Effect of natural pozzolan and recycled concrete aggregates on thermal and physico-mechanical characteristics of self-compacting concrete

•The apparent density of RSCC is lower than that of the NSCC.•The substitution of NP has a beneficial effect on the capillary of the concrete.•The substitution of 5, 10, 15 and 20% of NP reduces the conductivity.•The compressive strength is a decreasing function of the open porosity.•The possibility to deduce the ultrasonic pulse by determining the open porosity. To properly meet the environmental and ecological side the construction of environmentally friendly buildings has become very important and this can be done by recycling demolition waste to replace natural gravel in the construction of concrete mixtures with the use of additives as part of the investment in local materials. As well as the reduction of carbon dioxide emissions, all of this aims to reduce the excessive exploitation of natural resources. Thermal insulation of buildings has attracted a lot of attention in recent years as it became apparent that the greatest energy savings could be achieved by using appropriate thermal insulation for the building. In this experimental investigation, physico-mechanical and thermal properties of self-compacting concrete (SCC) composed of coarse aggregates and natural pozzolana (NP) are evaluated. Eleven concrete mixes were prepared in order to vary the substitution rate by weight of natural aggregates by recycled aggregates. The substitution rates were set at 50% and likewise, the cement has also been substituted from 5% to 20% by weight by natural pozzolan (NP). The results indicate that recycle SCC mixes that contain NP has a beneficial effect on the capillary dimension of the hardened cement paste, since the capillary absorption provides information on the rise of water through the open porosity of the concrete produced by the tension superficial liquid. The presence of NP reduces capillary pores by filling these pores with second-generation CS-H gel formed from pozzolan silica and portlandite, the hydrate resulting from the hydration of cement. It should be noted that the substitution of 20% NP reduces the thermal conductivity by 17% at 28 days and 19% at 120 days, compared to the reference (RSCC) and the substitution of 15% NP reduces the thermal conductivity by 22% at 28 days and 16% at 120 days, compared to the reference (NSCC). Finally, a good correlation between compressive strengths Cs (MPa), thermal conductivity ʎ (W/mk), ultrasonic pulse velocity V (m/s), dynamic elasticity modulus Ed (GPa)) and the open porosity ε (%).