Slump loss

Salts of a-sulfo fatty acid esters can work as emulsifying agents for the preparation of asphalt emulsions and asphalt-latex emulsions. The ester sulfonates improve the storage stability of the emulsions [101,102]. In the manufacture of lightweight gypsum products air bubbles have to be mixed into the slurries. The use of salts of sulfonated C10 l8 fatty acid alkyl esters as foaming agents produces uniformly distributed fine bubbles [103]. Salts of C10 16 fatty acid alkyl ester sulfonates can also be added to cement mixtures to prevent slump loss of the mixtures [104]. 

There is some indication that the higher-C3A-content cements lead to more rapid slump loss of superplasticized... 

Fig. 2.18 Slump loss at 21°C of superplasticized concretes with OPC and CAE or SNF ploymer-based admixtures. The figures on the slump-loss curves indicate the percentage of the superplasticizer active ingredient by mass of cement.

Temperature high temperatures may cause rapid slump loss and it may be necessary to use a retarder in conjunction with the AWA. 

Despite wide publication of the adverse effects that retempering causes, job site addition of extra water to compensate for slump loss is still a common practice, particularly in hot-weather conditions. Under these conditions, the use of both conventional and superplasticizing admixtures helps to minimize the amount of water required for re-tempering so that the loss of strength is minimized [46, 47], This is shown in Table 7.14. 

Corrosion inhibitors, like calcium nitrite, are accelerators and depending on their dosage may cause rapid slump loss and shorten the setting time when added at the batch plant. 

The rapid decay of workability due to high slump loss, posing retempering (adding extra water on site) problems. 

Fig. 7.33 Effect of temperature increase on slump loss (Mailvaganam [90]).

F/g. 7.35 Effect of type D admixture on slump loss initial slump 95-115 mm, temperature 30°C (Soroka and Ravina [94]). 

The replacement of Portland cement by fly ash class F (ASTM C 618) has been found to reduce the rate of slump loss in a prolonged mixed concrete, and the extent of the reduction is greater with increased cement replacement (Fig. 7.37). Fly ash also was found to be beneficial in reducing slump loss in concretes with conventional water-reducing and retarding admixtures [95], The effect of fly ash on reducing slump loss can be attributed to chemical and physical factors. It was found that the surface of fly ash particles may be partly covered with a vapor-deposited alkali sulfate that is readily soluble [103, 104], Thus the early hydration process of Portland cement is effected because sulfate ions have a retarding effect on the formation of the aluminates. Indeed, fly ash was found to be a more effective retarder than an... 

The soluble sulfate versus time curve for the cement containing the natural anhydrite is radically changed when CLS is present [130, 131]. The rate of solution of natural anhydrite, which is much slower than that of gypsum or calcium sulfate hemihydrate, is further retarded in the presence of chemical admixtures, which leads to a sulfate-starved system in the concrete, often producing rapid set and an increase in rate of concrete slump loss (Fig. 7.42). Apparently the adsorption of the lignosulfonate by the natural anhydride plus the rapid reaction between the soluble SO3 and the... 

With some cement-superplasticizer combinations, various problems have been reported such as low fluidification effect, rapid slump loss, severe segregation, extended set retardation and loss of entrained air. These are briefly reviewed below. 

Due to the rapid slump loss associated with first- and second-generation superplasticizers (high-range water-reducers), job site addition of such... 

---