Nanoindentation study of the interfacial zone between cellulose fiber and cement matrix in extruded composites

[EN] The present study shows the application of the nanoindentation technique to evaluate the properties of the cellulose fiber-cement matrix interfacial zone in composites prepared with an auger extruder. The degree of strength of the bond between fiber and matrix is recognized as important variable that influences macro-mechanical properties, such as modulus of rupture and toughness of cement based composites. The nanoindentation measurements showed the highest hardness and elastic modulus in the part inner of the cellulosic fiber after hydration process due to precipitation and re-precipitation of cement hydration products. These results indicate that mineralization of the cellulosic fibers can affect the stress distribution and interfacial bond strength in the cement based composite.The authors acknowledge by financial support provided by Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP, process no 2013/03823-8), Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES, process no 3886/2014) and Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq, process no 152069/2016), in Brazil. Special thanks for Fibria and Infibra for providing raw materials the development of this work.Teixeira, R.; Tonoli, G.; Santos, S.; Rayón, E.; Amigó, V.; Savastano, HJ.; Rocco Lahr, F. (2018). Nanoindentation study of the interfacial zone between cellulose fiber and cement matrix in extruded composites. Cement and Concrete Composites. 85:1-8. https://doi.org/10.1016/j.cemconcomp.2017.09.018S188

Impact of content and length of curauá fibers on mechanical behavior of extruded cementitious composites: Analysis of variance

[EN] The use of composite materials in construction has grown considerably in recent years, such as cementitious matrices and concrete reinforced with fibers. The vegetable fibers have become an alternative due to its abundance, low cost and low energy consumption for its production, and appropriate properties mechanical. Curauá fiber is a plant native from Amazonas harvested manually in commercial farming and it is used in the manufacture of ropes and baskets or as reinforcement in composite with organic matrix of components for cars, buses and trucks. On the other hand, the extrusion process can produce composites with high-density matrix with fibers, low permeability and good interface between fiber and matrix. This process is also compatible with the use of vegetable fibers as raw materials in the production of cost-effective construction elements such as ceiling panels and drywalls. The objective of this research was use the analysis of variance (ANOVA) for evaluating with rigor mathematical the influence of content and length of curauá fibers on the mechanical behavior of the extruded cementitious composites. Composites without fibers and reinforced with 1% and 2% by mass of fibers as well as 6 mm and 10 mm of length these curauá fibers were evaluated. The composites with fibers of 10 mm have showed better mechanical results. Besides, the composites with fibers curauá after 200 accelerated aging cycles were better than one non-aging.The authors acknowledge the financial support provided by Brazilian Agencies: Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Grant nº 2013/03823-8 and 2012/51467-3); Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Grant nº 3886/2014); and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Grant nº 406429/2015 and 312151/2016-0). The authors thank the Brazilian companies Fibria S.A., Infibra S.A. and Imbralit Ltda. for technical support to the development of this work.Teixeria, R.; Santos, S.; Christoforo, A.; Paya Bernabeu, JJ.; Savastano Jr., H.; Rocco Lhar, F. (2019). Impact of content and length of curauá fibers on mechanical behavior of extruded cementitious composites: Analysis of variance. Cement and Concrete Composites. 102:134-144. https://doi.org/10.1016/j.cemconcomp.2019.04.022S13414410

Mechanical and physical performance of low alkalinity cementitiouscomposites reinforced with recycled cellulosic fibres pulp fromcement kraft bags

The objective of this work was to study the addition of cellulosic pulp in low alkalinity cement composites as well as its mechanical behavior under bending stresses before and after accelerated aging cycles.The cellulosic pulp was obtained from recycled Portland cement kraft bags used for packaging. Lowalkaline cementitious matrices were tested, reducing from 80 to 85% the content of Portland cement, inorder to reduce the use of the conventional raw materials, energy cost and mainly to avoid a possiblealkaline degradation of the cellulosic pulps. The cement matrix resulted from the ternary blend Portlandcement gypsum pozzolan (fly ash or catalytic cracking catalyst residue), with 50% by weight of gypsumand different percentages by weight of pozzolans. These composites were prepared in the laboratory usinga slurry vacuum dewatering followed by pressing technique. The four point-bending tests were carriedout to evaluate the mechanical behavior of the low alkalinity cementitious composites and compositewithout pozzolans at 28 days and after soak and dry accelerated aging tests. The low alkaline cementcomposites presented average values of modulus of rupture about 10 MPa after the aging cycles, with theindication that its flexural strength was not significantly affected by the degradation tests. In addition, theaverage values of specific energy of these composites were also acceptable after 100 soak and dry cyclesas compared to the composites with the Portland cement plain matrix. These results suggest that theuse of low alkalinity ternary binder system can be an effective contribution in order to avoid the severedamage on cellulosic fibers (which occurred when traditional pure Portland cement matrix is applied).Authors would thank International Relationship Department of the Universitat Politecnica de Valencia for the scholarship awarded and to the financial support and scholarships provided by Brazilian Agencies Fapesp and CNPq for the work carried out at FZEA USP Pirassununga.Marmol De Los Dolores, G.; Santos, SF.; Savastano, HJ.; Borrachero Rosado, MV.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2013). Mechanical and physical performance of low alkalinity cementitiouscomposites reinforced with recycled cellulosic fibres pulp fromcement kraft bags. Industrial Crops and Products. 49:422-427. doi:10.1016/j.indcrop.2013.04.051S4224274

Effects of Eucalyptus pulp refining on the performance and durability of fibre-cement composites

Although Eucalyptus pulp has been widely used in the paper industry, there is limited information concerning its use as reinforcement in fibre-cement composites. The objective of this study was to evaluate effects of mechanical treatment (refining) of the Eucalyptus pulp on fibre properties as well as performance and microstructure of fibre-cement composites. The composites were evaluated before and after accelerated ageing cycles. The refining increased the capacity of Eucalyptus fibres to capture mineral particles, improving the adherence of the fibres with the matrix. This improved fibre-matrix interface led to better mechanical properties at 28 days of cure but higher mineralisation of fibres and consequently increased brittleness of composites after accelerated ageing (soak and dry) cycles. Unrefined fibres maintained the toughness of composites after ageing cycles. This indicates that refining may weaken the fibres thus affecting the mechanical performance (mainly decreasing modulus of rupture and toughness) of composites after ageing cycles. These results are useful for understanding effects of refined fibre conditions (morphology, mechanical strength and surface properties) on mechanisms of fibre-matrix adherence, fibre mineralisation and degradation of fibre-cement composites.FAPESP (05/59072-4, 07/05299-3)FAPEMIGCAPESCNP

Mechanical properties of cotton fabric reinforced geopolymer composites at 200-1000 °C

Geopolymer composites containing woven cotton fabric (0–8.3 wt%) were fabricated using the hand lay-up technique, and were exposed to elevated temperatures of 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. With an increase in temperature, the geopolymer composites exhibited a reduction in compressive strength, flexural strength and fracture toughness. When heated above 600 °C, the composites exhibited a significant reduction in mechanical properties. They also exhibited brittle behavior due to severe degradation of cotton fibres and the creation of additional porosity in the composites. Microstructural images verified the existence of voids and small channels in the composites due to fibre degradation