The development of lignin-based admixtures (LBAs) for cement-based composites is an alternative to valorizing residual lignins generated in biorefineries and pulp and paper mills. Consequently, LBAs have become an emerging research domain in the past decade. This study examined the bibliographic data on LBAs through a scientometric analysis and in-depth qualitative discussion. For this purpose, 161 articles were selected for the scientometric approach. After analyzing the articles’ abstracts, 37 papers on developing new LBAs were selected and critically reviewed. Significant publication sources, frequent keywords, influential scholars, and contributing countries in LBAs research were identified during the science mapping. The LBAs developed so far were classified as plasticizers, superplasticizers, set retarders, grinding aids, and air-entraining admixtures. The qualitative discussion revealed that most studies have focused on developing LBAs using Kraft lignins from pulp and paper mills. Thus, residual lignins from biorefineries need more attention since their valorization is a relevant strategy for emerging economies with high biomass availability. Most studies focused on production processes, chemical characterizations, and primary fresh-state analyses of LBA-containing cement-based composites. However, to better assess the feasibility of using different LBAs and encompass the multidisciplinarity of this subject, it is mandatory that future studies also evaluate hardened-sate properties. This holistic review offers a helpful reference point to early-stage researchers, industry professionals, and funding authorities on the research progress in LBAs. It also contributes to understanding the role of lignin in sustainable construction.

The performance of a low-purity magnesium oxide (magnesia) source for the synthesis of magnesium silicate hydrate (M-S-H) cements was evaluated. Magnesia-rich precursors were produced from a raw magnesite containing significant levels of impurities (e.g. silicon dioxide, aluminium oxide and ferric oxide), which was ground and calcined at different temperatures (600, 650 and 700°C). The alternative precursors were initially characterised by their physical, chemical, mineralogical and hydration properties. Cement pastes were then prepared using the calcined magnesite samples and commercial silica fume and evaluated in terms of mechanical performance (after 3, 7, 28 and 56 days of curing) and microstructure (after 7 and 56 days of curing). The pastes produced with the most reactive samples (calcined at 650°C and 700°C) exhibited compressive strength equivalent to or higher than that of the control mixture (prepared using high-purity commercial magnesia with the same mix proportions). Microstructural characterisation further revealed structural similarities among the M-S-H phases formed in all samples after 56 days of curing. These findings demonstrate the feasibility of using low-value magnesia-rich precursors to produce M-S-H binders through appropriate grinding and/or calcination strategies. Moreover, this study encourages further research on the valorisation of magnesia-rich industrial wastes for the development of more eco-efficient cement-based composites.

This study presents the characterization and a strategy for processing residual fines for their application in the production of magnesium silicate hydrate (M-S-H) binders. Quartzite mining waste (QW), soapstone waste (SW), and sugarcane bagasse ash (SCBA) were evaluated. Initially, the raw materials were characterized by XRF, XRD, FTIR, SEM/EDS, and thermogravimetry. The samples were then subjected to a grinding study and characterized by laser granulometry and SEM/SE. The processed QW and SW samples exhibited high fineness (D90 of 13.5 and 42.9 µm, respectively) and a well-graded and continuous particle size distribution. The processed SCBA presented a high SiO₂ content (60.1%), predominance of amorphous phase (53.7%), and a high specific surface area (49.9 m2/g). Based on the results, the QW and SW are expected to perform effectively as fillers, reducing costs and contributing to the microstructure and mechanical performance of the matrices. The SCBA, in turn, stands out as a potential source of reactive silica (SiO2) for the synthesis of M-S-H cements. The study aligns with circular economy principles and offers alternatives for utilizing industrial waste in the Brazilian construction industry, opening new possibilities for research on eco-efficient M-S-H systems.