Durability and Smart Condition Assessment of Ultra-High Performance Concrete in Cold Climates

The goals of this study were to develop ecological ultra-high performance concrete (UHPC) with local materials and supplementary cementitious materials and to evaluate the long-term performance of UHPC in cold climates using effective mechanical test methods, such as “smart aggregate” technology and microstructure imaging analysis. The optimal UHPC mixture approximately exhibited compressive strength of 15 ksi, elastic modulus of 5,000 ksi, direct tensile strength of 1.27 ksi, and shrinkage of 630 at 28 days, which are characteristics comparable to those of commercial products and other studies. The tensile strength and modulus of elasticity in tension, dynamic modulus, and wave modulus show slight increases from the original values after 300 freeze-thaw (F-T) cycles, indicating that UHPC has excellent frost resistance in cold climates. Although porosity deterioration was observed in the F-T cyclic conditioning process, no internal damage (cracks or fractures) was found during imaging analysis up to 300 cycles. Since structures for which UHPC would be used are expected to have a longer service life, more F-T cycles are recommended to condition UHPC and investigate its mechanical performance over time. Moreover, continuum damage mechanic-based models have the potential to evaluate damage accumulation in UHPC and its failure mechanism under frost attack and to predict long-term material deterioration and service life

Structural elements made with highly flowable UHPFRC: Correlating computational fluid dynamics (CFD) predictions and non-destructive survey of fiber dispersion with failure modes

Structural design with highly flowable Fibre Reinforced Concrete has to duly take into account the preferential alignment of fibers, which can be governed through the rheological properties of the fluid mixture and the casting process and by the geometry of the structure. The possibility of predicting the fiber alignment, by tailoring the casting process, and of non-destructively monitoring it, can foster more efficient structural applications and design approaches. Focusing on UHPFRC slabs with pre-arranged casting defects, the flow-induced alignment of the fibers has been predicted by means of a suitable CFD modelling approach and hence monitored via a non-destructive method based on magnetic inductance properties of the fiber reinforced composite. The comparison between the assessed data on the fiber orientation and the crack patterns as visualized by image analysis supports the effectiveness of casting flow modelling and non-destructive fiber dispersion monitoring in supporting the structural design of elements made with highly flowable fiber reinforced cementitious composites

Fibre reinforced concrete column-supported flat slabs : from material and structural characterization to design and economic optimization

Tesi en modalitat de compendi de publicacionsFibre reinforced concrete (FRC) has proven to be a suitable material for statically indeterminate elements. The FRC column-supported flat slabs with partial or even total substitution of reinforcing steel bars constructed within the scope of this thesis provided the positive outcomes from both technical and sustainability perspectives, being a supporting evidence for this statement. Despite the successful experiences of FRC slab construction, the widespread use of this technology is still hindered because of a number of factors related to the general comprehension of the material’s properties, design procedure, and accurate assessment of both technological and economic aspects. In this context, further research is required to complement the current scope of knowledge, providing to practitioners and researchers a clear example of structural capacity of FRC column-supported flat slabs. Moreover, straightforward procedures focused on the design and following evaluation of the potential technological and economic benefits due to use of FRC should be de-rived. Therefore, a rather comprehensive doctoral thesis that covers the majority of the above-mentioned topics is proposed herein. The first part of the study focuses on the material characterization and analysis of the flexural behavior of FRC column-supported flat slab. A full-scale FRC slab was constructed and tested under different load magnitudes, assessing the structural response at both ultimate and serviceability limit states. The results derived proved the sufficient flexural strength at ultimate conditions along with the capacity of moment redistribution and the ductility of the system. Furthermore, the studied FRC slab evidenced the acceptable performance in terms of cracking and deflections. Subsequently, the straightforward design-oriented method is proposed to estimate the structural response of FRC column-supported flat slabs in terms of flexural strength, cracking control, and instantaneous deformations. The results derived were compared with a nonlinear analysis, highlighting a suitable accuracy and precision of the proposed approach. Finally, an industrial-oriented study was carried out with the main objective of elaborating a simplified method for the preliminary comparison of traditional and FRC solutions for column-supported flat slabs in terms of economic benefits. The results reflected an increment of direct costs for both fibre and hybrid (fibre + reinforcing steel bars, HFRC) solutions; however, these increments can be compensated by the reduction of the construction period and, as a consequence, time-dependent costs (i.e. preliminaries, equipment costs, overheads, and finance costs).El hormigón reforzado con fibras (HRF) ha demostrado ser un material adecuado para elementos sujetos a condiciones de contorno que conducen a hiperestaticidad. La construcción de forjados de HRF soportados por pilares ha proporcionado resultados positivos tanto desde el punto de vista técnico como de la sostenibilidad. A pesar de las experiencias de éxito en la sustitución parcial o incluso total del refuerzo tradicional (barras de acero) por fibras, el uso de esta tecnología todavía sigue siendo limitada debido a una serie de factores relacionados con la compresión general de las propiedades de HRF, los métodos de diseño junto con el análisis de los aspectos tecnológicos y económicos. En este contexto, se hace necesario continuar investigando el comportamiento de las losas bidireccionales de HRF con el objeto de complementar el marco actual de conocimiento, proporcionando a los profesionales evidencias de la capacidad estructural de este tipo de elementos. Además, la industria requiere los métodos de diseño prácticos junto con herramientas para llevar a cabo el análisis comparativo de diferentes soluciones en términos de beneficios tecnológicos y económicos. Por este motivo, se plantea una tesis doctoral generalista que abarca la mayoría de los temas mencionados en el ámbito de la tecnología de los forjados de losa maciza de hormigón reforzado con fibras. La primera parte del estudio se enfoca en la caracterización del material y posterior análisis del comportamiento a flexión de un forjado de HRF soportado por pilares. Para ello, se ha construido y ensayado una losa a escala real bajo diferentes magnitudes de carga, evaluando la res-puesta estructural del elemento en estado límite de servicio y último. Los resultados obtenidos han mostrado la suficiente resistencia a flexión bajo las cargas últimas junto con una elevada ductilidad y capacidad de redistribuir los esfuerzos en el sistema hiperestático. Asimismo, la losa de HRF analizada ha cumplido con los requisitos del estado límite de fisuración y de deformaciones. Posteriormente, se propone un método de diseño analítico para estimar la respuesta estructural de las losas de HRF soportadas por pilares en términos de resistencia a flexión, control de fisuración y de deformaciones instantáneas. Los resultados derivados se compararon con un análisis no lineal mediante el método de los elementos finitos, destacando una precisión adecua-da desde el punto de vista ingenieril del método propuesto. En la última parte se presenta un método simplificado para llevar a cabo un análisis comparativo de soluciones tradicionales y de HRF para las losas apoyadas sobre pilares en términos eco-nómicos. Los resultados del estudio comparativo demostraron un incremento de los costes directos para las soluciones con fibra (sustitución parcial o total del refuerzo tradicional); sin embargo, este incremento de los costes puede compensarse debido a la reducción del periodo de construcción y, como consecuencia, reducción de los costes indirectos (costes de maquinaria y herramientas, gastos de administración y dirección técnica, costes financieros).Postprint (published version

Non-destructive test approach for assessing the amount of fibre in polymeric fibre reinforced concrete

Over the past decade, significant efforts have been made to develop polymeric-based macro-fibre reinforced concrete (PFRC) for structural applications. Consequently, remarkable growth has been reported in the use of this type of fibres as concrete reinforcement. However, advances in quality control methods for PFRC lie behind any progress observed in polymeric fibre (PF) technology. In particular, cost-effective and efficient test procedures for quantifying the amount of fibre in fresh/hardened concrete matrices are, to the author’s best knowledge, non-existent, hindering the expansion of this innovative concrete reinforcement. This paper discusses a non-destructive method based on measuring electrical impedance to assess the content of polymeric fibres embedded in concrete matrices. A detailed experimental programme was performed to prove the capacity of the test method to obtain reliable results. The results confirm that the test approach proposed herein has interesting potential as a quality control method.Postprint (published version

DESIGN AND PERFORMANCE OF SELF-CONSOLIDATING AND THIXOTROPIC ULTRA-HIGH-PERFORMANCE CONCRETE FOR INFRASTRUCTURE CONSTRUCTION AND REHABILITATION

The objective of this research is to develop two classes of ultra-high-performance concrete (UHPC), one with self-consolidating consistency and the other with improved thixotropy. Tailoring the rheological properties of low yield stress UHPC can improve dispersion and orientation of steel fibers used in the design of UHPC, hence enhancing the tensile and flexural properties. Similarly, improving the thixotropy of UHPC can enable unique performance for the design of thin bonded bridge deck overlay. The research investigated various thixotropy enhancing admixtures to enhance the structural build-up at rest of UHPC. A total of 16 bonded overlay slab specimens were used to investigate the effect of overlay thickness, fiber volume, and shrinkage of self-consolidating UHPC on the performance of such composite elements. Test results indicated that the key factors influencing the tensile/flexural properties of UHPC due to fiber orientation included the fiber embedment length, fiber number, and fiber-matrix bond strength. Fiber distribution of UHPC was found to depend on the rheological properties of the suspending mortar and casting method. The use of welan gum or diutan gum was more effective to enhance thixotropy compared to other specialty admixtures. Low-shrinkage UHPC led to crack-free overlay even after 30 months of outdoor exposure with temperature varying from -10 to 40°C. Such UHPC overlay slabs exhibited 85% to 135% higher flexural capacity compared to latex-modified concrete overlay slabs. The increase of overlay thickness from 25 to 50 mm led to 30% to 40% enhancement in flexural capacity of UHPC overlay slabs. Such improvement was 15% to 20% when the fiber volume increased from 2% to 3.25% --Abstract, p. i

Development of active microwave thermography for structural health monitoring

Active Microwave Thermography (AMT) is an integrated nondestructive testing and evaluation (NDT&E) method that incorporates aspects of microwave NDT and thermography techniques. AMT uses a microwave excitation to generate heat and the surface thermal profile of the material or structure under test is subsequently measured using a thermal camera (or IR camera). Utilizing a microwave heat excitation provides advantages over traditional thermal excitations (heat lamps, etc.) including the potential for non-contact, selective and focused heating. During an AMT inspection, two heating mechanisms are possible, referred to as dielectric and induction heating. Dielectric heating occurs as a result of the interaction of microwave energy with lossy dielectric materials which results in dissipated microwave energy and a subsequent increase in temperature. Induction heating is a result of induced surface current on conductive materials with finite conductivity under microwave illumination and subsequently ohmic loss. Due to the unique properties of microwave signals including frequency of operation, power level, and polarization, as well as their interaction with different materials, AMT has strong potential for application in various industries including infrastructure, transportation, aerospace, etc. As such, this Dissertation explores the application of AMT to NDT&E needs in these important industries, including detection and evaluation of defects in single- or multi-layered fiber-reinforced polymer-strengthened cement-based materials, evaluation of steel fiber percentage and distributions in steel fiber reinforced structures, characterization of corrosion ratio on corroded reinforcing steel bars (rebar), and evaluation of covered surface cracks orientation and size in metal structures --Abstract, page iv

High performance fiber reinforced concrete for the shear reinforcement: experimental and numerical research

High performance fiber reinforced concrete (HPFRC) is developing rapidly to a modern structural material with unique rheological and mechanical characteristics. Despite applying several methodologies to achieve self15 compacting requirements, some doubts still remain regarding the most convenient strategy for developing a HPFRC. In the present study, an innovative mix design method is proposed for the development of high17 performance concrete reinforced with a relatively high dosage of steel fibers. The material properties of the developed concrete are assessed, and the concrete structural behavior is characterized under compressive, flexural and shear loading. This study better clarifies the significant contribution of fibers for shear resistance of concrete elements. This paper further discusses a FEM-based simulation, aiming to address the possibility of calibrating the constitutive model parameters related to fracture modes I and II.The research in this paper is part of the project "DURCOST - Innovation in reinforcing systems for sustainable pre-fabricated structures of higher durability and enhanced structural performance" with reference number of PTDC/ECM/105700/2008, supported by FCT. The authors also thank the collaboration of the following companies: Casais to manufacture the moulds, Ibermetais for supplying the steel fibres, Secil/Unibetao for providing the Cement, BASF for supplying the superplasticizers. The first author acknowledges the research grant in the ambit of this project

Performance of a multi-layer aligned steel fibre reinforced concrete beam:A preliminary investigation towards 3D printing

Fibre alignment and 3D concrete printing have become increasingly popular in research and industry while these technologies face a lack of deep integration. Aligning steel fibres in concrete is different from in mortar systems due to the interference originated from coarse aggregate. This paper reports the results of an experimental programme investigating manufacturing reinforced concrete by placing concrete and aligned steel fibres in multi-layer in replicating the 3D printing. The X-ray CT scan was deployed to characterise the fibre distribution by digitally colouring the fibre orientation deviation and calculating the fibre orientation efficiency which reached 0.77 in this study. 4-point bending tests were performed on beam specimens of the multi-layer aligned steel fibre reinforced concrete to assess the flexural performance. Alignment of the steel fibres resulted in 56% increase of the ultimate load resistance compared to that being two-dimensionally distributed. A model for estimating the tensile strength of multi-layer aligned steel fibre reinforced concrete was developed with consideration of the layer proximity to the neutral axis of the beam. Change of the concrete composition was observed to yield influences on the interface bond performance between the fibre layer and concrete and the influences were quantified by correlating experimental data. This study revealed that the space characteristics of the fibre distribution in multi-layer required concrete mix constituent of good rheology to develop adequate bond performance for further additive manufacturing without formwork

Proceedings of IWAMISSE 2018 the International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices

The International Workshop on Advanced Materials and Innovative Systems in Structural Engineering: Seismic Practices, IWAMISSE 2018, is co-organised by The International Federation for Structural Concrete Turkey Branch, fib-Turkey, and Istanbul Technical University, ITU, on November 16, 2018 at ITU. The International Federation for Structural Concrete, fib, is a not-for-profit association formed by 45 national member groups and approximately 1000 corporate and individual members. The fib’s mission is to develop at an international level the study of scientific and practical matters capable of advancing the technical, economic, aesthetic and environmental performance of concrete construction. Istanbul Technical University (ITU) was established in 1773 and is a state university which defined and continues to update methods of engineering and architecture in Turkey. It provides its students with innovative educational facilities while retaining traditional values, as well as using its strong international contacts to mould young, talented individuals who can compete not only within their country borders but also in the global arena. With its educational facilities, social life and strong institutional contacts, ITU has always been preferred by Turkey’s most distinguished students since its foundation and has achieved justified respect. The workshop covers the topics of advanced materials and innovative systems in structural engineering with a focus on seismic practices as well as other issues related with steel fiber reinforced concrete, anchors/fasteners, precast structures, and recent advances on different types of structural systems such as reinforced concrete, steel, and reinforced masonry structures. This proceeding book contain sixteen papers from ten countries worldwide. We have no doubt that the up-to-date subjects covered during the workshop will be extremely beneficial for the workshop participants both from academia and industry. We would like to thank all authors for their contributions to the workshop as well as the members of the International Scientific Committee for their rigorous work for reviewing the papers. We also gratefully acknowledge the support of the sponsoring companies and we express our sincere thanks to organization committee for their tireless efforts in the overall organization of the workshop. Many thanks go as well to undergraduate and graduate students from ITU for their assistance during all stages of the workshop