Despite growing demands for its use and many desirable properties, concrete has inherent weaknesses, including brittleness and low tensile strength. It is prone to degradation in various environmental conditions, such as chemical reactions with deleterious ions and shrinkage, leading to frequent repairs over time. To address these issues, researchers have explored innovative solutions to limit crack formation and propagation and enhance concrete durability. One promising approach is to tailor concrete properties using nanomaterials. Every year, approximately 6–8 million tonnes of shrimp, crab, and lobster shell wastes are generated, requiring proper waste management. Chitin, the second most abundant natural biopolymer after cellulose, is readily available in seafood waste streams. This study aims to explore the prospect of chitin nanomaterials altering various properties and performance of cementitious systems across paste, mortar, and concrete and enhancing the durability of concrete infrastructures. Additionally, the study explores potential application areas and the environmental and economic aspect aspects of using chitin nanomaterials as an additive for cement composites.In this study, the chitin content of shrimp shell waste was oxidized to produce chitin nanocrystals (ChNC) and mechanically fibrillated to obtain chitin nanofibers (ChNF) for evaluation in different scales of cement composites, i.e., cement paste, mortar, and concrete. Chitin nanomaterials (ChNMs) have favorable properties like high specific surface area, high stiffness, and reactive surface functional groups like hydroxyl, carboxyl, and amide, depending on the production processes. Chitin nanomaterials significantly influenced the rheological and mechanical properties and durability of the cement composites. In cement paste, ChNC delayed the final set time by up to 106 minutes at 0.055 wt% of cement, while ChNF caused a maximum delay of 78 minutes at 0.035 wt% of cement. This delay was attributed to the electrostatic repulsion induced by nanochitin separating cement particles and delaying hydration reactions. The viscosity of fresh cement paste increased with ChNF but remained essentially unchanged with ChNC, likely due to the higher mobility of ChNC rod-shaped particles compared to the interconnected ChNF fiber network with restricted mobility in the paste. Similarly, in mortar, ChNF (0.075 wt% of cement) and ChNC (0.05 wt% of cement) delayed the final set time by 50 and 30 minutes, respectively, again likely by electrostatic dispersion effects. The delay in the setting time was also observed from the delayed peak heat rate of paste samples with ChNMs from the isothermal calorimetry test, which corroborates the findings from the setting time test. The rheological modifications show the prospect of ChNC and ChNF as viscosity-modifying admixtures and set retarders for various construction applications. Chitin nanomaterials had minimal impact on the heat of hydration of cement, with cumulative heat values of 232.0 J/g for ChNF and 227.8 J/g for ChNC, compared to 229.7 J/g for the control after three days of hydration. In cement paste, nanochitin at 0.05 wt% of the binder dosage significantly enhanced the 28-day flexural strength by approximately 40% and compressive strength by up to 12%. ChNF (0.05 wt%), with its higher aspect ratio, exhibited the most significant enhancements in flexural strength and fracture energy, improving them by 24% and 28%, respectively. Solid-state nuclear magnetic resonance (NMR) analysis revealed that ChNF (0.05 wt% of cement) strengthened the calcium–silicate–hydrate (C-S-H) structure, showing a 41% increase in polymerization and a 9% increase in silicate chain length at 28 days. The strength improvement with chitin nanomaterial was most likely from nano reinforcement, alteration of the C-S-H, or both, based on NMR results, rather than nucleation of cement hydration, since only a minor alteration of the heat of hydration was observed with chitin nanomaterials. The effect of nanochitin on the durability of cementitious systems was extensively evaluated in terms of alkali-silica reactivity (ASR), sulfate resistance, and drying shrinkage. Importantly, chitin nanomaterials mitigated expansion due to ASR, reducing it by up to 23% at 0.05 wt% of cement. Their ability to refine the matrix structure, modify pore size distribution, and bind alkali ions likely contributed to improved ASR performance. Additionally, all chitin-modified mortars exhibited lower expansion under sulfate exposure, reducing expansion from sulfate attack by 22%–28%. The presence of higher portlandite and lower ettringite and gypsum content indicated improved sulfate resistance, likely due to pore refinement and the potential binding of Al³⁺ and Ca²⁺ ions. However, no significant reduction in drying shrinkage was achieved with the nanochitin additives. This study provides a thorough evaluation of cementitious composites incorporating ChNMs in paste, mortar, and concrete. The analysis aims to identify the most appropriate applications for these materials. ChNMs have been found to delay setting time, improve rheological properties, and enhance engineering characteristics, making them appealing to various stakeholders in the concrete industry, including readymix concrete producers and masonry workers. Concrete structures such as pavements, bridge decks, and transportation infrastructure, which are susceptible to ASR, could benefit from ChNMs by reducing harmful reactions and boosting durability. Additionally, concrete used in sewer systems and wastewater treatment plants, which face exposure to aggressive ions, could see improved chemical resistance with the inclusion of ChNMs. The environmental and economic feasibility of ChNMs for cementitious composites were also assessed. The A1 to A3 stages of the life cycle according to ISO 21930 were considered for the life cycle assessment of the ChNMs. The life cycle assessment started with the processing of shell waste after transporting it to a shell processing plant. Based on the environmental life cycle assessment (LCA) studies in the literature, global warming potential (GWP) was found to be 395.73 kg CO2 eq/kg of ChNC. For ChNF, GWP was 11.5 kg CO2 eq/kg based on the computed GWP for cellulose nanofiber from pulp. Using these values at the optimal dosage in the structural concrete mixture, it was estimated that ChNC could increase the GWP of concrete by 2% at a dose of 0.05 wt% of cementitious materials. ChNF added less than 1% to the concrete GWP at a dose of 0.05 wt% and 0.1 wt% of cement. The addition of ChNF reduced GWP normalized to the flexural strength of concrete by 7.86%, considering the enhancements in flexural strength. Chitin is an abundant natural material on earth, with existing large-scale industrial production facilities worldwide for chitin and chitosan, potentially ensuring a consistent supply of chitin powder for nanomaterial synthesis. At the yield of 2.26% (44.2 kg wet shrimp shell yields 1 kg of ChNMs) the 4.9 million metric tons of bark waste from the seafood industry can produce 288,122 metric tons of chitin powder that yields 110,860 metric tons of chitin nanomaterials. Technoeconomic studies of ChNC production at bench scale showed that the cost of ChNC could range from $72.89 to $83.58 per kilogram, and the cost of ChNF can vary between $57.33 and $58.02 per kilogram. Based on these values, at 0.05 wt% dose, the added cost to the per m3 concrete will be between $9.3 and $11.1 for ChNF and between $11.9 to $13.6 for ChNC. Considering the concrete price of $250/m3, ChNMs will add an additional cost of 4% to 5%, which is less than the added price from admixture and fiber typically added to the concrete. The comprehensive evaluation of this study highlights the potential of chitin as a biomass source for high-performance structural nanofibers and nanocrystals, offering an innovative approach to repurposing seafood waste to advance sustainable construction material

This report is a comprehensive review of natural and human-made materials with the potential to reduce cement content in concrete by partially replacing portland cement or as additives. The review aims to reveal possible source materials as alternative supplementary cementitious materials (ASCMs) to coal-burned fly ash and ground granulated blast furnace slag as these SCMs supplies rapidly decline. Information required to estimate supplies of each ASCM was gathered, and ASCM candidates with enough abundance to support California’s concrete paving sector were identified for further laboratory evaluation. In addition, the required chemical, thermal, and mechanical treatments of the source materials were gathered so the environmental and economic impacts of the processes could be considered. A review of scientific literature on the technical performance of the studied materials in cement paste, mortar, or concrete was also conducted when that information was available.

The reviewed feedstock material categories include biomass sources, construction and demolition wastes, natural pozzolans (volcanic and sedimentary materials), and post-consumer waste. As part of the biomass category, biopolymer-based nanomaterials were also included in the review for their promise to reduce cement content from added strength. The following information was included for each material considered in this report: feedstock description, the potential mechanism of performance in concrete, physical and chemical properties, feedstock supplies and processing method, technology readiness level (TRL), a summary of technical performance in cementitious systems based on the scientific literature, environmental impacts of the production phase, and cost considerations.

Based on the comprehensive information gathered, several materials present potential as ASCMs, fillers, and admixtures for the California paving industry. However, most materials identified are at TRL 3 or 4, requiring more research and development to move toward implementation. In addition, some of these ASCMs may not fully satisfy the current regulations for SCMs. For example, biomass ash from some sources may contain a high alkaline content and a greater than 6% unburnt carbon content. Furthermore, some natural pozzolans impose a high water demand and have slow strength gain. In addition, the reported performance in the literature for the biobased nanomaterials studied is conflicting and performance data in concrete is scarce. Finally, some reviewed materials were not selected for more advanced laboratory evaluation because a supplier was not found in California. These materials include municipal solid waste ash, wastewater treatment sludge, and seashell waste. In addition, ground glass, harvested coal-burnt fly ash, and fines from carpet recycling were not chosen for laboratory evaluation because they are being investigated in other Caltrans and non-Caltrans research contracts.