Modern underwater concrete construction has enabled the creation of large, durable maritime infrastructure, but current methods are slow, expensive, and environmentally intrusive, making them unsuitable for expeditionary or military operations. Traditional approaches rely on cast-in-place or precast elements, requiring extensive formwork, specialized equipment, and significant transportation of raw materials, which limits their applicability at greater depths and in austere environments. Recent advances in terrestrial 3D concrete printing have demonstrated rapid, flexible construction without formwork, but these systems are not yet adapted for underwater use due to challenges in materials, hardware, and environmental conditions. DARPA envisions a subsea harvest-to-print 3D construction system to address the critical limitations of current underwater construction methods. The future system will enable rapid, flexible, and environmentally conscious underwater 3D printing for expeditionary and commercial applications through development of state-of-the-art underwater construction equipment and by leveraging in situ seafloor sediments and seawater in concrete mixes. Building on the DARPA Trenton program’s demonstration of printable, low-binder concrete formulations using native sediments, this SBIR topic will develop and demonstrate fully submersible critical subsystems for a 3D concrete construction system in near-shore or medium depth environments. Key innovations for the integrated harvest-to-print system include sediment harvesting and processing, adaptive concrete formulation, marinized printing hardware, and real-time quality control.The Phase II program will fund the development and near-shore demonstration of critical subsystems, with each performer focusing on one or more of the following tracks. The goal is to demonstrate critical subsystems and lay the foundation for future development of a fully autonomous, deepwater-capable system.Program Constants (apply to all tracks):• Proposed subsystems must be prototypable within $3M budgets per performer• Solutions must be interoperable for future integration• Marinization experience is favorable• Proposed solutions must use seawater in concrete formulations• Seafloor sediments include: o Coarse, low water absorption sediments such as sand (<100µm)o Fine, high-water absorption sediments such as clay (<50µm)Track 1: Marinized Underwater 3D Concrete Printer for Near-Shore Demonstration• Design, build, and demonstrate a fully submersible 3D concrete printer for operation at shallow depths (> 5 meters) near-shore up to medium depth (< 100 meters).• Architectures for this prototype can include topside-controlled material supply (sediment, binder, water) via hoses/cables or limited onboard storage, with the awareness that future iterations will move toward fully underwater harvest-to-print systems.• Demonstrate printing of a self-supporting structure (e.g., arch, wall, slab, or pile).• Include basic underwater deployment/retrieval and remote operation.Track 2: Sediment Transportation Subsystem• Develop a modular, marinized concrete transportation system that can effectively “pump” materials through a subsea harvest-to-print system, including through the 3D printer. Materials needing transport include: o Unprocessed, wet seafloor sedimentso Processed, dry seafloor sedimentso Low binder (= 20%) concrete mixes• Develop a sediment dewatering capability that can be incorporated in-line along the material transportation path.• Demonstrate compatibility with a range of sediment types and ability to deliver a consistent, pumpable mix.• Design for future automation; manual/semiautomatic operation is acceptable for Phase II.Track 3: In-Line Mixing and Quality Control at the Nozzle• Develop an in-line, marinized, multi-part mixing system (at or near the nozzle) capable of handling variable seafloor sediment/binder ratios and ensuring homogeneous mix.• The system should be capable of handling both extremes of seafloor sediments and their concrete mixes.• Integrate basic sensors for real-time monitoring of mix quality (e.g., viscosity, flow rate, temperature).• Demonstrate ability to adjust mix parameters in response to sensor feedback (manual or semi-automated).Track 4: Sediment-Based Concrete Formulation and Data-Driven Optimization• Systematically characterize a representative library of locally available sediment types relevant to Hoboken program applications, including coarse, low-water-absorption sediments (e.g., sand, <100 µm) and fine, high-water-absorption sediments (e.g., clay, <50 µm), with particular emphasis on sediment types likely to be encountered in near-shore and expeditionary environments relevant to the target applications listed below.• Develop and execute a structured experimental matrix to evaluate the effects of sediment type, gradation, binder content, water-to-binder ratio, admixtures, and mix procedure on concrete printability (e.g., open time, extrudability, buildability, layer adhesion), compressive and flexural strength development, setting time, and durability under near-shore and underwater conditions.• Build a structured, machine-readable database of sediment physical and chemical properties, mix design parameters, processing conditions, and concrete performance metrics, designed from the outset to serve as a training and validation library for AI and machine learning models.• Ensure the training data library provides sufficient breadth and depth of coverage across relevant sediment types, environmental conditions, and target application performance requirements to support generalizable model training.• Develop a beta AI concrete formulation tool capable of: (a) predicting concrete compressive strength and printability metrics from input sediment characteristics and mix design parameters, and (b) recommending optimized mix designs for user-specified performance targets.• Collaborate with hardware performers to validate formulations through printing trials, provide mix designs compatible with hardware constraints, and contribute to joint interface definition.• Demonstrate successful underwater 3D printing of at least one structural element using a mix design recommended by the AI concrete formulation tool, conducted in coordination with at least one hardware track performer.Demonstrate successful underwater 3D printing of at least one structural element using an optimized formulation output through the AI concrete formulator. The AI tool should be developed with awareness that future iterations will move to onboard capability becoming part of feedback loops to dynamical monitor and adjust processes throughout the future harvest-to-print system.
