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The use of pre-hydrated cement in formulation of mortar and concrete is common because there is not always effective control on the cement production, grinding, transportation and subsequent storage. This paper presents a case study on the optimization of admixture for use with prehydrated cement by assessing changes in the rheological properties of Portland cement artificially pre-hydrated. The cement was artificially pre-hydrated by exposure to relative humidity (RHs) of 90%, in an environment of NH4Cl saturated solution. Additionally, the cement pastes were evaluated with and without superplasticizer. Stepped flow test using a parallel-plate geometry was the method choose to evaluate the rheological behavior, apparent viscosity, yield stress and hysteresis area of each paste at the early age. Oscillatory rheometry was conducted to evaluate the storage modulus (G’), comparing the consolidation with the hydration kinetics obtained by calorimetric evaluation of the same suspensions. Initial rheometer results indicate that the pre-hydrated sample presents lower level of shear stress than the reference sample, because of the higher reactivity of the non-pre-hydrated sample. Resumo A utilização de cimento pré-hidratado na formulação de argamassas e concretos é comum, pois nem sempre há um controle efetivo na produção do cimento, moagem, transporte e posterior armazenamento. Este trabalho apresenta um estudo de caso sobre a otimização de aditivo para uso com cimento pré-hidratado, avaliando as mudanças nas propriedades reológicas do cimento Portland pré-hidratado artificialmente. O cimento foi pré-hidratado artificialmente por exposição à umidade relativa (URs) de 90%, em ambiente de solução saturada de NH4Cl. Adicionalmente, as pastas de cimento foram avaliadas com e sem superplastificante. O teste de fluxo escalonado usando uma geometria de placas paralelas foi o método escolhido para avaliar o comportamento reológico, viscosidade aparente, tensão de escoamento e área de histerese de cada pasta em idade precoce. A reometria oscilatória foi realizada para avaliar o módulo de armazenamento (G'), comparando a consolidação com a cinética de hidratação obtida pela avaliação calorimétrica das mesmas suspensões. Os resultados iniciais do reômetro indicam que a amostra pré-hidratada apresenta menor nível de tensão de cisalhamento do que a amostra de referência, devido à maior reatividade da amostra não pré-hidratada.

In the industrial processing of vermiculite, a fine residue is generated for which an application that allows its large-scale use has not been developed yet. The association with Portland cement in mortar and concrete compositions may be an alternative, because of the chemical composition of vermiculite with high amount of aluminum, silicon and magnesium, similar to other additions used in substitution to Portland cement. However, due to high specific surface area of vermiculite compared to cement, its use may affect the rheological properties and the water demand, thus limiting its application. This work was carried out with the objective of evaluating the impact on rheological properties of cement pastes prepared with partial replacement of Portland cement by vermiculite fine residues, both as obtained and calcined. The vermiculite fine residue contents were varied from 5 to 20%, and the compositions were submitted to a stepped flow test, with changes in the shear rate. There were almost no changes in rheological properties in suspensions with 5% of cement substitution by vermiculite fines. However, when >10% of vermiculite was used, considerable changes in flow could be observed as a function of both the residue content and the nature of the vermiculite (as-obtained or calcined). The YODEL and Interference models, based on the physical characteristics of the particles, were applied to estimate the yield stress (YODEL) and viscosity (Interference), and the calculation results indicated that there was a good correlation with the experimental data, indicating than the rheological properties of the pastes were directly related to physical properties of the particles.

The effect of time on soil properties, noticeable in many earthworks, is recognized by geotechnicians. For example, secondary compression and aging pre-consolidation are considered in geotechnical design, and strain rate is standardized in geotechnical laboratory and field tests. Elastic-plastic models, from rigid-perfect plastic to Modified Cam Clay, which do not consider the effects of time, solve most geotechnical problems. However, solutions for prolonged settlements, landslides, debris flow and mudflow could profit from a deeper understanding of rheological models. In fact, rheological concepts, despite not always clearly stated, have been used to address some of these problems, and may also be important for using new materials in geotechnical practice (tailings, sludge, soil-polymer mixtures and other materials with water content higher than the liquid limit). This paper introduces basic concepts of rheology for geotechnicians, specially highlighting viscoelasticity under simple shear stress, which explains with reasonable accuracy well known phenomena dependent on time in soils. The objective is to bring geotechnicians to rheology and show another important tool to access geotechnical problems. On the other hand, a brief explanation of geotechnical tests is presented for rheologists not acquainted with geotechnical engineering. Geotechnical tests procedures are discussed in the light of rheology concepts, terminology is clarified, examples of application of rheology in geotechnics are presented, and determination of soil rheological parameters by traditional geotechnical tests as well as by tests on concrete is commented.

Adding TiO2 tocoating mortars is carried out to promote self-cleaning through photocatalytic activity. However, this addition influences the workability of the mortar and, consequently, the application stage as the TiO2 used can present a large number of fine particles and a high surface area, increasing the demand for mixing water, requiring consistency adjustments before coating. In this work, three mortars (two with the addition of different types of TiO2 and one reference) were developed on a laboratory scale to maintain similar workability, using the flow table test. The amount of kneading water was changed to maintain a spread of 220 ± 10 mm and the content of air-entrained was kept constant, around 25%. The mortars were evaluated using the squeeze flow method. Then, a blind test was performed to assess the mason sensitivity during handling and application of the coating, and all mortars were considered similar. However, the yield of the compositions with TiO2 addition was lower compared to the reference composition, making it possible to explain the results based on the physical parameters of the formulations and with a more in-depth analysis of the rheological indices obtained by the squeeze flow test.

The paper discusses the potential of fillers in CO2 mitigation in the cement industry. A historical overview of the use of fillers is presented as well as the limits of filler use given in cement standards. Globally, limestone filler currently represents only 7% of average worldwide cement composition. The limits of the current route to adding filler in cement by means of intergrinding are discussed. An innovative technology, that compensates binder dilution by a reduction of the water required for good rheological behavior, is presented; this allows clinker replacement rates of up to 70%. The theory that enables the design of such multimodal particle size distributions with high particle packing and low-water demand is presented, and examples of its application in concrete production are given. The efficiency in terms of CO2 mitigation is demonstrated by comparing concrete formulations designed with this innovative approach with a global benchmark of current technology. New filler minerals, as well as the effects of high-filler content on production processes and on durability are also discussed.

The squeeze flow test provides relevant information about the macroscopic rheological behavior of mortars. Nevertheless, the identification and characterization of micro and meso physical phenomena is necessary for a more thorough analysis. This work presents an experimental methodology that combines the squeeze flow test with a pressure mapping system for the rheological evaluation of cement-based mortars. Two compositions were analyzed, with and without viscosity modifying cellulose ether based admixture, and the liquid phase migration was quantified to support the interpretation of the results. The developed pressure mapped squeeze flow (PMSF) method allowed for reliable measurement of the evolution of the pressure distribution on the whole area of the squeezed sample, and the results were compared with theoretical models for different flow types and rheological behaviors. The presence of the cellulose ether admixture resulted in more homogeneous flows, which enabled bigger displacements and generated less fluctuations in the pressure distributions.

Squeeze flow rheological technique is based on the compression of a cylindrical sample between parallel plates and is used to determine the flow properties of food, pharmaceuticals, composites, suspensions, including cementitious materials. This work summarizes the main experimental developments on squeeze-flow for the evaluation of mortars that have been performed in Brazil for the last 15 years and supported the creation of the Brazilian standard test method applied to rendering and masonry mortars (ABNT NBR 15839:2010). The paper exemplifies possible test setups (configuration, geometry, velocity, roughness) for different types of mortars and situations, the use of porous substrate (ceramic or concrete blocks) as the bottom plate, and a method to measure phase separation induced by the. A complementary instrumentation (interfacial pressure mapping) for the assessment of pressure evolution during flow is also presented – forming the pressure mapped squeeze flow method (PMSF) – which allows for identification of transitions in flow type and localized pressure peaks resulting from microstructural changes like particle jamming. The technique was also employed to study and develop laboratory mixing methods for mortars, as the resulting flow curves are very sensitive to the material’s agglomeration state. Finally, rheological parameters of mortars by squeeze-flow and rotational rheometry were compared showing that yield stress have some degree of agreement, whereas viscosity values from these techniques are complex to be related.

The mixing procedure used to make paste, mortar or concrete has an important influence on the hydration kinetics and rheological properties of cementitious materials. In this study, different shear mixing procedures were studied to evaluate the effect on the kinetics of hydration for Portland cement paste by isothermal calorimetry over 72 h. The rheological properties of the same pastes in terms of yield stress (Pa) and apparent viscosity (Pa.s) were also studied with the same mixing procedures: manual, 2500 rpm and high shear mixing at 10000 rpm. To compare the heat flow over the time of each mixing procedure with the stiffening, an oscillatory rheometry evaluation with continuous flow was carried out. All the tests were carried out in triplicate and the variability was evaluated.

Particle Size Distribution (PSD) has impact on the workability of concretes because it affects the particle packing and particle mobility during flow. In continuous concrete production, keeping always the same PSD is not possible. So, it is important to understand how this variability affects concrete properties. The research described in this paper evaluated a more sustainable low-binder concrete, with focus on particle size variability of the aggregates. Applying particle packing and dispersion concepts, rheological control, use of limestone fillers and appropriate choice of material, a reference concrete with low binder consumption (3.7 kg/m3/MPa) was developed. On this reference concrete, PSD variations were applied: a coarser and a finer version for each aggregate was tested and two levels of fines content were also evaluated. Mixing behavior and rheological properties were determined by a concrete mixing rheometer (Pheso Poli-USP) with planetary configuration. An acceptance criterion was established based on mixing torque and all concrete outside the limits had their water content adjusted until they met the specifications. After that, mechanical strength was evaluated at 28 days of age. The obtained results indicate that PSD variations affected both the mixing and flow of concrete. Especially higher fines content and presence of a finer natural sand increased the torque levels during the mixing process and shear cycles and lead to higher mixing power demand. The water correction, adopted to overcome the rheological changes, affected hardened state properties (up to 10% on compressive strength). As these findings are specific to the analyzed concrete and considered PSD variations, this research aimed to explain more generally the influence of the several variables. The surface area of the granular material, solids concentrations and mean distance between the fine and coarse particles are some quantitative parameters useful for predicting rheological aspects of concrete compositions.

Mortars and concretes are subjected to diverse rheological situations during their processing and application. Their behavior can be predicted for most situations by rotational rheometry and/or squeeze flow. However, very high strain rates that occur during impact are very difficult to be properly simulated using these methods. Especially for rendering mortars, impact behavior (during manual or spray application) is important not only regarding productivity and rebound issues but also because the initial mortar-substrate contact extension strongly affects the interfacial bond strength, which is one of the renders most critical hardened properties. The present work introduces initial developments towards an impact rheometry technique intended primarily for cementitious and other suspensions used in construction. The technique is based on a pressure mapping system that measures area and force with a thin and flexible sensor at 100 Hz. Mortars were applied manually, by continuous spraying, and by free fall. Results showed that in manual application, pressures up to 50 kPa took place, whereas in the mechanical procedure the pressure values were considerably lower (>5 kPa) since the force is distributed in small portions of material by the spray. Some of these results can be useful to compare projection techniques and equipment, for the development of nozzles, and to set free fall drop heights to better simulate manual applications and even allow more realistic molding procedures for mortar-substrate tensile bond tests.

Concrete greenhouse gas emissions are mostly from cement. A relevant strategy for the concrete greenhouse gas emissions abatement is the increase of the efficiency in the use of its binder. For this, it is important to understand the packing and the mobility of the concrete particles and their effects on its rheological behavior in the fresh state and the mechanical properties in the hardened state. Currently, the mix design methods are empirical, as opposed to this experimental optimization, the computational optimization emerges, based on predictive models. Thus, the objective of the study is to use the physical model based on particle mobility to predict the rheological behavior of commercial concretes. The method consisted in the following steps: characterization of raw materials; eco-efficiency analysis of 60 formulations of a concrete plant using the binder intensity concept; and a parameter estimation for a descriptive model of slump in function of mobility variables. These concrete formulation binder intensities were between 7.5 and 10.5 kg/m3/MPa, in which the rise of specified fck and maximum aggregate size have a positive impact on this index, while the slump growth has a negative effect. For the base formulations, the mobility variable MPT (Maximum Paste Thickness) showed good correlations with the specified slump (R2 0.99), as well as the model presented a good adjustment to the data (R2 0.94). These results allow an improvement in the mix design methodology using computational optimization, which can lead to an increase on the eco-efficiency of the commercial concretes.

Concrete, the major construction material used in the construction industry worldwide, presents a huge environmental impact producing about 7% of the global carbon dioxide. Given the concerns related to global warming, studies have been focusing on distinct approaches aiming to reduce the amount of Portland cement (PC), which is the least sustainable ingredient of the mixture, by adopting alternative mix-design strategies such as the use of particle packing models (PPMs). However, there is currently a lack of data on the efficiency of the use of continuous PPMs to reduce PC while maintaining or improving concrete fresh and/or hardened properties. This work aims to investigate the impact of current and modified versions of continuous PPMs on the fresh (rheological behaviour) and hardened (compressive strength, modulus of elasticity, porosity, and permeability) state of mixtures designed with low and moderate amounts of PC. Results demonstrate that eco-efficient concrete may be produced through current and modified continuous PPMs without compromising the fresh and hardened properties of the material. Nevertheless, further durability and long-term investigations must be performed on systems with reduced PC contents.

Mixing is one of the mortar processing steps (the others being proportioning, transport and application) that, due to its apparent operational simplicity, has been somewhat undermined. However, the mixing process quality has direct influence on the mortar's rheological behavior and its hardened state properties. In this context, this study's objective is to assess the influence of two mixing parameters (time and water addition rate) on the characteristics of the produced mortar. Both mixing and flow measurements were performed in a rotational rheometer developed at POLI/USP-Brazil. In this equipment, the mixing strain rate is given as a function of torque evolution. Mortar tensile strength, modulus of elasticity and volumetric porosity were evaluated in its hardened state. "Bad mixing" conditions can arise from too short mixing times or too slow water loading. These bad mixing conditions led to mortars with lower mechanical strength and more unfavorable rheology, meaning high thixotropy and flow curve loops with big hysteretic area. When admixture was employed, mixing resulted in a mortar with higher entrained air leading to negative effects on the mechanical properties of the hardened material.

The use of self-compacting concrete in civil construction industry presents various advantages, since the material shows adequate workability during fresh state. When fiber reinforcement is used, there are changes in its behavior that require attention. This study aimed to evaluate the applicability of rheological tests and the correlation between its results and those obtained with regular tests used to control SCCs. In that sense, different mixtures of SCC with different steel fiber contents were produced in order to be analyzed in the experimental program described. Rotational rheology tests and slump flow and L-box tests were performed. The results showed that slump flow test did not present good correlations with rheological parameters. On the other hand, this test was able to point out the risk of segregation of the mixtures with higher fiber contents. A good correlation was obtained between the L-box test results and rheological parameters. The L-box was also able to show loss in the passing ability of SCC related to the rise of plastic viscosity and yield stress. These tests also presented a good correlation with the rheological parameters when lower fiber contents were used. Although the rheometry test was unable to evaluate these problems, this kind of test gave more objective and reliable data on variations in rheological parameters related to the increase of fiber content, and proved to be a more reliable test to this kind of application, especially when applied together with the conventional tests. RESUMO O uso de concreto autoadensável na construção civil apresenta várias vantagens, desde que o material apresente trabalhabilidade adequada no estado fresco. Quando é utilizado o reforço com fibras, há alterações nas propriedades no estado fresco, que nem sempre são detectadas com a utilização de ensaios convencionais normalizados. Este estudo buscou avaliar o potencial de aplicação de ensaios reológicos e a relação com os ensaios comumente utilizados para aceitação de CAAs. Com essa finalidade, foram elaboradas misturas de CAA com fibras de aço em diferentes teores e realizaram-se ensaios de reometria rotacional, espalhamento e Caixa L. Os resultados mostraram que o ensaio de espalhamento não apresentou boa correlação com os parâmetros reológicos medidos, mas permitiu detectar o risco de segregação dos concretos com maior teor de fibras. O ensaio de caixa L obteve boa correlação com os valores obtidos no reômetro, demonstrando perda na habilidade passante em função do aumento da viscosidade plástica e tensão de escoamento, especialmente para baixos teores de fibras, mas apresentou bloqueio entre barras para grandes quantidades de fibras. O ensaio de reometria forneceu dados mais objetivos sobre variação nos parâmetros reológicos, apontando um comportamento pseudoplástico do concreto utilizado no trabalho. Ficou claro o aumento da viscosidade com o aumento do teor de fibras como uso da reometria, fornecendo informações confiáveis mesmo para maiores teores de fibras. Isto comprova que a reometria é um ensaio bastante adequado para este tipo de aplicação.

This study analyses the impact of substituting limestone fillers for cement on the rheological behaviour and drying shrinkage of microconcretes that are used for repair coatings. Three microconcretes were formulated with limestone filler contents of 80%, 60% and 20% by weight in relation of the total fines (cement and limestone filler). The total fines and water contents were kept constant in all of the formulations result in mixtures with similar volume of paste. The rheological behaviours of the mixtures were evaluated using a rheometer with planetary motion. The specimens were then moulded for mechanical characterisation and to measure the drying shrinkage. The porosity of the pastes was also evaluated using the mercury intrusion porosimetry (MIP). Rheological properties such as the yield stress and viscosity were influenced by the amount of cement that was replaced by fillers. Larger volumes of filler in the paste produced lower yield stresses and, consequently, higher slump values were obtained. However, the plastic viscosity increased with the filler content. In the hardened state, greater substitutions of cement by fillers decreased the drying shrinkage. This will cause lower differential shrinkage between the repair material and the existing substrate, generating lower tensile stresses in the repair material (repair coating) and therefore less potential for cracking of this. The experimental shrinkage results were compared to values that were obtained by the ACI 209, CEB-FIP90, B3 and GL2000 shrinkage prediction models. The models were found to overestimate the amount of shrinkage with increased substitution of cement by filler in the paste. Therefore, these models should be calibrated considering other factors such as the quantity of filler used in cement replacement. That consideration could optimize the use of these models in the design stage to verify if the values of expected shrinkage are within usually accepted limits for this application.

Demand on freshwater tends to increase in the next years; consequently, the production of water treatment sludge (WTS) shall increase as well. Beneficial reuse of WTS as a geotechnical material may be an important strategy to reduce the environmental impacts due to improper WTS disposal. However, even after dewatering WTS consistency is closer to fluids rather than soils. Aiming to the reuse of WTS at considerable amounts, the incorporation of additives to stabilize WTS may be an interesting alternative in the future. For this purpose, the knowledge of rheological characteristics of WTS in fresh state is mandatory. This paper presents a brief about viscoelasticity and rheology concepts, preliminary results of WTS rheological behavior, and two different methods, rotational rheometry and laboratorial miniature Vane test, to evaluate WTS behavior. Rheological tests indicated that Cubatao WTS presents shear thinning behavior at low shear rate, shear thickening at high shear rate, and suggested thixotropic behaviour at low shear rates. Rotational rheometry may be a powerful tool to characterize rheological behavior of WTS, since is very fast method, adapted to pastes and fluids, and can be applied to different conditions of solicitation. Vane test is limited to high water content materials, and higher quantities of sample is needed, but is standardized, and a minimum disturbance of sample occurs. Both methods may be appropriated to characterize WTS and the choosing of the best method depends on the research purpose.

The current compressive strength test for cement classification is performed under a fixed water to cement ratio according to the Brazilian and European standards, regardless the consistency obtained. However, under practical conditions the amount of water required is related to the rheological need to obtain and maintain a desired workability. Intrinsic cement characteristics influence the water demand such as the cement particle’s granulometry, specific surface area, density, the presence or not of water reducing admixtures, chemical and mineralogical nature of raw materials, etc., influence particles agglomeration state. Because water demand influences the mechanical properties of cement based products, the compressive strength class under a fixed water to solids ratio specified by the standards may not be representative for the user. The present work investigates the influence of mixing conditions on mini-slump spread results, a test that has been used for many years but never standardized. Cement paste samples were produced with varied mixing conditions (time and rotation speed) using a conventional stirrer and subjected to mini-slump spread test immediately after mixing and at fixed hydration times. Results show that mixing and hydration time do influence on mini-slump spread. At lower rotation speeds, results variability increases. Under fixed time after first contact with water, increasing rotation speed leads in a reduction of results variability and increase the test’s repeatability on cement pastes. Resumo O ensaio de resistência do cimento, segundo às normas brasileiras e europeia atuais, é realizado com uma relação água/cimento fixa em massa, independente da consistência obtida. No entanto em condições normais de uso, a quantidade de água é uma variável definida com a finalidade de manutenção da consistência dos materiais cimentícios para obter trabalhabilidade adequada. Características intrínsecas dos ligantes, como distribuição de tamanho de partículas, área superficial especifica, densidade e natureza química ou mineralógica, ou extrínsecas, como presença de aditivos, temperatura ambiente e da água, tempo e energia de processamento, etc., podem afetar de forma distinta o estado de aglomeração e, consequentemente, a necessidade de líquido para a mistura. Como a demanda de água influencia a resistência mecânica dos produtos, a utilização da relação água/cimento fixa torna, em termos práticos, a classificação do cimento pela resistência pouco significativa para o usuário. Neste trabalho foi investigada a influência das condições de mistura na repetibilidade do ensaio de mini-slump, bastante usado para avaliação da quantidade de água nas composições, mas não normatizado. Pastas de uma mesma amostra de cimento foram misturadas por diferentes tempos e/ou rotações, usando um agitador mecânico convencional, e submetidas ao ensaio de mini-slump imediatamente após o ensaio ou após o mesmo tempo de contato com a água. Observou-se influência significativa nos resultados: quanto maior a rotação ou a manutenção do tempo de mistura, menor a variabilidade do espalhamento mini-slump sendo que a influência é mais sensível para diferenças de rotação.

RESUMO Grandes quantidades de materiais finos (na forma de pó) são coletados e armazenados nas pedreiras, constituindo um sério problema ambiental, pela falta de destinação específica para esse resíduo. No entanto, esses materiais poderiam ser utilizados como um fíler em concreto autoadensável (CAA), o qual necessita de um grande volume de finos na sua constituição. Desta forma, neste trabalho, foram investigados os efeitos do fíler calcário (empregado como referência), fíler diabásico e gnáissico, nas propriedades de CAAs. A influência da mineralogia, forma e tamanho das partículas foram avaliadas por meio de ensaios no estado fresco (monopontos e reométricos) e ensaios no estado endurecido de CAAs. Os resultados mostraram que concretos contendo fíler gnáissico ou diabásico podem apresentar propriedades reológicas similares aos concretos contendo fíler calcário, quando apresentam distribuição granulométrica e tamanho de partícula similar ao fíler calcário usualmente utilizado (d50 entre 30 e 40 µm). Além disso, CAAs contendo fíler diabásico apresentaram resistência à compressão superior aos concretos dosados com os demais fílers. Diante dos resultados, pode-se concluir que os fílers de diabásio e gnaisse apresentam potencial para serem utilizados como materiais alternativos ao fíler calcário em CAA, embora possam demandar maior quantidade de aditivo superplastificante para atingir propriedades comparáveis no estado fresco. ABSTRACT Large amounts of powders have been collected in quarries and storage of these by-product dusts is a serious environmental concern. However, these materials may be used as a filler in self-compacting concrete (SCC), which requires a large amount of fines in its composition. Thus, in this paper, the effects of limestone filler, diabase, and gneiss quarry powder on the properties of self-compacting concrete were investigated. The influence of the mineralogy, shape and particle size distribution were evaluated by rheometry, and by fresh and hardened concrete properties. SCC containing gneissic or diabasic powder can show rheological parameters values very similar to those of SCC containing limestone filler when the material has the same particle size to that of an usual limestone filer (d50 between 30 e 40 um). SCC containing diabasic powder showed higher compressive strength than that of SCC containing limestone filler or gneiss powder. It was found that diabasic and gneissic quarry powders could be used successfully for producing SCC, although a higher superplasticizer content was required than that of SCC containing limestone filler.

A mistura dos materiais sólidos com a água é uma das etapas mais importantes no preparo das argamassas. A condução do procedimento que é adotado interferirá nas propriedades no estado fresco, assim como no endurecido. A Norma ABNT NBR 13276:2005 indica que os materiais sólidos sejam introduzidos no líquido já disposto no recipiente. Essa ordem de introdução dos materiais é o inverso do que ocorre na prática e pode resultar na falta de homogeneidade da mistura. Estudos anteriores observaram que adicionar o líquido aos materiais sólidos de forma fracionada melhora as propriedades reológicas dos sistemas. Assim, utilizando uma argamassadeira de laboratório e uma mesma formulação, foram estudados distintos procedimentos de mistura em que a água é adicionada no material sólido em etapas. Esses procedimentos foram confrontados com o indicado pela ABNT NBR 13276:2005, e o comportamento reológico (squeeze-flow e ciclos de cisalhamento) e as propriedades no estado endurecido (resistência à tração por compressão diametral e módulo de elasticidade dinâmico) foram avaliados. Verificou-se que a adição do líquido ao material sólido em etapas distintas conduz a sistemas mais fluidos e com melhor desempenho no estado endurecido. The mixing of solid materials with water is one of the most important steps in the preparation of mortars. The mixing procedure interferes with both fresh and hardened properties. The ABNT NBR 13276:2005 indicates that the solids should be added to the liquid in the mixer container. This order of introduction of materials is the reverse of what occurs in practice and it may result in the lack of homogeneity of the mix. Previous studies have found that adding the liquid to solid material in steps improves the rheological properties of the systems. Thus, using a laboratory mixer and the same mortar formula, various mixing procedures in which water is added to the solid material in steps were investigated. These procedures were compared with that described by ABNT NBR 13276:2005, and rheological behavior (squeeze-flow and shear cycles) and mechanical properties (splitting tensile strength and dynamic modulus of elasticity) were evaluated. The results showed that the addition of liquid to solid material in different stages resulted in more fluid systems and improved performance in the hardened state

Producing cementitious materials with low CO2 emissions is a key challenge for sustainability, considering the increasing demand for cement and the inefficacy of current industrial solutions. Improving the efficiency of binder use is mandatory, so that binder replacement by inert fillers with lower environmental loads is an alternative, which demands careful control of the rheological behaviour to decrease the water demand of pastes. Dispersion and packing models are well known, but other less explored parameters of raw materials (surface area, density, roughness) and paste (water content, distance between particles) determine the interaction among particles, affecting the paste's rheological behaviour. The aim of this paper is to assess the influence of inert fillers on the rheological behaviour of cementitious pastes. A range of 12 inert fillers with varied aspects was evaluated. The results indicated a good agreement between the Casson viscosity and the interference parameter calculated using the interference model.

Polycarboxylates are frequently used as additives to concrete production in the construction industry. The additive increases the dispersion of the particles, reduces the amount of water, and improves the mechanical properties of concrete in the fresh and settled state. However, although it is well known that polycarboxylate additives enable the production of high performance concretes, their presence may affect on both kinetics and thermodynamics of cement's particles during hydration reaction through consolidation. While the flow of heat released by the hydration reaction can be measured by isothermal calorimetry, concrete consolidation can be measured by oscillatory rheometry. The results obtained separately, when considered together could better illustrate the effect of the additives on the cement setting. This was the main subject in this work. Therefore, cement pastes containing commercial CPIIE-32 were evaluated by simultaneous heat of hydration and rheological measurements with different amounts of polycarboxylate. The results obtained separately, when considered together can better illustrate the effect of additive content during the hardening, and this approach is presented as a main objective of this work. For this, cement pastes formulated with CPII-32 were evaluated according to the variation of the content of polycarboxylate and the results showed that the rate of consolidation(promoted by the joint action of the chemical reaction and particle agglomeration)has direct relation with the level of the additive.

A presença de aditivos incorporadores de ar (AIA) em suspensões cimentícias torna esses materiais sensíveis às etapas de processamento e às condições ambientais de preparo das composições. Diversos estudos têm sido reportados em literatura avaliando o efeito de incorporadores de ar nas propriedades de materiais cimentícios, sobretudo no estado endurecido. Porém o efeito da temperatura na incorporação de ar e nas propriedades reológicas dessas composições tem sido menos investigado, sendo este o objetivo do presente trabalho. Para tanto, foram avaliadas as características de pastas cimentícias, compostas por cimentos CPIIF ou CPIIE e dois tipos de AIA, em função da variação da temperatura. O conceito de viscosidade cinemática foi adotado na análise dos resultados para compensar diferenças de inércia das pastas com densidades distintas. Os resultados mostraram que o tipo de cimento, a presença do aditivo e a temperatura influenciaram significativamente na incorporação de ar e nas propriedades reológicas.

In the present work the squeeze flow technique was used to evaluate the rheological behavior of cement-based mortars containing macroscopic aggregates up to 1.2 mm. Compositions with different water and air contents were tested at three squeezing rates (0.01, 0.1 and 1 mm/s) 15 and 60 min after mixing. The mortars prepared with low (13 wt.%) and usual water content (15 wt.%) presented opposite behaviors as a function of elapsed time and squeezing speed. The first lost its cohesion with time and required higher loads when squeezed faster, while the latter became stiffer with time and was more difficult to be squeezed slowly as a result of phase segregation. Due to the increase of air content, the effects of this compressible phase became more significant and a more complex behavior was observed. Rheological properties such as elongational viscosity and yield stress were also determined.

Chemical admixtures increase the rheological complexity of cement pastes owing to their chemical and physical interactions with particles, which affects cement hydration and agglomeration kinetics. Using oscillatory rheometry and isothermal calorimetry, this article shows that the cellulose ether HMEC (hydroxymethyl ethylcellulose), widely used as a viscosity modifying agent in self-compacting concretes and dry-set mortars, displayed a steric dispersant barrier effect during the first 2 h of hydration associated to a cement retarding nature, consequently reducing the setting speed. However, despite this stabilization effect, the polymer increased the cohesion strength when comparing cement particles with the same hydration degree.

This paper presents a rheological investigation of pure gypsum (PG) and a commercial gypsum–lime–filler plaster (CP) using the modified Vicat apparatus and squeeze flow method. The samples were tested at several different intervals after manual or mechanical mixing. The results confirmed squeeze flow to be more sensitive in determining fresh paste behavior than the modified Vicat apparatus. PG set faster when prepared in mechanical mixer than when manually mixed. Conversely, the CP composition presented longer setting when mixed mechanically. The study also included the analysis of two ready-to-use polymer-based products for leveling and rendering (drywall joint compound – DJC; acrylic putty – AP) measured by squeeze flow and compared to the commercial composition.

This paper reports an experimental investigation regarding the influence of the squeeze velocity, during positioning of the parallel-plate gap, on the rotational shear flow behaviour of a cement paste. The descent of the upper plate was performed using diverse speeds while the normal force generated due to the compression of the paste was recorded. The slower the plate speed, the higher the resulting normal force. This behaviour was caused by liquid–solid separation, which is more likely to occur at slow squeeze velocities. Phase separation was confirmed by assessing, via microwave drying, the water contents of the trimmed portion of the paste sample and of the portion actually subjected to rotational shear cycles. Owing to the variation of water/cement ratio induced by liquid radial migration, paste's Bingham yield stress and plastic viscosity were significantly affected by squeeze speed, and both rheological parameters presented an inversely proportional relationship with this experimental variable.

Rheology studies the deformation and flow of matter and seeks to describe the deformations of material depending on the time they are exposed to mechanical actions. This paper proposes to understand the behavior of fresh mortar adhesives in Squeeze Flow tests based on rheological characterization of different commercial compositions. In the tests, flow of material results from the application of a compressive load on the sample in the fresh state which causes displacement due to stresses generated during radial shear flow. We performed further physical characterizations of mortars and viscosity on material passing the through a sieve with a 0.075 mm sieve opening with the objective of basing the analysis of the results obtained from Squeeze Flow tests. It was observed that the mortars studied showed differences in rheological behavior, probably resulting from synergistic action of some of the composition parameters, especially the particle size distribution and particle morphology. A reologia estuda a deformação e o escoamento da matéria buscando descrever as deformações dos materiais dependentes do tempo, quando os mesmos são expostos a ações mecânicas. O presente trabalho propõe o entendimento do comportamento no estado fresco de argamassas colantes, com base na caracterização reológica de diferentes composições comerciais, a partir do ensaio "Squeeze Flow". Neste ensaio, o escoamento do material decorre da aplicação de uma carga de compressão sobre a amostra no estado fresco, a qual ocasiona deslocamentos no seu interior, devido a esforços de cisalhamento radiais originados durante o fluxo. Foi realizada ainda a caracterização física das argamassas e a viscosidade da fração passante na peneira da fração passante na peneira de abertura 0,075 mm, com o objetivo de embasar a análise dos resultados obtidos com o Squeeze Flow. Observou-se que as argamassas estudadas apresentam diferenças de comportamento reológico, decorrente provavelmente, de ação sinérgica de alguns parâmetros da composição, com destaque para a distribuição granulométrica e morfologia das partículas.

A principal etapa de preparação das argamassas consiste na mistura dos materiais sólidos com água. A introdução do líquido conduz a uma série de eventos de aglomeração e desaglomeração no sistema, que, por sua vez, irão resultar em esforços durante essa etapa. Estudos previamente realizados demonstraram a capacidade de mensuração desses esforços através de curvas que relacionam o torque com o tempo em equipamentos como os reômetros. Nessa perspectiva, o objetivo deste trabalho é avaliar como o tempo influencia a energia de mistura e as propriedades reológicas de argamassas de revestimento com e sem a utilização de aditivo dispersante. O material foi misturado no reômetro rotacional do tipo planetário por tempos distintos (17, 47, 87 e 297 s) e em seguida foi submetido a três ciclos de cisalhamento consecutivos. Em tempos curtos verificou-se que a energia de mistura é baixa, não sendo capaz de romper os aglomerados e homogeneizar o sistema, resultando em materiais reologicamente instáveis e menos fluidos. Por sua vez, a mistura de 297 s demonstrou ser mais eficiente, produzindo uma argamassa estável e fluida. Nas argamassas com o dispersante, os níveis de energia de mistura envolvidos foram mais baixos, e o sistema tendeu a homogeneizar-se mais rapidamente, além de ter resultado em argamassas mais fluidas. The main step of mortar processing consists in mixing the powder materials with water. The addition of the liquid into the granular system promotes a set of agglomeration and dispersion phenomena, which result in variations of the forces required to shear the mortar during mixing. Previous studies demonstrated that is possible to measure the mixing energy through torque vs. time curves. The aim of this work is to evaluate the influence of mixing time on mixing and rheological behaviors of a rendering mortar. The material was mixed for different times on a rotational rheometer (17, 47, 87 and 297 s) and then submitted to 3 consecutive shear cycles. At short times, the resulting mixing energy was low and unable to break the agglomerates and to homogenize the system; hence the mortar was rheologically unstable and less fluid. On the other hand, the 297-second mixing was efficient, producing a fluid and stable mortar.

Resumo A adaptabilidade a diferentes tipos de materiais (concretos, argamassas, fibrocimento, etc.) e aplicações (injeção, bombeamento, spray, extrusão, etc.) é essencial para utilização de materiais à base de cimento. Cada material ou sistema de aplicação demanda um conjunto de características específicas da pasta fluida. Portanto, um ensaio adequado para avaliar o comportamento reológico destes materiais deve identificar todas as propriedades requeridas para cada situação. A maior dificuldade está na obtenção de uma única técnica capaz de simular todas as situações simultaneamente. Como alternativa, este trabalho propôs avaliar o comportamento reológico de uma pasta de cimento por uma associação de técnicas reológicas, tais como: reometrias rotacionais tradicionais de fluxo e oscilação e, um método menos explorado, o squeeze-flow. Os resultados mostraram que uma única técnica não é capaz de determinar as propriedades reológicas fundamentais nem de simular todas as solicitações que os materiais podem sofrer durante sua mistura, transporte e aplicação. Técnicas complementares foram necessárias, permitindo assim identificar o comportamento da pasta de cimento sob diferentes solicitações. Abstract The adaptability to different classes of material (concrete, mortars, fiber-cement, etc.) and methods of application (injection, pumping, spraying, casting, extrusion, etc.) is an essential feature of cement pastes. Each material or application system requires a set of characteristics of the fluid pastes. Therefore, an adequate rheological test to characterize rheological behavior should identify all the required properties for each situation. The main problem associated with this approach is the lack of a single technique able to perform a thorough characterization. As an alternative, this work proposes to evaluate the behavior of a cement paste by associating traditional flow and oscillatory rheometry, with the less explored squeeze-flow testing method. The results showed that a single technique cannot evaluate the fundamental properties nor simulate the mixing, transport and application methods. Complementary techniques were necessary to identify the rheological behavior under different requirements.

Este estudo ilustra o impacto da calcinação de resíduo de bauxita (RB) nas propriedades de suspensões formuladas com cimento Portland, tanto no estado fresco como no endurecido. As suspensões foram avaliadas contendo uma razão constante de água-cimento e teor de resíduo variando de 5% a 20% em peso e em substituição ao cimento. As propriedades reológicas e a resistência mecânica foram alteradas em função do aumento do teor de RB, mas a calcinação não teve influência no resultado final obtido, seja no estado fresco ou no endurecido. Assim, pode-se afirmar que a utilização de resíduo de bauxita, natural ou calcinada, em formulações com cimento Portland pode reduzir o consumo de cimento, sendo uma alternativa para a utilização de uma grande quantidade deste tipo de resíduo. This research work shows the impact of bauxite residue (BR) calcination on the rheological and hardened properties of Portland cement suspensions. These suspensions were evaluated with water-to-cement ratio of 0.5 and variations of residue content from 5% to 20% in partial substitution of cement. Both properties had influence of BR content, but had a negligible influence of calcination. Therefore, it can be inferred that the utilization of BR, in nature or calcinated, in formulations with Portland cement, may reduce the consumption of cement, being an alternative to use large amounts of this type of residue.

The mixing process of fiber-containing cementitious suspensions is a crucial factor to obtaining a good dispersion of fibers and guarantee adequate mechanical performance of the hardened products. The addition of fibers into the suspension causes reduction of the fluidity of the system due to factors inherent to the fibers, the matrix and their interaction. During mixing, these interactions make dispersion and homogenization processes more difficult due to the formation of fibers - particles agglomerates. Conventional techniques to assess workability of mortars are inadequate to evaluate the rheological behavior of fiber-reinforced systems, in which parameters like viscosity and yield stress are not completely taken into account. Therefore, this work employs rotational rheometry to evaluate the influence of fiber and water addition sequences on mixing and rheological behavior of mortars containing Polyvinyl Alcohol (PVA) fibers. Constant test parameters were: mixing time of 317s; impeller velocity 126.5 rpm; water flow 128g/s. A constant mix design was used with a water content of 16%wt, and a 0.2%vol of fibers were added to the reference composition. Four mixing sequences were studied: S1 and S2 are based on the addition of fibers at different stages of the mixing process; while in S3 and S4 not only the fibers are added at different stages, but also the water addition is performed in two steps (25% first and 75% latter).Results showed that it is possible to optimize the mixing step of fiber-containing systems by changing the moment of fiber addition into the mixture. The introduction of fibers after mixing the dry mortar with water, when it already had achieved its fluidity point, demanded a lower mixing effort and produced a more flowable material. RESUMO O processo de mistura de suspensões cimentícias contendo fibras é uma etapa crucial para que se obtenha uma boa distribuição das fibras, garantindo os benefícios que as mesmas podem trazer ao desempenho mecânico. A introdução das fibras na suspensão tende a provocar redução na fluidez. Isso ocorre devido a uma série de fatores inerentes às fibras, à matriz e, à interação entre elas. Durante a mistura, essas interações tornam a dispersão e homogeneização mais difícil devido à formação de aglomerados de partículas e fibras. Técnicas convencionais de avaliação da trabalhabilidade são insuficientes para avaliar o comportamento reológico de sistemas reforçados com fibras porque parâmetros como viscosidade e tensão de escoamento não são considerados em sua totalidade. Assim, este trabalho propõe utilizar técnicas de reometria rotacional, para avaliar a influência da sequência de adição da fibra e da água na mistura e no comportamento reológico de argamassas. O tempo de mistura é mantido fixo em 317s, a velocidade do equipamento é 126,5rpm e a taxa de adição de água 128g/s para todas as sequências. Uma mesma composição granulométrica foi usada fixando o teor de água em 16% e o de fibra em 0,2%. Quatro sequências de mistura foram estudadas: S1 e S2 são baseadas na adição das fibras em diferentes estágios do processo de mistura, enquanto na S3 e S4, não só as fibras são adicionadas em diferentes estágios, mas também a água é adicionada em duas etapas (primeiro 25% e depois 75%). Os resultados indicaram que é possível otimizar o preparo de sistemas com fibras de PVA modificando etapas simples do processo como o momento de introduzir as fibras. Entre as sequências avaliadas concluiu-se que introduzir as fibras após a homogeneização prévia dos materiais, no ponto de fluidez, tende a produzir sistemas mais fluidos e com menor esforço para mistura.