Author(s)

M. M. Kassim

Abstract

In this study, the influence of revibration on the compressive strength of retarded concrete is examined at late lag time intervals before and after the initial and final setting times. The time lag intervals ranged from about 2 hrs to 8 hrs and the retarder dosages of the used cement weight ranged from 0.5% to 1.5%. Results from this study indicate that the maximum compressive strength is achieved when the concrete is revibrated after 2 hrs 35 min with 0.5% of retarder dosage for any workability. Furthermore, higher dosages of the retarder do not reduce the compressive strength of the concrete when it is revibrated at late lag time intervals even near its final setting time. The use of setting retarder in high doses and revibration of the concrete reduces the air-voids in hardened concrete. Keywords: revibration, retardation, workability, fresh concrete, compressive strength. 1 Introduction It is essential to place concrete continuously to avoid cold joints in structures such as beam-column intersection and large constructions (bridge decks and turbine foundations). In these types of structures, micro transverse cracks could form in the fresh concrete because of the changes in deflection and rotation over supports during construction due to the dead weight of the concrete. Additionally, theses cracks might result from a lapse in time between revibration and the final setting of the earlier poured layers of concrete. (CCAA Report [1] and Krishna et al. [2]). Previous studies indicate that revibration improves many of the qualities of hardened concrete since it is carried out within about 4 hours from the mixing time. Compressive strength increases approximately 14%. Water tightness and

Keywords

revibration, retardation, workability, fresh concrete, compressive strength.