Query: Silica Fume

title: Environmental impact assessment of fly ash and silica fume based geopolymer concrete
abstract: Alkali activated geopolymer is an attractive solution to limit the adverse consequences of cement manufacturing. In this paper, an evaluation of environmental impacts of geopolymer containing fly ash and silica fume is conducted. Life cycle assessment is performed by benchmarking the environmental impacts of three geopolymer concrete mixes against the conventional cement concrete, namely: fly ash geopolymer (with hydroxide and silicate of sodium) fly ash silica fume blend geopolymer (with hydroxide and silicate of sodium) and fly ash silica fume blend geopolymer (with sodium hydroxide) Impact analysis is performed by using ReCiPe midpoint and endpoint methods in life cycle assessment software UMBERTO NXT using database of Ecoinvent 3.0. Sensitivity analysis is performed to determine the effect of transportation. One mix design for each concrete of equal water to binder ratio and 28 days compressive strength of more than 35 MPa is analysed. Results of life cycle assessment indicate that alkaline activators and cement are the major sources of negative environmental impacts for geopolymer and cement concrete, respectively. Global warming potential of geopolymer concretes is lower than conventional cement concrete. Fly ash silica fume geopolymer concrete activated without sodium silicate has lowest environmental impacts. Transportation of raw materials is found to increase the overall negative of all four concrete mixes. Cost reduction of 10.87% 17.77% per unit volume is achieved with the use of fly ash silica fume based geopolymer concrete. Sustainability in terms of cost and environmental benefits of geopolymer concrete can be further increased by using silica fume. It can be concluded that the use of fly ash silica fume blended geopolymer in the construction industry has huge possibility to improve its sustainability. Furthermore, waste management can be effectively done by utilization of industrial by products in concrete.

title: Silica fume and waste glass in cement concrete production: A review
abstract: The vast emission of greenhouse gases from industrial wastes is a global problem. The non biodegradable nature of industrial wastes like silica fume, glass, bottom ash, and rubber tyres increases the severity of the problem. Past studies suggest that the use of waste materials in the cement and construction industry could be a viable solution to prevent natural resources from extinction. The chemical composition of silica fume and waste glass are attracting cement and concrete industries as a sustainable solution. In recent years, green concrete is very popular among researchers and academicians, but green concrete is still at an early stage. This paper studies the influence of silica fume and waste glass on the workability, strength, and durability properties of concrete. Moreover, the microstructural analysis was also studied.

title: Effect of fly ash and silica fume on hardened properties of foam concrete
abstract: In this study, the effects of foam content as well as fly ash and silica fume inclusion on some physical and mechanical properties of foam concrete, subjected to various curing regimes, were researched. Totally, forty five series of foam concrete mixtures were prepared at three replacement levels of fly ash and silica fume (0, 10 and 20% by weight of cement) at three foam contents (0, 31 and 47% by volume) and at three curing regimes (7 and 28 day standard water curing and autoclave curing) Density, water absorption, compressive strength and thermal conductivity values of the mixtures were determined on prismatic specimens with dimensions of 40 x 40 x 160 mm. The density (oven dry) water absorption, compressive strength and thermal conductivity results of the foam concrete were found to be between 873 1998 kg/m3, 3.5 35.9% 1.5 88.1 MPa and, 0.239 0.942 W/m.K, respectively. A balanced benefit with regard to both compressive strength and water absorption of foam concrete was found in the mix with density of 1320 kg/m3. Particularly in the mixtures having high foam content, silica fume introduction resulted in superior compressive strength values and greater compressive strength/thermal conductivity ratios than fly ash introduction.

title: Improvement in concrete behavior with fly ash, silica fume and coconut fibres
abstract: Concrete is one of the most widely used construction material in spite of some inherited issues (brittleness, weak in tension, etc. A lot of effort has been made to alter concrete behavior with the help of additives e.g. cementitious material, fibres, etc. Now a days, combination of additives are gaining popularity. Researchers have studied fibre reinforced concrete, silica fume concrete and fly ash concrete, separately; but until now, the study is not carried out on coconut fibres with addition of fly ash and silica fume in concrete. In this work, the mechanical properties of fly ash silica fume plain concrete (FA SPC) and fly ash silica fume coconut fibre reinforced concrete (FA SCFRC) are investigated. The silica fume content is 15% by cement mass, with addition of 0% 5% 10% and 15% fly ash content, by cement mass, are added. Coconut fibres having a length of 50 mm and content of 2% by cement mass, are added for FA SCFRC. The stress strain curves, load deflection curves and load time curves for FA SPC and FA SCFRC are recorded against compression, flexure and split tension loadings, respectively. It is revealed that FA SCFRC has generally enhanced properties than that of their respective FA SPC. As a nutshell, FA SCFRC with 10% fly ash content demonstrates overall best mechanical properties than that of FA SPC.

title: Estimating the optimal mix design of silica fume concrete using biogeography based programming
abstract: The use of silica fume in concrete mixtures has been dramatically increased in concrete industry, especially for achieving high strength concrete. An accurate model of estimating the compressive strength and optimal mix design of silica fume concrete can save in time and cost. In this study, the biogeography based programming (BBP) was used as a symbolic regression method to predict the compressive strength of silica fume concrete, while the constrained biogeography based optimization (CBBO) was used to estimate its optimal mix design. For this purpose, a comprehensive database was gathered from various published documents. From the collected data, about 75% of all data was employed to train the model, while the rest was used to verify the developed model. The amounts of cement, water, silica fume, coarse aggregate, fine aggregate, superplasticizer, as well as the maximum size of aggregate and concrete age were selected as the effective input variables of the model. The compressive strength of silica fume concrete was considered as the only output variable. The results show that the BBP model can be successfully used for the prediction of the compressive strength of silica fume concrete with acceptable accuracy. In addition, a graphical user interface was designed which allows the users to estimate the optimal mix design of silica fume concrete.

title: Effect of silica fume on durability of self compacting concrete made with waste recycled concrete aggregates
abstract: Due to adhered mortar in recycled concrete aggregates, some of the properties of concrete made with these types of aggregates, such as water absorption, porosity, electrical resistivity, and chloride ion penetration, may be affected. In this study, silica fume was used as a part of cementitious materials to improve the properties of self compacting concrete (SCC) which were made with fine and coarse recycled aggregates. Three series of mixtures were made in the laboratory. In the first and second series, coarse recycled aggregates with replacement of 25% 50% 75% and 100% were used with and without silica fume. In the third series, 25% of fine recycled aggregates were replaced with fine natural aggregates. Slump flow and J ring tests were considered for fresh state of SCC. The compressive strength, water absorption, ultrasonic pulse velocity, electrical resistivity, and chloride ion penetration tests were performed for hardened concrete. The use of silica fume improved the properties of fresh SCC. The results showed that silica fume can reduce water absorption and porosity. The silica fume showed that can resulted in a significant increase in electrical resistivity. On the other hand, the replacement of 25% of recycled aggregates did not have a significant effect on electrical resistivity, the electrical resistivity decreased by increasing the amount of replacement. Silica fume was very effective in controlling chloride ion penetration and reducing total charge passed. Silica fume also controlled the temperature of the solutions used during the test which indicates the control of the movement of ions in the penetration into concrete.

title: Combination effects of rubber and silica fume on the fracture behaviour of steel fibre recycled aggregate concrete
abstract: The use of recycled concrete aggregate and crumb rubber in structural concrete is a sustainable way to reduce the detrimental impacts of solid waste on the environment and address the shortage of natural resources. For the safe and economical design of rubberized steel fibre recycled aggregate concrete (RSRAC) the mechanical behaviour of RSRAC modified with silica fume needs to be properly understood. In the present study, the coupling effects of crumb rubber and silica fume on the fracture behaviour of RSRAC were examined for the first time. The results from a series of tests on a notched beam and cylinder under three point bending and compression, where the RSRACs were incorporated with crumb rubber with a volume substitution of fine aggregate by 0% 5% 10% 15% and 20% are presented and discussed. The results indicated that the combination of rubber and silica fume exhibited excellent coupling effects on the fracture performance of RSRAC. Regarding reducing the negative effects of rubber, the replacement of 10% cement by silica fume was superior to the addition of 3% silica fume. When considering the mechanical improvement, the RSRAC with 5% rubber and 10% silica fume seems to be a more environmentally friendly material compared with normal concrete for structural elements.

title: Nano silica and silica fume modified cement mortar used as Surface Protection Material to enhance the impermeability
abstract: In corrosion environment, corrosion ions can easily penetrate from the surface into the inside of the concrete due to the porous structure of the surface; in this case, concrete can inevitably suffer from the damage. In this study, an attempt to use nano SiO2 (NS) and silica fume (SF) modifying cement mortar as a Surface Protection Material (SPM) was made, in order to promote penetration resistance of the whole system. SPM was coated on the surface of matrix, and then interfacial bond strength between matrix and SPM was measured; shrinkage consistency was also considered; the chloride penetrability of the system was examined as well. To reveal the mechanism, effect of NS and SF on pore structure, Interfacial Transition Zone (ITZ) hydration process, and compressive strength of SPM were investigated. The results show that matrix coated with SPM on the surface has a good integrity, with excellent interfacial bond strength and little difference in shrinkage, and chloride diffusion coefficient of the system was considerably declined, in comparison with the matrix, showing an excellent penetration resistance. The mechanism behind is that SPM, which was modified with SF NS, shows the excellent impermeability, and this kind of material existing on the surface can noticeably obstruct the chloride ions penetrating into the inside. In cement hydration process, SF and NS can not only consume a large amount of CH to form dense C S H, but also exert the grading filling effect, resulting in the decline in porosity, the increase in density, the improvement in microstructure of ITZ, and the enhancement in mechanical performance. The findings can provide useful experience for the design of the cement based materials servicing in high corrosion environment.

title: Durability performance of structural concrete containing silica fume and marble industry waste powder
abstract: This paper presents the results of an experimental investigation of durability properties carried out on 16 concrete mixes containing marble waste powder and silica fume as partial replacement of ordinary Portland cement. The latter was partially replaced at different ratios of silica fume (0% 2.5% 5% 10% and marble waste powder (0% 5% 10% 20% In all concrete mixes, constant water/binder ratio of 0.45 and target initial slump of S2 class (50 90 mm) were used. Workability and bulk density tests were carried out on fresh concrete, while compressive strength, electrical resistivity, water absorption, durability to sodium sulphate, magnesium sulphate and sulphuric acid attack tests were performed to evaluate some relevant properties of concrete in the hardened state. It was found that the strength and durability of concrete containing marble waste powder tend to decline for replacement ratios over 10% but satisfactory results were obtained below that level of replacement. Regarding the use of silica fume, it was observed that it improves the strength and durability of concrete with marble waste powder by offsetting the decline of its properties relative to conventional concrete. In addition to obtaining approximately the same results as the original concrete mix, using 20% marble waste powder and 10% silica fume as partial replacement of cement resulted in a 30% cement reduction which decreases the harmful effects of cement industry on the environment.

title: Enhancement of mechanical and electrical properties of graphene/cement composite due to improved dispersion of graphene by addition of silica fume
abstract: Incorporation of graphene into cement based materials has attracted extensive attention of many researchers. Achieving effective dispersion of graphene can contribute to improving the mechanical and other properties of the cement composite. In this study, the effects of silica fume content on compressive strength and electrical resistivity of the graphene/cement composite were investigated. The distribution of graphene and silica fume in cement matrix was observed by scanning electron microscopy (SEM) and the pore structure of the composite was analyzed by mercury intrusion porosimetry (MIP) Results revealed that silica fume was capable of facilitating the dispersion of graphene and increasing the interfacial strength between graphene and cement matrix. Moderate amount of silica fume can refine the pore structure of the cement paste. Incorporation of appropriate amount of silica fume can increase the compressive strength and reduce the electrical resistivity of the composite. However, the extra amount of silica fume had a negative effect on mechanical and electrical performances.