Levels Of Silica Fume Research Articles

Enhancing Cementitious Concrete Durability and Mechanical Properties through Silica Fume and Micro-Quartz

The existing body of literature has witnessed extensive research efforts dedicated to exploring the impact of supplementary cementitious materials (SCMs) possessing pozzolanic characteristics on concrete. Nevertheless, the holistic concept of micro-scale fillers has frequently been a subject that remains insufficiently explored. This study endeavors to formulate binary cementitious systems that incorporate silica fume (SF) and micro-quartz filler (MQF) to enhance the durability and mechanical properties of cementitious concrete. We systematically investigate the effects of varying replacement levels of SF and MQF, alongside changes in the water-to-binder (w/b) ratio. With w/b ratios spanning 0.25 to 0.40, we explored replacement levels of 8, 10, and 12% (wt.) for SF, and 5, 8, 10, 15, 25, and 35% (wt.) for MQF. The findings revealed a consistent decrease in porosity and permeability as the replacement levels increase. Notably, a marked increase in compressive strength is observed with SF replacement, reaching its peak at an 8% MQF replacement level. Even as MQF replaces 15% of SF, concrete mixtures with 12% SF consistently exhibit superior strength. Importantly, MQF’s ultrafine particle size mirrors SF’s impact on enhancing compressive strength, porosity reduction, and permeability, despite its high crystalline structure. The study employs an analysis of variance (ANOVA) to rigorously assess the influence of each variable on the studied responses.

Correlation between diffusion coefficient values of chloride ions obtained through column and ion migration tests in cementitious matrices with varying contents of silica fume and mortar

Abstract Corrosion is one of the main phenomena that lead to pathological manifestations in reinforced concrete structures under aggressive environments. with the chloride ion being the most responsible for its occurrence. In this way, understanding the transport mechanisms of this ion through the microstructure of the concrete is of fundamental importance to prevent or delay the penetration of these aggressive agents to guarantee a durable structure. In the literature, there are extensive studies concerning the diffusion of chlorides in concrete and the influence of pozzolanic additions in this mechanism. However, only a few correlate the different methods of analysis. This work aims to determine the chloride ion diffusion coefficients in concrete containing various levels of silica fume (5%, 10%, and 15%) or varying the mortar content (54%, 80%, and 100%), and compares the results obtained through column tests and chloride migration tests. It was observed that, although the techniques used were quite distinct, the diffusion values obtained were similar, contributing to the validation of both techniques. Furthermore, the variation in the mortar ratio causes a reduction in the interfacial transition zone of coarse aggregate/mortars and an increase in the content of aluminates, which promotes a similar effect to the use of silica fume.

Evaluation and Multi-Objective Optimization of Lightweight Mortars Parameters at Elevated Temperature via Box-Behnken Optimization Approach.

In this research, the mechanical properties of lightweight mortars containing different percentages of additional powder materials has been investigated using response surface methodology (RSM). Box–Behnken design, one of the RSM techniques, was used to study the effects of silica fume content (5, 10, and 15%), vermiculite/cement (V/C) ratio (4, 6, and 8), and temperature (300, 600, and 900 °C) on the ultrasonic pulse velocity (UPV), bending strength, and compressive strength of lightweight mortars. Design expert statistical software was accustomed to determining and evaluating the mix-design of materials in mortar mixtures and temperature effect on mortars. After preliminary experimental research of the relationships between independent and response variables, regression models were built. During the selection of the model parameters, F value, p-value, and R2 values of the statistical models were taken into account by using the backward elimination technique. The results showed a high correlation between the variables and responses. Multi-objective optimization results showed that the critical temperatures for different levels of silica fume (5–10–15%) were obtained as 371.6 °C, 306.3 °C, and 436 °C, respectively, when the V/C ratio kept constant as 4. According to the results obtained at high desirability levels, it is found that the UPS values varied in the range of 2480–2737 m/s, flexural strength of 3.13–3.81 MPa, and compressive strength of 9.9–11.5 MPa at these critical temperatures. As a result of this research, RSM is highly recommended to evaluate mechanical properties where concrete includes some additional powder materials and was exposed to high temperature.

Compressive strength modeling of blended concrete based on empirical and artificial neural network techniques

ABSTRACT This article exhibits an experimental study carried out to investigate the combined effect of Silica Fume (SF) and Metakaolin (MK) on the fresh and hardened properties of concrete. The replacement levels of SF were adopted as 5%, 10%, 15%, 20% while that of MK were 5%, 10%, 15%, 20% and 25%. The results for cube testing revealed that the use of SF and MK produces considerably good strength concrete. Based on the experimental observations, an approach to predict the compressive strength using regression modeling was suggested. The result of which rendered a reasonable agreement with the available test data. Moreover, two Artificial Neural Network (ANN) models have also been proposed to predict the compressive strength of concrete using the data obtained from the experimental exercise. Randomized stratification method was used to divide the data samples into training and testing subsets in line with machine learning best practices. The results of the ANN models were found to be in good agreement with experimental values. When compared with the results of empirical models, the respective ANN models gave a better prediction for the compressive strength. This substantiates the reliability of ANN over the empirical models.

Enhancing the Hardened Properties of Recycled Concrete (RC) through Synergistic Incorporation of Fiber Reinforcement and Silica Fume.

Portland cement concrete is fragile in tension and it has numerous negative impacts on the environment. To deal with these issues, both fiber reinforcement and recycled materials can be utilized to manufacture sustainable and ductile concrete. In this study, the synergistic effects of high-performance mineral admixture silica fume and glass fiber reinforcement were investigated on the hardened properties of RC. For this purpose, two concrete mix families, namely, NC and RC were prepared. To understand the benefits of synergistic utilization of glass fiber and silica fume, in both NC and RC, 0.5% glass fiber was incorporated with three different levels of silica fume. i.e., 0%, 5%, and 10%. Both strength and permeability-related durability properties were investigated. Results revealed that combined incorporation of 0.5% fiber and 10% silica fume can help in the production of RC having better mechanical and durability performance compared to reference “NC”. Simultaneous incorporation of silica fume and glass fiber produces a combined effect greater than their individual effects on both mechanical and permeability properties of concrete. Silica fume plays a very dominant and positive role in the development of CS, WA, and CIPR of RC, whereas glass fiber plays a vital role in upgrading STS and FS of RC and whereas, with the addition of 0.5% glass fiber, RC can yield 8–9 times higher flexural toughness than that of the plain NC.

Effects of different silica fume dosages on early-age behavior and cracking resistance of high strength concrete under restrained condition

High strength concrete (HSC) containing silica fume (SF) is widely utilized in construction practices, and its cracking resistance attracts considerable attentions. Previous studies mostly focus on the single parameter of concrete, however, the evaluation of early-age cracking resistance of HSC containing different SF dosages considering different early-age parameters is limited. The present study investigated the effect of different SF dosages on the temperature process, autogenous shrinkage, restrained stress, and creep by utilizing Temperature Stress Test Machine to evaluate the cracking resistance of early-age HSC containing SF. Four concrete mixtures with a 0.33 water/binder ratio were prepared at different replacement levels of SF (0%, 5%, 10%, and 15% of cement by weight). The analysis and experimental results indicated that, when the SF dosage in the HSC increased, (1) the cracking resistance of HSC decreased at early age; (2) the temperature drop, cracking time, cracking stress, and ratio of cracking stress to axial tensile strength decreased; (3) the autogenous shrinkage as well as restrained stress rate increased; (4) the basic tensile creep, specific tensile creep, and creep-shrinkage ratio increased.

Evaluating the durability of recycled concrete made of coarse recycled aggregate concrete containing silica-fume and natural zeolite

This experimental study evaluates the durability of recycled aggregate concrete (RAC) containing silica-fume (SF) and natural zeolite (NZ). For this purpose, four levels of recycled coarse concrete aggregates (RCA) were replaced with natural coarse aggregates (NCA). To compare the effect of pozzolans, three levels of SF (5%, 10%, and 15%) and three levels of NZ (10%, 20%, and 30%) were replaced with cement. To evaluate the durability of RAC, 28 mixed designs were made and the following were measured: compressive strength (CS), water absorption by immersion (WA by immersion), water absorption by capillary (WA by capillary), electrical resistance (ER), electrical conductivity (EC) and rapid chloride penetration test (RCPT). The results indicated that WA by immersion and WA by capillary of RAC increased with enhanced RCA incorporation. On the other hand, the pozzolanic reaction of 10% of SF and 10% of NZ decreased capillary pores and structural weakness of full-scale RAC. However, due to the internal chemical changes of RAC, contrary to the WA by immersion and WA by capillary, compared to conventional concrete (CC), a lower EC and unchanged ER values of RC100 containing pozzolans were seen. The scanning electron microscopy (SEM) revealed that compared to NZ, a 10% of SF significantly improved the microstructure of full scale RAC.

Effect of Silica Fume in Concrete on Mechanical Properties and Dynamic Behaviors under Impact Loading.

The effect of silica fume (SF) in concrete on mechanical properties and dynamic behaviors was experimentally studied by split Hopkinson pressure bar (SHPB) device with pulse shaping technique. Three series of concrete with 0, 12%, and 16% SF as a cement replacement by weight were produced firstly. Then the experimental procedure for dynamic tests of concrete specimens with SF under a high loading rate was presented. Considering the mechanical performance and behaviors of the concrete mixtures, those tests were conducted under five different impact velocities. The experimental results clearly show concrete with different levels of SF is a strain-rate sensitive material. The tensile strength under impact loading of the tested specimens was generally improved with the increasing content of SF levels in concrete. Additionally, the tensile strength under impact loading of the concrete enhances with the increase of the strain rates. Finally, failure modes, dynamic tensile strength, dynamic increase factor (DIF), and critical strain are discussed and analyzed. These investigations are useful to improve the understanding of the effect of SF in concrete and guide the design of concrete structures.

Effect of nano-clay on workability, mechanical, and durability properties of self-consolidating concrete containing mineral admixtures

The effects of nano-clay (NC) addition on fresh state, mechanical, and durability properties of plain and blended cement self-consolidating concrete (SCC) incorporating mineral admixtures as supplementary cementitious materials were investigated. Mineral admixtures such as silica fume (SF), class F fly ash (FA), rice husk ash (RHA), and ground granulated blast furnace slag (GGBFS) were used as partial replacement of cement. Initially, SCC mixes with 1%, 2%, and 3% NC as cement replacement, by weight, were prepared and the workability properties (i.e. slump flow, T50 and V-funnel flow time, and passing ability ratio via L-box test), the mechanical properties (i.e. compressive strength, splitting tensile strength, the modulus of elasticity and the ultrasonic pulse velocity), and the durability properties (i.e. water absorption, water penetration depth via water permeability test, electrical resistivity, chloride migration coefficient and the time-dependent corrosion current variation via impressed voltage test) were determined for evaluating the effectiveness of NC inclusion on characteristics of SCC. According to the results, the addition of NC to plain SCC satisfied all the required specifications for SCC as per EFNARC (European Federation for Specialist Construction Chemicals and Concrete Systems). While the addition of 3% NC by weight of cement improved the durability performance significantly, its effects on mechanical properties were observed to be limited. However, NC replacement dosage of 3%, by weight of cement, can be considered as the optimal content for SCC in comparison with the NC replacement of 1% and 2%. In the second step of this experiment, the effects of 3% NC inclusion on properties of blended cement SCC containing optimum levels of SF, FA, RHA and GGBFS (15%, 30%, 15%, and 45%, respectively, based on literature) were assessed. The results indicated that by incorporating 3% NC in blended cement SCC, satisfactory workability and mechanical properties can be achieved. Remarkable enhancements were also observed in durability properties of blended cement SCC with the presence of NC compared to that of the reference concretes confirming that a small dosage of NC can effectively be used to make big improvements in the properties of environmentally friendly SCC mixes.

Study of High Strength Concrete Using Microsilica

The framework of bridges, buildings, roads etc. need concrete. The concrete which is being used is not able to fulfil the contemporaneous needs. In India High Strength Concrete (HSC) is preferred for manufacturing practices and at the same time High Performance Concrete is used at high level. The properties of HSC are improved like mechanical and durability are improved by using silica fume in concrete. HSC has made the work of construction company more rewarding to design tall, long and light structures. HSC is helpful in designing buildings with good number of floors, wide area bridges and slim structure. The products like fly-ash, copper slag, silica fume etc. are produced by industries which leads to various environmental problems. The experiment on silica was done which stated that no strength is lost in silica-fume concretes. The experiment comprises four levels of silica-fume at the rate of 0%, 5.5%, 8.0%,9.5% and 11.0% which results high strength concrete.

Performances evaluation of binary concrete designed with silica fume and metakaolin

The use of various pozzolanic and cementitious materials not only has an environmental and economic impact, by the reduction of Portland cement clinker production, but also could significantly improve the strength and durability performances of concrete. Silica fume (SF) is a well-known and largely used pozzolanic material due to numerous improvements that could provide to concrete while metakaolin (MK) even with quite similar performance is still less popular in concrete industry. The present study investigates and compares the key mechanical properties and durability performances of binary concrete mixes designed with different replacement levels of SF and MK varying from 5% to 25% of Portland cement (PC).The results indicate that using both SF and MK in a partial substitution of PC could significantly improve strengths and durability performances of blended cement concrete mixes in comparison with the control PC-concrete. Meanwhile, SF-concrete seems to perform better than MK-concrete with regards to strength development and resistance to freezing-thawing while MK-concrete has exhibited a better performance with regard to carbonation and chloride ions ingress. Furthermore, although economical assessment showed an increase in the cost of concrete made with SF/MK due to the fact that SF/MK are more expensive than PC, environmental assessment revealed that significant reduction of the embodied CO2 (ECO2) is generated when using MK, and especially SF as a partial substitution of PC. Designing a binary SF and MK concretes may help towards producing clean and environmentally friendly concrete material.

PERFORMANCE OF STEEL MICRO FIBER REINFORCED MORTAR MIXTURES CONTAINING PLAIN, BINARY AND TERNARY CEMENTITIOUS SYSTEMS

Steel micro fibers provide strengthening, toughening and durability improvement mechanisms in cementitious composites. However, there is not much data in the literature regarding how the extent of their effectiveness changes depending on the type of matrix being reinforced. For clarifying this point, the influence of a constant volumetric ratio (1%) of 6 mm long steel micro fibers on the performance of 5 mortar mixtures was investigated and were prepared using plain, binary and ternary cementitious systems. A total of 10 mixtures were cast. The mineral admixtures used in the study include silica fume (SF), metakaolin (MK) and a Class C fly ash (FA). While the replacement levels of SF and MK were 10% by weight of the total mass of the binder, this ratio was chosen as 30% for FA. In addition to the behavior of the mixtures under compressive, flexural and impact loads, abrasion, water absorption, chloride ion penetration, freezing-thawing resistance and drying shrinkage characteristics of the mixtures were determined. Test results indicate that generally the refinement in the pore structure of the matrix provided by mineral admixtures and the increase in resistance against growth and coalescence of micro-cracks provided by fibers produce a synergistic effect and improve the investigated performances of the mixtures.

Pozzolanic Reactivity of Silica Fume and Ground Rice Husk Ash as Reactive Silica in a Cementitious System: A Comparative Study.

This study comparably assessed the pozzolanic effect of silica fume (SF) and ground rice husk ash (RHA) as supplementary cementing materials on the properties of blended cement pastes and concretes. A commonly commercial silica fume (SF) and locally-produced rice husk ash (RHA) samples with two finenesses (one with larger size than cement and the other with smaller size than cement) were used in this study. Material properties of SF and RHA were experimentally characterized. Hydration and mechanical properties of cement pastes incorporating SF and RHA were determined by thermogravimetric analysis (TGA) and compressive strength tests, respectively. Properties of concretes regarding workability, mechanical property, durability, and microstructure were evaluated. Results showed that, although the finely ground RHA used in this study possessed lower SiO2 content and higher particle size compared to SF, it exhibited comparable pozzolanic reactivity with SF due to the nano-scale pores on its each single particle, leading to a higher specific surface area. The optimal replacement levels of SF and RHA were 10% by weight of cement in pastes and concretes. Although addition of SF and RHA led to a significant reduction in slump for the fresh mixtures, inclusion of up to 30% of SF or 15% of ground RHA did not adversely affect the strength of concretes. At the same mix, incorporation of finely-ground RHA in cement composites provided comparable mechanical properties, hydration degree, and durability with SF blended cement composites, owing to the porous structure and high specific surface area of RHA particles. Microstructure morphology analysis of concretes explored by scanning electron microscopy (SEM) further validated the strength and the durability test results.

Mechanical and durability properties of waste rubber fiber concrete with and without silica fume

Availability of natural sand conforming to required standards for use in concrete is diminishing day by day and is severely affecting the construction industry. On the other hand, disposal of used rubber tyres is an environmental, health and esthetic problem as its recycling is extremely difficult. In this paper, a systematic experimental investigation is carried out on concrete with rubber fibers (obtained by grinding waste rubber tyres) as partial replacement of fine aggregates, to evaluate the compressive strength, density, water permeability, static modulus of elasticity, dynamic modulus of elasticity and chloride diffusion. Rubber fibers have been used with three different water–cement ratios (0.35, 0.45 and 0.55). Six levels of rubber fibers contents (0, 5, 10, 15, 20 and 25%) as partial replacement of sand and three levels of silica fume (0, 5 and 10%) as partial replacement of cement have been considered. Microstructure analysis of rubber fiber sample by scanning electron microscope and Energy dispersive X-ray analyzer has been carried out. Compressive strength, static and dynamic modulus of elasticity of waste rubber tyre fiber concrete are found to decrease with the increase in the replacement level of fine aggregates by rubber fibers.

MECHANICAL PROPERTIES OF HEAVY WEIGHT CONCRETE USING HEAVY WEIGHT COARSE-AGGREGATE AS HEMATITE (FE58 HIGH GRADE IRON ORE)

Density concrete is commonly used for radiation shielding of nuclear-reactors and other structures like counter weights, coating of off-shore pipelines. Density concrete or heavy weight concrete is designed by using heavy weight aggregates such as hematite, magnetite, barite etc. The material is called hematite is used in this special concrete. Integral part of this paper is replacing coarse-aggregate by hematite aggregate partially from 0 to 50% volume at 25% intervals. The concrete mix as per IS-10262-(2009) is used for M25 and M35 grades of concrete and in this only coarse aggregate is replaced with heavy weight hematite coarse aggregate and natural sand is used as fine aggregate and three levels of silica fume at 5%, 10% and 15% are used by weight of cement. All mixes are designed for 100mm slump. Water-cement ratio as per grade of concrete

Effect of silica fume and ground pumice on compressive strength and modulus of elasticity of high strength concrete

This paper presents the results of experimental study on compressive strength and secant modulus of elasticity of high strength concrete (HSC) containing different levels of silica fume, ground pumice and silica fume together with ground pumice. Three concrete series with water–binder ratios of 0.25 and a constant total binder content of 450kg/m3 were designed. The compressive strength and secant modulus of elasticity of these concrete series were determined. The experimental results clearly reveal the use of silica fume and silica fume together with ground pumice with a very low water–binder ratio in the production of HSC. The highest compressive strength and secant modulus of elasticity are obtained in the concrete mixtures containing 15% silica fume and 15% silica fume together with 5% ground pumice. The relationship between the compressive strength and secant modulus of elasticity of HSC was also discussed. New two equations for modulus of elasticity of concrete containing different levels of silica fume, ground pumice and silica fume together with ground pumice have been proposed. The experimental results of dependent modulus of elasticity of concrete were compared with the results of various equations proposed by some of national building codes and the authors, and also the results of new equations proposed in this study.

The influence of supplementary cementing materials on water retaining characteristics of hydrated lime and cement mortars in masonry construction

The purpose of this paper is an investigation of the possible role of supplementary cementing materials (SCMs) on the water retaining ability of hydrated lime (CL90) and Portland cement (PC) mortars. Desorptivity (R) defines the water retaining ability of mortars in the freshly-mixed wet state. Transfer sorptivity (A) defines the ability of the substrate to withdraw water from the wet mix. The time to dewater (t dw), is an expression derived from the sharp front theory, and enables calculation of the time taken for a wet mortar joint to be dewatered by an absorbent substrate. The results show that the very water retaining CL90 mortars become progressively more water releasing with increased volume fraction replacement levels of both ground granulated blast-furnace slag (GGBS) and fly ash (FA). On the other hand, the very water releasing PC mortars become more water retaining with the addition of silica fume (SF). Results also show that transfer sorptivity increases as the volume fraction replacement levels of GGBS and FA increases in CL90 mortars and decreases with increased volume fraction replacement levels of SF in PC mortars. Since the time taken to dewater a mortar joint (t dw) is inversely proportional to the squared transfer sorptivity, t dw can be dramatically altered by the addition of SCMs in both CL90 and PC mortars. These parameters have important practical consequences, not only in the initial adhesion of the mortar to the substrate but also in the strength of the set material. The ability to manipulate the water retaining properties can also allow construction time to be reduced.

Mechanical properties of high-strength concrete incorporating copper slag as coarse aggregate

Copper slag is a by-product obtained during the matte smelting and refining of copper. Current options of management of this slag are recycling, recovering of metal, production of value added products and disposal in slag dumps or stockpiles. This paper presents the results of a study undertaken to investigate the feasibility of using copper slag as coarse aggregates in high-strength concrete. The effects of replacing limestone coarse aggregate by copper slag coarse aggregate on the compressive strength, splitting tensile strength, and rebound hammer values of high-strength concretes are evaluated in this work. Concrete mixtures containing different levels of silica fume were prepared with water to cementitious materials ratios of 0.40, 0.35, and 0.30. The percentages of the cement replacements by silica fume were 0%, 6%, and 10%. The use of copper slag aggregate compared to limestone aggregate resulted in a 28-day compressive strength increase of about 10–15%, and a splitting tensile strength increase of 10–18%. It can be concluded from the results of this study that using copper slag as coarse aggregate in high-strength concrete is technically possible and useful.

The effect of high temperature curing on the strength and carbonation of pozzolanic structural lightweight concretes

An experimental study on the compressive strength and carbonation depth of lightweight concrete mixes that contain pulverized fuel ash (PFA) and silica fume (SF) as cement replacements is presented in this paper. Mixes that had a relatively high replacement level of PFA at 25, 40, and 55% and of SF at 5, 10, and 15% by weight were compared. The results indicated that accelerated curing at 60 °C for 3 days improved the 28-day compressive strength of the PFA- and SF-incorporated mixes but resulted in higher carbonation of the mixes compared with that under normal temperature curing. Mixes that had 25% PFA or 5–10% SF as partial cement replacements had slightly higher strength under accelerated curing and slightly lower strength under normal curing than the control mix. At higher replacement levels of PFA and SF, further lower strength and higher carbonation was observed.

Alkali release characteristics of blended cements

This paper presents results of an experimental program conducted to investigate the capacity of hydration products of different cementing materials to retain “bound” alkalis when the alkalinity of the surrounding solution drops. The study covered paste samples containing high-alkali Portland cement and various levels of silica fume and/or fly ash. The results showed that the ability of the hydration products of cement-fly ash systems to bind alkalis is a function of the CaO content of the fly ash, the binding increasing as the calcium content decreases. High-alkali fly ashes (Na 2O e > 5.0% and CaO in the range of 15% to 20%) showed considerable amounts of alkali contributed to the test solutions. Silica fume does not have a high capacity to retain alkalis in its hydration products; however, ternary blends containing silica fume and fly ash have excellent capacity to bind and retain alkalis.