Superplasticized Portland cement concrete

Previous work on superplasticized Portland cement concrete containing fly ash or blast furnace slag has shown that such mixes require 10% less admixture than reference Portland cement concrete to attain the same workability. Therefore, a given dosage may produce higher water reduction. The reason for the reduced admixture requirement has not been determined. It is probably due to the lowering (dilution) of the C3A content... 

Table 7.15 Effect of mode of addition of CAE, SMF and SNF superplasticizers on the slump of Portland cement concrete mixes (Collepardi)...

Bouzoubaa, N., Zhang, M.H., and Malhotra, V.M. (1998) Superplasticized Portland cement production and compressive strength of mortars and concrete. Cement and Concrete Research 28, 1783-1796. 

The use of superplasticizers, e.g., pol5maphthalene formaldehyde (PNS) and pol mielamine formaldehyde (PMS), appear to improve flowability of CAC concrete loss in workability appears to be too rapid. Normal range water reducers, e.g., hydrocarboxylic acids, function in a manner similar to their role in portland cement 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). 

Silica fume. Silica fume (SF) is a waste product of manufacturing ferro-sihcon alloys. It consists of an extremely fine powder of amorphous silica. Average particle diameter is about 100 times smaller than that of Portland cement and the specific surface area is enormous 13000-30000 m /kg compared to 300-400 m /kg for common Portland cements. Silica fume shows an elevated pozzolanic activity and is also a very effective filler. For these reasons, addition of silica fume to Portland cement may lead to a very low porosity of the cement paste, increasing the strength and lowering the permeability. It is usually added in the proportion of 5 to 10 % and it is combined with the use of a superplasticizer in order to maintain adequate workability of the fresh concrete. 

Hrazdira, J. (1994) Role of superplasticizers in gypsumless Portland cements. American Concrete Institute SP-148, pp. 404-416. 

Dhir, R.K., Zhu, W.Z., and McCarthy, M.J. (1998) Use of Portland PFA cement in combination with superplasticizing admixtures. Cement and Concrete Research 28,... 

The replacement of a part of Portland cement by fly ash or crushed limestone flour improves the rheology of concrete mix and allows reduction of the amount of superplasticizers necessary to obtain the required workability. 

When Portland cement is partly replaced by fly ash, SF or blast-furnace slag, then usually better flowability of the fresh mix is obtained and lower dosages of superplasticizers are possible. This is quite profitable from an economic viewpoint, because superplasticizer is an important part of the cost of concrete components. 

Jansen, D., J. Neubauer, E Goetz-Neunhoeffer, R. Haerzschel and W. D. Hergeth (2012b). Change in reaction kinetics of a Portland cement caused by a superplasticizer - Calculation of heat flow curves from XRD data . Cement and Concrete Research 42(2) ... 

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