A Comparative Analysis of the Rebound Hammer and Ultrasonic Pulse Velocity in Testing Concrete

This work presents a study on the comparison between some non-destructive testing tech-niques (Rebound Hammer and Ultrasonic Pulse Velocity). Tests were performed to com-pare the accuracy between the rebound hammer and the ultrasonic pulse velocity methodin estimating the strength of concrete. Eighty samples (cubes of 150 x 150 x 150) wereprepared using two mix designs of 1:2:4 and 1:3:6 with a constant w=c ratio of 0.45 andwere tested at 7, 14, 21 and 28 days. The slump test was between 62 - 78mm. The resultsobtained from the non-destructive testing methods were correlated with the compressivestrength results which showed that a higher correlation existed between the Rebound Ham-mer and the compressive strength than the Ultrasonic Pulse Velocity. The rebound ham-mer readings had a correlation coecient of 0.794 while the ultrasonic pulse velocity hada correlation coecient of 0.790 for the 1:2:4 mix and the rebound hammer readings for1:3:6 was 0.783 and that for the ultrasonic pulse velocity was 0.777. Statistical analysisof the results obtained showed that there was no signicant dierence between the meansof the two methods for both mix at a 0.05 level of signicance

Suitability of Saw Dust Ash-Lime Mixture for Production of Sandcrete Hollow Blocks

The use of saw-dust ash (SDA) mixed with 45% slaked lime for production of sandcrete hollow blocks was investigated. The aim was to determine the percentage SDA lime and water-cement ratio that would give the 28-day maximum strength. Saw dust was burnt and the ash sieved using a 150 micrometer sieve. The ash mixed with 45% slake lime was used to partially replace ordinary Portland cement (OPC) in various proportions. Fifteen blocks for each proportion were moulded using the mix of 1:8 and water-cement ratio of 0.50. Sprinkling of water on the blocks commenced after three days. The blocks were cured by complete immersion in water at room temperature. Three blocks were tested for strength at each of the ages of 7, 14 and 28 days for each proportion of OPC/SDA-lime. The 90:10 (cement: SDA-lime) proportion which gave the highest strength was further investigated for various water-cement ratios. It was concluded that for a mix of 1:8, 10% replacement of OPC by SDA-lime gave the maximum strength at water-cement ratio of 0.55 and was recommended for the production of sandcrete hollow blocks. The blocks should be used for low-income housing and non-load bearing walls