Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science

Accurate camber prediction in prestressed concrete bridge beams is important to all parties involved in bridge design and construction. Many current prestress loss prediction methods, necessary for proper camber calculation, were developed many years ago and are predicated on assumptions that may no longer be valid as higher strength concrete, wider beam spacing, and longer span lengths become more commonplace. This throws into question which models are appropriate for use in camber calculation by the bridge engineers and contractors of today. Twenty-seven high-strength concrete modified 79 in. Bulb Tee beams with a design compressive strength of 9,000 psi were periodically measured to determine camber growth. Most available models for concrete creep and shrinkage were used to calculate creep and shrinkage strain. The modulus of elasticity equation of each model was used to predict modulus of elasticity of the studied mix. The Shams and Kahn compressive strength and modulus of elasticity equations were modified in order to approximate measured modulus of elasticity. The creep, shrinkage, and modulus of elasticity equations were used as inputs to an incremental time step method. The time-dependent change in beam curvature calculated by the time step method was used to calculate theoretical camber using the Moment-Area method. Predicted camber, using inputs from each considered model, was then compared with measured camber to determine the most accurate camber prediction models. Season of casting was also examined to determine what, if any, affect ambient temperature has on camber growth. For the studied beams, the Shams and Kahn Model for creep, shrinkage, and modulus of elasticity, used as inputs for an incremental time step analysis, were found to most accurately predict camber values. Lower concrete compressive strength was observed for test cylinders from beams cast in summer versus beams cast in winter. Differences in beam deflection based on season of casting showed mixed results. / Master of Science

Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC. / AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.

Este estudo avaliou quantitativamente a contração de polimerização em função do aumento dos valores de densidade de potência irradiados em compósitos à base de metacrilatos e silorano, e qualitativamente a interface restauradora em relação à abertura de fendas marginais, em função da variação do tipo de substrato dentário. As resinas Filtek Z250 e Filtek P90 foram fotoativadas com 200, 400, 600, 800 e 1000 mW/cm2, em um volume constante de 12 mm3, e os valores de contração aferidos por meio da máquina de ensaios universal. Para análise qualitativa da interface restauradora, preparos cavitários classe V de 2x2x2 mm foram restaurados em incisivos bovinos, fotoativados com os mesmos valores de irradiância, e analisados em microscopia eletrônica de varredura nas interfaces da parede circundante em esmalte, parede circundante em dentina e parede axial. Os resultados quantitativos da contração de polimerização foram analisados pelo teste ANOVA a dois critérios e Tukey (p0,05), enquanto para os dados qualitativos os testes Mann-Whitney, Kruskal-Wallis e Miller foram empregados. O aumento progressivo da densidade de potência influenciou diretamente na contração de polimerização dos materiais estudados, não obstante a resina composta à base de silorano ter demonstrado valores significativamente menores. A integridade marginal sofreu influência do subtrato dentário bem como da densidade de potência utilizada, para as duas resinas estudadas. / Shrinkage is a limitation of resin composite, compromising the clinical longevity of the restorative procedure. In an attempt to reduce their harmful effects, researchers have studied monomers with lower values of contraction. As a result, low-shrinkage composites wer developed. This study evaluated quantitatively the shrinkage by a universal testing machine as a function of power density increase based on methacrylates, comparing them with silorane based resin, and qualitatively regarding gap formation between the adhesive interface as function of tooth substrate. Resin Filtek P90 and Filtek Z250 were polymerized with the device Blue Star 3 with 200, 400, 600, 800 and 1000 mW/cm2 keeping volume constant in 12 mm3. For qualitative analysis of restorative interface, class V cavity preparations in bovine incisors were restored in (2x2x2 mm), photoactivated with the same values of irradiance, and analyzed by scanning electron microscopy at the interface of the wall surrounding enamel, dentin and axial. The quantitative results of the polymerization shrinkage were analyzed by two-way ANOVA and Tukey\'s test (p0,05), while qualitative data for the Mann-Whitney, Kruskal-Wallis and Miller were employed. The progressive increase in power density directly influenced the polymerization shrinkage of the materials studied, despite the silorane based resin have demonstrated significantly lower values. The marginal integrity was influenced by the dental substrate and the power density used.

Atualmente o maior impacto ambiental do concreto como material de construção origina-se das emissões de CO2 durante a produção do cimento. Uma das alternativas atualmente utilizadas para minimizar este impacto, é a utilização de adições minerais como substituição ao cimento. Entre as diferentes adições utilizadas, o uso de fíler calcário parece ser uma alternativa interessante para melhorar a sustentabilidade do uso do concreto na construção. Consequentemente, o presente estudo foca a análise do impacto da substituição do cimento por fílers de origem calcária (dolomita) no comportamento do concreto em estado fresco e endurecido, especialmente focando-se numa avaliação reológica e na retração por secagem do material. Para tal fim, foram formulados três microconcretos com teores de fíler calcário de 80%, 60% e 20% em relação ao peso dos finos totais (cimento mais fíler calcário). O teor de finos totais e de água foram mantidos constantes para todas as formulações resultando em misturas com similar volume de pasta. O comportamento reológico das misturas foi avaliado num reômetro de movimento planetário. Foram moldados corpos de prova para caracterização mecânica e acompanhamento da retração por secagem. A porosidade das pastas também foi avaliada usando a porosimetria por intrusão de mercúrio. As propriedades reológicas como a tensão de escoamento e a viscosidade foram influenciadas pelo teor de substituição de cimento por fílers. Maiores volumes de fílers na pasta produziram menores tensões de escoamento e, por consequência, maiores valores de abatimento foram obtidos. No entanto, a viscosidade plástica aumentou com teor de fílers. No estado endurecido, a maior substituição de cimento por fílers diminui a intensidade da retração por secagem devido ao menor teor de cimento na pasta e a modificações na estrutura porosa do material. Os resultados experimentais da retração foram comparados com os valores obtidos pelos modelos de previsão da retração: ACI 209, CEB-FIP, B3 e GL2000. Observou-se que os modelos superestimam os valores da retração conforme aumenta a substituição de cimento por fílers na pasta. Portanto, esses modelos devem ser calibrados considerando outros fatores, tais como: a quantidade de fíler utilizado em substituição de cimento. Esta consideração poderia otimizar o uso dos modelos em fase de projeto para verificar se os valores da retração esperados estão dentro dos limites normalmente aceitos. / Currently the biggest environmental impact of concrete as a building material originates in CO2 emissions during the production of cement. For this reason, one of the alternatives currently used to reduce these emissions is the use of mineral additions as cement replacement. Among the different additions used, the use of limestone fillers to replace cement appears to be an interesting alternative for improve the sustainability of the concrete used in construction. Consequently, this study focuses on the analysis of the impact of the replacement of cement by limestone fillers in fresh and hardened concrete, especially focusing on rheological behavior and shrinkage of the material. To this end, three microconcretos were formulated with fillers limestone content of 80%, 60% and 20% by weight relative to the total fine (limestone fillers and cement). The total content of fine and water were held constant for all formulations resulted in mixtures with similar volume of paste. The rheological behavior of the mixes was evaluated in a planetary motion rheometer. For mechanical characterization and measurement of shrinkage, specimens were molded. The porosity of the pastes was also evaluated using mercury intrusion porosimetry. The rheological properties such as yield stress and viscosity were influenced by the amount of cement that was replaced by fillers. Further filers volumes in the pulp produced smaller flow stress and, consequently, higher allowance values were obtained. Larger volumes of filler in the paste produced lower yield stresses and, consequently, higher slump values were obtained. However, the plastic viscosity increased with filers content. In the hardened condition, the largest cement replacement by limestone fillers reduced the intensity of shrinkage due to the lower content of cement paste and changes in the porous structure of the material. The experimental results of shrinkage were compared with the values obtained by shrinkage prediction models: ACI 209, CEB-FIP, B3 and GL2000. It was observed that the models overestimate the shrinkage values with increasing cement replacement by limestone fillers. Therefore, these models must be calibrated considering other factors such as the amount of fillers used as cement replacement This consideration would optimize the use of these models in the design phase to verify that the values of the expected shrinkage are within the limits normally accepted.

Mudanças volumétricas presentes na matriz cimentícia, oriundas dos processos de hidratação e de secagem do compósito cimentício, geram uma tendência de fissuração no material. Em pisos de concreto, a presença de tal manifestação patológica, decorrente do fenômeno da retração por secagem, é extremamente preocupante. Desta forma, a realização de esforços visando avaliar a influência de materiais constituintes do traço do concreto e seus proporcionamentos, com o intuito de reduzir a tendência de fissuração do material, gerada pelo fenômeno da retração por secagem, é extremamente válida. Para isto, foram avaliados fatores controláveis como o consumo de água (175l/m³; 190l/m³; 205l/m³), o teor de adição de microfibras de polipropileno (0g/m³; 300g/m³; 600g/m³; 900g/m³), o tipo de cimento (CP IV; CP V-ARI) e a idade, variável para cada ensaio realizado. Os ensaios empregados para esta avaliação foram o de resistência à compressão uniaxial, resistência à tração na flexão, retração por secagem livre e retração por secagem restringida. Os resultados dos ensaios mecânicos demonstraram a influência significativa do tipo de cimento e da idade avaliada na resistência do concreto. O teor de adição de microfibras de polipropileno exerceu uma pequena influência, porém significativa, com incrementos de 5% nos resultados mecânicos do ensaio de resistência à compressão uniaxial para os traços com teores de adição de 300g/m³ e 600g/m³. No entanto para o ensaio de resistência à tração na flexão, tal variável não se demonstrou significativa. O fator consumo de água não influenciou significativamente nos resultados correspondentes aos ensaios mecânicos, uma vez que a relação a/c manteve-se constante para todos os concretos estudados. No ensaio de retração por secagem livre, o tipo de cimento não demonstrou significância relevante para os resultados obtidos. Comportamento este, também observado para o teor de adição de microfibras de polipropileno, o qual não reduziu a magnitude da retração por secagem livre. Diferentemente do observado para a variável consumo de água, a qual influenciou significativamente nos dados obtidos, demonstrando a existência de uma relação direta entre a mesma e o fenômeno estudado. No ensaio de retração por secagem restringida, a tendência de fissuração dos concretos estudados foi influenciada significativamente pelo consumo de água presente na mistura. Conjuntamente, os resultados obtidos neste ensaio demonstraram que o teor de adição de microfibras de polipropileno é uma variável que deve ser proporcionada como os demais materiais constituintes do traço do concreto, ou seja, a quantidade incorporada no compósito cimentício não pode ser um valor determinado, semelhante para qualquer tipo de concreto. / Volumetric changes present in the cement paste matrix, coming from the processes of hydration and drying of cementitious composites, generate a cracking tendency in the material. In the concrete floor, this cracking tendency is extremely worrying. In this sense, efforts to evaluate the influence of important parameters in the mixture proportions of concrete, for decrease the cracking tendency due to drying shrinkage, it’s extremely valid. So, parameters were assessed like the consumption of water (175l/m³; 190l/m³; 205l/m³), the addition content of polypropylene staple fiber (0g/m³; 300g/m³; 600g/m³; 900g/m³), the type of cement (CP IV; CP V-ARI) and age, different for each test performed. The tests performed for this assessment were the compressive strength, flexural tensile strength, unrestrained drying shrinkage and restrained drying shrinkage. The results of mechanical tests shown the significant influence of the kind of cement and age assessed in the strength of concrete. The addition content of polypropylene staple fiber exerted little influence on the results of mechanical tests, but it was significant, with increases of 5% in the results of compressive strength for the mixtures with addition levels of 300g/m³ e 600g/m³. However for the flexural tensile strength, this parameter didn’t show significant. The water consumption didn’t influence significantly the results of mechanical tests, since the ratio a/c was constant for all concretes studied. In the unrestrained drying shrinkage, the kind of cement didn’t show importance for the results. This behavior also observed for the addition content of polypropylene staple fiber, which didn’t reduce the magnitude of free drying shrinkage. However, the water consumption influenced significantly in the results, demonstrating the existence of a direct relationship between it and the phenomenon studied. In the restrained drying shrinkage, the cracking tendency of the concrete studied was significantly affected by the consumption of water present in the mixture. Together, the results of this test showed that the addition content of polypropylene staple fiber is a parameter that should be provided as the others materials of the concrete mixture, i.e., the amount of polypropylene staple fiber incorporated into the cementitious composite can’t be a value fixed, similar to any type of concrete mixture.

Time dependent deformations in concrete, both creep and shrinkage, play a critical role in prestressed concrete structures, such as bridge girders, nuclear containment vessels, etc. These strains result in lossess, through release of prestress, and thereby influence the safety of these structures. The present study comprises of an experimental and analytical program to assess the levels of creep and shrinkage in normal and heavy density concrete. The experimental program includes tests on creep using standard cylinder specimen, while shrinkage studies have been conducted using prism specimen, both under controlled environmental conditions. The experimental results suggest that creep and shrinkage strains are higher in heavy density concrete than in normal concrete. This may be attributed to the relatively smaller pore structure of heavy density concrete, that results in larger availability of free water and a relatively slower hydration process in comparison to normal concrete. While there is some scatter in the results, creep strains decrease with age of loading and both creep and shrinkage strains are smaller when the relative humidity is higher. Statistical model reported in the literature for normal concrete is able to predict the test results for both normal and heavy density concrete quite well. Long term predictions of creep and shrinkage using this model, accounting for uncertainties, is also projected and shown to predict some long term measured results not used in the model calibration. The long term predictions are sensitive to the initial data used in model calibration.

Previous studies on wood instability have identified some wood basic properties which influence the timber distortion and shape changes while the wood is losing or gaining moisture. These properties include wood anisotropic shrinkage, equilibrium moisture content (EMC) in both desorption and adsorption, fibre saturation point (FSP) and water diffusion coefficient. This study investigated the stability related wood properties and their variations within the stems of the New Zealand grown radiata pine trees. The basic density, EMC and shrinkage for the earlywood and the latewood were also experimentally determined. In taking into account these properties and their variations, an analytical model was developed to simulate the wood distortion. The equilibrium moisture content was determined at 30°C and humidity range from 27% to 90%. It was found that the EMC difference between the earlywood and the latewood was negligible. The experimental results also show that the EMC decreases from pith towards the bark over the disc cross section and the trend is most obvious at high humidities (70-90%). Along the tree height, the EMC decreases from ground towards the top of the stem. The tangential shrinkage results were highly variable but, in general, the latewood has higher values than the earlywood. The opposite trend was found for the longitudinal shrinkage, higher values for the earlywood than the latewood. In the tree height direction, the tangential shrinkage was found to decrease with the tree height. This follows the same trend as the microfibril angle which in general also decreases with the tree height. The fibre saturation point (FSP) was determined from the tangential shrinkage values at different equilibrium moisture contents. These were taken as the intersection point of the tangential shrinkage line with the moisture content axis. The experimental results have revealed a trend that the FSP decreases from the pith towards the bark and also decreases with the tree height. Similar behaviour was found for the tangential and longitudinal swelling during the adsorption. The moisture transport within radiata pine was investigated based on the diffusion theory under transient and isothermal condition of 30°C. The moisture dependant diffusion coefficient was derived from the experimental data using the inverse analysis method. The surface emission coefficient was determined by taking into account the variable surface moisture content, wood density and the ambient conditions. In the experiments, 138 samples in total (46 samples for each XIV of the longitudinal, tangential and radial directions) were used and their diffusion coefficients were determined for both the adsorption and the desorption with moisture content ranging from 6% to 22%. The derived diffusion coefficients are comparable with the reported data in the literature. Further investigation of the wood type influence on the diffusion coefficient revealed that compression wood has the lowest diffusion coefficients in the three directions (longitudinal, tangential and radial) both in the desorption and in the adsorption. In addition, the moisture content has the least influence on the diffusion coefficient in the compression wood. Investigation on the effects of the wood density has shown that in general, the diffusion coefficient decreases with increasing wood density although the correlations are only significant for the longitudinal direction in desorption. An analytical model for the simulation of the wood twist was developed which is based on the geometry and geometrical changes of the grains aligning non parallel to the pith. A board consists of numerous such grains which change the length and shape with moisture content change. The model predictions confirm that the grain angle, the tangential and longitudinal shrinkage and the conical angle all affect the development of the board twist. However, the discrepancies between the model prediction and the experimental data are significant, partly due to the experimental uncertainties and partly due to the model errors. In this study, sound velocity in the longitudinal direction was measured for the test samples used in the shrinkage experiments. The results revealed that the correlations between the sound velocity and the volumetric shrinkage at oven dry are significant. Based on this finding, the relationship between the tangential shrinkage and the radial shrinkage, the tangential shrinkage can be predicted from the sound velocity measurements. As the tangential shrinkage has significant influence on the wood distortion, this method can be used to segregate logs which may be prone to wood distortion.

Mudanças volumétricas presentes na matriz cimentícia, oriundas dos processos de hidratação e de secagem do compósito cimentício, geram uma tendência de fissuração no material. Em pisos de concreto, a presença de tal manifestação patológica, decorrente do fenômeno da retração por secagem, é extremamente preocupante. Desta forma, a realização de esforços visando avaliar a influência de materiais constituintes do traço do concreto e seus proporcionamentos, com o intuito de reduzir a tendência de fissuração do material, gerada pelo fenômeno da retração por secagem, é extremamente válida. Para isto, foram avaliados fatores controláveis como o consumo de água (175l/m³; 190l/m³; 205l/m³), o teor de adição de microfibras de polipropileno (0g/m³; 300g/m³; 600g/m³; 900g/m³), o tipo de cimento (CP IV; CP V-ARI) e a idade, variável para cada ensaio realizado. Os ensaios empregados para esta avaliação foram o de resistência à compressão uniaxial, resistência à tração na flexão, retração por secagem livre e retração por secagem restringida. Os resultados dos ensaios mecânicos demonstraram a influência significativa do tipo de cimento e da idade avaliada na resistência do concreto. O teor de adição de microfibras de polipropileno exerceu uma pequena influência, porém significativa, com incrementos de 5% nos resultados mecânicos do ensaio de resistência à compressão uniaxial para os traços com teores de adição de 300g/m³ e 600g/m³. No entanto para o ensaio de resistência à tração na flexão, tal variável não se demonstrou significativa. O fator consumo de água não influenciou significativamente nos resultados correspondentes aos ensaios mecânicos, uma vez que a relação a/c manteve-se constante para todos os concretos estudados. No ensaio de retração por secagem livre, o tipo de cimento não demonstrou significância relevante para os resultados obtidos. Comportamento este, também observado para o teor de adição de microfibras de polipropileno, o qual não reduziu a magnitude da retração por secagem livre. Diferentemente do observado para a variável consumo de água, a qual influenciou significativamente nos dados obtidos, demonstrando a existência de uma relação direta entre a mesma e o fenômeno estudado. No ensaio de retração por secagem restringida, a tendência de fissuração dos concretos estudados foi influenciada significativamente pelo consumo de água presente na mistura. Conjuntamente, os resultados obtidos neste ensaio demonstraram que o teor de adição de microfibras de polipropileno é uma variável que deve ser proporcionada como os demais materiais constituintes do traço do concreto, ou seja, a quantidade incorporada no compósito cimentício não pode ser um valor determinado, semelhante para qualquer tipo de concreto. / Volumetric changes present in the cement paste matrix, coming from the processes of hydration and drying of cementitious composites, generate a cracking tendency in the material. In the concrete floor, this cracking tendency is extremely worrying. In this sense, efforts to evaluate the influence of important parameters in the mixture proportions of concrete, for decrease the cracking tendency due to drying shrinkage, it’s extremely valid. So, parameters were assessed like the consumption of water (175l/m³; 190l/m³; 205l/m³), the addition content of polypropylene staple fiber (0g/m³; 300g/m³; 600g/m³; 900g/m³), the type of cement (CP IV; CP V-ARI) and age, different for each test performed. The tests performed for this assessment were the compressive strength, flexural tensile strength, unrestrained drying shrinkage and restrained drying shrinkage. The results of mechanical tests shown the significant influence of the kind of cement and age assessed in the strength of concrete. The addition content of polypropylene staple fiber exerted little influence on the results of mechanical tests, but it was significant, with increases of 5% in the results of compressive strength for the mixtures with addition levels of 300g/m³ e 600g/m³. However for the flexural tensile strength, this parameter didn’t show significant. The water consumption didn’t influence significantly the results of mechanical tests, since the ratio a/c was constant for all concretes studied. In the unrestrained drying shrinkage, the kind of cement didn’t show importance for the results. This behavior also observed for the addition content of polypropylene staple fiber, which didn’t reduce the magnitude of free drying shrinkage. However, the water consumption influenced significantly in the results, demonstrating the existence of a direct relationship between it and the phenomenon studied. In the restrained drying shrinkage, the cracking tendency of the concrete studied was significantly affected by the consumption of water present in the mixture. Together, the results of this test showed that the addition content of polypropylene staple fiber is a parameter that should be provided as the others materials of the concrete mixture, i.e., the amount of polypropylene staple fiber incorporated into the cementitious composite can’t be a value fixed, similar to any type of concrete mixture.

Mudanças volumétricas presentes na matriz cimentícia, oriundas dos processos de hidratação e de secagem do compósito cimentício, geram uma tendência de fissuração no material. Em pisos de concreto, a presença de tal manifestação patológica, decorrente do fenômeno da retração por secagem, é extremamente preocupante. Desta forma, a realização de esforços visando avaliar a influência de materiais constituintes do traço do concreto e seus proporcionamentos, com o intuito de reduzir a tendência de fissuração do material, gerada pelo fenômeno da retração por secagem, é extremamente válida. Para isto, foram avaliados fatores controláveis como o consumo de água (175l/m³; 190l/m³; 205l/m³), o teor de adição de microfibras de polipropileno (0g/m³; 300g/m³; 600g/m³; 900g/m³), o tipo de cimento (CP IV; CP V-ARI) e a idade, variável para cada ensaio realizado. Os ensaios empregados para esta avaliação foram o de resistência à compressão uniaxial, resistência à tração na flexão, retração por secagem livre e retração por secagem restringida. Os resultados dos ensaios mecânicos demonstraram a influência significativa do tipo de cimento e da idade avaliada na resistência do concreto. O teor de adição de microfibras de polipropileno exerceu uma pequena influência, porém significativa, com incrementos de 5% nos resultados mecânicos do ensaio de resistência à compressão uniaxial para os traços com teores de adição de 300g/m³ e 600g/m³. No entanto para o ensaio de resistência à tração na flexão, tal variável não se demonstrou significativa. O fator consumo de água não influenciou significativamente nos resultados correspondentes aos ensaios mecânicos, uma vez que a relação a/c manteve-se constante para todos os concretos estudados. No ensaio de retração por secagem livre, o tipo de cimento não demonstrou significância relevante para os resultados obtidos. Comportamento este, também observado para o teor de adição de microfibras de polipropileno, o qual não reduziu a magnitude da retração por secagem livre. Diferentemente do observado para a variável consumo de água, a qual influenciou significativamente nos dados obtidos, demonstrando a existência de uma relação direta entre a mesma e o fenômeno estudado. No ensaio de retração por secagem restringida, a tendência de fissuração dos concretos estudados foi influenciada significativamente pelo consumo de água presente na mistura. Conjuntamente, os resultados obtidos neste ensaio demonstraram que o teor de adição de microfibras de polipropileno é uma variável que deve ser proporcionada como os demais materiais constituintes do traço do concreto, ou seja, a quantidade incorporada no compósito cimentício não pode ser um valor determinado, semelhante para qualquer tipo de concreto. / Volumetric changes present in the cement paste matrix, coming from the processes of hydration and drying of cementitious composites, generate a cracking tendency in the material. In the concrete floor, this cracking tendency is extremely worrying. In this sense, efforts to evaluate the influence of important parameters in the mixture proportions of concrete, for decrease the cracking tendency due to drying shrinkage, it’s extremely valid. So, parameters were assessed like the consumption of water (175l/m³; 190l/m³; 205l/m³), the addition content of polypropylene staple fiber (0g/m³; 300g/m³; 600g/m³; 900g/m³), the type of cement (CP IV; CP V-ARI) and age, different for each test performed. The tests performed for this assessment were the compressive strength, flexural tensile strength, unrestrained drying shrinkage and restrained drying shrinkage. The results of mechanical tests shown the significant influence of the kind of cement and age assessed in the strength of concrete. The addition content of polypropylene staple fiber exerted little influence on the results of mechanical tests, but it was significant, with increases of 5% in the results of compressive strength for the mixtures with addition levels of 300g/m³ e 600g/m³. However for the flexural tensile strength, this parameter didn’t show significant. The water consumption didn’t influence significantly the results of mechanical tests, since the ratio a/c was constant for all concretes studied. In the unrestrained drying shrinkage, the kind of cement didn’t show importance for the results. This behavior also observed for the addition content of polypropylene staple fiber, which didn’t reduce the magnitude of free drying shrinkage. However, the water consumption influenced significantly in the results, demonstrating the existence of a direct relationship between it and the phenomenon studied. In the restrained drying shrinkage, the cracking tendency of the concrete studied was significantly affected by the consumption of water present in the mixture. Together, the results of this test showed that the addition content of polypropylene staple fiber is a parameter that should be provided as the others materials of the concrete mixture, i.e., the amount of polypropylene staple fiber incorporated into the cementitious composite can’t be a value fixed, similar to any type of concrete mixture.