Extruded Cement Based Composites Reinforced With Sugar Cane Bagasse Fibres R.S. Teixeira1, a*, G.H.D. Tonoli2, b, S.F. Santos3, c, J. Fiorelli3, d, H. Savastano JR3, e, F.A. Rocco Lahr1, f 1
Escola de Engenharia de São Carlos, Universidade de São Paulo, Avenida Trabalhador São Carlense, 400, 13566-590, São Carlos/SP, Brazil.
2
Universidade Federal de Lavras, Departamento de Ciências Florestais, Campus Universitário, Caixa Postal 3037, 37200-000, Lavras/MG, Brazil.
3
Faculdade de Zootecnia e Engenharia de Alimentos, Universidade de São Paulo - Avenida Duque de Caxias Norte, 225, 13635-900 – Pirassununga/SP, Brazil. a
[email protected],
[email protected],
[email protected] d
[email protected];
[email protected],
[email protected]
Keywords: cellulosic fibre, mechanical properties, extrusion process, building materials, renewable resources, ordinary Portland cement
Abstract. 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. Introduction The extrusion process involves the formation of cohesive fibre-cement composites by forcing it through a die that can be adjusted to the various shape configurations. These sections are then cut to the desired length [1]. The process is continuous, making it most suitable for industrial production. The advantage of extrusion is that it is an economical mass-production method capable of producing not only flat shapes, but also structural and hollow shapes. Extrusion technology is a potential candidate for low cost commercial applications [2]. This process allows the use of a variety of waste materials have been successfully incorporated into the matrix, including fly ash [3], silica fume [3,4] and slag [5]. This process also permits the use of vegetable fibres as raw materials in the production of fibre-cement such as ceiling elements. An interesting alternative for achieving low cost reinforcement of cementitious materials is the use of natural fibres which grow abundantly in nature. Many attempts have been made to obtain practical applications. These include studies of fibres from rice husk [6], sugar cane bagasse [7], zacate [8], jute [9], sisal [10], and bamboo [11], among others.
Sugar cane fibre (SCF) reinforced cement composites have been studied for the improvement of the characteristics of building material. The building industry has the maximum potential for the utilization of these materials through their conversion into various kinds of building panels and blocks, as they provide a low cost source of reinforcing materials for cementitious composite products. Precedent studies conclude that SCF can be used for the production of cement-bonded composite materials and show high levels of performance in the presence of moisture and alternate wetting and drying cycles and therefore can be recommended for both internal and external applications in buildings [12]. Sugar cane fibre can be used as convenient materials for cement matrix reinforcement. Taking into account the fibre mechanical properties, with a suitable mix design, it is possible to develop a material with appropriate properties for building purposes. The objective of this study was to evaluate the reinforcement of the sugar cane bagasse fibres in cement based extruded materials under the effect of accelerated ageing cycles. The composite cementitious was analysed by SEM and PIM; and the fibre-cement composites produced by extrusion were evaluated by mechanical and physical tests. Experimental Fibre. Sugar cane (Saccharum officinarum) fibre used in this study was taken from the Baldin Agroenergia plant in Pirassununga/SP, Brazil. Sugar cane bagasse fibre (SCF) was originated from residues of the agroindustry. Some properties of these fibres are presented in Table 1. Table 1 Macro fibre properties [13]
Sugar cane bagasse fibre
Young’s Modulus (GPa)
Tensile strength (MPa)
Elongation (%)
27.1
222
1.1
Composite mix design. Formulations used in cementitious composites reinforced with sugar cane fibre (SCF) are described in Table 2 [14]. Table 2 Mix design used in the production of composites Content [% by volume] Raw material
SCF 0%
SCF 1.5%
SCF 5%
a
Portland Cement [CPV-ARI] 70 70 70 Crystalline silica # 500 b 27 25.5 22 Sugar cane fibre 0 1.5 5 Unbleached eucalyptus pulp c 3 3 3 (a) NBR 5733 [15] (clinker + gypsum = 100 - 95% by mass; carbonate material = 0 - 5%) provided by Câue, (b) 500 mesh (0,025mm), provided by Jundu Ltda, (c) Provided by Fibria S.A.
Portland cement and crystalline silica particles distribution was performed by a laser particle size analyzer (Malvern Mastersizer S long bed, version 2.19). Cement and crystalline silica particles showed 50% of its mass less than 12 and 6 µm respectively. The matrix is composed of CPV ARI cement (NBR 5733 Brazilian Standards) and crystalline silica "filler". Crystalline silica was used as partial replacement for Portland cement, with the aim of reducing costs and to reach the best dense packing in the mixture [16]. Unbleached eucalyptus pulp was used as secondary reinforcement in cementitious composites. The water soluble polymers, high range water reducer (HRWR) provided by Aditex and polyether carboxylic provided by Grace was used as lubricant, representing 1% of total composite mass. Hydroxypropyl methyl cellulose (HPMC) and carboxylate polyether (surfactant) were used as rheological modifiers to promote pseudo-plastic behaviour of the cement paste which, in turn, enabled the extrusion process.
Cement matrix and 1% of HPMC by dry mass were mixed and homogenized at low speed (mixture distributive), without water, in a mechanical Amadio planetary mixer (capacity of 20 L). After this stage, the eucalyptus unbleached pulp was added, subsequently, with the introduction of 1% of surfactant (ADVA 190). Before the composites production, the cement paste was re-homogenized in the extruder, feeding it and taking three times the mass. In accordance with the die in use, 15 mm thick composites were extruded. An extrusion vacuum helical screw equipment (Auger type), Gelenski, MVIG-05, was adopted. Pads with 200 mm x 50 mm x 15 mm (Fig. 1a and 1b) were then sealed wet in a plastic bag to cure at room temperature for two days and immersed in water during 26 days. Specimens of required dimensions (90 mm x 20 mm x 15 mm) were cut wet using a diamond saw cooled with water. After 2 days, samples were kept at laboratory conditions, with temperature of 27 ± 2ºC and 65 ± 5% of relative humidity prior to mechanical testing [17].
(a) 50 mm
(b) 15 mm
Fig.1. (a) Placing an extruded composite on a metal plate; (b) side view illustrating the pad exit at the nozzle. Scanning electron microscopy (SEM). Scanning electron microscopy (SEM) was used with secondary electron (SE) detector, operated at 10.0 kV accelerating voltage, for visualization of the surface fibre morphologies These were performed on the same surface specimens in an effort to obtain semi-quantitative compositional information. Samples were carbon coated before being analyzed in a Zeiss LEO 440 microscope. Mercury intrusion porosimetry. Mercury intrusion porosimetry was carried out using Micromeritics Poresizer 9320 with operative pressures of up to 200 MPa. Specimens were cut with a cubic side length of approximately 5mm and were completely dried prior to evaluation. The technique was adopted in order to evaluate the pore size distribution as it is usually applied in the characterization of cement-based materials [18,19]. Mechanical characterization of the composites. Mechanical tests were performed in an Instron electromechanical machine, model 5569 equipped with 5 kN load cell. A four-point bending configuration was employed in the determination of modulus of rupture (MOR) and Tenacity (TE) values. A major span of 75 mm and 5 mm/min deflection rate were adopted in bending test. Eqs. 1and 2 define MOR and TE respectively: MOR =
P ⋅ Lv b.h 2
(1)
where P is the maximum load, Lv is the major span between the supports; b and h are the specimen width and depth respectively. (2)
Tenacity (Eq. 2) was defined as energy absorbed during bending test divided by specimen crosssectional area. Absorbed energy was obtained by integration of area below the load deflection curve to the point corresponding to a reduction in load carrying capacity to 90% of the maximum reached. Physical characterization tests. Water absorption (WA) and apparent porosity (AP) values were obtained from the average of six specimens for each mix design, following procedures specified by ASTM C 948-81 [20] Standards. Soak/dry accelerated ageing cycles. The soak/dry accelerated ageing test involved comparative analysis of physical and mechanical composites performance, before and after soak/dry cycles. Specimens were successively immersed in water at 20 ± 5°C during 170 min, followed by the interval of 10 min, and then exposed to temperature of 70 ± 5°C for 170 min in a ventilated oven and with the final interval of 10 min. This procedure was based on recommendations of the EN 494 [21] Standards. Each soak/dry set represents one cycle and was performed for 200 cycles [14]. Results and discussion
16 14 12 10 8 6 4 2 0
MOR (MPa)
MOR (MPa)
Mechanical and physical properties of the composites. Fig. 2 shows the correlation between modulus of rupture (MOR) and water absorption (WA) of cementitious composites with 0, 1.5 and 5% reinforced of sugar cane fibre (SCF) with 28 days of cure (Fig. 2a) and after 200 accelerated ageing cycles (Fig. 2b). The MOR results did not present differences between the levels of reinforcement with 28 days of cure (Fig. 2a), but the water absorption (WA) increased for the amount of 5% of fibre. The increase of WA is related to the incorporation of large amounts of FBC that causes defects in the microstructure and affects the packaging [21]. Cementitious composites cementitious presented undifferentiated results for the different levels of SCF after 200 ageing cycles. 28 days
0%
Effect of Fibre
1.5% 5%
14
15
16
17 18 19 20 Water Absorption (%)
16 14 12 10 8 6 4 2 0
No tendency of fibre effect 0% 1.5% 5%
11
200 cycles 12
13 14 15 Water Absorption (%)
800
TE (J/m2)
TE (J/m2)
(a) (b) Fig.2. Modulus of rupture (MOR) vs. water absorption (WA) of the composites: (a) 28 days of cure and (b) after 200 accelerated ageing cycles.
28 days
600 400 200
600
0% 1.5% 5%
No tendency of fibre effect
400
Effect of fibre
0% 1.5% 5%
800
200
0
200 cycles
0 25
27
29
31
33
35
Apparent porosity (%)
20
22
24
26
Apparent porosity (%)
(a) (b) Fig.3. Tenacity (TE) vs. apparente porosity (AP) of the composites: (a) 28 days of cure and (b) after 200 accelerated ageing cycles.
Fig. 3 shows the correlation between tenacity (TE) and apparent porosity (AP), of cementitious composites with 0, 1.5 and 5% reinforcement of sugar cane fibre (SCF) after 28 days of cure (Fig. 3a) and after 200 accelerated ageing cycles (Fig. 6b). TE is related to the impact energy absorbed. The tenacity (TE) average results ranged from 370 J/m2 for the composite with 0%, to 330 J/m2 for the composite with 1.5% and 700 J/m2 for composite with 5% reinforcement of SCF with 28 days. This result is related to the incorporation of the higher content of SCF in the composite, and leading to the higher fracture energy. The AP of the composite after 200 cycles showed lower values in relation to the AP with 28 days, this behaviour may indicate that the adhesion between fibre and matrix was improved after accelerated ageing cycles, as a consequence of re-precipitation of hydration products of cement into and around the fibres and consequent filling of pores at the interface between fibre and matrix, thus reducing water absorption (Fig. 2b) and porosity (Fig. 3b) [22]. This result is in agreement with Savastano Jr. et al. [23] and Tonoli [24] where the cementitious composites presented an increase in the values of MOR and TE and a decrease of the water absorption and apparent porosity with 28 days of cure. Microstructure characteristics of the composites. Fig. 4a presented the fibre matrix interface fracture surface SEM image of cementitious composite reinforced with 5% of SCF at 28 days. Individual SCF with low specific contact area can be observed inside of the matrix (Fig. 4a – arrows). The dimensional variation of the fibre matrix interface occurs due to the fibre shrinkage upon drying. This kind of deboning is common in composites reinforced with vegetable fibres and it prejudices the adherence between the two phases [25]. The fracture surface of SCF reinforced matrix after 200 accelerated ageing cycles is depicted in Fig. 4b. During the accelerated ageing cycles, free ions formed by dissolution of cementitious phases of Portland cement penetrated into the lumen (Fig. 4b – arrows) of the SCF, causing the degradation of the SCF [26]. The internal lumen of filaments appeared free from the deposition of hydration products (or fibre petrifaction). This behavior can also be attributed to the alkali behavior of the cement based matrix which may have mineralized the fibres so drastically, degrading them and losing their effectiveness [27].
(a) (b) Fig.4. Fracture surface (SEM) images of composite cementitious reinforced with 5% of sugar cane fibres: (a) 28 days of cure (arrows – deboning fibre-matrix); (b) after 200 accelerated ageing cycles (arrows - cementitious phases of Portland cement penetrated into the lumen). Fig. 5 shows the behavior of the pore size distribution of cementitious composites extruded with 0, 1.5 and 5% by mass of SCF. Peaks between 6 and 40 nm showed great variation between the two different levels of reinforcement SCF. Composites with 5% of fibre had higher peaks in relation to plain matrix without fibre. This statement can be explained by the fibres inside the composite which leads to higher porosity and therefore to major defects. The peaks between 6 and 100 nm are related to the typical pores distribution formed during hydration of the matrix. These results were also found by Tonoli et al. [28] that studied fibre cement with different levels of refining of cellulosic fibres. The range between 104 and 105 nm (large pores) can be attributed to air entrapment due to the inclusion of high levels of SCF. The range from 100 to
Mercury intruded(mL/g)
10000 nm diameter was associated to low porosity in composite with 5% of SCF, contrarily to results presented by Tonoli et al. [28]. This difference can be explained by the manufacturing based on the extrusion process that submits the mixture to high pressure promoting its compaction and decreasing of pore sizing especially in the region close to the external surface (die effect). 0.08 0.07 0.06 0.05
0% 1.5% 5%
0.04 0.03 0.02 0.01 0.00
1000000 100000
10000
1000
100
10
1
Pore diameter(nm)
Fig.5. Mercury intrusion porosimetry (MIP) in composites extruded with 0, 1.5 and 5% of sugar cane bagasse fibre with 28 days of age. Conclusions Fibre-cement composites with 0, 1.5 and 5% by volume of sugar cane fibre produced by Auger extrusion process had their performances evaluated, with special interest in evaluation degradation under accelerated soak & dry tests, leading to the following conclusions: • The modulus of rupture (MOR) results present similar values between the levels of reinforcement at 28 days of cure and after 200 cycles, but with 28 days of cure increased on the water absorption (WA) due to the incorporation of large amounts of sugar cane fibre (SCF) that causes defects in its microstructure and affects the packaging of the composite. • The apparent porosity (AP) of composites after 200 cycles showed lower values in relation to the AP with 28 days, this behaviour may indicate that adhesion between fibre and matrix was improved after accelerated ageing cycles, as a consequence of re-precipitation of the cement hydration products into and around the fibres and consequent filling of pores at the interface between fibre and matrix, thus reducing water absorption and porosity. • The fracture surface SEM image presents sugar cane fibre (SCF) with low specific contact area inside the matrix. The dimensional variation of the fibre occurs due to fibre shrinkage upon drying. This kind of deboning is common in composites reinforced with vegetable fibres and affects the adherence between the phases • The fracture surface SEM image of sugar cane fibre (SCF) reinforced after 200 accelerated ageing cycles showed by dissolution of cementitious phases of Portland cement penetrated into the lumen of the SCF, causing the degradation of the SCF. This behavior can also be attributed to the alkalinity of the matrix behavior carried in the SCF which may have mineralized fibres so drastically, degrading them and losing their effectiveness. • In the mercury intrusion porosimetry test, the peaks between 6 and 100 nm are related to the typical pores distribution of the matrix formed during hydration. The range between 104 and 105 nm (large pores) can be attributed to air entrapment due to the inclusion of high levels of SCF. • In the mercury intrusion porosimetry test, the range from 100 to 10000 nm diameter was associated to low porosity, this difference can be explained by the manufacturing based on the extrusion process that submits the mixture to high pressure promoting its compaction and decreasing of pore sizing especially in the region close to the external surface.
The motivation for this work in extruded cementitious composites was to evaluate an alternative model of production using vegetable fibre as reinforcement. This study showed different behaviour in cementitious composites in relation to the processes normally used (suction and pressing), as result of porosity and accelerated ageing cycles. Further studies should be conducted to optimize the results. Acknowledgment Financial support for this research project was provided by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) in Brazil. The authors were supported by grants offered by CNPq, Brazil. Sugar cane bagasse was provided by Baldin Agroenergia and Eucalyptus pulp by Fibria Celulose S.A., in Brazil. References [1] [2] [3] [4] [5] [6]
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