En los últimos años, el análisis numérico de problemas acoplados, como los procesos de degradación de materiales y estructuras relacionados con los efectos medioambientales, ha cobrado especial importancia en la comunidad científica de la mecánica del hormigón. Problemas de este tipo son por ejemplo el ataque químico, el efecto de altas temperaturas o la retracción por secado.Tradicionalmente, los análisis acoplados existentes en la literatura se han realizado a nivel macroscópico, considerando el material como un medio continuo y homogéneo. Sin embargo, es bien conocido que el origen de la degradación observada a nivel macroscópico, a menudo es debida a la interacción entre los áridos y el mortero, sobre todo cuando se dan cambios de volumen diferenciales entre los dos componentes. Esta es la razón por la que el análisis mesomecánico está emergiendo como una herramienta potente para estudios de materiales heterogéneos, aunque actualmente existen escasos modelos numéricos capaces de simular un problema acoplado a esta escala de observación.En esta tesis, la aplicabilidad del modelo meso-mecánico de elementos finitos, desarrollado en el seno del grupo de investigación durante los últimos quince años, se extiende al análisis de problemas acoplados higro-mecánicos y químico-mecánicos, con el fin de estudiar la retracción por secado y el ataque sulfático externo en muestras de hormigón. La generación numérica de mesogeometrías y mallas de elementos finitos con los áridos de mayor tamaño rodeados de la fase mortero se consigue mediante la teoría de Voronoï/Delaunay Adicionalmente, con el fin de simular las principales trayectorias de fisuración, se insertan a priori elementos junta de espesor nulo, equipados con una ley constitutiva basada en la mecánica de fractura no lineal, a lo largo de todos los contactos entre árido y matriz, y también en algunas líneas matriz-matriz.La aportación principal de esta tesis es, conjuntamente con la realización de análisis acoplados sobre una representación mesoestructural del material, la simulación no solo de la formación y propagación de fisuras, sino también la consideración explícita de la influencia de éstas en el proceso de difusión.Los cálculos numéricos se realizan mediante el uso de los códigos de elementos finitos DRAC y DRACFLOW, previamente desarrollados en el seno del grupo de investigación, y acoplados mediante una estrategia staggered. Las simula-ciones realizadas abarcan, entre otros aspectos, la evaluación del compor-tamiento acoplado, el ajuste de parámetros del modelo con resultados experimentales disponibles en la bibliografía, diferentes estudios del efecto de los áridos en la microfisuración inducida por el secado y las expansiones debidas al ataque sulfático, así como el efecto simultáneo de los procesos gobernados por difusión y cargas de origen mecánico. Los resultados obtenidos concuerdan con observaciones experimentales de la fisuración, el fenómeno de spalling y la evolución de las deformaciones, y muestran la capacidad del modelo para ser utilizado en el estudio de problemas acoplados en los que la naturaleza heterogénea y cuasi-frágil del material tiene un papel predominante.

The influence of drying parameters namely residence time before drying, drying temperature, drying time, relative humidity, and slip recipe on the drying rate of slip cast sanitary wares, predominantly lavatories and toilet closets, was studied. The drying temperatures were changed from 80 oC to 110 oC with an increment of 10 oC. The drying time was changed from 10 to 7 h with a decrease of 1 hour. Relative humidity of the environment was changed from 60 to 75 %. The percent weight loss, percent residual moisture and the percent shrinkage of the samples were determined by weighing and measuring the samples before and after the tests. The percent weight loss was within the range of 6.5 to 6.6 % after holding the as cast samples for 6 hours at ambient casting shop conditions while it was within the range of 17.96 to 18.10 % when subsequently dried for 10 hours at 110 oC in the dryer. The percent shrinkage was within the range of 2.9 - 3.0 % after holding the as cast samples 6 h at ambient laboratory conditions. No shrinkage was observed in the sample when it was subsequently dried for 10 hours at 110 oC in the dryer. Optimum moisture content of dried wares was obtained after drying for 8 hours at 100 oC in the dryer. It has been seen that the relative humidity of the dryer at the beginning of the drying should be lower than 75 %. As the non-plastic content in the recipe of the sanitary ware slip increased, drying shrinkage and residual moisture content decreased. The results of this study showed that through increasing the residence time up to 6h with a casting shop environment of approximately 30 oC and 60 % relative humidity, the drying time could be safely reduced from 10 h to 8 h with a drying temperature of 100 oC for the test plates. The same approach can be used for more complex shapes, e.g., WC closets, basins, tanks etc. in EczacibaSi Vitra plant. Once the drying time was reduced, the amount of natural gas per ware would be reduced to a certain extent. Aside from that the reduction in the drying time would increase the quantity of the drying cycles per week so that more wares could be dried. When all these observations were taken into account, this thesis study could also be utilized by other sanitary ware producing companies whose processes require slip cast drying.

Apesar dos avanços tecnológicos e do conhecimento disponível sobre o concreto e suas propriedades, muitas estruturas apresentam-se degradadas prematuramente. Assim, são necessárias frequentes intervenções para reparo havendo, em consequência, consumo de quantidades expressivas de materiais, com importantes impactos financeiros e ambientais. A preocupação crescente com o desempenho das estruturas de concreto tem incentivado vários segmentos da sociedade a buscarem soluções que assegurem sua durabilidade. Nesse sentido, muitas pesquisas acadêmicas vêm sendo desenvolvidas para melhor entender o comportamento do concreto frente a diferentes condições de uso, considerando-se suas propriedades mecânicas e de durabilidade. Esta pesquisa teve por objetivo analisar o desempenho de concretos frente à retração por secagem, após terem sido submetidos ao pré-carregamento. Foram utilizados os cimentos CP V ARI e CP IV, nas relações a/c 0,35, 0,50 e 0,70, e adotadas as idades de cura de 7 e 28 dias. Nas idades 1, 3 e 7 dias, os concretos foram submetidos a carregamentos de 25%, 50% e 75% da carga média de ruptura à tração na flexão (NBR 12142, ABNT, 2010). Realizou-se o ensaio para determinação da retração por secagem (ASTM C157/C157M-08, 2014e1), em concretos de referência e nos pré-carregados. Foram também realizadas análises complementares, como determinação da velocidade da onda ultrassônica (NBR 8802, ABNT, 2013), porosimetria por intrusão de mercúrio e microtomografia de raios X. Comparando-se o desempenho dos concretos pré-carregados ao dos concretos de referência, o cimento CP V ARI apresentou redução da retração média, exceto para a relação a/c 0,35 com cura de 7 dias. Nos concretos com cimento CP IV, a retração média diminuiu para a relação a/c 0,70, com ambas as idades de cura. O pré-carregamento provocou, em maior ou menor grau, a associação de dois diferentes efeitos. Por um lado, a compactação ocasionou a quebra dos compostos menos resistentes da matriz, havendo um efeito físico de redução dos vazios capilares, além da exposição de grãos anidros. Em paralelo, ocorreu a microfissuração do concreto, favorecendo, também, a exposição de grãos anidros. A cura por imersão possibilitou a continuidade da hidratação, com a formação de novos produtos resistentes na matriz, reduzindo as porosidades total e efetiva e, portanto, a taxa da retração do concreto. Além da densificação da matriz, a cura prolongada possibilitou a hidratação dos grãos anidros de cimento expostos nas paredes das microfissuras, favorecendo a sua autocicatrização (self-healing), o que contribuiu com a recuperação da capacidade resistente dos concretos, frente aos esforços da secagem. Assim, a associação destes fatores promoveu a redução da retração por secagem nos concretos estudados, principalmente nos mais porosos. / The growing concern with the performance of structures has encouraged several segments of society to find solutions to improve concrete durability. Several studies have been made to provide a better understanding of the mechanical properties and concrete durability in different conditions. This study assessed the drying shrinkage performance of preloaded concrete. Cement types CP V ARI, equivalent to Portland type III (ASTM C150/C150M-16e1) and CP IV, equivalent to Portland type IP (ASTM C595/C595M-16) were used with w/b = 0.35, 0.50 and 0.70 and curing ages of 7 and 28 days. At the ages of 1, 3 and 7 days, concrete mixes were subject to loads of 25%, 50% and 75% of their mean ultimate flexural strength (Brazilian Standard NBR 12142, ABNT, 2010). Drying shrinkage in reference and preloaded concrete was determined according to ASTM C157/C157M-14e1. Additional tests included ultrasound pulse velocity (NBR 8802, ABNT, 2013), mercury intrusion porosimetry (MIP) and X-ray microtomography. Preloaded CP V ARI cement concrete showed a drop in mean shrinkage when compared with the reference mix, except for the mix with w/b = 0.35 cured for 7 days. For CP IV cement, mean shrinkage dropped with w/b =0.70 for both curing ages. Early loading caused a compaction effect, promoting the weakest compounds of the matrix to be broken, filling the capillary voids. In this process some unhydrous grains probably were exposed. On the other hand, microcracking also occurred, lefting unhydrated grains exposed in the microcracks walls. Due to immersion curing, the availability of water promoted the hydration continuity. New resistant hydrates filled the large voids and reduced the total and effective porosities in the cement matrix. The hydration of anhydrous grains in the microcracks walls had led to self-healing, with partial resistance capacity recovery. The combined effect of these factors promoted the drying shrinkage reducing, mainly for the more porous concrets.

Apesar dos avanços tecnológicos e do conhecimento disponível sobre o concreto e suas propriedades, muitas estruturas apresentam-se degradadas prematuramente. Assim, são necessárias frequentes intervenções para reparo havendo, em consequência, consumo de quantidades expressivas de materiais, com importantes impactos financeiros e ambientais. A preocupação crescente com o desempenho das estruturas de concreto tem incentivado vários segmentos da sociedade a buscarem soluções que assegurem sua durabilidade. Nesse sentido, muitas pesquisas acadêmicas vêm sendo desenvolvidas para melhor entender o comportamento do concreto frente a diferentes condições de uso, considerando-se suas propriedades mecânicas e de durabilidade. Esta pesquisa teve por objetivo analisar o desempenho de concretos frente à retração por secagem, após terem sido submetidos ao pré-carregamento. Foram utilizados os cimentos CP V ARI e CP IV, nas relações a/c 0,35, 0,50 e 0,70, e adotadas as idades de cura de 7 e 28 dias. Nas idades 1, 3 e 7 dias, os concretos foram submetidos a carregamentos de 25%, 50% e 75% da carga média de ruptura à tração na flexão (NBR 12142, ABNT, 2010). Realizou-se o ensaio para determinação da retração por secagem (ASTM C157/C157M-08, 2014e1), em concretos de referência e nos pré-carregados. Foram também realizadas análises complementares, como determinação da velocidade da onda ultrassônica (NBR 8802, ABNT, 2013), porosimetria por intrusão de mercúrio e microtomografia de raios X. Comparando-se o desempenho dos concretos pré-carregados ao dos concretos de referência, o cimento CP V ARI apresentou redução da retração média, exceto para a relação a/c 0,35 com cura de 7 dias. Nos concretos com cimento CP IV, a retração média diminuiu para a relação a/c 0,70, com ambas as idades de cura. O pré-carregamento provocou, em maior ou menor grau, a associação de dois diferentes efeitos. Por um lado, a compactação ocasionou a quebra dos compostos menos resistentes da matriz, havendo um efeito físico de redução dos vazios capilares, além da exposição de grãos anidros. Em paralelo, ocorreu a microfissuração do concreto, favorecendo, também, a exposição de grãos anidros. A cura por imersão possibilitou a continuidade da hidratação, com a formação de novos produtos resistentes na matriz, reduzindo as porosidades total e efetiva e, portanto, a taxa da retração do concreto. Além da densificação da matriz, a cura prolongada possibilitou a hidratação dos grãos anidros de cimento expostos nas paredes das microfissuras, favorecendo a sua autocicatrização (self-healing), o que contribuiu com a recuperação da capacidade resistente dos concretos, frente aos esforços da secagem. Assim, a associação destes fatores promoveu a redução da retração por secagem nos concretos estudados, principalmente nos mais porosos. / The growing concern with the performance of structures has encouraged several segments of society to find solutions to improve concrete durability. Several studies have been made to provide a better understanding of the mechanical properties and concrete durability in different conditions. This study assessed the drying shrinkage performance of preloaded concrete. Cement types CP V ARI, equivalent to Portland type III (ASTM C150/C150M-16e1) and CP IV, equivalent to Portland type IP (ASTM C595/C595M-16) were used with w/b = 0.35, 0.50 and 0.70 and curing ages of 7 and 28 days. At the ages of 1, 3 and 7 days, concrete mixes were subject to loads of 25%, 50% and 75% of their mean ultimate flexural strength (Brazilian Standard NBR 12142, ABNT, 2010). Drying shrinkage in reference and preloaded concrete was determined according to ASTM C157/C157M-14e1. Additional tests included ultrasound pulse velocity (NBR 8802, ABNT, 2013), mercury intrusion porosimetry (MIP) and X-ray microtomography. Preloaded CP V ARI cement concrete showed a drop in mean shrinkage when compared with the reference mix, except for the mix with w/b = 0.35 cured for 7 days. For CP IV cement, mean shrinkage dropped with w/b =0.70 for both curing ages. Early loading caused a compaction effect, promoting the weakest compounds of the matrix to be broken, filling the capillary voids. In this process some unhydrous grains probably were exposed. On the other hand, microcracking also occurred, lefting unhydrated grains exposed in the microcracks walls. Due to immersion curing, the availability of water promoted the hydration continuity. New resistant hydrates filled the large voids and reduced the total and effective porosities in the cement matrix. The hydration of anhydrous grains in the microcracks walls had led to self-healing, with partial resistance capacity recovery. The combined effect of these factors promoted the drying shrinkage reducing, mainly for the more porous concrets.

Os resíduos de concreto apresentam grande potencial para serem reciclados quando comparados com outros resíduos, entretanto, o número de estudos realizados no Brasil é muito pequeno dificultando a utilização deste material em dosagens estruturais. Em virtude disso, desenvolveu-se um estudo teórico-experimental visando caracterizar algumas propriedades do agregado e do concreto reciclado; no estudo teórico exploraram-se aspectos relacionados à geração, deposição, processos para recuperação, britagem, casos práticos, pesquisas envolvendo reciclados de concreto e as recomendações normativas existentes. No desenvolvimento experimental, analisou-se a influência do período decorrido entre a moldagem e a reciclagem do concreto nas propriedades dos agregados e concretos. Os resultados indicam que resíduos reciclados logo após sua geração, contribuem positivamente para as propriedades mecânicas do concreto, devido à existência de grande quantidade de partículas não-hidratadas de cimento, tais concretos obtiveram resultados superiores para a resistência à compressão e tração quando comparados aos concretos com agregados naturais. / The concrete residues show a large potential to be recycled when compared with other residues; however, the number of studies in Brazil is very small hindering the use of this material in structural dosage. By virtue of that, it was developed a theoretical-experimental study to characterize some properties of aggregate and recycled concrete; in the theoretical study it was explored aspects related to the generation, deposition, processes for recovery, crushing, practical cases, researches involving recycled of concrete and the existent normative recommendations. In the experimental development, it was analyzed the influence of the period elapsed between the molding and the recycling of the concrete in the properties of the aggregates and concretes. The results indicate that residues recycled soon after generation, these contribute positively to the mechanical properties of the concrete due to the existence of large amount of nonhydrated cement particles, such concretes obtained results superiors for the compression strenght and tensile strenght when compared to the concretes with natural aggregates.

The Soil Water Retention Curve (SWRC) of different soils has been researched thoroughly by multiple Geotechnical Engineers. The interpretation of the SWRC for a specific soil leads to the identification of certain properties of the soil. The SWRC typically involves a plot of suction measurements (on a logarithmic scale) against the volumetric water content or degree of saturation of the soil. This project aims to determine a manner in which concrete properties (such as durability, porosity, shrinkage, strength and stiffness) can be estimated through suction measurements. The Dew Point PotentiaMeter (WP4C) apparatus was used to measure the suctions of different concrete mixtures, as well as to derive the water retention curve of concrete. A cement paste study was first conducted to determine whether this apparatus is able to deliver representative results, which it is. It was discovered that the water retention curve of concrete is similar to a bimodal SWRC identified by Geotechnical Engineers. Thereafter, a mortar study was completed to determine if the water retention curves can be used to estimate different concrete properties. Three different porosity tests were investigated during this research study, namely the X-ray test, the Mercury Intrusion Porosimetry (MIP) test and a simple test method described in the durability index testing procedure manual assembled by University of Cape Town, University of the Witwatersrand and CoMSIRU. It was concluded that the MIP test and the simple test method described in the durability index testing procedure manual gave the most comparable results with regards to literature. The shrinkage of the concrete mixture was investigated to determine a relationship between the suctions and the shrinkage of the concrete. Different strength tests of all the concrete mixtures were also investigated, namely the flexural test, the compressive test, the splitting cylinder test and the E-value test (stiffness). It was concluded that there was a definite trend between the suction measurements and the specific concrete properties tested. The water retention curve has the potential to describe various properties of different concrete mixtures. / Dissertation (MEng (Structural Engineering))--University of Pretoria, 2020. / Civil Engineering / MEng (Structural Engineering) / Unrestricted

The present research is conducted to investigate long term (more than two years) free and confined drying shrinkage magnitude and behaviour of self-compacting concrete (SCC) and compare with normal concrete (NC). For all SCCs mixes, Portland cement was replaced with 0-60% of fly ash (FA), fine and coarse aggregates were kept constant at 890 kg/m3 and 780 kg/m3, respectively. Two different water binder ratios of 0.44 and 0.33 were examined for both SCCs and NCs. Fresh properties of SCCs such as filling ability, passing ability, viscosity and resistance to segregation and hardened properties such as compressive and flexural strengths, water absorption and density of SCCs and NCs were also determined. Experimental results of free drying shrinkage obtained from this study together with collected comprehensive database from different sources available in the literature were compared to five existing models, namely the ACI 209R-92 model, BSEN-92 model, ACI 209R-92 (Huo) model, B3 model, and GL2000 model. To assess the quality of predictive models, the influence of various parameters (compressive strength, cement content, water content and relative humidity) on the drying shrinkage strain are studied. An artificial neural network models (ANNM) for prediction of drying shrinkage strains of SCC was developed using the same data used in the existing models. Two ANNM sets namely ANNM1 and ANNM2 with different numbers of hidden layer neurones were constructed. Comparison between the results given by the ANNM1 model and the results obtained by the five existing predicted models were presented. The results showed that, using up to 60% of FA as cement replacement can produce SCC with a compressive strength as high as 30 MPa and low drying shrinkage strain. SCCs long-term drying shrinkage from 356 to 1000 days was higher than NCs. Concrete filled elliptical tubes (CFET) with self-compacting concrete containing FA up to 60% are recommended for use in construction in order to prevent confined drying strain. ACI 209R-92 model provided a better prediction of drying shrinkage compared with the other four models. However, a very high predictability with high accuracy was achieved with the ANNM1 model with a mean of 1.004. Moreover, by using ANNM models, it is easy to insert any of factors effecting drying shrinkage to the input parameters to predict drying shrinkage strain of SCC. / Ministry of Higher Education, Libya

Yes / As a viable option to upcycle construction and demolition waste (CDW) into value-added materials, geopolymer technology is emerging. Most studies investigate CDWs in a separated form or in combination with mainstream pozzolanic/cementitious materials focusing only on fundamental properties of geopolymer pastes, not considering to scale such materials to the level of their application in the forms of structural mortars/concretes or to characterize long-term performance/durability. This study investigated the development and characterization of ambient-cured mortars with mixed CDW-based geopolymer binders and untreated fine recycled concrete aggregates (FRCA). Mixture of CDW-based roof tile (RT), red clay brick (RCB), hollow brick (HB), concrete (C), and glass (G) was used as the precursor, while ground granulated blast furnace slag (S) was used in some mixtures to partly replace CDW precursors. Compressive strength, durability-related parameters including drying shrinkage, water absorption, and efflorescence, microstructure and materials sustainability were evaluated. Results showed that 28 d compressive strength results above 30 and 50 MPa is achievable with the entirely CDW-based and slag-substituted mortars, which were found improvable to have entirely CDW-based structural concretes. Drying shrinkage of the mortars is slightly higher than that of conventional cementitious/geopolymeric systems although it can be minimized significantly through mixture optimization. Water absorption values remain comparable with the literature. CDW-based geopolymer mortars outperform Portland cement mortars in terms of CO2 emission and energy requirement. Our findings show that via utilizing CDW-based constituents in mixed form as precursor and waste aggregates, it is possible to develop greener construction materials with acceptable strength and long-term performance. / This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 894100. The authors also wish to acknowledge the support of the Scientific and Technical Research Council (TUBITAK) of Turkey provided under project: 117M447.

Yes / The focus of the construction industry has shifted towards the development of al-ternative, eco-friendly and green construction materials due to the energy-inefficient and carbon-intensive nature of Portland cement (PC) production and aggregate quarrying. Meanwhile, increased number of repetitive re-pair/renovation/maintenance activities and demolition operations for the end-of-life buildings generate significant amounts of construction and demolition waste (CDW). For the purposes of sustainability and upcycling wastes into high-value-added materials with improved greenness, components from CDW streams can be used in producing geopolymer concretes without using PC and natural aggre-gates, given the rich aluminosiliceous nature of CDW components. The focus of current work is therefore on the analysis of durability of aspects (i.e., drying shrinkage and resistance against sulfate attack, cyclic freezing-thawing, and chlo-ride penetration) of geopolymer concretes made entirely of CDW. Different types of bricks, tile, concrete, and glass were used in mixed form as precursors for ge-opolymerization while different-size grains of waste concrete were used as recy-cled aggregates. As alkali activators, sodium hydroxide, calcium hydroxide and sodium silicate were used. In a companion mixture, CDW-based precursors were replaced with slag and class-F fly ash. Results showed that sulfate and cyclic freeze-thaw exposure did not cause any noticeable weight and compressive strength loss in CDW-based geopolymer concretes, while chloride penetration was found comparable to PC-based concrete. While drying shrinkage was found high in entirely CDW-based geopolymer concrete and resulted in surface mi-crocracks, it was possible to lower the drying shrinkage substantially via substi-tution of CDW-based precursors with fly ash and slag. / The authors also wish to thank the support of Scientific and Technical Research Council (TUBITAK) of Turkey provided under projects: 218M102 and 117M447. / This paper is from the fib Symposium 2023, Building for the future: Durable, Sustainable, Resilient. 5-7 Jun, Istanbul, Turkey.

O objetivo deste trabalho é controlar a incidência de fissuras em fibrocimentos aplicando o conceito de materiais com gradação funcional através da protensão química gerada pela aplicação de silicato de sódio alcalino entre as camadas dos fibrocimentos. Atualmente é bastante comum os fibrocimentos apresentarem fissuras ao longo das bordas devido aos gradientes de umidade gerados durante a estocagem das pilhas de telhas no pátio das indústrias. O potencial da protensão química foi avaliado através da porosidade total, da quantificação das fases hidratadas, da retração por secagem e do desempenho mecânico. A aplicação de silicato de sódio alcalino no ligante CPII F provocou retração por secagem 1,5 vezes maior que a referência aos 91 dias. O módulo de ruptura (MOR) não sofreu alteração, mas o limite de proporcionalidade da matriz (LOP) aumentou em torno de 95%. O módulo de elasticidade dinâmico foi 13 % maior. O aumento da retração por secagem e o ganho de desempenho mecânico apontam o potencial da protensão química para o controle da fissuração em fibrocimentos produzidos pelo processo Hatschek. / The objective of this work is controlling the incidence of cracks in fiber cement, using the concept of functionally graded materials through the chemical prestressing, generated by application of alkaline sodium silicate among fiber cement layers. Currently, its very common the fiber cements present cracks along the edges due to moisture gradients, caused during storage of piles of tiles in the courtyard of the industry. The chemical prestressing potential was evaluated through of the total porosity, the quantification of hydrate phases, the drying shrinkage and the mechanical performance. The application of alkaline sodium silicate in the cement CPII F caused drying shrinkage 1,5 times greater than the reference to 91 days. The modulus of rupture (MOR) didnt suffer change, but the proportional limit of matrix (LOP) increased by around 95%. The dynamic modulus of elasticity was 13% higher. The increase of drying shrinkage and the mechanical performance gain indicate the chemical prestressing potential to control the cracking in fiber cement produced by the process Hatschek.