Development of an Admixture for Self-Leveling Concrete

In the past decade, many efforts have been undertaken to develop highly-workable concrete which consolidates under its own weight without any vibration, specially in Japan. The admixtures used in such concrete are mainly composed of high water reducing superplasticizers, fine limestone dust and viscosity agents to maintain not only high flowability but high segregation resistance of the concrete. The water to cement ratio is generally lower than 0.55. A new admixture is proposed in the present study. It is a mixture of a superplasticizer and an accelerator with plasticizing properties which also acts as a viscosity agent. The composition of the self-leveling concrete is as follows. The total amount of fine materials (cement + fly ash or cement + ground limestone) is 370kg/m^3, while the cement content (normal portland cement CEMI 52.5) is 260kg/m^3. The water to cement ratio is 0.73. The mechanical performances of the hardened concrete is better than those of a usual French building concrete. The compressive strengths at 16 hrs, 7 days, and 28 days are 8, 30, and 3 MPa, respectively. The unrestrained drying shrinkage reaches 600 to 700mm/m, at 90 days as predicted from the 28 day results.