28 days after the concrete 415 kg/cm2 and then does not show significant strength concrete . Pozzolan concrete without silica and rice husk increasing mixing time increases the compressive strength of concrete 375 kg/cm2 in 28 days from the time the concrete mixing process increase the resistance of shows . Ash consumption in the non - crystalline silica , which is 88% of the project , has shown its high pozzolanic activity . Physical and chemical (XRF) examination showed that rice husk ash used in this project within the requirements of ASTM C-618 for pozzolan is located . XRD results show that the consumer is fully amorphous silica from rice husk ash . As the electro - microscopic pictures (sem) is observed in samples without Nano - silica and pozzolan rice husk , the concrete has uneven texture and large crystals are clearly visible which are connected with needle - shaped crystals and large pores are clear in concrete . However , the concrete samples with Nano - silica and rice husk pozzolan , concrete has a more amorphous structure which are homogeneous and integrated together . And the porosity of the concrete is significantly reduced , which increases the resistance of concrete.

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Sulfate attack is a series of physico-chemical reactions between hardened cement paste and sulfate ions. Sulfate ion penetration into the cement results in the formation of voluminous and deleterious phases such as gypsum and ettringite which are believed to cause deterioration and expansion of concrete; However, there is no direct relationship between Ettringite or solids formation during the sulfate attack and the amount of expansion. Concrete deterioration due to sulfate attack depends on multiple elements, however, in experimental studies, the implementation of the elements and obtaining the results in a short time are very difficult. Therefore, the significance of theoretical and software modelling along with in experimental studies, reducing the time and cost, increases so much as to achieve reliable results. Thermodynamic simulations, in this research, are employed according to the method of minimizing Gibbs free energy in order to better understand the external sulfate attack and the behaviour of mortar samples made of ordinary Portland cement and blended cements.GEM software helps in studying the microstructure of cement, volume and type of phases formed in sulfate solutions under different conditions. With this software, a virtual laboratory of materials could be created, which simulates natural processes such as hydration, sulfate attack, and factors that affect them with less time and cost. This modeling type could be utilized for cement systems in order to calculate sets of stable phases. A system achieves thermodynamic equilibrium when there is no more spontaneous tendency for change. GEM software which is able to calculate the stable phase as a function of reactants, temperature and pressure is employed. In this software chemical interactions involving solids, solid solutions, metls, gas/fluid mixture, aqueous electrolyte, (non-)electrostatic surface complexation, and ion exchange can be considered simultaneously in the chemical elemental stoichiometry (+ electrical charge) of the system, i.e. without any mass balance constraints for ligands or surface sites. GEMS simulates various mass-transfer processes and reaction paths, such as mixing; But this software cannot replace our knowledge of physical chemistry. Type and volume of phases formed during the sulfate attack and factors affecting that such as cement chemistry, rice husk ash and sulfate solution with different concentrations were studied With the help of this method. Simulation of mortar samples was performed in sodium sulfate with concentrations of 4 and 44 g per liter and 10 and 15 percent rice husk ash substitution. Mortar samples at 20 ° C and water-cement ratio of 0.5 is assumed. Rice husk ash substitution has an effective role in microstructures improvement, reduced impermeability, and volume of forming products. Sodium sulfate is more dangerous and destructive compared to other sulfates like calcium sulfate or potassium sulfate and forms phases with higher volumes. The results clearly indicate that rice husk ash, consumed portlandite completely and produced maximum volume of calcium silicate hydrate(C-S-H) by 15 percent replacement and also there is not a simple relationship between the increase of formed phases by the penetration of sulfate ions and the observed expansion. Generally, the results correspond to the studies and in experimental results which have examined micro structure.

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Nowadays, cement is broadly applied to stabilize the soil to improve the mechanical and engineering properties of different soils and to control their deformations and swelling behavior. Nevertheless, due to the high expenses, civil engineers have always been trying to find an economic pozzolanic alternative for cement. In this regard, lots of construction materials such as fly ash, lime, blast furnace ash, pond ash, rice husk ash, etc are added to differentsoil materials to find an optimum replacement for the cement. Among the mentioned materials, rice husk ash (RHA), which is widely available in Guilan, Iran, is an environmentally dangerous material (if dumped in the nature). Hence, application of this material will be both economically and environmentally useful. Also, due to its high applicability, it can be easily applied in civil constructions. Hence, application of RHA in civil/construction projects will be considerably useful. On the other hand, different fibers (e.g. plastic, polyester, polypropylene, etc) are used for engineering purposes to both control the process of crack initiation and increase the material mechanical properties. the length of applied fibers, also, their percentage is two famous controlling parameters of applying fibers in soil stabilization programs. In this paper, a new soil stabilization method is introduced to stabilize Anzali sand using the combination of cement and RHA. Also, the possibility of cement replacement with RHA is investigated. Polypropylene fibers in 0.2 and 0.4 percentages are also added to the samples to control the growth of tensile cracks and to evaluate their effect on the compressive strength of stabilized samples. Hence, cement in 3, 5, 7.5, 10 percentages, also, RHA in 3, 5, 7.5, 10, 12 and 15 percentages are added to the sand samples to increase their compressive strength. Samples are cured for 28 days and unconfined compressive strength tests are conducted on the stabilized and reinforced samples. Based on the test results, compressive strength of all the samples were increase as cement and RHA percentages were increased. Also, RHA is introduced as a capable replacement additive for the cement. In order to make a generalization and provide a relationship for practitioners to use the results of the present study, different techniques can be adopted. Among them, artificial intelligence techniques are most in demanding ones. Neural networks, gen programming languages, genetic algorithms and evolutionary approaches can be applied to provide such relationships. In this paper, evolutionary approaches are considered and using evolutionary polynomial regression technique, simple predictive equation for forecasting UCS is proposed. In this regard, based on the results of conducted un-confined compressive strength tests, Evolutionary Polynomial Regression (EPR) technique is applied and a high accuracy predictive relationship for forecasting UCS of cement-RHA stabilized and polypropylene reinforced sand is presented (coefficient of determination of 94.4%). In addition, sensitivity analysis based on Cosine Amplitude Method (CAM) is carried out to investigate the most and the least effective materials on the compressive strength of samples. CAM analysis showed that although cement and RHA have meaningful effect on the determination of UCS, polypropylene percentage is the most sensitive additive controlling the variation of UCS.