Wollastonite Microfibers Research Articles

Soil reinforcement through addition and subsequent carbonation of wollasonite microfibres

This study describes the application of wollasonite microfibres for stabilising soil with the additional function of sequestering CO2. The high aspect ratio, needle-like structure of wollasonite imparted a microfibre mechanical reinforcement whilst the associated high surface area promoted carbonation. The originality of this paper lies in two unique aspects: the first stage assessed the efficacy of incorporating wollastonite microfibres inside the soil mass, while the second stage addressed the mechanical performance of the fibre-reinforced soil after different CO2 pressures and carbonation times. In these two stages, the unconfined compressive strength (UCS), indirect tensile strength (ITS) and flexural strength (FS) were determined. The test results indicated that the inclusion of the fibres increased the peak and post-peak response during unconfined compressive strength (UCS) tests, while also improving the ITS and FS. The UCS peak stress was further improved when the fibre-reinforced soil was subjected to the carbonation process. This work impacts the soil stabilisation industry through a novel soil strengthening process that also promises an effective route to combat climate change through sequestration of CO2.

Comparison of Permeability and Drying Shrinkage of Self Compacting Concrete Admixed with Wollastonite Micro Fiber and Fly Ash

Cement substitution in self compacting concrete (SCC) is emphasized to conserve environment, reduce cost and utilize waste materials. This paper focuses on comparing the permeability and drying shrinkage of SCC containing Wollastonite micro fiber (WMF), a cheap pozzolanic fiber with respect to flyash. Microsilica was added for providing required viscosity to maintain homogeneity of the mixes. Trials to check flowability, passability and segregation resistance were conducted on binary, ternary and combined mixes of binder material. Results showed that drying shrinkage reduced by 49% for WMF reinforced concrete, whereas it increased by 1.25% for flyash ones as compared to normal concrete. Permeability coefficient decreased by 82% and 74%, respectively. Capillary voids influenced the permeability of hardened concrete, but drying shrinkage was largely influenced by the rate of gain of tensile strength and expanding ettringite. Notably, flyash is not a reliable admixture for controlling drying shrinkage of high flow concretes.

Laboratory-Scale Model of Reinforced Alkali-Activated Agro-Waste for Clayey Soil Stabilization

Abstract This study assessed the laboratory model investigation to evaluate the feasibility of using reinforced alkali-activated binder for the purpose of soil stabilization. This paper consisted of two stages. The first stage investigated the efficacy of incorporating alkali-activated binder in conjunction with reinforcement inclusion, which improves satisfactory mechanical properties in treated soil. As such, in the first stage, palm oil fuel ash (POFA) and wollastonite microfibers were incorporated in the form of precursor and dispersed discrete reinforcement, respectively. In this stage, the unconfined compressive strength (UCS) was used as a practical indicator to investigate strength development. In the second stage of this study, a model procedure of interaction between a strip footing model and stabilized clayey soil by column technique was examined. From the perspective of strength development, alkali-activated agro-waste showed, undoubtedly, a very effective method to enhance the peak strength of investigated soil. Besides, the inclusion of the reinforcement material in alkali-activated samples increased the peak stress and improved the post-peak behavior, namely by modifying the original brittle response of the stabilized soil into a more ductile one. Depending on the replacement area ratio, results of the second phase showed that a considerable bearing capacity increase of up to 197 % of treated columns could be achieved.

Application of Alkali-Activated Agro-Waste Reinforced with Wollastonite Fibers in Soil Stabilization

AbstractThis study addresses the feasibility of using palm oil fuel ash (POFA) as a precursor in alkali activation reactions, as well as mineral wollastonite microfibers as discrete reinforcement. ...

Quantitative 2D Restrained Shrinkage Cracking of Cement Paste with Wollastonite Microfibers

AbstractPlastic shrinkage cracking in restrained cement pastes reinforced with wollastonite particles of micro and submicron sizes was studied using a quantitative two-dimensional (2D) cracking experiment. A series of blended paste mixes with portland cement and different grades of wollastonite fibers were developed and tested under low vacuum conditions. Testing parameters included four grades of wollastonite with aspect ratio in the range of 3∶1–20∶1 and average particle size ranging from 33 to 2,000 μm at 15% cement replacement. Wollastonite beneficially altered the shrinkage cracking morphology by arresting crack growth, wherein crack lengths and widths were reduced by a factor of two, and the area by a factor of three when compared with the control specimens. However, the initial evaporation rate, early age diffusivity, and cumulative moisture loss increased. Influence of the microfibers in controlling early age drying were related to the porosity of the microstructure using mercury intrusion porosim...

Effect of Wollastonite Microfiber on Ultra-High-Performance Fiber-Reinforced Cement-Based Composites Based on Application of Multi-Scale Fiber-Reinforcement System

The development of ultra-high-performance fiber-reinforced cement-based composites (UHP-FRCCs) was motivated by the need for a new and versatile material with high energy absorption capacity. With its excellent cracking resistance and consequent long life, UHP-FRCC is suitable for use in seismic design applications. The present study proposes a material design concept based on a multi-scale fiber-reinforcement system. In this approach, long, thick macrofibers are blended with short, thin mesofibers and microfibers. Such a combination of macrofibers, mesofibers, and microfibers is expected to enhance the mechanical properties of the composite under tension. However, the ductility of cement-based composites reinforced solely by microfibers is largely unknown. Therefore, in this study, the authors assessed whether microfiber improves the ductility of UHP-FRCC in two series of experiments. Wollastonite, which is a needle-shape mineral, is employed as a microfiber, and two different types of steel fibers are used as meso- and macrofibers. First, the enhanced toughness was evaluated in three-point bending tests on notched mortar beams. Second, the influence of wollastonite microfiber on the mechanical properties of the blended multi-scale fiber-reinforcement system was evaluated in uniaxial tension tests. Blends of macrofibers, mesofibers, and wollastonite microfibers exhibited strong reinforcement characteristics. The results indicate that the ductility of composites reinforced with wollastonite microfibers is highly dependent on the microfiber contents and type of fiber used and that blending of micro-, meso-, and macrofibers produces a highly ductile UHP-FRCC. Thus the material design concept based on the multi-scale fiber-reinforcement system proposed in this paper was shown to be effective in increasing the ductility of UHP-FRCC, even under uniaxial tension.

EXPERIMENTAL INVESTIGATION OF MICRO-REINFORCED, ALKALI-ACTIVATED GROUND GRANULATED BLAST FURNACE SLAG WITH WOLLASTONITE

The alkali activation of ground granulated blast furnace slag with a potassium-based solution has demonstrated production of a cementating material with early compressive strength higher than concretes based on ordinary Portland cement. This strength can be increased by reinforcing the paste with wollastonite micro-fibers. This paper presents the results obtained when an alkaliactivated slag paste was reinforced with two types of wollastonite, NYAD G and wollastocoat. Compressive strength, setting time, and microscopic structure were analyzed as a function of type of wollastonite and percentage of wollastonite added. All properties were compared to potassium-based alkali-activated slag without wollastonite. Based on a 28 day compressive strength curve, it was determined that the optimal loading of wollastonite in slag generated an average compressive strength of 55.1 MPa, an increase in strength of 60% from the wollastonite-free sample. Higher loading of wollastonite was shown to significantly reduce the setting time of the samples. The cost of all samples was compared to concrete based on ordinary Portland cement using average prices in western New York. It was found that the cost of AAS is about 6.4 times higher than regular concrete, for this reason alternative uses for microreinforced samples were explored.

OPTIMIZATION OF ALKALI ACTIVATION OF GROUND GRANULATED SLAG WITH MINING TAILS

Previous studies have shown that the reinforcement of alkali activated ground granulated blast furnace slag (GGBFS) with Wollastonite micro-fibers enhances the compressive strength and thermal stability of the composite. Compressive strength of alkali activated slag with 10% of Wollastonite per mass reached a 7 day compressive strength of 55.15 MPa (8000 psi). However, the estimated cost of this formulation is six times greater than similar concretes based on ordinary Portland cement. Different aggregates were tested to reduce the cost of this formulation. It was found that when mine tailings were added, the 7 day compressive strength reached 41.36 MPa( 6000 psi)), the setting time doubled and the cost was reduced by 2/3. These results are promising for the development of a cost effective formulation. Based on these results, a two factorial design with a three level design of experiments was conducted to explore the joint effect of Wollastonite and mine tailings on alkali activated GGBFS. In order to find the significant factors, the compressive strength would act as the response variable. The setting time and cost of each combination is also considered to find the optimal combination resulting from the experiment.

Effects of shrinkage reducing admixture and wollastonite microfiber on early-age behavior of ultra-high performance concrete

In this study, the effect of incorporating shrinkage reducing admixtures (SRA) and/or wollastonite microfibers on the early-age shrinkage behavior and cracking potential of ultra-high performance concrete (UHPC) was explored. Wollastonite microfibers were added at rates of 0%, 4% and 12% as partial volume replacement for cement, while SRA was added at 1% and 2% by cement weight. Results show that the reinforcing effect induced by wollastonite microfibers mitigated the reduction in compressive strength induced by SRA. Addition of wollastonite microfibers to SRA mixtures did not impart a significant change in the measured free shrinkage strain, while it enhanced the cracking resistance compared to that of mixtures incorporating SRA alone. Moreover, adding wollastonite microfibers reduced the leaching of SRA from concrete under submerged conditions, thus leading to higher efficiency of SRA in reducing shrinkage. Partially replacing cement with natural wollastonite microfibers also leads to a reduction in the cement factor, which represents economic and environmental benefits.

Micro Fiber Reinforced Cement Paste and Mortar Overlays-A Review

All cement composites have same deficiencies; weak tensile strength (brittleness) and limited deformation capacity in the presence of cracking. Due to these deficiencies they need repairing and rehabilitation from time to time in order to prolong the life of existing concrete structures. An overlay of cement composite (upto 100 mm) is considered one of the most practical approach and economical options available but it envisaged to have suffer durability of pavement structure due to debonding and spalling. To inculcate such shortcoming, employment of micro-fibers reinforced cement composites is believed to be a viable solution. For a thin sheet fiber reinforced cement concrete having initial flaw of approximately 60 μm, fibers with diameter ＜30 μm will be deemed microdiameter fibers. Generally micro-fibers are fine fibers with lengths less than 10 mm and diameters in range 25-40 μm. With their high specific surface areas (＞ 200 cm^2/g), they provide a large number of fibers in a given section of the composites and thus furnish more effective reinforcing mechanisms at the microcracking level (cracking due to thermal and mechanical shrinkage). This review paper has been framed in a manner to compile the available literatures related to overlays using micro-fibers and to serve as a literature reservoir for research scholars. In the present paper, role of fiber in the performance of concrete, mechanism of microcracks form and grow in the frontal process zones and application of various micro-fibers in high performance concrete were discussed. Advantages of thinner fibers over thicker fibers, role of polypropylene fiber (PP fiber), Poly Vinyl Alcohol (PVA), steel micro-fibers, carbon micro-fibers, wollastonite micro-fiber were discussed elaborately.

Effect of Natural Wollastonite Microfibers on Early-Age Behavior of UHPC

In this study, the effect of incorporating wollastonite microfibers in ultrahigh performance concrete (UHPC) on its early-age properties was investigated. Wollastonite microfibers were added at 0, 4, 8, and 12% as partial volume replacement for cement. Results show that the early-age properties of UHPC mixtures incorporating wollastonite microfibers are highly affected by the microfiber content and aspect ratio. Increasing the wollastonite microfiber content resulted in a compressive strength comparable to or higher than that of the control mixture without microfibers. Wollastonite microfibers reduced shrinkage strains and increased cracking resistance compared to that of the control mixture. However, no significant improvement in the flexural behavior was achieved with the addition of wollastonite microfibers because of a sudden rupture of microfibers within the matrix. Wollastonite microfibers can act as an internal restraint for shrinkage, reinforcing the microstructure at the microcrack level, and leading to an enhancement of the early-age engineering properties of UHPC matrix. Partially replacing cement with natural wollastonite microfibers leads to a reduction in the cement factor, which represents economic and environmental benefits.

Influence of surface treatment on hybrid wollastonite-polyethylene composite resins for rotational moulding

The purpose of this research was to develop a reinforcing material for polyethylene-based composite manufacture by rotational moulding. Wollastonite, sisal fibres and PE are premixed by blending and compounding with a single screw extruder and then granulated to particles with diameter about 0.5 mm prior to rotational moulding, for which the mixture is placed in a mould that is heated from the outside to 250 °C for a period of about 10 min. Aminosilane was used as a surface treatment for wollastonite. It was found that incorporating wollastonite microfibres improved the tensile properties of the system. When wollastonite fibres were coated with aminosilane, the impact strength and processability were enhanced greatly. Sisal fibres were added to improve the impact properties. Scanning electron microscopy revealed good adhesion between the coated fibre reinforcement and the polyethylene matrix at the fracture surface. The mechanism of this phenomenon is discussed.

Effect of Coupling Agents and Particle Size on Mechanical Performance of Polyethylene Composites Comprising Wollastonite Micro-Fibres

The usefulness of rotational moulding (rotomoulding) as a polymer processing technique is often limited by the selection of polymers, which in most cases happens to be polyethylene (PE). In the present study, PE polyethylene was blended with wollastonite microfibres and maleated polyethylene (as a coupling agent) with the purpose of developing an improved material for rotational moulding. The incorporation of wollastonite fibres without any coupling agent improved the tensile strength, but showed a reduction in impact strength. As expected, the most significant enhancement due to wollastonite was in the tensile modulus.. The addition of a coupling agent improved both the impact strength and the processability, especially when wollastonite was coated with aminosilane. Scanning electron microscopy revealed good adhesion between the coated fibre reinforcement and the polyethylene matrix at the fracture surface.

Fibre reinforcement and fracture response in geopolymeric mortars

ABSTRACTThe inorganic polymeric cement called geopolymer or PSS, has been studied in recent years as a binder for mortar and concrete. The present work reports the fracture toughness studies in mortars made of PSS cement matrix reinforced by wollastonite microfibers (Ca(SiO3)). KI‐curves for PSS cement composites were determined according to the superposition asymptotic assumption and compared with reference Portland cement (PC) composites. The maximum toughness gain occurs in both composite systems with Vf = 2%. For higher fibre volumes (3 and 5%), KI values decrease, due to an increase in porosity. Microstructural analyses showed that toughening mechanisms, as debonding and pullout of the fibers, are more common in PSS cement composites than in the reference PC composites. The difference of toughness between PSS and PC cement (0% of fibers) is about 80%. This demonstrates the high performance of these geopolymeric materials.

Stability of portland cement-based binders reinforced with natural wollastonite micro-fibres

The stability of Portland cement-based binders reinforced with natural wollastonite micro-fibres was investigated for hydration periods up to one year. The wollastonite microfibres imbedded in the hydrated cement paste were examined employing a scanning electron microscopy technique. Composite specimens were also periodically evaluated by flexural strength testing and microstructural characterization including mercury intrusion porosimetry, helium gas pycnometry, and isopropyl alcohol saturation measurement. The amount of Ca(OH) 2 in the hydrated matrices was also determined by differential scanning calorimetry. Wollastonite micro-fibres imbedded in hydrated cement-silica fume matrices remained stable after prolonged hydration and exhibited no surface or bulk deterioration. The flexural strength and overall pore structure of the Portland cement-based binders reinforced with wollastonite micro-fibres also remained essentially unchanged and unaffected. Flexural toughness and the post peak deflection, however, were observed to decrease with hydration time. The amount of Ca(OH) 2 in the hydrated matrices decreased slightly at advanced hydration times. The observed behaviour is discussed.

The flexural toughness and ductility of portland cement-based binders reinforced with wollastonite micro-fibres

An analysis of the flexural toughness and ductility of Portland cement-based binders reinforced with natural wollastonite micro-fibres is reported. The flexural toughness was calculated as the sum of finite area increments under the entire load-deflection curve and the ductility was determined from the deflection in the post-peak region. Load-deflection curves were created with numerical data obtained in flexural tests employing the computer controlled MTS system. Five series of specimens were investigated. A series of specimens made with cement and blended with different amounts of silica fume served as reference systems. The other four series of specimens contained seven different concentrations of wollastonite micro-fibres, each series having a different amount of silica fume. Results showed that the flexural toughness of the cement-silica fume system decreased non-linearly as the amount of silica fume in the mixture increased. The flexural toughness of the cement-wollastonite composite system and the cement-silica fume-wollastonite composite system was observed to increase almost linearly as the concentration of the wollastonite micro-fibres in the composite matrices increased. The increase of the flexural toughness with increasing concentration of wollastonite micro-fibres in the composite mixtures was influenced by the amount of silica fume. The ductility of the composite matrices increased nonlinearly with increase in concentration of wollastonite micro-fibres in the composite mixtures. The amount of silica fume in the composite matrix had no significant role in modification of ductility in the composite system. Differences in observed properties are discussed.

Mechanical properties and microstructure of high alumina cement-based binders reinforced with natural wollastonite micro-fibres

Results of an investigation to determine the dependence of mechanical properties on microstructure of high alumina cement (HAC)-based binders reinforced with natural wollastonite micro-fibres are reported. Two composite systems were studied. One was the HAC-wollastonite system the other the HAC-silica fume-wollastonite system. In both systems, wollastonite micro-fibres varying from 2% to 15% by volume were blended with the base cement matrix. The composite specimens were evaluated by flexural testing and microstructural characterization including mercury intrusion porosimetry, helium gas pycnometry, and isopropyl alcohol saturation measurements. Flexural strength of both composite systems increased linearly with concentration of wollastonite micro-fibres. The replacement of HAC with silica fume resulted in a small reduction of the flexural strength. Variation in flexural toughness, ductility, total porosity and pore size distribution between composite systems is discussed.

The effect of wollastonite micro-fibre aspect ratio on reinforcement of Portland cement-based binders

Reinforcement of Portland cement-based binders with natural wollastonite microfibres has been further investigated with emphasis on the effect of fibre geometry on property modification. Wollastonite micro-fibres were separated into five different size groups before addition to cement and cement-silica fume matrices. The aspect ratio (length/width) of the wollastorite micro-fibres was determined by scanning electron microscopy technique. Systematic experimentation including flexural tests, mercury intrusion porosimetry, helium gas pycnometry, and isopropyl alcohol saturation measurement showed that, at constant micro-fibre content, the flexural strength and total porosity of the composites remained essentially unchanged and independent of the aspect ratio of the wollastonite micro-fibres. However, the volume of coarse pores, the pore size distribution, the flexural toughness and overall ductility characteristics of the hydrated cement and cement-silica fume matrices were observed to change systematically as the aspect ratio of wollastonite micro-fibres was increased. A discussion of the differences in the observed properties is presented.

Flexural strength and microstructure of cement binders reinforced with wollastonite micro-fibres

An investigation of cement composite behaviour showed that a flexural strength in excess of 28 MPa (4080 psi) can be readily attained in normal cement paste by incorporating an optimum amount of silica fume and 11.5% by volume of natural wollastonite micro-fibres. Systematic experimentation showed that modification of the flexural strength and the microstructure in hydrated cement and cement-silica fume matrices by addition of natural wollastonite micro-fibres is strongly controlled by the proportion of the various components. A discussion based on results obtained in bending tests, mercury intrusion porosimetry, helium gas pycnometry, and isopropyl alcohol saturation measurement, is presented in terms of composite theory and difference in observed properties.

Mechanical properties of high performance cement binders reinforced with wollastonite micro-fibres

Factors that influence the flexural strength characteristics of the cement-water and the cement-silica fume-water systems reinforced with inorganic wollastonite micro-fibres are discussed. The effect of the wollastonite micro-fibres on matrix pore structure was investigated using mercury intrusion porosimetry and helium gas pycnometry. Fibre-matrix interaction was also examined using the conduction calorimetry method. Results indicated that natural wollastonite micro-fibres are effective in improving both pre-peak and post-peak load behaviour. The results are discussed in terms of composite theory and matrix microstructure.