La méthode du mortier de béton équivalent (MBE)—Un nouvel outil d’aide à la formulation des bétons adjuvantés

Materials and Structures (Impact Factor: 1.39). 04/2012; 33(8):475-482. DOI: 10.1007/BF02480524

ABSTRACT L’article présente une nouvelle méthode d’aide à la formulation des bétons adjuvantés. Elle consiste à concevoir, à partir
d’une composition de béton, un mortier, dit mortier de béton équivalent (MBE), dont les propriétés rhéologiques sont corrélables
à celles du béton. Le but est de diminuer le nombre de gâchées de béton. La démarche de mise au point de la méthode, son champ
d’application et ses limites sont présentés. Le mode opératoire ainsi que le matériel nécessaire sont détaillés. Un exemple
de corrélation entre les propriétés rhéologiques mesurées sur MBE et celles mesurées sur le béton associé est présenté. Parallèlement
aux suivis rhéologiques, des suivis thermiques sur MBE peuvent être effectués. Ils permettent d’anticiper les effects de différents
adjuvants sur le temps de prise du béton. On montre que les décalages observés par suivi thermique traduisent bien les écarts
de résistances aux très courtes échéances. En associant suivis rhéologiques et suivis thermiques, la méthode MBE permet de
sélectionner rapidement parmi différents adjuvants celui qui répond le mieux aux exigences d’efficacité (rapport dosage/coût),
de maintien rhéologique et de délai de décoffrage.
This paper deals with a new method to design concrete containing admixture. Its principle is to design a mortar, deduced from
the concrete composition and called concrete equivalent mortar (CEM), for which the rheological properties display correlation
with those of concrete. The aim is to reduce the amount of concrete batches. This article presents the scientific approach
which has led to this method, its field application and limits. The test procedure and the apparatus are detailed. An example
of correlation between the rheological properties measured on CEM and on the corresponding concrete is presented. After monitoring
fluidity versus time relationship, thermal measurements on CEM were carried out. These measurements allow to anticipate the
effects of different admixtures on the setting time. One shows that the setting delays obtained on CEM are in good agreement
with the difference of compressive strengths measured at early age. With rheological and thermal results, the CEM method permits
to select between numerous admixtures, which is the most likely to fit in with the specifications of effectiveness (proportion/cost
ratio), capacity of keeping the rheological properties over time and delay of formwork removal.

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    ABSTRACT: The falling-head method determined using a permeameter cell is commonly used to study permeability (k) of soils and facility of fluids to travel through a solid skeleton. A research program was undertaken to evaluate the suitability of such test for assessing permeability of freshly mixed mortars and concrete. Validation of k values with respect to bleeding and surface settlement responses and correlations with permeability calculated using empirical soil models are established. The falling-head method was found appropriate to assess the effect of mixture composition (i.e., binder content, water-to-cement ratio, and chemical/mineral admixtures) on permeability variations. Concrete incorporating coarse aggregates exhibited greater permeability levels than those determined on mortars. Despite the differences in chemical nature between soil and mortar, the actual k values determined by testing were found to be well correlated to those calculated by using several previously reported empirical soil models. DOI: 10.1061/(ASCE)MT.1943-5533.0000630. (C) 2013 American Society of Civil Engineers.
    Journal of Materials in Civil Engineering 05/2013; 25(5):580-588. DOI:10.1061/(ASCE)MT.1943-5533.0000630 · 1.32 Impact Factor
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    ABSTRACT: Fine recycled concrete aggregates (FRCA) also called recycled sand, having particle sizes smaller than 5 mm, are essentially composed of mortar and hardened cement paste. Therefore they induce a large water demand which makes them hard to recycle into mortar and concrete. In this paper, the properties of mortars containing FRCA have been studied, including fresh properties, mechanical properties and interfacial transition zone (ITZ) microstructure. The influence of saturation state of FRCA (dried or saturated) on the properties of mortars of identical compositions has first been studied. The results showed that the slump of mortars containing dried FRCA is always larger than that of mortars containing saturated FRCA. Indeed, in the case of dried FRCA, the theoretical amount of absorbed water is added at the beginning of mixing leading to a temporary increase of the initial efficient W/C ratio and volume of paste, leading to a better workability before its absorption into FRCA. On the contrary, the absorbed water in saturated FRCA is not readily available and thus cannot contribute to increase the initial efficient W/C ratio. Moreover, the compressive strength of mortars containing dried FRCA is always larger than that of mortars made with saturated FRCA, which is attributed to a thinner interfacial transition zone improving its mechanical properties. The influence of the fraction of recycled sand and of the granular class of recycled sand on the mechanical properties of mortars has then been studied with saturated FRCA. The compressive strength of mortars decreases quasi linearly as the replacement percentage of recycled sand increases. Moreover, it is shown that the finer fraction of recycled sand (0/0.63 mm) has the worse effect on the mechanical properties of mortars.
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    ABSTRACT: The strength development of self-compacting mortars (SCM) containing calcined silt (CS) and ground brick waste (GWB) was investigated. The variables are the nature of addition (CS and GWB) in the binder and the heat curing at different temperatures (20 ºC and 60 ºC) at 7 and 14 days of curing. Two temperatures 20 and 60 ºC were applied to samples with intermediate levels (depending on the drying method applied to precast) for 18 hours in total. In this study, a Portland cement (CEMII), Calcined silt (750 ºC for 5 hours), ground waste brick, were used in the binders of SCM. The results show that the compressive strength to 14 days of mortars, increases with annealing (60 ºC) compared to that measured at 20 ºC. Also, values of compressive strength of mortars at 14 days that are close to those obtained without 28 days curing treatment. Indeed, a strength gain of about 20.5% and 27.3% was obtained respectively for the SCM with GWB and the SCM with CS. However, a small change in mass recorded for both types of mortars.
    Materials Research 10/2013; 16(5):1058-1064. DOI:10.1590/S1516-14392013005000094 · 0.48 Impact Factor