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Concrete can be characterized as a brittle material with a low tensile strength and strain capacity. A more ductile material can be achieved by the use of fibres in the concrete. Indeed fibre concrete shows a softening response after cracking. Fibres of various shapes and sizes and produced from different materials can be used. Hybrid fibre concrete is defined as concrete containing combinations of different types of fibres. Synergy is the phenomenon where acting of two or more subjects together leads to a better result than the action of the same subjects independently of each other. That means that applied to hybrid fibre concrete one could suppose that the synergy of short and long fibres leads to an improved tensile response of the hybrid fibre concrete, compared to the arithmetic sum of tensile responses of two concretes, one of which contains only long and the other only short fibres in the same dosage as the hybrid fibre concrete. This contribution presents the mechanical properties (compressive strength, tensile behaviour according to RILEM TC162-TDF) of a number of steel fibre concretes. Part of them are hybrid steel fibre concretes. The investigated parameters are: steel fibre type and fibre dosage. The program includes 15 different steel fibre concrete mixes. The obtained results of CMOD (crack mouth opening displacement) controlled bending tests show that the short fibres (L=13mm) are very effective in the region of the small crack widths while the longer fibres (L=35mm) with the hooked end provide a good ductility at large crack openings. The efficiency of the very short fibres (L=6 mm) in concrete with normally used aggregates is rather small. For most hybrid mixes, no synergetic effect has been found. [ABSTRACT FROM AUTHOR]

Research work on textile reinforced concrete (TRC for short) and Engineered Cementitious Composites (ECC for short) has been carried out to improve durability and service life of structures recently. Combining both advantages of TRC and ECC, this paper associates both carbon textile and short-cut PVA fiber as reinforcements for investigating a new anti-cracking technique of concrete structure, which can make the cracks innocuously disperse and improve the load bearing capacity. Accordingly, a kind of predominant composite material with excellent abilities of crack resisting and controlling is developed. Influences of the surface treatment of textile, the water-binder ratio, the volume fraction of PVA fiber on crack resisting and the load bearing capacity of the tested component have been investigated using the experiments on four-point bending specimens. As a result, the material shows prominent toughness and superior crack controlling with multiple fine cracks; the surface treatments of textile obviously improve bond properties between roving and ECC; the integrated performances of this composite material are improved evidently with just 0.5% increase of the volume content of PVA fiber. [ABSTRACT FROM AUTHOR]

Due to the limited resources and its high cost steel became a more and more expensive building material. Increased number of research worker found their way towards ultra high performance concretes (UHPC). They have a high potential for this use, but the casting procedure is very difficult. Normally the very high compressive strength is achieved by using a high amount of cement and silica fume, an extremely reduced water cement ratio and using high-strength aggregates with the diameter of sand. To improve workability a high amount of very efficient superplasticers are added. To improve the ductility of the cement matrix different types of fibers are added. The mixes are hardened under high pressure and increased temperature, often under a combination of both, makes the manufacturing very complicated. In Germany compressive strength of about 200 MPa and a bending tensile strength of 20 MPa can be achieved in laboratories. The task of this research programme was to develop a concrete with a compressive strength of about 400 MPa and a bending tensile strength in the range of 50 MPa to be used in a 35 mm thin plate exposed to low dynamic to impact loads. About the failure of ultra high performance fiber reinforced cement composite under dynamic loading only few results are known in the literature. Therefore a nonlinear three-dimensional finite element analysis system (Straus7®, G+D Computing Pty Limited) was used. [ABSTRACT FROM AUTHOR]

Radar measurements are nowadays widely used for non-destructive testing of concrete structures [1]. Nevertheless mainly profiles are measured and interpretation is done by examination of raw data only. [ABSTRACT FROM AUTHOR]

The trough structure N at the main station of Berlin guides North-South tracks from the lowermost plane of station to ground level. High ground water level required the coupling of the trough and under water concrete slab to ensure safety against up-lift. Due to this coupling, high thermal restraint in the trough slab will arise. The assessment of restraint necessitated certain assumptions. For their verification and for other reasons, the German Railways decided the online-monitoring of certain quantities relevant to restraint for the representative block N14. In this report, the techniques and results of monitoring from the day of casting of the trough slab of block N14 on the 8th July 2003 till the end of 2005 are presented. Beyond that, the measured stresses at the centre of trough slab will be compared with computed thermal stresses, in order to assess the forecasting quality of the applied engineering models. [ABSTRACT FROM AUTHOR]

The response of concrete structures exposed to explosive and impulsive loading is an important safety issue. Numerical modelling can be used to predict the dynamic response. However, a proper prediction is only possible when the material behaviour of concrete and the failure mechanisms at high loading rates are known. The importance to know and understand the rate dependency of concrete was recognised by Reinhardt. In the early eighties he initiated experimental and theoretical research in Delft on the behaviour of concrete under dynamic tensile loading. [ABSTRACT FROM AUTHOR]

The jammed aggregate is the prime, load-bearing phase in compressed concrete. The Interfacial Transition Zones (ITZs) around all aggregate grains constitute a second phase in the form of an interconnected spatial structure of shells. ITZs delineate gradients in structure descriptors of which the configuration-sensitivity governs the ITZ's extent. Concurrent algorithm-based discrete element computer simulations of concrete can offer unbiased information on configuration-sensitive parameter gradients. Such systems (SPACE and HADES) are used for studying gradient structures, such as relevant for transport-based durability issues. This paper touches upon the various aspects of a sound methodological approach to studying properties linked to the aggregate in concrete. [ABSTRACT FROM AUTHOR]

According to the European Standard Draft prEN 12602 [1] the manufacturer of prefabricated reinforced components of autoclaved aerated concrete shall declare the flexural strength from tests. In the absence of test results an estimate of the tensile strength or flexural strength, respectively, may be obtained by using equations. These equations were regarded to be based on insufficient investigations and were verified in the context of a research work performed at the Otto-Graf-Institute of Materialprüfungsanstalt Universität Stuttgart. This work presents a statistical evaluation of the obtained results and provides a proposal for standardisation. [ABSTRACT FROM AUTHOR]

Expanded perlite is a porous, lightweight material with good thermal insulation properties. Construction materials made of expanded perlite are frequently used in modern buildings for thermal insulation. However, they do not always present sufficient thermal inertia. A solution to increase this inertia is to incorporate a phase change material to make a granular phase change composite. Granular phase change composites are made of granular porous materials and phase change materials by means of vacuum impregnation method. In this study, panels have been made by incorporating phase change composites. Experimental studies have been carried out by measuring temperatures through the panels. The thermal performance of panels subjected to temperature variation is presented in this paper. Experimental results show that incorporation of phase change composites allows the apparent heat capacity to be increased and thus thermal insulation becomes more effective. [ABSTRACT FROM AUTHOR]

The strength of no-slump concrete is mainly achieved by a high particle packing density (ppd), which causes a strong interlocking of the coarse aggregates. Also inert fillers like fly ash are enhancing the strength by help of interlocking of micro-sized particles (Bornemann 2005). Both the compressive strength in the green and hardened state is enhanced. However, additional water or liquifier is needed to keep a sufficient workability. Accordingly there's often a lack of water for the cement hydration process, that is either retained by the filler or is replaced by high superplasticizer content. Anyway there is a discrepancy to be noted between high green strength (little water needed) and high compression strength of hardened concrete (more water needed). The stickiness of a filler-optimized mixture causes hindrances in manufacturing, yet another problem. Another theory, wherein green strength is explained by capillary forces between micro-sized particles (Wierig 1972) seems to fail. Capillary forces have a maximum effect on particles with diameters from 0.1-1 mm, while friction forces are dominant when particle diameters exceed 1 mm (Bornemann 2005). [ABSTRACT FROM AUTHOR]

Knowledge of the tension softening process of concrete is essential to understand fracture mechanisms, to analyze fracture behaviour and to evaluate the properties of concrete. Many different tests on uniaxial tension with elimination of secondary flexure have been performed in Tohoku Institute of Technology. Based on the results, some new formulas were proposed and a suitable artificial neural network was introduced to describe tension softening curves. [ABSTRACT FROM AUTHOR]

Facilities for storing, decanting, manufacturing, handling and using water-hazardous materials must be constructed, erected and operated in such a way that no water contamination need be feared. When designing components for this purpose, it is necessary to ensure that the penetration front of the medium demonstrably fails to reach the side of the component opposite to the wetted side, allowing a margin for safety [1]. An actual overview of the design of concrete structures for the containment of hazardous materials is given in [2, 3]. A research programme was started in the 1990ies to analyse the reduction potential of the penetration of water-hazardous liquids and the improvement of concrete ductility especially with respect to increase the ultimate tensile strain by using silica fume, polymer dispersions and different types of aggregate. In the following, parts of the research programme are introduced and results are given. [ABSTRACT FROM AUTHOR]

The design of demountable concrete buildings could be a very interesting construction method in the future. For this purpose the main challenge for engineers and architects would be that the structural design has to be in a way that enables the completely dry assembling of the building structure and that all elements can be demounted without damage because the elements should be available for the reuse and for sale. Finally the interior fittings also should be demountable and separable. This leads to numerous environmental and economic advantages. For demountable floor slabs a construction method with use of aluminium foam for prefabricated Al-bars in joints and some results of tests are shown. The investigations were quite successful and the suitability of the material concerning the mechanical requirements could be shown. [ABSTRACT FROM AUTHOR]

The knowledge of the average concentration of persistent and toxic organic substances in indoor air is basic to estimate the hygienic effects of contaminated indoor air. It is well known that the concentration of SVOC in indoor air depends on climatic conditions as well as the ventilation habits of the occupants. Based on the physicochemical properties and the high toxic potential dioxin-like PCB and PCDD/F are appropriate substances to study these influences on indoor air quality. The present paper describes the contamination of indoor air with dioxin-like polychlorinated Biphenyls ( PCB, coplanar and mono-ortho-substituted) and polychlorinated Dibenzodioxins and -furans (PCDD/F) in buildings with PCB coated ceiling panels. A number of public buildings (schools, universities) in Germany are equipped with such PCB coated ceiling panels. The coating consists of high-chlorinated Biphenyls (Clophen A 60). Dioxin-like PCBs and PCDD/F are relevant impurities of technical PCB-mixtures [4, 5]. Dioxin-like PCBs and PCDD/F in indoor air were determined under standardised conditions (ISO 16000-1; VDI 4300 Bl. 2) and real-life conditions (short, repeated ventilation actions) in dependence on the seasonable changes. The present work proves the dominating influence of the indoor temperature [1-3, 9]. An increase of the indoor temperature from 20 to 25 °C leads to an increase of the concentration of dioxin-like PCB from 30 ng/m3 to 90 ng/m3 (sum 12 dioxin-like PCB). A comparable effect of temperature or seasonable changes can be proved for 2,3,7,8-TCDF in the indoor air of these buildings. The concentration increases from 10 pg 2,3,7,8-TCDF /m3 in winter times up to approx. 25 pg/m3 in the summer season. Normally the concentration of dioxin-like PCB and PDDD/F in indoor air are quoted in toxicity equivalents (TE). Based on the TEF established in 1998 by the World Health Organisation the calculated concentration for dioxin-like PCB ranges from 5 pg WHO-TE/m3 in the winter season up to 14 pg WHO TEQ/m3 in summer times. Normal ventilation accomplished by the occupants (short, repeated opening of the windows), reduces the concentrations of dioxin-like PCB in indoor air up to 60% in the summer season. In winter times, when normally only few ventilation actions are carried out, almost no effect of those ventilation actions can be observed. In Germany a tolerable daily intake (TDI) for dioxin-like PCB and PCDD/F via indoor air of 5 pg WHO-TEQ/m3 is discussed [7, 8]. The revision of WHO-TEF in 2005 influences the appraisal for the exposure situation in these buildings. Applying the new WHO-TEF for dioxin-like PCBs established by WHO in 2005 on the concentration of dioxin-like PCB in indoor air the WHO-TE is reduced to a level of 2 to 4 pg WHO-TE/m3. [ABSTRACT FROM AUTHOR]

Although a growing number of requirements for sustainable building are being laid down, there are still many uncertainties and different views on the benchmarks for evaluation and on how to implement sustainable building in practice. The principles for considering aspects of sustainability in the design, execution, use and deconstruction of concrete structures will be established in the joint research project "Sustainable Construction with Concrete" with the aim of promoting sustainable building with concrete and establishing it firmly in practice. In a state of the art report [1] the most important open questions had been compiled and structured as basis for this joint research project. The German Committee for Structural Concrete is coordinating the work which is funded by the German Ministry for Education and Research (ref. no. 0330502 and 0330780) and many industrial partners. With the aim of the project in mind, aspects of sustainability must be integrated into existing principles for design and execution,existing evaluation methods, as well as those under development, must be tailored to the needs and boundary conditions of concrete construction,proposals for technical solutions that will contribute to sustainable development, in particular at the interfaces of individual phases of the life-cycle of structures, will be made available to the parties involved in construction, taking their various responsibilities into account,planning tools and new information and communication tools tailored to the needs of the various actors will be developed to ensure the transfer of the relevant information throughout the life-cycle of a structure. [ABSTRACT FROM AUTHOR]

The concept of double wall containments without liner has been developed during the last years as an alternative to reinforced concrete containments with steel liner. The leakage behaviour of prestressed concrete containment walls has been investigated with several test setups at different levels of both complexity and representation. Most of the experimental test setups showed a large variation of obtained results. The influence of steam condensation inside the cracks was taken into account by only a few experiments (Herrmann et al. 2002, Granger et al. 2001). For a better understanding of the leakage behaviour of cracks through reinforced concrete walls which are subjected to air-steam mixtures at elevated temperatures and pressures it is necessary to perform numerical simulations. A 2D Finite Element Model consisting of a fluid model and a structural model has been used to calculate the leakage behaviour of cracked concrete walls with the Finite Element Program ADINA. Further details of the structural model can be found in (Niklasch et al. 2005). In every time step the fluid model and the structural model are solved iteratively. [ABSTRACT FROM AUTHOR]

The fulfilment of the needs of modern society — not only at present, but also for future generations — is a basic principle which underlies the idea of sustainable development. German legislation on recycling economics and waste disposal [1] is thus based primarily on the principle of waste avoidance, where the reduction of the amount and detrimental effects of waste are paramount. Secondary to this, is the use of waste as a material or for energy production. In the building industry, this entails the development and realisation of material cycles. By reusing construction materials at a qualitatively equivalent level, the volume of waste production is reduced and natural resources are conserved. Cost-effectiveness and the advantages gained by using the material are decisive for the applicability of the recycled material. [ABSTRACT FROM AUTHOR]

Acid Mine Drainage (AMD) is a phenomenon that occurs when abandoned coalmines fill with water and leach out into the environment. AMD is a persistent industrial pollution problem throughout western Maryland, West Virginia and Virginia. Noting the severity of the problem, efforts have been made to abate acid mine drainage in underground mines using blends of coal combustion byproducts (CCP) and limekiln dust (LKD). In this article, the causes of the AMD are highlighted and its consequences on the environment are briefly discussed. The properties of selected CCB materials are reviewed and suitable CCB grout mix proportions are formulated. The grout mixes were designed to achieve sufficient workability so as to flow freely around obstacles and develop sufficient compressive strength to carryout the overburden with the ultimate aim of forming solid barriers and preventing acid mine drainage. In addition, the early age properties of the grout mixes, which include setting time, bleeding and workability were studied and the compressive strength developments were investigated. All materials used for this study were obtained from by-product suppliers. The findings of this research work have demonstrated the practicality and feasibility of developing CCP grouts for abating Acid Mine Drainage. Based on the encouraging test results, relevant conclusions are made and recommendations are forwarded. [ABSTRACT FROM AUTHOR]

For detection of tendon ruptures in post-tensioned concrete structures such as prestressed beams of bridges or building roofs, the magnetic flux leakage technique is the only non-destructive testing method available. In case water penetrates the duct, e.g. due to inadequate grouting, hydrogen-induced corrosion of the steel tendons may be caused, eventually leading to cracks of single strands and finally to a collapse of the entire structure. [ABSTRACT FROM AUTHOR]

Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is difficult. Available techniques either lack the required resolution or may induce additional cracks. The technique presented in this paper allows identification of microcracks while avoiding artifacts induced by unwanted restraint, drying, or temperature variations. Small cylindrical samples of cement paste are cast around steel rods of different diameters. The rods restrain the autogenous shrinkage and may cause crack formation. After one month storage at 32°C, liquid gallium is intruded into the cracks under pressure and the samples are cooled. When the gallium solidifies, the crack pattern is frozen and can subsequently be analyzed by a number of techniques. A numerical analysis of the results was performed considering the mechanical properties of the cement pastes and the geometry of the samples. The experimental results and the numerical analysis showed that samples with larger steel rods (3 and 6 mm diameter) had the highest probability of developing microcracks. [ABSTRACT FROM AUTHOR]

Corrosion of reinforcing steel is modeled phenomenologically as corrosion losses of three phases. At the 1st phase, corrosion is initiated in reinforcement. The rate of the corrosion loss decreases at the 2nd phase under aerobic conditions. At the 3rd phase of anaerobic corrosion, the expansion of reinforcing steel due to corrosion product nucleates concrete cracking. In order to identify the onset of corrosion and the nucleation of concrete cracking based on this model, continuous AE monitoring in reinforced concrete specimens was conducted in a cyclic wet and dry test. High AE activities were characteristically observed twice during the corrosion process. AE parameter analysis of hits, events and locations demonstrates that AE monitoring is readily applicable to detect the corrosion in rebar and to identify the corrosion process. [ABSTRACT FROM AUTHOR]

The deterioration of concrete in structures is a major problem throughout the world. This has prompted research on methods of predicting the service life of both existing and new structures. Current prediction methods are still very basic and, before they can be used with confidence more reliable information on the properties of the concrete in these structures is needed. In this paper a range of test methods for determining the strength and transport properties of concrete are discussed from the perspective of research at Queen's University Belfast on advances made over the past thirty years. The initial focus was on in-situ strength testing and this led to the pull-off test and the development of the LIMPET. However when it became apparent that durability was a matter of much greater concern to practising engineers, measurement of permeation properties became a priority. This led to the development of the AUTOCLAM which was found to give extremely useful correlation in the laboratory and on site between the air and water permeability and durability. Subsequently problems associated with the ingress of chlorides into concrete have been recognised and in response the PERMIT has been developed which allows the diffusion characteristics of the "covercrete" to be determined. Using a combination of such approaches simple durability based criteria can be developed for concrete and the remaining life of existing structures estimated. As far as new construction is concerned the above methods can be used to develop durability related design criteria and in the future continuous monitoring techniques could prove to be useful. In the context of the latter, chemical fibre optic sensors are currently being developed to detect pH changes in concrete. However their long term reliability is yet to be proven. [ABSTRACT FROM AUTHOR]

Nowadays, the non-destructive evaluation of structural components allows the detection of cracks and other types of flaws with a high resolution. When cracks are involved in mechanical failure events, fracture mechanics provides concepts for lifetime prediction of components when component geometry, material characteristics and load intensity under steady state or impact loading are known. Under fatigue loads additionally material laws have to be observed. Bringing together these disciplines, quantitative non-destructive testing for lifetime prediction is possible. Due to measurement uncertainties related to crack size geometry, material Parameters' inherent scatter and load history are not unambiguously assessable. Therefore, statistical distributions are assumed (e. g. Normal or Weibull) and probabilistic fitness for service assessment (FFS) is performed rather than a deterministic one. This concept of combining quantitative non-destructive testing and probabilistic FFS assessment works well for metals. The fracture mechanics analysis under predominantly static loading has at its core the so called Failure Assessment Diagram (FAD). Hereby, an illustrative tool for condition monitoring is supplied which is also accepted in design rules and codes. Software which addresses the criticality of cracks and other flaw types in the shell of cylindrical pressure vessels was developed. The application of the concept of probabilistic fracture mechanics using Monte Carlo simulation is demonstrated for one example from pipelines. [ABSTRACT FROM AUTHOR]

In recent years the combination of measuring large concrete areas with dry ultrasonic transducers and reconstruction calculation imaging the location of construction elements and defects has been further developed and presents itself now as a precise tool to survey the inner condition of concrete elements. Examples of large area applications at test specimens and post-tensioned concrete bridges are presented. [ABSTRACT FROM AUTHOR]

Professor Reinhardt and his employees are besides us at the Technische Universität Berlin the experts in using the permanent magnetism to determine the health of prestressed concrete structures to find out whether they are free of prestressed wire breakages or whether they must be repaired. Professor Reinhardt enjoys an extremely high technical reputation in civil engineering, this does not have to be emphasized. I would like to stress that Professor Reinhardt is a quite special colleague regarding his kindness, his helpfulness, humanity and modesty. One has many comrades in arms but only few colleagues. I would like to take this opportunity to thank him for much good advice and for the fact, that I have a trusting, reliable and high appreciated colleague in him. I would like to now turn to a topic that connects us both. [ABSTRACT FROM AUTHOR]

Sensing methods including Non-destructive testing and monitoring techniques are fundamental tools for performing an efficient condition management system for structures in service. They can on one hand support regular visual inspections and help on the other side to assess the actual condition and performance of a building. These methods provide reliable data for the stakeholders to estimate the necessity for current and future investments into a structure. The main purpose of a monitoring system in civil structures is to support activities of engineers in doing structural assessment. A monitoring technique which is presented consists of a wireless sensor network using different types of sensors including MEMS. Wireless sensor networks (WSN) can be used to monitor a certain region of a structure providing data about different physical measures. Some properties to be measured in-situ are the Eigenvibrations of the structure, humidity and temperature outside and inside the structure, unusual stress and strain, and the detection of cracks and other deteriorations. An embedded sensor system is developed to acquire the structural condition and a wireless network propagates the sensor data towards a common base station where further analysis is performed. [ABSTRACT FROM AUTHOR]

Nearly thirty-thousand miles of the U.S. Interstate Highway system has been constructed of concrete, particularly in areas of heavy anticipated traffic volumes [1]. Concrete is usually chosen over asphalt because of superior durability, visibility, traction, cost-efficiency and smoothness [2]. Another advantage of concrete pavements is that they can be rapidly constructed utilizing slipform paving techniques. The slipform paving process has made highway construction faster and more cost-effective since its development during the late 1940s. As a result, it is used extensively by the worldwide paving industry. Different from fixed-form paving, slipform paving brings together concrete placing, casting, consolidation, and finishing into one unique process. In the slipform paving process, a stiff concrete mixture with a slump less than 51 mm is placed in front of a paver. As the paver moves forward, the mixture is spread, leveled, consolidated (by internal vibrators and surface vibrators), and then extruded. After extrusion, the fresh concrete slab can hold its shape for further surface finishing and curing until the concrete sets. Because of the low consistency of the mixture, a great deal of vibration is required to remove entrapped air and consolidate the concrete. However, internal vibrators can cause over-consolidation if the vibration frequency is too high, or if the paving machine moves too slow. As a result, a significant reduction in the air content occurs in addition to aggregate segregation [3]. Both of these problems can lead to vibrator trails and even more seriously, longitudinal cracks. [ABSTRACT FROM AUTHOR]

The reaction of alite with water can be accelerated by adding mineral admixtures such as limestone powder. Two different effects will be discussed in this paper. Firstly, the heterogeneous nucleation of C-S-H phases on surfaces showing a high chemical affinity towards these phases. Secondly, an accelerating effect occurs because of the high specific surface of the admixtures. C-S-H phases can grow on these additional surfaces and thus the dissolution of alite can proceed unhindered leading to a higher degree of hydration for this clinker mineral. Both effects together can be used to improve the performance of blended cements. [ABSTRACT FROM AUTHOR]

The hydration of portland cement can be modelled in a simple way by a degree of hydration based model, in which the heat production rate is the product of two factors. The first factor is depending on the state of the hydration process, represented by the degree of hydration. The second factor is depending on the actual temperature. This model has already been proposed in 1982 by Prof. H.W. Reinhardt. This paper gives an overview how this model can be extended towards blended cements, like blast furnace slag cement, or towards powder rich cement systems as present in self-compacting concrete (e.g. with limestone filler). The analytical model can be extended with an extra reaction, describing the influence of the blast furnace slag or the limestone filler. Especially in the case of self-compacting concrete, the model parameters depend on composition parameters like cement/powder ratio. [ABSTRACT FROM AUTHOR]

Although numerous regulations and guidelines cover the composition and properties of concrete and its components, the actual process of concrete production, i.e. mixing, is to all intents and purposes left to the user. According to DIN EN 206 the concrete components are to be blended so that a homogeneous mixture is produced. The duration of mixing is to be chosen to produce sufficient blending of the materials. It is decisive that water and superplasticizer are evenly distributed down to a fine scale and that agglomerates are sufficiently dispersed. If insufficient mixing energy is used, the properties expected from the composition chosen cannot be achieved. The necessary duration of mixing depends particularly on the type of mixer as well as the composition of the concrete. Due to the low water content with respect to the content of fines (<0.125 mm) and the high dosage of admixtures, the production of self-compacting concrete (SCC) and ultra high strength concrete UHPC requires more mixing energy to homogenise the concrete components. In concrete plants, mixing times above 4 min for SCC and 12 min for UHPC are not uncommon. This limits the rate of concrete production in comparison with vibrated concrete and is therefore an important financial factor. This paper considers the effect of mixing time, mixing tool speed and concrete composition on the homogenisation of ultra high performance concrete. In addition, a model approach based on mixing power is presented for the calculation of the necessary mixing time for different concrete compositions. [ABSTRACT FROM AUTHOR]

When considering deep excavations supported by diaphragm walls, it is well known that it is very important to consider the effects of the construction process. [ABSTRACT FROM AUTHOR]

Blast-furnace slag (BFS), a by-product of the steel production, is commonly used in the production of blast-furnace slag cements but can also be added to the concrete mixture separately. The effect of BFS on the hydration process and on the setting of the fresh concrete has not been investigated thoroughly, certainly when high percentages of the cement are replaced by the slag. Therefore, calorimetric and ultrasonic measurements were performed on fresh mixtures made with increasing Portland cement replacement by BFS. With increasing BFS content, the second peak in the heat production rate under isothermal conditions appears earlier and a third peak attributed to the hydration of BFS becomes clearer. This slag reaction can also be observed as a second steep increase in the ultrasonic velocity curves. Thus, BFS clearly influences the early hydration and setting of the concrete mixtures. [ABSTRACT FROM AUTHOR]

The influence of the mix composition on the early-age autogenous shrinkage of high-strength cement paste with and without silica fume and the resulting crack formation were investigated. The mechanisms of autogenous shrinkage were studied systematically by linking the measured deformations to hydration kinetics and to pore structure data. The time t0 which assigns the transition from the plastic state to a solid structure was determined by analysis of the measured strain rate. It was demonstrated that the autogenous shrinkage correlates reasonably well with the self-desiccation and the thereby expected capillary stresses. The crack formation was detected using acoustic emission (AE) analysis. AE measurements were performed simultaneously on hardening silica fume cement pastes with and without external restraint of deformation. The results showed that the intense autogenous shrinkage during the acceleration period of cement hydration was associated with the begin of micro cracking shortly after t0, irrespective of the existence of external restraint. The cracking was more pronounced in the case of restraint. [ABSTRACT FROM AUTHOR]

Numerical simulations proved to be a very valuable tool for handling different problems dealing with production, testing and application of building materials. This holds true for the simulation of the concrete behaviour in a fresh, as well as in a hardened state; however, continuous modelling of concrete behaviour throughout the various stages of "concrete life" has yet to be developed. The need for such a numerical simulation is obvious. The mixing and placement of fresh concrete can have a significant effect on hardened concrete with regard to mechanical performance and durability, as well as other properties. This paper presents a numerical approach based on the Distinct Element Method (DEM) which is a means for continuous simulation of fresh concrete during the working and hardening process, as well as the subsequent behaviour of hardened concrete. [ABSTRACT FROM AUTHOR]

In order to investigate the probability of cracking of hardening concrete in terms of the maximal allowable crack width, a full-scale concrete element has been evaluated. For this, evaluation, In order to investigate this issue, a concrete element has been simulated which measures a thickness of 1m and a height of 3m. The length deformations of the wall are considered to be fully restraint by 100%. The ambient conditions are taken into account, as well as the concrete mix parameters (see Table 1). TEMPSPAN, which is an acronym for TEMPeratuur (temperature) and SPANningen (stresses), is used to calculate the hardening stresses which develop during hardening. [ABSTRACT FROM AUTHOR]

In the last 15 years the application of high-workability concretes has increased significantly. Such concretes have a spread value larger than 55 cm according to DIN EN 12350-5 (2000) and are classified into the consistency classes F5, F6 (vibrated concretes) and Self-Compacting Concretes (SCC) according to DIN EN 206-1 (2001). Using SCC a mechanical compaction is not necessary anymore. [ABSTRACT FROM AUTHOR]

This paper deals with the mechanical properties of mortars with internal curing, by means of water-entrainment with super absorbent particles (SAP). The use of SAP in high performance concrete is focusing on the mitigation of autogenous deformation, arising from self-desiccation. The effect of SAP in mortars subjected to several curing conditions and different water/cement ratio was analysed. The curing conditions ranged between 30 and 100%RH at 20°C temperature. Water/cement ratio ranged between 0.25 and 0.35 for both reference and internal cured mixtures. Tensile and compressive strength tests were performed at different ages. Results include weight loss measurements with time and its relation to environmental conditions and strength. Internal curing by means of SAP was efficient in maintaining the mechanical properties of mortars regardless the variation of external relative humidity. [ABSTRACT FROM AUTHOR]

In this paper, the setting and hardening periods for concrete are studied by means of "equivalent" mortar. Two categories of mortars can be envisaged: one has the same thermal properties as the one of the relative concrete, another one presents the same specific area of the aggregates. The experimental approach is based on the use of a P-wave propagation device at low frequency (200 Hz). The wave velocity and two pressure ratios, which are linked to the wave damping and Poisson effect, are monitored during time. The evolutions of rheological moduli during setting are then obtained by inverse analysis, by means of a viscoelastic behaviour law obtained from a periodic homogenisation modeling. These mechanical quantities proved that only very restricted relations can be obtained from concrete to mortar equivalences. [ABSTRACT FROM AUTHOR]

Capillary suction of concrete is one of the different processes, which reduce the potential service life of reinforced concrete structures substantially. If concrete is exposed to marine environment or in permanent or periodical contact with saline water dissolved chloride can be transported into the porous structure of concrete during capillary absorption of water. By surface impregnation of concrete with silane (protective surface impregnation) or by adding silane to fresh concrete (integral water repellent concrete), capillary suction can be practically suppressed. As a consequence chlorides can not penetrate into water repellent concrete or at least at a substantially reduced rate. It may be concluded that service life of reinforced concrete structures may be considerably increased by making concrete water repellent. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation into the effects of freeze-thaw cycling on the FRP-concrete interfacial bond behavior. The strain distributions in the concrete and FRP are determined using the displacements obtained from an optical technique based on digital image correlation (DIC). The influence of freeze-thaw on stress transfer during fracture is studied. The results of the strain analysis are used to establish the non-linear material law for shear fracture along the FRP-concrete interface for specimens subjected to freeze-thaw cycles. The results show that freeze-thaw cycling produces significant decrease in the ultimate load transferring capacity and the interfacial fracture energy. [ABSTRACT FROM AUTHOR]

There is an increasing necessity to apply retrofitting measures to external elements made of concrete employing a wide variety of procedures and materials. In this context, questions regarding moisture behaviour and the related transport processes occurring under natural climatic conditions as well as the risks thus involved always occur. These questions can either be answered with the help of experiments or by numerical simulations. Because experiments are often time-consuming and, in some cases, both problematic and expensive, intensive work has been done over the past few years on the development of mathematical approaches and procedures to evaluate real thermal and moisture transfer processes. The present problem of such calculation methods lies mainly in the availability of the required material properties or transport coefficients. If these are present, moisture calculation procedures can make a considerable contribution towards the estimation, evaluation and optimization of the moisture behaviour of external structural components under real climatic conditions. As far as the moisture properties of concrete as a building material are concerned, a great deal of investigatory work still needs to be done. Within the framework of this study, the material properties and transport coefficients needed to apply moisture calculation procedures to a selected, commonly used type of concrete are to be determined. The moisture transport calculations carried out using these parameters and the PC program WUFI [4] are to be compared, for validation purposes, with laboratory and field measurements. [ABSTRACT FROM AUTHOR]

This paper presents the valuation of a new method of controlled localized attack used to study the susceptibility of the high strength steels resistance to Stress Corrosion Cracking (SCC). The innovation of this method resides in raising the study of the growth of the fissure combining electrochemical and mechanical parameters. The method consists of several stages: constant load and controlled potential test in the media, mechanical test in air and fractographic study. It allows calculating the crack propagation rate and the fracture toughness in the same test, where the crack is not produced by fatigue. First of all, the way of concentration of the damage has been selected. Before, a few tests were carried out to know the influence of the applied potential on the crack propagation. Finally, it has been possible to apply the Surface Mobility Mechanism (SMM) in order to approach the identification of the SCC mechanism operating. [ABSTRACT FROM AUTHOR]

For a safe design of TRC (Textile reinforced concrete) load bearing structures the loss of strength of TRC as a consequence of weathering should be modelled. In part 1, possible reasons for the loss of strength of a state-of-the art AR-glass textile reinforced concrete were discussed. These findings are first used in this paper as a base for a corrosion model, describing the loss of strength in lab conditions. Subsequently, temperature and humidity were continuously measured during outdoor weathering and implemented into the model. [ABSTRACT FROM AUTHOR]

Textile reinforced concrete (TRC) is an innovative material for thin-walled, structural elements with a high load-bearing capacity. For a safe design of TRC load bearing structures ambitious investigations were carried out to predict the time-dependent loss of strength of the AR-glass reinforcement embedded in fine grained concrete as a consequence of weathering. In the present paper possible reasons for the loss of strength of state-of-the art AR-glass reinforcement in nowadays cementitious mixtures are described and their relative importance is discussed, based on new results. In the accompanying paper (part 2), these results are used to present a durability model under complex weathering conditions. [ABSTRACT FROM AUTHOR]

High-strength thin steel wires or strands used today for bridging in the form of free tendons are combined into units of great load bearing capacity. They are bundled or form a closed wire system. According to mechanical and chemical influence the structural members are submitted to fatigue loading and may undergo irreversible structural modifications and cracks which may extend and continue until fracture. The presentation describes the different failure mechanisms. [ABSTRACT FROM AUTHOR]

Reinforcement corrosion leads into several damages which influence the structural load-bearing capacity, among which can be mentioned the cracking of concrete cover. The oxides produced by rebar corrosion induce the development of internal stresses that may crack the concrete. In spite the phenomenon is well known, quantitative descriptions of development and magnitude of stresses produced by a corroding rebar to concrete are scarce and although there are several models in the literature they do not universally reproduce the experimental results. This work presents a critical review of the available experimental evidence on the amount of internal expansion needed for concrete cover cracking and formulas to estimate the expansion. Also, it is presented the confirmation of the pressure needed for concrete cover to crack together with the experimental technique used for the verification of the assumptions and the crack width monitoring. Finally, a simple model to estimate the concrete cover cracking pressure due to corrosion is presented. [ABSTRACT FROM AUTHOR]

This paper presents the results of freeze thaw resistance tests performed on a reference mixture and a mixture with superabsorbent polymer (SAP) addition. The SAP mixture showed 40% less scaling than the reference mixture and a slight increase of the compressive strength. A simulation performed with the Hard Core Soft Shell model (HCSS) explains the good performance of the SAP mixture with the formation of a number of small, spherical and closely-spaced voids within the cement paste, which have the same function as air entrainment. [ABSTRACT FROM AUTHOR]

In this study, cellulose fiber reinforced gypsum based materials are investigated numerically and experimentally. This composite material is applied e.g., to sheath and brace timber frame wall elements. It shows a macroscopic response with pronounced strain softening. Due to its capability to dissipate high energy in cyclic loading and its pronounced damage tolerance, the specific material exhibits a high potential in seismically loaded structures. The finite element simulations of the homogenized fracture behavior and the strain localization are performed on the basis of the Plastic-Damage model proposed by Lubliner et al. [1] and Lee and Fenves [2] which have been applied mostly to quasi-brittle materials such as concrete, mortar or ceramics. The ABAQUS user subroutine of Rahman et al. [1] enables the simulation of these composites. A newly developed modification of this subroutine allows now to assign the subroutine to the structural level such as the softening zone and components subjected to tension threshold and tension-compression loading. The input data are gained from quasi-static cyclic uniaxial tensile and compression experiments by applying parameter identification. [ABSTRACT FROM AUTHOR]

There is an increasing need for the use of numerical methods in road design. Here, the main difficulty lies in modeling the highly complex, nonlinear material behaviour of asphalt. In the following paper, a material model based on relationships for quasibrittle materials is presented. This model is intended to describe asphalt behaviour under different loading types within the framework of the finite element method. [ABSTRACT FROM AUTHOR]

Structures like bridges, concrete pavements, cooling- and wind towers are exposed beside damaging environmental influences to cyclic mechanical loading scenarios. Therefore, the reliability of such structures depends among other influences on the degree of structural damage due to fatigue loading. In order to estimate the state of a structure it is necessary to know the development of the crucial material properties during its service lifetime. [ABSTRACT FROM AUTHOR]