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

The natural moisture content of aggregate affects the mixing water content in two ways:

Mori et al.[i] examined mixes with 74 different types of aggregate and varying water absorption values. The authors concluded that the slump flow value tends to prominently decrease with an increase in natural moisture content of fine aggregate for mixtures with 0.35 w:c ratio as opposed to 0.5 w:c ratio.

A strong influence on slump flow was observed by Sakai et al.[ii] when the amount of water was changed by + 5 kg/m². These effects were reduced when a viscosity agent was added to these mixtures. Similar observations of slump flow variations were made by Ushijima, et al.[iii] They varied the amount of water added to the mixture in such a way so as to simulate a change of aggregate moisture content between -1% to +1.5%. According to their results, the slump flow increased nearly 100 mm when the aggregate surface moisture content was increased about 1%. Highuchi[iv] studied the effects of surface moisture of aggregates on concrete properties and the electric power consumed by the mixer. He observed that all the following parameter: viscosity, the power consumption of the mixer, and the O-funnel time increased with an increase in the surface moisture content of sand. The values of power consumption of the mixer were used by Nishizaki et al.[v] to adjust the composition of SCC which varied due to fluctuations in the moisture content of the fine aggregate.

The above findings were recently confirmed by Deshpande[vi] who changed the SSD moisture condition of sand and pea gravel two folds from a completely dry state of aggregates to twice the water content of SSD. During the tests, the moisture content was varied in such way that sand and the pea gravel both had the same moisture content, i.e., either both were simultaneously in dry condition or both were in SSD condition. Due to these conditions, the w:cm ratio varied from 0.281 to 0.379.

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. The latter values varied from as low as 4s for mixtures cast with aggregates in dry condition and as high as 10s for mixtures cast with aggregates in 2 × SSD condition.

Figure 6. Slump flow and T₅₀ values for variations in

moisture content of aggregates

The decrease in slump values observed in Fig. 6 is further augmented after some rest time. This phenomenon is attributed to the higher thickening rate of mixtures made at lower w:cm. Fig. 7 shows variations in V-funnel flow time measured either immediately after mixing (curve a) or 20 minutes after mixing (curve b) for mixes containing aggregate with different initial moisture content. It can be seen that when tested immediately after mixing, the V-funnel flow time for mixes with dry aggregate increases from 9s to 19s when tested at 0 and 20 minutes after mixing, respectively. For the same time intervals, the corresponding increase in the V-funnel flow time is only 2-second for mixtures with aggregates in the SSD condition.

Figure 7. V-funnel flow time for mixtures with aggregate

in various moisture conditions

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[i] Mori, H., Tanigawa, Y., Wakabyashi, S., and Yoshikane, T. (1996). "Effect of Characteristics of Aggregate on Properties of High-Fluidity Concrete." Transactions of the Japan Concrete Institute, 18, 53-60.

[ii] Sakai, G., Shgematsu, K., Yurugi, M., and Sakata, N.; (1994). "Flow Stabilizing Properties of Special Viscosity Agent." The 37th Japan Congress on Materials Research.

[iii] Ushijima, S., Harada, K., and Taniguchi, H. (1995). "Fundamental Study in the Practical Use of High Performance Concrete." Concrete Under Severe Conditions, E& FN SPON.

[iv] 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.

[v] Nishizaki, T., Kamada, F., Chikamatsu, R., and Kawashima, H.; (1999). "Application of High-Strength Self-Compacting Concrete to Prestressed Concrete Outer Tank for LNG Storage." Proceedings of the First International Rilem Symposium on Self-Compacting Concrete, Stockholm, Sweden, 629-638.

[vi] Deshpande, Y. S. (2006). "Development of Rapid-Setting Self-Compacting Concrete to Production Variabilities ", Purdue University.