Silica fume, also known as micro silica, is a by-product of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. This material and laccase-modified silica fume used as alternative low-cost adsorbent materials for dye removal from aqueous solutions. The silica fume was modified to maximize its adsorption capacity. For this purpose, the laccase enzyme was purified and immobilized on silica fume. Batch adsorption experiments have been performed as a function of pH, contact time, temperature, and adsorbent dosage. The equilibrium data were analyzed using Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption model provided a better fit to the data. The kinetic data were evaluated with pseudo-first-order and pseudo-second-order kinetic models. The adsorption process undergoes pseudo-second-order kinetic as proved by the high value of R2. The thermodynamic parameters such as free energy, enthalpy, and entropy were also determined. These parameters indicated that the adsorption of Acid Fuchsin dye onto silica fume and laccase-modified silica fume was a spontaneous, endothermic, and entropy-driven process. The results show that both of them, especially laccase-modified silica fume, can be used as alternative low-cost adsorbents for dye removal from aqueous colored solutions or effluents.

Deterioration of concrete structures in the Gulf region is a serious problem. Penetration of Chloride ion into concrete is responsible for such early deterioration. Determination of chloride diffusion coefficient is an effective way to predict the service life of concrete structures.In order to investigate the performance of concrete mixtures in such environments, ordinary and silica fume concrete mixtures containing various water to cementitious materials ratios were used. Rapid chloride permeability test and determination of diffusion coefficient of chloride ion penetration in accordance with bulk diffusion test under laboratory conditons simulated to Persian Gulf climate, and site investigation were performed. Concentration of chloride ions in various depths of concrete specimens was measured using acid soluble chloride test method.Test results show that silica fume reduces the chloride penetration and the diffusion coefficient in concrete mixtures. Different models were made for rapid chloride test results, and diffusion coefficient, of concretes maintained in the hot and corrosive environments of the Persian Gulf. The models which were calibrated with real data obtained from the concrete structures are capable to predict the penetration and service life of concrete structures in such corrosive environments.

Plastic shrinkage is one of the most important parameter, which must be considered in hot weather concreting. If plastic shrinkage is not prevented, cracking will be significant, especially if silica fume is used in the mix. In this paper, the effect of silica fume in bleeding and evaporation was investigated in laboratory. The results showed that in restrained shrinkage, beside relative humidity, temperature and wind velocity, the sun radiation is also a very important factor in cracking characteristic. But the effect of sun radiation is not considered in ACI 305 R-96 nomogram. The results showed that in terms of crack initiation time, crack width and total cracking area, concrete containing silica fume is more severe than concrete with no silica fume. Reduction of water-cement ration in concrete with silica fume makes the concrete more sensitive towards cracking. The results of this project also showed that the severity of the cracking is not related only to compressive strength or bleeding of the concrete but all environmental factors like sun radiation and also silica fume in mix, have important role.

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

Corrosion of steel is one of the essential potential dangers and threats in concrete structures. Corrosion of steel embedded in reinforced concrete plays a key role in reducing the strength and durability of reinforced concrete. Several studies have proposed that alternative approaches to enhancing the performance of reinforced concrete and its resistance to corrosion. In this article, the results of steel corrosion embedded in reinforced concrete with silica fume and Nano-silica particles are presented. In the testing phase, samples with a mixture of these particles ranging from 0 to 133 grams were generated, and their performance was compared applying Corrosion Potential (OCP), Electrochemical Impedance Spectroscopy (EIS), Linear Polarization (LPR), and TOEFL polarization tests. The results demonstrate that silica fume is effective in reducing the permeability of the concrete against malicious (adverse) ions, but nano-silica had far satisfying performance in reducing the corrosion rate of steel embedded in concrete.

The improvement of geotechnical properties of weak soils is of interest through the resources shortage. Therefore, this study focused on the effect of silica fume as industrial waste products and nano-silica on geotechnical characteristics and micro-structural properties of kaolinite clay as a soft soil with poor strength properties. Silica fume was added to the kaolinite clay to enhance the strength with 5, 10 and 15%. Moreover stabilized soil with nano-silica were fabricated with 1, 2 and 3% by dry weight of the soil. Then, Atterberg limits, standard proctor, unconfined compressive strength, and California bearing ratio tests were conducted. In addition, the micro-structural changes of soil samples through the stabilization were examined using scanning electron microscope. The results indicated that silica fume and nano-silica increase the optimum water content and decrease the maximum dry density of the stabilized soils. Addition of 15% silica fume and 3% nano-silica to kaolinite clay improved the unconfined compressive strength at curing age of 28 days by up to 70% and 55%, respectively. Also, the results of soaked California bearing ratio test after 7 days of curing demonstrated that 15% of silica fume and 3% nano-silica increased the California bearing ratio values about two times more than the raw soil. Scanning electron microscope (SEM) images were then utilized to evaluate the effects of additives on the kaolinite clay soil. It was concluded that silica fume and nano-silica filled pore space between clay particles and a dense matrix were formed. This textural event caused an improvement in compressive strength of stabilized soils.

Recently, Nanotechnology has caused a vast breakthrough worldwide and scientists in different fields have used it. Nano particles have been gaining increasing attention and been applied in many fields to fabricate new material with novel function due to their unique physical and chemical properties. Therefore, using Nano-silica as a Nano-scale additive in concrete is under further inspection by researchers. Recent contribution to the development of building materials compromise adding colloidal Nano-silica to concrete. In this paper, the influence of Nano-silica addition on mechanical and durability properties of concrete as compared with silica fume has been studied. Tests include compressive strength, water permeability, rapid chloride penetration and electrical resistance test. Moreover, microstructure of the cement paste incorporating Nano-silica and Silica-fume were studied through X-ray diffraction and Scanning electron microscope tests. The experimental results show that Nano-silica as an artificial pozzolanic material can improve the compressive strength, water penetration resistance and electrical resistivity of concrete and reduce the chloride diffusion more effectively than SF at early ages. In addition, utilizing NS in cement paste improve its microstructure at early days.

Because of the growing importance of sustainability in the global market, as well as the negative environmental consequences of cement manufacturing, partial replacement of Portland cement (PC) with supplementary cementitious materials (SCMs) such as silica fume (SF) has become increasingly popular. The purpose of this study was to build a framework for sustainable practices based on eighteen sustainability indicators, which included technical, economic, and environmental factors. Cementitious matrixes were generated by replacing PC with SF at different percentages of the mass of the matrix: 0, 5, 6.5, 7.5, 8.5, and 10%. Several laboratory experiments were carried out to obtain an accurate evaluation, including the measurement of setting times, compressive strength, capillary water absorption, and surface electrical resistivity on mortar specimens, which were used as technical indicators. The environmental implications of products were also evaluated using a life cycle approach, and sensitivity analysis was performed to develop a robust sustainability assessment model for SF substitution. In addition, According to the findings, SF has the potential to raise the sustainability score by at least 36.4% and as much as 118.2%. When compared to all of the other combinations evaluated, the specimen containing 8.5% SF achieved the greatest sustainability score and was the most sustainable mixture. The concept and technique used in this study can be applied to other SCMs of a similar nature.

Now a days high strength and high performance concrete are being widely used all over the world. Most applications of high strength concrete have been in high rise buildings, long span bridges and in some special applications in structures. In developed countries, using high strength concrete in structures today would result in both technical and economical advantage. In high strength concrete, it is necessary to reduce the water/cement ratio and which in general increases the cement content. To overcome low workability problem, different kinds of pozzolanic mineral admixtures (fly ash, rice husk ash, metakaoline, etc.and chemical admixtures are used to achieve the required workability.In the present experimental investigation, the mechanical properties of high-strength concrete of grades M40 and M50, at 28 days characteristic strength with different replacement levels of cement with silica fume or micro silica of grade 920-D are considered. Standard cubes (150mm x 150mm x 150mm), standard cylinders (150mm dia x 300mm height) and standard prisms (100mm x 100mm x500mm) were considered in the investigation. In all, 144 specimens were cast with and without silica fume. The mechanical properties viz., compressive strength, flexural strength and splitting tensile strength, and stress-strain characteristics of high strength concrete with various replacement of silica fume viz., 3%, 6%, 9%, 12% and 15%, has been considered. The investigations revealed that the use of waste material like silica fume improved the mechanical properties of high strength concrete witch is otherwise hazardous to the environment and thus may be used as a partial replacement of cement.