Synopsis By using the two-point test for workability, the effect of concentration of superplasticizing admixture upon workability has been found to be independent of the types of admixture and cement, Differences in the effects of proprietary admixtures are due to their different solids contents. The yield value of concrete decreases to a minimum, beyond which further additions of admixture promote segregation. Loss of workability is not necessarily more rapid in flowing concrete, and re-dosing enables workability to be maintained for more than 160 minutes without detriment the hardened strength. The melamine formaldehyde admixture caused more rapid workability loss than the naphthalene formaldehyde admixture tested, but a specific interaction between the former and a cement of low C₃A/SO₄ ratio was found. An acceptance criterion for flowing concrete is proposed.