Yes / Self-sensing concrete used in coating form for structural health monitoring of concrete structures has the merits of cost-effectiveness, offering protective effect on structural components, enabling electrical measurements unaffected by steel reinforcement and is also convenient to maintain and replace. This paper investigates the feasibility of using self-sensing cement mortar coating containing carbon nanotube-nano carbon black (CNT-NCB) composite fillers (CNCFs) for damage monitoring of concrete beams. The self-sensing cement mortar coated to concrete beams demonstrated outstanding electrical conductivity (resistivity ranging from 18 to 85 Ω·cm). Under monotonic flexural loadings, self-sensing cement mortar coating with 1.8 vol.% CNCFs featured sensitive self-sensing performance in terms of capturing the initiation of vertical cracks at pure bending span of concrete beams, with fractional change in resistivity (FCR) reaching up to 60.6%. Moreover, FCR variations of self-sensing cement mortar coating exhibited good synchronization and stability with the variation of mid-span deflections of concrete beams during cyclic flexural loadings irrespective of the contents of CNCFs and cyclic amplitudes. Remarkably, it was found that FCR of cement mortar coating basically showed a progressive upward tendency, representing irreversible increase in the resistance during cyclic loading. The irreversible residual FCR indicated the crack occurrence and damage accumulation of concrete beams. / National Science Foundation of China (52368031, 51978127 and 52178188) and the China Postdoctoral Science Foundation (2022M710973)

Ultrasonic testing of concrete is often used for the assessment of its uniformity, strength, modulus of elasticity, durability and etc. therefore, the related parameters of testing such as the transducer frequency, the specimen geometry and etc. are well-known. On the other hand, most of the concrete properties are affected by the cement and the mechanical as well as some durability properties of cements are determined through cement mortars. Applications of ultrasound on determining the properties of cement mortars are quite limited. Therefore, the required specimen dimensions, transducer frequencies have not yet been established for cement mortars. In this study, ultrasonic pulse velocity (UPV) of mortars was determined with different transducers of different frequencies for different size ans shape of specimens. Within the scope of the experimental program, three different ultrasonic frequencies (54 kHz, 82 kHz, and 150 kHz) were utilized and the relation between ultrasonic testing frequency and specimen shape was experimentally investigated. It was concluded that the mechanical properties of mortar was adversely affected by the water-to-cement ratio. It was also observed that, when the length/wavelength ratio increases, the measured UPV with different transducer frequencies tends to converge to a single value. Finally, it was also concluded that an increase in moisture content of the mortar mixtures causes an increase in UPV and a decrease in compressive strength.

[pt] O desenvolvimento de tecnologias que utilizem energias limpas e a gestão integrada dos resíduos domiciliares e industriais visando uma reengenharia nos conceitos sócio-empresariais é uma necessidade urgente. A sociedade, principalmente nos países desenvolvidos, prioriza produtos de empresas que possuam atividades socialmente corretas. A indústria da construção civil, como uma das maiores geradoras de resíduos, podendo chegar a 3000 kg/hab.ano, não pode se eximir desta atitude. Uma vez que consome grandes quantidades de recursos naturais, um grande número de estudos para substituição de bens naturais não renováveis está sendo realizado nesse setor, aliando materiais convencionais com resíduos industriais e urbanos. Um dos materiais que vem sendo utilizado nestas pesquisas são as embalagens pós- consumo de PET ( polietileno tereftalato ), resíduos que estão atingindo percentuais cada vez maiores na composição do lixo urbano, com presença crescente no meio ambiente. Esse trabalho visa apontar uma nova perspectiva de utilização desse material, propondo a substituição parcial da areia natural, por material granulado oriundo de garrafas de PET, objetivando a produção de argamassas para uso na construção civil. No presente estudo, foram realizadas substituições nas proporções de 10, 30 e 50% , tendo sido observado a melhor possibilidade de utilização do percentual de 30%, devido a não ter apresentado perdas significativas na plasticidade e nas resistências a compressão e a tração. Foi possível concluir que o compósito obtido tem potencial para ser utilizado na confecção de artefatos de concreto, sem grande responsabilidade estrutural e em mobiliários urbanos, além de seu uso permitir uma economia significativa de volumes de areia lavada, um recurso natural cuja extração tem causado grandes danos ao ecossistema dos rios e suas margens. / [en] The development of technology that uses clean energy and the integrated management of domestic and industrial residues aiming at a new engineering in the social and company relationship, is a urgent necessity. The society, mainly in developed countries, are already giving priority to the products of companies that possess identity with socially correct activities. The industry of construction, as one of the larger generator of residues, that produces around 3000kg/hab.year, and can not exempt of this purpose. Since the civil construction consumes great amount of natural sector resources, a large number of studies aiming at the substitution of natural sand, considered a non renewable material, is being carried out, particularly by, mixing conventional material with industrial and urban residues. The material used in these this study, was granulated PET (polyethylene tereftalate), obtained from beverage bottles, residues that are reaching a high percentage in the composition of the urban wastes. The objective of this research aimed at create a new perspective for construction materials, by crushing bottles of PET and using the produced material as a substitute of the natural sands for production of mortar. In this study was used the PET/sand ratios of 10, 30 and 50%, being 30%, the best ratio observed, due to a still good workability, an acceptable compressive and tensile strengths. The innovation, proposed in this study for instance, in the production of pieces of concrete, without great structural value, and in urban furnitureleading to a significant economy of volumes of sands, a resource whose extraction has been caused great damages to the present ecosystem of the rivers and in its edges.

<p>With over 30 billion tons of global annual production, concrete is the most used construction material in the world. Its manufacturing is associated with a strong environmental impact due to the high natural resources’ consumption, energy consumption, and a large generation of wastes and pollutants with significant global consequences. There are many different approaches to reduce the environmental impact of cementitious materials. Two examples are: (i) the use of recycled aggregate (RA) such as recycled concrete aggregate (RCA) and recycled plastics, or supplementary cementitious materials (SCMs) such as biomass ashes to reduce the use of natural aggregates and cement, respectively, and (ii) using nano-additives (for instance, nano-TiO2) to enhance material’s performance and to provide the material new properties that may have a positive proactive effect during its service life (i.e., photocatalytic properties that may reduce different pollutants concentrations from the environment). These approaches have been widely studied in standard conditions. However, boundary conditions such as temperature or moisture can be critical factors that directly or indirectly affect the effect of these approaches on the sustainability of cementitious composites in all stages of their life, from curing to service conditions.</p> <p>It is known that curing temperature influences the effect of using recycled materials (such as RCA or SCMs) on the mechanical properties of cementitious materials. However, there were no studies concerning the influence of curing temperature on the nano-TiO2 addition effect on mechanical properties of cementitious composites. A potential change will affect composites’ sustainability; if curing temperature influences the effect of nano-TiO2 on strength, the cement content needed to achieve a given performance will variate. This study concluded that curing temperature is a key factor that changes the effect of TiO2 nanoparticles on mechanical properties and pore structure of Portland cement mortars; the lower the curing temperature, the higher the positive effect of TiO2 on compressive strength.</p> <p>Besides the use of nano-TiO2, the substitution of NA with RCA might significantly benefit the sustainability of cementitious composites. However, the use of RCA may lead to a reduction in strength. On the other hand, the addition of nano-TiO2 mixtures containing RCA might offset this reduction in strength. Nevertheless, studying their effects on the composites’ performance under extreme conditions is critical to assess the actual environmental impact since durability is one of the main pillars of cementitious materials sustainability. This study concluded that even though RCA may be beneficial to increase sustainability aspects in terms of net waste generation and natural abiotic depletion, its potential negative effects on high-temperature resistance should be considered to not lead to structural problems during its lifetime, especially if used in combination with nano-TiO2. The addition of low percentages of nano-TiO2 has a negative effect on the high-temperature resistance of mortar containing 100% RCA. Differences in thermal properties between old aggregate, old cement paste, and new cement paste with nano-TiO2 may induce internal stresses at high temperatures that can produce a failure at lower strength due to the weaker interfacial transition zone (ITZ) between the stronger new cement paste (with nano-TiO2) and the old cement paste. To the same extent, it is important to understand how extreme temperatures impact the effect of other recycled materials in cementitious composite performance. This study found that recycled polypropylene (re-PP) fibers may mitigate the strength loss caused by high-temperature exposure, enhance the residual flexural strength, and increase the energy absorption capability. The changes in the fiber-matrix ITZ after cooling observed through an optical microscope suggested that the mechanical improvements are related to an enhancement of the fiber-matrix ITZ after high-temperature exposure and cooling.</p> <p>The next part of the dissertation focused on studying the thermal conductivity susceptibility to ambient conditions variation and how RCA substitution can affect this susceptibility. Understanding the effect of RCA on the thermal conductivity of cementitious composites would be crucial to assess their effects on the environmental impact during service life as part of a building component. Results showed that the higher percentage of porosity (due to RCA utilization) increases the susceptibility of thermal conductivity to moisture. Thus, actual moisture content and temperature should be considered when assessing the effect of RCA on thermal conductivity and its influence on sustainability in terms of energy savings when used as part of building envelops.</p> <p>Finally, the last part of this dissertation focused on assessing the impact of curing temperature on the sustainability of sugarcane bagasse ash (SCBA) as a partial replacement of cement in mortars. An experimental campaign was performed to evaluate the effect of partial replacement of cement with SCBA on compressive strength as a function of curing temperature. Hence, a life cycle assessment (LCA) was performed from the extraction of the raw materials to the material production part of the life cycle, using as a functional unit 1 m3 of mortar with the same compressive strength as the reference mixture (plain Portland cement mortar without SCBA) cured at the same temperature. Results showed that a replacement of 97 kg of cement by SCBA (per m3 of mortar) may produce a reduction of the environmental impacts two times higher when the curing temperature was 45°C than when the temperature was 21°C. Results clearly indicate that the sustainability of SCBA utilization as a partial replacement for cement will be higher when mortar is poured in hot regions or during days with higher temperatures. Therefore, external curing temperature is an important factor that should be considered when assessing the sustainability of cementitious composites containing sugarcane biomass ashes.</p>

[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