1. Problem And Architectural Premise

The dominant approach for embedding electrochemical storage in cementitious building elements has been to disperse active material, graphite particulates, carbon-black aggregates, sorbent fibers, uniformly throughout the structural pour. The dispersion approach is appealing because it requires no modification to standard concrete-placement workflows, but it suffers from three fundamental constraints. First, the volume fraction of active material is bounded by the structural mix design: above approximately 8 to 12 percent by volume, the compressive strength of the cured concrete falls below the 28-day target of 25 to 40 MPa typical of structural concrete. Second, the active material is sealed inside the cured matrix; once the pour cures, no electrolyte can be refreshed, no active material can be replenished, and no service intervention is possible across the 50 to 100 year design life of the building. Third, the dispersion geometry produces extremely long ionic-conduction paths through a high-tortuosity matrix, depressing usable round-trip efficiency to the 30 to 55 percent range and producing time constants for charge and discharge measured in hours rather than minutes.

The architectural premise of cavity-bath storage is that the structural element should be treated not as the storage medium but as a hosted enclosure containing engineered storage cells with defined geometry, defined active-material loading, defined ionic transport paths, and defined service interfaces. Concrete is excellent at compressive load, fire resistance, and dimensional stability over decades; it is poor at ionic conduction and impossible to service after cure. By segregating the storage volume from the structural volume, placing the storage volume inside an engineered cavity within the structural pour, both functions can be optimized independently. The structural element retains its full design strength because the cavity is geometrically and reinforcement-wise accommodated in the structural calculation. The storage cell occupies a clean, defined geometry with engineered ionic paths, accessible terminations, and serviceable interfaces. The shift from dispersion to engineered cavity is the central premise from which every other primitive in this disclosure follows.

2. Core Architectural Primitive

The core architectural primitive is a sacrificial formwork body, placed inside the rebar cage prior to pour, that occupies the volume the storage cavity will eventually inhabit. The formwork body is shaped to the desired cavity geometry, typically a slab, column, or beam form factor with internal aspect ratios from 1:1 (cubic) to 50:1 (long-thin column), and is composed of a material engineered to be removed cleanly after the surrounding concrete has reached design cure strength. Removal proceeds by burnout, dissolution, biodegradation, or a combination, leaving behind a void of precisely the formwork geometry, with concrete walls of nominal 25 to 75 mm thickness on all sides and reinforcement bars passing through the cavity in pre-engineered positions.

The cavity walls are not bare concrete; they are conditioned during the pour to present a low-permeability, ion-tolerant interior surface. Conditioning occurs via integral admixtures (silica fume, metakaolin, or proprietary pozzolanic blends) that densify the interfacial transition zone and reduce permeability below 10⁻¹² m/s, and via post-cure surface treatments (epoxy-amine, polyurea, or fluoropolymer linings) applied through the cavity ports after formwork removal. The result is a cavity whose walls function as the cell's outer enclosure with structural-grade mechanical integrity, fire resistance to ASTM E119 ratings, and chemical compatibility with the intended electrolyte chemistry.

Within the cavity, hollow non-corroding reinforcement bars, carbon-fiber-reinforced polymer (CFRP) at 1500 to 2400 MPa tensile strength, or glass-fiber-reinforced polymer (GFRP) at 700 to 1000 MPa, pass through in pre-engineered positions, performing two simultaneous functions. They serve as the structural reinforcement that the cavity volume would otherwise have removed from the structural cross section, and they serve as ionic and material conduits because their hollow bores can carry electrolyte, gas-phase reactants, or active-material slurry through the structural element. The dual function is what makes the architecture coherent: every reinforcement member that the structural calculation requires is also an electrochemical service member that the cell can use. This collapses what would otherwise be two parallel infrastructures, structural reinforcement and storage plumbing, into a single integrated bar count.

3. Sacrificial Formwork Class And Removal Modes

The sacrificial formwork material is selected from four broad classes. The first class is biodegradable polymers: cellulose-derived materials (lignocellulose composites, cardboard laminates), starch-derived foams, and polylactic acid (PLA) bodies, with bulk densities of 0.05 to 0.5 g/cm³ and compressive strength sufficient to resist concrete placement pressures of 20 to 80 kPa without deformation. The second class is water-soluble materials: sodium-silicate-bound aggregate forms, polyvinyl alcohol (PVA) foams, salt-bound carbohydrate composites, and water-soluble extruded polymer cores. The third class is thermoset-then-burnout materials, polymers that survive the alkaline 50 to 80 °C exotherm of cementitious cure but pyrolyze cleanly under a controlled post-cure thermal cycle at 250 to 500 °C, leaving carbonaceous residues below 0.1 percent by mass. The fourth class is microbially-digestible materials, cellulose-rich substrates digestible by introduced fungal or bacterial cultures under engineered humidity and temperature conditions.

Three formwork-removal modes follow from the material classes. Burnout removal applies controlled heating at 1 to 5 °C/min ramp rates, holds at peak temperature for 2 to 12 hours, and requires the host structural element to tolerate the thermal cycle without spalling, readily achievable for high-density structural concrete with pre-conditioning moisture content below 3 percent. Dissolution removal applies a flush of water (or, for sodium-silicate forms, a dilute acid) through the cavity ports at flow rates of 0.5 to 5 L/min for 6 to 48 hours, with effluent collection and recycling. Biodegradation removal introduces microbial cultures through the cavity ports along with appropriate moisture and nutrient conditions, holding the cavity at 25 to 40 °C and 80 to 95 percent relative humidity for 7 to 30 days until the formwork mass has been digested below detection limits. Each removal mode admits a distinct operational economics, regulatory profile, and envelope of acceptable feedstock chemistries; for site-cast installations the dissolution mode is generally preferred, while for precast modules the burnout mode is generally preferred.

4. Hollow Rebar And Cavity Thermal Manifold

Hollow non-corroding rebar with outer diameters of 12 to 32 mm and inner bore diameters of 6 to 22 mm threads through the cavity in patterns engineered to satisfy both the structural reinforcement schedule and the electrochemical service plan. CFRP bars provide tensile reinforcement at strength-to-weight ratios approximately five times that of A615 Grade 60 steel, with the additional advantages of zero corrosion potential in alkaline cementitious environments and electrical insulation between bars. GFRP bars are used where a lower-cost alternative is acceptable and where the slightly lower elastic modulus (approximately 40 to 60 GPa versus 120 to 150 GPa for CFRP) is compatible with the structural design. Bar bores are sealed at the cavity walls by elastomeric grommets compatible with the electrolyte chemistry; bores terminate at external manifolds at the structural element's edge faces.

A subset of the hollow rebar, typically 10 to 30 percent of the total bar count, functions as a cavity thermal manifold rather than as electrolyte conduit. Thermal-manifold bars carry a working fluid (typically a 30 to 50 percent propylene-glycol/water mixture) at flow rates of 1 to 10 L/min and inlet temperatures controlled between 5 and 45 °C, providing direct conductive coupling between the cell's electrochemical operating temperature and the building's HVAC loop. Manifold geometry, bar count, bar spacing, bar surface area, is engineered to provide overall heat-transfer coefficients of 50 to 500 W/m²·K between the cell interior and the working fluid, sufficient to extract 100 to 5000 W per cell during high-current cycling and to inject equivalent heat during cold-weather discharge. The thermal coupling admits the cell to participate in HVAC operations as a programmable thermal mass, smoothing both the building's heating load and the cell's electrochemical thermal envelope under credentialed control.

5. Cavity Ports, Fill Modes, And Inert-Atmosphere Loading

Cavity ports are engineered penetrations at the structural element's edge faces that admit external interfacing without compromising structural integrity. Each port is a stainless-steel or fluoropolymer-lined sleeve cast integrally with the structural pour, terminating at a bolted face flange compatible with standard ANSI Class 150 or DIN PN16 piping interfaces. Four port classes are disclosed: electrolyte ports (for electrolyte refresh and circulation, typically 12 to 50 mm bore), active-material ports (for slurry or particulate active-material loading and refresh, typically 25 to 100 mm bore), gas-phase ports (for activator gas admission, vent gas exhaust, and inert-atmosphere purge, typically 6 to 25 mm bore), and electrical-terminal ports (for current collector exit, typically a fluoropolymer-insulated copper or aluminum bus penetration with hermetic seal).

Cavity fill operations admit three modes. Passive fill loads active material once during initial commissioning through the active-material ports, with no refresh interface beyond the initial load. Active fill maintains a continuous or scheduled circulation of active material through dedicated inlet and outlet ports, admitting refresh, reclamation, and chemistry change-out across the cell's service life. Hybrid fill combines an initial bulk load with periodic on-demand refresh of a fraction of the active inventory, balancing the simpler plumbing of passive fill against the lifetime extension of active fill. The selection drives port count, port sizing, and external piping requirements.

For chemistries that are oxygen-sensitive or moisture-sensitive, most metal-anode and many sorbent chemistries, cavity loading proceeds under engineered inert atmosphere. The cavity is purged through the gas-phase ports with dry nitrogen or argon to oxygen levels below 10 ppm and dew points below −60 °C, monitored by inline sensors. Active material is loaded through the active-material ports while the cavity remains under positive inert-gas pressure of 5 to 20 kPa above ambient. The inert-atmosphere loading procedure is recorded as a credentialed event in the cell's lineage chain, with sensor traces retained for regulatory and warranty purposes. After loading, gas-phase ports are sealed or maintained under controlled atmosphere depending on the chemistry's lifecycle requirements.

6. Operating Parameters And Engineering Envelope

The engineering envelope for cavity-bath cells is bounded on multiple axes. Cavity volume per cell ranges from 0.5 L (small embedded cells in non-structural partitions) to 200 L (large cells in primary load-bearing columns or beams). Cavity wall thickness is bounded below by structural-cover requirements for the surrounding concrete (typically 25 mm minimum for interior service, 50 mm for exterior, 75 mm for fire-rated) and above by the marginal structural cost of additional cover concrete. Cavity aspect ratios are bounded by formwork stability during pour and by ionic-transport-path length within the cell; the practical envelope is 1:1 to approximately 50:1 with an internal characteristic length below 500 mm.

Operating temperature within the cavity is held between 5 and 60 °C for most disclosed chemistries, controlled through the thermal manifold; transient excursions to 80 °C are tolerated by the cement-bound enclosure but not preferred. Internal cell pressure is held between −5 and +50 kPa relative to ambient, well below the burst envelope of the cavity wall. Electrolyte refresh rates range from zero (passive fill) to 0.1 cell volumes per day (aggressive active fill); active-material refresh rates range from zero to 0.01 cell volumes per day. Round-trip Coulombic efficiency for cavity-bath cells in the disclosed envelope ranges from 75 to 95 percent depending on chemistry; round-trip energy efficiency from 65 to 90 percent. Per-cell discharge power ranges from 50 W to 50 kW depending on cell size and chemistry, with C-rates from C/20 to 2C bounded by ionic-transport limits across the cavity's characteristic length.

7. Alternative Embodiments

Several alternative embodiments fall within the disclosure. A slab embodiment places a thin, wide cavity (e.g., 50 mm thick by 1000 mm by 3000 mm) within a floor slab, with hollow rebar in the orthogonal in-plane directions and ports along one or two edges; the slab embodiment maximizes electrode surface area per cavity volume and is well-suited to chemistries with planar current collectors. A column embodiment places a tall, narrow cavity (e.g., 200 mm by 200 mm by 3000 mm) within a structural column, with hollow rebar running vertically and ports at the column's top and bottom; the column embodiment is well-suited to gravity-assisted electrolyte circulation and to flow-battery chemistries. A beam embodiment places an intermediate-aspect cavity (e.g., 150 mm by 300 mm by 6000 mm) within a horizontal beam, combining vertical hollow rebar for shear reinforcement with horizontal ports for service access.

Multi-cavity arrays place several cavities within a single structural element, separated by structural webs of 50 to 150 mm cured-concrete thickness that maintain structural continuity across the element while admitting parallel electrochemical operation of multiple cells. Inter-cavity electrical interconnection is routed through dedicated conductor channels cast into the structural webs. Multi-cavity arrays admit per-cell isolation for fault containment and per-cell servicing without taking the entire structural element offline. A retrofit embodiment installs cavity-bath cells into existing structural elements through core-drilling: a cylindrical bore of 50 to 300 mm diameter is drilled into a column, beam, or slab; a pre-fabricated modular cavity-bath cell with integrated ports is inserted; and the annular space is grouted with a structural cement mortar to restore load-path continuity. The retrofit primitive admits credentialed structural-storage on existing buildings without full reconstruction, a deployment pathway that no dispersion-class architecture supports.

8. Composition With Broader Architecture

The cavity-bath architecture composes with several adjacent primitives in the broader Adaptive Query disclosure stack. It composes with the cycling-induced compaction primitive (Provisional 64/052,368) because the constrained cavity geometry provides exactly the mechanical confinement required for osmotic-thermal compaction of the active electrode structure to proceed; the cavity wall and the hollow rebar together supply the compressive boundary against which cycling-induced osmotic pressure equilibrates, and the resulting capacity-rise behavior turns the cavity-bath cell into an architecture that improves with use across its first 50 to 500 cycles. It composes with the credentialed admissibility profile because every cavity-port access event, every electrolyte refresh, every active-material exchange, every inert-atmosphere purge, every state-of-health probe, is recorded as a structured event in the cell's lineage chain, enabling per-cell warranty, regulatory tracking, and forensic reconstruction.

It composes with building HVAC and grid interfaces because the cavity thermal manifold provides direct fluid coupling to the building's hydronic loop, admitting the cell to function as a programmable thermal mass that absorbs daytime cooling load and releases nighttime heating load while simultaneously cycling electrically. It composes with structural fire engineering because the cement-bound cavity wall provides ASTM E119 fire ratings of 1 to 4 hours depending on wall thickness, allowing the cell to be sited in occupied spaces without violating life-safety codes. It composes with seismic engineering because the hollow rebar performs the same load-transfer function as conventional reinforcement, with the structural cross section's flexural and shear capacity computed under standard ACI 318 procedures using the as-cured cavity geometry as a known void.

State-of-health monitoring through cavity ports admits non-destructive measurement of electrochemical state, cycling history, electrolyte composition, gas-phase composition, and temperature distribution without compromising structural integrity. Periodic probe events, scheduled at intervals from daily to annual, are inserted through dedicated monitoring ports and removed after measurement, with each event timestamped and recorded. The monitoring data feeds the building energy-management system, the warranty database, and any applicable regulatory reporting interfaces. Probe instruments include reference-electrode rods, gas-phase chromatograph samplers, electrolyte-conductivity probes, embedded fiber-optic distributed-temperature sensors, and acoustic-emission transducers; each instrument's interface is engineered to mate cleanly with a standard cavity-monitoring port without on-site adaptation, and each measurement event is recorded as a credentialed entry in the per-cell lineage chain. The composition with monitoring infrastructure converts the cavity-bath cell from a passive component into a continuously observable asset whose electrochemical state, structural state, and service history are known to the operator across the full multi-decade service life of the host building.

9. Prior-Art Distinctions

Several prior-art lines are adjacent to but distinct from the cavity-bath architecture. Conventional sealed-cell battery enclosures (steel-cased prismatic cells, plastic-cased pouch cells, cylindrical 18650 and 21700 form factors) are external to the structural element and provide no structural function; the cavity-bath cell, by contrast, is integral to the structural pour and inherits the structural element's load-bearing, fire-resistant, and seismic performance. Dispersed-substrate concrete batteries, Hubler-class and successor literature in which active material is mixed homogeneously with the cementitious binder, share the host of concrete but lack the engineered cavity geometry, the hollow non-corroding rebar dual function, and the cavity-port serviceability that define this disclosure.

Sacrificial formwork has appeared in prior art for the creation of mechanical voids in concrete (HVAC ducts cast in place, post-tensioning tendon ducts), but never in conjunction with hollow non-corroding reinforcement that simultaneously serves as electrochemical conduit, never with cavity-port external interfacing for active-material refresh, and never under inert-atmosphere loading protocols. Hollow rebar has appeared in prior art for post-tensioning and for embedded sensing, but never as a dual-function ionic conduit and structural reinforcement member. Core-drilled retrofit of structural elements has appeared in prior art for utility penetrations, but never as a method to install pre-fabricated electrochemical cells into existing buildings. The combination of all of these elements, cavity, formwork, hollow rebar, ports, fill modes, removal modes, retrofit, monitoring, in a single coherent architectural primitive is the subject matter newly recited in this disclosure.

10. Disclosure Scope

This primitive is disclosed under U.S. provisional application 64/050,895, filed April 27, 2026. The disclosure recites the sacrificial cavity formwork primitive across all four material classes (biodegradable polymers, water-soluble materials, thermoset-then-burnout materials, microbially-digestible materials); the three formwork-removal modes (burnout, dissolution, biodegradation); the hollow non-corroding rebar dual-function primitive in CFRP and GFRP embodiments; the cavity manifold thermal-coupling primitive with engineered overall heat-transfer coefficients; the four cavity-port classes (electrolyte, active-material, gas-phase, electrical-terminal); the three fill modes (passive, active, hybrid); inert-atmosphere loading protocols with engineered oxygen and dew-point limits; cell-volume aspect-ratio engineering across slab, column, and beam embodiments; multi-cavity arrays within structural elements with engineered structural webs; the core-drilled retrofit primitive for installation in existing structural elements; and in-place state-of-health monitoring through cavity ports with credentialed event recording. The disclosure is intended to support continuation and divisional applications across each of these sub-primitives as warranted by the prosecution record and as the operational data set from deployed cells matures.