Propiedades y durabilidad de los cementos adicionados con metacaolín

This 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% MgSO4 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.El 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 MgSO4 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

Propiedades y durabilidad del cemento con adición de metacaolín: mortero y hormigón

This article explores the effect of metakaolin, a pozzolan, on concrete performance. Compressive and splitting tensile strength were found for specimens cured for up to 360 and 90 days, respectively. Changes were recorded in the compressive strength of specimens exposed to salt (chloride and sulfatechloride solutions), and chloride penetration and binding capacity were measured. The findings were compared to the results for concrete prepared with ordinary Portland (OPC) and moderate heat of hydration (Type II) cement. MK was found to have a very positive effect on 28-day concrete strength, due to microstructure improvement of the hydrated cement. Replacing cement with metakaolin effectively raised concrete resistance to chloride attack. Concrete containing metakaolin proved to be substantially more durable in sulfate-chloride environment.En este trabajo se estudia el efecto del metacaolín sobre las prestaciones del hormigón. Las probetas curadas a 360 y 90 días se sometieron a ensayos de resistencia a compresión y de tracción indirecta respectivamente. Se hizo un seguimiento de la resistencia a la compresión de los materiales ante el ataque de sales (soluciones de cloruro y de sulfato-cloruro) y, se midió la penetración de cloruros y la capacidad de los hormigones de inmovilizar estos iones. Los resultados se compararon con los obtenidos con hormigones elaborados con cemento pórtland ordinario (OPC) y, con cemento de calor de hidratación moderado (tipo II). El MK resultó influir muy positivamente en la resistencia del hormigón a 28 días debido a la mejora de la microestructura del cemento hidratado. La sustitución de cemento por metacaolín aumentó la resistencia del hormigón al ataque de cloruros. El hormigón con metacaolín demostró ser más duradero en entornos de sulfato-cloruro que los hormigones elaborados con OPC o con cemento de tipo II. Los perfiles de concentración de cloruros a distintas profundidades y la diferencia entre los contenidos de cloruro libre y total, mostraron claramente que el cemento con metacaolín reducía la penetración de cloruros en el hormigón y, aumentaba su capacidad para combinar con iones cloruro. La conclusión general fue que podía fabricarse material puzolánico utilizable, mediante la activación térmica del caolín local

Incorporation of cement bypass flue dust in fly ash and blast furnace slag-based geopolymer

This work utilizes cement kiln dust in fly ash and blast furnace slag-based geopolymer. Geopolymer cement was produced using different compositions of ground, granulated blast furnace slag with fly ash and cement bypass flue dust. Crystalline sodium metasilicate pentahydrate was used as an activator at 10, 15 and 20% (by weight) of the geopolymer source materials. The geopolymer is formed in the solid state like ordinary Portland cement. The mechanical and chemical properties of the geopolymeric materials were examined. Measuring of mechanical properties by compressive strength of the hardened geopolymer pastes at different curing ages; microstructure was evaluated by X-ray diffraction (XRD) and scanning electron microscope (SEM); thermal properties were estimated by thermogravimetry analysis (TGA) and derivative thermogravimetric analysis (DTG). The results indicate that the compressive strength of the geopolymer pastes is increased with higher Na2SiO3.5H2O content. The geopolymeric properties were enhanced by higher pH, which helps in the dissolution of geopolymer source materials during geopolymerization. SEM showed that mixes containing 15 and 20% sodium metasilicate had more compact and dense structures. On the other hand, GGBFS mix (G-20) exhibits more hydration and geopolymeric products during TGA/DTG compared with other mixes which contain FA with/without GGBFS. Keywords: Cement bypass flue dust, Geopolymer, Ground granulated blast furnace, Fly as

دراسة عملية التأدرت لأسمنت خبث الأفران العالية والأسمنت الحديدي باستخدام ظاهرة موسباور

Mossbauer spectra have been measured for the hydrated blast-furnace slag cement and Portland cement pastes at different times of hydration of 1. 3. 7. 28 and 90 days. The spectra showed the existence of iron atoms, Fe3 (T) and Fe3 (0) states of iron. It was found that, as the time of hydration was increased, the Fe3 (0) content decreased, while the Fe3 (T) content increased. The Fe' (T) /SFe34" percentage was calculated for the two types of cement as a function of the time of hydration. A correlation has been found between this ratio and the compressive strength of the hardened cement paste.تم في هذا البحث دراسة أطياف موسباور لكل من عجائن أسمنت خبث الأفران العالية والإسمنت البورتلاندي بعد التأدرت لفترات زمنية مختلفة (يوم ، ثلاثة أيام ، سبعة أيام ، ثمانية وعشرون يوما ، تسعون يوما) ولقد أظهرت نتائج تحليل بارامترات موسباور لأطياف هذه العجائن أن هناك نقص في محتوى أيونات الحديديك في المواقع ثمانية التأذر وزيادة أيونات الحديديك في المواقع رباعية التأذر وذلك بزيادة زمن التأدرت . وقد تم حساب النسبة المئوية لمحتوى أيونات الحديديك رباعية الترابط إلى المحتوى الكلي لأيونات الحديديك عند أزمنة التأدرت المختلفة لكل من نوعي الإسمنت تحت الدراسة ، وأمكن إيجاد علاقة بين قوة تحمل الضغط الميكانيكي للعجينة المتصلدة وقيم درجة التأدرت المحسوبة من هذه النسبة المئوية (ح+3/ مجموع ح +3)

Physico-mechanical properties of high performance concrete using different aggregates in presence of silica fume

Heavy weight high performance concrete (HPC) can be used when particular properties, such as high strength and good radiation shielding are required. Such concrete, using ilmenite and hematite coarse aggregates can significantly have higher specific gravities than those of concrete made with dolomite and air-cooled slag aggregates. Four different concrete mixes with the same cement content and different w/c ratios were designed using normal dolomite aggregate, air-cooled slag by-product and two different types of iron ore aggregates. High performance concrete (grade-M60) can be achieved using superplasticizer to reduce the water/cement ratio; the effect of SF on the performance of concrete was studied by addition of 10% silica fume to the total cement content. The physico-mechanical properties of coarse aggregates and hardened concrete were studied. The results show that, Ilmenite coarse aggregate gives higher physical and mechanical properties than the other aggregates. Also, addition of 10% silica fume developed a stronger and a denser interfacial transition zone (ITZ) between concrete particles and the cement matrix. Crushed air-cooled slag can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with crushed hematite and ilmenite. Heavy density concrete made with fine aggregates of ilmenite and air-cooled slag are expected to be suitable as shielding materials to attenuate gamma rays