Holmer Savastano

Brazilian waste fibres as reinforcement for cement-based composites

Fibre reinforced cement-based composites were prepared using kraft pulps from sisal and banana waste and from Eucalyptus grandis pulp mill residues. The study adapted conventional chemical pulping conditions for the non-wood strands and a slurry vacuum de-watering method for composite preparation followed by air-curing. Plain cement paste and Pinus radiata kraft reinforced cement composites were used as reference materials. Mechanical testing showed that optimum performance of the various waste fibre reinforced composites was obtained at a fibre content of around 12% by mass, with flexural strength values of about 20 MPa and fracture toughness values in the range of 1.0–1.5 kJ m−2. Experimental results showed that, of the waste fibres studied, E. grandis is the preferred reinforcement for low-cost fibre-cement.

Potential of alternative fibre cements as building materials for developing areas

Abstract 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.

Transition zone studies of vegetable fibre-cement paste composites

Abstract The transition zone of short filament fibres randomly dispersed in a paste of ordinary Portland cement was analysed. Composites with vegetable fibres (malva, sisal and coir) were compared with those with chrysotile asbestos and polypropylene fibres. The composites were prepared for testing at the ages of 7, 28, 90 and 180 days. The water-cement ratio was 0.38; at the age of 28 days specimens with w c = 0.30 and a w c = 0.46 were also tested. Mechanical tests evaluated the composite tensile strength and ductility. Backscattered electron imaging (BSEI) and energy dispersive spectroscopy (EDS) were used to identify the major properties of the fibre-matrix interface. Mainly for vegetable fibre composites the transition zone is porous, cracked and rich in calcium hydroxide macrocrystals. These characteristics are directly related to the fibre-matrix bonding and to the composite mechanical performance.

Plant fibre reinforced cement components for roofing

Abstract 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.

Mechanically pulped sisal as reinforcement in cementitious matrices

Abstract The performance as reinforcement of fibres obtained from commercial and by-product sisal (Agave sisalana) by thermomechanical pulping and chemi-thermomechanical pulping (CTMP) processes was investigated. Ordinary Portland cement (OPC) and chemically activated blast furnace slag (BFS) were examined as binders. The flexural strengths of OPC- and BFS-based composites incorporating 8% fibre reinforcement by mass were similar at 28 days and ranged from 18 to 22 MPa. Corresponding modulus of elasticity values were in the region of 11 GPa for the OPC-based composites and 7 GPa for the BFS-based composites. Water absorption values at 8% fibre content lay in the range of 21–31% by mass and density values in the region of 1.5 g/cm3. Fracture toughness increased with fibre content, reaching a value of 1.6 kJ/m2 at a content of 12% in the case of by-product sisal CTMP in the BFS matrix. Scanning electron microscopy provided interfacial bonding information that can be related to the mechanical performance of these fibre-reinforced pastes.

Performance and Durability of Cement Based Composites Reinforced with Refined Sisal Pulp

This work evaluates the influence of three different intensities of refinement of sisal pulp and the effect of accelerated aging cycles on the behavior of composites. Fiber-cements were prepared by the slurry de-watering method and pressing as a crude simulation of the Hatschek process. Mechanical behavior of composites was evaluated by four-point bending test at 28 days, and after 50 and 100 wet/dry cycles. Refinement of pulp and aging have increased the strength and bulk density of composites and decreased the toughness and porosity. The best mechanical performance after aging was achieved for samples with highly refined fibers.

Ground iron blast furnace slag as a matrix for cellulose-cement materials

Abstract The use of ground iron blast furnace slag (BFS) as a low-cost alternative to ordinary Portland cement (OPC) binders in fibre-cement products was examined. Both high quality softwood fibres and residual sisal from agricultural waste were chemically pulped and used as reinforcement. Composites based on several different binder formulations consisting of slag chemically activated by mixtures of gypsum and hydrated lime displayed their optimum strength and fracture toughness properties at fibre contents between 8% and 12%, with values in the ranges of 14.7–24.5 MPa and 1.13–2.36 kJ/m2, respectively. Corresponding flexural moduli lay in the range 4.3–7.8 GPa and, at 12% fibre content, the composites possessed water absorption values up to 34% by mass and densities in the region of 1.3 g/cm3. A formulation of BFS activated by 10% gypsum and 2% lime presented a good compromise between strength and energy absorption combined with a reasonable price.

Impact of bleaching pine fibre on the fibre/cement interface

The goal of this article was to evaluate the surface characteristics of the pine fibres and its impact on the performance of fibre–cement composites. Lower polar contribution of the surface energy indicates that unbleached fibres have less hydrophilic nature than the bleached fibres. Bleaching the pulp makes the fibres less stronger, more fibrillated and permeable to liquids due to removal the amorphous lignin and its extraction from the fibre surface. Atomic force microscopy reveals these changes occurring on the fibre surface and contributes to understanding the mechanism of adhesion of the resulting fibre to cement interface. Scanning electron microscopy shows that pulp bleaching increased fibre/cement interfacial bonding, whilst unbleached fibres were less susceptible to cement precipitation into the fibre cavities (lumens) in the prepared composites. Consequently, bleached fibre-reinforced composites had lower ductility due to the high interfacial adhesion between the fibre and the cement and elevated rates of fibre mineralization.

Hybrid Reinforcement of Sisal and Polypropylene Fibers in Cement-Based Composites

Several studies using vegetable fibers as the exclusive reinforcement in fiber-cement composites have shown acceptable mechanical performance at the first ages. However, after the exposure to accelerated aging tests, these composites have shown significant reduction in the toughness or increase in embrittlement. This was mainly attributed to the improved fiber-matrix adhesion and fiber mineralization after aging process. The objective of the present research was to evaluate composites produced by the slurry dewatering technique followed by pressing and air curing, reinforced with combinations of polypropylene fibers and sisal kraft pulp at different pulp freeness. The physical properties, mechanical performance, and microstructural characteristics of the composites were evaluated before and after accelerated and natural aging. Results showed the great contribution of pulp refinement on the improvement of the mechanical strength in the composites. Higher intensities of refinement resulted in higher modulus of rupture for the composites with hybrid reinforcement after accelerated and natural aging. The more compact microstructure was due to the improved packing of the mineral particles with refined sisal pulp. The toughness of the composites after aging was maintained in relation to the composites at 28 days of cure.

Extruded Cement Based Composites Reinforced with Sugar Cane Bagasse Fibres

The extrusion process can produce composites with high-density matrix and fibre packing, low permeability and fibre matrix bond strengthening. This process is also compatible with the use of vegetable fibres as raw materials in the production of cost-effective construction elements such as ceiling panels. Sugar cane bagasse fibres (SCF), one of the largest cellulosic agroindustrial by-products of sugar and alcohol industry available in Brazil, are a renewable resource usually used as a biomass fuel for the boilers. The remaining bagasse is still a source of contamination to the environment, so there is a great interest on exploiting novel applications to sugar cane bagasse fibres. In this work, the effect of SCF on extruded cementitious composite performance was evaluated. Three different contents of SCF were considered, using cellulose pulp as secondary micro-reinforcement to improve the resistance to the appearance of microcracks. Composites were prepared using a laboratory Auger extruder with vacuum chamber and were tested after 28 days of water curing and after 200 accelerated ageing cycles. Modulus of rupture (MOR) and Tenacity (TE) of extruded composites were assessed by four point bending test. Water absorption and apparent volume were determined by water immersion. Microstructure behavior was evaluated by mercury intrusion porosimetry and scanning electron microscopy (SEM). Results indicated that the introduction of larger fibres increased tenacity (TE) at 28 days and favored a higher amount of macropores (0.1 to 1 mm); SEM observations confirmed that fibre degradation occurred after 200 cycles.