Self-Consolidating High Performance Concrete – SCC – Self-Compacting & Highly Flowable Concrete

Emborg[i] concluded that the properties of SCC are more sensitive to both, deviation from the designed target and mixing technique. Due to high cementitious content, SCC typically requires longer mixing time compared to normal concrete, and it was noted that this might lead to a reduction in the capacity of the concrete plant, which might cause supply bottlenecks at the site.[ii] This longer mixing time is needed for securing complete structural breakdown of the SCC mixtures in order to utilize its superb flow properties.

In general, concrete mixers can be classified as either a free fall type (tilting drum) mixers or forced paddle mixers, Emborg and Takada et al.[iii] The free fall mixers (also called drum mixers or gravity mixers) are predominantly used at larger plants in northern Europe and Southern Asia.

The forced paddle mixers could be of two types: pan mixers (also called forced pan mixers) and pugmill mixers (also called mortar mixers in the USA). The pan mixers have a vertical axis of rotation and consist of cylindrical, horizontal pan (fixed or rotating) and one or two sets of rotating blades. The pugmill mixers typically consist of a horizontal drum and one or two rotating horizontal shafts with attached blades. Forced pan mixers have higher mixing efficiency than drum or mortar mixers (Deshpande and Olek,[iv] and Takada et al.).

Takada et al. performed laboratory investigation of the effect of mixer type on fresh concrete properties of SCC and concluded that for the same composition and mixing sequence, tilting drum mixer increases the V-funnel flow times of SCC as compared to SCC mixed in pan mixer, and to achieve the same slump flow (650±30 mm), smaller amounts of superplasticizer (SP) were needed in the tilting drum mixer. By contrast, SCC produced in pan mixer was found to be prone to changes, which compromised the robustness of the mixtures.

Similar trends were observed by Deshpande, 2006. Mixtures with the same w:p volume ratio were mixed in a mortar mixer and a conventional laboratory pan mixer. It was observed that for the same mixing sequence and mixing time, the mixtures produced using the pan mixer had higher viscosity as compared to the mixtures mixed in the mortar mixer. Mixtures mixed in the mortar mixer required lower dosages of polycarboxylate based superplasticizer to produce rapid-set SCC (RSSCC) with the same slump flow as compared to the dosages required for the mixtures mixed in the pan mixer.

In turn, Emborg noted that the robustness is also a function of the mixer volume and in industrial full scale mixers, the variations in properties are smaller than those produced by laboratory mixers.

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[i] Emborg, M. (2000). "Final Report of Task 8.1." Proposal No0BE96-3801, 1-65.

Higuchi, M.; (1998). "State of the Art Report on Manufacturing of Self-Compacting Concrete." Proceedings of the International Workshop on Self-Compacting Concrete, Kochi, Japan, 360-367.

[ii] Lowke, D., and Schiessl, P.; (2005). "Effect of Mixing Energy on Fresh Properties of SCC." Proceedings of the Fourth International Rilem Symposium on Self-Compacting Concrete and Second North American Conference on the Design and Use of Self-Consolidating Concrete, Chicago, USA.

[iii] Takada, K., Pelova, G. I., and Walraven, J.; (1998). "Influence of Mixing Efficiency on the Mixture Proportion of General Purpose Self-Compacting Concrete " International Symposium on High-Performance and Reactive Powder Cements Sherbrooke, Canada, 19-39.

[iv] Deshpande, Y. S., and Olek, J.; (2005). "Effect Of Mixing Equipment And Mixing Sequence On Rapid -Setting Self-Consolidating Concrete." pp. in 2^nd North American Confer. & 4^th Intern. RILEM Confer. On Self-Consolidating Concrete, Chicago, 2005.