Recycled crumb rubber is a material created by grinding and commutating used tyres. There is no doubt that the increasing piles of tyres create environmental concerns. The long term goal of this ...paper is to find a means to dispose of the crumb rubber in lightweight self-compacting concrete (SCC) and still provide a final product with good engineering properties. This paper has considered replacement of natural normal-weight aggregates with crumb rubber aggregates and lightweight scoria aggregate together with the addition of macro fibres which provides a sustainable alternative which assists in minimizing the environmental damages associated with the disposal of waste tyres. Also, the purpose of this study is to determine the effect of fibres on fresh and mechanical properties in additional to the performance of the concrete after exposure to elevated temperatures. Investigation has been performed after concrete exposure to both room and elevated temperatures. Fibre reinforcement were added to a control mix containing 80% replacement of traditional coarse aggregate with lightweight scoria aggregate and 20% replacement of traditional fine aggregate with crumb rubber aggregate. Steel and polypropylene (PP) fibres were explored so as to ascertain the benefits each fibre can provide through a range of temperatures. Nine mixes were prepared; a control mix and four mixes per each fibre with increasing fibre addition. Chemical admixture dosages were adjusted so as to achieve the desired slump flow. Experimental program investigated the fresh properties of the SCC through slump flow, slump flow T500 and J-ring tests. Mechanical properties were investigated after 28 days curing, standard 100 × 200 mm cylinder specimens were subjected to compressive and indirect tensile tests after exposure to 25, 100, 300, 600 and 900 °C. Compiled results will be compared to those of the control mix.
This paper proposes numerical models for the study of fracture of fiber reinforced concrete. The composite material behavior is described at the macroscale and at the mesoscale. The macroscale model ...considers homogeneous equivalent continuum properties taken from experimental curves of the composite. In order to reproduce the effect of the random distribution of steel fibers within the cementitious matrix, random values of equivalent elasticity modulus and equivalent tensile strength are assigned to solid and cohesive elements, respectively. The mesoscale model represents the fiber explicitly inside the concrete matrix through cohesive interface elements with steel properties. In this case, fibers are located and oriented randomly in the matrix. In addition, to allow matrix fracture, cohesive elements with softening constitutive behavior are placed at the edges of the solid elements in the meso and macroscale models. The numerical models were applied to the simulation of a direct tensile laboratory test for a steel fiber reinforced concrete. The macroscale model uses probability functions to define the mechanical properties for each element. The predicted fracture paths and load capacity present satisfactory results when compared to those obtained experimentally. In the mesoscale model, distinct mechanical properties are applied for the steel fibers and for the cementitious matrix. The results from the mesoscale approach reinforce the concept that fiber dispersion and orientation affect the structural load capacity and matrix brittleness. In addition, cohesive interface elements proved to be an attractive approach to predict fracture propagation in the composite material.
The use of new methods to strengthen and rehabilitate existing concrete and masonry structures is one of the challenges that the engineering community is facing in recent years. In this field, ...composite materials are acquiring more and more success, due to lower invasiveness and ease of application if compared to more traditional systems (e.g. steel plates or reinforced concrete jacketing).
This work, based on experimental investigations, aims to propose a comparison between three different methods as possible strengthening solutions for existing concrete elements. Twenty compression tests were conducted on reduced scale concrete columns, realized by using a low performance concrete, in order to reproduce the poor mechanical properties of most existing structures. Two of them were left unconfined, while the other ones were reinforced by using Fiber Reinforced Polymer (FRP), Fiber Reinforced Cementitious Matrix (FRCM) or High Performance Mortar (HPM) systems. The effectiveness of the different strengthening techniques and the main differences in terms of structural response were investigated. Experimental results were then compared with predictions deriving from guidelines and theoretical models from the literature.
Filigrane Bauwerke aus Textilbeton Rempel, Sergej; Will, Norbert; Hegger, Josef ...
Beton- und Stahlbetonbau,
01/2015, Letnik:
110, Številka:
S1
Journal Article
Recenzirano
Abstract
Der innovative Verbundwerkstoff textilbewehrter Beton (kurz: Textilbeton) eröffnet neue Möglichkeiten für den Betonbau und bietet besondere Vorteile in vielen Bereichen des Bauwesens. Im ...Gegensatz zur Stahlbewehrung sind die Textilien nicht korrosionsgefährdet, sodass die Betondeckung auf wenige Millimeter reduziert werden kann. Damit sind architektonisch anspruchsvolle Betonkonstruktionen möglich, die sich vor allem in der Schlankheit und den geschmackvollen Sichtoberflächen widerspiegeln. Zusätzlich bieten sie ökologische und ökonomische Vorteile. Das Potenzial lässt sich in den realisierten Anwendungsprojekten erkennen. Der Beitrag stellt ausgewählte filigrane Bauwerke vor, die nur durch den Einsatz des Textilbetons entstehen konnten. Dabei wird sowohl auf selbsttragende als auch tragende Baustrukturen eingegangen.
Filigree Textile‐Reinforced‐Concrete constructions
The innovative composite material Textile‐Reinforced‐Concrete (TRC) enables new possibilities for concrete constructions and offers the building industry many advantages. In contrast to steel reinforcement the technical textiles are not vulnerable to corrosion. The consequence is the minimization of the concrete cover. The results of the remaining millimeters are architectonical challenging concrete constructions, which stand out through slenderness and elegant surfaces. Additionally TRC structures provide ecological and economic efficiency. The realized projects prove the potential of TRC. The paper introduces filigree constructions, which only could be fulfilled with Textile Reinforced Concrete. Especially the self‐supporting and bearing structures will be presented.
The geopolymer recycled concrete specimens were produced by using hypergolic or calcined coal gangue, slag, fly ash and recycled aggregate as the raw materials. Five different ratios of recycled ...coarse aggregate to total coarse aggregate and two types of geopolymer recycled concrete schemes (hypergolic coal gangue and calcined coal gangue respectively) were designed for specimen preparation. The compressive strength and splitting tensile strength of the specimens were studied, and the microstructure of the specimens was analyzed by scanning electron microscopy. It is demonstrated by the mechanical property test that the compressive and splitting tensile strength first drop and then grow with the increased mixing ratio of recycled coarse aggregate when the turning point occurs at the mixing ratio of about 30–50%. The microstructure analysis shows that the key factors affecting the mechanical properties of the recycled concrete include the internal porous structure, micro-cracks and the interface bonding ability between geopolymer and recycled coarse aggregate.
Corrosion causes mass loss of steel bars, concrete cracking, and interface degradation in reinforced concrete, highly compromising the safety and durability of civil infrastructure. This research ...proposes a smart reinforced concrete instrumented with a distributed fiber optic sensor for in-situ monitoring, presents an innovative method to quantify mass loss of steel bar using unique distributed sensor data, and studies corrosion-induced expansion of steel bar in steel fiber reinforced concrete. Electrochemical test and the distributed sensor data were used to understand the corrosion deterioration process of the steel-concrete composite. Effect of the steel fiber on the deterioration process is evaluated under different concrete surface conditions, and the underlying mechanisms are investigated. The results indicate that steel fibers reduced the corrosion rate of steel bars by mitigating electron transfer from the steel bar, delaying concrete cracking, and limiting the crack width. The effect of concrete surface defects shows a transition phenomenon. This research gains insights into the corrosion deterioration mechanism and strategies for improving the long-term durability of steel-concrete composite.
•Self compacting concrete (SCC) has been prepared with incorporation of wastes produced by coal thermal power plants and construction industry.•Various combinations have been prepared with ...incorporation of Coal Bottom Ash (CBA), Fly Ash (FA) and Coarse Recycled Concrete Aggregates (RCA).•The performance of SCC combinations has been evaluated through experimental examination of mechanical and long term properties.•Metakaolin (MK) has been used to recompense loss in performance due to incorporation of CBA and RCA.•Utilization of CBA, FA and RCA promotes sustainability and leads to conservation of natural resources.
Conservation of natural products and recycling in concrete industry wastes are the foremost needs of the current period. Intense utilization of alternate materials in concrete manufacturing has already been initiated from the past few decades. The present investigation has been piloted to evaluate the overall feasibility of Self Compacting Concrete (SCC) prepared with Coal Bottom Ash (CBA) and Recycled Coarse Concrete Aggregates (RCA) by replacing of Normal Fine Aggregates (NFA) and Normal Coarse Aggregates (NCA) respectively. The performance of SCC prepared with coal industry by-products Fly Ash (FA), CBA and construction industry wastes (RCA) has been evaluated experimentally. Various mechanical (compressive and tensile) and long-term (chloride permeability, capillary suction, accelerated carbonation, electrical resistivity, ultrasonic pulse velocity) properties of SCC prepared with different proportions of RCA and CBA have been estimated. The investigation inferences that the incorporation of constant amount of CBA (10%) along with varying content of RCA (up to 50%) has been proved to be advisable for the use in construction industry as enhanced/equivalent performance compared to that of control SCC has been achieved. Ample variation in the results of experiments conducted on SCC mixes has been noticed with increase in content of RCA. To capture the observed loss in the behavior of SCC prepared with higher alternate levels (>50% RCA) and CBA, Metakaolin (MK) has been inculcated. The attained findings revealed that the inclusion of MK (along with other by-products) results in comparable/at-par performance for SCC prepared up to full alternate levels (100%) of NCA with RCA.
Selected chapters from the German concrete yearbook are now being published in the new English "Beton-Kalender Series" for the benefit of an international audience. Since it was founded in 1906, the ...Ernst & Sohn "Beton-Kalender" has been supporting developments in reinforced and prestressed concrete. The aim was to publish a yearbook to reflect progress in "ferro-concrete" structures until - as the book's first editor, Fritz von Emperger (1862-1942), expressed it - the "tempestuous development" in this form of construction came to an end. However, the "Beton-Kalender" quickly became the chosen work of reference for civil and structural engineers, and apart from the years 1945-1950 has been published annually ever since. Ultra high performance concrete (UHPC) is a milestone in concrete technology and application. It permits the construction of both more slender and more durable concrete structures with a prolonged service life and thus improved sustainability. This book is a comprehensive overview of UHPC - from the principles behind its production and its mechanical properties to design and detailing aspects. The focus is on the material behaviour of steel fibre-reinforced UHPC. Numerical modelling and detailing of the connections with reinforced concrete elements are featured as well. Numerous examples worldwide - bridges, columns, fa´+¢ades and roofs - are the basis for additional explanations about the benefits of UHPC and how it helps to realise several architectural requirements. The authors are extensively involved in the testing, design, construction and monitoring of UHPC structures. What they provide here is therefore a unique synopsis of the state of the art with a view to practical applications.
Based on the Institute of Concrete Technology's Advanced Concrete Technology Course, these four volumes are a comprehensive educational and reference resource for the concrete materials technologist. ...An expert international team of authors from research, academia and industry has been brought together to produce this unique series. Each volume deals with a different aspect of the subject: constituent materials, properties, processes and testing and quality. With worked examples, case studies and illustrations throughout, the books will be a key reference for the concrete specialist for years to come.
•Effect of fly ash (FA) addition on changes in the Interfacial Transition Zone (ITZ) were investigated.•Analysis of the relationship between the microcracks width in the ITZ and mechanical parameters ...of composites.•The environmental and utilitarian aspects were taken into account.•The 20% fly ash cement binder causes favorable changes in the mature concrete.•Ecological benefits resulting from the presented studies are given.
The paper presents results of tests on the effect of the addition of siliceous fly ashes (FA) in the amount of: 0, 20 and 30% by weight of cement on the interfacial microcracks and mechanical parameters in plain concrete. The environmental and utilitarian aspects of the analyzed problem were taken into account in the studies.
The analyses were carried out based on the results of the macroscopic and microstructural tests.
During macroscopic investigations fracture toughness (KIIc) and compressive strength (fcm) of concretes were assessed, whereas based on microscopic examinations, the average width of the microcracks (Wc) in the Interfacial Transition Zone (ITZ) of coarse aggregate with cement matrix was evaluated.
In the own testing, it was demonstrated that there is a direct relationship between the observed Wc and designated fcm and KIIc. Based on these results, it was found that with the decrease of the Wc, the mechanical parameters increases. Using the 20% FA cement binder causes favorable changes in the microstructure and affects the improvement of mechanical parameters of mature concrete. Moreover, such treatments also causes a lot of benefits – both from the point of view of ecology and sustainable construction.
