Civil and built-environment systems: hand-considered hypotheses, 1801–1900
One hundred, written in sequence. Each was framed before the next was started; the label gives the argument's shape, not its topic. The forms were kept apart on purpose — a bound is not a threshold, a threshold is not a reversal, and an artefact that mimics an effect is not a misattribution — because those distinctions decide what experiment would actually refute the claim. None has been tested. Figures offered as scale are illustrative estimates, not measurements, and no literature is cited because none was consulted while writing.
Concrete, mortar and cementitious durability
Misattribution
H1801. Map cracking on a bridge pier is read as alkali–silica reaction whenever gel is suspected, yet the same pattern forms when the outer 25 mm dries faster than the core and shrinkage is restrained by the reinforcement below. If that is the cause, the cracks should stop at the depth where the drying front stalls and should carry no gel. Cores logged by petrography and scanned by ultrasonic tomography separate the two in one operation.
Hidden term
H1802. Chloride diffusion coefficients measured by bulk immersion carry a term for chloride bound to the C-S-H, and that term is not constant: it grows as the free concentration falls, so a profile fitted with one apparent D will underpredict ingress at low exposure concentrations. Refitting the same profile with binding switched off, using an isotherm measured separately, should move the fitted D by an amount that tracks the isotherm's slope rather than the paste's porosity.
Identity
H1803. Phenolphthalein marks a depth that is not the depth of actual CO2 conversion, because the indicator turns near pH 9 while the conversion front sits near pH 10 to 11 in a partly carbonated zone. Mapping the front on a companion slice by thermogravimetry should place it consistently behind the pink boundary, and the offset should widen in blended cements whose pH buffer is weaker.
Bound
H1804. Capillary rise in a fired clay brick is limited by the largest throat that remains continuously water-filled, not by total porosity, so a highly porous brick with coarse connected pores can draw water to a lower height than a denser brick whose pores are finer. Mercury intrusion on the same specimens, followed by a rise test on matched cut prisms, should show the maximum height scaling with that throat radius rather than with the absorption coefficient.
Threshold
H1805. Rain driven against a hairline crack does not reach the reinforcement until the delivery rate exceeds what the crack's walls can absorb, so the onset is set by sorptivity and crack width rather than by wind pressure alone. A spray rig that holds pressure constant while stepping the water rate should find a sharp onset, and the onset rate should halve when the crack is pre-wetted.
Reversal
H1806. At fixed air content, raising concrete strength can reduce freeze–thaw durability because the bubbles that survive in a denser matrix are fewer and larger, coarsening the void spacing even though the paste itself is stronger. Casting three mixes of increasing strength at the same target air content and measuring spacing factor before testing should show durability peaking in the middle mix rather than in the strongest one.
Count
H1807. Only three parameters of a chloride ingress profile can be independently identified from one core: surface concentration, apparent diffusivity, and the ageing exponent. Fitting the same profiles with the exponent fixed and comparing the residual ridge with profiles from a second exposure age should expose any fourth parameter as a direction in which the data carry no information.
Artefact mimics effect
H1808. Reports of autogenous healing in cracked concrete often measure a healed surface rather than a restored ligament, because carbonation precipitates calcite across the crack mouth within days and blocks the water that would reveal the interior. Curing identical specimens in CO2-free water and in air should separate the two, since only the air-cured set will show a load recovery that disappears when the mouth is ground back.
Scale argument
H1809. Accelerated carbonation at 3 per cent CO2 is not a sped-up version of the 0.04 per cent of the atmosphere, because the higher concentration favours bicarbonate formation and suppresses the pH gradient that controls the front in service. Exposing the same concrete at four concentrations and collapsing the curves with an exponent fitted to each should yield exponents that drift with concentration, which would make the acceleration factor a function of the variable it is meant to replace.
Inversion of standard practice
H1810. Steam curing is used to gain early strength, but it coarsens the pore structure of the outer skin and can leave concrete that resists chloride ingress less well than the same mix cured at ambient temperature. Companion cubes, steam-cured and moist-cured to equal 28-day strength and then tested for chloride migration, isolate the curing effect from the strength effect.
Selection effect
H1811. Condition surveys overstate deterioration because inspectors sample the members that already look bad, so the severity distribution maps where engineers looked rather than where damage is. Re-coring at randomly selected coordinates on the same structures, including the visually sound members, should shift the distribution toward better condition. The apparent benefit of any maintenance intervention should shrink at the same time.
Unit trap
H1812. Site water additions are corrected from slump by assuming a fixed aggregate moisture, but the correction is applied in litres per cubic metre while slump responds to the water film on the fines, so the two are not the same quantity and the error grows with fines content. Batching two mixes with the same slump but different sand gradations, then measuring the actual water by oven-drying the fresh mix, should show a water difference the correction does not predict.
Derived quantity
H1813. Equivalent age at 20 °C is treated as a state variable for maturity, yet the activation energy it depends on shifts with water-to-binder ratio and with the presence of slag. Two specimens brought to the same equivalent age along different temperature paths, then tested for bound water and strength, should differ by more than the maturity rule allows, which would make equivalent age a bookkeeping device rather than a physical coordinate.
Hidden variable
H1814. Delayed ettringite formation is indexed to curing temperature, but the expansion that follows depends on the concrete's internal relative humidity after cooling, which is set by the curing regime and the element's thickness rather than by peak temperature alone. Sealing half the specimens immediately after steam curing and drying the other half in the same thermal cycle should produce expansions that separate by humidity while sharing one temperature history.
Path dependence
H1815. Concrete loaded after it has dried creeps differently from concrete dried while under load, and the difference survives a return to the same moisture state, which means creep is not a function of the current stress and humidity. Running the two sequences on twin specimens and reloading both at the same condition should leave a residual strain offset that no single compliance function can reproduce.
Crossover
H1816. Air permeability and water absorption rank porous building stones in opposite orders at low and high saturation, because gas flow follows the largest connected pores while liquid uptake follows the finest continuous ones. Measuring both on stones whose pore-size distributions are known from mercury intrusion should locate the crossover at the saturation where the two networks stop being the same network.
Conservation argument
H1817. Alkali–silica reaction in a sealed element must slow as the alkali inventory is consumed, so a specimen that keeps expanding at a constant rate is receiving alkali from outside. De-icing salt and adjacent grout are the plausible sources. Wrapping half the prisms in an alkali-impermeable jacket and leaving the other half exposed should produce divergent histories, with the wrapped set flattening.
Null result
H1818. Across a portfolio of bridges, 28-day strength should show no useful correlation with 40-year carbonation depth once cover and curing are accounted for, because both are governed by the surface paste rather than by the cube strength. A stratified sample that pairs each low-strength bridge with a high-strength bridge of equal cover and age is the only version of the comparison that can support or kill the claim.
Feedback
H1819. Crack width in a restrained slab is not a fixed consequence of shrinkage but a feedback variable: a wider crack dries its own faces, which raises local shrinkage, which widens the crack further until the reinforcement engages. Monitoring width and internal humidity together through a controlled dry-down should show the humidity at the crack face falling ahead of the bulk, with the width rising in steps that track those drops.
Threshold
H1820. There is a cover-to-bar-diameter ratio below which corrosion products crack the cover before the bar loses meaningful section, and that ratio is set by the free expansion of rust against the concrete's tensile strain capacity rather than by cover in millimetres alone. Casting specimens at four bar diameters with identical cover and driving corrosion at a controlled rate should show first cracking at lower steel loss as the diameter grows.
Steel, connections and fatigue
Misattribution
H1821. Weld-toe cracking in a fillet weld is assigned to the stress concentration of the toe, but when the electrode has absorbed moisture the hydrogen that enters the heat-affected zone produces the same crack path at the same location. Beads deposited with dried and deliberately damped electrodes, at equal heat input and toe angle, should show the damped set cracking at lower applied strain.
Hidden term
H1822. Strain readings from resistance gauges bonded to steel at elevated temperature contain a creep term from the adhesive that looks like additional mechanical strain, and over a year of bridge monitoring the term is large enough to matter. Cycling an unloaded dummy gauge through the site's temperature history should produce an apparent strain of the same magnitude. That signal can then be subtracted from the live channels.
Identity
H1823. Plain steel's fatigue limit and the threshold below which corrosion fatigue does not propagate may be one crack-arrest condition shifted by anodic dissolution rather than two mechanisms. A cathodic potential that suppresses dissolution but not crack-tip strain should collapse the corrosion-fatigue curve onto the air curve at low stress ranges, while the high-range branches stay apart.
Bound
H1824. Shot peening's gain in fatigue life is bounded by how much of the induced compressive stress survives the first few thousand cycles, not by the surface stress measured immediately after treatment. X-ray diffraction after interrupted cycling should show the benefit decaying with the same relaxation constant as the residual stress, so a treatment with a higher initial stress but faster relaxation loses its advantage.
Threshold
H1825. Fretting at a bolted lap joint does not begin at any nonzero slip; it begins when slip amplitude exceeds the elastic accommodation of the contact patch, which is set by bolt preload and plate stiffness. A rig that holds preload constant while stepping cyclic slip should show acoustic emission starting at a sharp amplitude and not at a sharp load.
Reversal
H1826. Under a broken passive film and a small anode-to-cathode area ratio, a stainless steel fastener can lose section faster than a galvanised carbon-steel one, because the stainless cathode is efficient while the zinc sacrifices itself over a large area. Immersing both types in chloride solution with a controlled anode area should reverse the usual ranking at a specific area ratio. That ratio is measurable and is not the ratio assumed in the standards.
Count
H1827. A flange with N bolts does not have N independent preloads, because equilibrium fixes one relation among the clamp forces and leaves at most N−1 independent states. Instrumenting every bolt and tightening in two sequences to the same torque should produce clamp vectors whose difference lies in that one-dimensional null direction.
Artefact mimics effect
H1828. Acoustic emission attributed to crack growth in a fatigue test can come from fretting in the loading fixture, and the two sources are not separated by amplitude alone. Running a dummy specimen with a saw-cut instead of a crack, at the same load and frequency, should produce a hit rate that accounts for a measurable share of the crack emissions and whose spectrum matches the fixture resonance.
Scale argument
H1829. Fatigue tests on small specimens cannot be scaled to large members by stress alone, because the probability of finding an initiating inclusion in the highly stressed volume grows with that volume and the small specimen is effectively screened. Three sizes at identical stress, with life plotted against stressed volume, should give a slope steeper than the elastic prediction, which would identify initiation as the controlling step.
Inversion of standard practice
H1830. Cathodic protection is usually set to the most negative potential the coating will tolerate, but overprotection generates alkali at the steel and disbonds the coating, after which current concentrates at the bare patch. Stepping a protected panel through a range of potentials while mapping adhesion should show adhesion loss beginning at a potential less negative than the conventional criterion. The conventional criterion would then be protecting the coating at the expense of the steel.
Selection effect
H1831. Probability-of-detection trials recruit inspectors who are told the specimen contains a defect, so the measured rate describes motivated search rather than routine inspection and risk models built on it are optimistic. Repeating the trial with blind specimens under a realistic workload should lower detection at small sizes and change the ranking of inspection methods.
Unit trap
H1832. Stress-intensity factors quoted in MPa√m and in ksi√in differ by about 1.1, so a retrofit check that mixes a toughness from one system with a stress from the other can land inside the scatter while being systematically wrong. Recomputing a set of archived checks in one unit system should reveal a bias that follows the source of each input rather than the detail.
Derived quantity
H1833. Remaining fatigue life from Miner's rule is not a physical quantity because it depends on the order of load blocks and not only on their sum, so two histories with identical damage fractions can leave different crack lengths. Applying the same spectrum in ascending and descending order to twin specimens and measuring crack length by compliance should separate them even when the rule predicts equality.
Hidden variable
H1834. In riveted girders straightened after fabrication, the residual field from that operation, not the service load, sets the stress ratio at the critical hole, which is why identical details perform differently on nominally identical bridges. Hole-drilling a few rivets on each bridge and comparing residual stress with the cracking pattern should cluster the cracked bridges at one end of the distribution.
Crossover
H1835. At small sizes a welded detail is stronger than a bolted one, but above a length threshold the bolted connection wins because weld inspection reliability falls with length while slip resistance does not. Matched pairs across a range of lengths, with the same inspection effort applied to both, should show the ranking reversing at a length set by the inspection method.
Feedback
H1836. Corrosion is modelled as a current that consumes steel, but rust occupies more volume than the steel it replaces, so the cover cracks, the crack admits chloride, and the current rises. The rate becomes a function of the damage it has already caused. Measuring current density and cover strain together on an accelerated specimen should show the current stepping up at the moment strain begins to accelerate.
Path dependence
H1837. Corrosion pits on a steel pile take a depth distribution that depends on the sequence of wetting and drying, not on total time of wetness, because a dry period concentrates chloride at the meniscus while a long wet period dilutes it. Exposing coupons to the same total wet hours arranged as many short cycles versus few long ones should produce different pit-depth distributions at equal mass loss.
Null result
H1838. Concrete resistivity should show no correlation with corrosion rate on a structure under cathodic protection, because the protection current, not the concrete's ionic resistance, sets the steel potential. Measuring both on protected and unprotected zones of the same element should show the correlation present outside the protected zone and absent inside it.
Ground, foundations and earthworks
Misattribution
H1839. Differential settlement of a framed building is blamed on a soft pocket, but a rigid raft on uniform soil still settles differentially when the column loads are uneven, because the raft redistributes pressure only over a limited distance. The measured profile, set against a model on a uniform soil, should reproduce much of the pattern without invoking any variability.
Hidden term
H1840. Every levelling reading contains the movement of the benchmark, and in an urban excavation the benchmark often sits on a building responding to the same excavation. A deep rod extensometer anchored below the influence zone, compared with the surface benchmark, should expose a common-mode component that belongs to the benchmark rather than to the ground. The true settlement is the difference between the two records.
Identity
H1841. In a normally consolidated clay, secondary compression and primary consolidation are one process sampled at two time scales, with the end-of-primary criterion an arbitrary point on a continuous strain–log-time curve. Running a load step for ten times the conventional duration and looking for a break in slope should find none, which would make the separation an artefact of test duration.
Bound
H1842. Bearing capacity of a footing on sand does not grow in proportion to width, because the failure zone is limited to a few widths and confinement at that depth does not increase with the footing. Model footings at three widths in the same sand should show capacity rising more slowly than the classical linear rule, with the deviation growing as the footing approaches the tank size.
Threshold
H1843. Basal heave in a deep excavation has a critical depth that depends on undrained strength and wall embedment but not on wall bending stiffness, so stiffening the wall below that depth buys nothing. Centrifuge tests at increasing depth with two wall stiffnesses should show the same heave onset for both.
Reversal
H1844. Tip grouting is normally beneficial, but over-grouting can fracture the sand around a pile and reduce the shaft friction already mobilised, so capacity can fall as grout volume rises. Loading instrumented piles at three grout volumes should show capacity peaking and then declining. The decline should appear as a loss of shaft resistance rather than end bearing.
Count
H1845. A rigid raft on heterogeneous soil has at most two settlement modes the superstructure can feel: uniform translation and tilt, with higher-order distortion absorbed by the raft's own bending. Instrumenting a raft at many points and decomposing the field into principal modes should show the third and higher modes carrying less than the measurement noise.
Artefact mimics effect
H1846. Apparent liquefaction in a centrifuge model can be a boundary artefact, because pore pressure generated near the rigid container wall migrates inward and reaches the instruments at a delay that mimics liquefaction onset. Repeating the test with a flexible boundary or with instruments moved away from the wall should shift the apparent onset while the soil behaviour is unchanged.
Scale argument
H1847. Small-scale footing tests in sand cannot reproduce the particle crushing under a prototype's confining stress, so the measured capacity is governed by dilation rather than crushing and the scaling law changes at a stress threshold. Three g-levels in the same sand should show the capacity factor departing from the constant-friction prediction above the stress where crushing begins.
Inversion of standard practice
H1848. Compacting a fill to a very high relative density is read as conservative, but a stiff dense crust over a loose layer can punch through during loading and produce a more brittle response than a moderately compacted fill. Plate tests on two fills, one dense and one moderate, over the same loose layer should show the denser crust failing at smaller displacement but with a sharper drop.
Selection effect
H1849. Boreholes are placed where a problem is suspected, so a site investigation overstates the frequency of weak layers and understates the extent of competent ground. Layer statistics from the investigation, set against those from a grid of boreholes placed without prior information, should shift the weak-layer proportion downward. The design's conservatism is then a property of the sampling plan, not of the site.
Unit trap
H1850. Liquefaction assessments that use uncorrected SPT blow counts can classify a dense sand at depth as loose, because the same N corresponds to different relative densities at different confining stresses. Recomputing a case-history set with both conventions should show the misclassification concentrated where the overburden correction is largest.
Derived quantity
H1851. A liquefaction potential index is a weighted integral of factor of safety over depth, so two profiles with the same index can have opposite layering and the index cannot say which layer liquefies first. Constructing two profiles with equal index but reversed layer order and testing both in the centrifuge should produce different surface settlements and pore-pressure histories.
Hidden variable
H1852. Design groundwater levels for basements are usually taken from the level measured during investigation, but the critical level for uplift is the annual maximum, which at a tidal or river margin can be metres higher and lagged by weeks. A continuous logger through a full hydrological cycle should show the design level exceeded often enough to change the required ballast. The design value is a snapshot of the day the borehole was open.
Crossover
H1853. At small loads a shallow foundation is stiffer than a pile group because the cap and the soil above it contribute immediately, while at large loads the piles win because the shallow foundation's zone of influence is limited. Loading both side by side to the same settlement should show the load-sharing ratio crossing over at a displacement that scales with footing width.
Feedback
H1854. Groundwater withdrawal lowers the water table, increases effective stress, and compacts the aquifer, which lowers the surface and changes the gradients that feed the same wells, so pumping and subsidence are coupled. A subsidence record compared with the pumping history should show the drawdown needed to sustain a given yield rising as the surface falls. The well field is mining its own head.
Threshold
H1855. Slope stability in an unsaturated clay slope is controlled by suction, and there is a rainfall intensity below which the wetting front does not reach the slip surface before suction recovers. Monitoring suction at two depths through a wet season should show the deep sensor responding only to events above an intensity threshold.
Identity
H1856. Apparent cohesion in an unsaturated triaxial test and capillary cohesion inferred from the soil–water characteristic curve are the same quantity while the pore water is continuous, and they separate only when the water phase becomes disconnected. Suctions on both sides of the air-entry value should show the estimates coinciding at low suction and diverging once the water phase breaks up.
Conservation argument
H1857. In a closed tunnel drive the volume lost at the face must appear at the surface as a settlement trough, so a trough volume smaller than the face loss means the ground moved laterally or into the tunnel. Trough volumes from surface levelling and from inclinometers in the surrounding soil should locate where the missing volume went.
Path dependence
H1858. Small-strain stiffness in a sand is not a function of its current density alone: a sample that reached that density by cyclic loading has a different stiffness from one ploughed to the same density, and the difference persists after unloading. Shear-wave velocity before and after a sequence of small cycles at constant density should show a set that does not return to its initial value.
Drainage, sewers and urban water
Misattribution
H1859. Root intrusion is the usual explanation for a blocked sewer, but CCTV often shows roots entering through a joint that was already leaking, so the root follows the defect rather than causing the blockage. Blockage frequency on reaches with and without joint defects, at similar root exposure, should show the defect predicting blockage better than root presence does.
Hidden term
H1860. Culvert capacity computed from inlet control omits the outlet's backwater, which on a flat catchment can raise tailwater above the barrel invert for most of the design storm and convert the culvert to outlet control. Measuring headwater and tailwater together through a storm should show capacity falling short of the inlet prediction when tailwater rises, not when flow peaks.
Identity
H1861. Inflow and infiltration are separated by their time signatures, but within a single storm they are the same water: fast roof runoff and slow joint leakage enter the same pipe and differ only in travel time. A tracer that tags the roof runoff should recover the fast component, leaving the slow one. The split should depend on storm duration rather than on pipe condition.
Bound
H1862. Permeable pavement discharge is bounded by the subgrade's infiltration rate, not by the surface block's permeability, so a more permeable block over a low-permeability subgrade cannot increase system capacity. A full-scale test with two surface materials over the same subgrade, instrumented at the base, should show identical outflow once the subgrade is saturated.
Threshold
H1863. Gully spacing is set by spread, but there is an intensity above which a gully stops capturing because the approach flow's momentum carries it past the grating, and that intensity depends on longitudinal slope more than on open area. A full-scale gully at three slopes over a range of approach flows should show capture efficiency collapsing above a threshold Froude number rather than a threshold flow.
Reversal
H1864. Increasing the longitudinal slope of a storm sewer is read as increasing capacity, but on steep grades the flow can become supercritical and a hydraulic jump at a downstream transition can choke the pipe. The same pipe at three slopes with a fixed downstream condition should show capacity peaking at an intermediate slope and falling as the jump moves upstream.
Count
H1865. The rational method's hydrograph has at most three parameters that one outflow record can identify: time to peak, peak flow, and a recession constant; a fourth merely absorbs the shape of the rainfall. Fitting two- and four-parameter models to the same events and comparing error on held-out storms should show no improvement from the extra parameters.
Artefact mimics effect
H1866. Dry-weather flow that rises during rain is often called infiltration, but a meter near a downstream junction can register a false rise when water backs up and changes the velocity profile the meter assumes. The downstream meter, read against a redundant meter upstream during the same event, should show a rise without a corresponding volume arriving from above.
Scale argument
H1867. Clogging tests on permeable concrete use a sediment gradation chosen for convenience, and the clogging rate depends on the ratio of sediment size to pore size more than on sediment mass, so a lab result cannot be scaled to a pavement receiving wind-blown dust. The same pavement with three gradations spanning the field range should collapse the rate onto a curve in the size ratio rather than in the mass.
Inversion of standard practice
H1868. Sewer cleaning is scheduled to remove sediment, but aggressive jetting can scour the protective biofilm and expose the crown to hydrogen sulphide, so a cleaned pipe can deteriorate faster than a moderately sedimented one. Corrosion on reaches under high- and low-frequency cleaning, with the same sewage, should show the high-frequency reaches losing wall thickness faster. The cleaning interval would then be a corrosion variable.
Selection effect
H1869. Flow gauges sit at accessible points, usually downstream of the largest confluence, so the monitored reach has the most mixing and the least extreme response while the flashiest sub-basin is ungauged. A temporary gauge at a headwater outlet should show a higher peak flow per unit area than the long-term gauge.
Unit trap
H1870. Rainfall intensity in mm/h and runoff in L/s/ha are related by a factor that depends on the averaging interval, so a design combining a short intensity with a long runoff coefficient can underestimate the peak by the ratio of the intervals. Recomputing the design with both quantities on the same interval should remove a discrepancy now absorbed into a safety factor.
Derived quantity
H1871. The curve number is derived from rainfall–runoff pairs and is not a soil property, so it drifts with antecedent moisture and with the largest storm in the calibration record. Splitting a gauge record into dry and wet antecedent subsets and fitting each separately should give curve numbers differing by more than the design's assumed range.
Hidden variable
H1872. The design storm is taken from a record too short to contain the largest event, so the design intensity is a truncated estimate, and the truncation is not random: the missing events are the ones that would have changed the layout. The design storm from the full record, set against that from its most recent half, should show the design value rising as the record lengthens. The design is a function of record length, not only of climate.
Building physics and envelopes
Misattribution
H1873. Mould on an interior wall is attributed to high indoor humidity, but the surface at a thermal bridge can fall below the dew point while the room's mean humidity is unremarkable, so the mould maps the geometry rather than the air. Infrared thermography during a cold snap, compared with a spore sample map, should show growth confined to the bridge's cold stripe.
Hidden term
H1874. An in-situ U-value measured over a short campaign includes the wall's heat storage, which makes the apparent value lower than steady state in the hours after a temperature change and higher during a warm spell. Running the measurement for two weeks and separating steady from transient components should show the short campaign's apparent value falling outside the two-week confidence interval.
Identity
H1875. Air leakage and vapour diffusion through a wall may be two regimes of one pore-network transport model, which would mean a membrane that is airtight is also vapour-tight unless it is deliberately perforated. The distinction between the two tests would then be the pressure gradient applied. Measuring both on one membrane over a range of pressures should show the two permeabilities connected by a single pore-size distribution.
Bound
H1876. Envelope airtightness is bounded by its penetrations, not by wall area, because a few unsealed service entries can dominate leakage and membrane over the field of the wall cannot compensate. A blower-door test before and after sealing the penetrations, with the membrane unchanged, should show most of the improvement coming from the penetrations.
Threshold
H1877. Convective heat loss in a vertical cavity begins only above a critical Rayleigh number, so a cavity narrower than a threshold insulates better than a wider one even though the wider cavity holds more air. Measuring U-values of three cavity widths at the same temperature difference should show the narrowest performing best, with the ranking reversing above the critical width.
Reversal
H1878. Adding insulation outboard normally reduces moisture risk, but in a hot-humid climate with a strong inward vapour drive a thick outer layer can push the dew point into the structural layer. The result is interstitial condensation where there was none. Testing two walls, one insulated outboard and one inboard, under the same conditions should show the condensation plane moving rather than disappearing.
Count
H1879. A hygroscopic material has at most two independent moisture storage parameters a sorption isotherm can identify: a monolayer capacity and a cavity-filling capacity, with the rest following from the pore-size distribution. Fitting one-, two-, and three-parameter models to measured isotherms of five materials should show the third parameter's confidence interval spanning zero in every case.
Artefact mimics effect
H1880. A blower-door result can be distorted by stack effect and wind, which add a pressure difference the fan must overcome, and averaging pressurisation and depressurisation does not remove the distortion when the two are asymmetric. Repeating the test at three wind speeds and plotting derived leakage against wind should show a slope that identifies the bias rather than a building characteristic.
Scale argument
H1881. Small-chamber measurements of volatile emission are limited by boundary-layer resistance at the sample surface, so the emission rate per unit area depends on chamber airflow and not only on the material. One product at three chamber sizes and two air-change rates should show the apparent rate converging only when the boundary layer is thinner than the sample's diffusion length.
Inversion of standard practice
H1882. Increasing ventilation is the standard remedy for indoor moisture, but in a humid climate a higher rate can raise the indoor vapour load faster than it removes it, because the outdoor air carries more moisture than the indoor air. Two identical rooms, one ventilated at twice the rate of the other, should show the higher-rate room's relative humidity rising rather than falling during a humid period. The remedy becomes the source.
Selection effect
H1883. Buildings that volunteer for energy audits are run by people who already care about energy, so measured retrofit savings are contaminated by sample selection and overstate what the measure would achieve elsewhere. Volunteers, matched against a group recruited without mention of energy, should consume less before any intervention.
Unit trap
H1884. Low-frequency noise complaints are assessed with A-weighted levels, which discount the frequencies that cause the complaint, so a plant room that passes the dB(A) criterion can still be the source of a disturbance. Re-measuring with C-weighting and a third-octave spectrum should show the low-frequency energy the A-weighting removed, and the complaint should track that energy.
Derived quantity
H1885. Daylight factor is derived from an overcast sky and a horizontal illuminance, so it does not describe a room under direct sun, and two rooms with equal factors can have very different glare exposure. Measured vertical illuminance over a sunny day, set against the factor, should show the ranking changing with sun angle, which the single number cannot express.
Hidden variable
H1886. Occupant behaviour, not envelope performance, dominates measured heating demand in identical dwellings, and the behaviour correlates with orientation through the occupant's own comfort adjustment. Identical flats on opposite orientations, with submetered heat and window-opening logs, should lose most of their apparent orientation effect once window opening and thermostat set points enter the model.
Crossover
H1887. Natural ventilation removes heat more efficiently than mechanical at low occupancy because fan energy and duct gains are absent, but at high occupancy the required airflow exceeds what buoyancy can deliver. One room at three occupancy densities with both systems should show the crossover at a density that depends on stack height.
Feedback
H1888. Thermal mass reduces peak overheating but releases stored heat at night when ventilation is usually lower, so a heavyweight room can be cooler in the afternoon and warmer before dawn than a lightweight one. Monitoring two matched rooms through a heatwave should show the peak time shifting and the night-time minimum rising in the heavyweight room.
Path dependence
H1889. A wall's final moisture content depends on the order in which wet trades were completed, because gypsum and render release water into a cavity that may already be sealed by a vapour barrier, leaving no path out. Two walls of the same materials built with opposite sequences of sealing and wet work should show different equilibrium moisture after a year.
Null result
H1890. Across retrofitted houses, added insulation thickness should show no correlation with measured gas consumption once pre-retrofit consumption and household size are controlled, because the rebound in internal temperature absorbs the theoretical saving. A before-and-after design with a control group is needed to show the null, and the null would make the theoretical saving a poor predictor of the bill.
Monitoring, measurement and assessment
Misattribution
H1891. Loss of prestress in a post-tensioned bridge is assigned to concrete creep, yet the measured force drop also contains anchorage seating and grout shrinkage, and those terms finish within weeks while creep continues for years. Reading the load cell at one day, one month and one year should show a fast early drop that cannot be creep. The slower creep term that remains should be smaller than the design allowance.
Hidden term
H1892. Fibre-optic strain readings include the thermal expansion of the fibre and its coating, and the coating can expand several times more than silica, so a cable bonded to concrete reports a strain that is partly its own response. A bonded cable and a free reference cable at the same temperature should give the coating's contribution directly.
Identity
H1893. Tilt at the top of a retaining wall and settlement along its base are two projections of one displacement field, so a wall that tilts without settling and one that settles without tilting can produce the same top displacement. Measuring both with independent instruments should show the decomposition. The sum should close only when the wall's own bending is included.
Bound
H1894. Reported crack width from a distributed sensor is gauge length times average strain, so the same crack reads wider on a short gauge and narrower on a long one, and the number is a property of the installation as much as of the crack. Three gauge lengths across one controlled crack should show the reported width falling in proportion to gauge length, which would make a single acceptance threshold gauge-dependent.
Threshold
H1895. Acoustic emission from a growing fatigue crack is detectable only when the crack advances by more than a threshold amount per cycle, so a slow crack can be silent while a fast one is loud, and silence is not evidence of safety. Three stress ranges at the same crack length should show the hit rate falling below the noise floor at the lowest range.
Reversal
H1896. Longer monitoring is assumed to give better estimates of a structure's dynamic properties, but in a structure whose stiffness changes with environmental conditions a longer record can widen the apparent modal variability and make the estimate less repeatable. One-week and one-year records from the same structure should show the longer record producing a wider interval before correction and a narrower one after. Record length and estimate quality are not the same axis.
Artefact mimics effect
H1897. A sudden drop in a vibrating-wire strain record can be read as a crack opening, but the same drop appears when the coil is disturbed by a nearby electromagnetic source or when cable capacitance changes with moisture. Repeating the measurement with an unstrained dummy gauge on the same cable route should reproduce the drop and identify it as an instrument event.
Crossover
H1898. At short gauge lengths a distributed fibre-optic sensor resolves cracks better than a long-gauge sensor, but at long lengths the long-gauge sensor is more stable because it averages local bond slip. Both sensors on one beam through a range of crack widths should show the ranking reversing at a width that depends on bond length.
Conservation argument
H1899. In a monitored building the sum of measured storey drifts must equal the measured roof displacement, so a set of readings that does not close indicates a measurement error rather than a structural one. The sum of drifts, set against an independent roof reading from a total station, should locate the faulty storey. Closure is a free check on the whole array.
Threshold
H1900. Ground-penetrating radar will miss a void beneath a reinforced slab below a size threshold set by bar spacing, because the mesh reflection masks the deeper event within one range bin. Surveying test slabs with voids of decreasing size at fixed depth should show detection collapsing at a size that scales with bar spacing rather than with wavelength.
Status
100 of the sequence. The entries run from H1801 to H1900 without a gap. They were written as physical claims about structures, ground, water and envelopes — each one a statement that could fail — rather than as a survey of what is known. None has been tested; the value of a hypothesis list is the ideas, and the value of a test is separate.
If one of these is worth an experiment, it is H1804 — that capillary rise in brick is set by the largest continuous throat rather than by porosity. It is checkable with a saw, a tray of water and a mercury porosimeter, and it would change how bricks are specified for damp exposure.
Incoprea Research · hand-considered hypotheses 1801–1900 · 3 November 2026 · ~/Desktop/Nov3/