FRENCH SPECIFICATIONS FOR SCC: CONCLUSIONS OF THE FRENCH NATIONAL SCC PROJECT (PN

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1 FRENCH SPECIFICATIONS FOR SCC: CONCLUSIONS OF THE FRENCH NATIONAL SCC PROJECT (PN Sylvie Lecrux (1), François Cussigh (2), Michel Guerinet (3). (1) CTG Italcementi Group, France (2) GTM Construction, France (3) EIFFAGE Construction, France Abstract In order to better understand self-compacting concretes and to facilitate their industrial development, a French national project has been created (PN B@P in French). This project involved 50 different partners from building industry and public works, and its total budget was around All partners of the PN B@P have shared their knowledge to develop tools for production follow-up, quality control, tests on jobsite and to give advice for the building contract. Moreover, this work had to take into account European projects that were in progress. Among all questions to which this national project had to answer, one of the main queries was to know if SCC could respect the same current standards (for example EN , future NF EN , etc.) than conventionally-vibrated concrete, or if we had to adapt them. From the production to durability of hardened SCC without forgetting transport, placing, cure, facing, adhesion to reinforcement, construction joint, shrinkage, sensitivity to cracking, different modulus, all researches have been completed by different task groups. After technical studies, only social and economic SCC impacts were missing. Now, all information necessary to a good use of SCC on building sites or in pre-cast plants is available in France. Keywords: SCC, shrinkage, creep, durability, cure, modulus, socio-economic impact. 1. INTRODUCTION The objective of the French national SCC project was to give all the bases for a correct and security use of SCC. With this intention many companies and laboratories joined into carry out several theses, experimental programs (in laboratory and on building site), as well as a "real size" experimental jobsite. The results of these works allowed the drafting of the new recommendations of the French Association of the Civil Engineering, a monograph of works realized in SCC, a file on the socio-economic impacts and a book summarizing the researches on the SCC properties [1][2]. This article which can t present the entirety of the results obtained, only some extracts of the recommendations (modulus, shrinkage, creep and 1049

2 durability) essential for the application of official texts and some socio-economic impacts are presented. This article follows a publication presented in Chicago in 2005 on the relevance of three tests on fresh concrete and their correlation to characteristics measured on concrete in situ according to their casting method.[3] 2. ABOUT SCC SPECIFICATIONS The SCC differ from the conventional concrete mainly by their properties in a fresh state and their capacity of moulding, coating and compaction by gravity alone. They are classified into three categories according to their field of application. The classification is carried out according to the flow index, the horizontal or vertical casting and the thickness (see Table1) [1][3]. Table 1: Definition of SCC categories Horizontal casting Thickness 300mm Thickness > 300mm Vertical casting I I < I < The flow index I : the smallest mesh of reinforcement which the concrete will have to pass through. Category 1: for SCC horizontal casting, thickness 300mm and flow index I >100mm. Category 2: essentially for SCC horizontal casting with a high thickness (> 300mm) or for usual vertical casting. The flow index has to be higher than 80mm. Category 3: reserved for flow index smaller than 80mm (slender or high congested work parts). For categories 2 and 3, there are 2 under-classes (2a, 2b and 3a, 3b) depending on the maximal length of the horizontal SCC placement (5m for 2a and 3a, 10m for 2b and 3b). The workability of the SCC breaks up into three main characteristics: mobility in unclosed environment (determined by the slump-flow test), mobility in confined surroundings (determined by the L-box test), stability (resistance to the segregation and bleeding determined by the sieve stability test). The properties required by the SCC according to their category are presented in Table 2. Table 2: Conformity criteria for the properties of SCC in function of their category Category 1 2a 2b 3a 3b Boundary 20% 20% 15% 15% 10% value for sieve stability Boundary value for L- box No particular prescription with 2 with 2 with 3 with

3 Note 1: it should not have bleeding during the sieve stability test. Note 2: the sieve stability can exceptionally be higher than the value specified in the table without exceeding 30% if one has the proof of no segregation for similar applications. 3. SCC CURING The studies undertaken between 2000 and 2003 on different concrete mix designs (laboratory and industrial compositions) on small and average size elements, showed that indicators of durability (carbonation, capillary absorption and chemically combined water content) are enough discriminating to highlight the effect of a wet cure of short duration or the application of a curing agent, comparatively to an absence of cure on the durability of the concrete s skin. The "real size" experimental jobsite allowed studying the influence of the curing of industrial SCC (intended for slabs and walls), such as it can be practised on building site, on the durability. The test of durability adopted to study the concrete curing is the carbonation in accelerated conditions. The conclusions were: 1/ confirmation of the discriminatory character (especially for C25/30) of the tests of accelerated carbonation, measurement of capillary absorption, measurement of the rate of hydration; 2/ confirmation of the greatest susceptibility of the C25/30 concretes compared to the C40/50 concretes to a "defect" of cure. The PN B@P experiments tend to show that there is no specificity of the SCC. The facility of realization of large-sized horizontal surfaces in SCC or high walls should not make forget the peremptory necessity to protect the concrete from an early evaporation, source of cracking and reduction of the properties of durability of the cover concrete. It is recommended to immediately apply a cure after the casting of the concrete as it should also be the case with a traditional concrete [4][5]. 4. INSTANTANEOUS AND DELAYED DEFORMATIONS The content by volume of aggregates of the SCC usually carried out in France lies between 53% and 67%. That of the vibrated concretes lies between 66% and 73%. The properties of deformation of the concrete (modulus, creep, shrinkage) are functions of the characteristics of each phase and of their proportion. Experimental and theoretical studies showed that by taking the same set of components and the same composition of the paste, the deformations of the concrete increase when the volume of paste increases. The SCC deformation should thus be on average larger than those of the vibrated concretes. This increase in the deformations, although real, is not however as marked as that envisaged by the models described in the literature. On the one hand, the diversity of the mix design and in particular of the mineral additions used, leads to a diversity of behaviours. On the other hand, the experiments highlight a considerable contribution of the mineral additions (pozzolanic or not) with the properties of hardened concrete [6][7][8][9][10][11]. A detailed analysis of the properties of instantaneous and deferred deformation from the SCC was carried out by Group A of PN B@P. It revealed that there is no major deterioration of behaviour compared to a conventional concrete. However, for the applications requiring the taking into account of the corresponding characteristics, tests are necessary for each SCC mix [1]. 1051

4 5. MECHANICAL CHARACTERISTICS For the laws of evolution of the compressive strength with the age, the formulas of the BAEL and standard EN apply well to the SCC of the type C25/30 and C40/50. As for the vibrated concretes, these mix designs are enough random to envisage the strength at young age. For the relation of tensile strength by splitting /compressive strength, the formulas of the BAEL and EN relating to the vibrated traditional concretes apply well to the SCC also [12]. 6. DURABILITY The durability of the concretes is the aptitude of material to resist the mechanisms of deteriorations to which it can be exposed. A concrete structure must preserve its strength and continue to fulfil its structural function throughout its useful and specified lifespan. The physical or chemical aggressions can be of internal or external origin. The SCC durability is governed by mechanisms similar to those known for the conventional concrete. Overall durability is related to the mix parameters affecting concrete density and chemical composition of the binder (and the mineralogy of the aggregates as far as alkali-aggregate reaction is concerned). The rules applicable to ordinary concrete also apply to self-compacting concrete (French standard DTU 21 or NF P , NF EN or fascicule 65A of the CCTG) [1]. 6.1 Alkali-aggregate reaction The French decisional diagram (in the course of updating) of qualification of the aggregates with respect to the alkali-aggregate reaction is independent of the self-compacting character or not of concretes in which the aggregates will be used. In addition, the concrete test is applicable to all the concretes independently of their rheological properties. The only precision to be brought relates to the calculation of active alkaline content of the concrete mix. Indeed, the SCC can contain viscosity modifiers admixtures (VMA) which have not been standardized yet. Without precise knowledge of this type of products, it would be necessary to consider the total alkaline of the VMA as active [1]. 6.2 Reinforcement corrosion: penetration of chloride ions and carbonation The SCC have a volume of paste more important than the traditional concretes and a specific rheology different from the traditional fluid concretes. These differences can modify the inter-connected porosity of the SCC. However, the studies carried out with the CEBTP and the LERM on the influence of the mode of cure on the durability of the SCC, showed that the coefficients of diffusion of the chloride ions of the SCC are comparable to the coefficients of the conventional concretes which presented the same water on equivalent binder ratio (D Cl m 2 /s for SCC C25/30 and to m 2 /s for SCC C40/50). The kinetics of carbonation in accelerated conditions are similar for both SCC and conventional concrete [1]. 1052

5 6.3 Sulfate attacks Exogenous sulfate attack The durability of the traditional concretes with respect to exogenous sulfate attacks is governed by the choice of the binder (chemical barrier) and the porosity of the concrete (physical barrier) related to ratio water/equivalent binder. It is the same for the SCC. Internal sulfate attack (DEF) The concomitant factors necessary to the formation of the deferred ettringite formation in the traditional concretes are as follows: 1. the heating characterized by the maximum temperature in the concrete(> 65 C) and the length of the stage 2. alkaline content 3. sulfate content 4. tricalcium aluminate content 5. high relative moisture 6. the nature of the aggregates. These factors are valid for a SCC as well as for a conventional concrete. The presence of specific chemical admixtures in the SCC has no direct impact on this process [1]. 7. OTHERS PROPORTIES The bonding of SCC to reinforcement is similar to that of ordinary concrete. In some configurations (upper layers in thick pieces), the better stability of SCC with respect to bleeding eliminates the defects encountered with some ordinary concretes and can improve the quality of bonding [13]. The facings obtained with the SCC are potentially better than with the ordinary concretes, particularly as regards to defects associated with formwork watertightness and vibration. More uniform colours can be obtained. On the other hand, SCC can have a propensity to develop blowholes as result of their resistance to segregation. To limit the blowhole phenomenon, the placement method should be optimized and high-slump mixes used within acceptable stability limits [13]. 8. SOCIO-ECONOMIC IMPACT The objectives of the group D of PN B@P were to define interests of SCC, to develop the assets compared to the traditional concrete and to measure the socio-economic contributions of this new concrete. Five topics of reflection were thus defined: 1/ man and his working conditions (noise, safety and painfulness), 2/ quality and architecture (durability, fire endurance and facing), 3/design and execution, economic interest (total reflection on the design, the organization, means and deadlines) and 4/ incidences on the technical specifications and standards. In this article, only items 1 and 2 will be approached. Concerning the working conditions, a study was carried out in collaboration with the CNAMTS (French national sickness insurance fund) on 4492 cases of industrial accidents related to the fabric from 1995 to 2002 and which generated days of sick leaves (SL). 1053

6 This study showed that the contribution of the SCC would have made it possible to avoid 2.5% of the days of SL. This ratio applied to the totality of the days of SL for the fabric per annum represents days [2]. Concerning the design and execution, subject to modifications of some texts in force, it would be possible: to reduce thicknesses of elements or structures, to avoid adaptation for cold joints; to save passive reinforcement from 5 to 10% (covering); to save from 2 to 3% of volume in the prestressed works by tightening of sheaths etc These studies were also completed by an analysis of the costs for the precast factories as well as for the traditional building sites [2]. ACKNOWLEDGEMENTS The authors acknowledge financial support of IREX for the PN B@P and RGCU, and thank all participants of the PN B@P for many helpful discussions on these results. REFERENCES [1] Group A of PN B@P, Recommandations pour l emploi des BAP, Documentation scientifiques et techniques de l association française de génie civil (AFGC), (in French and in English) [2] M. Guerinet, Les impacts socio-économique des BAP, Projet national de R&D, les bétons autoplaçants, IREX and PN B@P, november, (in French) [3] Lecrux, Cussigh, Guerinet, Guillot, Semenadisse and Dykes, French specifications for SCC acceptance on site : the outcome of the french national SCC project (PN B@P), proceedings of SCC 2005, Chicago, 2005, pp [4] L. Linger, Cure des BAP, CST of june 15th 2004, PN B@P axe 3-3, (in French) [5] L. Hasni, Durabilité des BAP du site de Guerville en fonction du mode de cure, rapport final, PN B@P axe 3-3, october (in French) [6] R. Le Roy, Déformations instantanées et différées des bétons à hautes performances, Etudes et Recherches OA 22, LCPC Paris, 1996, pp. 377 (in French) [7] R. Le Roy, D. Duval, F. De Larrard, Grand Viaduc de Millau - Essais de retrait et de fluage sur les 2 BHP, rapport d'étude pour l'aioa, october (in French) [8] R. Le Roy, F. De Larrard, G. Pons, Calcul des déformations instantanées et différées des BHP, Bulletin des LPC, Spécial XIX, mai 1996, pp (in French) [9] T. Sedran, Self compacting concrete, report for task 4 for LCPC, testing SCC. (in French) [10] A. M. Poppe, G.D. Schutter, Cement hydration in the presence of high filler contents, Cement and Concrete Research, 35, 2005, pp [11] F. De Larrard, concrete mixture proportioning, a scientific approach, E et FN SPON, Londres, [12] L. Hasni, Etude des caractéristiques mécaniques des bétons autoplaçants à l état durci, LC/02/BAP/4.1./79 and 78, PN B@P, axe 4-1, (in French) [13] Bétons autoplaçants, recommandations provisoires, documents scientifiques et techniques de l Association Française de Génie Civil, july (in French) 1054