Waste management is an important issue form Morocco. According to many possibilities, recycling construction and demolition wastes (CDW) as aggregates replacing naturel aggregate for concrete is a solution that deserves to be evaluated. In this study three sample of concrete are tested. 2 with different percentages of recycled aggregates Their properties are compared to the concrete with natural aggregates. Concrete is realized and tested in thermal conductivity (cylindrical 5x3.23 specimens). With quantity of recycled aggregates is (0 %, 10 %, 20 %) in different temperature (20°. 30°.40°.50°C). Numerical modeling with FORTRAN program was proposed for comparing between experimental and numerical results. It is shown that the use of recycled aggregate as replacement for natural aggregate in concrete decreases the thermal conductivity. we also see that the value of the thermal conductivity decrease with the increase of the temperature of the ambient air 20 degrees up to 50 degrees for the 3 samples Normal concrete and concrete with recycled aggregate. For the three samples the numerical and experimental results were in good agreement. The following conclusions can be drawn from this work: that according to the thermal properties, the recycled aggregate concrete possible to be used in the same applications as conventional concrete