Fiber Cement Composites Research Articles

Microstructural characterization of cellulose fibres in reinforced cement boards

The microscopic analysis of the different cellulose fibre cement composites is presented. The observations of the fibres in optical microscope in transmitted light and in scanning electron microscope are described. The micro computed tomography (micro-CT) and SEM were used to determine the distribution of the fibres in the matrix. The investigated fibre cement boards were produced by extrusion process and panels were cured in natural conditions. The main goal of the research was application of different microscopic methods to analyze the fibres distribution as a result of a different methods of their production. Micro-CT was used for 3D visualization of fibres distribution in three different fibre cement boards. It was possible to determine the average diameter of the fibres and their concentration using the high-resolution mode of micro-CT scanning procedure. Finally, a procedure which can be applied as a useful tool for analysis of the different procedures used in production of fibre cement boards is described. This procedure can be successfully used in the quality control system of cellulose fibre distribution in cement composites.

Development of Electrically Conductive Composite Sensors with the Addition of Functional Fillers

The paper presents the development results of "smart" pressure-sensitive fibre-cement compositematerials as well as thin-film coating sensors designed to detect disruptions of the base materialstructure. Basic material characteristics of fine-grained and coarse-grained cement matrices wereacquired during the research. The benefits and influence of conductive inorganic components,metallic components in the form of iron fillings and steel wires, and last but not least carbon-basednon-metallic fibrous reinforcement, have been verified. Thin-film epoxy resin coatings were enrichedwith amorphous carbon black, multi-walled carbon nanotubes (MWCNT) and natural micronizedgraphite. The article closely describes the measurement of electrical and electro-mechanical(piezoresistive) properties of conductive fibre-cement composites and thin-film organic coatings in anon-loaded state, during static loading and especially during dynamic ballistic and shock tests on thefall tower. Specific electrical characteristics and the course of change in electric conductivity wasexpressed as electrical resistivity (the real component of the impedance).The performed experiments confirmed excellent electrical conductivity of dense steel-fibrereinforced composites and graphite-doped hybrid fibre reinforced concrete. The coatings showedsignificant and permanent changes in impedance in the order of tens of ohms. The newly developedfibre composites and coating layers change the impedance during destructive and non-destructivedynamic loading tests. The impedance changed not only during failure of the matrix, but also in thecase of indirect impact. Moreover, carbon reinforced concrete with incorporated graphite showedsome piezoresistive properties. These detection materials were intended to be part of a ballistic-resistant monitoring system.

Use of glass powder residue for the elaboration of eco-efficient cementitious materials

Abstract The glass powder is a waste resulting of the manufacturing process of flat glass (regular glass). This study evaluates the eco-efficiency of cement production using glass powder residue as partial replacement of cement. The glass powder residue (GPR) was used as partial replacement up to 50% by weight in cement pastes to evaluate the potential use of this matrix for application in fiber cement composites. For mortar specimens, the percentage of substitution of cement (up to 20% by weight) was used to evaluate the applicability of the glass powder in masonry construction. Primarily, several experiments such as thermogravimetric analysis, compressive strength tests, pozzolanic activity and durability tests were carried out to evaluate the potential use of GPR in cement industry. Secondly, to evaluate the eco-efficiency of the material elaborated, the energy demand of cement partially replaced by glass powder residue and the energy performance of mortars were calculated using mathematical equations. The results showed that GPR presents a pozzolanic activity and a free calcium hydroxide cement matrix is obtained when the ordinary Portland cement is partially replaced by 50% by weight of GPR in cement pastes. Moreover, the partial replacement of cement by 10% by weight of GPR leads to an increase of physico-mechanical properties of mortars. Finally, the energy consumption per MPa of mortars partially replaced by GPR (10 and 20% by weight) is lower than the one of original Portland cement suggesting the eco-efficiency of GPR for applications in cement production and the elaboration of cementitious materials. According to the results of the study, the residue from polishing process of flat glass can be used for the elaboration of green cement and eco-efficient cementitious materials.

Degradation behavior and kinetics of sisal fiber in pore solutions of sustainable cementitious composite containing metakaolin

Degradation of cellulose is the primary cause for the premature failure of natural fibers in the alkaline environment of cementitious systems. However, the degradation behavior and kinetics of cellulosic fibers in cementitious composites have not been thoroughly understood. In this study, the aging kinetic of cellulose exposing to pore solutions of cementitious materials is experimentally investigated and a model for service-life prediction of cellulose in cement is developed. To assess the impact of cement hydration on degradation behavior of cellulosic fibers and understand the correlations between fiber degradation and alkaline environment of cement, an approach to directly assess degradation rate of the embedded fibers was developed by determining fiber's tensile properties, thermal decompositions, crystallinity, and microstructures. The results indicate a strong dependence of degradation of sisal fiber on alkalinity of cement pore solutions. By incorporating 30 wt% metakaolin clay, the hydration of cement was modified and a mild environment was generated. Concentration of OH− was reduced and the pore solution becomes from oversaturated to unsaturated for calcium hydroxide after 7 days. As a result, tensile strength loss of the aged fiber was mitigated and the service life of cellulose was extended by 13.7 times.

Early Age Carbonation of Fiber-Cement Composites under Real Processing Conditions: A Parametric Investigation

This paper presents the outcome of a comprehensive experimental program undertaken to study the performance of cellulose pulp and synthetic PVA (polyvinyl alcohol) based fiber-cement composite under both carbonated and non-carbonated curing conditions at early age. The composites were produced at different rolling pressures (2.5 to 9.0 bar) and subjected to various curing conditions in which the effects of CO2 pressure (1 to 3 bar) and curing time (3 to 9 h) were studied. The mechanical properties (modulus of elasticity (MOE), modulus of rupture (MOR), and toughness), as well as the physical properties (porosity, bulk density, and water absorption), were measured for all samples. Scanning electron microscopy (SEM) was used to investigate the effect of carbonation on porosity change and adhesion of fiber-matrix. A parametric investigation of the effects of the carbonation curing period, CO2 pressure, and rolling pressure on the improvement of the physical and mechanical properties during carbonation curing was performed. Results showed that fiber-cement composites cured with an elevated CO2 pressure of 3 bar, rolling pressure of 3 bar, and 5 h of curing time provided optimal curing conditions resulting in the most desirable mechanical and physical properties. However, toughness was greatly reduced with the increase of the CO2 pressure, curing time, and rolling pressure. Additionally, the carbonation curing improved the bonding between the fiber and the cement matrix because of the precipitation of calcite particularly in the pores of the interfacial transition zone (ITZ) between the cement matrix and the fibers.

Vegetable fiber as reinforcing elements for cement based composite in housing applications – a Brazilian experience

Vegetable fibers are a hierarchical structure material in the macro, micro and nanometric scales that have been used as reinforcement in cementitious materials. In nanoscale, the nanofibrillated cellulose has the advantage of having good mechanical performance and high specific surface, which contributes to improve the adhesion between fiber and matrix. In hybrid reinforcement, with micro and nanofibers, nanofibrillated cellulose forms bonding with the matrix and acts as stress transfer bridges in the nano-cracking with corresponding strengthening of the cementitious composite. Processing has a strong influence on performance of the fiber cement composite. Two fabrication methods were evaluated: (i) slurry dewatering followed by pressing and (ii) extrusion. The extrusion process strongly depends on the rheological characteristics of the fresh cement material but it can better organize the microstructure of the fiber cement due to the partial orientation of the fibers in the extruder direction. Curing process also plays a key role in the performance of the final product. Accelerated carbonation at early age is a promising technology and a strategy to mitigate the durability problems with the composite materials; it decreases porosity, promotes a higher density in the interface guarantying a good fiber–matrix adhesion and a better mechanical behavior. Alternative MgO-SiO2 clinker free binder is also presented as a suitable alternative to cementitious products reinforced with cellulosic pulps. Finally, mechanical behavior of fiber cement under flexural loading is evaluated by modulus of rupture, fracture toughness, the initial crack growth resistance in cement matrix, and fracture energy that is obtained to evaluate the influence of toughening mechanisms promoted by fibers, such as pullout and bridging, on the mechanical performance of the composites. Degradation during the service life is also crucial for the evaluation of the durability of the resulting materials and components in real applications exposed to different environmental conditions as roofing, partitioning or ceiling elements. It can be concluded that more sustainable and high performance components based on engineered natural raw materials for civil construction can bring valuable contributions for the affordable housing in particular to developing region.

Prevention of concrete structures from collapsing

At the end of the 20th century requirements on using electrical properties of building materials emerged for application in heating of trafficable surfaces, grounding of electrostatic charges in floors, shielding of electro-magnetic fields and diagnosis of concrete structure state in the course of time. For this reason, it was necessary to design special fibre-cement elements able to transfer any mechanical impulse to an electricallymeasured signal detected as a change in electrical resistance with computer outputs. Regarding previous research studies, it was concluded that special fibre-cement composites are able to conduct electric current under specific conditions. This property is ensured by using of various kinds of carbon materials. Though carbon fibres are less conductive than metal fibres, composites with carbon fibres were evaluated as better current conductors than the composites with metal fibres. By means of various kinds of carbon particles and fibres it is possible to design cement composites with an ability to monitor changes in electrical conductivity of concretes. The designed composites are assembled with conductive wires and connected with a special electronic equipment for monitoring of changes in alternate voltage passing through the tensometer within mechanical loading of a concrete element in which the composite is integrated. The tensometers are placed preferably into parts of the concrete elements subjected to compression, such as simple reinforced columns or upper parts of longitudinal beams. Several tests of repeated loading and simultaneous monitoring of vertical as well as horizontal prefabricated concrete elements were carried out and evaluated.

Methods for characterization of fresh and hardened state of fibre concrete

Design, preparation and testing of fibre-cement composites are a task of wide range of research workplaces and universities in our country and abroad. However, a question on homogeneity of all cement matrix components and mainly optimal dispersion of fibre reinforcement in a mixture has not been yet solved sufficiently. A research team from the Research Institute for Building Materials has designed new experimental devices for the Discovery Hybrid Rheometer to measure rheological properties of fresh cement-based mixtures. The aim of research works was to find suitable homogenization techniques, design of mixing process and optimal dosing of individual components. By means of these actions it is possible to achieve the best dispersion of selected fibre types in fine-grained cementitious matrixes, which is subsequently verified in hardened composites at first by non-destructive and then by destructive methods. At the first stage non-destructive testing by means of ultrasound waves was carried out at first on a compact test slab with dimensions 500 × 500 × 40 mm and subsequently on individual test specimens with dimensions 250 × 40 × 40 mm, cut from the test slab according to a designed pattern. At the second stage destructive testing of test specimens was performed, mainly evaluation of flexural strength with 4-point bending and subsequently preparation of thin sections from the failure area for observation by means of polarizing microscopy to assess their structural integrity. The aim of research works was to find a method for monitoring homogeneity of cement composites reinforced with both metal and non-metal fibres before being subjected to mechanical loading.

RECYCLING TEXTILE RESIDUES INTO CEMENT COMPOSITES

Changing wastes into raw materials is one of the most favored options for waste management, as it diverts wastes from landfill and saves resources. Fibers, either vegetable (cellulosic) or synthetic, may be added to cement pastes in order improve the properties of concrete or mortar by reinforcement. At the same time, if the source of fibers is wastes, then such processes make ways for recycling. In the work described here we studied the compatibility of residues from the nonwoven textile industry with Portland cement, with the aim of manufacturing reinforced fiber-cement composites. The methodology was based on the monitoring of the temperature of cement setting, and when fiber or other materials were added to cement pastes. Results showed that the textile waste from needling machines investigated here is not compatible with cement. The reason is ascribed to a higher cotton content (65%), which enables cation exchange to occur in cement suspensions, and that disturbs cement setting reactions. On the other hand, however, synthetic fibers do not seem to hinder cement setting.

Influence of natural fibers characteristics on the interface mechanics with cement based matrices

Abstract The use of Natural Fibers in cementitious composites is an innovative technical solution but, they are characterized by a complex microstructure and significant heterogeneity, which influence their interaction with cementitious matrices, whose identification requires further advances in the current state of knowledge. The present study summarizes the results of a wide series of pull-out tests carried out on sisal, curaua and jute fibers. Then, the experimental results are employed in an inverse identification procedure aimed at unveiling the key features of the aforementioned bond-slip laws. Morphological, chemical, physical and mechanical characterization of the natural fibers were correlated with the resulting bond properties within the embedding matrix. The obtained results in terms of relevant parameters, such as bond strength and fracture energy (under pull-out stresses) of the fiber-matrix interface, pave the way for future studies intended for a better understanding of the structural response of Natural Fiber Reinforced Cementitious Composites.

Development of sandwich panels combining Sisal Fiber-Cement Composites and Fiber-Reinforced Lightweight Concrete

This research proposes the development of an innovative structural panels based on the use of thin outer layers of Sisal Fiber-Cement Composites (SiFCC) together with a core layer of Polypropylene Fiber-Reinforced Lightweight Concrete (PFRLC).The influence of sisal fibers was studied in two different ways, short sisal fibers (50 mm) randomly distributed in the matrix, and long unidirectional aligned sisal fibers (700 mm) applied by a cast hand layup technique. Lightweight aggregates and polypropylene fibers were used in the concrete layer forming the panel's core in order to reduce its density and improve its post-cracking tensile strength and energy absorption capacity.The behavior of the sandwich panels in four-point bending test is described, and the various failure mechanisms are reported. Mechanical properties of both SiFCC and PFRLC were obtained, which were also used in the numerical simulations. Pull-off tests were performed to evaluate the bond strength between the outer SiFCC layers and the core PFRLC. The results revealed that the long sisal fibers were more effective in terms of providing to the panel higher flexural capacity than when using short sisal fibers, long fibers ensured the development of a deflection hardening behavior followed by the formation of multiple cracks, while short sisal fibers promoted a softening response after cracking.

Influence of Cellulosic Fibres on the Physical Properties of Fibre Cement Composites

Nowadays, there are new approaches directing to processing of non-conventional fibre-cement composites for application in the housing construction. Vegetable cellulosic fibres coming from natural resources used as reinforcement in cost-effective and environmental friendly building products are in the spotlight. The applying of natural fibres in cement based composites is narrowly linked to the ecological building sector, where a choice of materials is based on components including recyclable, renewable raw materials and low-resource manufacture techniques. In this paper, two types of cellulosic fibres coming from wood pulp and recycled waste paper with 0.2%; 0.3% and 0.5% of fibre addition into cement mixtures were used. Differences in the physical characteristics (flowability, density, coefficient of thermal conductivity and water absorbability) of 28 days hardened fibre-cement composites are investigated. Addition of cellulosic fibres to cement mixture caused worsening the workability of fresh mixture as well as absorbability of hardened composites due to hydrophilic nature of biomaterial, whereas density and thermal conductivity of manufactured cement based fibre plaster are enhanced. The physical properties of cement plasters based on cellulosic fibres depend on structural, physical characteristics of cellulosic fibres, their nature and processing.

Cellulose Associated with Pet Bottle Waste in Cement Based Composites

The present study was to evaluate the effect of polyethylene terephthalate (PET) particle sizes on the mechanical and physical properties of extruded fiber-cement composites with different particle sizes combined to cellulose pulp in the production of fiber cement by the extrusion process. The design consisted of four formulations, one composed of 5% cellulose and the other three with 2.5% cellulosic pulp and 2.5% of PET particles with different particle sizes. Physical, mechanical and microstructural tests were performed without aging cycles and after 200 and 400 accelerated aging cycles. The degradation of vegetable fibers in the cement and the decrease of properties with aging was observed. PET particles were more resistant in alkaline environment and did not degrade. However, particle size did not exert great effect in the physical and mechanical properties of the composite. Thus, the use of PET particles shows potential as a reinforcement for fiber-cement composites.

Definition of optimal parameters for supercritical carbonation treatment of vegetable fiber-cement composites at a very early age

This paper presents a study of cellulose pulp fiber-cement composites subjected to supercritical carbonation at a very early age. The raw materials used for the creation of cementitious composite mixes include: Portland cement, limestone filler, and cellulose pulp. Composites were produced by a slurry vacuum dewatering process and subjected to curing conditions which studied the effect of supercritical carbonation concentration (0% and close to 100% of CO2), the effect of cellulosic pulp (unbleached or bleached), and durability. All samples were subjected to mechanical, physical, and microstructural tests. The initial period of thermal curing (varying from 24h to 48h) and exposure time to carbonation (from 1h to 2h), did not have a statistically significant effect on the mechanical performance of the composites. However, the flexural test results of carbonated composites reinforced with bleached pulp showed a statistically significant improvement when compared to unbleached pulp reinforcement (24% increased average modulus of rupture). Thus, for cementitious composites cured with supercritical carbonation, the use of bleached cellulosic pulp, 24h of thermal hydration and 1h in an environmental chamber provided the optimal curing conditions and the most desirable properties in this study.

Non-Destructive and Destructive Monitoring Methods of Fibre Concrete Homogeneity

Design, preparation and testing of fibre-cement composites are a task of wide range of research workplaces and universities in our country and abroad. However, a question on homogeneity of all cement matrix components and mainly optimal dispersion of fibre reinforcement in a mixture has not been yet solved sufficiently. Within testing of properties of such designed composites there is usually a realized fact, that variability of these properties is distinctive mainly for the reason of uneven dispersion of commonly used fibres in a whole matrix volume. Elimination of this phenomenon could be achieved by means of a design of the optimal homogenization process of dry mixture components with fibre reinforcement. The aim of research works was to find suitable homogenization techniques, design of mixing process and optimal dosing of individual components. By means of these actions it is possible to achieve the best dispersion of selected fibre types, both metal and non-metal, in fine-grained cementitious matrixes, which is subsequently verified in hardened composites at first by non-destructive and then by destructive methods. Four different fibre-cement mixtures were chosen as representatives for commonly used reinforcement in fibre-cement composites and test specimens with a thickness of 40 mm were prepared using processes suitable for the specific fibre reinforcement. At the first stage non-destructive testing by means of ultrasound waves was carried out at first on a compact test slab with dimensions 500 x 500 x 40 mm and subsequently on individual test specimens with dimensions 250 x 40 x 40 mm, cut from the test slab according to a designed pattern. At the second stage destructive testing of test specimens was performed, mainly evaluation of flexural strength with 4-point bending and subsequently preparation of thin sections from the failure area for observation by means of polarizing microscopy. A purpose of all these research works is finding of correlation between testing by means of destructive and non-destructive methods.

Effect of moisture on the thermoelectric properties in expanded graphite/carbon fiber cement composites

Abstract A kind of dry mixing and pressing process was introduced to prepare expanded graphite/carbon fiber cement composites (EG-CFRC). Significant effect of moisture on the thermoelectric properties of EG-CFRC was observed. The higher the moisture content is, the greater the absolute Seebeck coefficient. The maximum of absolute Seebeck coefficient 11.59 μV/°C was obtained with moisture of 14.98% at 33 °C. Simultaneously, the maximum of electrical conductivity 0.78 S cm −1 was got with moisture of 11.44%. Furthermore, the largest power factor 7.85×10 −4 µW m −1 K −2 was calculated at 33 °C with moisture of 11.44%. The carrier scattering, polarization effects and high density defects interface of EG-CFRC are attributed to the enhancement of thermoelectric properties in the case of higher moisture content.

Improvement of bagasse fiber–cement composites by addition of bacterial nanocellulose: an inverse gas chromatography study

The design of green fiber-reinforced nanocomposites with enhanced properties and durability has attracted attention from scientists. The present study aims to investigate the potential of bacterial nanocellulose (BNC) as a green additive for fiber–cement composites. Inverse gas chromatography (IGC) was used to evaluate the influence of incorporation of BNC as powder or gel, or coated onto the bagasse fibers, on the fiber–cement composite (FCC) surface. The results indicated that BNC incorporation made the FCC surface more reactive, increasing the dispersive component of the surface energy. The most relevant effects were found for BNC incorporation as gel or coated on the fibers. Incorporation of BNC as gel resulted in a predominantly organic FCC surface with substantial decreased surface basicity (K a/K b ratio from 2.88 to 5.75). IGC also showed that FCC with BNC incorporated as gel was more susceptible to hydration. However, BNC coated on fibers prevented fiber mineralization, increasing the inorganic materials at the surface, which caused an increase in the surface basicity (K a/K b ratio decrease to 2.00). These promising results could contribute to development of a new generation of green hybrid composites. The IGC technique enabled understanding of the physicochemical changes that occur on deliberate introduction of nanosized bacterial cellulose into fiber–cement composites.

Experimental and numerical analysis of short sisal fiber-cement composites produced with recycled matrix

The proper use of renewable or recycled source materials can contribute significantly to reducing the environmental impact of construction industry. In this work, cement-based composites reinforced with natural fibres were developed and their mechanical behaviour was characterised. To ensure the composite sustainability and durability, the ordinary Portland cement matrix was modified by adding metakaolin and the natural aggregate was substituted by 10 and 20% of recycled concrete aggregate. Compression and splitting tensile tests indicated that mechanical strength did not seem to be affected by recycled content. Flat sheets were cast in a self-compacted cement matrix and bending tests were performed to determine the first crack, postpeak strength and cracking behaviour of the composites. The use of short sisal fibre as reinforcement of recycled cement matrices results in a composite with multiple cracking and increment in strength after first crack. The modelling of composites using the finite-element method allowed to determine the tensile stress−strain behaviour of material and to design possible applications of this new sustainable material.

Degradation of natural fiber in ternary blended cement composites containing metakaolin and montmorillonite

The influence of a coupled substitution of metakaolin and montmorillonite in Portland cement on degradation of natural fiber was investigated. In addition to durability of fiber-cement composites, degradation of the embedded natural fiber was directly investigated by means of tensile properties, crystallinity, chemical components and microstructure. The results indicate that the combination of these clay minerals validates their synergic effect on mitigating fiber’s deterioration by modifying hydration products and reducing alkalinity of pore solutions in cement. Correlations between cement hydration and fiber degradation demonstrate that both mineralization and alkali hydrolysis of natural fiber can be substantially mitigated through this method.

Hybrid fiber and ultrahigh performance cementitious composites

Hybrid fiber and ultrahigh performance cementitious composites