Key Engineering Materials Vol. 517

Abstract: The use of hemp-lime as a construction technique is a novel approach which combines renewable low carbon materials with exceptional hygrothermal performance. The hemp plant can grow up to 4m over a four month period, with a low fertilizer and irrigation demand, making it very efficient in the use of time and material resources. All parts of the plant can be used the seed for food stuffs, the fibre surrounding the stem for paper, clothing and resin reinforcement, and the woody core of the stem as animal bedding and aggregate in hemp-lime construction. The unique pore structure of the woody core (shiv) confers low thermal conductivity and thermal and hygric buffering to hemp-lime. The construction technique promotes good air tightness and minimal thermal bridging within the building envelope. All these factors combine to produce low carbon, hygrothermally efficient buildings which are low energy both in construction and in use, and offer opportunities for recycling at end of life. This paper reports on the hygrothermal performance of an experimental hemp-lime building, and on the development of a computerized environmental model which takes account of the phase change effects seen in hemp-lime.

Abstract: Flexion tests were performed (ASTM D790) for two biodegradable composites, the first one made of pine resin as matrix and henequen fibers as reinforcement, varying the percentage reinforcement. The second composite made of a matrix of cellulose obtained from a mixture of recycled paper and water and reinforced with maize bract fibers (the leaves that cover the corn cob) and infiltrated with pine resin. Five samples were evaluated for each compound in an Instron universal machine (load cell: 5 kN). For the henequen fibers and pine resin composite specimens were prepared according to standard by the method of hot casting resin, henequen fibers both short and long (127mm, 10mm) were included prior to discharge the matrix. The drying was at room temperature for 1 minute. Tests were conducted with different compositions of matrix / reinforcement by varying the amount of fiber in 26%, 20% and 14% of the specimen. The long fibers longitudinally traverse the specimen (127mm) and short fibers (10 mm) are dispersed in the mixture. The second composite is produced from corn fiber preforms and cellulose by the method of compression molding, dried in oven at 100 ° C for 2 hours. The preforms were infiltrated with pine resin by compressed air (25 psi). We analyzed the effect of corn fiber content in weight percentages of 10%, 30% and 50% with respect to cellulose and two lengths of corn fiber (22.25μm and 487 μm). Under study conditions, corn fiber generates a negative effect on the flexural strength of the compound. By increasing the fiber content of corn and its size, the bending strength decreased in almost all cases, is attributed to a lack of uniformity in the distribution of corn fibers. However, flexural strength values obtained were similar to materials such as wood, found in the literature. This projects the potential of the compound to replace, in certain applications, non-sustainable material

Abstract: Rice production in Brazil in 2010 was approximately 12,2 million tons, and to reach that amount several planting techniques were used with different strains of rice in different rice-growing areas. Since Rice Husk Ash (RHA) is the pozzolan of vegetable origin most studied by researchers working in the area of pozzolanic materials, the present paper evaluates the influence that the form of planting, the climate, the soil, the strain of rice and the origin/amount of nitrogen-based fertilizers used in rice cultivation has on the chemical composition and crystallographic properties of RHA. The results obtained in this paper, confirm the importance of carrying out routine chemical analysis and X-Ray diffraction to maintain the quality control of the CCAs produced, because in situations of large-scale production, husks of different origins may be used.

Abstract: Fibre-cement products had been widely used in the world due to their versatility as corrugated and flat roofing materials, cladding panels and water containers presented in large number of building and agriculture applications. The main reason for incorporating fibres into the cement matrix is to improve the toughness, tensile strength, and the cracking deformation characteristics of the resultant composite. One of the drawbacks associated with cellulose fibres in cement application is their dimensional instability in the presence of changing relative humidity. The objective of the present work is to evaluate the effect of surface treatment of eucalyptus cellulose pulp fibres on the processing and dimensional changes of fibre-cement composites. Surface modification of the cellulose pulps was performed with methacryloxypropyltri-methoxysilane (MPTS), aminopropyltri-ethoxysilane (APTS) and n-octadecyl isocyanate, an aliphatic isocyanate (AI), in an attempt to improve their dimensional instability into fibre-cement composites. X-ray photoelectron spectroscopy (XPS) showed the chemical changes occurred at the surface, and contact angle measurements showed the changes in the surface energy. MPTS-and AI-treated fibres presented lower hydrophilic character than untreated fibres, which led to lower water retention values (WRV). APTS increased the water retention value of the pulp and improved the capacity of hydrogen bonding of the fibres. MPTS-and AI-treated fibres led to low final water/cement ratios and reduced volume changes after pressing. MPTS-treated fibres decreased the water and dimensional instability of the fibre-cement composites, while the contrary occurred with APTS-modified and AI-modified fibres.These results are promising and contribute for new strategy to improve processing and stability of natural fibres-reinforced cement products.

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.

Abstract: One of the main problems in using vegetable fibers as reinforcement in aggressive cement matrix is the penetration of alkaline products in the porous structure of the filaments, making them very fragile with the time. In this sense a series of physical and chemical methods of surface modification has been used in order to improve its characteristics. The plasma surface modification technique is a physical method surface modification that utilizes ionized gas at low pressure to change the chemical nature and the substrate surface morphology of both organic and inorganic materials without changing their intrinsic properties. This is considered an environmentally friendly process without generation of contamination and has a low operating cost compared to some chemical (such as silane based) treatments. In the present study, the sisal fibers were treated with methane plasma generated by direct electric current during 10, 20 and 30 min with gas flow of 5 cm³/s and current of 0.10 A. The study presents some mechanical, physics and chemical characteristics of sisal fiber after being subjected to treatment with methane cold plasma. The results presented indicate that treatment with methane cold plasma induced changes in sisal fibers at all times of exposure to treatment (10, 20 and 30 min). However, the major changes in structural and mechanical components may be seen in fibers treated with 10 min of exposure to plasma.

Abstract: This study presents the results of the mechanical characterization of short jute fiber cement mortar composites. Compression, direct tension and bending tests were performed to determine the first crack, post-peak strength, toughness and fracture processes of the composites. To ensure the composite durability, the ordinary Portland cement matrix was modified by adding metakaolin to consume the calcium hydroxide generated during Portland cement hydration. The composites were produced using reinforcement ratios of 2% and 3% of short jute fiber (25 mm) in a self-compacting matrix of maximum packing. Jute plant is easy to grow in the Amazon region of Brazil where arrived in early 30s coming from Asia and represents the main economic activity of the Amazon riverine population. The tensile behavior of this high performance natural reinforcement was determined in the present study using 30 mm long fiber. Composites with high toughness, strength and multiple cracking processes under bending load were obtained when volume fractions equal to 3% were used as reinforcement.

Abstract: Sugar cane bagasse ash (SCBA) is a byproduct rich in silica, which it is present as of both crystalline and amorphous phases. This paper aims to evaluate the effect of grain size of residual SCBA particles on the solubility of silicate species in alkaline solutions that still needs examination. The influence of the amorphous character of the material was also investigated. Physical characterization was performed by the assessment of density and specific area of powder samples. Chemical and mineralogical characterizations were performed using different techniques including x-ray fluorescence, x-ray diffraction, infrared spectroscopy and scanning electron microscopy. The results indicate that the grinding process reduces the specific area of the particles of ash in a non linear fashion. The controlled burning of sugar cane bagasse increased the amorphous character of the ash. Nonetheless both factors affected the solubility of silicates, the degree of crystalinity appears to be the most important factor.

Abstract: This paper describes the study of lime/metakaolin pastes using impedance spectroscopy during the first three weeks after mixing. Changes in the composition, structure and morphology were obtained using scanning electron microscopy, energy dispersive analysis of X-rays, differential scanning calorimetry, thermal gravimetric analysis and mercury intrusion porosimetry. The impedance data was studied with reference to changes in ac conductivity, relative permittivity and bulk resistance. Electrical behaviour was found consistent with structural and compositional changes. This study highlights the importance of impedance spectroscopy as a method for the non destructive monitoring and evaluation of lime based hydraulic binders.

Abstract: Rice is produced in many countries in the world, and this product permits to feed a lot of people, most of them in developing countries. Approximately one tone of rice produces 200 Kg of rice husk, and when this rice husk is burnt 20% of rice husk ash (RHA) is obtained. A very important part of rice husk is abandoned in the field producing environmental problems. RHA can be obtained by controlled combustion, when this fact occurs, a good quality RHA is produced. This RHA can be used as a pozzolanic material in mixtures with lime or Portland cement, producing good mechanical properties and durability. In this work a preliminary results about the influence of RHA/lime ratio on workability and mortars strength was studied. The results showed that mortars workability improves when RHA/lime ratio do. Compressive strength (Cs) of mortars with different RHA/lime ratios was studied, in this sense, for 28 days curing time at 20°C an increase of Cs when RHA/lime ratio do is observed. However for 90 and 180 days curing time a maximum or Cs for RHA/lime equal to 2 is obtained. The lowest and highest Cs values obtained were 6 and 18 MPa respectively, when 20°C curing temperature was used. When curing temperature increases until 65°C similar tendency of Cs respecting RHA/lime ratio was observed. A preliminary study of binders for using in mortars tiles reveals that at least low quantities of Portland cement must be included in binder composition in order to obtain short term strengths that make easy tile demoulding process.