THE INFLUENCE OF ULTRAFINE GCC ON THE PROPERTIES OF SELF COMPACTING CONCRETE

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1 THE INFLUENCE OF ULTRAFINE GCC ON THE PROPERTIES OF SELF COMPACTING CONCRETE P.Gonnon (1) and Hans Werner Roeth (2) (1) OMYA SAS 5 Rue de l Aiguillon, ZI Lyon-Nord, GENAY, France (2) OMYA Group Marketing, Switzerland 1. INTRODUCTION The properties and advantages of Self Compacting Concretes are well-known in the meantime: extra-ordinary flowability, perfect filling of the mould even in the presence of dense reinforcement, improved workability etc. Compared to normal standard concretes these SCC s are showing a significantly increased content of fine and ultra-fine materials. Originally the fines had the only task to stabilize the very liquide concrete and to avoid any kind of segregation. Currently other parameters are coming to the fore as durability and robustness for instance, which have their roots in an optimized low water-cement resp. waterbinder-ratio. In this regard OMYA have done an essential step and developed BETOFLOW, which is an ultrafine Calciumcarbonate addition on a slurry basis. Betoflow OM65% combines the classical filler effect with the fluidizing properties of a lubricant. Both together allow to produce a SCC with outstanding properties as a clear gain in density, strength and mechanical resistance. This paper will show how Betoflow OM65% as an industrial ultrafine mineral concept can enable SCC to overcome technical barriers as water demand, architecural improvements, stability performance as well as pozzolanic effects. 2. MATERIALS 2.1 Cement The cement being used during this study has been a French Portland Cement CEM I 52,5 R CE CP2 NF. Its mineralogical composition due to Bogue looks as follows: 217

2 C 3 S = 59,0 % C 2 S = 14,6 % C 3 A = 10,3 % C 4 AF = 8,3 % The density of the cement comes to 3,13 t/m3 and the specific surface (Blaine) lays at cm2/g. Strength figures of the mortar are 40 MPa (2 days) and 65 MPa (28 days). 2.2 Aggregates The used aggregates are a broken sand (0-4 mm) and crushed stones (5-12,5 mm), both with an absolute density of ρ s,g = 2,5 t/m 3. Their granulometric analyses are shown in figure 1: Granulométries des granulats et du ciment ,1 0,01 0,001 Ciment Gravillon 4/12,5 Sable 0/4 Figure 1 : Granulometric parameters of cement and aggregates 2.3 BETOFLOW OM65% Betoflow OM65% is a liquid concrete additive on basis of an ultrafine chalk, produced in the OMYA plant of Omey/Champagne, which is certified according to ISO 9001-V2000. Its solid content exceeds 65% and the Omya-technology allows a d 50 of 2,2 μm. The Betoflowfacilities at Omey are working on an industrial scale. The size distribution of Betoflow compared with a silica fume is shown in figure 2: 218

3 Comparaison courbes granulométriques CILAS ,0 90,0 80,0 70,0 60,0 %<...µm 50,0 40,0 30,0 20,0 10,0 0,0 100,0 10,0 1,0 0,1 Diamètre (µm) Bétoflow Fumée de silice densifiée Figure 2 : Granulometric parameters of Betoflow and silica fume 2.4 Superplasticizer The used superplasticizer has been a modified polycarboxylate out of the Optima-family of Chryso. It is a ready-for-use liquid acrylic co-polymer, the ph-value lays at 5,5 with a solid content of 34,5 % and a density of 1,1 kg/l. 3. REFERENCE RECIPES AND CHARACTERISTICS To determine the influence of the BETOFLOW OM65% on the main characteristics of the ultra-liquid concrete the following parameters have to be measured: - slump flow - air content - density - shrinkage - compression strength The dosage of Betoflow has been varyed on four different stages : 0, 10, 12 and 14 % of the cement-weight. The max. size of the aggregates has been 12,5 mm. All details of the four recipes are shown in Table 1: 219

4 Table 1: Recipes without and with BETOFLOW OM 65% Dosage E 0 E 1 E 2 E 3 Cement CEM I 52,5 [kg/m 3 ] BETOFLOW OM65% [kg/m 3 ] Sand 0/4 mm [kg/m 3 ] Aggregates 4/12,5mm [kg/m 3 ] Water [kg/m 3 ] Superplasticizer [l/m 3 ] Fresh concrete properties: Slump flow [mm] Air content [%] 0,7 0,7 0,8 0,8 Density [t/m 3 ] 2,360 2,370 2,363 2, EXPERIMENTAL RESULTS 4.1 Slump Flow The increasing amount of Betoflow and the lowered portion of water lead to a reduced w/c-ratio as shown in figure 3. Due to the fluidizing properties of Betoflow the consistencies of the different recipes remain on a nearly stable level (figure 4). Figure 3 Figure 4 220

5 4.2 Strength development The four single concrete recipes have been produced according to table 2: Table 2: Strength development without and with BETOFLOW OM 65% Dosage E 0 E 1 E 2 E 3 Cement CEM I 52,5 [kg/m 3 ] BETOFLOW OM65% [kg/m 3 ] Sand 0/4 mm [kg/m 3 ] Aggregates 4/12,5mm [kg/m 3 ] Water [kg/m 3 ] Superplasticizer [l/m 3 ] hours [MPa] 15,8 23,7 26,7 29,3 48 hours [MPa] 27,8 39,8 42,7 44,8 7 days [MPa] 37,0 53,3 53,0 56,7 28 days [MPa] 44,3 61,8 65,0 65,5 90 days [MPa] 48,0 68,0 69,3 74,5 365 days [MPa] 47,5 70,7 71,2 73,2 - The strength figures have been measured in six steps between 24 hours and 365 days. The cylindric samples (16 x 32 cm) have been stored under constant temperature conditions (20 C) after demoulding Analysis of the strength development Table 3: Survey of compressive strength ratios Compressive Strength ratio E 0 E 1 E 2 E rc 2/7 0,75 0,76 0,79 0,81 rc 2/28 0,63 0,64 0,66 0, rc 2/90 0,58 0,59 0,62 0, In presence of the ultrafine ground limestone slurry BETOFLOW OM65% a significant increase in early- as well as final-strength figures can be stated. As higher the percentage of this additive is - as stronger is the effect. The free Ca 2+ -ions on the surface of the microscopic fine Calcium carbonate particles accelerate the hydration process. Parallel to this catalytic entity the filling effect of the limestone fines increases the concrete density in addition. 221

6 4.3 Setting of fresh concrete Due to the fine slurry BETOFLOW OM65% the setting time of the fresh concrete paste starts slightly faster, but not dramatically. The difference comes to approx. 40 minutes under constant temperature as well as hygrometric conditions, as they could be realized for instance at the CETE de Lyon (Le Centre d Études Techniques de L Équipement), which is shown in figure 5: Setting of fresh concrete Strength [MPa] Figure 5: Setting Time [min] E 0 E 1 5. CONCLUSION The producer of a high-strength concrete has the choice either to improve its rheological as well as mechanical properties by adding an organic superplasticizer and/or to expand its size distribution with ultrafine products as silica fumes, meta-kaolin or limestone-fines. BETOFLOW OM65% is an innovative tool which is considered to work as an ultrafine filler and which is able to support the activity of the organic additive and to reduce the porosity of the concrete matrix, which is important from durability aspects. 222

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