Workability adjustment and sensitivity of different fine cement mixtures to polycarboxylate ether-based superplasticizer

Abstract

From previous studies, the most effective superplasticizer on workability was the polycarboxylate ether-based superplasticizer (PCE). For example, when the optimum dose, corresponding to the highest strength, was slightly exceeded, there was a possibility of a sharp drop in strength, even if the segregation was not noticeable. At construction sites, however, the workability adjustment is required to control the slump loss. The question here is how sensitive are different fine cement mixtures that are differently blended with fine additions, like silica fume, to a small increment of this superplasticizer at different water content. In this study, this sensitivity was studied throughout four series of different fine mixtures. For each series, two water to cement ratios (w/c) were used, 0.35, and 0.45, while the superplasticizer dose, the superplasticizer to cement ratio, was varied from 0.011 to 0.0132 (g/g) for each (w/c) ratio. It was found that the small PCE increment caused strength improvement for some mixtures, while it caused strength reduction for others. When the content of both sand and silica fume were reduced, the small increment, along with increasing (w/c) ratio, could significantly decrease the strength by 7.5 MPa. Accordingly, it was concluded that the effect of the dose increment could be related to the actual water content rather than the (w/c) ratio. Hence, an indicator of the actual water content was proposed, which was useful to define a safe method for workability adjustment.