Os primeiros estudos sobre pavimentos de concreto continuamente armados (PCCA) foram desenvolvidos em zonas cujo clima característico é o temperado (EUA, Holanda e Bélgica), não se tendo estudos técnicos acerca do comportamento do pavimento em ambiente tropical. A premissa de funcionamento do PCCA está baseada na não execução de juntas de retração, obrigatórias em pavimentos de concreto simples (PCS), ou seja, as fissuras devido à retração do concreto ocorrem aleatoriamente, sendo controladas pela elevada taxa de armadura longitudinal disposta longitudinalmente ao longo de toda a extensão do pavimento. Como essa armadura não possui função estrutural, pois é colocada acima da linha neutra da placa, no banzo comprimido, sua função é manter as fissuras fortemente apertadas, garantindo suavidade ao rolamento e elevada transferência de carga (LTE), a qual ocorre pelo intertravamento dos agregados nas faces fissuradas, proporcionando assim um pavimento de alta durabilidade e que dispende baixíssimos custos com manutenção. No Brasil, a primeira experiência com PCCA teve início no ano de 2010, quando foram construídas quatro seções de 50 m de extensão cada, consideradas curtas em comparação aos 400 m de extensão de um PCCA rodoviário que podem ser alcançados ao final de um dia de trabalho. O monitoramento contínuo de tais seções mostrou haver uma diferença muito significativa de comportamento, comparado aos PCCA tradicionais, no que tange o tempo decorrido para estabelecimento do padrão de fissuração (a primeira fissura surgiu um ano após a construção), bem como espaçamento médio entre as fissuras, devido à curta extensão das placas e a inexistência de um sistema de ancoragem nas extremidades. Assim, para melhor compreender o comportamento de pavimentos de concreto com armadura contínua com padrões condizentes à realidade rodoviária em ambiente tropical, em janeiro de 2016, foi construído no campus da Universidade de São Paulo o primeiro PCCA de longa extensão do Brasil, com 200 m de comprimento. Foram empregados quatro diferentes tipos de concreto, variando o tipo de cimento e o tipo de agregado, bem como foram empregados aço galvanizado e aço comum. Para entender o comportamento do pavimento sob as condições climáticas brasileiras foram realizados três estudos: levantamento de fissuras (espaçamento e abertura), modelagem analítica do espaçamento entre fissuras através de modelos de previsão de retração em concreto e testes com FWD para avaliação da eficiência de transferência de carga (LTE) entre as fissuras. A análise do padrão de fissuração mostrou que o desenvolvimento das fissuras aconteceu conforme a literatura técnica, tendo início na primeira semana após a concretagem e atingindo aproximadamente 60% do número total de fissuras antes do primeiro mês. As seções centrais possuem o maior número de fissuras, pois estão ancoradas pelas seções de extremidade, onde o surgimento das fissuras é mais lento por conta da falta de ancoragem. As aberturas das fissuras mostraram-se maiores nas posições com aço galvanizado devido à menor aderência aço-concreto nesse caso, em comparação às posições com aço comum. O modelo de previsão de retração no concreto que melhor se aproximou do espaçamento médio desenvolvido em campo foi o modelo do Eurocode 2, com diferenças em torno de 30%, aproximadamente. As análises de LTE mostraram um desempenho muito satisfatório, apesar de a LTE nas regiões com aço galvanizado ter resultado menor do que a LTE nas regiões com aço comum. / The first studies on continuously reinforced concrete pavements (CRCP) were developed in areas in which the typical weather is temperate (United States, Netherlands and Belgium), with no technical studies carried out in tropical weather. CRCP structural premise is based on a slab without construction joints which are required in jointed plain concrete pavements (JPCP); i.e., CRCP cracks due to concrete shrinkage occur randomly being controlled by the high longitudinal reinforcement percentage, positioned longitudinally along the pavement length. As the longitudinal reinforcement has no structural role, because it is placed above the slab neutral axis, in the compression zone, its main function is to keep cracks strongly tight, ensuring a smooth ride and high load efficiency transfer (LTE) at cracks, which occurs through aggregates interlocking, thereby providing a highly durable pavement with low maintenance costs. The first experience with CRCP in Brazil started in 2010, when four experimental sections were constructed. Each section is 50 meters long, short when compared to the traditional CRCP that can extend for over 400 meters providing that concrete pouring does not stop. Continuous monitoring of these sections has shown that the short CRCP behaves differently from traditional CRCP, regarding the time taken for the cracking pattern full development (the first crack was visible on the surface one year after the construction), as well as average cracking space due to the slab\'s short extension and lack of anchorage. Therefore, in order to fully analyze the behavior of a traditional CRCP under tropical weather, in January 2016, the first long extension CRCP in Brazil was built, at the University of São Paulo campus, with 200 meters length. Four types of concrete were applied in the construction, varying cement and aggregate type. Galvanized and ordinary steel were used as well. To analyze the pavement behavior under Brazilian climatic conditions, three studies were carried out: cracks surveys (spacing and width), analytical modeling crack spacing through shrinkage prediction models and Falling Weight Deflectometer testing to evaluate the crack\'s load transfer efficiency (LTE). Cracking pattern analysis has shown cracks development consistent with technical literature. The first cracks appeared during the first week after concrete placement and, before the first month, about 60% of the total cracks number had developed. Central sections presented greatest number of cracks as they are anchored by the outer sections, where cracking occurs slower due to the lack of anchorage. Cracks width was higher in areas with galvanized steel due to the weaker steel-concrete bond, when compared to areas with common steel. The shrinkage prediction model for concrete that better approached the average field crack spacing was the Eurocode 2, with mean difference of 30%. LTE analysis has shown a quite satisfactory performance, even though LTE in areas with galvanized steel is lower than LTE in areas with common steel.

O objetivo do trabalho é analisar e compreender os efeitos das características do fibrocimento reforçado com fibras sintéticas na retração por secagem deste compósito. A importância social do fibrocimento como material de construção, justifica a realização do presente trabalho, de modo a expor como acontece a retração por secagem neste compósito, e desta forma auxiliar o meio técnico na mitigação das manifestações patológicas relacionadas à retração e contribuindo para a redução do importante problema da indústria produtora de fibrocimento, que é a fissuração de borda nas telhas onduladas. Para tal buscou-se demostrar o efeito da porosidade e distribuição de tamanho de poros na retração por secagem. Além disso, foram realizados experimentos onde se variou o tipo de cimento utilizado, as quantidades de todas as matérias-primas envolvidas, além da aplicação de tratamentos modificadores da movimentação higroscópica, manipulando diretamente a tensão capilar causadora da retração. Concluiu-se que a porosidade elevada do fibrocimento faz com que a retração por secagem deste compósito seja fortemente influenciada pela porosidade total do mesmo, com correlação direta com a quantidade de mesoporos. Além disso, no estudo de caso realizado concluiu-se que a redução da retração devido à redução da tensão superficial da água do poro, se refletiu em menor fissuração de borda nas telhas onduladas. / The objective is to analyze and comprehend the effects of properties of cement based composite reinforced with synthetic fibers, on drying shrinkage of such composite. The social importance of fiber cement as construction material justifies the execution of the present work, in order to expose how drying shrinkage occurs on this composite and by those means to assist the technical community on mitigating pathological manifestations related to shrinkage, thus contributing for the reduction of an important problem on fiber cement industry, the edge cracking on corrugated sheets. In order to achieve this goal, it was sought to demonstrate the effect of porosity and pore size distribution on drying shrinkage. Moreover, experiments were performed, varying the type of cement used and the quantities of all materials involved, in addition to the application of treatments that modify hygroscopic movement, directly manipulating the capillary tension which causes shrinkage. It was concluded that the elevated porosity of the fiber cement causes drying shrinkage of this composite to be strongly influenced by its total porosity, directly correlated to the quantity of mesopores. Furthermore, in the case study performed it was concluded that shrinkage reduction due to the reduction of pore water surface tension was reflected into minor edge cracking on corrugated sheets.

In respect of autogenous and drying shrinkage and the effects of relaxation creep during the hydration cycle, roller compacted concrete in dams has to date been universally assumed to behave in the same manner as conventional mass concrete, despite notional evidence to the contrary on prototype dam structures, particularly in respect of high-paste RCC. While the results of laboratory materials testing and associated early behaviour analyses for RCC have been published, no conclusive example exists in the public domain whereby predicted behaviour is confirmed through measured behaviour on a comprehensively-instrumented prototype dam structure. In his PhD thesis, Quentin Shaw presents evidence to indicate that the early behaviour of RCC, and particularly high quality, high-paste RCC in dams, is quite different to that of CVC. Referring to instrumentation records from Wolwedans and Knellpoort dams in South Africa, Çine Dam in Turkey, Wadi Dayqah Dam in Oman and Changuinola 1 Dam in Panama, indications of less than expected shrinkage and stress relaxation creep during the hydration cycle in the constituent RCC are documented. Taking the comprehensively-instrumented and monitored Wolwedans Dam, the actual materials behaviour of the constituent RCC is evaluated through the replication of the prototype behaviour on a finite element model. Through this analysis, it is clearly demonstrated that the level of shrinkage and stress relaxation creep that would be traditionally assumed in RCC simply did not occur. In fact, the analyses suggested that no shrinkage, or creep was apparent. The reasons for the different behaviour of high-paste RCC compared to CVC are subsequently explored. With Wadi Dayqah Dam as the only example evaluated where some drying shrinkage and/or stress relaxation creep was obviously apparent, the evident susceptibility of this lean RCC mix, with a high w/c ratio, a high content of non-cementitious fines, natural gravel aggregates, a high aggregate water absorption and placement in a very dry environment, is noted. However, it is considered to be the combination of a strong aggregate skeletal structure developed through roller compaction and a low w/c ratio that results in a particularly resilience in high-paste RCC to early shrinkage and creep. It is also recognised that temperature and gravity effects in an arch dam structure will tend to limit, or even eliminate containment stresses in the critical load-carrying upper section and that this will reduce the risk and impact of stress relaxation creep. Consequently, a new understanding of the early behaviour of RCC in large dams is presented, suggesting that a high quality RCC mix in an arch dam can be designed for a cumulative shrinkage and stress relaxation creep under the hydration cycle of approximately 20 microstrain, compared with a more traditionally accepted value of between 125 and 200 microstrain. The implications of these findings on the design of large RCC dams are demonstrated to be significant, particularly in respect of RCC arch dams. In addition, suggestions are made for the requirements in respect of RCC mix design for negligible shrinkage and creep, while an approach to combine the use of field measurement with structural modelling to predict and demonstrate actual RCC behaviour is briefly discussed. / Thesis (PhD)--University of Pretoria, 2011. / Civil Engineering / unrestricted

Alkali activated materials, especially when activated with waterglass, are subjected to substantial drying shrinkage that hinders their broader industrial application. The effect of shrinkage reducing admixtures (SRA), based on poly(propylene glycol), on drying shrinkage of alkali activated blast furnace slag (BFS) mortars was studied. The aim of this thesis is to determine the efficiency of SRA as well as the influence of different type of alkali activator with varying silicate modulus on drying shrinkage characteristics. It was observed that the high amount of alkalis positively influenced the effect of SRA. The higher the amount of alkalis, the lower the drying shrinkage was. It also caused more water to be incorporated in the alkali activated structure and prevent it from evaporation. Thus, the weight change of such mortars was the lowest. Reduced effect of SRA on mechanical strength properties was observed in mortars with low amount of alkalis which was connected with delayed hydration resulting in insufficient amount of created C-S-H gel. The presented thesis further discussed and underlines the role of different kinds of alkali ions as well as their amount on the properties of alkali activated BFS systems.

Volume changes are one of the priority characteristics of concrete that plays an important role place mainly in the durability of structures as such. These low volume changes are required especially for structures as: industrial concrete floors, massive structures and waterproof structures. One of the possibilities in reducing these changes is the use of mineral admixtures with suitable grain curve of aggregate. Another possibility is the use of shrinkage reducing admixtures. There can occur problem with efficiency (long term age) with other components of the mixture. Therefore, the effort of this work is to use the avaible processes for maximum reduction of shrinkage and hydration temperatures.

[EN] The test for determining the resonance frequencies has traditionally been used to investigate the mechanical integrity of concrete cores, to assess the conformity of concrete constituents in different accelerated durability tests, and to ascertain constitutive properties such as the elastic modulus and the damping factor. This nondestructive technique has been quite appealed for evaluation of mechanical properties in all kinds of durability tests. The damage evolution is commonly assessed from the reduction of dynamic modulus which is produced as a result of any cracking process. However, the mechanical behavior of concrete is intrinsically nonlinear and hysteretic. As a result of a hysteretic stress-strain behavior, the elastic modulus is a function of the strain. In dynamic tests, the nonlinearity of the material is manifested by a decrease of the resonance frequencies, which is inversely proportional to the excitation amplitude. This phenomenon is commonly referred as fast dynamic effect. Once the dynamic excitation ceases, the material undergoes a relaxation process whereby the elastic modulus is restored to that at rest. This phenomenon is termed as slow dynamics. These phenomena (fast and slow dynamics) find their origin in the internal friction of the material. Therefore, in cement-based materials, the presence of microcracks and interfaces between its constituents plays an important role in the material nonlinearity. In the context of the assessment of concrete durability, the damage evolution is based on the increase of hysteresis, as a result of any cracking process. In this thesis three different nondestructive techniques are investigated, which use impacts for exciting the resonant frequencies. The first technique consists in determining the resonance frequencies over a range of impact forces. The technique is termed Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). It consists in ascertaining the downward resonant frequency shift that the material undergoes upon increasing excitation amplitude. The second technique consists in investigating the nonlinear behavior by analyzing the signal corresponding to a single impact. This is, to determine the instantaneous frequency, amplitude and attenuation variations corresponding to a single impact event. This technique is termed as Nonlinear Resonant Acoustic Single Impact Spectroscopy (NSIRAS). Two techniques are proposed to extract the nonlinear behavior by analyzing the instantaneous frequency variations and attenuation over the signal ring down. The first technique consists in discretizing the frequency variation with time through a Short-Time Fourier Transform (STFT) based analysis. The second technique consists of a least-squares fit of the vibration signals to a model that considers the frequency and attenuation variations over time. The third technique used in this thesis can be used for on-site evaluation of structures. The technique is based on the Dynamic Acousto- Elastic Test (DAET). The variations of elastic modulus as derived through NIRAS and NSIRAS techniques provide an average behavior and do not allow derivation of the elastic modulus variations over one vibration cycle. Currently, DAET technique is the only one capable to investigate the entire range of nonlinear phenomena in the material. Moreover, unlike other DAET approaches, this study uses a continuous wave source as probe. The use of a continuous wave allows investigation of the relative variations of the elastic modulus, as produced by an impact. Moreover, the experimental configuration allows one-sided inspection. / [ES] El ensayo de determinación de las frecuencias de resonancia ha sido tradicionalmente empleado para determinar la integridad mecánica de testigos de hormigón, en la evaluación de la conformidad de mezclas de hormigón en diversos ensayos de durabilidad, y en la terminación de propiedades constitutivas como son el módulo elástico y el factor de amortiguamiento. Esta técnica no destructiva ha sido ampliamente apelada para la evaluación de las propiedades mecánicas en todo tipo de ensayos de durabilidad. La evolución del daño es comúnmente evaluada a partir de la reducción del módulo dinámico, producido como resultado de cualquier proceso de fisuración. Sin embargo, el comportamiento mecánico del hormigón es intrínsecamente no lineal y presenta histéresis. Como resultado de un comportamiento tensión-deformación con histéresis, el módulo elástico depende de la deformación. En ensayos dinámicos, la no linealidad del material se manifiesta por una disminución de las frecuencias de resonancia, la cual es inversamente proporcional a la amplitud de excitación. Este fenómeno es normalmente denominado como dinámica rápida. Una vez la excitación cesa, el material experimenta un proceso de relajación por el cual, el módulo elástico es restaurado a aquel en situación de reposo. Este fenómeno es denominado como dinámica lenta. Estos fenómenos ¿dinámicas rápida y lenta¿ encuentran su origen en la fricción interna del material. Por tanto, en materiales basados en cemento, la presencia de microfisuras y las interfaces entre sus constituyentes juegan un rol importante en la no linealidad mecánica del material. En el contexto de evaluación de la durabilidad del hormigón, la evolución del daño está basada en el incremento de histéresis, como resultado de cualquier proceso de fisuración. En esta tesis se investigan tres técnicas diferentes las cuales utilizan el impacto como medio de excitación de las frecuencias de resonancia. La primera técnica consiste en determinar las frecuencias de resonancia a diferentes energías de impacto. La técnica es denominada en inglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Ésta consiste en relacionar el detrimento que el material experimenta en sus frecuencias de resonancia, con el aumento de la amplitud de la excitación. La segunda técnica consiste en investigar el comportamiento no lineal mediante el análisis de la señal correspondiente a un solo impacto. Ésta consiste en determinar las propiedades instantáneas de frecuencia, atenuación y amplitud. Esta técnica se denomina, en inglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Se proponen dos técnicas de extracción del comportamiento no lineal mediante el análisis de las variaciones instantáneas de frecuencia y atenuación. La primera técnica consiste en la discretización de la variación de la frecuencia con el tiempo, mediante un análisis basado en Short-Time Fourier Transform (STFT). La segunda técnica consiste en un ajuste por mínimos cuadrados de las señales de vibración a un modelo que considera las variaciones de frecuencia y atenuación con el tiempo. La tercera técnica empleada en esta tesis puede ser empleada para la evaluación de estructuras in situ. La técnica se trata de un ensayo acusto-elástico en régimen dinámico. En inglés Dynamic Acousto-Elastic Test (DAET). Las variaciones del módulo elástico obtenidas mediante los métodos NIRAS y NSIRAS proporcionan un comportamiento promedio y no permiten derivar las variaciones del módulo elástico en un solo ciclo de vibración. Actualmente, la técnica DAET es la única que permite investigar todo el rango de fenómenos no lineales en el material. Por otra parte, a diferencia de otras técnicas DAET, en este estudio se emplea como contraste una onda continua. El uso de una onda continua permite investigar las variaciones relativas del módulo elástico, para una señal transito / [CA] L'assaig de determinació de les freqüències de ressonància ha sigut tradicionalment empleat per a determinar la integritat mecànica de testimonis de formigó, en l'avaluació de la conformitat de mescles de formigó en diversos assajos de durabilitat, i en la terminació de propietats constitutives com són el mòdul elàstic i el factor d'amortiment. Esta tècnica no destructiva ha sigut àmpliament apel·lada per a l'avaluació de les propietats mecàniques en tot tipus d'assajos de durabilitat. L'evolució del dany és comunament avaluada a partir de la reducció del mòdul dinàmic, produït com resultat de qualsevol procés de fisuración. No obstant això, el comportament mecànic del formigó és intrínsecament no lineal i presenta histèresi. Com resultat d'un comportament tensió-deformació amb histèresi, el mòdul elàstic depén de la deformació. En assajos dinàmics, la no linealitat del material es manifesta per una disminució de les freqüències de ressonància, la qual és inversament proporcional a l'amplitud d'excitació. Este fenomen és normalment denominat com a dinàmica ràpida. Una vegada l'excitació cessa, el material experimenta un procés de relaxació pel qual, el mòdul elàstic és restaurat a aquell en situació de repòs. Este fenomen és denominat com a dinàmica lenta. Estos fenòmens --dinámicas ràpida i lenta troben el seu origen en la fricció interna del material. Per tant, en materials basats en ciment, la presència de microfissures i les interfícies entre els seus constituents juguen un rol important en la no linealitat mecànica del material. En el context d'avaluació de la durabilitat del formigó, l'evolució del dany està basada en l'increment d'histèresi, com resultat de qualsevol procés de fisuración. En esta tesi s'investiguen tres tècniques diferents les quals utilitzen l'impacte com a mitjà d'excitació de les freqüències de ressonància. La primera tècnica consistix a determinar les freqüències de ressonància a diferents energies d'impacte. La tècnica és denominada en anglés: Nonlinear Impact Resonant Acoustic Spectroscopy (NIRAS). Esta consistix a relacionar el detriment que el material experimenta en les seues freqüències de ressonància, amb l'augment de l'amplitud de l'excitació. La segona tècnica consistix a investigar el comportament no lineal per mitjà de l'anàlisi del senyal corresponent a un sol impacte. Esta consistix a determinar les propietats instantànies de freqüència, atenuació i amplitud. Esta tècnica es denomina, en anglés, Nonlinear Single Impact Resonant Acoustic Spectroscopy (NSIRAS). Es proposen dos tècniques d'extracció del comportament no lineal per mitjà de l'anàlisi de les variacions instantànies de freqüència i atenuació. La primera tècnica consistix en la discretización de la variació de la freqüència amb el temps, per mitjà d'una anàlisi basat en Short-Time Fourier Transform (STFT). La segona tècnica consistix en un ajust per mínims quadrats dels senyals de vibració a un model que considera les variacions de freqüència i atenuació amb el temps. La tercera tècnica empleada en esta tesi pot ser empleada per a l'avaluació d'estructures in situ. La tècnica es tracta d'un assaig acusto-elástico en règim dinàmic. En anglés Dynamic Acousto-Elastic Test (DAET). Les variacions del mòdul elàstic obtingudes per mitjà dels mètodes NIRAS i NSIRAS proporcionen un comportament mitjà i no permeten derivar les variacions del mòdul elàstic en un sol cicle de vibració. Actualment, la tècnica DAET és l'única que permet investigar tot el rang de fenòmens no lineals en el material. D'altra banda, a diferència d'altres tècniques DAET, en este estudi s'empra com contrast una ona contínua. L'ús d'una ona contínua permet investigar les variacions relatives del mòdul elàstic, per a un senyal transitori. A més, permet la inspecció d'elements per mitjà de l'accés per una sola cara. / Eiras Fernández, JN. (2016). Studies on nonlinear mechanical wave behavior to characterize cement based materials and its durability [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/71439 / TESIS / Premios Extraordinarios de tesis doctorales