Photoacoustic (PA) technique has been applied to measure the effective thermal
diffusivity (αeff) of hydrating cement pastes with a varying water to -cement ratio (w/c) and for
variable duration (d) of hydration. Four samples with w/c = 0.3, 0.4, 0.5 and o.6 were
prepared. The frequency variation of the PA signal for each sample was recorded at the
begining (0 d), as well as one week and one month of hydration. The effective thermal
effusivity (eeff) was obtained by measuring the variation of the signal with modulation
frequency and the corresponding values of the effective thermal conductivity (keff) were
calculated. The results for keff show a decrease at higher w/c (0.6), no change for other
samples has been observed. The thickness of the duplex film of Ca(OH)2 and C-S-H formed
on the surface of the samples of w/c = 0.5 were determined using the effective layer model in
the 0 d and after one month of hydration; a remarkable increase was observed in the last case.