This study evaluates the bonding condition of concrete slabs with varying porosity levels (20% to 80%) at cold joint interfaces by analyzing surface wave dispersion ve-locity profiles. A dual-receiver setup was employed to compare the waveform and dispersion characteristics along the test lines that crossed cold joints and those that did not. While wave velocity reduced for lower wavelengths at lower void levels, more significant reductions were observed across the entire wavelength range at higher porosity levels. This demonstrates that Rayleigh-wave dispersion can effectively assess cold joints generated by artificial voids with known void ratios.