Influence of microwave oven calcination on the pozzolanicity of sugar cane bagasse ashes (SCBA) from the cogeneration industry

[EN] This study evaluates the effects of microwave oven calcining conditions on the pozzolanicity of sugar cane bagasse ashes (SCBA) generated by the electric power cogeneration industry. The calcining temperatures varied between 600 ºC and 800 ºC, and the permanence times were 60 min in an electric oven and 30, 45 and 60 min in a microwave oven. To evaluate the behaviour of the ashes according to different calcining conditions, we carried out the following analyses: granulometric distribution (laser diffraction), oxide percentages (XRF), loss on ignition (LOI), powder X-ray diffraction (XRD), pozzolanic reactivity, determination of amorphous silica content and thermogravimetry of hydrated lime pastes (DTG). The results show that SCBA calcination in a microwave oven results in ashes with greater pozzolanic reactivity and a significantly more efficient burning process than in an electric oven.The authors would like to thank the CNPq-Brazil (Project: 200133/2017-9) for financial support.Rossignolo, J.; Borrachero Rosado, MV.; Soriano Martinez, L.; Paya Bernabeu, JJ. (2018). Influence of microwave oven calcination on the pozzolanicity of sugar cane bagasse ashes (SCBA) from the cogeneration industry. Construction and Building Materials. 187:892-902. https://doi.org/10.1016/j.conbuildmat.2018.08.016S89290218

Effect of Pyrogenic Silica and Nanosilica on Portland Cement Matrices

[EN] In this work, the effect of pyrogenic silica and nanosilica on the properties of portland cement matrices is compared. Two chemically and mineralogically similar mineral additions (amorphous silica) with different particle size and specific surface area were used to prepare pastes and mortars with different solids substitutions of cement by silica. These samples were used to measure water and superplasticizer demand, setting time, hydration kinetics, water absorption by capillary suction, and compressive strength. It was found that specific surface area, rather than particle size, played a crucial role in the amount of water and superplasticizer necessary to obtain a desired workability in pastes and mortars. Such water and superplasticizer demands had a delaying effect on the setting time and hydration kinetics of pastes. Nevertheless, compressive strength results at different curing ages of mortars were found to have a direct correlation with the porous structure of the matrix, rather than with the specific surface area of the silica particles. It was concluded that regardless of its higher specific surface area and greater effect on the fresh state properties of pastes, pyrogenic silica was less efficient than nanosilica to increase the compressive strength of mortars, being considered a less efficient pozzolanic material.Tobón, J.; Mendoza-Reales, O.; Restrepo, O.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2018). Effect of Pyrogenic Silica and Nanosilica on Portland Cement Matrices. Journal of Materials in Civil Engineering. 30:1-10. https://doi.org/10.1061/(asce)mt.1943-5533.0002482S1103

Effect of different high surface area silicas on the rheology of cement paste

[ES] Efecto de diferentes sílices de alta área superficial sobre la reología de pastas de cemento. Este tra¬bajo estudia el efecto de la nanosílice (NS) sobre la reología de pastas de cemento por comparación con sílices de alta área superficial: humo de sílice (SF) y pirosílice (PS). Las pastas fueron fabricadas con diferentes rela¬ciones agua-material cementante y sustituciones sólidas de sílice. Fueron ejecutados ensayos de demanda de agua, tiempo de fraguado y reología. Se encontró que la NS y SF disminuyen la viscosidad plástica, mientras que la PS la aumenta. Solo la PS tuvo efecto sobre el límite elástico. La NS presentó mayor disminución de la viscosidad, independientemente de su alta demanda de agua. Se concluyó que el comportamiento de las pastas con NS y SF es gobernado por el efecto de ¿rodamiento¿ de la sílice, por su grado de aglomeración y por su impacto en la fracción de sólidos. El comportamiento de las pastas con PS es gobernado por su capacidad de absorber agua.[EN] This work studies the effect of nanosilica (NS) on the rheology of cement paste by comparing it with two high specific surface area silicas: silica fume (SF) and pyrogenic silica (PS). Portland cement pastes were produced with different water-to-cementing material ratios and different solid substitutions of cement by silica. Water demand, setting time, and rheology tests were performed. Results showed that NS and SF decreased plastic viscosity, while PS increased it. Only PS was found to have an effect on yield stress. NS showed the most decreasing effect on viscosity, regardless of its higher water demand. It was concluded that the behavior of pastes containing NS and SF is governed by the "ball-bearing" effect from silica particles, by their agglomeration degree, and their impact on the solid volume fraction. The behavior of pastes containing PS is governed by its ability to absorb a portion of the mixing water.Tobón, J.; Mendoza, O.; Restrepo, O.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2020). Effect of different high surface area silicas on the rheology of cement paste. Materiales de Construcción. 70(340):1-9. https://doi.org/10.3989/mc.2020.15719S19703401. Kwan, A.K.H.; Li, Y. (2013) Effects of fly ash microsphere on rheology, adhesiveness and strength of mortar. Constr. Build. Mater. 42, 137-145.2. Jal, P.K.; Sudarshan, M.; Saha, A.; Patel, S.; Mishra, B.K. (2004) Synthesis and characterization of nanosilica prepared by precipitation method. Coll. Surf. A Physicochem. Eng. Asp. 240 [1-3], 173-178.3. El Sokkary, T. M.; Assal, H. H.; Kandeel, A. M. (2004) Effect of silica fume or granulated slag on sulphate attack of ordinary portland and alumina cement blend. Ceram. Int. 30 [2], 133-138.4. Gutsch, A.; Krämer, M.; Michael, G.; Mühlenweg, H.; Pridöhl, M.; Zimmermann, G. (2002) Gas-Phase production of nanoparticles. KONA Powder Part. J. 20, 24-37.5. Singh, L.P.; Karade, S.R.; Bhattacharyya, S.K.; Yousuf, M.M.; Ahalawat, S. (2013) Beneficial role of nanosilica in cement based materials - A review. Constr. Build. Mater. 47, 1069-1077.6. Björnström, J.; Martinelli, A.; Börjesson, L.; Panas, I.; (2004) Accelerating effects of colloidal nano-silica for beneficial calcium-silicate-hydrate formation in cement. Chem. Phys. Lett. 392 [1-3], 242-248.7. Mendoza Reales, O.A.; Silva, E.C.C.M.; Paiva, M.D.M.; M.; Duda, P.; Toledo Filho, R.D. (2017) The role of surface area and compacity of nanoparticles on the rheology of cement paste 25.3. ACI Symp. Pub. 320, 25.1-25.14. https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/51701063.8. Tobón, J. I.; Mendoza Reales, O.; Retrepo, O.J.; Borrachero, M.V. (2018) Effect of pyrogenic silica and nanosilica on Portland cement matrices. J. Mater. Civ. Eng. 30 [10], 1-10.9. Mehdipour, I.; Khayat, K.H. (2018) Understanding the role of particle packing characteristics in rheo-physical properties of cementitious suspensions: A literature review. Constr. Build. Mater. 161, 340-353.10. Boukendakdji, O.; Kadri, E.H.; Kenai, S. (2012) Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of selfcompacting concrete. Cem. Concr. Compos. 34 [4], 583-590.11. Park, C.K.; Noh, M.H.; Park, T.H. (2005) Rheological properties of cementitious materials containing mineral admixtures. Cem. Concr. Res. 35 [5], 842-849.12. Deng, H.; Li, H. (2018) Assessment of self-sensing capability of carbon black engineered cementitious composites. Constr. Build. Mater. 173, 1-9.13. Mendoza-Reales, O.A.; Arias Jaramillo, Y.P.; Ochoa Botero, J.C.; Delgado, C.A.; Quintero, J.H.; Toledo Filho, R.D. (2018) Influence of MWCNT/surfactant dispersions on the rheology of Portland cement pastes. Cem. Concr. Res. 107, 101-109.14. Quercia, G.; Hüsken, G.; Brouwers, H.J.H. (2012) Water demand of amorphous nano silica and its impact on the workability of cement paste. Cem. Concr. Res. 42 [2], 344-357.15. Norhasri, M.S.M.; Hamidah, M.S.; Fadzil, A.M. (2017) Applications of using nano material in concrete: A review. Constr. Build. Mater. 133, 91-97.16. Bowen, P. (2002). Particle size distribution measurement from millimeters to nanometers and from rods to platelets. J. Dispers. Sci. Technol. 23 [5], 631-662.17. Staiger, M.; Bowen, P.; Ketterer, J.; Bohonek, J. (2002) Particle size distribution measurement and assessment of agglomeration of commercial nanosized ceramic particles. J. Dispers. Sci. Technol. 23 [5], 619-630.18. Hidalgo, A.; Petit, S.; Domingo, C.; Alonso, C.; Andrade, C. (2007) Microstructural characterization of leaching effects in cement pastes due to neutralisation of their alkaline nature. Part I: Portland cement pastes. Cem. Concr. Res. 37 [1], 63-70.19. Srinivasan, S.; Barbhuiya, S.A.; Charan, D.; Pandey, S.P. (2010) Characterising cement-superplasticiser interaction using zeta potential measurements. Constr. Build. Mater. 24 [12], 2517-2521.20. de Larrard, F. (1999) Concrete mixture proportioning a scientific approach, E. & F.N. Spon, London.21. Banfill, P.F.G. (2006) Rheology of fresh cement and concrete. Rheol. Reviews 2006. 61-130.22. Burneau, A.; Barres, O.; Gallas, J.P.; Lavalley, J.C. (1990) Comparative Study of the Surface Hydroxyl Groups of Fumed and Precipitated Silicas. 2. Chatracterization by infrared spectroscopy of the interacctions with water. Langmuir. 6 [8], 1364-1372.23. Xie, X-L.; Liu, Q-X.; Li, R.K-Y.; Zhou, X-P.; Zhang, Q-X.; Yu, Z-Z.; Mai, Y-W. (2004) Rheological and mechanical properties of PVC/CaCO3 nanocomposites prepared by in situ polymerization. Polymer. 45 [19], 6665-6673.24. Asavapisit, S.; Fowler, G.; Cheeseman, C.R. (1997) Solution chemistry during cement hydration in the presence of metal hydroxide wastes. Cem. Concr. Res. 27 [8], 1249-1260

Use of ancient copper slags in portalnd cement and alkali activated cement matrices

Some Chilean copper slag dumps from the nineteenth century still remain, without a proposed use that encourages recycling and reduces environmental impact. In this paper, the copper slag abandoned in landfills is proposed as a new building material. The slags studied were taken from Playa Negra and Púquios dumps, both located in the region of Atacama in northern Chile. Pozzolanic activity in lime and Portland cement systems, as well as the alkali activation in pastes with copper slag cured at different temperatures, was studied. The reactivity of the slag was measured using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), X-ray diffraction (XRD), electrical conductivity and pH in aqueous suspension and Fourier Transform Infrared Spectroscopy (FTIR). Furthermore, copper slag-Portland cement mortars with the substitution of 25% (by weight) of cement by copper slag and alkali-activated slag mortars cured at 20 and 65 C were made, to determine the compressive strength. The results indicate that the ancient copper slags studied have interesting binding properties for the construction sector.Nazer, A.; Paya Bernabeu, JJ.; Borrachero Rosado, MV.; Monzó Balbuena, JM. (2016). Use of ancient copper slags in portalnd cement and alkali activated cement matrices. Journal of Environmental Management. 167:115-123. doi:10.1016/j.jenvman.2015.11.024S11512316

Durability of glass fiber reinforced cement (GRC) containing a high proportion of pozzolans

[EN] Glass fiber reinforced cement (GRC) is an excellent composite for architects and engineers because it can be molded to produce laminar panels or to create complicated designs. GRC is a fine concrete reinforced with alkali-resistant glass fibers at 3¿5% per mass. However, fiber durability is limited because of the aggressiveness of the alkaline medium produced during Portland cement hydration (effect of portlandite). The objective of this study is to assess GRC with high Portland cement replacement with pozzolans (ground fly ash or a mixture of ground fly ash and sonicated silica fume) in order to reduce the corrosion of the fibers. The selected high-content pozzolan (60% replacement) composites were tested under different conditions: aging, drying¿wetting, freezing¿thawing, and chemical attack (ammonium chloride and sulfuric acid). The modulus of rupture and toughness were determined. Composite behavior showed that the samples with pozzolans not only better resisted aging, but also physical and chemical attacks, and specimens presented a better modulus of rupture and toughness than the samples prepared with 100% Portland cement (control specimens). Due to the good behavior in durability terms, the high pozzolan content GRC products are suitable in potential corrosive environments for sunscreens, drainage channels, cable trays, sound barriers, or pavements.This research was funded by Spanish Ministry of Education and Science and FEDER funds (Project BIA 2004-00520)Lalinde, LF.; Mellado Romero, AM.; Borrachero Rosado, MV.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2022). Durability of glass fiber reinforced cement (GRC) containing a high proportion of pozzolans. Applied Sciences. 12(7). https://doi.org/10.3390/app1207369612

Determining corrosion levels in the reinforcement rebars of buildings in coastal areas. A case study in the Mediterranean coastline

This paper describes a study of the damage caused by corrosion to the reinforcement rebars of a 40-year old building used as a car park at a distance of 20 m from the sea. The corrosion levels of the building s structural elements, including beams, joists and columns were analyzed by optical and electron microscopy. Carbonation depths and chloride contents (Volhard method) of the concrete cover were measured in situ. EDX was used to analyze the condition of the reinforcement surfaces and the morpholog and composition of the oxides. A high degree of corrosion was observed in all the above elements, carbonation had reached the depth of the reinforcement in all the samples studied, and the concrete chloride levels were far in excess of the recommended maximums. The study of the reinforcement rebars revealed different types of oxides of varying morphologies, compaction and coloring according to chloride content. A comparison with previous studies allowed us to verify the presence of crystals of at least akaganeite, lepidocrocite and goethite.Moreno, JD.; Bonilla Salvador, MM.; Adam Martínez, JM.; Borrachero Rosado, MV.; Soriano Martinez, L. (2015). Determining corrosion levels in the reinforcement rebars of buildings in coastal areas. A case study in the Mediterranean coastline. Construction and Building Materials. 100:11-21. doi:10.1016/j.conbuildmat.2015.09.059112110

Carbon footprint of geopolymeric mortar: Study of the contribution of the alkaline activating solution and assessment of an alternative route

[EN] CO2 emissions associated with geopolymeric mortar prepared using spent fluid catalytic cracking catalyst (FCC) were compared to those calculated for plain ordinary Portland cement (OPC) mortar. Commercial waterglass used for preparing the alkaline activating solution for geopolymeric mortar was the main contributing component related to CO2 emission. An alternative route for formulating alkaline activating solution in the preparation of the geopolymeric binder was proposed: refluxing of rice husk ash (RHA) in NaOH solution. Geopolymeric mortar using rice hull ash-derived waterglass led to reduced CO2 emission by 63% compared to the OPC mortar. The new alternative route led to a 50% reduction in CO2 emission compared to geopolymer prepared with commercial waterglass. Replacement of commercial waterglass by rice hull ash- derived waterglass in the preparation of the geopolymer did not cause a significant decrease in the mechanical strength of the mortar. CO2 intensity performance indicators (Ci) for geopolymeric mortars were lower than that found for OPC mortar, indicating that the new route for activating solution led to the lowest C-i valueThe authors are grateful to the Spanish Ministry of Economy and Competitiveness (Project GEOCEDEM BIA 2011-26947), and to Generalitat Valenciana (Project 3018/2009) and 'Centro de Cooperacion al Desarrollo' of the Universitat Politecnica de Valencia (ADSIDEO COOPERACIO, Project COMBURES) for supporting this study, and to DACSA S. A. for supplying RHA samples.Mellado Romero, AM.; Catalan, C.; Bouzón, N.; Borrachero Rosado, MV.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2014). Carbon footprint of geopolymeric mortar: Study of the contribution of the alkaline activating solution and assessment of an alternative route. RSC Advances. 4(45):23846-23852. doi:10.1039/C4RA03375BS2384623852445Phair, J. W. (2006). Green chemistry for sustainable cement production and use. Green Chemistry, 8(9), 763. doi:10.1039/b603997aParvulescu, A., Rossi, M., Pina, C. D., Ciriminna, R., & Pagliaro, M. (2011). Investigation of glycerol polymerization in the clinker grinding process. Green Chem., 13(1), 143-148. doi:10.1039/c0gc00107dMymrin, V., de Araújo Ponte, H., Ferreira Lopes, O., & Vazquez Vaamonde, A. (2003). Environment-friendly method of high alkaline bauxite’s Red Mud and Ferrous Slag utilization as an example of green chemistry. Green Chem., 5(3), 357-360. doi:10.1039/b300495nFernández Bertos, M., Li, X., Simons, S. J. R., Hills, C. D., & Carey, P. J. (2004). Investigation of accelerated carbonation for the stabilisation of MSW incinerator ashes and the sequestration of CO2. Green Chem., 6(8), 428-436. doi:10.1039/b401872aJ. L. Provis and J. S. J.van Deventer, Geopolymers. Structure, processing, properties and industrial applications, Woodhead Publishing Limited and CRC Press LLC, UK, 2009F. Pacheco-Torgal and S.Jalali, Eco-efficient Construction and Building Materials, Springer, London, 2011Pacheco-Torgal, F., Castro-Gomes, J., & Jalali, S. (2008). Alkali-activated binders: A review. Construction and Building Materials, 22(7), 1305-1314. doi:10.1016/j.conbuildmat.2007.10.015Pacheco-Torgal, F., Castro-Gomes, J., & Jalali, S. (2008). Alkali-activated binders: A review. Part 2. About materials and binders manufacture. Construction and Building Materials, 22(7), 1315-1322. doi:10.1016/j.conbuildmat.2007.03.019Komnitsas, K., & Zaharaki, D. (2007). Geopolymerisation: A review and prospects for the minerals industry. Minerals Engineering, 20(14), 1261-1277. doi:10.1016/j.mineng.2007.07.011Duxson, P., Fernández-Jiménez, A., Provis, J. L., Lukey, G. C., Palomo, A., & van Deventer, J. S. J. (2006). Geopolymer technology: the current state of the art. Journal of Materials Science, 42(9), 2917-2933. doi:10.1007/s10853-006-0637-zTashima, M. M., Akasaki, J. L., Castaldelli, V. N., Soriano, L., Monzó, J., Payá, J., & Borrachero, M. V. (2012). New geopolymeric binder based on fluid catalytic cracking catalyst residue (FCC). Materials Letters, 80, 50-52. doi:10.1016/j.matlet.2012.04.051Rodríguez, E. D., Bernal, S. A., Provis, J. L., Gehman, J. D., Monzó, J. M., Payá, J., & Borrachero, M. V. (2013). Geopolymers based on spent catalyst residue from a fluid catalytic cracking (FCC) process. Fuel, 109, 493-502. doi:10.1016/j.fuel.2013.02.053Tashima, M. M., Soriano, L., Monzó, J., Borrachero, M. V., & Payá, J. (2013). Novel geopolymeric material cured at room temperature. Advances in Applied Ceramics, 112(4), 179-183. doi:10.1179/1743676112y.0000000056Tashima, M. M., Akasaki, J. L., Melges, J. L. P., Soriano, L., Monzó, J., Payá, J., & Borrachero, M. V. (2013). Alkali activated materials based on fluid catalytic cracking catalyst residue (FCC): Influence of SiO2/Na2O and H2O/FCC ratio on mechanical strength and microstructure. Fuel, 108, 833-839. doi:10.1016/j.fuel.2013.02.052Duxson, P., Provis, J. L., Lukey, G. C., & van Deventer, J. S. J. (2007). The role of inorganic polymer technology in the development of ‘green concrete’. Cement and Concrete Research, 37(12), 1590-1597. doi:10.1016/j.cemconres.2007.08.018Habert, G., d’ Espinose de Lacaillerie, J. B., & Roussel, N. (2011). An environmental evaluation of geopolymer based concrete production: reviewing current research trends. Journal of Cleaner Production, 19(11), 1229-1238. doi:10.1016/j.jclepro.2011.03.012Turner, L. K., & Collins, F. G. (2013). Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete. Construction and Building Materials, 43, 125-130. doi:10.1016/j.conbuildmat.2013.01.023M. Weil , K.Dombroswski and A.Buchwald, in Geopolymers. Structure, processing, properties and industrial applications, ed. J. L. Provis and J. S. J. van Deventer, Woodhead Publishing Limited and CRC Press LLC, UK, 2009, pp. 194–210Salas, A., Delvasto, S., de Gutierrez, R. M., & Lange, D. (2009). Comparison of two processes for treating rice husk ash for use in high performance concrete. Cement and Concrete Research, 39(9), 773-778. doi:10.1016/j.cemconres.2009.05.006Payá, J., Monzó, J., Borrachero, M. ., Mellado, A., & Ordoñez, L. . (2001). Determination of amorphous silica in rice husk ash by a rapid analytical method. Cement and Concrete Research, 31(2), 227-231. doi:10.1016/s0008-8846(00)00466-xJ. Bejarano , C.Garzón, R.Mejía de Gutiérrez, S.Delvasto and M.Gordillo, in II Simposio Aprovechamiento de residuos agro-industriales como fuente sostenible de materiales de construcción, Valencia, Spain, 2010, pp. 409–418Bouzón, N., Payá, J., Borrachero, M. V., Soriano, L., Tashima, M. M., & Monzó, J. (2014). Refluxed rice husk ash/NaOH suspension for preparing alkali activated binders. Materials Letters, 115, 72-74. doi:10.1016/j.matlet.2013.10.001IPCC , Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories, Greenhouse Gas Inventory Reference Manual, Workbook, 1997, vol. 2V. Årskog , S.Fossdal and O. E.Gjørv, in Proceedings of the International Workshop on Sustainable Development and Concrete Technology, Beijing, China, 2004, pp. 193–200Peris Mora, E. (2007). Life cycle, sustainability and the transcendent quality of building materials. Building and Environment, 42(3), 1329-1334. doi:10.1016/j.buildenv.2005.11.004Damineli, B. L., Kemeid, F. M., Aguiar, P. S., & John, V. M. (2010). Measuring the eco-efficiency of cement use. Cement and Concrete Composites, 32(8), 555-562. doi:10.1016/j.cemconcomp.2010.07.009J. Davidovits , in Geopolymer, Green Chemistry and Sustainable Development Solutions World Congress Proc., 2005, pp. 9–15McLellan, B. C., Williams, R. P., Lay, J., van Riessen, A., & Corder, G. D. (2011). Costs and carbon emissions for geopolymer pastes in comparison to ordinary portland cement. Journal of Cleaner Production, 19(9-10), 1080-1090. doi:10.1016/j.jclepro.2011.02.010IDAE Instituto para la Diversificación y Ahorro de la Energía, http://www.idae.es/index.php, Ministerio de Industria, Energía y Turismo, Secretaría de Estado de Energía, Madrid, EspañaPAS 2050 , Specification for the assessment of the life cycle greenhouse gas emissions of goods and services, British Standards Institution, UK, 2011Yang, K.-H., Song, J.-K., & Song, K.-I. (2013). Assessment of CO2 reduction of alkali-activated concrete. Journal of Cleaner Production, 39, 265-272. doi:10.1016/j.jclepro.2012.08.00

Resistance to acid attack of alkali-activated binders: Simple new techniques to measure susceptibility

[EN] Two rapid tests were developed to evaluate the resistance to acid attack by ordinary Portland cement (OPC) and alkali-activated pastes. Acid neutralisation capacity (ANC) at pH 7, 4 and 2 was monitored with powdered pastes. In parallel, a `combined-pH assay¿ with a single sample was used to sequentially assess ANC at different pH values. A mass loss/consumed acid monitoring technique has been also developed in order to assess monolithic samples. The OPC paste showed the most degradation. Among the alkaliactivated pastes, those with the lowest calcium content (fly ash and spent-FCC catalyst) had the best performance.Mellado Romero, AM.; Martha Iris Pérez-Ramos; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2017). Resistance to acid attack of alkali-activated binders: Simple new techniques to measure susceptibility. Construction and Building Materials. 150:355-366. https://doi.org/10.1016/j.conbuildmat.2017.05.224S35536615

Effect of an admixture from Agave americana on the physical and mechanical properties of plaster

[EN] Physical and mechanical properties of a plaster paste added with an organic admixture, of the leaves of Agave americana, were studied. Plastic consistency behavior was evaluated and the water/gypsum(w/g) ratio was determined for each dosage of the admixture. Admixtur eeffect on setting was evaluated too. The chemical transformation of the hemihydrated form to gypsum (dihydrated form) was studied using a novel technique based on a moisture analyzer by halogen light. Flexural and compressive strengths were measured. The results show that ,for the same consistency, accordingly mechanical strengths were improved too. The setting times were increased which would enhance the application time of plaster and would reduce plastic shrinkage, common problems in this type of material. The changes in these physical properties not substantially affect the final mechanical strengths.Se estudiaron algunas propiedades físicas y mecanicas de pastas de yeso de construcción, adicionadas con un aditivo orgánico, producto de las plantas de agave americana. Se evaluó el comportamiento plástico de la pasta mediante ensayos de consistencia y se determinó, para cada dosificación su relación a/y. Se evluó la incidencia dell aditivo en los tiempos de fraguado. La transformacion de hemihidrato a dihidrato se realizó mediante una novedosa tecnica basada en un analizador de humedad por luz halógena. Se midieron las resistencias mecánicas a flexo-tracción y compresión. Los resultados muestras que, para una misma consistencia se mejoran las resistencias mecánicas. Los tiempos de fraguado de las pastas se aumentaron, lo que ayudaría a mejorar los tiempos de aplicación del yeso y a disminuir las retracciones plásticas. Las modificaciones de estas propiedadesfísicas no afectan considerablemente a las resistencias mecánicas finalesJ.C. Ochoa would like to thank Fundacion Carolina (the Carolina Foundation) for the scholarship granted to conduct this study, Universidad Nacional de Colombia(National University of Colombia) for the time granted, and the Instituto de Ciencia y Tecnologia del Hormigon-ICITECH (Institute of Science and Technology of Concrete) at Universitat Politecnica de Valencia for the human and material resources.Ochoa, J.; Bonilla Salvador, MM.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2013). Efecto de un aditivo extraído de la planta Agave americana sobre las propiedades físicas y mecánicas de un yeso. Materiales de Construcción. 63:79-92. doi:10.3989/mc.2013.05111S799263(1) Hornbostel, C.: "Tipos, usos y aplicaciones", Materiales para la Construcción, Limusa S.A y C.V, 2002.Camarini, G., & De Milito, J. A. (2011). Gypsum hemihydrate–cement blends to improve renderings durability. Construction and Building Materials, 25(11), 4121-4125. doi:10.1016/j.conbuildmat.2011.04.048Arikan, M., & Sobolev, K. (2002). The optimization of a gypsum-based composite material. Cement and Concrete Research, 32(11), 1725-1728. doi:10.1016/s0008-8846(02)00858-xÇolak, A. (2006). Physical and mechanical properties of polymer-plaster composites. Materials Letters, 60(16), 1977-1982. doi:10.1016/j.matlet.2005.12.062Rubio-Avalos, J. C., Manzano-Ramírez, A., Luna-Bárcenas, J. G., Pérez-Robles, J. F., Alonso-Guzmán, E. M., Contreras-García, M. E., & González-Hernández, J. (2005). Flexural behavior and microstructure analysis of a gypsum-SBR composite material. Materials Letters, 59(2-3), 230-233. doi:10.1016/j.matlet.2004.07.054Çolak, A. (2001). Characteristics of acrylic latex-modified and partially epoxy-impregnated gypsum. 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Degradation Process of Postconsumer Waste Bottle Fibers Used in Portland Cement-Based Composites

[EN] The degradation of synthetic fibers derived from postconsumer wastes and used in fiber-reinforced cement mortars was studied. Polyethylene terephthalate (PET) and high-density polyethylene postconsumer bottles were immersed in an alkaline medium of a 1-M solution of sodium hydroxide and portland cement paste. Then, the fibers¿ surfaces were analyzed by scanning electron microscopy (SEM). This study showed that the fibers have a progressive surface deterioration over time when immersed in either of the two media. Degradation of fibers immersed in pozzolan-portland cement pastes was also observed. The results from the degradation process of these fibers show that it was stronger when they were immersed in the portland cement system (pH ¿ 12.9), although the pH value was lower than that of the NaOH solution (pH ¿ 13.8), suggesting that the degradation process in portland cement also depends on the formation of solid hydration products. The preliminary results of this study show overall good behavior of the studied fibers. This behavior generally improves when using pozzolans. Considering that fibers and pozzolans are obtained from wastes, and therefore have low economic and environmental costs, the possibility of using these materials in developing countries should be considered. The use of these wastes would, on the one hand, improve the properties of construction materials, and on the other, enable proper management of waste that could otherwise eventually pollute the environment.Fernández Iglesias, ME.; Paya Bernabeu, JJ.; Borrachero Rosado, MV.; Soriano Martinez, L.; Mellado Romero, AM.; Monzó Balbuena, JM. (2017). Degradation Process of Postconsumer Waste Bottle Fibers Used in Portland Cement-Based Composites. Journal of Materials in Civil Engineering. 29(10):04017183-1-04017183-9. doi:10.1061/(ASCE)MT.1943-5533.0002007S04017183-104017183-9291