Effect of Type of Superplasticizer on loss of Workability of Self-Leveling Concrete
J. Ambroise and J. Pera
Appears on pages(s):
bleeding; flow; fly ash; segregation; shrinkage; superplasticizer
Self-leveling concrete presents a remarkable fluidity: the static flow measured by means of a truncated cone (0inf = 225 mm; O sup = 170 mm ; h = 12Omm) reaches 600 mm within 10 seconds. Such concrete is particularlysuitable for casting horizontal structural elements and allows a considerable workmanship reduction. Sometimes, this concrete has to be transported and the flow must be maintained for one hour or more. Therefore, a study was conducted to investigate the influence of the superplasticizer on the loss of workability of self-leveling concrete. The viscosity agent used in this study was a solution of modified starch (10 % solids); its content was kept constant over all the study. Two types of inorganic materials were tested; fly ash and powdered limestone. The total cement + mineral admixture was kept constant at 400 kg/m3, and the amount of water was adjusted for each composition. Five types of commercially available superplasticizers were analyzed: a melamine sulfonate, a naphthalene sulfonate, a polyacryalate, and two polycarboxylates. Their dosage was adjusted to a get an initial flow of 600 mm within 10 seconds. The following tests were carried out: loss of workability within one hour, segregation, bleeding, plastic shrinkage, strength at 18 hours, and 28 days. The main finding of this study is that only one type of polycarboxylate associated with modified starch allows the concrete to keep its initial flow for more than one hour.