Showing papers on "Silica fume published in 2020"

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.

Mechanical and fracture properties of ultra-high performance geopolymer concrete: Effects of steel fiber and silica fume

Abstract: This study investigates the effects of steel fiber and silica fume on the mechanical and fracture properties of ultra-high performance geopolymer concrete (UHPGC). Four volume fractions of steel fiber (0%, 1%, 2% and 3%) and four contents of silica fume by the mass of total binders (5%, 10%, 20% and 30%) were used. The mechanical and fracture properties evaluated include the compressive, splitting tensile and ultimate flexural strengths, modulus of elasticity, flexural behavior, fracture energy and stress intensity factor. In addition, the correlations among the compressive and splitting tensile strengths, and compressive strength and elastic modulus were studied. The results indicated the increase of steel fiber dosage resulted in the decrease of the workability, but the continuous improvement of mechanical and fracture performance of UHPGC. The empirical equations for predicting elastic modulus of conventional ultra-high performance concrete overestimated the elastic modulus of UHPGC, however some prediction formulas for the splitting tensile strength of PC-based concretes could be applied for UHPGC. Silica fume had a complicated influence on workability and hardened properties of UHPGC, which is strongly dependent on its amount. The inclusion of 10% silica fume induced the increase of the flowability, but the sharp degradation of the mechanical performance, while the specimens with 20% and 30% silica fume possessed the superior mechanical characteristic to that with 5% silica fume. The steel fiber dosage could be decreased without sacrificing the mechanical and fracture performance of UHPGC, via the increase of silica fume content.

Compressive strength prediction of eco-efficient GGBS-based geopolymer concrete using GEP method

Abstract: Geopolymer concrete (GPC) could be used as an environmental-friendly alternative solution for concrete production due to the detrimental impacts of cement production on the environment. Since obtaining an optimal mix design, and subsequently, predicting the compressive strength of mortar using experimental means is costly and time-consuming, employing soft-computing techniques could facilitate and accelerate this approach. In this research, gene expression programming (GEP) was used to develop numerical models for predicting the compressive strength of GPC based on ground granulated blast-furnace slag (GGBS). Through an experimental program, an extensive database of the compressive strength of GGBS-based GPC consisting of 351 specimens obtained from 117 different mixtures was generated. The five most effective parameters, including specimen age, sodium hydroxide (NaOH) solution concentration, natural zeolite (NZ), silica fume (SF), and GGBS content, were considered as the modeling input parameters. Using GEP algorithm, simplified and practical mathematical equations were proposed to predict the compressive strength of GGBS-based GPC mortar. Performance, high accuracy, and predictability of the proposed equations were validated by the conducted sensitivity and parametric analyses. The obtained results could promote the re-use of GGBS for GPC development, which in turn will lead to environmental and economic advantages.

Effect of Coconut Fiber Length and Content on Properties of High Strength Concrete.

Abstract: Recently, the addition of natural fibers to high strength concrete (HSC) has been of great interest in the field of construction materials. Compared to artificial fibers, natural fibers are cheap and locally available. Among all natural fibers, coconut fibers have the greatest known toughness. In this work, the mechanical properties of coconut fiber reinforced high strength concrete (CFR-HSC) are explored. Silica fume (10% by mass) and super plasticizer (1% by mass) are also added to the CFR-HSC. The influence of 25 mm-, 50 mm-, and 75 mm-long coconut fibers and 0.5%, 1%, 1.5%, and 2% contents by mass is investigated. The microstructure of CFR-HSC is studied using scanning electron microscopy (SEM). The experimental results revealed that CFR-HSC has improved compressive, splitting-tensile, and flexural strengths, and energy absorption and toughness indices compared to HSC. The overall best results are obtained for the CFR-HSC having 50 mm long coconut fibers with 1.5% content by cement mass.

Estimating strength properties of geopolymer self-compacting concrete using machine learning techniques

Abstract: There has been a persistent drive for sustainable development in the concrete industry While there are series of encouraging experimental research outputs, yet the research field requires a standard framework for the material development In this study, the strength characteristics of geopolymer self-compacting concrete made by addition of mineral admixtures, have been modelled with both genetic programming (GEP) and the artificial neural networks (ANN) techniques The study adopts a 12M sodium hydroxide and sodium silicate alkaline solution of ratio to fly ash at 033 for geopolymer reaction In addition to the conventional material (river sand), fly ash was partially replaced with silica fume and granulated blast furnace slag Various properties of the concrete, filler ability and passing ability of fresh mixtures, and compressive, split-tensile and flexural strength of hardened concrete were determined The model development involved using raw materials and fresh mix properties as predictors, and strength properties as response Results shows that the use of the admixtures enhanced both the fresh and hardened properties of the concrete Both GEP and ANN methods exhibited good prediction of the experimental data, with minimal errors However, GEP models can be preferred as simple equations are developed from the process, while ANN is only a predictor

Fresh, strength and microstructure properties of geopolymer concrete incorporating lime and silica fume as replacement of fly ash

Abstract: The need to cure fly ash-based geopolymer at elevated temperatures has limited the practicability and sustainability of the composite. Hence, there is an imminent need to find ways at which fly ash-based geopolymers can be cured at ambient conditions. This paper presents the results from the experimental investigation of the effect of lime and silica fume on the properties of geopolymer concrete cured at ambient conditions. Lime and silica fume were used as the partial replacement of fly ash as an aluminosilicate precursor and the corresponding effects on the fresh, strength and microstructure of the geopolymer concrete were investigated. The findings from this study showed that the slump and setting times of the geopolymer concrete increases with increasing silica fume content and reduces with increasing lime content. Also, the use of lime and silica fume as 7.5% and 2% respectively, replacement of fly ash yielded the highest compressive strength. Microstructural investigation showed that the combined use of lime as silica fume in GPC resulted in a densified microstructure.

Influence of supplementary cementitious materials on rheological properties of 3D printed fly ash based geopolymer

Abstract: 3D printed fly ash based geopolymer was prepared with fly ash and quartz sand as main raw materials while slag powder and silica fume as supplementary cementitious materials. In this paper, anhydrous sodium silicate powder was used as activator and ATTAGEL-50 thixotropic thickener was used as 3D printing additive. The effect of slag powder and silica fume on the rheological properties of 3D printed fly ash based geopolymer was studied. The results show that the apparent viscosity, thixotropic property, plastic viscosity and yield stress of geopolymer first increased and then decreased with the increase of slag powder and silica fume respectively. Compared with the Bingham (BH) model, the Herschel- Bulkley (H–B) model is more accurate and more suitable for characterizing the rheological model of fly ash based 3D printed geopolymer. The suitable content for slag powder is 10%. On the basis of adding slag powder, silica fume was also used to replace the fly ash, the suitable content for silica fume is 10% in this fly ash-slag powder based 3D printing geopolymer. According to the SEM observations, it is found that the interior of the printing layer of the 3D printing block is more conducive to the production of the geopolymer gel than the interlaminar surface of the printing layers. It is found that the printing layers are connected with each other through bridges.

Utilization of industrial and agricultural wastes for productions of sustainable roller compacted concrete pavement mixes containing reclaimed asphalt pavement aggregates

Abstract: Asphalt pavement recycling has become a common practice across the globe and has been successfully employed in construction of new pavements. While several studies considered utilization of reclaimed asphalt pavement (RAP) aggregates for flexible and rigid pavements, very few attempted its possibility for roller compacted concrete pavements (RCCP). Additionally, studies on the possibility of enhancing the proportion of RAP for RCCP are very scanty. The present study is an attempt to increase the potential of RCCP mixes containing 50% RAP (dust contaminated & stiffened asphalt coated: 50RAP via including various industrial and agricultural wastes such as Silica Fume, Fly ash, and Sugarcane ash as partial replacement of conventional cement. It was observed that the inclusion of the stated admixtures had an insignificant effect on the density of the fresh RCCP mixes, however, increased the moisture demand considerably. In fact, the results firmly indicated the potential of silica fume for RAP-RCCP blends, as, it not only enhanced the physical and mechanical properties, but found to improve the durability of RCCP mixes considerably. Also, utilization of silica fume was found to be economical & environmentally friendly amongst all wastes: with reduced initial construction cost & CO2 emissions by up to 8.4% & 9.7%. As far as the other industrial wastes are concerned, 15% fly ash could also be utilized for producing sustainable RCCP mixes, whereas, higher dosage of fly ash (30%) and sugarcane ash (10 & 15%) may be employed as base layer material of conventional concrete pavements.

Energy Savings Associated with the Use of Fly Ash and Nanoadditives in the Cement Composition

Abstract: The paper presented herein investigates the effects of using supplementary cementitious materials (SCMs) in quaternary mixtures on the compressive strength and splitting tensile strength of plain concrete. In addition, environmental benefits resulting from the proposed solutions were analysed. A total of four concrete mixtures were designed, having a constant water/binder ratio of 0.4 and total binder content of 352 kg/m3. The control mixture only contained ordinary Portland cement (OPC) as binder, whereas others incorporated quaternary mixtures of: OPC, fly ash (FA), silica fume (SF), and nanosilica (nS). Based on the obtained test results, it was found that concretes made on quaternary binders containing nanoadditives have very favorable mechanical parameters. The quaternary concrete containing: 80% OPC, 5% FA, 10% SF, and 5% nS have shown the best results in terms of good compressive strength and splitting tensile strength, whereas the worst mechanical parameters were characterized by concrete with more content of FA additive in the concrete mix, i.e., 15%. Moreover, the results of compressive strength and splitting tensile strength are qualitatively convergent. Furthermore, reducing the amount of OPC in the composition of the concrete mix in quaternary concretes causes environmental benefits associated with the reduction of: raw materials that are required for burning clinker, electricity, and heat energy in the production of cement.