Comparison of the characteristic leaching behavior of cements using standard (EN 196-1) cement mortar and an assessment of their long-term environmental behavior in construction products during service life and recycling

Abstract

The uncertain environmental properties of cements, when used in construction materials, during these materials' service life and any “secondary life” (construction debris), have been raised as matters of concern due to the increasing use of alternative fuels and raw materials in the manufacture of cement clinker. A comparison of the leaching behavior of a range of traditional cement types, assessed in standard mortar prisms, with two non-traditional special cements, made using alternative fuels/raw materials, has shown that the leachability from these special cements does not exceed the leachability from the traditional cements. For relevant constituents, such as Cr, even a lower leachability is observed in spite of a higher total composition. This illustrates that an evaluation of cement based on total concentration of either the anhydrous cement or the cement-based product, in which it is used, is not a valid means of judging environmental impact. The emphasis in environmental evaluation has been on the properties during service life of cement-based products. This stage of life of a cement-based product has proved to be of limited concern. The emphasis should be focused on the “second life” of cement-based products. If construction debris is reused as aggregate in concrete, again leachability is of limited concern as the chemical environment dictated by the cement matrix ensures a low leachability. When construction debris are reused as hydraulically unbound aggregate, e.g., in road stabilization, environmental issues prove to be relevant as oxyanionic species (e.g., chromate, sulfate, molybdate, vanadate) may exceed critical limits according to Dutch regulations. With the possible exception of Cd, metals such as Pb and Zn are unlikely to become critical environmentally, even in the “second life” of cement-based products. When environmental criteria for cement-based products are developed they should be based on leachability of standard mortar and not on concentration to guarantee environmental compatibility during service life, “second life” and “end of life” scenarios.