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Methodology for flocculant selection in fibre–cement manufacture
Abstract
In the Hatschek process used to produce fibre–cement products, it is necessary to use a suitable flocculant when asbestos is substituted by pulp fibres. The right selection of flocculant is crucial in the industrial process due to its effects on mineral fines retention, dewatering and formation and, as a consequence, on the overall efficiency of the machine. This paper presents a two-step methodology for flocculant selection in the fibre–cement manufacture. The first step is based on the study of the flocculation processes and the flock properties, using a focused beam reflectance measurement (FBRM). This technique allows the study of flock size, flock stability and flock resistance to shear forces, reflocculation tendency and reversibility of the flocks, as well as the optimal flocculant dosage for each particular fibre–cement suspension. The second step uses a drainage vacuum tester to study retention and dewatering. The two techniques give important and complementary informations that allow a proper selection of the best flocculant for the fibre–cement manufacture.
... Corrugated asbestos-free fiber-cement roofing sheets are composite building materials essentially made of a cementitious matrix composed by Ordinary Portland Cement and fine mineral particles (limestone, silica fume or metakaolin), and reinforced with a mix of cellulose pulp and polymeric fibers. Sheets are frequently formed using the Hatschek process as piled monolayers that are profiled to improve impact resistance and water shed capability [1][2][3][4]. ...
... It is worth noting that the curvature of the disks caused by sheet corrugation was small enough in this case to be disregarded in the calculation of the face area. The total mass of each sheet (M sheet ) can thus be predicted by: (2) in which A flat is the flat area of each commercial sheet, including the curvatures caused by corrugation (for the tested products, A flat = 1.586 m 2 , a value given by the manufacturers). ...
... Due to the peculiarities of the Hatschek process [1][2][3][19][20], a 5-mm thick sheet may contain a stack of 12 to 20 monolayers that are not uniform in composition and instead have a fiber rich side and a fiber poor side. If the vacuum belt and rollers are not balanced during the film formation process, one region of the sheet may be more compressed than the other, resulting in layered zones of different densities and thus permeabilities, which helps to explain the lateral profile shown in Fig. 6a, with k 1 decreasing from left to right. ...
A rapid non-destructive experimental method was used to assess the permeability of different brands of commercial corrugated fibercement roofing sheets. In comparison to standardized methods that take up to 24 h to complete, the proposed method allowed for air and water permeability analyses in 5 and 30 min, respectively. The air permeability coefficient of tested sheets ranged from 1.4 × 10⁻¹⁶ to 1.6 × 10⁻¹⁴ m². The water permeability coefficient was one order of magnitude lower (2.8×10⁻¹⁷ to 6.6×10⁻¹⁶ m²), confirming the interference of hydrophobic/waterproofing components in the formulation. There was no direct relationship between sheet thickness and air or water permeation resistance.
... T The flocculant used to study the behavior of fiber-cement suspensions and to prepare the fiber-cement probes was an anionic polyacrylamide (APAM) with a molecular weight of 7.4 × 10 6 g/mol and a charge density of 13.4%, commonly used in the industrial Hatschek process (Negro et al., 2006). Flocculant was dissolved in distilled water to prepare solutions of APAM with a concentration of 1.5 g/L. ...
... The FBRM monitors the chord length distribution of the particles in suspensions in situ and on real time. The principle of the measurement and the details of the applied methodology have been described by the authors in previous references (Blanco et al., 2002;Hubbe, 2007;Jarabo et al., 2012a;Kerekes and Schell, 1992;Negro et al., 2006Negro et al., , 2007. ...
... This equipment has two jars separated by a barrier: the upper jar keeps the fiber-cement suspensions stirred up to the addition of the flocculant dosage. The second jar contains a mesh at the bottom to carry out the dewatering of the suspension and it is connected to a vacuum pump and to a probe where filtrate is stored and weighted on real time and the final volume of filtrate is measured (Negro et al., 2005(Negro et al., , 2006. In a typical trial, 400 mL of fiber-cement suspension, prepared with water saturated in Ca(OH) 2 , were stirred at 600 rpm during 6 min in the upper jar. ...
The possibility of using wastes, such as corn stalk and hemp core, as raw material for asbestos-free fiber-cement is quite feasible, considering environmental and economic aspects. However, although there are many studies on the use of other agricultural wastes, there is a lack of information on the characterization of these pulp fibers and their use as reinforcement in fiber-cement corrugated sheets. In this chapter, the feasibility of using organosolv pulps obtained from corn stalk (Zea mays L.) and industrial hemp core (Cannabis sativa L.) as a source of reinforcement fibers in the production of fiber-cement is studied. The morphology of the pulp and its effect on flocculation, retention, and drainage processes and on physical and mechanical properties of the product are presented. Results show that the replacement of pine fibers by those from agricultural wastes, especially hemp core organosolv fibers, improves retention and drainage process while allowing to obtain a fiber-cement with similar physical and mechanical properties to that from pine Kraft fibers.
... T The flocculant used to study the behavior of fiber-cement suspensions and to prepare the fiber-cement probes was an anionic polyacrylamide (APAM) with a molecular weight of 7.4 × 10 6 g/mol and a charge density of 13.4%, commonly used in the industrial Hatschek process (Negro et al., 2006). Flocculant was dissolved in distilled water to prepare solutions of APAM with a concentration of 1.5 g/L. ...
... The FBRM monitors the chord length distribution of the particles in suspensions in situ and on real time. The principle of the measurement and the details of the applied methodology have been described by the authors in previous references (Blanco et al., 2002;Hubbe, 2007;Jarabo et al., 2012a;Kerekes and Schell, 1992;Negro et al., 2006Negro et al., , 2007. ...
... This equipment has two jars separated by a barrier: the upper jar keeps the fiber-cement suspensions stirred up to the addition of the flocculant dosage. The second jar contains a mesh at the bottom to carry out the dewatering of the suspension and it is connected to a vacuum pump and to a probe where filtrate is stored and weighted on real time and the final volume of filtrate is measured (Negro et al., 2005(Negro et al., , 2006. In a typical trial, 400 mL of fiber-cement suspension, prepared with water saturated in Ca(OH) 2 , were stirred at 600 rpm during 6 min in the upper jar. ...
In the last few years an increasing high interest has been drawn to the potential use of agricultural waste as raw material to produce structural reinforcement fibers for building materials, due to environmental and economical aspects. Corn is the world's most produced cereal in terms of quantity, what entails the generation of large quantities of waste. Despite this fact, only a few research works concerned with the use of fibers from waste corn stalks in the production of fiber-cement have been published and there is a complete lack of data on the characterization of these fibers.The objective of this research is to study the feasibility of using fibers obtained from corn stalk as reinforcement fibers in the production of fiber-cement through environmentally friendly cooking methods. This study encompasses the morphological characterization of the fibers and the study of the effects that the use of these fibers has on the flocculation, retention and drainage of the fiber-cement suspensions and on the mechanical and physical properties of the final product.The results obtained in the tests confirmed the high potential of the corn stalk as a source of fibers for the manufacture of a fiber-cement capable of meeting the requirements of demanding applications.
... Recently, a methodology based on monitoring flocculation and measuring retention and drainage 2 has been developed for flocculant selection. 2 This method is complemented by taking into account the flocculation kinetics, the behavior and evolution of the formed flocs, and the effect of the flocculant on product strength. 1, 3 Thus, different studies have been carried out considering the flocculation efficiency and the product quality: ...
... 24 This method was developed to avoid the limitations of methods based on electrokinetic or optical properties of the particles, and it has been successfully applied in the paper industry for monitoring flocculation and floc breakage. 2,[23][24][25][26][27][28][29] ...
... The principles of the measurement and the details of the applied methodology to monitor flocculation have been described in previous papers. 2,23,27 Images of the suspension were taken by a continuous videomicroscopy device, PVM 800, manufactured by Mettler Toledo, Lasentec, Seattle, WA. The procedure for taking images with the PVM and for monitoring flocculation with the FBRM is the same; the only difference is the probe used. ...
Flocculation has been a key issue for fiber cement manufacturing since cellulose or poly(vinyl alcohol) (PVA) fibers are used to replace asbestos. Due to the complexity of flocculation, many fiber cement companies face difficulties in optimizing it, which leads to unpredicted production problems and lower process efficiency. This paper studies the behavior of a dual system (PFR/PEO) and compares it with two anionic polyacrylamides commonly used in this industry. The work was carried out using a focused beam reflectance measurement as a sensor to monitor the flocculation process in real time. Results show that the proposed alternative dual system induces the formation of larger but less stable flocs than the ones obtained with the anionic polyacrylamides. A flocculation mechanism was proposed for the dual system consisting of the initial adsorption of the phenol−formaldehyde resin (PFR) onto the particles, which provides junction points for bridge formation by poly(ethylene oxide) (PEO). The flocculation kinetics induced by the dual system is determined by the PFR dosage.
... The main differential characteristics with other members of the group are the acicular morphology ( Fig. 1) and the high and active surface that reach the highest values for natural materials, close to 340 m 2 /g. Other important characteristics are related to the thermal and chemical stability of the structure that allows keeping stable properties at temperatures up to 300°C within a wide pH range (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) and very low electrolyte sensitivity, which is a very important characteristic in saturated cation media as the cement slurries. In addition to this, sepiolite does not show any reactivity during cement setting process [1,2]. ...
... The principle of the measurement and the details of the applied methodology have been described by the authors in previous Refs. [14][15][16][17][18]. A laser beam is generated by a diode and focused in a focal point in the plane next to the external surface of the probe windown, inside the suspension (Fig. 3). ...
... After 15 s of contact time between flocculant and mixture, the stirring was stopped, the barrier was removed and the suspension was drained to the second jar in which an 18 mesh wire was located. The suspension was drained under vacuum (0.2 atm) through the filter and a computerized balance recorded the mass of drained water over time [14]. The drainage curve was analysed in order to obtain the drainage rate for the different flocculants. ...
This research is focused on the study of the effect of rheological grade sepiolite on flocculation, retention and drainage of fiber–cement suspensions by using a focused beam reflectance measurement probe and a vacuum drainage tester. Results show that the sepiolite could be used in the manufacture of fiber–cement to increase the retention of solids and the drainage rate especially in mixtures containing poly(vinylalcohol) fibers.
... The degree of order within the fiber is reduced and there is an increase in the surface area of the fiber. In addition, with very strong cellulose-swelling agents, it is possible to reach a critical point where the [13] entire crystalline structure of the fiber is disrupted and the fiber structure is lost [39]. ...
... The presence of sugar in the chemical composition of hemicellulose and lignin in the wood fibers may have unfavorable effects upon the setting [39] and hardening of cement. To overcome this problem the fibers can be treated and/or the cement matrix can be modified through chemical additives. ...
... Consequently, the use of a flocculant is usually required to retain mineral particles in the composite sheet, with anionic polyacrylamides (A-PAMs) being the most frequently employed agents. 8,9 Moreover, additives can also be used to improve the properties of the matrix; for example, silica fume, microsilica, clay, mica, rheological-grade sepiolite, flocculants, and hydrophobic additives. 4,5 Metakaolin is a dehydroxylated form of the clay mineral kaolinite, and is used to accelerate cement hydration and to induce the pozzolanic reaction. ...
... The principle of the measurement and the details of the applied methodology have been described by the authors in the references. 8,9,14,15 A laser beam is generated by a diode and focused in a focal point in the plane next to the external surface of the probe window, inside the suspension. The focal point describes a circular path at a constant speed of 2000 m/s (78,740 in./s) due to the rotation of the focusing lens. ...
Asbestos has traditionally been used to provide reinforcement to cement, but since it
was banned, new formulations have been studied to obtain a product with similar
properties to the asbestos-cement sheets in the Hatscheck process. Asbestos presents a
high degree of mineral particles retention and allows easy processing given the good
rheological properties of the slurry it forms, ensuring a standardized and low cost
manufacturing process (Brown, 1998). The current asbestos-free technology requires
using a set of products to individually provide some of these properties. Depending on
the final use of the product and the curing technology, this set of products may consist
of: (1) reinforcing fibers and (2) additives to improve the matrix properties and/or the
interactions between the matrix and fibers.
Many different natural fibers (pine, sisal, hemp, eucalyptus, etc.) and synthetic fibers
(polyvinyl alcohol (PVA), polypropylene, polyacrylonitrile, etc.) have been tried as
reinforcing fibers (Zheng and Feldman, 1995; Savastano et al., 2000). The interaction of
cellulose and PVA fibers with mineral particles is weak due to the organic nature and
the low density of these fibers. Consequently, the use of a flocculant is usually required
to retain mineral particles in the composite sheet, with anionic polyacrylamides (APAMs)
being the most frequently employed agents.
Moreover, additives can be also added to improve the properties of the matrix. The
sepiolites are rheological additives specially manufactured to be used in the production
of fiber-reinforced cement without asbestos. Sepiolite is used to increase thixotropy of
cement slurries for easier processing, to prevent sagging and to provide a better final
quality in the manufacture of fiber-reinforced cement products. This clay is a hydrated
magnesium silicate of the Palygorskitas group, characterized by its high specific surface
area (340 m2/g) and the acicular morphology of the particles. These features give a high
capacity to interact with mineral fillers (Kavas et al., 2004).
Both industrial experience and research have shown that the addition of sepiolite to the
fiber–cement mixture is particularly efficient in modifies the humidity of the sheet and
this may contribute to the improving the interlaminar bonding, particularly in
corrugated sheets prepared by the Hatscheck process, while improving process stability
and surface finishing (Kavas et al., 2004; Fuente et al., 2010). However, there is only
little information published about the interactions between sepiolite and the rest of the
components of the slurry and about its effects on the process and on the product
properties (Jarabo et al., 2010). Therefore, the aim of this research is to study the effect
of using sepiolite as a rheological aid on the asbestos free fiber-cement manufacture
process and on the physical and mechanical properties of the fiber-cement sheets when
they contain natural fibers and mixes of synthetic and natural fibers with sepiolite.
The effect of sepiolite on the flocculation of the slurry and on the floc properties were
studied by monitoring the chord size distribution in real time employing a focused beam
reflectance measurement (FBRM) probe. The effect of sepiolite on retention and
drainage of fiber-cement suspensions were determined by using a vacuum drainage
tester. Probes were prepared with and without using sepiolite and physical and
mechanical properties were measured after 28 days curing, by following the procedures
specified in ASTM C 948-81 and by using the universal testing machine Emic DL-
30,000.
Two rheological grade sepiolites, A and B, were tested. The surface of sepiolite B had a
higher anionic charge density than that of sepiolite A and a slightly higher specific area.
The results show that sepiolite increased floc size and floc stability in fiber-cement
suspensions and that it increase the retention of solids and the drainage rate especially in
mixtures containing polyvinyl alcohol fibers. Furthermore, the effects of sepiolites A
and B on the process were shown to be similar (Figure 1.a).
However, the selection of the sepiolite used as a rheological aid was a key for the
quality of the final product. The addition of sepiolite to the mixture M1 decreased the
bulk density and the elastic modulus and those effects increased with the anionic charge
density of the sepiolite. Despite the effect on the physical properties, the use of sepiolite
with a moderate-low anionic charge surface (sepiolite A) improved the mechanical
strength of the fiber-cement product (Figure 1.b).
Therefore, sepiolite could be used in the manufacture of fiber-cement to improve the
process and the product mechanical properties, but the selection of the sepiolite plays a
key role in the mechanical properties of the fiber-cement products.
... The high water absorption of the fibre prejudices the on-line processing of the green sheet known informally by operator as: low drainage rates or "elephant skin" appearance. Indeed, usually, the appearance of such a phenomenon is visible when the green sheet has high humidity content (Negro et al., 2006a). Contrarily, if the humidity is very low, then the de-lamination process will appear, being more problematic and usual for suspensions with low amount of fine particles (Negro et al., 2006a) or when very low drainage rate occurs. ...
... Indeed, usually, the appearance of such a phenomenon is visible when the green sheet has high humidity content (Negro et al., 2006a). Contrarily, if the humidity is very low, then the de-lamination process will appear, being more problematic and usual for suspensions with low amount of fine particles (Negro et al., 2006a) or when very low drainage rate occurs. So this is a key issue for the industry and there is a serious lack of the available published literature on the subject. ...
Fibre-cement products had been widely used in the world due to their versatility as corrugated and flat roofing materials, cladding panels and water containers presented in large number of building and agriculture applications. The main reason for incorporating fibres inio the cement matrix is to improve the toughness, tensile strength, and the cracking deformation characteristics of the resultant composite. One of the drawbacks associated with cellulose fibres in cement application is their dimensional instability in the presence of changing relative humidity. The objective of the present work is to evaluate the effect of surface treatment of eucalyptus cellulose pulp fibres on the processing and dimensional changes of fibre-cement composites. Surface modification of the cellulose pulps was performed with methacryloxypropyltri-methoxysilane (MPTS), aminopropyltri-ethoxysilane (APTS) and n-octadecyl isocyanate, an aliphatic isocyanate (AI), in an attempt to improve their dimensional instability into fibre-cement composites. X-ray photoelectron spectroscopy (XPS) showed the chemical changes occurred at the surface, and contact angle measurements showed the changes in the surface energy. MPTS- and AI-treated fibres presented lower hydrophilic character than untreated fibres, which led to lower water retention values (WRV). APTS increased the water retention value of the pulp and improved the capacity of hydrogen bonding of the fibres. MPTS- and AI-treated fibres led to low final water/cement ratios and reduced volume changes after pressing. MPTS-treated fibres decreased the water and dimensional instability of the fibre-cement composites, while the contrary occurred with APTS-modified and AI-modified fibres. These results are promising and contribute for new strategy to improve processing and stability of natural fibres-reinforced cement products.
... However, the interaction of cellulose and PVA fibres with mineral particles is weak due to the organic nature and the low density of these fibres. Consequently, the use of a flocculant is usually required to retain mineral particles in the composite sheet [1][2][3][4], being anionic polyacrylamides (A-PAMs) the most frequently used agent [4][5][6][7]. ...
... A computer calculates the chord length of the particle on the basis of the reflectance time and focal point speed. Each measurement provides a particle chord length distribution representative of the size and shape of the population of particles in the suspension, the mean of which (mean chord size) is selected to study flocculation, deflocculation and reflocculation processes [3,12,13]. ...
Sepiolite is used to increase thixotropy of cement slurries for easier processing, to prevent sagging and to provide a better final quality in the manufacture of fibre-reinforced cement products. However, the effect of sepiolite on flocculation and its interactions with the components of fibre cement are yet unknown. The aim of this research is to study the effects of sepiolite on the flocculation of different fibre-reinforced cement slurries induced by anionic polyacrylamides (A-PAMs). Flocculation and floc properties were studied by monitoring the chord size distribution in real time employing a focused beam reflectance measurement (FBRM) probe. The results show that sepiolite increases floc size and floc stability in fibre-cement suspensions. Sepiolite competes with fibres and clay for A-PAMs adsorption and its interaction with A-PAM improves flocculation of mineral particles.
... The different chemical composition and hygroscopic character of cellulose fibres make the compatibility between fibres and cement particles highly complex [1,2]. In the Hatschek process for fibrecement fabrication, the behaviour of cellulose fibres depends on their morphological properties. ...
... The retention and drainage studies were performed with a vacuum drainage tester (VDT) previously described by Negro et al. [2]. This equipment consists basically of two jars separated by a barrier (usually a latex membrane): the upper jar is used to keep the fibrecement suspensions stirred until homogenization. ...
The objective of the present research was to evaluate the effect of fibre morphology (e.g., length, width, fibrillation, broken ends, content of fines and number of fibres per gram) on flocculation and drainage properties of fibre–cement suspensions and on physical properties of the fibre–cement composites. Mechanical refining was used to change the morphological properties of Eucalyptus and Pinus pulps. Results show that the mechanical refining increased the size of the formed flocs and decreased the concentration of free small particles (with dimensions between 1 and 20 µm) as a consequence of the increased fibrillation and content of fines, which increased the capacity of the fibres to capture the mineral particles. High levels of refining were necessary for Pinus pulp to obtain cement retention values similar to those obtained by unrefined Eucalyptus pulp. This is due to the higher number of fibres per gram in Eucalyptus pulp than in Pinus pulp. Pulp refining improved the packing of the particles and, although decreased the drainage rate, it contributed to a less porous structure, which improved the microstructure of the composite.
... For bridging and patching mechanisms, particle size distribution and removal analyses can be selected to determine the optimum dose due to the significant difference in the required dosing ). In addition, focused beam reflectance Effect of salts on the zeta potential of the colloidal particle (Barkan 2005) measurement may also be used as a tool to understand the floc properties in real time under different conditions (Blanco et al. 1996(Blanco et al. , 2002Negro et al. 2006). Ahmad et al. (2021a, b) also reported that the utilization of too much dosage of plant-based coagulants may lead to lower removal efficiencies since the coagulant itself contributes to the color and addition of organic matter. ...
The increasing intensification of the aquaculture industry requires the development of new strategies to reduce the negative impacts of wastewater on the environment. Plant-based coagulants/flocculants, regarded as one of the environmentally
friendly technologies for wastewater treatment, show good performance in the removal of suspended solids from wastewater. The aforementioned technology involves the utilization of plants as coagulants/flocculants in the treatment process and produces nontoxic sludge as treatment by-products. The produced sludge could be converted into valuable compounds used in agriculture. This review summarizes coagulation–flocculation by using plant-based coagulants/flocculants, its mechanisms, operational factors that control the treatment process, and its application in the treatment of wastewater, especially aquaculture effluent. Moreover, this work discusses the potential utilization of aquaculture sludge as a valuable compound used in agriculture. The presented review aims to emphasize the potential of using plant-based coagulants/flocculants in the treatment of aquaculture effluent and explore the potential of using the produced sludge as fertilizer for plants to solve problems related to sludge handling and the toxicity of inorganic coagulants in a recirculating aquaculture system. This paper concluded that utilization of recovered nutrients in the form of solids is feasible for agricultural purposes, while a hydroponic system can be used to reclaim the nutrients in the form of solution.
... Moreover, flocs require certain strength to survive the mechanical shear in a turbulent fluid field, but few studies have been reported on quartz flocculation in the presence of both cofactor and PEO under different turbulence intensities. The flocs properties induced by cofactor-PEO are assumed to behave differently from those formed by PEO alone when subjected to turbulence, and floc properties such as strength and shear resistance have indicated important effects on papermaking [25] and fibre-cement production [26]. However, these effects are currently poorly understood in mineral processing. ...
The flocculation behaviors of quartz using a dual polymer system containing tannic acid (TAN) and poly(ethylene oxide) (PEO) were investigated in this study, with dynamic floc size monitoring by the in-situ focused beam reflectance measurement technique. Variables of concern and their influence on the flocculation process were investigated from both physicochemical and hydrodynamic aspects, including solution pH, TAN/PEO ratio, and shear intensity. Floc structure was characterized using confocal scanning microscopy in suspension as well as freeze-drying-SEM imaging method. It was found that prior addition of TAN significantly increased the flocculation efficiency of quartz by PEO at neutral and alkaline pH, but not in acidic solutions despite that PEO induced the largest floc size at pH 3.1 when used alone. An optimal TAN/PEO ratio of 2 was observed for the best flocculation of quartz under the experimental conditions. Additionally, tannic acid could increase the strength of flocs formed by PEO, and the shear resistance of the flocs increased with increasing TAN/PEO ratio. The dual polymer system also contributed to the re-flocculation of quartz under cycled shear conditions, a phenomenon that was not observed when PEO was used alone. Zeta potential and adsorption density measurements confirmed that the pathway of the dual polymer flocculation was via the initial formation of TAN-PEO associative complexes in solution and then bridging of quartz by the associative complexes. The TAN-PEO associative complexes showed different structures and configurations at different pH, in line with a change in hydrogen bonding, which in turn affected floc structures and properties under turbulent conditions. This study helps to understand the improved flocculation, shear resistance and re-flocculation of fine particles induced by dual polymer system.
... However, PAM chains are flexible, and are easily degraded under shear (Lewandowska 2006). So the re-conformation of PAM during application would affect its flocculation performances Girma et al. 2005;Negro et al. 2006;Wong et al. 2006;Rasteiro et al. 2008;Guezennec et al. 2015;Ma et al. 2017;Xiong et al. 2018). Therefore, modification of PAM with the intention to retain its flocculation performance is becoming one of the foci of the PAM flocculant (Guezennec et al. 2015). ...
Grafting polyacrylamide (PAM) chains onto microparticles may combine the advantages of the flocculation property of the former and the fast sedimentation of the later to realize better flocculation performance. In this work, inexpensive microcrystalline cellulose (MCC) microparticles, and monomer of acrylamide (AM) were mixed, and then irradiated under microwave. The obtained material was characterized by Fourier transform infrared spectroscopy and X-ray diffraction, and the results demonstrated successful modification of MCC with AM on the particle surface. The modification procedure has been carefully investigated to obtain an optimum preparation condition. Kaolin suspension was selected as a model to evaluate the flocculation properties of the obtained AM-MCC. Our results indicate that the AM-MCC with the highest grafting ratio of 95.5% exhibits the best flocculation performance, which is even better than that of PAM, and the turbidity can be decreased to 1.4% of the naked kaolin suspension within 2.5 min. Therefore, this work provides a low cost strategy to prepare biodegradable AM-MCC, which may have promising potential application in the water treatment and other fields.
... The flocculants induce the aggregation of particles, improving the retention at the primary sheet's formation and the drainage of water. This makes the formation of the composite sheets feasible and reduces the recirculating load of fine particles in the water system [117]. ...
Nanocelluloses (NCs) are bio-based nano-structurated products that open up new solutions for natural material sciences. Although a high number of papers have described their production, properties, and potential applications in multiple industrial sectors, no review to date has focused on their possible use in cementitious composites, which is the aim of this review. It describes how they could be applied in the manufacturing process as a raw material or an additive. NCs improve mechanical properties (internal bonding strength, modulus of elasticity (MOE), and modulus of rupture (MOR)), alter the rheology of the cement paste, and affect the physical properties of cements/cementitious composites. Additionally, the interactions between NCs and the other components of the fiber cement matrix are analyzed. The final result depends on many factors, such as the NC type, the dosage addition mode, the dispersion, the matrix type, and the curing process. However, all of these factors have not been studied in full so far. This review has also identified a number of unexplored areas of great potential for future research in relation to NC applications for fiber-reinforced cement composites, which will include their use as a surface treatment agent, an anionic flocculant, or an additive for wastewater treatment. Although NCs remain expensive, the market perspective is very promising.
... The size of the chords in the fibre-cement suspensions and their drainage and retention properties were monitored as described in Negro et al (2006), in order to evaluate the effect of using short fibre pulp in fibre-cement manufacturing processes. Eucalyptus pulp presents a number of fibres per gram four times higher than Pinus pulp (Fig.4a). ...
The objective of the current research is to evaluate the advantages of using hardwood short fibre pulp (Eucalyptus) as alternative to the softwood long fibre pulp (Pinus) and polymer fibres, traditionally used in reinforcement of cement based materials. The effect of the vegetable fibre length in the microstructure and in the mechanical performance of fibre-cement composites were evaluated before and after accelerated ageing cycles. Hardwood pulp fibres present improved dispersion in the cement matrix and provide higher number of fibres per unitary weight or volume, in relation to softwood long fibre pulp. The short reinforcing elements lead to an effective crack bridging of the fragile matrix, which contributes to the improvement of the mechanical performance of the composite after ageing. All the promising results signalise to the potential of the hardwood short fibre pulp (Eucalyptus) to partial replacement of the polymer fibres in air curing process.
... After 15 sec of contact time between flocculant and mixture, the stirring was stopped, the barrier was removed and the suspension was drained into the second jar in which an 18 mesh wire was located. The suspension was drained under a vacuum of 0,2 atm through the filter while a computerized balance recorded the mass of drained water over time (Negro et al., 2006b). The drainage curve was analysed in order to obtain the drainage rate for the different flocculants. ...
Sepiolite, an additive to modify rheological properties of cement, has been used during the last decade in fibre-reinforced cement manufacture to increase interlaminar bond between the films. However, the effect of Sepiolite on flocculation, retention and drainage of fibrecement is as yet unknown and the aim of this research, is to optimize its use in fibre-reinforced cement manufacture. The effect of Sepiolite on flocculation of fibrecement and on floc properties induced by anionic polyacrylamide was studied by monitoring the chord size distribution in real time by means of a focused beam reflectance measurement probe. The effect of Sepiolite on retention and drainage was evaluated by using a vacuum drainage tester. The use of Sepiolite increased the flocculation of the fibrecement and floc stability. Solids retention obtained with all of the tested mixtures was increased, and those mixtures containing PVA showed increased drainage rate.
... Different testing requirements should be applied to different fibre-cement products, e.g., profiled (corrugated) roofing sheets, facades, pipes, etc., and also with respect to different climatic conditions. Improvements and/or cost reductions relating to the fibre-cement fabrication process and the quality of the final products (in our case corrugated roofing sheets) can be achieved by varying different processing parameters (Ma et al. 2005;Vidovič et al. 1996;Negro et al. 2005;Negro et al. 2006;Beaudoin 1990). With regard to the fibres, their type, volume fraction and length are typical parameters that influence the mechanical properties (Ma et al. 2005). ...
The breaking load and the breaking moment during transversal and longitudinal loading of fibre-cement profiled (corrugated) sheets were measured on products manufactured on an industrial Hatschek machine, and the corresponding bending strengths were calculated. The influence of two processing parameters, i.e., the pressure applied to the green sheet directly during the manufacture and the content of the reinforcing organic fibres within the portland cement matrix, on the fracture strength of the products was studied and statistically analyzed assuming Weibull statistics. The Weibull parameters were compared for different fabrication conditions. While the fibres content influences considerably the Weibull modulus for both transversal and longitudinal loading, there is no correlation between the shaping pressure and Weibull modulus.
... For a neat cement paste, it was found that the flocculation is affected by the alkalis/alumina content, and nanoclay is one of the most influential admixtures with respect to the flocculation rate [10,11]. Furthermore, the effect of the flocculant on the fiber-cement suspension was observed during the manufacturing process [12][13][14]. ...
Coagulation of cement particles is an inevitable phenomenon of fresh cement-based materials undergoing solidification. Coagulation can be classified into two types, reversible flocculation and irreversible coagulation, wherein microstructural change affects the rheological properties, including shear thinning and thixotropy, and the hydration process. This paper attempts to measure the mechanical property and the coagulation of cement particles according to the mix proportions of cement paste. Experimental setups were proposed for two different types of coagulations using a laser backscattering instrument. Volume fraction and size distribution of coagulated particles were obtained, and their variations were discussed. From the obtained results the microstructural buildup of freshly mixed cement pastes can be divided into three categories: permanent coagulation and strong and weak flocculation.
... Blanco and coworkers used FBRM (now the M series, a significant upgrade on the early Partec instruments) in the study of flocculation in papermaking 18 and cements, 19,20 in both cases considering mixtures of mineral particles and fibers. They compared the extent of flocculation achieved with different flocculant products over time in stirred beakers and the capacity for reflocculation when the applied shear conditions are reduced. ...
Focused beam reflectance measurement (FBRM), where a scanning laser focused through a sapphire window measures real-time reflected chord distributions without solids dilution, is attractive for characterizing flocculation performance. An enhanced measurement principle in new FBRM instruments has implications for flocculation studies, demonstrated using hematite in synthetic Bayer liquor. Comparisons of previous (M500) and new (G400) instruments were compli- cated by the impact of their different physical dimensions upon flocculation hydrodynamics, but the G400 clearly meas- ured larger chords. The original measurement principle based on a reflected intensity threshold counts large low- density aggregates as multiple chords; in contrast, the change to “edge detection” (very low threshold) is more likely to see a single chord, an advantage for studying mineral systems (aggregates often >500 mm). The G400 also captures bimodal character in unweighted chord distributions, producing distinct peaks for aggregates and fines after suboptimal flocculation; such peaks are rarely well resolved in older FBRM.
... The flocculant employed to study the behavior of fiber-cement suspensions and to prepare the fiber-cement probes was an anionic polyacrylamide (APAM) commonly used in the industrial Hatschek process (Negro et al., 2006) with a molecular weight of 7.4 × 10 6 g/mol and a charge density of 13.4%. The flocculant was dissolved in distilled water to prepare solutions of APAM with a concentration of 1.5 g/L. ...
The aim of this paper is to study the feasibility of using cellulose fibers obtained from an agricultural waste, hemp core (Cannabis Sativa L.), through different new environmental friendly cooking processes for fiber-cement production. The physical and mechanical properties of the fiber reinforced concrete, which depend on the nature and morphology of the fibers, matrix properties and the interactions between them, must be kept between the limits required for its application. Therefore, the morphology of the fibers and how its use affects the flocculation, retention and drainage processes in the fiber-cement manufacture, and the mechanical and physical properties of the fiber-cement product have been studied.The use of pulp obtained by means of the hemp core cooking in ethanolamine at 60% concentration at 180 °C during 90 min resulted in the highest solids retention and the best mechanical properties among the studied hemp core pulps.
... The flocculation process of the fibres and fillers in the manufacture of cement, allows the real-time monitoring of all processes involving a change in particle size. The addition of flocculant allows observing the changes that occur in the solution during the flocculation process (Blanco et al., 2002;Negro et al., 2006b). In a typical trial, the probe was immersed in 400 mL of fibre suspension, prepared with Ca(OH) 2 saturated water and stirred at 800 rpm. ...
Nowadays, certain components of non-wood annual plants such as corn stalk and industrial hemp core are considered waste materials or used in low value applications; both by-products have a very low cost. On the other hand, given the large quantities of these materials generated worldwide and their renewable character, it is reasonable to explore new routes for their exploitation. The aim of this paper is to study the potential of both corn stalk (Zea Mays L.) and industrial hemp core (Cannabis Sativa L.) fibres as a renewable source of cellulose fibres in the production of fibre-cement. For each source of fibres, a number of chemical cooking treatments were studied. The morphological properties of the fibres were determined using a scanning electron microscope and a fibre and pulp morphological analyser. Pulp refining was carried out in a PFI mill to improve the characteristics of the fibres. In the case of corn fibres, different degrees of refining were applied. The fibre flocculation process was investigated using several polyacrylamides. The process was studied by monitoring the chord size distribution in real time by means of a focused beam reflectance measurement probe.The results indicated that both pulps can be used for the production of fibre-cement, having the two types of pulp morphological similarities with the pine fibres currently used.Through the flocculation process it was concluded the floc size depends on the length of the fibres.
... Mixture rules that correlate relevant properties with the composition of the product are indispensable in maintaining local control of fiber cement compositions. However, establishing such mixture rules for fiber cement can be a considerable task because the product is a combination of five or more raw materials, including Portland cement, mineral admixtures, fibers and organic additives [4]. The mixture must also be economically viable, easy to process and guarantee an adequate mechanical performance of the final product. ...
This work employing the screening strategy to examine thirteen mix proportions of six-component fiber cement formulations composed of ordinary Portland cement, ultra-fine cement, limestone filler, silica fume, cellulose and polyvinyl alcohol fibers. The vacuum de-watering technique was applied in the production of fiber cement specimens cured for 10 days and submitted to four-point bending tests. The mechanical properties such as limit of proportionality (LOP), modulus of elasticity (MOE), modulus of rupture (MOR) and specific energy (SE) were evaluated and these properties were correlated with the raw material fractions resulting in mixture rules. Results indicate that screening can be a promising methodology with which to generate coherent fiber cement mixture rules, optimize formulations in terms of costs and performance and even facilitate the choosing of formulations for functionally graded fiber cements.
... Retention and drainage studies were performed with the vacuum drainage tester (VDT) previously described by Negro et al. (2006b). This equipment consists basically of two jars separated by a barrier (usually a rubber membrane): the upper jar is used to keep the fibre-cement suspensions stirred until the homogenization. ...
This paper evaluates the advantages of using hardwood short fibre pulp (eucalyptus) as alternative to softwood long fibre pulp (pinus) and polymer fibres, traditionally used in reinforcement of cement-based materials. The effects of cellulose fibre length on microstructure and on mechanical performance of fibre–cement composites were evaluated before and after accelerated ageing cycles. Hardwood pulp fibres were better dispersed in the cement matrix and provided higher number of fibres per unitary weight or volume, in relation to softwood long fibre pulp. The short reinforcing elements lead to an effective crack bridging of the fragile matrix, which contributes to the improvement of the mechanical performance of the composite after ageing. These promising results show the potential of eucalyptus short fibres for reducing costs by both the partial replacement of expensive synthetic fibres in air curing process and the energy savings during pulp refining.
... However, the natural affinity of these organic fibers for the minerals used in fiber-cement manufacture is quite lower than the one presented by the asbestos [5][6][7][8]. Therefore, the process requires the use of flocculants that attach the minerals to the fibers forming the composite material [9,10]. Schultz et al. studied the effect of several flocculants on the aqueous suspensions of fibers and cement, observing that the highest drainage rate and flocculation grade were obtained with a high molecular weight APAM [11]. ...
The feasibility of using a dual retention system consisting on phenol–formaldehyde resin (PFR) and poly(ethylene oxide) (PEO) for fiber-cement manufacture was studied from the point of view of product properties. The effect of the dual system on fiber-cement properties was compared with the effect of a traditionally used anionic polyacrylamide (APAM), concluding that this dual system could be a good alternative to the traditional APAM. It improves considerably the product properties for all tried doses of PEO and PFR while an increase of APAM decreases product strength. The addition order of the components of the dual system and their doses were optimized. Doses of PEO and PFR lower than APAM ones allowed to improve fiber-cement properties, water removal during pressing and even retention, without significant effects on drainage rate.
Polyacrylamide (PAM) is one of the commonly used anti-washout admixture (AWA) in cement-based materials. However, PAM chains tend to be contracted under attacks from alkaline and metal ions in cement paste, resulting in low efficiency of washout resistance enhancement. Herein, the gelation of PAM is implemented to surmount this obstacle, in which the influence of gelation on the floc properties is evaluated by the light scattering method and the enhancing mechanism is explored as well. Unlike the contraction of PAM chains in cement paste, the resulting PAM-based hydrogel can unfold a three-dimensional network that enlarges the contact surface with cement particles and promotes the bridging interaction. As a result, the gelation of PAM essentially improves the floc strength and helps maintain its originally compact floc structure with an unchanged fractal dimension of approximately 2.50 under the elevated shear rates. Furthermore, fresh cement paste with the addition of 0.006% PAM-based hydrogel achieves a decrease of 10% in washout mass loss compared to that with the same dosage of PAM. The result of breakage-regrowth experiment shows the PAM-based hydrogel facilities a rapid reaggregation with a recovery factor of 76%, while the flocs in PAM modified cement paste are irreversible after breakage as its recovery factor is only 37%. This understanding is of great importance to chemical admixtures where gelation is a promising way to promote their interaction with cement particles. Moreover, floc properties provide a new perspective on understanding the early-stage behavior of fresh cement paste.
This paper provides an overview of the use of nanoclays in cement-based materials. The effect of nanoclays on shear rheological properties will be discussed, with a focus on structural build-up behavior. This macroscale flow behavior will then be tied to the effect of nanoclays on the fresh microstructure as characterized via in-situ particle size measurements and rheological techniques. This will provide insight on the mechanisms underlying the effect of nanoclays on fresh state properties through an improved understanding of their effect on flocculation and coagulation behavior. In addition, secondary effects nanoclays have on the hardening and hardened properties will also be discussed. Examples of casting applications in which nanoclays have been effectively utilized as rheological modifiers, i.e. reducing self-consolidating concrete formwork pressure, extrusion, semi-flowable concrete for slipform paving, and 3D concrete printing, will be presented. Finally, some thoughts on potential directions for future work will be shared.
Incorporating fly ash in a concrete mix significantly improves its consistency, resulting in lower viscosity. It is believed that the spherical shape of the fly ash particles is the main cause of the low viscosity. However, the physicochemical causality of the fly ash effect has not been deeply studied and there have been only limited experiments on the particles’ interactions. The use of laser backscattering measurement in this paper allowed the investigation of the agglomeration and dispersion of fly ash particles in an in situ paste. It was found that agglomerates composed of mixed particles develop in a fly ash–cement paste. Their dimensions are comparable to those in neat cement paste. More importantly, incorporating nano-scale spherical dispersed fly ash particles in the mix provides a ball-bearing effect between the micro-scale agglomerates. The viscosity of the mix consequently decreases.
Fresh concrete is a concentrated suspension of Portland cement and aggregates. Cement-based materials show a fluid-to-solid transition incorporating water, which allows us to cast and place a structure in field. Ease of construction requires a lower viscosity of cement-based materials, and it could be achieved by cement particle dispersion in water. In this study, a laser backscattering measurement identifies the cement dispersion in in situ samples, and their size distribution are parametrized using the occurrence rate of a Poisson process. The cement dispersion is unaffected by external shearing intensity while the concentration (or water-to-cement ratio) or the use of dispersant alters its degree. Finally, associating the dispersion measurement with the microstructural state determined by their viscosity curves makes it clear how the cement viscosity decreases.
Different strategies aimed at reducing the negative impact of fillers on paper strength have been the objective of many studies during the past few decades. Some new strategies have even been patented or commercialized, yet a complete study on the behavior of the filler flocs and their effect on retention, drainage, and formation has not been found in literature. This type of research on fillers is often limited by difficulties in simulating high levels of shear at laboratory scale similar to those at mill scale. To address this challenge, a combination of techniques was used to compare preflocculation (i.e., filler is flocculated before addition to the pulp) with coflocculation strategies (i.e., filler is mixed with a binder and flocculated before addition to the pulp). The effect on filler and fiber flocs size was studied in a pilot flow loop using focal beam reflectance measurement (FBRM) and image analysis. Flocs obtained with cationic polyacrylamide (CPAM) and bentonite were shown to have similar shear resistance with both strategies, whereas cationic starch (CS) was clearly more advantageous when coflocculation strategy was used. The effect of flocculation strategy on drainage rate, STFI formation, ash retention, and standard strength properties was measured. Coflocculation of filler with CPAM plus bentonite or CS showed promising results and produced sheets with high strength but had a negative impact on wire dewatering, opening a door for further optimization.
Flexographic printing technology is an economical, productive, low maintenance and versatile technology. However, the removal of these inks by the traditional flotation process during paper recycling is not possible since they remain dissolved in the waters, making necessary the development of alternative methods. Recent studies have pointed out the potential use of nanocellulose (NC) combined with a cationic polyacrylamide to remove flexographic inks from wastewater. The use of a natural polymer, as chitosan, would be an important improvement of this treatment due to NC and chitosan are the two most abundant natural polymers with interesting properties, as non-toxicity and biodegradability. Therefore, in this study the decolorization of three flexographic inks (copper phthalocyanine blue, carbon black and diarlyide yellow) by the sequential addition of cellulose nanofibers, produced from recycled paper, and chitosan, has been evaluated. Results show that this eco-friendly approach has a high potential for the removal of water-based inks with an almost 100% reduction of turbidity and ink from the wastewater. Moreover, the final sludge containing nanocellulose and inks could be used to reinforce the pulp of the middle layers of cartonboard, improving the mechanical properties of the product and reducing waste generation.
In this paper the application of the Weibull distribution for the evaluation of repeated measurements of some mechanical quantities on corrugated roofing sheets made from fibre-cement composites in the serial production of the company Esal d.o.o. Anhovo is described. The focus is on the breaking force in the transversal bending, loading and breaking moment during the longitudinal bending loading of the plate. For all cases the two Weibull parameters were calculated; especially important is the Weibull modulus, which gives the width of the distribution function of the measured quantity.
Over the past two decades, Cement Composite Boards (CCB) made of natural fibres without asbestos have been developed and used for internal and external wall, roofing, flooring, and cladding in some developed countries. Using selected natural cellulose fibres, it is possible to develop products for different uses with this new technology. This depends on the types of fibres used, its ratio in the mix design, the type, the amount of additive materials and also the method of processing and making. In this research, different specimens made of different types of cellulose fibres were studied and their properties were determined. The results indicate that the fibre contents and types affect the flexural behaviour and fracture mechanism of composite sheets significantly.
As natural concrete supplements, waste materials obtained from food industry plants can substitute synthetic supplements in concrete to help protect the environment. This is an experimental study for examining the effects of Tragacanth gum and sugar beet fiber additives on concrete behavior. Tragacanth gum and sugar beet fiber have numerous applications in industry. Concrete specimens were prepared at six different mixing ratios of additives and subsequently tested. Tensile and compressive strengths, modulus of elasticity, slump, air voids volume and failure modes of the concrete specimens were measured to determine the changes the concrete had undergone due to the addition of sugar beet fiber and Tragacanth gum. Compressive strengths of the samples were between 32 and 37 MPa while the obtained tensile strength is between 3.43 and 3.66 MPa. The results indicated that concrete slump in the specimens exhibited considerable flowability, as in the case of self-compacting concrete. Moreover, increasing the test parameters decreased compressive strength and increased the number of air voids in the concrete. Adding a combination of Tragacanth gum and sugar beet fiber increased air voids and flowability in the concrete. Finally, given the increased concrete slump and concrete setting time, a numerical model was presented using the obtained laboratory results for examining slump variations after mixing the concrete.
In the time since asbestos was banned, new mixtures have been studied to obtain a product with similar properties to the asbestoscement sheets in the Hatschek process. The aim of this research is to study the effect of two different sepiolites on the physical and mechanical properties of roofing fiber-cement sheets when they contain natural fibers or mixtures of synthetic and natural fibers. Studied properties included bulk density, water absorption, permeable void volume, modulus of rupture, proportional limit, specific energy, and modulus of elasticity. The results showed that fibercement sheets containing sepiolite had better performance in terms of flexural strength and that the characteristics of the sepiolite selected played a key role in the development of the mechanical properties of the fiber-cement products.
The objective of the present work is to evaluate the impact of the surface grafting of cellulose fibres on the processing, dimensional stability and mechanical performance of fibre–cement composites. The surface modification of the pulps was performed with methacryloxypropyltri-methoxysilane (MPTS), aminopropyltri-ethoxysilane (APTS) and n-octadecyl isocyanate, an aliphatic isocyanate (AI). X-ray photoelectron spectroscopy (XPS) showed that the chemical changes have indeed occurred at the surface, and contact angle measurements showed that the surface energy has also changed. MPTS- and AI-treated fibres presented lower hydrophilic character than untreated fibres, whereas APTS increased the water retention value of the pulp. MPTS-treated fibres decreased the water retention and improved dimensional stability of the fibre–cement composites, while the contrary occurred with other modified fibres. Fibre–cement strength was little influenced by fibre treatment, whereas AI-treated fibres contributed to higher specific energy (SE) and the lower SE value for APTS-treated fibres is an indication of the improvement on fibre to cement adherence. These results are promising and contribute toward new strategies to improve the processing and stability of natural fibre-reinforced cement products.
The need for sustainable, environmental friendly, energy efficient construction materials could justify the interest on fibre cement board produced from recycled waste cardboard. Waste cardboard has a low production cost and could show an appropriate compatibility with hydrated cement particles. This research was carried out in three phases. In the first phase of the research, the flexural behaviour of different amounts of fibre content (1–14%) in cement boards reinforced by waste cardboard was investigated. In the second phase, the optimum fibre content of 8% to achieve the highest flexural strength was determined. In the third phase, the effect of nanosilica fume and limestone powder on specimens reinforced by 8% fibre content was studied. The microstructure of specimens using Scanning Electron Microscope (SEM) was also carried out.The results show that flexural strength of cement composite board can be improved by adding 10% limestone powder and 3% nanosilica fume.
This paper is focused in the description of a new real-time methodology for flocculant selection in the fibre-cement manufacture based on studying flocculation and floc properties with a focused beam reflectance measurement (FBRM). Results were supported and confirmed by particle vision and measurement (PVM) analysis. Opposite effects of polyacrylamides characteristics on fibre cement flocculation and on final product were found: charge density resulted in increased product strength when dosage of polymer was low but decreased it at high dosages. The feasibility of using artificial neural networks (ANNs) to predict mechanical properties of fibre cement composites from the flocculation data obtained by in-line measurement in a Hatschek machine by the FBRM sensor is reported.
The reverse osmosis desalination is becoming an effective approach in seawater desalination to solve the shortage of freshwater resource. Since reverse osmosis desalination plants depend on high quality feed water to ensure. Turbidity is the most important factor of feed water of reverse osmosis desalination, and turbidity removal is a difficulty of desalination pretreatment. The alkalify flocculation desalination pretreatment technology is a cheap and effective way to reduce the turbidity of seawater. The flocculant, polyaluminiumferric chloride (PAFC), is an important additive for alkalify flocculation desalination pretreatment, and the dosage is crucial for the effect of desalination pretreatment. According to our experimental data and analysis, alkalized seawater by 9 g/L lime milk, flocculated by 9 ml/L PAFC and 3 ml/L starch solution, turbidity reduced to 0.8 NUT and meet the requirement of feed water of reverse osmosis desalination. The structure of magnesium hydroxide in floccule was regular from observed by scanning electron microscope and content improved with addition of starch from thermogravimetric analysis.
This work evaluates the advantages of using hardwood short fibre pulp (Eucalyptus) as alternative to softwood long fibre pulp (Pinus) and synthetic fibres, traditionally used in reinforcement of cement based materials. The effects of cellulose fibre morphology (e.g., length, width, fibrillation, content of fines and number of fibres per gram) on the processing, on the mechanical and physical performance and on the microstructure of fibre-cement composites were evaluated. Composites were evaluated before and after accelerated ageing cycles. Eucalyptus pulp fibres were better dispersed in the cement matrix and provided higher number of fibres per unitary weight or volume, in relation to Pinus long fibre pulp. The short reinforcing elements lead to an effective crack bridging of the fragile matrix, which contributes to the improvement of the mechanical performance of the composite after ageing. These promising results show the potential of eucalyptus short fibres for reducing costs by both the partial replacement of expensive synthetic fibres in air curing process and the energy savings during pulp refining. The effects of pulp bleaching were also evaluated, and showed that Eucalyptus bleached fibres are more reactive to bond with the cement matrix by hydrogen bonds. Bleached fibres improved the fibre-matrix interface, although they presented more signals of fibre mineralization. Mechanical refining was used to change the morphological properties of Eucalyptus and Pinus pulps. Results show that high levels of refining were necessary for Pinus pulp to obtain cement retention values similar to those obtained by unrefined Eucalyptus pulp. The mechanical refining increased the capacity of the fibres to capture the mineral particles improving the adherence of the fibres with the matrix. This improved fibre-matrix interface led to better mechanical properties at 28 days of cure, but turned brittle the composites after 200 ageing cycles. The chemical surface modification of cellulose pulp fibres was done in order to improve fibre-matrix bonding and to decrease fibre mineralization into the composite. Surface modification of the cellulose pulps was performed with Methacryloxypropyltri-methoxysilane (MPTS) and Aminopropyltri-ethoxysilane (APTS) and showed significant influence on the microstructure of the composites. Accelerated ageing cycles decreased modulus of rupture (MOR) and toughness (TE) of the composites with unmodified and modified fibres, however composites reinforced with MPTS-modified fibres presented fibres free from cement hydration products, while APTS-modified fibres presented accelerated mineralization. Higher mineralization of the fibres led to higher embrittlement of the composite after accelerated ageing cycles. These observations are therefore very useful for understanding the contribution of the different fibre conditions (chemical composition, mechanical strength, morphology and surface properties) to the mechanisms of fibre-matrix adherence, fibre mineralization and degradation of fibre-cement composites. Este trabalho avalia as vantagens do uso das fibras curtas de polpa de Eucalipto tanto como alternativa às fibras longas de polpa de Pinus, como também para fibras sintéticas, tradicionalmente usadas no reforço de materiais cimentícios. Os efeitos da morfologia (comprimento, largura, fibrilação, conteúdo de finos, número de fibras por grama, etc.) das fibras celulósicas no processamento, no desempenho mecânico e físico e na microestrutura dos compósitos de fibrocimento foram avaliados. Os compósitos foram avaliados antes e após ciclos de envelhecimento acelerado. Fibras de Eucalipto apresentaram melhor dispersão na matriz cimentícia e forneceram maior densidade de fibras em massa ou em volume, em relação às fibras de Pinus. As fibras curtas permitem um reforço efetivo da matriz frágil, diminuindo a propagação das fissuras, o que contribuiu para o melhor desempenho mecânico dos compósitos após envelhecimento. Estes resultados promissores mostram o potencial apresentado pelas fibras curtas de Eucalipto para reduzir custos, em vista da substituição parcial das fibras sintéticas em processos de cura ao ar, e durante o refino da polpa celulósica. O efeito do branqueamento das fibras também foi avaliado, e mostrou que as fibras branqueadas de Eucalipto são mais reativas para se ligarem por pontes de hidrogênio com a matriz cimentícia. Fibras branqueadas melhoraram a interface entre fibra e matriz, embora apresentassem mais sinais de mineralização (re-precipitação de produtos de hidratação dentro das fibras) do que as fibras não-branqueadas. O refino da polpa celulósica foi utilizado para modificar as propriedades morfológicas das fibras de Eucalipto e Pinus. Os resultados mostraram que são necessárias maiores intensidade de refino na polpa de Pinus para obter valores de retenção de sólidos do cimento similares àqueles obtidos com fibras não-refinadas de Eucalipto. O refino aumentou a capacidade das fibras de capturar as partículas minerais, melhorando a aderência das fibras com a matriz. Esta melhor interface entre fibra e matriz melhorou as propriedades mecânicas dos compósitos aos 28 dias de cura, mas os tornou mais frágeis após os ciclos de envelhecimento acelerado. A modificação química da superfície das fibras foi realizada com o objetivo de melhorar as ligações entre fibra e matriz e diminuir a mineralização da fibra dentro dos compósitos. Esta modificação química foi realizada com Metacriloxipropiltri-metoxisilano (MPTS) e Aminopropiltri-etoxisilano (APTS) e mostrou influenciar significativamente a microestrutura dos compósitos. Ciclos de envelhecimento acelerado diminuíram o módulo de ruptura (MOR) e a tenacidade (TE) dos compósitos com fibras não-modificadas e modificadas; entretanto, compósitos reforçados com fibras modificadas com MPTS apresentaram fibras sem produtos de hidratação do cimento em seu interior, enquanto que fibras modificadas com APTS apresentaram acelerada mineralização. Fibras mineralizadas tornam os compósitos mais frágeis após os ciclos de envelhecimento acelerado. Estas observações são, portanto, muito úteis para o entendimento da contribuição de diferentes condições das fibras (composição química, resistência mecânica, morfologia e propriedades de superfície) para os mecanismos de aderência entre fibras e matriz cimentícia, de mineralização das fibras e de degradação dos compósitos de fibrocimento.
ABSTRACT Achieving an optimumbalance between negatively and positively charged materials in a fiber slurry can be critical to the profitable operation of a paper machine. There is no consensus, however, regarding what tests to use and how to interpret the results. Papermakers are free to choose among several competing methods, including micro- electrophoresis,colloidal titrations with a color endpoint, streaming current titrations, and fiber-pad streaming potential methods. Each method has its strengths and weaknesses. It is critical to be aware ofthe potential weaknesses,and interferences with each method before selecting it for a given papermaking,application such as process control surveys of paper machine operations. An understanding of potential errors also can improve a user’s ability to drawreliab le conclusions.
Certain inorganic materials, which are known to have significant advantages over other construction materials in energy costs of production and fabrication, are weak in tension and against impact. These weaknesses are alleviated by the use of reinforcing fibers, often asbestos, whose effects on public health are now matters of increasing concern. The cost of wood pulp fibers per unit of reinforcement is shown to compare favorably with those of other reinforcing fibers such as asbestos and glass. The comparative energy requirements for obtaining the fibers depends on the method used for separating the wood pulp fibers. Recent work, particularly in Australia, aimed at developing asbestos-free fiber-cement products based on wood pulp fibers is described. The products are classified according to whether the water used in mixing remains or is removed before the cement is allowed to harden. The inclusion of wood pulp fibers in a cementitious matrix gives a composite having a higher modulus of rupture and a higher quasi-static and impact fracture energy. The increases in these properties are less than those produced by the inclusion of asbestos or glass fibers but are, nonetheless useful. 39 references, 7 figures, 4 tables.
Various bagasse fibre/cement composites have been prepared, the fibres having a random distribution in the composites. The influence of different parameters on the setting of the composite material has been studied: (1) botanical components of the fibre, (2) thermal or chemical treatment of the fibre, (3) bagasse fibre content and (4) added water percentage. This study shows a retarding effect of lignin on the setting of the composite, for small amount of heat-treated bagasse (200 °C) the behaviour of the composite is closely the same as the classical cement or cellulose/cement composite.
A methodology to study flocculation processes and floc properties using a non-imaging scanning laser microscope is presented in this paper. This methodology allows us to study floc stability and resistance to shear forces, re-flocculation tendency and reversibility of the flocs. Furthermore, optimal dosage of any polymer and the associated flocculation mechanism can be determined. In order to illustrate the technique, some examples applied to flocculation in papermaking are described. Although in this paper all the examples have been applied to papermaking, the developed methodology can be used in any process in which flocculation phenomena is involved.
On présente dans cet article une méthode pour étudier les procédés de floculation à l'aide d'un microscope laser à balayage sans imagerie. Cette méthode permet d'étudier la stabilité des flocs et leur résistance aux contraintes de cisaillement, la tendance à la refloculation et la réversibilité des flocs. De plus, on peut déterminer le dosage optimal de tout polymère et le mécanisme de floculation associé. Pour illustrer cette technique, quelques exemples appliqués à la floculation dans la fabrication du papier sont décrits. Cependant, même si dans cet article tous les exemples s'appliquent à la fabrication du papier, la méthodologie peut s'appliquer à tout procédé comportant des phénomènes de floculation.
Composites of blast furnace slag (BFS) based cement mortar reinforced with vegetable fibres are presented. Roofing components are produced with these composites through a simple and low-energy consuming method, including ordinary vibration and curing in a wet chamber. Composites reinforced with eucalyptus pulp, coir fibres and with a mixture of sisal fibre and eucalyptus pulp gave a suitable performance, with compressive strength higher than 20 MPa and modulus of rupture (MOR) higher than 3 MPa. The performance of tiles made with these composites is in accordance with international requirements, with maximum load higher than 450 N, in wet conditions.
Data are presented which show that the removal of water from the forming sheet on the paper machine depends upon both the drainage of water from the dilute stock and upon the response of the wet web to vacuum. Frequently conditions which favor more rapid drainage interfere with water removal by vacuum. The effects of furnish composition, degree of refining, basis weight, and chemical additives are shown. For the study of these relationships, a new testing apparatus, the Water Release Analyzer, is described.
The effect of the contact time between cationic polymers (polyacrylamides and cationic starches) and stock on retention and dewatering has been studied using a new type of equipment. Dewatering is carried out under low pressure and the addition of chemicals and other operations are controlled by a microprocessor. The retention often shows a maximum after a polymer contact time of 10-20 s. It is found that long contact times drastically reduce the effect of the added polymer. This is explained as being due to floc rupture, degradation of the polymer and poor reflocculation. The dewatering time is extremely sensitive to the polymer contact time and increases steadily with increasing contact time.
The purpose of this study was to determine the technical feasibility of employing magazine wastepaper fibers as reinforcement in thin cement. Wastepaper fiber-composites were first recycled. The samples were then technically evaluated versus virgin composites and were shown to posses acceptable flexural strength, dimensional stability, density, water absorption and moisture content. The differences of recycled fibers with virgin fibers in cement composites were verified using the specifics of the size distribution of the recycled fibers.
This paper compares laboratory test procedures which predict the performance of chemicals used to enhance retention or dewatering during the manufacture of paper. Key points of difference among the various laboratory methods include: • the presence or absence of fibre mat formation during the test • the optional application of vacuum • the presence or absence of pressure or velocity pulsations during dewatering • the use of automation in some test procedures. A well-chosen laboratory test can provide useful information without incurring the high cost and risks associated with full-scale evaluations of many different retention and drainage programmes and dosage levels. However, it is important to understand the compromises inherent in different lab-scale tests to guard against premature rejection of specific chemical programme options.
Fibre reinforcement in the form of asbestos fibres has been used in the cement industry for nearly a hundred years. Howeve, during the past twenty years a variety of new organic and inorganic fibres have been introduced into the construction industry, and the theoretical understanding of their behaviour at fibre volumes of between 0·1 and 10% in the compostte has been comprehensively developed. The major uses of steel and polypropylene fibres are in massive concrete structures whereas carbon, cellulose, glass, natura, polypropylene, and polyvinyl alcohol fibres are used in thin sheet products. The theory and practice of these relatively new bulk markets for fibres are reviewed, together with examples of the most widely used products.
Scanning laser microscopy (SLM) was used to evaluate the flocculation of an acid fine paper furnish by a treatment program consisting of starch, alum, cationic-poly(acrylamide) (C-PAM), and a colloidal silica microparticle. C-PAM caused a transient increase in floc size, as measured by the mean chord length parameter, which decayed rapidly under the influence of shear. Microparticle addition resulted in a more shear resistant reflocculation of the furnish, suggesting that the microparticle plays a role in increasing floc strength. An inverse correlation of SLM peak mean chord length with dynamic drainage jar (DDJ) turbidity was observed. Studies of salt-induced aggregation silica revealed that simple aggregation does not always effect an improvement in microparticle activity. These results suggest that the microparticle performance of aggregated silica depends upon details of the silica structure.
The flocculation of an alkaline fine paper furnish by a cationic flocculant and combinations of a cationic flocculant with colloidal silica or bentonite microparticles was evaluated by scanning laser microscopy (SLM) to derive information on floc properties such as floc size and shear stability. It was found that both types of microparticles affect reflocculation, although colloidal silica forms flocs with higher shear resistance than bentonite. The shear resistance of flocs produced by colloidal silica could be maximized by adjustment of the flocculant dosage. The results of these studies are consistent with a colloidal silica bridging mechanism in which silica molecules form bridges between polymer segments on different particles.
There are two distinct zones of water removal on the paper machine prior to the press section: (a) the forming zone, from slice to suction boxes, in which the water removal mechanism is some form of drainage, and (b) the vacuum zone, in which water is displaced in the wet sheet by air in response to vacuum. Data show how furnishes differ with respect to water removal in the two zones. Frequently, conditions that favor water removal in one zone are unfavorable in the other. Therefore, testing of stock samples for water removal on the paper machine requires consideration of this distinction.
A method for the qualitative and quantitative optimization of the use of polymers in paper mills has been developed. Traditionally optimization of the dosage of polymers in the paper and board industry is achieved by using techniques based on the electric charge of the particles. However, the flocculation phenomenon is based on an increase in the size of the particle aggregates, thus the new method is based on size measurements of the particle aggregates. By applying this technique it is possible to determine the effect of the different chemicals under papermaking conditions; get a better understanding of the interactions occurring in the pulp system; predict the influence of changes in the raw materials or papermaking conditions on chemical efficiency; and control and optimize the chemical flocculation processes.
This paper presents several uses of focused beam reflectance measurement (FBRM) as tool to measure flocculation. It includes information on the interaction of wet-end aids with the different pulp fractions, such as optimal polymer dosage and the resulting floc properties (floc size, strength, etc.). The study of the floc evolution over time under different conditions also allows us to identify flocculation mechanisms. The FBRM methodology provided a real-time, in-process monitor to establish the evolution of the resulting flocculation state and polymer efficiency under the influence of shear forces. The evaluation included a study of deflocculation and reflocculation processes occurring in the sample. We also looked at the problem of contaminants accumulation, as can occur with increased use of recovered paper and the closure of water systems. In addition, FBRM has been used to identify dissolved and colloidal material agglomeration and to study its influence on polymer demand for a given furnish.
Fibre reinforcement in the form of asbestos fibres has been used in the cement industry for nearly a hundred years. However, during the past twenty years a variety of new organic and inorganic fibres have been introduced into the construction industry, and the theoretical understanding of their behaviour at fibre volumes of between 0·1 and 10% in the composite has been comprehensively developed. The major uses of steel and polypropylene fibres are in massive concrete structures whereas carbon, cellulose, glass, natural, polypropylene, and polyvinyl alcohol fibres are used in thin sheet products. The theory and practice of these relatively new bulk marketsfor fibres are reviewed, together with examples of the most widely used products.MST/1950
This project evaluated the performance of thin fibre-cement elements produced from alternative raw materials using the Hatschek process, with a view to their use in low-cost housing. Sisal and banana fibres were prepared using mechanical and kraft pulping procedures while residual Eucalyptus grandis pulp was obtained from a commercial pulp mill. Granulated blast furnace slag (BFS) was used as the major component of an alternative hydraulic binder and ordinary Portland cement as a control. Composites were prepared using a slurry vacuum de-watering process, pressing and air-curing. At fibre contents of 8–12% by mass, moduli of rupture (MOR) up to 23 MPa and fracture toughness (FT) values in the range of 0.6–1.7 kJ/m2 were obtained at 28 days. After 12 months of exposure under temperate and tropical conditions, the MOR of the BFS-based composites had decreased to values in the range of 6.6–10.1 MPa. FT values remained stable or even increased with the weathering exposure. The results indicate that the mechanical performance of the composites being studied is currently satisfactory, but further optimisation of formulation and processing parameters should be investigated.
Thesis (Ph. D.)--Michigan State University. Dept. of Civil & Environmental Engineering, 1993. Includes bibliographical references (leaves 221-228). Microfilm.
Selecting and interpreting colloidal charge measure-ment. In: Scientific and technical advances in wet end chemistry
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Process options for the production of fibre-cement sheets
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Modelling drainage in the wire section of a Fourdrinier machine. UK: PIRA International
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Recycled fibers: viable means of reinforcing cement products
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- J P Won
- H Chowdhury
- K Ostowari
- A Nossoni
Souroushian P, Shah Z, Won JP, Chowdhury H, Ostowari K,
Nossoni A. Recycled fibers: viable means of reinforcing cement
products. In: 7th Inorganic-bonded Wood and Fiber Composite
Materials Conference, 2000. p. 153-64.
State-of-art-report on fibre reinforced concrete. Reported by ACI Committee 544
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Concrete and cement composites reinforced with natural fibres
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Selecting and interpreting colloidal charge measurement
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PIRA Conference, Barcelona, Spain, June 19-20, 2000.
Overview: fibre reinforcement in the cement and concrete industry
- Hannant
Reinforcement of thin cement product with wastepaper fibers
- P Soroushian
- Z Shah
- S Marikunte