Influence of MK on the reaction kinetics in MK/lime and MK-blended cement systems at 20°C

Frı́as, Moisés; Cabrera, J G

doi:10.1016/s0008-8846(00)00465-8

Cited by 155 publications

(74 citation statements)

References 11 publications

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“…The analytic results, expressed as percentages of fixed lime, indicate the high pozzolanic activity of the coal refuse activated at 600 • C. This value is similar than the obtained with an available commercial MK in UK. The commercial MK is mayor oxides of SiO 2 (51.60%) and Al 2 O 3 (41.30%), and a surface area of 15.0 m 2 /g [39] at all ages (except at 28 days).The mineralogical composition of commercial K was principally kaolinite and mica. Calcination at 600 • C/2 h produced total dehydroxylation of the K transforming it into MK, a highly pozzolanic product.…”

Section: Thermally Activated Materialsmentioning

confidence: 99%

Coal-Mining Tailings as a Pozzolanic Material in Cements Industry

et al. 2018

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Abstract:The generation of enormous volumes of mine-tailing waste is standard practice in the mining industry. Large quantities of these tailings are also sources of kaolinite-rich materials that accumulate in slag heaps, causing significant environmental degradation and visual impacts on the landscape. The consequences of coal refuse dumped in slagheaps calls for the study of eco-innovative solutions and the assessment of waste types. Moreover, the environmental benefits of reusing large amounts of contaminated waste are also evident. Hence, the objective of this investigation is to expand current knowledge of new siliceous-aluminium minerals and their pozzolanic activity. Four raw tailing samples are characterized to determine their chemical (by ICP/MS analysis), morphological (by SEM/EDX analysis), and mineralogical (by XRD analysis) compositions prior to their thermal activation that transforms the inert wastes at various temperatures into materials with cementitious properties. The results of XRD analysis following activation confirmed that the kaolinite content is fully transformed into metakaolinite. The coal refuse samples presented sufficiently reliable levels of pozzolanic activity for use as additives in industrial cements.

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Section: Thermally Activated Materialsmentioning

confidence: 99%

Coal-Mining Tailings as a Pozzolanic Material in Cements Industry

et al. 2018

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“…However, the decrease in the intensity of this endothermic peak with increasing the hydration age could be attributed to the reaction of CO 2 with CaCO 3 to form Ca(HCO 3 ) 2 . It may be attributed also to the increase in the degree of crystallinity of hydration products, which was considered as an indication for the degree of carbonation of the hardened pastes, [43].…”

Section: The Thermal Analyses Measuresmentioning

confidence: 99%

Metakaolin as an Active Pozzolan for Cement That Improves Its Properties and Reduces Its Pollution Hazard

Ibrahim¹,

Hagrass²,

Boulos³

et al. 2018

JMMCE

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Prepared metakaolin produced by calcination of a kaolin sample at 750˚C after soaking for 5 hrs was tested as an active pozzolan for locally produced cement. Blended pastes of partially replaced ordinary Portland cement with different metakaolin amounts 5%, 10% and 15% were prepared, then they were hydrated with water for various time intervals of 1, 3, 7, 14 and 28 days. At each time interval, the hydrated paste specimens were tested for compressive strength, hydration kinetics and followed up using differential scanning calorimetry, X-ray diffractometry analyses and scanning electron microscopy techniques. Results showed that the blended pastes OPC-MK10 recorded the highest compressive strength values at all the hydration times reaching 33. 10, 86.40, 101.20, 112, and 122 MPa with increasing the age of hydration as compared with the neat samples which recorded 31.70, 65.20, 72.6, 82 and 101.30 MPa respectively. Meanwhile, the OPC-MK10 blend showed a decrease in the free CaO content reaching 4.07%, 4.27%, 4.23%, 4.19%, and 4.11% CaO with increasing age of hydration compared with the neat samples which recorded 4.27%, 5.15%, 5.42%, 5.61%, and 5.96% CaO respectively. The DSC thermograms results for the hardened neat and OPC-Mk10 pastes at the 14 and 28 hydration days showed the formation of hydrated materials mainly calcium silicate hydrates, calcium sulphoaluminate hydrates and calcium aluminates hydrates. The X-ray diffractometry analyses of both hardened neat and OPC-MK10 showed that, the intensity of calcium hydroxide peaks of OPC-MK10 was lower than in case of neat OPC, while the peak of the hydration products of calcium silicate hydrates and calcium aluminates silicate hydrates of OPC-MK10 samples were of higher intensity than in case of neat OPC. Scanning electron microscopy micrographs indicated the formation of denser microstructure for the hardened OPC-MK10 paste as compared to neat OPC pastes after the 28 days age of hydration.

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“…Strätlingite (C 2 ASH 8 ) and C-S-H gel have been reported to be the most voluminous phases formed (11). Other authors (12)(13) have observed the formation of C 4 AH 13 in addition to C 2 ASH 8 and C-S-H gel at 20 ºC. At higher curing temperatures, hydrogarnet (C 3 AH 6 ), a cubic hydrated phase, has been detected along with the hexagonal phases C 2 ASH 8 and C 4 AH 13 (13)(14)(15).…”

Section: Materialesmentioning

confidence: 94%

“…Se ha afirmado que las fases hidratadas más importantes son la estratlingita (C 2 ASH 8 ) y el gel C-S-H (11). Según otros autores (12)(13), tanto el C 4 AH 13 como el C 2 ASH 8 y el gel C-S-H se forman a 20°C. A una temperatura de curado superior (condiciones hidrotérmi-cas), se ha detectado la formación de una fase cúbica hidratada, el hidrogranate (C 3 AH 6 ), además de las fases hexagonales hidratadas C 2 ASH 8 y C 4 AH 13 (13)(14)(15).…”

Section: Introductionunclassified

“…Según otros autores (12)(13), tanto el C 4 AH 13 como el C 2 ASH 8 y el gel C-S-H se forman a 20°C. A una temperatura de curado superior (condiciones hidrotérmi-cas), se ha detectado la formación de una fase cúbica hidratada, el hidrogranate (C 3 AH 6 ), además de las fases hexagonales hidratadas C 2 ASH 8 y C 4 AH 13 (13)(14)(15). También se ha identificado hidrogranate a temperatura ambiente en mezclas con un contenido menor de cal (16).…”

Section: Introductionunclassified

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Propiedades y durabilidad de los cementos adicionados con metacaolín

Abo-El-Enein¹,

Abbas²,

Ezzat³

2010

Mater. construcc.

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RESUMENEl presente trabajo evalúa el comportamiento puzolánico de metacaolín (MK), producto de la calcinación a distintas temperaturas de dos tipos de caolín local de composiciones químicas diferentes, al incorporarse al cemento en diferentes proporciones. Se preparó un cemento adicionado mediante la mezcla en seco de cemento Portland ordinario (OPC) y metacaolín (MK), a los que se añadió la cantidad óptima de agua para obtener una pasta de la consistencia deseada. Las probetas se curaron a una HR del 100% durante 24 horas, sumergiéndose posteriormente en agua durante 3, 7, 28, 90 o 180 días. A cada tiempo de ensayo se controló el grado de hidratación de las pastas endurecidas y se comprobó la resistencia a la compresión de las probetas cúbicas a las edades de curado establecidas. Los resultados obtenidos indican que la temperatura más adecuada para la calcinación del caolín es de 700°C y que el porcentaje óptimo de éste en la mezcla se encuentra entre el 25 y el 30%. Las fases que componen los productos resultantes de la hidratación se identificaron mediante ATD a distintas edades de curado. Se estableció la durabilidad del OPC puro y de las mezclas de OPC-MK en disoluciones de NaCl al 3% y MgSO 4 al 5% tras 30, 90 y 180 días de inmersión. Se concluyó que las pastas de OPC-MK muestran una elevada resistencia al ataque del ion cloruro.Palabras clave: cemento con adiciones, metacaolín, resistencia, durabilidad, microestructura. SUMMARYThis paper evaluates the optimal calcination temperature and replacement ratio to ensure high metakaolin (MK) pozzolanicity in blended cement. The MK used was prepared by firing two types of local at temperatures ranging from 700 to 850 ºC. Dry blends of ordinary Portland cement (OPC) and varying proportions of MK were mixed with the amount of water required to ensure optimal consistency of the resulting pastes. The specimens were cured at 100% RH for 24 h and then immersed in water for 3, 7, 28, 90 or 180 days. At each test time, the degree of hydration and compressive strength of the hardened cement pastes were measured The findings showed that the most suitable calcination temperature to obtain metakaolin is 700 ºC, while the optimal replacement ratio ranges from 25 to 30%. DTA was used to determine the phases comprising the hydration products forming at the ages studied. Pure OPC and OPC-MK specimens were immersed in 3% NaCl and 5% MgSO 4 solutions for 30, 90 and 180 days to measure their durability. The OPC-MK pastes immersed in the 3% NaCl solution were observed to be highly resistant to chloride attack. Persona de contacto/Corresponding author: rafikaa65@yahoo.com INTRODUCCIÓNExisten varios tipos de cemento Portland con caracterís-ticas distintas, que se clasifican principalmente en función de la evolución del calor (es decir, la temperatura que alcanzan y la velocidad a la que lo hacen) durante la hidratación, así como de la resistencia de la pasta ante los ataques químicos. Las características de cada mezcla de cemento dependen de las propiedades de sus principales fases, d...

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Influence of MK on the reaction kinetics in MK/lime and MK-blended cement systems at 20°C

Cited by 155 publications

References 11 publications

Coal-Mining Tailings as a Pozzolanic Material in Cements Industry

Coal-Mining Tailings as a Pozzolanic Material in Cements Industry

Metakaolin as an Active Pozzolan for Cement That Improves Its Properties and Reduces Its Pollution Hazard

Propiedades y durabilidad de los cementos adicionados con metacaolín

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