Non-linear moisture diffusion in concrete-Need some clarification

Hello,

      I've been struggling with this question for quite sometime. Need some help. I am solving a non-linear moisture diffusion equation over a full rectangular cross-section(200mmx200mm) under partially-saturated condition. Left and bottom boundaries are subjected to time-varying(sinusoidal) moisture boundary condition and other boundaries(right and top) are insulated. Experimental and some numerical results(quarter model) shows the moisture content to increase and stabilize after some time, but I am always getting the moisture profile to follow the same sinusoidal boundary profile over time. If there is anyone working on this or someone who understand the physics of diffusion please help me out.