Flowing concrete

Fig. 2.19 Strength development of high-strength flowing concrete containing melamine-based superplasticizer compared to concrete made with 400 kg of normal Portland cement per m in the stiff to low workability ranges (25-100 mm slump). 

The use of superplasticizers in air-entrained concrete has caused much debate. Two main problems are associated with superplasticized air-entrained concrete (1) a decrease in air content by 1-3% when slump is increased from 75 mm to 220 mm after the addition of the superpiasticizer to create flowing concrete, and (2) a change in the air void system to less desirable values. However, most investigators [10-11, 12] have shown that, although the air-void spacing factor required for adequate frost resistance is altered, the change did not necessarily affect the freeze-thaw durability of... 

Fig. 7.16 (a) 50 mm slump prior to the addition of a superplasticizer (b) collapsed slump of 100 mm generally used in flowing concrete (SKW, Trostberg, W. Germany). 

Fig. 7.17 Cores taken from 3-year-old slabs poured with (A) flowing concrete (B) 50 mm slump concrete. 

Fig. 7.18 The placing of slabs (a) by the use of flowing concrete and (b) by the traditional method.

Slab from flowing concrete 50 mm slump concrete... 

One of the significant limitations of the use of first- and second-generation superplasticizers in ready-mixed flowing concrete is the rapid decrease in the initially achieved high workability and this constitutes one of the chief constraints to their wider acceptance. Therefore, a number of major producers of admixtures have sponsored active research to improve the workability retention characteristics of their superplasticizers. Some recent developments [48] have shown promise, among these are materials based on acrylate polymers (AP). The AP-based materials are reported to be more effective than SNF- or SMF-based surplasticizers in terms of water reduction, slump increase and slump retention. Figure 7.19 shows the remarkable improvement in the retention of workability produced by the AP type superplasticizer compared to an SNF type. 

Table 7.16 Mix details and concrete characteristics for flowing concrete...

Bonzel, J. (1974). Directives for the production and manufacture of flowing concrete. Translation from Beton Herstellung Verwendung 24, 4.9.S. 342-4. 

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