From ancient to modern sustainable concrete

Abstract

The purpose of this paper is to show what ancient structures are made of and what can be done with today’s materials to produce more sustainable modern concrete. Some samples of mortars collected from the Tipasa archaeological site and the Forbidden City site were submitted to XRD and SEM analysis. The samples from Tipasa were predominately calcined clay and/or lime. The samples from the Forbidden site consisted of wood, clay, and dolomite. The main binder in both cases was a type of C-A-S-H gel occasionally containing Mg, K, and/or Cl. Most of today’s structures are based on portland cement. Achieving sustainable-development goals generally includes replacing part of the cement in concrete with industrial waste or calcined clay, especially metakaolin. More recently, wastepaper sludge ash (WSA) from the pulp and paper industry (possibly containing a certain quantity of metakaolin as well as some C3A and C2S) has been used in concrete. A microstructural study of hardened cement paste containing 40% WSA revealed the formation of hydrated products such as a type of C-A-S-H gel, ettringite, and calcium carboaluminate.