Experimental Study on a Low-Carbon Pervious Concrete Based on Alkali-Activated Binder and Recycled Aggregates

The uncontrolled urban development of the last century caused a high land consumption and strong non-renewable natural raw materials utilization. In order to solve the problems generated by soil sealing, the building sector has developed a pervious concrete manufactured with Portland cement and natural aggregates. Although this mixture mitigates the effects of soil sealing, the production of a Portland-based pervious concrete has a strong environmental impact. The purpose of this research is to investigate an alkali activated slag-based pervious concrete (AASPC) manufactured with tunnel muck (TM) as recycled aggregate instead of natural sand and gravel and to evaluate the relationship between aggregate size and physico-mechanical properties of no-fines concrete. Six different single-sized recycled aggregates from tunneling works (drilling and blasting technique) were used to produce six different AASPC that were characterized in terms of compressive strength, porosity and water permeability under constant and variable flow. Experimental results evidenced that the average size of aggregates strongly influences the open and total porosity of the materials, thus determining very different compressive strengths (from about 6 MPa for concrete with 16-22 mm gravel to 20 MPa for concrete made with 1-2 mm sand) and water permeability. Finally, the environmental impact of these mixtures (energy requirements, CO2 emissions and natural raw materials consumption) is strongly reduced in comparison to traditional Portland-based no-fines concrete at equal strength class.