11 - Alkali-activated concrete versus ordinary Portland cement concrete and Roman concrete when using sea sand and seawater

Abstract

Due to the scarcity of clean water and natural aggregates, the rich reserves of sea sand and seawater become progressively attractive. This chapter reviews the use of sea sand and/or seawater in two alkali-activated materials (AAM, specifically the alkali-activated slag or AAS, and geopolymer) and compared their performance against the conventional ordinary Portland cement (OPC) concrete and the ancient Roman concrete (RMC) under the effect of internal chlorides and sulfates on various properties. Research first started on the OPC, where chloride binding was mainly through the formation of salts such as the Friedel’s salt. The sulfates in the seawater, while damaging to the gel structure, are within the acceptable ranges. Subsequent studies slowly expanded to the AAM, and showed that AAS and geopolymer are more chemically stable against chlorides and sulfates. However, the chloride binding capacity of geopolymer is lower than the calcium-rich AAS. Growing interest also promoted the research on the RMC. The strong Al-tobermorite gels that were produced from years of pozzolanic reactions were the key to the long lifespan of the RMC, and may give insights to the making of modern high performance sea sand seawater concretes.