Design, Production and Placement of Self-Consolidating Concrete

The paper describes a new approach to determine the volume of the cement paste required to produce SCC irrespective of the granulometric characteristics of the aggregate. A test vessel has been designed which enables the determination of the void ratio of the aggregate and the necessary paste volume. The method has been applied to various aggregate (crushed quartz porphyry, crushed muschelkalk, gravel, fluvial sand). SCC mixtures have been designed according to the new approach, and it turned out that it has a good predictive potential as the mixture composition is concerned.

Flowable concrete (either compacted with some vibration or selfcompacting) is becoming a widely applied building material. Due to its flowable nature, reinforcing bars can become an obstacle, mixture components may float or segregate and the casting technique determines the orientation of fibers, if any. An increasing range of components is available to optimize concrete concerning rheological and hardened state properties and for the application under consideration. Flowable concrete offers an extended range of engineering properties and the potential for product innovation. fib Task Group (TG) 8.8 “Structural Design with Flowable Concrete” started in 2009 to facilitate the use of innovative flowable materials for the design of concrete structures. Taking into account research findings and practical experience, the main objectives of fib TG 8.8 are to write a state-of-the-art report and recommendations on the structural design with flowable concrete. fib TG 8.8 considers three aspects of flowable concrete: material properties, production effects and structural boundary conditions. This paper discusses the scope of fib TG 8.8 concerning the characteristics and the potential of flowable concrete and presents related design standards. fib TG 8.8 aims at promoting the application of flowable concrete, improving and adapting the concrete design and the production technology and its implementation in guidelines and codes.

An extensive investigation was undertaken to evaluate the influence of binder type, water-to-cementitious materials ratio (

w/cm

), type of coarse aggregate, and maximum size of aggregate (MSA) on workability and strength development of self-consolidating concrete (SCC) designated for precast, prestressed bridge girders. In total, 30 SCC mixtures were investigated. In total, 24 mixtures were non air-entrained and were prepared using crushed aggregate or gravel with three MSA of 10, 14, and 20 mm. The

w/cm

was set to a relatively low value of 0.33 and a higher value of 0.38. Three different binder compositions were investigated. The effect of slump flow consistency on performance was also investigated. Test results indicate that SCC made with the higher

w/cm

exhibited superior fluidity retention, passing ability, and filling capacity. Mixtures proportioned with the lower

w/cm

developed greater stability. Mixtures made with the crushed aggregate of 10 mm MSA exhibited greater passing ability, higher filling capacity, and better retention of air content than similar SCC prepared with 14 and 20 mm MSA. Mixtures proportioned with the gravel had superior passing ability, filling capacity and similar stability compared to those made with crushed aggregate of the same MSA.

Robustness is the ability of a concrete mixture to satisfy its defined requirement profile despite any unfavorable influences, they may be predictable or unpredictable. The objective of this study is to investigate ways to increase the robustness of SCC by means of specific mixture proportioning, especially in the fine grain and powder range. The Superplasticizer Based Approach and the characteristic boundary consistency curves are tools whereby the general robustness of grain compositions can be estimated. Furthermore the Superplasticizer based Water Demand is proven to be a useful tool to characterize grain compositions concerning their packing density, which in turn is an important information to ensure the necessary surplus of fines in the overall mixture proportioning. By several examples it is demonstrated how little changes in the powder composition can cause major changes in concrete properties and how such influences can be determined effectively.

Concretes for self-compacting concrete (SCC) applications have to combine a high fluidity and fluidity retention with high segregation resistance. This optimal rheological behaviour is obtained by combining a suitable aggregate grading curve with correct rheological properties of the suspending matrix (i.e. the cement paste). It is shown in this paper how these rheological properties can be influenced by polycarboxylate-based superplasticizers. Furthermore it is shown that relatively easy tests can be used to access the rheological properties of both the fresh cement paste and the concrete quantitatively. It is demonstrated that a new superplasticizer leads to an improved robustness in the formulation of SCC.

Varying ambient temperatures in plants or on construction sites during casting of SCC can cause serious problems affecting the fresh concrete performances, such as rheological properties and setting time, with consequences for the hardened properties in the structure. By sensible choices of the components, the robustness of SCC mixtures against temperature variations can be improved. However, this aspect has not been the focus of intensive research yet. In this study the effects of varied ambient temperatures on the early performance of differently composed SCC mixtures are investigated, with emphasis on changes in rheology, early deformations, heat evolution and setting. Focus is placed on the study of the influence of the polycarboxylate ether molecule type as well as different viscositymodifying agents on the temperature robustness. Effects on the relevance for practical concrete applications are evaluated, which will provide a reliable framework of possible actions on the appropriate use of admixtures for SCC.

SCC can encompass a wide range of concrete rheology. Previous research has shown the importance of specific rheological characteristics for application requirements such as reduced formwork pressure, increased static and dynamic segregation resistance, and increased pumpability. The required rheological characteristics for different applications are discussed in terms of yield stress, plastic viscosity, and thixotropy. Micromortar rheology measurements were conducted with four different high-range water reducers (HRWR) and two different water/cement ratios to demonstrate potential differences in rheology due to HRWR selection. The results indicated that HRWR selection can significantly impact micromortar rheology.

The successful application of self-compacting concrete depends more and more on the exact knowledge of the rheological properties during mixing, handling and placement. Rheological investigations with mortar compositions of similar flowability reveal that different Portland cements of similar fineness affect static yield stress and thixotropy differently. Higher amounts of superplasticizer added to adjust flowability reduce the static yield stress and thixotropy of the mortar and the segregation resistance of the equivalent concrete. This behaviour can be explained by superplasticizer adsorption and surface coverage by the adsorbed polymer on the cement particles. Surface coverage affects inter-particle forces as well as nucleation probability at the surface. An increase in superplasticizer dosage leads to a higher surface coverage by polymers. At higher surface coverage the effective layer thickness increases and causes a reduction in the maximum attraction between the particles. Furthermore, the number of available nucleation sites decreases and the bridging distance between the particles increases. Less force is needed to disperse the particles, static yield stress and thixotropy become lower. The results illustrate the importance of understanding the inter-particle interactions in concrete if rheological properties, workability and segregation resistance are to be controlled.

This study deals with the rheological properties of self-consolidating concrete (SCC) incorporating various percentages of metakaolin (MK) and silica fume (SF) as a partial replacement of cement. Plastic viscosity and yield stress were evaluated at different slump flow values using a concrete viscometer. The effect of high range water reducing admixture (HRWRA) dosage and the total time for flow, the time to reach 500 mm diameter (T50), and the final diameter of the slump flow test were also investigated and studied in this research program. The results showed that the plastic viscosity and the yield stress increase with the increase of the percentage of MK. The results also demonstrated a correlation between the final slump flow diameter and the yield stress similar to that presented in the literature.

A major requirement on self-compacting concrete (SCC) is the resistance to any kind of separation. In the presented studies the segregation behavior of aggregates was analyzed systematically. The rheology of selfcompacting mortars was dealt with at first. Following, the segregation of particles of different size, shape and density in various mortars was examined. The aim was to find an analytical relation to estimate the risk of sedimentation, using the characteristics of the particles and those of the mortars. The classification of the aggregates according to their potential segregation is rather simple. But the description of the segregation resistance of the mortar is much more difficult. It is not possible to evaluate a mortar solely based on the rheological properties. The mixture composition must always be considered as well. Tests on concrete samples were conducted additionally to determine the influence of the overall system of SCC on the sedimentation of the aggregates.

Measurement artifacts in concrete or mortar rheometers often prevent the user from having access to absolute correct values of the rheological parameters of the tested material. As there does not exist any rheometer giving access to the “correct” or “real” values of these parameters, it is even not possible to estimate the order of magnitude of the error induced by these artifacts. It is however possible to have access to the local and real rheological behavior law by measuring local velocities and local concentrations of particles through Magnetic Resonance Imaging (MRI) techniques. In this paper, we compare macroscopic measurements and local MRI measurements of the behavior of suspensions of natural sand particles and bi-disperse spherical particles in model yield stress fluids (emulsions). In doing so, we seek to illustrate the potential consequences of artifacts on the measurements of the flow curve of cementitious materials. We reach the conclusions that particle migration is at the origin of the discrepancy between concrete rheometers.

The investigation presented herein was intended to study the influence of long transportation time and extreme temperature on the fresh performance of self-consolidating concrete. The study is useful in simulating concrete mixing and hauling by means of concrete truck mixer during extreme temperature. Temperatures of 43 and -0.5oC, to simulate hot and cold weathers, were used to evaluate the unconfined workability (slump flow), flow rate (T50), and dynamic stability (VSI) of the matrices transported for 60 and 80 minutes. Mixing and transporting under the temperature of 21oC and transportation duration of 10 minutes was adopted as the control condition. Polycarboxylate-based high range water-reducing admixture (HRWRA) and viscosity-modifying admixture (VMA) were used to produce self-consolidating concretes with slump flow of 635 ± 25 mm, VSI of 0, and T50 of 2 to 5 seconds. The test results revealed that the selfconsolidating concrete mixed and transported under extreme temperature experienced slump flow loss in elevated temperature and slump flow gain in cold environment, when compared to the equivalent concrete produced under the reference condition. While the flow rate/plastic viscosity of the selected matrix increased in the cold temperature, the concrete remained highly stable irrespective of the selected temperature.

In practice, self-compacting concrete (SCC) is considered as a simple extension of conventional vibrated concrete (CVC) when pumping is concerned. The same equipment, materials, pumping procedures and guidelines used for CVC are applied when pumping SCC. On the other hand, it has been clearly shown that the rheological properties and the mix design of SCC are different than CVC. Can the same pumping principles employed for CVC be applied for SCC? This paper compares the some published results of pumping of CVC with those for SCC. A first striking difference between pumping of CVC and SCC is the flow behaviour in the pipes. The flow of CVC is a plug, surrounded by a lubricating layer, while during the flow of SCC, part of the concrete volume itself is sheared inside the pipe. As a result, the importance of viscosity increases in case of SCC. Due to the low yield stress of SCC, the behaviour in bends is different, but quite complex to study. Due to the lower content of aggregate and better stability of SCC, as it is less prone to internal water migration, blocking is estimated to occur at lower frequency in case of SCC.

The flow conditions near solid surfaces (no-slip, slip, lubrication) were investigated using the results of gravimetric flow tests, full scale instrumented pump tests and rheological measurements on matrix, mortar and self-compacting concrete. Modeling with the measured data could fit plug-flow with a 0.6-1 mm thick lubrication layer of matrix having similar lubrication layer viscosity as the lower values of Kaplan: 175-320 Pa.s/m. Visualization of boundary flow conditions and flow profiles and measurements of concrete sticking to different pipe materials related to increased flow rate along smooth acryl and reduced along rougher rubber surfaces. The existence of plug flow during SCC pumping may be questioned and possible causes for formation of a lubricating layer and a plug are discussed as well as a brief review of void formation at the surface

Today’s concrete structures call for high-tech construction materials, for example self-compacting high-performance concrete (SCHPC) as self-compacting high-strength concrete (SCHSC) and self-compacting ultra-high-strength concrete (SCUHSC). These concretes are defined as concretes with special properties. This development aims to increase the packing density through the selection of coarse and fine aggregates combined with a reduction in the water-to-binder ratio (

w/b

). To achieve this goal, state-of-the-art concrete plants need to meet certain minimum requirements. In an effort to realize shorter construction times and develop new concrete process technologies, and in view of ever-increasing degrees of component loading, international research has been going on for approximately 30 years for materials that have led, among other things, to the development of high-performance concrete. A trend towards the development of customized concretes, for example of SCHPC, can also be observed in the German construction industry.

Computational modeling of fresh SCC flow is a comprehensive and time consuming task. The computational time is additionally increased when simulating casting of reinforced sections, where each single reinforcement bar has to be modeled. In order to deal with this issue and to decrease the computational time, an innovative approach of treating a reinforcement network as a porous medium is applied

.

This contribution presents the model for concrete flow through reinforced sections, based on Computational Fluid Dynamics (CFD), coupling a single-phase flow model for SCC and a continuum macroscopic model for porous medium. In the last part of this paper, numerical simulations are compared with experimental results obtained on model fluids.

The simulation of the flow of fresh grout allows predicting the filling behavior at defined conditions. Hereby, the production process can be optimized. In Mol (Belgium), a field testing site for storage of nuclear waste material has been developed in the past decades. At this location, the Economic Interest Grouping EURIDICE investigates the possibility to store containers with nuclear waste material in horizontal underground tunnels. The space between the tunnel lining and the waste containers could be filled with a cement-based grout. The aim is to create a solid body without voids that can withstand ground settlements. Since the filling process cannot be visually observed a study was carried out in order to predict the filling by simulating the fresh grout flow with computer software. The objective of the study was to determine a proper filling strategy for this project. The experiments were carried out at the Delft University of Technology in The Netherlands. The Nuclear Research & Consultancy Group in Petten, The Netherlands, simulated the filling process with OpenFOAM, a software package that is based on Computational Fluid Dynamics (CFD). The study consisted of three parts: firstly, the rheological characteristics (thixotropy, yield value and plastic viscosity) of the fresh grout were determined, secondly, a parameter-study was carried out on the filling behavior of the grout with a scaled Plexiglas version (maximum length: 5.76 m) of the underground tunnel and finally, simulations were performed and compared to experimental results. This paper describes the case-study and experimental results, and compares the filling behavior determined from experiments and computer simulations using CFD.

SCC is nowadays a worldwide used construction material. However, heterogeneities induced by casting may lead to variations of local properties and hence to a potential decrease of the structure’s load carrying capacity. The heterogeneities in SCC are primarily caused by static and dynamic segregation. The present paper reports property maps for a beam based on particle distributions at the end of casting derived from numerical flow simulations. A finite volume based numerical model is used to predict particle distributions at the end of casting, which are then converted into property maps using semi-empirical relations from the literature.

In the course of the wider use of concretes with pourable consistency more and more practice-relevant and economic questions arise. The pressure of concrete on formwork is one of those questions. In the literature very contradictory statements are depicted partially to the pressure of concrete on formwork when using concretes with pourable consistency. Therefore the aim of the research project was to examine the influence of the rheological properties of selfconsolidating concretes (SCC) and vibrated concretes (VC) with consistencies F5/F6 according to DIN EN 206-1:2001-07 on the formwork pressure. The research project was divided into two steps: “Development and investigation of model mixtures for self-compacting concrete (SCC) and vibrated concrete (VC) respectively” and “Measurements of formwork pressure in constructional elements like walls”. In the first step basis mixtures had to be developed. Concretes with F5/F6 consistencies, two powder-type SCC (PT), and two viscosity-agent-type SCC (VAT) were used. The latter mixtures differed considerably in viscosity. Thus all relevant cases regarding the rheological properties were covered by these pourable concrete mixtures. In the second step systematic investigations were conducted to determine the effect of the rheological properties on the fresh concrete pressure on the formwork of constructional elements (walls). By concreting in a precast element plant a reference to practice was given.

Various prediction models, based on experimental results to evaluate formwork pressure exerted by self-consolidating concrete were established based on extensive laboratory evaluation. The models are based on the measurements of the structural build-up of the concrete with rest time and placement characteristics of the concrete. The latter includes the rate of rise of the concrete in the formwork, concrete temperature, and minimum dimension of the formwork. This paper presents the results of two campaigns of field validation carried out at Sherbrooke, Quebec, and Skokie, Illinois, to validate the prediction models. The results confirm that the established models offer adequate prediction of form pressure exerted by self-consolidating concrete.

A material model for fresh concrete pressure, if designed on a physically sound basis, enables the calculation of the formwork pressure of different kinds of concrete, depending on their rheological properties. In this paper, the concept and results of experimental and rheological investigations on fresh concrete pressure are presented. Within this experimental program a special formwork model for the fresh concrete pressure was designed. A material model was developed, describing the behaviour of formwork pressure, depending on various aspects and materials. In order to verify and adjust this material model, a series of experiments on real formwork systems were performed.

The presented investigations were conducted at the Institut für Massivbau and contributed to a joint research project including several German research institutes [1]. A number of experimental tests on highly workable concretes were carried out. Small scale material analyses as well as measurements of the formwork pressure on large specimens were carried out. Based on the test results an analytical model for the calculation of the concrete pressure on vertical formwork was developed. The analytical model takes into account the time dependent material parameters of the fresh concrete, the specific properties of highly workable vibrated concretes and self-compacting concretes (SCC) as well as operation aspects. A proposal for the design of formwork, based on the experimental tests and the semi-probabilistic safety concept was developed. It was found that even for highly workable concretes, the design load is often lower than the hydrostatic concrete pressure.

There is an increasing interest of developing and using composite cements, e.g. to reduce CO2-emmissions in cement production. This paper discusses results from an investigation of the influence of composition of ternary composite cements on the drying shrinkage of a typical low cost SCC for buildings (

w/cm

= 0.55) as used in Norway. Various Portland cements (CEM I), Portland fly ash cements (CEM II/A-V), Portland limestone cements (CEM II/A-L) and a Portland-composite cement (CEM II/B-M) were tested. The fineness of clinker phase, fly ash and limestone were varied systematically in the cements. Shrinkage was determined from length measurements of 500 mm long prisms, 100 x 100 mm in cross section, stored in water from demoulding until 7 days of age and then at 50% RH until 12 months of age. As expected, increased fineness and early reactivity of the cements increased shrinkage. The results showed, however, that the drying shrinkage was not significantly affected by the cement type. I.e. replacing up to 35% of the clinker by fly ash and limestone did not influence the drying shrinkage.

It is indicated that the risk of early age shrinkage cracking on highstrength self-compacting concrete (SCC) increases due to autogenous shrinkage caused by low water-to-cement ratio (

w/c

) and high cement content. For the purpose of reducing the shrinkage strain of high-strength SCC, three kinds of shrinkage-reducing concrete materials, shrinkage-reducing admixture (SRA), blast furnace slag aggregate (BFS) and limestone aggregates were examined. It was found that these materials each showed excellent shrinkage-reducing effect better than each ordinary material when they were used separately. In addition, the authors have found that the shrinkage-reducing mechanisms were individually different and the shrinkage-reducing effect was approximately 45% to 61% when used all together.

One of the most challenging problems that can confront a repair engineer is that the completed structure is a monolithic mass that is free from cracks, especially with regard to the plastic shrinkage cracking in concrete flatwork. The more roughness in the surface of substrate, there will be more bond strength between substrate and repair overlay. But, meanwhile, the more roughness, more restraints induced in overlay, which during shrinkage, tensile stresses will be generated in repair materials. The results of investigation reported herein concern the effect of the type of repair materials on free and restrained plastic shrinkage properties. Four types of repair materials were used in this work are plane self-consolidating concrete (SCC), SCC containing silica fume (SF), SCC containing SF and latex (Styrene Butadiene Rubber), and SCC containing SF, latex, and fiber. To roughen the surface of substrate base, dents were used to provide restraints. The panels were subjected to severe combination of wind, temperature, and relative humidity. The test program includes: settlement strain, free and restrained shrinkage strain, evaporation and bleeding rates, and crack characteristic measurements. The results show that, while the rates of evaporation and bleeding affect shrinkage, it is over shadowed by other factors, such as fiber type, binder type and use of latex. The results show that, a significant improvement was observed for SCC with latex and fiber exhibiting the lowest plastic settlement and shrinkage strains, as well as crack area and longest time to first cracking. The plane SCC exhibited almost twice the settlement and shrinkage strains than SCC with latex and fiber.

Shortening the hardening time of SCC allows the precast concrete industry to respond to its challenge of productivity and extend the scope of application of these materials. Indeed, reducing the elapsed time between mixing fresh concrete and demoulding the concrete products represents a key factor for a faster rotation of the equipment and reduces the global cost of production. The results of the study show that it is possible to accelerate significantly the hardening kinetics of SCC. Applying an optimized thermal treatment on SCC mixture based on conventional constituents and suitable admixtures enables one to produce concrete that stays workable for 30 minutes and reaches compressive strength up to 25 MPa after 4 hours of curing and more than 80 MPa at 28 days. The influence of the thermal treatment, the use of hardening accelerator and ultrafine particles were evaluated.

The paper deals with time-dependent increase of compressive strength, splitting tensile strength and modulus of elasticity as well as with compressive stress-strain curves of self-compacting concrete (SCC) made with crushed limestone aggregate and high content of limestone filler. The characteristics under consideration were tested at the ages of 1, 3, 7, 28, 180, 360 and 720 days. Time evolution of the strength characteristics and modulus of elasticity was estimated with analytical models given in European code Eurocode 2. The study revealed that the models can adequately predict time evolution of the SCC characteristics, when coefficient

s

in the models is equal to 0.17, 0.08 and 0.25 for compressive strength, tensile strength and modulus of elasticity, respectively. These values of coefficient

s

are quite different from the value 0.2 proposed by Eurocode 2 for used cement strength class.

SCC has been used in various applications, such as pavements, marine structures, shallow foundations, etc. that can be concomitantly exposed to sulfaterich environments and frost action. To evaluate the resistance of SCC mixtures to sulfate attack considering the effect of frost action, the present study introduces accelerated testing procedure combining the exposure to aggressive magnesium and mixed magnesium-sodium sulfate solutions with freezing-thawing cycles. After five months of exposure, the results showed that SCC mixtures incorporating high dosage of fillers (limestone and ultrafine kaolin) had inferior physicomechanical properties relative to the other SCC mixtures. Thermal and microscopy analyses indicated that mutual effects of sulfate attack and freezing-thawing cycles caused severe distress in such cementitious systems.

In this paper the bond mechanism of steel reinforcement to concrete and the shear capacity are examined. Tests have been conducted on conventional vibrated concrete (CVC) and self-compacting concrete (SCC). The results from pull-out tests on 200 mm cube specimens show that for the same compressive strength the maximum bond stress for SCC is as high or higher than for CVC and this for all tested diameters (8, 12 or 16 mm). The bond stress increases with increasing bar diameter. The specimens were loaded at constant rate and during testing the slip of the bars and the applied load were recorded. The four-point loading tests point out a slightly decreased shear capacity of SCC in respect to CVC with the same compressive strength. The shear capacity decreases with increasing shear span-to-depth ratio a/d (2 to 3) for all the tested concrete types. During the testing the maximum applied load was recorded and the crack and failure mechanism were observed.

Self-compacting concrete (SCC) can be considered as one of the most revolutionary innovations in the worldwide concrete construction industry and is rapidly gaining acceptance as a potential replacement for normal concrete (NC). Due to its rheological characteristics, fresh SCC has the ability to flow under its own weight and adequately fill highly congested concrete members without the need of external compaction. The modified composition of SCC, compared to NC, may have consequences on the hardened concrete properties. One of the most important issues is the steel-toconcrete bond, which for NC has been observed to be significantly affected by the concrete depth under the horizontal bars of deep elements, a phenomenon called “top-bar effect”. Design codes usually confront this bond reduction by applying a correction factor. The present paper examines the occurrence of top-bar effect in SCC columns with transverse reinforcement bars in various heights by performing pull-out tests to estimate the anchorage capacity of reinforcement bars, in terms of the bond stress curve as a function of slip.

SCC can have very different rheological properties depending on the application and local mix design traditions. By definition, SCC should encapsulate the reinforcement bars to ensure proper bond strength, however, variations in bond strength may at least theoretically occur dependent on the rheological properties and the flow characteristics history near the individual bar. Especially, the bond strength may be questioned for SCC with a slump flow in the range 500-580 mm which is often used to obtain good control of flowing concrete as well as high segregation resistance. This paper presents the results of an experimental program investigating the relationship between the rheological parameters yield stress and plastic viscosity and bond strength of reinforcement bars. A reference conventional slump concrete requiring vibration to consolidate and several SCCs of equivalent strength class but with varying rheological parameters as measured by the 4CRheometer were prepared. Batches of 250 liters were cast into a formwork containing 12 mm diameter ribbed reinforcement bars fixed horizontally. The distance of SCC flow in the formwork was 2.5 m. Bond and compressive strengths were tested after 7 days of curing. The results indicate that the bond strength is not significantly influenced by the rheological properties of SCC and that the bond strength corresponds to that of conventional concrete.

Self-consolidating concrete (SCC) is widely used in the construction industry. SCC is a high performance concrete with high workability and consistency allowing it to flow under its own weight without vibration and makes the construction of heavily congested structural elements and narrow sections easier. Recently, fiber-reinforced polymer (FRP) reinforcements, with their excellent mechanical and non-corrosive characteristics are being increasingly used as a replacement for conventional steel reinforcement. In spite of the wide spread of SCC applications, the bond behaviour of FRP bars in SCC has not been fully studied. This paper presents the results of the first phase of an experimental study on the bond characteristics of sand coated CFRP bars in SCC beams. The experimental program of this phase consists of four SCC beams. All beams had the same geometric dimensions and were reinforced with single CFRP bar (12.7 mm in diameter). All beams were tested up to failure by four point bending regime with the shear span vary from 550 to 950 mm. The test results were used to evaluate the bond strength at different embedded lengths. These preliminary test results showed that the ACI 440.1R-06 [1] over estimated the development length of the CFRP bars in SCC, while CAN/CSA-S6-06 [2] equation is unconservative.

Self-compacting fiber-reinforced concrete (SC-FRC) combines the benefits of highly flowable concrete in the fresh state with the enhanced performance in the hardened state in terms of crack control and fracture toughness provided by the wirelike fiber-reinforcement. Thanks to the suitably adapted rheology of the concrete matrix, it is possible to achieve a uniform dispersion of fibers, which is of the foremost importance for a reliable performance of structural elements. Balanced viscosity of concrete may also be helpful to drive the fibers along the concrete flow direction. An ad-hoc designed casting process may hence lead to an orientation of the fibers “tailored” to the intended application, which is along the anticipated directions of the principal tensile stressed within the structural element when in service. This converges towards a “holistic” approach to the design of structure made with highly flowable/self-consolidating FRC, which encompasses the influence of fresh state performance and casting process on fiber dispersion and orientation and the related outcomes in terms of hardened state properties. The fib task Group 8.8 “Structural design with highly flowable concrete”, sub-group fiber concrete, appointed in April 2009, aims at drafting recommendations to facilitate and spread the use of these innovative materials, merging together research findings and practical experience.

Fiber addition may lead to a strong modification of a cementitious material rheological behavior. First, the existence of a transition in the evolution of the material rheological behavior is shown relatively to the fiber volume fraction, in isotropic state. This transition occurs at a critical fiber volume fraction between a regime in which hydrodynamic effects govern the rheological behavior and a regime in which direct mechanical contacts between fibers are predominant. Then the orientation process induced by a casting flow is highlighted. The effect of yield stress on the orientation process is specially studied. Orientation of large amount of fibers is derived from the equation describing a single fiber orientation.

The dispersion and the orientation of fibers in concrete can be governed through a suitably balanced set of fresh state properties and a carefully designed casting procedure, if proved effective. This would allow one to achieve a mechanical performance of the fiber-reinforced cementitious composite which is optimal to the foreseen structural application, even keeping the fiber content at relatively low values (e.g. maximum 1% by volume) and aligning them with the direction of the principal tensile stress within the structural element when in service. Modeling the casting of fresh concrete, through suitable numerical tools, in order to anticipate the direction of flow lines, along which fibers may orient, and optimize the whole process to the foreseen structural application is of the foremost importance. Monitoring fiber dispersion related issues through suitable non destructive methods would also be crucial for reliable, time and cost-effective quality control. In this paper a pioneer study has been performed in the above said framework. The results are really encouraging and pave the way towards a holistic approach to the design of self-consolidating fiber-reinforced concrete structures.

The shear behavior of reinforced “Z”-shaped push-off specimens made with self-compacting concrete (SCC) and self-compacting fiber-reinforced concrete (SCFRC) was analyzed by means of experimental tests. Testing consisted of two phases. Firstly, specimens were precracked subjected to linear load along the shear plane. During this first phase three precracked levels were distinguished (without precrack, thin and thick precrack). Then, precracked specimens were tested under direct shear load. The shear behavior along the shear plane was analyzed by means of the crack opening and shear displacement versus shear load process. Variables were: the type of concrete (SCC, or SCFRC with different fibers contents: 40 kg/m

3

or 60 kg/m

3

), the transversal reinforcement (TR) and the precrack width. The analysis was specially focused on the study of aggregate interlocking. The failure occurrence is better controlled thanks to the presence of fibers, the shear behavior is more ductile.

This paper describes the results of an experimental campaign aimed at investigating the long-term behaviour of beams cast using fiber-reinforced self-compacting concretes containing either steel or synthetic fibers in comparison with that of plain self-compacting concrete beams with standard reinforcement. The flexural behaviour of six different beams was investigated in a long-term four point bending test under constant loading. All the beams were pre-cracked before the long-term test. The tests showed that fibers have an important role in controlling the increase of crack opening over time. The greatest reduction in the delayed crack opening was obtained using a mixture of steel and macro synthetic fibers.