Experimental Investigation of Delayed Vibration Effects on the Density and Compressive Strength of Concrete

The vibration of concrete is significantly important in concrete compaction. It helps in reducing air entrapment and ensures proper performance of hard concrete. However, on construction sites, there is often a time delay between mixing and vibrating concrete which is not well understood. This study aims to review the impact of delayed vibration on concrete density and compressive strength for different strengths of concrete (M20, M25, and M30). Concrete blocks were subject to vibration after periods of 0, 30, 60, and 90 min after completion of mixing. In total, 24 blocks were prepared for each strength specification and tested for compressive strength and density at intervals of 7 and 28 days. From the measurements, it was observed that the delayed vibration has a non-linear effect on concrete properties and the effect depends heavily on the strength of concrete mix used. In the case of M20 concrete, the density moved from 2244 kg/m3 to 2290 kg/m3 after delaying for 30 min and then went down as waiting time increased. Similarly, M25 concrete had the highest density after waiting for 60 min, indicating improvement in packing of sand particles when vibration was delayed. The compressive strength results supported the density observations, meaning that by controlling the degree of delay in vibration, the concrete performance can also be influenced without having a continuing effect on the properties of concrete. In general, it can be concluded that the response of concrete to vibration delay is specific for each concrete mix. Moderate delays between approximately 30–60 min for M20 concrete, 60 min for M25 concrete, and 60–90 for M30 concrete would yield the best performance according to the current investigation.