Superplasticized Portland cement

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... 

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 interaction of superplasticizers with Portland cement is the most complicated situation of all because of reactions between the various components of the cement and the competition, for example between the superplasticizer and gypsum for reaction with C3A. However, in general ... 

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). 

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

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,... 

Superplasticizers used in combination with Portland cement are distinctly less effective with high-alumina cement. A product based on sul-fonated phenol formaldehyde was found to be more effective than naphthalene-type and melamine-type resins (Banfill and Gill, 1993). The retarding effect associated with the use of superplasticizers may be overcome by simultaneously adding a lithium salt to the mix (Gill et al., 1986). 

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. 

Figure 13. Conduction calorimetric curves of portland cement hydrated at different temperatures in the presence of SMF superplasticizer.

Cabrera, J. G., and Lynsdale, C. J., The Effect of Superplasticizers on the Hydration of Normal Portland Cement, 2nd ACI/CANMETInt. Symp. on... 

Hrazdira, J., Role of Superplasticizers in Gypsum-less Portland Cement,... 

---