Papers by Keyword: Pulse Velocity

Abstract: This paper presents a study on the relationship between porosity and compressive strength for geopolymer paste. In this research, geopolymer paste was made from fly ash class F based geopolymer mixed with alkaline activator; sodium hydroxide solution and sodium silicate solution. Twelve mixes were cast in 50mm x 50mm x 50mm moulds and the samples were cured for 24 hrs at 60 °C in the oven. The samples were examined after 7, 14, 28 and 90 days in terms of porosity test, pulse velocity test and compressive strength test. It was concluded that the sample at day 90 had the highest compressive strength of 56.50 N/mm² had porosity 3.77%. Thus, the sample with lowest porosity had highest pulse velocity 3303 m/s during ultrasonic testing with lowest transmission time 15.17 μs. Keywords: porosity, compression strength, geopolymer, pulse velocity

Abstract: Two coarse-grained granitic rocks - charnockite and biotite granite were studied with the aim of estimating their unconfined compressive strength from simpler non-destructive test values. The simpler tests were the ultrasonic pulse velocity, the Schmidt hammer rebound, and the specific gravity. Another test carried out was the moisture absorption. The rocks had compressive strength in the range 115-250 MPa, Schmidt hammer rebound number or index of 35-55, and pulse velocity of 3.4-5.5 km/s. The correlation coefficients between the uniaxial compressive strength and the rebound number were 0.86 and 0.81 for the biotite granite and the charnockite, respectively. Products of the rebound index and the pulse velocity and the specific gravity improved the correlation coefficients to 0.94 and 0.91 respectively. The high correlation factors implied that the compressive strength can be estimated using the simpler tests parameters. These simpler parameters also relate indirectly to geomechanical properties of the rocks such as drillability, boreability and machine tool wear. The moisture absorption alone and its combination with the rebound number correlated inversely and poorly with the compressive strength. The correlation coefficient ranged between 0.45 to 0.67. The moisture absorption therefore proved to be a poor predictor of the uniaxial compressive strength of the rocks.

Abstract: Three rocks - biotite granite, dolerite, and marble - were studied for the use of ultrasonic pulse velocity in predicting their uniaxial compressive strength. The rocks differed in mineralogy, texture, and strength. The mineralogy and texture influence to varying degree the strength and the pulse velocity. Correlations between the compressive strength and the sonic velocity were highest in the marble (0.94-0.97), and lowest in the granite (0.68). The low correlation in the granite was attributed to the different mineral contents, the presence of biotite, the complexity in the grain boundary shape and the tortuosity of the wave path through the rock. The use of acoustic impedance and stiffness constant improved the strength of correlation in the marble but not in the dolerite and granite.

Abstract: In this study, pulse velocities calculated from the time taken by pulses emitted by a transducer to traverse a known thickness of the concrete is utilized in building up a correlation between pulse velocity and strength of concrete cubes and between pulse velocity and age of concrete. Three different arrangements of transmitters and receivers were studied to cover the varieties of problems likely to be encountered on a site. These are direct transmission, semi-direct transmission and indirect transmission. For a particular mix proportion and aggregate size a calibration curve was obtained for in-situ testing of concrete. These curves can be used to determine the relative in-situ strength of similar members or structures.