Moisture content changes during drying were investigated in the present work. Particular emphasis was placed on the initial stage of drying of saturated concrete, where moisture contents are high: For this stage of drying, experimental data are lacking, and no comprehensive theory exists to describe it.The present investigation was performed experimentally and numerically for drying of cylinders with one exposed end, made of normal weight and lightweight concrete with varying water to cement ratio (w/c). The gravimetric technique was employed to obtain the spatial distribution of moisture content. The experimental results obtained indicate that drying of concrete becomes diffusion controlled when the average moisture content decreases below 70 to 80% of the initial saturation. Typical drying rates are in the order of magnitude of 0.18 kg/day/m 2 and 0.02 kg/day/m 2 for the first and the second stage of drying, respectively.The lightweight concrete cylinders as compared to those made of normal weight concrete exhibited higher levels of moisture content throughout the process. At high w/c ratios, the moisture profiles for both types of cylinders, as expected, show steeper changes with time. Large, constant drying rates were observed both experimentally and numerically in the beginning of the drying.The numerical model developed is based on a generalized mathematical formulation for mass and heat transfer in porous media, and its predictions are in agreement with the experimental data within the uncertainty range of the input data.

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Nomenclature a = thermal diffusivity, m 2 s −1 c = velocity of the thermal propagation, m s −1 F 1 , F 2 = intermediate functions f 1 , f 2 = source functions of F 1 , F 2 H ( ) = Heaviside's unit step function I n ( ) = modified Bessel function of the first kind and order n L( ) = Laplace transform L −1 ( ) = inverse Laplace transform l = mean free path of a molecule, m p = dimensionless quantity to designate position of the wave front q = heat flux, W m −2 r = radial or spatial coordinate, m r i = inner radius, m r o = outer radius, m r γ = relative thickness of the hollow sphere, = r i /r o S = heat source, W m −3 s = Laplace transform variable T = temperature, K T wi = temperature of inner surface, K T wo = temperature of outer surface, K T γ = relative temperature change, = (T wi − T 0 )/(T wo − T 0 ) T 0 = initial temperature, K t = time, s v = velocity of phonon or electron, m s −1 β = intermediate function ε = dimensionless characteristic time, = aτ/r 2 o η = dimensionless position (= r/r o ) θ = dimensionless temperature, = (T − T 0 )/(T wo − T 0 ) λ = thermal conductivity, W m −1 K −1 ξ = dimensionless time, = at/r 2 o τ = thermal characteristic (or relaxation) time, s Superscript ∼ = Laplace transformed function

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