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Modified High Performance Concrete

2. MB modifiers influence on properties of concrete and concrete mixtures
2.2. MB concrete mixture properties
Water consumption	Generally, concrete mixtures containing MB modifiers demand smaller quantities of water in comparison with normal mixtures which don't contain plasticizing admixtures.   Water consumption of MB concrete mixtures depends on plasticizer and fly ash content (on MB brand), as well as on MB dosage.   In Figure 15 characteristic tendency for water consumption variations depending on content of C–3 superplasticizer and modifiers dosage is shown. Figure 16 shows the tendency depending on fly ash content in mineral part and modifiers type correspondingly.

Figure 15	Relative Water Demand of Concretes with MB–01 (Cement=500 kg/m3; Slump=20–24 сm)
Figure 16	Influence of Various Types of MB on Water Demand of Cement Systems

Bleeding and segregation

Even high–slump MB concrete mixtures are subject to bleeding to a smaller degree than normal mixtures and, therefore, characterized by increased adhesion – non segregation and strongly pronounced thixotropy [31].   Figure 17 shows the modifiers type influence on water separating ability of high–slump concrete mixtures (according to Russian Standard ГОСТ 10181–2000) in comparison with normal mixture containing superplasticizer.

Figure 17	Influence of Various Types of MB on Bleeding of Concrete Mixtures

A high degree of adhesion is proved by testing results for a cast–in–place pile (of 24 m length) concrete homogeneity obtained while dropping freely a high–slump MB–01 concrete mixture from the great height (Fig. 18).

Figure 18	Characteristics of Concrete Homogeneity for a cast–in–place pile executed while dropping a high–slump MB concrete mixture from the great height

	Increased adhesion shows with MB dosage increase and provides not only concrete homogeneity for vertically formed structures height, but a good pump ability of mixtures as well.
Air content	MB introduction into concrete mixtures with plasticity characterized by a slump of 10 cm and more, generally, doesn't result in entrained and entrapped air volume increase.   In less plastic mixtures with slump < 10 cm an insignificant entrapped air volume increase is possible near the boarding, which results from increased viscosity of such mixtures.
	To form prescribed cement paste porous structure in order to increase concrete frostresistance, the air entraining admixtures providing extra air entrainment into concrete mixtures with its volume to be promoted up to the level of 3–6% or gas forming admixture are used along with MB. Figure 19 shows the influence of the most applicable air entraining admixtures «СНВ» and gas forming emulsion «КЭ 30–04» on the volume of entrained air and gas formed in concrete mixture with MB–01 dosage = 10% of cement weight [32]. With MB–01 content over 10% of cement weight, the dosages of air entraining admixtures may be increased.

Figure 19	Influence of Air Entraining (AEA) and Gas Forming (GFA) Admixtures on Air (Gas–) Content in Concrete Mixtures (Cement=480 kg/m3; МB=48 kg/m3; W/C=0.32; Slump=18–20 сm)

Slump loss in time

Workability of MB concrete mixtures can be kept up within the longer time than that of the ordinary mixtures. The more time stable consistency is ensured by MB properties, i.e. by the presence of setting regulator and superplasticizer in particular and proves to be a favorable factor in conditions of prolonged transportation by truck mixers.   It is clear from Fig.20 that actually MB–01 [31] mixtures slump doesn't change for transportation time within the limits of 1.5–2.0 hours.

Figure 20	Time Dependent Plasticity Alteration (Cement=400 kg/m3; W/C=0.38; t=+20°C)

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Research Institute for Concrete and Reinforced Concrete Center for Modified Concrete 109428, Russia, Moscow, 2 Institutskaya, 6 Tel.: (095) 171–0573, 174–7635, 174–7629, 174–7606 Fax: (095) 174–7591 Е-mail:mb@niizhb.ru; info@master-concrete.com