International Concrete Abstracts Portal

Laboratory studies have been carried out to determine the leachability of the adsorbed superplasticizer (an Na-sulfonated naphthalene formaldehyde condensate) and its location within the structure of hardened cement tastes. The superplasticizer, labelled with 35 S, was incorporated in a reference cement-based grout (90 percent Type 50, 10 percent silica fume, 0.4 ó w/c ó 0.6). Static leaching tests were used to determine the release of labelled superplasticizer to solutions as a function of temperature, groundwater composition, and grout surface area to groundwater volume ratio. The quantity of 35 S in the leachate was determined using liquid scintillation counting. Electron-microautoradiography combined with scanning electron microscopy and energy dispersive x-ray spectroscopy were used to identify the cement phases containing the labelled superplasticizer. The results show that superplasticizer can be leached from grouts, but the cumulatively released quantities are very small (approximately 10(12 kg/mý). Most of the released superplasticizer appears to come from the capillary pore space of the hardened grout; however, some release may result from dissolution of the cement phases. Increasing temperature and/or grout surface area to groundwater volume ratio increases the release rate of superplasticizer. Analyses, using electron-microautoradiography and scanning electron microscopy, indicate that the majority of the adsorbed super plasticizer resides on the C-A-H phases and the calcium-rich phases of C-S-H in the cement.

Effects of calcium polystyrene sulfonate-based superplasticizer (SP.PSS-Ca) and sodium b-naphthalene sulfonate-based superplasticizer (SP.NSF-Na) on concrete behavior were studied. The SP.PSS-Ca does not contain sodium and potassium (Na, K), the cause of alkali-aggregate reaction, and hence is less harmful than SP.NSF-Na. SP.PSS-Ca gave a larger increase of slump, smaller increase of air content, smaller air loss, and slump loss than SP.NSF-Na at the same dosage. The dosage of SP.PSS-Ca was 70 percent of that required for SP.NSF-Na to obtain the required slump. SP.PSS-Ca did not increase the air content to flowing concrete of base concrete, but SP.NSF-Na increased it. SP.PSS-Ca showed lower air loss and slump loss (0.6 percent, 3.5 cm/90 min) than SP.NSF-Na (2.0 percent, 7.0 cm/90 min). Other properties such as bleeding, setting time, and compressive strength were similar with SP.PSS-Ca and SP.NSF-Na. Thus SP.PSS-Ca can be considered to have better properties as a superplasticizer than SP.NSF-Na.

Except for degree of effectiveness, plasticizers and superplasticizers have very similar effects on the workability of hydraulic mixtures. In a microscopic scale, however, their action clearly differs by the effective deflocculation and the high dispersion of the cement particles obtained with superplasticizers. This behavior was the basis of development of two test procedures. The first one makes it possible to discriminate between both types of admixture. Furthermore, it reveals possible specific interactions with the cement used and makes it possible to assess the period of activity of a superplasticizer. The second procedure allows easy and quick assessment of the minimum active dosage required of a superplasticizer for a given cement. Though often higher than the percentages recommended by the manufacturers, the values agree well with those obtained by a vibratory compaction test on cement mortar. This test also allows a quick assessment of the relative effectiveness of various superplasticizers. From a study on 17 admixtures and two cements (one portland and one with granulated slag), it appeared that: an admixture supplied as a plasticizer may actually be a superplasticizer; an admixture may behave as a plasticizer or as a superplasticizer according to the nature of the cement; and the period of activity of the superplasticizers was generally longer with the slag cement.

To study the interaction between either a given superplasticizer with different portland cements or the interaction of different superplasticizers on a given portland cement, a special apparatus called RHEOPUMP was developed. It is possible with this app

The influence of alkali sulfate on the viscosity of cement paste containing a superplasticizer was studied by using rotational viscometer. The mechanism of the action of superplasticizer on the fluidity of cement paste was also investigated. A larger amount of superplasticizer was rapidly adsorbed onto C3A and C4AF compared to that on C3S and C2S. The presence of alkali sulfate inhibited the adsorption of superplasticizer on C3A and C4AF, thus permitting increased adsorption on C3S and C2S. The reduction of viscosity of cement paste by superplasticizer is dependent mainly on its adsorption onto C3S and C2S. Therefore, an increase in alkali sulfate leads to an increase in the adsorption of superplasticizer on C3S and C2S, and results in reduced viscosity of cement paste. Excessive amount of alkali sulfate, however, compressed the electric double layer, providing an increase in viscosity of cement paste. Based on the results, it was concluded that there was an optimum alkali sulfate level with respect to the fluidity of cement paste containing the superplasticizer.