Preparation and evaluation of the influence of modified fiber flour wood on the properties of the fresh condition of cement-based mortars
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Wood fibers were used as fillers in the partial cement matrix by replacing the cement to a content of 1% by weight of cement. The effect of wood fibers on porosity and compressive strength has been studied. The results obtained show an improvement in the compressive strength of more than 40% with 1% by weight of wood fibers. The addition of wood fibers shows a good pore reduction, and the best result was obtained with the emulsion of a mixture incorporating 1% by weight of wood fibers in the presence of an anionic surfactant (SDBS). The degree of hydration of the cement increases with the wood fibers. This property was confirmed by Fourier transform infrared spectroscopy. These analyzes revealed that the presence of wood fibers generates and promotes the hydration of the cement, producing more calcium silicate gel and portlandite, which affects the compressive strength which gives a strong improvement.
KeywordsWood Fiber Portland cement composite Degree of cement hydration Mechanical properties Microstructural properties
Calcium silicate hydrates
Ordinary Portland cement NT 47-01:1983
Critical micellar concentration
Wood fiber treated with a soda solution
Wood fiber treated with sodium hydroxide solution and EDTA solution
- Wood modified
Wood fiber modified by esterification with acetic anhydride
The use of the plant fibers represents a new stake in front of problems facing the recycling of composites strengthened with synthetic fibers . It appears from the literature and in touch with this subject that even if the concept is not new, it is not applied, at the moment, to the industrial scale and the majority of the related products remain unexploited, with the exceptions of sawdust which are used as fuels .
The concept of strengthening the cement matrix with plant fibers was developed as a potential substitute for asbestos fibers in 1940 . The use of plant fibers in the reinforcement of building materials is a relatively old field, noting for example the impregnation as horse hair in filling mortars or the manufacture of earth blocks reinforced with straw. In cement-based composites, cellulose fibers have been used as pulp, short fibers, long fibers or fabrics [3, 4]. However, the traditional methods used did not obey any technological development and scientific analysis until 1970, when the first work was done to replace asbestos fibers in prefabricated profiled fiber cement elements  composites, cellulose fiber has been used as pulp, short fibers, long fibers or fabrics [3, 4].
Rice et al.  studied the possibility of substituting the synthetic fibers by natural fibers such as the coconut, the sugar cane, the bugs and the fibers of banana’ trees. He showed that the epoxy strengthening of concretes of polymer by the fiber of coconut slightly more than the others. Surface treatment of the cellulose fibers with various coupling agents, surface the durability of fiber and fiber–matrix interaction was reported in several studies. Ceylon coupling agents were found to be effective in modifying the natural fiber–matrix interface; silone treatment of cellulose fibers changes the surface topography, surface chemical structure, and thermal degradation of cellulose fibers .
Reinforcement of mineral binders (cement, concrete or gypsum) has been a major concern for several decades. Efforts have therefore been made to replace the usual reinforcing agents such as glass fibers or asbestos fibers with organic agents (extracts of biomass), such as sisal, kraft or cellulosic fibers . To stabilize the plant fiber, three categories of treatment can be mentioned in the bibliography: thermal, physical and chemical.
Govin et al.  used a method called “roasting” for the treatment of fibers. This technique therefore consists of heating the wood fibers under an inert atmosphere up to 280 °C for a relatively long time to modify its structure. This process made it possible to limit the degradation of the fibers, so it kept its mechanical properties to a minimum value. Chemical treatment is the most studied technique worldwide; it consists of replacing the hydroxyl groups, highly hydrophilic and responsible for the swelling of the wood, by hydrophobic groups . Several studies have shown the importance of treating plant fibers with chemical solutions to increase the adhesion between the fiber and the matrix and consequently to improve the mechanical properties. Toledo et al.  immersed sisal and coconut in three solutions of different pH values; first, treated the fibers in water at pH = 8.3 (weakly basic medium), then in a lime solution Ca(OH)2 at pH = 12 and finally in a solution of NaOH soda at pH = 11. The purpose of this type of treatment is to determine the impact of pH and the effect of calcium ions on the outer wall of the plant fibers after immersion.
Baley et al. [12, 13] studied the impact of different chemical treatments (soda, acetic anhydride, formic acid, EDTA, lime saturated water and a polyethylene solution) on the bond between linen fibers and polyester resin and compared them to the system glass–polyester. The interfacial characterization was carried out by removing the unit fiber from a micro drop of this thermosetting matrix. The interpretation of the results thus obtained has shown that the proposed treatments lead to a marked increase in the fiber–liner–polyester bond. The treatment with EDTA leads to an increase in the rupture stress of the composites. On the other hand, the influence of the two other treatments is low on the mechanical properties.
HM Saleh et al. [14, 15, 16, 17] show that the cementation of 3% of biological waste generated during phytoremediation using the dried aquatic plant Veronica anagallis-aquatica gave a satisfactory compressive strength of solidified material resulting from more than 13 MPa. The high hardness value exceeded 25 MPa and was obtained in samples hardened in seawater or groundwater due to pore-sealing mineral salts. In another work, SB Eskander and HM Saleh [18, 19, 20, 21, 22, 23] have studied the effect of incorporation the spinning wastes in cement and mortars, the performance of aging cement–polymer composite immobilizing borate waste simulates during flooding scenarios, the leaching behavior in the natural cement–clay composite incorporating a truly spent radioactive liquid scintillator.
In previous studies, our groups have shown that the adsorption of cationic surfactant on bleached cellulose fibers greatly enhances the aptitude of the substrate to uptake dissolved organic compounds from aqueous media [24, 25, 26, 27, 28]. The improved solute adsorption was ascribed to the accumulation of the organic solutes within the aggregated domains formed by the self-assembly of surfactant monomers at the cellulose/water interface. However, the desorption of the surfactant molecules from the cellulose surface impeded the regeneration of the substrate by extraction of the trapped solute once it is exhausted. Then, a chemical grafting of hydrocarbon structures that mimics the aggregated domains generated by the adsorbed surfactant molecules was accomplished . The aptitude of the ensued modified substrate to uptake dissolved organic solute in aqueous media has been investigated in a batch and in continuous operations.
In this condition, the main environmental benefits such as biodegradability and renewal will be reduced. The purpose of this study was to evaluate the effect of treating wood fibers with anhydride and polymers derived from renewable resources, on the properties of wood fiber and cement-based composite. Water absorption and mechanical testing were done on wood fiber. Extraction tests were performed to evaluate the interface link. For the characterization of composites reinforced with 1% of wood fibers, compression tests were carried out.
Integration of wood fibers as a reinforcing agent in polymer-based composite materials: wood fibers form a rigid network, resulting from strong interactions between nanoparticles, is supposed to be governed by mechanical percolation mechanisms.
The addition of wood fibers improves the bending strength, the energy absorption of the cement paste, an increase in the cumulative heat of hydration and the degree of hydration of the cement of the reinforced wood fibers.
The increase in the degree of hydration of the cement can be explained by the steric stabilization, which is responsible for the dispersion of the cement particles and by the effect of wood fibers which provide a channel for the transport of the water through the ring of hydration products (i.e., high density CSH) to non-hydrated cement particles and improve hydration.
In this work, we continue our research regarding the potential use of modified wood fiber substrate as a new composite material with the cement matrix strengthened with vegetables fibers.
Materials and methods
The wood fibers were recovered from industrial waste, the fibers were washed in hot water (50 °C) to remove surface residues, such as a mucilage extraction process, and cut to the length of 40 μm.
Chemical composition and physical characteristics of Portland cement (wt%)
Loss on ignition
The additive used in our work is a commercial, analytical grade anionic surfactant were used as received, namely sodium dodecyl benzene sulfonate (SDBS). The critical micellar concentration (CMC) in deionized water (25 °C) determined by conductimetry is 1.1 × 10−3 mol L−1.
The Fourier transform infrared (FTIR) spectroscopy was used to analyze the composition change of the treated sisal. FTIR spectrum was obtained from KBr pellets with a Perkin Elmer spectrometer used in transmission mode with a resolution of 2 cm−1 in the range of 400–4000 cm−1.
CP/MAS 13C solid state NMR
Cross polarization/magic angle spinning (CP/MAS) 13C solid state NMR experiments were performed with Bruker 300 spectrometer operating at a 13C frequency of 75 MHz. the contact time for CP was 1 ms and the delay time for acquisitions was 5 s. Chemical shifts were referred to tetramethylsilane (TMS).
The measure of the angle of contact is a technique bound to the capacity of a liquid in Spread out on a surface by wet ability. The principle of this characterization thus consists to measure the angle enter the tangent of the profile of a drop of the liquid put down on the substratum, and the surface of the substratum. She allows measuring the energy of surface of the liquid or of solid. In our work, we used the method of the angle of contact to deduct hydrophilic or hydrophobic character of the surface of the sample. In our case, we used the water, polar solvent, as liquid of measure of angle of contact, this liquid allows to deduct the hydrophobic character (short angle, low energy of surface) or hydrophilic (small angle, big energy of surface) from the surface. The contact angle used in this work device lead by a fast Pulnix TM 6701AN camera (capable of delivering 200 images from 100 to 320 pixels s−1) is used to track the evolution of the shape of the drop every 5 ms. The data is then processed directly in a computerized manner by means of a specific image processing program which makes it possible to follow the evolution of the contact angle as a function of the measurement time.
Treatment processing by the soda
Treatment processing by EDTA
The vegetable fibers so handled by the soda require a treatment processing with a having complexes agent, it is about some ethylenediaminetetraacetic acid (EDTA). This stage of treatment processing was realized by the dumping of wood fibers in a containing aqueous solution 1 g of EDTA in 99 cm3 of the water (of concentration 1%). The treatment processing lasts 10 min. The use of the EDTA (C10H16N2O2) aims at preventing the fixation (binding) of the ions calcium Ca2+ on the surface of the fibers, exceptionally by pectin. Indeed, the molecules of EDTA train a very stable complex with the calcium, and as a consequence contribute to the destruction of the complex pectin–calcium on the surface of the fibers. The treatment processing with the EDTA allows increasing the constraint in the break of realizing mortars, while fixing the minimum of calcium to the surface of the fibers, because the existence of the latter of surface influences the constraint in the break. The treatment processing in the EDTA seems to lead at the beginning of separation of fibers some of the others, by degrading the amorphous constituents of fibers (Fig. 1b).
Treatment by esterification
This study involves the grafting of linear alkyl chains with different lengths of wood fibers by esterification using fatty acid anhydride. We exploited the hydroxyl functions of wood–fibers to condense them by acylation with C12 anhydride at different levels. Due to the low reactivity of the carboxylic acid functions present in the wood fibers with respect to the esterification reactions, we have activated this function by converting it into a much more reactive anhydride than the method of elaboration and characterization of the composites studied . By the following three stages: preparation of materials (cement, fibers and water), elaboration of the studied composites and preparation of the molds. The implementation of composites is done using our methods; we tried to make three forms of samples shown in Fig. 1c. After homogenization of the fresh material, it is put into place in molds. 24 h later, the samples were removed and left to continue drying in ambient air for 10 days.
Formulation of the cementitious product
Shapes and dimensions of specimens
Results and discussion
Characterization of modified fibers
Analysis by infrared spectroscopy FTIR
The wood fiber modified in this study obtained by heterogeneous esterification with C12 anhydride. The modified wood fiber was analyzed by FTIR and solid state NMR.
Analysis by CP/MAS 13C solid state NMR
Contact angle measurement
Recovery of pores
The hydration of cement favors the liberation of a very important quantity of calcium ions, the addition of a low concentration by adjuvant anionic (anionic surfactant SDBS) can assure the electrostatic neutralization. If we add a higher concentration of this additive, we shall have in this case an excess of the molecules of SDBS in the mixture. By arriving at the CMC (critical micellar concentration), the molecules of the additive group together by forming micelles responsible for the superficial cover of complex Ca2+/pectin, and as a result of recovery of pores in composites.
Electrokinetic study of the fiber wood suspensions handled by SDBS in the presence of a cement matrix
Characterization physical appearance
In this part, we have solved one of the major concerns about our subject, namely the problem of water absorption. This last factor is responsible for the decarbonization of steels in cementitious materials and therefore negatively affects their life expectancy.
Absorbance in water
Young’s modulus “E”
Young’s modulus values of the different samples
Compressive strength (MPa)
Cement + 0% wood modified
Cement + 2% wood modified
Cement + 1.5% wood modified
Cement + 1% wood modified
Cement + 0.5% wood modified
In this work, the fiber wood modified potential, as reinforcement for a cementitious matrix, was investigated. Due to its hydrophilic potental, high reactivity and high-specific surface area: the addition of modified wood fiber has shown an improvement in the mechanical and microstructural properties aoàf the new composite: modified wood fiber-portland cement.
The experimental results have shown that the incorporation of the fiber wood modified has greatly enhanced the compressive strength. The highest strength property was observed by adding 1 wt% of the fiber wood modified. On the other hand, these samples showed the effectiveness of the grafting of the hydrocarbon chains on the surface of the fibers, in the reduction of the absorbed rate in water compared with only cement. This feature has been further improved by adding to the composite in the fresh state an amount of an anionic additive (SDBS).
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