The response of hydrating cement paste through setting are monitored using ultrasonic reflection measurements performed using horizontally polarized shear waves (SH) reflected off of the hydrating cement paste. Changes in the ultrasonic signal through setting are related with changes in the porosity and stiffness of an equivalent water-filled poroelastic material, which provides identical acoustic impedance. The rate of increase in the shear modulus of the porous material is shown to correspond well with rate of hydration indicated by temperature changes. The porosity obtained from the poroelastic equivalent representation, is identical to capillary porosity obtained from themo-gravimetric analysis.