Fiber Cement Composites Research Articles

Cellulose modified fibres in cement based composites

The objective of the present work is to evaluate the effect of surface modification of cellulose pulp fibres on the mechanical and microstructure of fibre–cement composites. Surface modification of the cellulose pulps was performed with Methacryloxypropyltri-methoxysilane (MPTS) and Aminopropyltri-ethoxysilane (APTS) in an attempt to improve their durability into fibre–cement composites. The surface modification showed significant influence on the microstructure of the composites on the fibre–matrix interface and in the mineralization of the fibre lumen as seen by scanning electron microscopy (SEM) with back-scattered electron (BSE) detector. Accelerated ageing cycles decreased modulus of rupture (MOR) and toughness (TE) of the composites. 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 mechanisms of degradation of fibre–cement composites.

Optimal use of flocculants on the manufacture of fibre cement materials by the Hatschek process

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.

High speed tensile behavior of sisal fiber cement composites

The experimental behavior of sisal fiber reinforced cement composites subjected to high speed tension load was studied. High strain rates were achieved by using a high rate servo-hydraulic testing machine. A state-of-the-art high speed Phantom camera was also used to take images from the specimen during the test. The images were used in a digital image correlation model to determine the displacement fields and to calculate crack spacing. The effect of strain rate was investigated by comparing static and dynamic tensile tests which were performed at strain rates ranging from 5.5 × 10 −6 to 24.6 s −1, respectively. A numerical tension stiffening model based on nonlinear finite difference method was used to simulate tensile cracking behavior of sisal fiber cementitious composites. The composite presented strain rate sensitivity for ultimate tensile strength and strain capacity with a dynamic amplification factor of 1.26.

Effect of fibre morphology on flocculation of fibre–cement suspensions

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.

Effect of silica fumes on the permeability of fiber cement composites

In this study, the pore systems of cement‐based composites were investigated using absorption, rapid chloride penetration, rapid migration, ponding, mercury intrusion porosimetry (MIP), and scanning electronic microscopy (SEM). Direct current polarization resistance and other permeability parameters were used as indices to justify the effects of fiber and silica fume addition on the permeability of cover concrete. Cement‐based composites containing 10% silica fumes were found to have higher compressive strength, lower absorption, lower coefficient of chloride ion diffusion, lower penetration of chloride ions and higher polarization resistance than those of control specimens. Composites with a combined addition of fiber and silica fume further increased polarization resistance and compressive strength. Addition of silica fumes further improves the permeability of fiber cement composites due to the positive effect from pozzolanic reaction, which produces denser and more homogeneous structures in the matrix. Use of silica fumes or lower w/cm ratio instead of adding fiber in the composites would more effectively increase durability indices such as diffusion coefficient, penetration depth and polarization resistance.

Supplementary cementitious materials for mitigating degradation of kraft pulp fiber-cement composites

Kraft pulp fiber reinforced cement-based materials are being increasingly used where performance after exposure to environmental conditions must be ensured. However, significant losses in mechanical performance due to wet/dry cycling have been observed in these composites, when portland cement is the only cementitious material used in the matrix. In this research program, the effects of partial portland cement replacement with various supplementary cementitious materials were investigated. Binary, ternary, and quaternary blends of silica fume, slag, Class C fly ash, Class F fly ash, metakaolin, and diatomaceous earth/volcanic ash blends were examined for their effect on the degradation of kraft pulp fiber-cement composite mechanical properties (i.e., strength and toughness) during wet/dry cycling. After 25 wet/dry cycles, it was shown that binary composites containing 90% slag, 30% metakaolin, or greater than 30% silica fume did not exhibit any signs of degradation, as measured through mechanical testing and microscopy. Ternary blends containing 70% slag/10% metakaolin or 70% slag/10% silica fume were also effective in preventing degradation. A reduction in calcium hydroxide content and the stability of the alkali content due to supplementary cementitious material addition were shown to be primary mechanisms for improved durability.

Effect of Moisture State on Mechanical Behavior and Microstructure of Pulp Fiber-Cement Mortars

An investigation involving mechanical testing and microstructural characterization was undertaken to examine the influence of moisture state at the time of testing on the performance (i.e., strength, toughness, and failure mode) of pulp fiber-cement composites. Samples, prepared with fiber volume fractions of 0, 1.2, and 2.0%, were tested in oven dry, air dry, and wet states. Both compressive and flexural strength were found to be greatest in the oven dry state, presumably due to increased fiber and matrix strength as well as increased fiber/cement bonding which occurs with the controlled removal of water. Flexural toughness, however, was decreased for oven dry samples, and greater fiber fracture (as opposed to the more ductile failure mode of fiber pull-out) was observed in the oven dry samples. It is proposed that this results from differential shrinkage in the fibers’ S1 and S2 layers and increased fiber/cement bonding with drying.

Bamboo and wood fibre cement composites for sustainable infrastructure regeneration

This paper describes the development of eco-friendly bamboo and wood fibre cement composites from agriculture wastes for applications in the housing and building industries, and for sustainable infrastructure regeneration. Bamboo flakes and fibres from oil palm tree fronds were produced and tested for their sugar content and effect on the setting and strength development of the portland cement matrix. To counteract the adverse effects on cement hydration, chemical accelerators, cement replacement materials or a combination of both were used in the manufacture of the composite boards. With the bamboo, the composition of the particleboard was optimized in terms of bamboo–cement ratio and the type and amount of chemical admixture to produce a composite with satisfactory strength and dimensional stability. For the production of wood fibre cement composites, cement replacement materials such as fly ash, rice husk ash and latex were used in conjunction with chemical admixtures to counteract the adverse effect on the hydration characteristics of the cement matrix. Tests were then carried out to optimize the amount and type of cement replacement material and chemical admixtures to produce boards with adequate strength and dimensional stability. All the strength and dimensional stability tests reported in the paper were carried out according to Malaysian Standard MS 934. The paper emphasizes the need for holistic design combining chemical admixtures, cement replacement materials and modern production technology to produce a wide range of cement-bonded composite boards, which will satisfy international standards and can be widely used for infrastructure regeneration.

Durabilidade de compósito biomassa vegetal-cimento modificado por polímero

A durabilidade de compósito biomassa vegetal-cimento é um dos fatores mais importantes para a colocação desse material no mercado consumidor. A utilização de polímeros em concreto e argamassa, com o objetivo de melhorar sua durabilidade, é cada vez mais freqüente. Este estudo visou à caracterização de propriedades físicas e mecânicas de compósito biomassa vegetal-cimento modificado com polímeros e a análise da durabilidade desse compósito. Foi testado um polímero de base acrílica em compósitos produzidos com resíduo de Pinus caribaea. Foram realizados ensaios de envelhecimento acelerado, por meio de ciclos de molhamento e secagem, por imersão em água quente e ensaio de envelhecimento natural. As propriedades físicas do compósito avaliadas foram a massa específica aparente e a absorção total de água por imersão. As propriedades mecânicas foram determinadas por meio de ensaios de resistência à tração na flexão, analisando-se a tensão e a energia de ruptura. Os corpos-de-prova foram extraídos de placas executadas por simples prensagem. Ensaios de microscopia eletrônica de varredura foram utilizados para observar o estado da fibra e da matriz após os processos de envelhecimento. O uso de polímero melhorou o desempenho mecânico do compósito nas primeiras idades e também promoveu significativa redução da capacidade de absorção de água, demonstrando que o uso desse material pode vir a melhorar a durabilidade desses compósitos, uma vez que reduziu sensivelmente sua capacidade de absorção.

Microstructural and chemical effects of wet/dry cycling on pulp fiber–cement composites

The microstructural and chemical mechanisms responsible for pulp fiber–cement composite degradation during wet/dry cycling are being investigated through environmental scanning electron microscopy (ESEM), energy dispersive spectroscopy (EDS), and mechanical testing. Based on these results, a three-part progressive degradation mechanism for cast-in-place kraft pulp fiber–cement composites is proposed, which involves: (1) initial fiber–cement or fiber interlayer debonding, (2) reprecipitation of needle-like or sheath-like ettringite within the void space at the former fiber–cement interface or between the S1 and S2 fiber layers, and (3) fiber mineralization due to reprecipitation of calcium hydroxide filling the spaces within the fiber cell wall structure. This investigation also revealed that kraft pulp fibers exhibit poor resistance to degradation due to their inferior dimensional stability, as compared to thermomechanical pulp (TMP) fibers. TMP fibers contain significant amounts of lignin, which is alkali sensitive. Despite this, TMP fiber–cement composite exhibit improved resistance to degradation during wet/dry cycling. It is proposed that this improvement in durability may be attributed to the presence of lignin in the cell wall restricting fiber dimensional changes during wetting and drying, and hence, minimizing fiber–cement debonding. Additionally, it is proposed that lignin acts as physical barrier to calcium hydroxide formation within the fiber cell wall, minimizing fiber mineralization of TMP fibers.

Polyacrylamide induced flocculation of a cement suspension

The use of cellulose, instead of asbestos, in the fibre cement composites manufacture, using the Hatschek process, reduces cement retention and makes necessary to use a flocculant which is crucial for the plant productivity. The use of different types and doses of polyacrylamides (PAM) as well as the addition process, have been studied to obtain an in-depth knowledge of floc properties. A real-time methodology has been used to study size, shape, strength and reversibility of formed flocs, based on a focused beam reflectance measurement (FBRM) system. The results have been corroborated by particle vision and measurement (PVM) analysis. This paper shows that anionic PAM (A-PAM) are the most suitable to induce cement flocculation and to obtain optimal properties of the formed flocs. This is because the flocculation process is enhanced by the interaction of the Ca 2 + ions, produced by the cement hydration, with the carboxylic groups of the polymer chains. Cations not only increase the stiffness of the chains, improving floc strength, they also enhance the importance of the patching aggregation mechanism when the initial bridges are broken. Higher molecular weight polymers improve initial aggregation but the effect of anionic charge is more important for a stable flocculation with time under variable shear conditions. Results show that the optimal dosage is between 100 and 200 ppm.

Discussion of “Resistance Changes during Compression of Carbon Fiber Cement Composites” by Farhad Reza, Gordon B. Batson, Jerry A. Yamamuro, and Jong S. Lee

Discussion of “Resistance Changes during Compression of Carbon Fiber Cement Composites” by Farhad Reza, Gordon B. Batson, Jerry A. Yamamuro, and Jong S. Lee

Closure to “Resistance Changes during Compression of Carbon Fiber Cement Composites” by Farhad Reza, Gordon B. Batson, Jerry A. Yamamuro, and Jong S. Lee

Closure to “Resistance Changes during Compression of Carbon Fiber Cement Composites” by Farhad Reza, Gordon B. Batson, Jerry A. Yamamuro, and Jong S. Lee

Effects of flocculants and sizing agents on bending strength of fiber cement composites

Wood fiber is used to replace asbestos in the manufacture of fiber cement due to its high availability, low cost and good reinforcement properties. The different chemical composition of the cellulose fibers makes its compatibility with the cement much more complex than that of asbestos fibers. In the Hatschek process a suitable flocculant is needed when using cellulose fibers. The right selection of the flocculant is crucial due to its effect on mineral fines retention, dewatering and formation and, as a consequence, on the overall efficiency of the machine. This paper shows how anionic poly-acryl-amides (A-PAM), the most common flocculants used in Hatschek machines, have a negative effect on the bending strength properties of fiber cement sheets. In order to overcome this problem fiber surface treatment, with sizing agents, is proposed in this paper. Sizing with styrene-acrylate copolymers and alkyl ketene dimer produces an increase in bending strength properties.

Breaking load and bending strength prediction in manufacture of fibre cement composites using artificial neural networks and a flocculation sensor

Abstract The optimisation of the flocculation process during fibre cement production is a new key issue for the fibre cement industry. Many companies face difficulties in optimising the flocculant dosage in real time, which leads to product strength losses. This paper shows the feasibility of using artificial neural networks (ANNs) to establish correlations between flocculation data, in-line measured in a Hatschek machine by a focused beam reflectance measurement (FBRM) sensor, and mechanical properties of final composites. The results show a clear relationship between the mechanical properties of fibre cement composites and the flocculation process and that these are determined in real time. Three ANNs have been created to predict breaking load for 48 h and 7 days and bending strength for 7 days, to obtain good correlations between the predicted and the real values.

Durability of thermomechanical pulp fiber-cement composites to wet/dry cycling

Previous research efforts on pulp fiber-cement composites have largely concentrated on kraft pulp fiber composites. In this research program, thermomechanical pulp (TMP) fibers were investigated as an economical alternative to kraft pulp fibers as reinforcement in fiber-cement composites. Prior to wet/dry cycling, TMP composites exhibited increased first crack strength, but lower peak strength and lower post-cracking toughness, as compared to unbleached and bleached kraft pulp composites at equivalent fiber volume fractions. It is believed that this behavior can be attributed to the lower tensile strength and shorter fiber length of TMP fibers as compared to kraft fibers. After 25 wet/dry cycles, TMP composites showed losses in first crack (peak) strength and post-cracking toughness. However, TMP composites exhibited a slower progression of degradation during wet/dry cycling than composites containing bleached or unbleached kraft fibers.

Influence of flocculant molecular weight and anionic charge on flocculation behaviour and on the manufacture of fibre cement composites by the Hatschek process

Although in the industrial Hatschek process it is necessary to use flocculants to improve retention, dewatering and formation, the use of flocculants may also decrease the strength of the final product. This paper studies the influence of the molecular weight and the anionic charge of anionic polyacrylamides on the flocculation behaviour of fibre cement suspensions and on the bending strength of the final product. Flocculants influence the density of the final product and in-turn the lowering of the density results in strength reduction. Results showed that an increase in the flocculant molecular weight reduces the bending strength of the composites significantly due to its density reduction. However, an increase in flocculant anionic charge increases the bending strength of composites. Therefore, in order to optimise the fibre cement process, it is necessary to use flocculants with high anionic charge and medium molecular weight.

A review of Australian research into natural fibre cement composites

Abstract Over the last three decades considerable research has been committed to finding an alternative fibre to replace asbestos in fibre cement products. Australian research was centred on natural fibres and ultimately it was a natural fibre, wood pulp fibre, that was responsible for the greatest replacement of asbestos in the beleaguered global fibre cement industry. This review reports some of the Australian research that was carried out to establish natural fibres as a suitable reinforcement for cement products. Much research data is locked away in the archives of companies. The preparation and properties of the fibres are discussed briefly as well as their compatibility with existing processing technology. Some explanation of the bonding and microstructural behaviour (under load) within these composite materials is presented and related to their performance in service. The spread of the Australian wood fibre cement technology and the range of applications for which the natural fibre cements are used are discussed briefly, particularly with reference to USA and Asian activities.

Microstructure and mechanical properties of waste fibre–cement composites

This paper examines the microstructure of composite materials containing fibrous wastes (as reinforcement in granulated blast furnace slag or ordinary Portland cement matrices). Both secondary and back-scattered electron imaging and energy dispersive X-ray spectroscopy were used for compositional analysis. Evaluation of both fractured and cut surfaces provided the morphological and bonding information that was related to mechanical performance obtained from flexural tests. Sisal and Eucalyptus grandis pulps showed satisfactory bonding to the cement matrix, with fibre pullout predominating as indicated by high values of energy absorption. In contrast banana pulp reinforced composites exhibited fibre fracture as the main failure mechanism. In all analysed composites, partial fibre debonding and matrix micro-cracking were dominant at the interfaces. However, there was no evidence of a porous transition zone or massive concentration of calcium hydroxide at the interface.

Durability of kraft pulp fiber–cement composites to wet/dry cycling

Abstract If pulp fiber–cement composites are to be used for exterior applications, the effect of cyclical wet/dry exposure must be known. In this research program the effects of three fiber treatments—beating, bleaching, and drying—were investigated to identify those that may minimize effects of environmental aging and degradation during wet/dry cycling. After 25 wet/dry cycles, all composites showed significant losses in first crack strength, peak strength, and post-cracking toughness. The majority of losses in mechanical properties occurred within the first 5 wet/dry cycles, though ductile fiber failure was still observed by scanning electron microscopy (SEM). A three-part progressive degradation mechanism during wet/dry cycling is proposed: (1) initial fiber–cement debonding, (2) reprecipitation of hydration products within the void space at the former fiber–cement interface, and (3) fiber embrittlement due to fiber cell wall mineralization. Unbeaten fiber–cement composites exhibited greater peak strength and post-cracking toughness, prior to cycling, while no significant differences were seen after 25 cycles. The effects of fiber beating varied prior to and after cycling. Unbleached fiber–cement composites exhibited the slowest progression of degradation during cycling. The initial drying state appeared to have no effect on composite performance after 25 wet/dry cycles.