Optimization of Cement Grouts Containing Silica Fume and Viscosity Modifying Admixture

There is an increasing need to identify the effect of mix composition on the rheological properties of cementitious grouts using minislump, Marsh cone, cohesion plate, washout test, and cubes to determine the fluidity, the cohesion, and other mechanical properties of grouting applications. Mixture proportioning involves the tailoring of several parameters to achieve adequate fluidity, cohesion, washout resistance and compressive strength. This paper proposes a statistical design approach using a composite fractional factorial design which was carried out to model the influence of key parameters on the performance of cement grouts. The responses relate to performance included minislump, flow time using Marsh cone, cohesion measured by Lombardi plate meter, washout mass loss and compressive strength at 3, 7, and 28 days. The statistical models are valid for mixtures with water-to-binder ratio of 0.37–0.53, 0.4–1.8% addition of high-range water reducer (HRWR) by mass of binder, 4–12% additive of silica fume as replacement of cement by mass, and 0.02–0.8% addition of viscosity modifying admixture (VMA) by mass of binder. The models enable the identification of underlying factors and interactions that influence the modeled responses of cement grout. The comparison between the predicted and measured responses indicated good accuracy of the established models to describe the effect of the independent variables on the fluidity, cohesion, washout resistance and the compressive strength. This paper demonstrates the usefulness of the models to better understand trade-offs between parameters. The multiparametric optimization is used to establish isoresponses for a desirability function for cement grout. An increase of HRWR led to an increase of fluidity and washout, a reduction in plate cohesion value, and a reduction in the Marsh cone time. An increase of VMA demonstrated a reduction of fluidity and the washout mass loss, and an increase of Marsh cone time and plate cohesion. Results indicate that the use of silica fume increased the cohesion plate and Marsh cone, and reduced the minislump. Additionally, the silica fume improved the compressive strength and the washout resistance.

Optimisation of rheological parameters and mechanical properties of superplasticised cement grouts containing metakaolin and viscosity modifying admixture

The objective of this research was to optimise the rheological parameters, hardened properties, and setting times of cement grouts containing metakaolin (MTK), viscosity-modifying agent (VMA) and superplasticiser (SP). All mixes were made with water-to-binder ratio (W/B) of 0.40. The replacement of cement by MTK was varied from 6% to 20% (by mass), and dosages of SP and VMA were varied from 0.3% to 1.4%, and 0.01% and 0.06% (by mass of binder), respectively. Increased SP led to an increase in fluidity, reduction in flow time, plate cohesion, rheological parameters, and an increase in the setting times. Increased VMA demonstrated a reduction in fluidity, an increase in Marsh cone time, plate cohesion, yield stress, and plastic viscosity. Results indicate that the use of MTK increased yield stress, plastic viscosity, cohesion plate, and flow time due to the higher surface area associated with an increase in the water demand. MTK reduced mini-slump and setting times, and improved compressive strength.

Neural Network Modeling of Rheological Parameters of Grouts Containing Viscosity-Modifying Agent

The development of artificial neural network (ANN) models to predict the rheological behavior of grouts is described is this paper and the sensitivity of such parameters to the variation in mixture ingredients is also evaluated. The input parameters of the neural network were the mixture ingredients influencing the rheological behavior of grouts, namely the cement content, fly ash, ground-granulated blast-furnace slag, limestone powder, silica fume, water-binder ratio (w/b), high-range water-reducing admixture, and viscosity-modifying agent (welan gum). The six outputs of the ANN models were the mini-slump, the apparent viscosity at low shear, and the yield stress and plastic viscosity values of the Bingham and modified Bingham models, respectively. The model is based on a multi-layer feed-forward neural network. The details of the proposed ANN with its architecture, training, and validation are presented in this paper. A database of 186 mixtures from eight different studies was developed to train and test the ANN model. The effectiveness of the trained ANN model is evaluated by comparing its responses with the experimental data that were used in the training process. The results show that the ANN model can accurately predict the mini-slump, the apparent viscosity at low shear, the yield stress, and the plastic viscosity values of the Bingham and modified Bingham models of the pseudo-plastic grouts used in the training process. The results can also predict these properties of new mixtures within the practical range of the input variables used in the training with an absolute error of 2%, 0.5%, 8%, 4%, 2%, and 1.6%, respectively. The sensitivity of the ANN model showed that the trend data obtained by the models were in good agreement with the actual experimental results, demonstrating the effect of mixture ingredients on fluidity and the rheological parameters with both the Bingham and modified Bingham models.

Modelling the performance of self-compacting SIFCON of cement slurries containing limestone powder using genetic programming technique

The paper explores the potential of applicability of Genetic programming approach (GP), adopted in this investigation, to model the combined effects of five independent variables to predict the mini-slump, the plate cohesion meter, the induced bleeding test, the J-fiber penetration value, and the compressive strength at 7 and 28 days of self-compacting slurry infiltrated fiber concrete (SIFCON). The variables investigated were the proportions of limestone powder (LSP) and sand, the dosage rates of superplasticiser (SP) and viscosity modifying agent (VMA), and water-to-binder ratio (W/B). Twenty eight mixtures were made with 10-50% LSP as replacement of cement, 0.02-0.06% VMA by mass of cement, 0.6-1.2% SP and 50-150% sand (% mass of binder) and 0.42-0.48 W/B. The proposed genetic models of the self-compacting SIFCON offer useful modelling approach regarding the mix optimisation in predicting the fluidity, the cohesion, the bleeding, the penetration, and the compressive strength.

Effect of Mix Proportions on Rheological and Hardened Properties of Composite Cement Pastes

There is an increasing need to identify the effect of mix composition on the rheological properties of composite cement pastes using simple tests to determine the fluidity, the cohesion and other mechanical properties of grouting applications such as compressive strength. This paper reviews statistical models developed using a fractional factorial design which was carried out to model the influence of key parameters on properties affecting the performance of composite cement paste. Such responses of fluidity included mini-slump, flow time using Marsh cone and cohesion measured by Lombardi plate meter and unit weight, and compressive strength at 3 d, 7 d and 28 d. The models are valid for mixes with 0.35 to 0.42 water-to-binder ratio (W/B), 10% to 40% of pulverised fuel ash (PFA) as replacement of cement by mass, 0.02 to 0.06% of viscosity enhancer admixture (VEA), by mass of binder, and 0.3 to 1.2% of superplasticizer (SP), by mass of binder. The derived models that enable the identification of underlying primary factors and their interactions that influence the modelled responses of composite cement paste are presented. Such parameters can be useful to reduce the test protocol needed for proportioning of composite cement paste. This paper attempts also to demonstrate the usefulness of the models to better understand trade-offs between parameters and compare the responses obtained from the various test methods which are highlighted. The multi parametric optimization is used in order to establish isoresponses for a desirability function of cement composite paste. Results indicate that the replacement of cement by PFA is compromising the early compressive strength and up 26%, the desirability function decreased.

Influencia de la adición de nanosílice y microsílice en el comportamiento mecánico, microestructural y durable de un hormigón autocompactante

Desde mediados de la década de los 80 se está investigando sobre el hormigón autocompactante. Cada día, su uso en el mundo de la construcción es más común debido a sus numerosas ventajas como su excelente fluidez ya que puede fluir bajo su propio peso y llenar encofrados con formas complicadas y muy armados sin necesidad de compactaciones internas o externas. Por otra parte, la búsqueda de materiales más resistentes y duraderos, ha dado lugar a la incorporación de adiciones en materiales a base de cemento. En las últimas dos décadas, los ensayos con los nanomateriales, ha experimentado un gran aumento. Los resultados hasta ahora obtenidos pueden asumir no sólo un aumento en la resistencia de estos materiales, pero un cambio es su funcionalidad. Estas nanopartículas, concretamente la nanosílice, no sólo mejoran sus propiedades mecánicas y especialmente sus propiedades durables, sino que pueden implicar un cambio sustancial en las condiciones de uso y en su ciclo de vida. Este trabajo tiene como principal objetivo el estudio de las propiedades mecánicas, características microestructurales y durables de un hormigón autocompactante cuando se le agrega como adición nanosílice, microsílice y mezcla binarias de ambas, como adición al cemento. Para ello se han realizado 10 mezclas de hormigón. Se utilizó como referencia un hormigón autocompactante obtenido con cemento, caliza, árido, aditivo modificador de viscosidad Se han fabricado tres hormigones con la misma dosificación pero con diferentes contenidos de nanosílice. 2,5%, 5% y 7,5% Tres dosificaciones con adición de microsílice 2,5%, 5% y 7,5% y las tres restantes con mezclas binarias de nanosílice y microsílice con respectivamente2,5%-2,5%, 5%-2,5% y 2,5%-5%, sobre el peso del cemento. El contenido de superplastificante se modificó para conseguir las características de autocompactabilidad. Para observar los efectos de las adiciones añadidas al hormigón, se realiza una extensa campaña experimental. En ella se evaluaron en primer lugar, las características de autocompactabilidad del material en estado fresco, mediante los ensayos prescritos en la Instrucción Española del hormigón estructural EHE 08. Las propiedades mecánicas fueron evaluadas con ensayos de resistencia a compresión, resistencia a tracción indirecta y módulo de elasticidad. Las características microestructurales fueron analizadas mediante porosimetría por intrusión de mercurio, el análisis termogravimétrico y la microscopía electrónica de barrido. Para el estudio de la capacidad durable de las mezclas se realizaron ensayos de resistividad eléctrica, migración de cloruros, difusión de cloruros, carbonatación acelerada, absorción capilar y resistencia al hielo-deshielo. Los resultados ponen de manifiesto que la acción de las adiciones genera mejoras en las propiedades resistentes del material. Así, la adición de nanosílice proporciona mayores resistencias a compresión que la microsílice, sin embargo las mezclas binarias con bajas proporciones de adición producen mayores resistencias. Por otra parte, se observó mediante la determinación de las relaciones de gel/portlandita, que las mezclas que contienen nanosílice tienen una mayor actividad puzolánica que las que contienen microsílice. En las mezclas binarias se obtuvo como resultado que mientras mayor es el contenido de nanosílice en la mezcla mayor es la actividad puzolánica. Unido a lo anteriormente expuesto, el estudio de la porosidad da como resultado que la adición de nanosílice genera un refinamiento del tamaño de los poros mientras que la adición de microsílice disminuye la cantidad de los mismos sin variar el tamaño de poro medio. Por su parte, en las micrografías, se visualizó la formación de cristales procedentes de la hidratación del cemento. En ellas, se pudo observar, que al adicionar nanosílice, la velocidad de hidratación aumenta al aumentar la formación de monosulfoaluminatos con escasa presencia de etringita. Mientras que en las mezclas con adición de microsílice se observan mayor cantidad de cristales de etringita, lo que confirma que la velocidad de hidratación en estos últimos fue menor. Mediante el estudio de los resultados de las pruebas de durabilidad, se observó que no hay diferencias significativas entre el coeficiente de migración de cloruros y el coeficiente de difusión de cloruros en hormigones con adición de nano o microsílice. Aunque este coeficiente es ligeramente menor en mezclas con adición de microsílice. Sin embargo, en las mezclas binarias de ambas adiciones se obtuvo valores de los coeficientes de difusión o migración de cloruros inferiores a los obtenidos en mezclas con una única adición. Esto se evidencia en los resultados de las pruebas de resistividad eléctrica, de difusión de cloruros y de migración de cloruros. Esto puede ser debido a la suma de los efectos que producen el nano y micro adiciones en la porosidad. El resultado mostró que nanosílice tiene un papel importante en la reducción de los poros y la microsílice disminuye el volumen total de ellos. Esto permite definir la vida útil de estos hormigones a valores muy superiores a los exigidos por la EHE-08, por lo que es posible reducir, de forma notable, el recubrimiento exigido en ambiente de alta agresividad asegurando un buen comportamiento en servicio. Por otra parte, la pérdida de masa debido a los ciclos de congelación-descongelación es significativamente menor en los hormigones que contienen nanosílice que los que contienen microsílice. Este resultado está de acuerdo con el ensayo de absorción capilar. De manera general, se puede concluir que son las mezclas binarias y más concretamente la mezcla con un 5% de nanosílice y 2,5% de microsílice la que presenta los mejores resultados tanto en su comportamiento resistente con en su comportamiento durable. Esto puede ser debido a que en estas mezclas la nanosílice se comporta como un núcleo de activación de las reacciones puzolánicas rodeado de partículas de mayor tamaño. Además, el extraordinario comportamiento durable puede deberse también a la continuidad en la curva granulométrica por la existencia de la microsílice, el filler calizo, el cemento, la arena y la gravilla con tamaños de partículas que garantice mezclas muy compactas que presentan elevadas prestaciones. Since the middle of the decade of the 80 is being investigated about self-consolidating concrete. Every day, its use in the world of construction is more common due to their numerous advantages as its excellent fluidity such that it can flow under its own weight and fill formworks with complicated shapes and congested reinforcement without need for internal or external compactions. Moreover, the search for more resistant and durable materials, has led to the incorporation of additions to cement-based materials. In the last two decades, trials with nanomaterials, has experienced a large increase. The results so far obtained can assume not only an increase in the resistance of these materials but a change is its functionality. These nano particles, particularly the nano silica, not only improve their mechanical properties and especially its durable properties, but that may imply a substantial change in the conditions of use and in their life cycle. This work has as its main objective the study of the mechanical properties, the microstructural characteristics and durability capacity in one self-compacting concrete, when added as addition to cement: nano silica, micro silica o binary mixtures of both. To this effect, 10 concrete mixes have been made. As reference one with a certain amount of cement, limestone filler, viscosity modifying additive and water/binder relation. Furthermore they were manufactured with the same dosage three mix with addition of 2.5%, 5% and 7.5% of nano silica by weight of cement. Other three with 2.5%, 5% and 7.5% of micro silica and the remaining three with binary mixtures of 2.5%-2.5%, 5%-2.5% and 2.5%-5% of silica nano-micro silica respectively, b weight of cement, varying only the amount of superplasticizer to obtain concrete with characteristics of self-compactability. To observe the effects of the additions added to the concrete, an extensive experimental campaign was performed. It assessed, first, the characteristics of self-compactability of fresh material through the tests prescribed in the Spanish Structural Instruction Concrete EHE 08. The mechanical properties were evaluated by compression strength tests, indirect tensile strength and modulus of elasticity. The microstructural properties were analyzed by mercury intrusion porosimetry, thermogravimetric analysis and scanning electron microscopy. To study the durability, were performed electrical resistivity tests, migration and diffusion of chlorides, accelerated carbonation, capillary suction and resistance to freeze-thaw cycles. The results show that the action of the additions generates improvements in the strength properties of the material. Specifically, the addition of nano silica provides greater resistance to compression that the mix with micro silica, however binary mixtures with low addition rates generate higher strengths. Moreover, it was observed by determining relationships gel/portlandite, that the pozzolanic activity in the mixtures with nano silica was higher than in the mixtures with micro silica. In binary mixtures it was found that the highest content of nano silica in the mix is the one with the highest pozzolanic activity. Together with the foregoing, the study of the porosity results in the mixture with addition of nano silica generates a refinement of pore size while adding micro silica decreases the amount thereof without changing the average pore size. On the other hand, in the micrographs, the formation of crystals of cement hydration was visualized. In them, it was observed that by adding nano silica, the speed of hydration increases with increasing formation monosulfoaluminatos with scarce presence of ettringite. While in mixtures with addition of micro silica, ettringite crystals are observed, confirming that the hydration speed was lower in these mixtures. By studying the results of durability testing, it observed that no significant differences between the coefficient of migration of chlorides and coefficient of diffusion of chlorides in concretes with addition of nano or micro silica. Although this coefficient is slightly lower in mixtures with addition of micro silica. However, in binary mixtures of both additions was obtained values of coefficients of difusion o migration of chlorides lower than those obtained in mixtures with one of the additions. This is evidenced by the results of the tests electrical resistivity, diffusion of chlorides and migration of chlorides. This may be due to the sum of the effects that produced the nano and micro additions in the porosity. The result showed that nano silica has an important role in the pores refining and the micro silica decreases the total volume of them. This allows defining the life of these concretes in values to far exceed those required by the EHE-08, making it possible to reduce, significantly, the coating required in highly aggressive environment and to guarantee good behavior in service. Moreover, the mass loss due to freeze-thaw cycles is significantly lower in concretes containing nano silica than those containing micro silica. This result agrees with the capillary absorption test. In general, one can conclude that the binary mixture and more specifically the mixture with 5% of nano silica and 2.5% silica fume is which presents the best results in its durable behavior. This may be because in these mixtures, the nano silica behaves as cores activation of pozzolanic reactions. In addition, the durable extraordinary behavior may also be due to the continuity of the grading curve due to existence of micro silica, limestone filler, cement, sand and gravel with particle sizes that guarantees very compact mixtures which have high performance.

The role of formulation excipients in the development of lyophilised fast-disintegrating tablets

Despite recent Success, many fast-disintegrating tablets (FDTs) still face problems of low mechanical strength, poor mouth-feel and higher disintegration times. This Study aimed to optimise FDTS using a progressive three-stage approach. A series of hardness, fracturability and disintegration time tests were performed on the formulations at each stage. During Stage 1, tablets were prepared in concentrations between 2% and 5% w/w, and were formulated at each concentration as single and combination bloom strength gelatin (BSG) using 75 and 225 BSGs. Analysis revealed that both hardness and disintegration time increased with an increase in gelatin concentration. A combination (5% gelatin) FDT comprising a 50:50 ratio of 75:225 BSGs (hardness: 13.7 +/- 0.9 N and disintegration time: 24.1 +/- 0.6 s) was judged the most ideal, and was carried forward to Stage II: the addition of the saccharides sorbitol, mannitol and sucrose in concentrations between 10% and 80% w/w. The best properties were exhibited by mannitol-containing formulations (50%-hardness: 30.9 +/- 2.8 N and disintegration time: 13.3 +/- 2.1 s), which were carried forward to the next stage: the addition of viscosity-modifying polymers to improve mouth-feel and aid pre-gastric retention. Addition of carbopol 974P-NF resulted in the enhancement of viscosity with a compromise of the hardness of the tablet, whereas Pluronic F127 (6%) showed an increase in disintegration time and viscosity with retention of mechanical propel-ties. (C) 2008 Elsevier B.V. All rights reserved.