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.

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Re-vibration of sequential layers of relatively deep structural members after a particular time harms the strength and water permeability properties of the concrete. The harmful effects can be observed in lightweight concrete due to the floating tendency of lightweight aggregate. In this experimental study, the influence of adding retarder plasticizer and silica fume on water permeability properties of re-vibrated lightweight concrete was investigated. The effects of re-vibration at different time lags on compressive strength and permeable voids ratio were studied. Absorption, sorptivity, and water penetration depth under pressure were also studied. Results show that the addition of a retarder increased the compressive strength and reduced the permeability for all mixes, even though the mixes were re-vibrated before the final set of the cement. Similar effects were found in mixes that contained silica fume as partial replacement of cement, except the sorptivity properties of concrete when compared with the control mixture. A linear relationship between permeable voids and water absorption was set.

In relatively deep structural members, re-vibration is applied to sequential layers after they are initially hardened. This may cause harmful effects on strength properties, especially on lightweight concrete (LWC). In this experimental study, the effects of re-vibration on LWC properties were thoroughly investigated. Local lightweight crushed pumice rock named “Bonza,” as well as set retarding admixture and silica fume (SF) were used to produce four different mixes of LWC. These mixes were re-vibrated at different time lags (0:00, 2:50, 4:30, and 5:30 [h:min]). After the re-vibration process, compressive and tensile strength properties, as well as pulse velocity, density, and permeable voids volume of hardened concrete mixes, were investigated. Results showed that using the setting retarder and partial SF replacement of Portland cement, the density, compressive, and tensile strength properties were increased in all re-vibrated mixes when the re-vibration was accomplished before the final set time of the cement. A lack of correlation between ultrasonic pulse velocity, density, and compressive strength was also detected. Furthermore, a linear relationship was found between permeable voids volume and compressive strength of all mixtures.