In a broader and more practical sense, the term robustness that is adopted here describes robustness as the ability of a given mixture to maintain its fresh properties and uniformity during processing, casting, and due to some small changes to the composition of the mixture due to some small changes in the mixture’s ingredients contents. H., “Workability, Testing and Performance of Self-Consolidating Concrete,” ACI Materials Jr., Vol 96(3) 346-353, 1999. Tattersall and Banfill[i] and Banfill[ii] showed that the yield stress and plastic viscosity values are exponential functions of the water and superplasticizer contents, and the flow characteristics of the cementitious materials are related to structural buildup during rest and structural breakdown due to remixing. Due to these conditions, the w:cm ratio varied from 0.281 to 0.379. Slump flow and T50 values for variations in moisture content of aggregates Figure 6 shows that the slump flow was reduced from about 790 down to about 670 mm, and even larger variations were recorded for the T50 test. This phenomenon is attributed to the higher thickening rate of mixtures made at lower w:cm. V-funnel flow time for mixtures with aggregate in various moisture conditions Fig. 143-153, in Self-Compacting Concrete, Proceedings, 3rd Intern.
and Oberg, P., “Effects of constituents on the workability and rheology of self-compacting concrete,” pp. Consequently, robustness increases by incorporation of density modifiers, and with regards to fines, the best density modifiers is slag, followed in decreasing order by ground dolomite, ground limestone, and ground quartz. The incorporation of VMA controls bleeding and segregation and increases the robustness of the SCC, while the low water content provides mostly the required level of viscosity. Mori et al.[i] examined mixes with 74 different types of aggregate and varying water absorption values.
4 also indicates that the sedimentation rate can be reduced by increasing the content of the fines with high specific density. In such mixtures, the VMA is used to reduce the variability of the SCC that can arise from changes in material properties and placement conditions. If the natural moisture content of the aggregate is lower than SSD, then the amount of mixing water is increased. “On the Effect of Coarse Aggregate Fraction and Shape on the Rheological Properties of Self-Compacting Concrete,” Cem.
Similar to the fluidity, the viscosity is readily changed by changing the superplasticizer and aggregate contents (Fig. The effects of the latter on viscosity cannot be overlooked as the effects are as important as the role of superplasticizer. The optimum addition time ‘window’ was found to be 2 to 4 minutes for the naphthalene- and melamine-based admixtures, but 0 and 0.5 minutes for polycarboxylic-based admixture. A.,” Mathematical model for the flow curve of cement paste,” Magazine Concr.
The figure also shows that the effect of aggregate on viscosity is exponential. Deshpande and Olek prepared 27 mixtures of RSSCC and found that the time in which the superplasticizer was added affects the rheological properties.
Clearly, all these ingredients, especially water, superplasticizer, and aggregate, affect the rheological properties differently. G., “A Viscometric Study of Cement Pastes Containing Superplasticizers with a Note on Experimental Techniques,” Magazine of Concr. The results of this study indicate that early addition of superplasticizer enhances dispersion of cement and increased the flowability of the RSSCC mixture, especially for mixtures mixed in mortar mixer.