From Technical Lignins to Sustainable Cement Superplasticizers: A Concise Review

The construction sector is under enormous pressure to reduce the overall environmental impact of its activities, which, for cement production alone, cause over 2 Gt/yr of CO2 emissions (2022). Given the massive scale of concrete production, even minor components such as plasticizers, typically required in quantities of only a few percent of the dry cement mass, correspond to production volumes of many tens of Mt/yr, making their sustainability highly relevant. Lignin is the second most abundant renewable biopolymer on Earth and is currently used in concrete formulations mainly as a low-performance cement plasticizer. Despite this limited application, lignin represents an underexploited but highly attractive raw material for the development of environment-friendly concrete additives, owing to its abundance and availability from industrial biomass residues. The purpose of this review is to provide a specific and up-to-date overview of the various approaches for developing sustainable, high-performance concrete plasticizers based on lignins derived from industrial waste streams. The state of the art in the field is put into perspective by considering the various industrial sources of original technical lignins, the processes that led to their formation, and potential strategies for improving their characteristics. A quick overview of the patent history of the field complements the analysis of the scientific literature. An integral part of this work is a concise introduction to the fundamentals of cement chemistry and rheology, which are essential for understanding the technological requirements for effective concrete admixtures and for enabling cross-disciplinary research between the lignin and cement communities.