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Question 1Moisture in Concrete: Sources, Transport, and Effects

Which mechanism moves water vapor through the pore network of concrete under a vapor pressure gradient without bulk air flow?

  1. Capillary suction
  2. Osmosis
  3. Hydrostatic pressure flow
  4. Diffusion Correct answer.

Explanation

Diffusion is the transport of water vapor molecules driven by a vapor pressure (concentration) gradient through the air-filled pore space, without bulk gas movement. It dominates in unsaturated, relatively dry concrete where continuous liquid pathways are absent.

Question 2Moisture in Concrete: Sources, Transport, and Effects

Which type of water in hardened cement paste is held most weakly and is the first to be removed on drying?

  1. Chemically bound water in hydrates
  2. Adsorbed water on pore surfaces
  3. Interlayer water in C-S-H
  4. Free capillary water in large pores Correct answer.

Explanation

Free water held in larger capillary pores is only weakly influenced by surface forces and evaporates first during drying. Stronger binding occurs for adsorbed surface water, interlayer water, and finally chemically bound water in hydrate structures.

Question 3Moisture in Concrete: Sources, Transport, and Effects

A concrete slab shows a dark, damp-looking area at its base after rain. Which process most directly explains liquid water entering the unsaturated near-surface pores?

  1. Thermal diffusion
  2. Electro-osmosis
  3. Vapor condensation
  4. Capillary absorption Correct answer.

Explanation

Capillary absorption draws liquid water into unsaturated pores by surface tension, producing the wet front and darkening seen at the slab base. This sorptivity-driven uptake is distinct from vapor-driven processes.

Question 4Moisture in Concrete: Sources, Transport, and Effects

Which concrete property primarily controls the rate of capillary absorption of water?

  1. Thermal conductivity
  2. Sorptivity Correct answer.
  3. Modulus of elasticity
  4. Compressive strength grade

Explanation

Sorptivity quantifies the rate of capillary uptake per unit area per square root of time and is the property used to characterize absorption. It depends on pore structure and connectivity rather than on strength class alone.

Question 5Moisture in Concrete: Sources, Transport, and Effects

In a drying concrete element, where does the steepest moisture gradient typically develop?

  1. Uniformly across the section
  2. In the coarse aggregate particles
  3. At the center of the section
  4. Near the exposed evaporating surface Correct answer.

Explanation

Evaporation at the exposed surface creates a steep moisture gradient in the near-surface layer, which dries faster than the interior. The core remains wetter longer because vapor must diffuse through the increasingly dry cover zone.

Question 6Moisture in Concrete: Sources, Transport, and Effects

Which factor increases the equilibrium moisture content of concrete exposed to a given relative humidity?

  1. Larger maximum aggregate size
  2. Higher curing temperature
  3. Lower ambient relative humidity
  4. Higher porosity of the cement paste Correct answer.

Explanation

More porous paste provides greater internal surface area and pore volume to hold adsorbed and capillary water, raising equilibrium moisture content at a given humidity. Aggregate size and curing temperature do not directly set the sorption capacity.

Question 7Moisture in Concrete: Sources, Transport, and Effects

Which source of moisture is internal to the concrete itself rather than environmental?

  1. Humidity in the surrounding air
  2. Driving rain on a facade
  3. Groundwater rising by capillary action
  4. Residual mixing water not consumed by hydration Correct answer.

Explanation

Water added at batching that is not chemically bound by hydration remains as internal moisture and can redistribute or evaporate later. This internal reservoir is distinct from external sources such as rain, groundwater, or ambient humidity.

Question 8Moisture in Concrete: Sources, Transport, and Effects

Which term describes water that has been chemically incorporated into hydrate phases such as C-S-H and ettringite?

  1. Gel pore water
  2. Capillary water
  3. Bound water Correct answer.
  4. Free water

Explanation

Bound water is chemically combined in the crystal or gel structure of hydrates and is not free to migrate under normal service conditions. It is distinguished from free, capillary, and gel pore water that occupy void space.

Question 9Moisture in Concrete: Sources, Transport, and Effects

A concrete floor slab-on-grade is placed directly on soil with no vapor retarder. Which transport path most directly allows ground moisture to reach the slab underside?

  1. Thermal migration from the slab edge
  2. Capillary rise and vapor flow from the moist subgrade Correct answer.
  3. Rainwater absorption through the slab's top surface
  4. Vapor diffusion through the slab from dry indoor air

Explanation

Moisture from a moist subgrade can move upward by capillary action and vapor diffusion into the slab when no retarder interrupts the path. This is a common cause of elevated slab moisture and floor-covering failures.

Question 10Moisture in Concrete: Sources, Transport, and Effects

Why does a concrete slab often show higher measured moisture emission after the building is enclosed and air-conditioned in summer?

  1. The vapor pressure gradient from cool indoor air to warm slab drives inward flow Correct answer.
  2. The slab gains moisture from increased internal curing
  3. Air conditioning adds water vapor to the slab
  4. Cooling the slab increases hydration and releases water

Explanation

When indoor air is cooler and drier than the slab, the vapor pressure gradient can reverse and drive moisture inward rather than outward, altering emission behavior. The direction and magnitude of vapor flow depend on the vapor pressure difference, not temperature alone.

Question 11Moisture in Concrete: Sources, Transport, and Effects

Two concrete mixes have equal strength but different water-cement ratios. Which is expected to have lower permeability and slower moisture transport?

  1. The mix with the lower water-cement ratio Correct answer.
  2. Both mixes transport moisture equally
  3. The mix with the higher water-cement ratio
  4. The mix with larger aggregate

Explanation

A lower water-cement ratio produces a finer, less connected pore structure, reducing permeability and slowing both liquid and vapor transport. Equal strength does not guarantee equal transport properties because pore connectivity differs.

Question 12Moisture in Concrete: Sources, Transport, and Effects

Which effect does sustained high internal moisture have on the durability of embedded steel reinforcement?

  1. It promotes corrosion by supporting ionic transport and oxygen availability at the steel Correct answer.
  2. It reduces the risk of chloride ingress
  3. It eliminates carbonation of the cover
  4. It passivates the steel permanently

Explanation

High moisture in the pore solution supports ionic conduction and, with oxygen, enables corrosion of embedded steel once passivity is lost. Saturated conditions can limit oxygen but wet-dry cycles are especially damaging because they supply both water and oxygen.

Question 13Moisture in Concrete: Sources, Transport, and Effects

A relative humidity sensor in a concrete slab reads 80 percent at 40 percent depth. What does this reading indicate about the moisture condition?

  1. The slab is fully saturated at that depth
  2. The pore vapor is in equilibrium with a partially dried condition at that depth Correct answer.
  3. The slab contains no moisture
  4. The reading reflects only surface condensation

Explanation

An in-situ RH of 80 percent at depth indicates the pore system is partially dried and the vapor is in equilibrium with that moisture state. It does not mean full saturation, which would correspond to near 100 percent RH.

Question 14Moisture in Concrete: Sources, Transport, and Effects

Which sequence correctly orders the relative mobility of water in concrete from most mobile to least mobile?

  1. Bound water, free water, capillary water
  2. Capillary water, bound water, free water
  3. Free water, capillary water, bound water Correct answer.
  4. Bound water, capillary water, free water

Explanation

Free water in large voids moves most readily, capillary water is held by surface tension and moves less freely, and bound water is chemically fixed and essentially immobile under service conditions. This ordering reflects the strength of binding in each state.

Question 15Moisture in Concrete: Sources, Transport, and Effects

What is the primary reason a vapor retarder is placed beneath a slab-on-grade?

  1. To improve thermal insulation of the slab
  2. To bond the slab to the subgrade
  3. To limit upward moisture vapor transmission from the subgrade Correct answer.
  4. To increase the slab's compressive strength

Explanation

A vapor retarder interrupts the path for subgrade moisture to move into the slab, reducing moisture-related floor-covering failures. It is a transport barrier rather than a structural or thermal component.

Question 16Moisture in Concrete: Sources, Transport, and Effects

Which measurement method directly quantifies the rate of water vapor passing through a concrete specimen under a defined vapor pressure difference?

  1. Water vapor transmission test Correct answer.
  2. Rapid chloride permeability test
  3. Schmidt rebound test
  4. Ultrasonic pulse velocity

Explanation

A water vapor transmission test measures the steady-state vapor flow through a specimen under a controlled vapor pressure difference, yielding a transmission rate. The other methods assess strength, ionic permeability, or elastic properties rather than vapor transport.

Question 17Moisture in Concrete: Sources, Transport, and Effects

Why can wet-dry cycling be more damaging to concrete than continuous immersion?

  1. It drives cycles of absorption and drying that concentrate salts and promote cracking Correct answer.
  2. It prevents any moisture movement
  3. It eliminates capillary suction
  4. It stops carbonation completely

Explanation

Wet-dry cycles repeatedly fill and empty pores, transporting and concentrating dissolved salts near the drying zone where crystallization pressure can crack the concrete. Continuous immersion does not produce the same concentration and crystallization cycles.

Question 18Moisture in Concrete: Sources, Transport, and Effects

A concrete wall shows efflorescence on its exterior face. Which moisture process is most directly responsible?

  1. Alkali-silica reaction consuming pore water
  2. Carbonation shrinkage of the surface layer
  3. Vapor diffusion outward carrying dissolved salts that crystallize at the surface Correct answer.
  4. Freeze-thaw of saturated interior pores

Explanation

Efflorescence forms when moisture migrating through the concrete dissolves soluble salts and carries them to the evaporating surface, where they crystallize as a white deposit. The driving force is moisture transport to the drying face.

Question 19Moisture in Concrete: Sources, Transport, and Effects

Which statement about the relationship between relative humidity and drying shrinkage of concrete is correct?

  1. Shrinkage increases as the pore relative humidity drops below saturation Correct answer.
  2. Shrinkage is greatest at 100 percent relative humidity
  3. Shrinkage is independent of pore relative humidity
  4. Shrinkage decreases as the concrete dries

Explanation

Drying shrinkage develops as moisture is lost from the pore system, particularly as relative humidity falls and capillary tension and disjoining pressure change. The greatest shrinkage generally occurs over the range of moderate to low humidity as water is removed.

Question 20Moisture in Concrete: Sources, Transport, and Effects

In a diffusion-controlled drying process, how does the drying rate of a thick concrete section change as the dry surface layer thickens?

  1. It stays constant regardless of depth
  2. It increases linearly with time
  3. It decreases because the diffusion path lengthens Correct answer.
  4. It becomes independent of the vapor gradient

Explanation

As the dry layer thickens, vapor must diffuse over a longer path, so the drying rate falls and the process slows. This produces the characteristic decreasing drying rate period in thick sections.

Question 21Moisture in Concrete: Sources, Transport, and Effects

A slab has a measured in-situ relative humidity of 92 percent at half depth. Which interpretation best reflects the implications for a moisture-sensitive floor coating?

  1. The slab must be saturated before coating
  2. The slab is dry enough for immediate coating
  3. The reading proves no vapor gradient exists
  4. The slab may still emit moisture at a level that risks coating failure and warrants further drying Correct answer.

Explanation

An in-situ RH near 92 percent indicates substantial moisture remains, and coatings applied too early may blister or debond from vapor pressure buildup. Further drying and verification are prudent before applying a moisture-sensitive finish.

Question 22Moisture in Concrete: Sources, Transport, and Effects

Which combination of conditions most strongly accelerates carbonation-induced loss of passivity in reinforced concrete?

  1. Moderate humidity with a permeable, unsaturated cover Correct answer.
  2. High internal moisture and low permeability
  3. Low humidity with a sealed surface
  4. Continuous saturation with no oxygen access

Explanation

Carbonation proceeds fastest at moderate humidity where pores are partly gas-filled, allowing carbon dioxide ingress, and a permeable cover admits more gas. Very high saturation blocks gas diffusion, while very dry conditions slow the reaction.

Question 23Moisture in Concrete: Sources, Transport, and Effects

Why does the moisture diffusivity of concrete decrease markedly as the material dries below a certain relative humidity?

  1. Vapor pressure gradients disappear
  2. Loss of continuous liquid pathways and increased tortuosity reduce liquid transport Correct answer.
  3. Pore water becomes more mobile as films thin
  4. Hydration stops and creates new pores

Explanation

As pores drain, continuous liquid pathways break up and transport shifts to slower vapor diffusion through a more tortuous network, lowering apparent diffusivity. The remaining water is held in finer pores and thin films with reduced connectivity.

Question 24Moisture in Concrete: Sources, Transport, and Effects

A laboratory specimen is conditioned at 65 percent relative humidity to a constant mass before a vapor transmission test. What is the main purpose of this conditioning?

  1. To remove all bound water from the hydrates
  2. To saturate the pores fully
  3. To establish a reproducible, defined moisture state for comparison Correct answer.
  4. To increase the specimen's compressive strength

Explanation

Conditioning to constant mass at a specified humidity establishes a reproducible moisture state so transmission results are comparable between specimens and laboratories. It does not saturate or dehydrate the hydrates.

Question 25Moisture in Concrete: Sources, Transport, and Effects

Which mechanism best explains why moisture can migrate through apparently saturated concrete even when no hydraulic head is applied?

  1. Diffusion of water vapor through air-filled pores only
  2. Capillary and film transport along connected pore surfaces driven by suction gradients Correct answer.
  3. Osmotic flow through the aggregate
  4. Bulk flow of air through the concrete

Explanation

Even in nearly saturated concrete, suction gradients drive liquid movement along connected pores and surface films without an applied hydraulic head. This film and capillary transport differs from vapor diffusion, which requires air-filled pores.

Question 26Moisture in Concrete: Sources, Transport, and Effects

In hardened concrete, water held in the smallest gel pores (roughly below 2.5 nm) is best described by which statement?

  1. It is physically adsorbed and remains largely unfrozen even well below 0 °C Correct answer.
  2. It is identical in mobility to capillary water in pores above 50 nm
  3. It behaves as free bulk water and drains readily under gravity
  4. It is chemically bound and cannot be removed by any drying method

Explanation

Water in gel pores is strongly influenced by adsorption forces at the pore wall, so it is neither free bulk water nor chemically combined water. Because of these surface forces, gel-pore water does not freeze at the normal bulk freezing point and can remain unfrozen to very low temperatures. This distinguishes it from capillary water, which freezes closer to 0 °C depending on pore size.

Question 27Moisture in Concrete: Sources, Transport, and Effects

A basement wall made of dense concrete is exposed to wet soil on one face and dry interior air on the other. Which transport process dominates the slow, long-term movement of water vapor through the wall?

  1. Osmotic flow driven by differences in dissolved salt concentration
  2. Hydrostatic pressure flow driven by the groundwater head
  3. Capillary suction driven by surface tension in fine pores
  4. Diffusion driven by the vapor pressure gradient across the wall Correct answer.

Explanation

When one face is wet and the other is exposed to drier air, a vapor pressure gradient exists across the wall thickness. Under these conditions vapor moves through the pore system by diffusion, which is slow and continues as long as the gradient persists. Capillary suction and hydrostatic flow require liquid continuity or a pressure head, which is not the dominant condition described here.

Question 28Moisture in Concrete: Sources, Transport, and Effects

A concrete slab is cast with a water-cement ratio of 0.55 and moist-cured for seven days. Which change would most reduce the rate at which the slab later releases moisture to a drying environment?

  1. Increasing the sand content while keeping the total water content unchanged
  2. Adding a retarder so that the slab stays plastic longer after placement
  3. Increasing the aggregate maximum size while keeping the paste volume constant
  4. Lowering the water-cement ratio and extending moist curing before drying begins Correct answer.

Explanation

A lower water-cement ratio reduces capillary porosity and refines the pore structure, while extended moist curing increases the degree of hydration and further blocks transport paths. Together these reduce the effective diffusivity and slow moisture release during drying. The other changes either do not alter the paste pore structure or act mainly on fresh properties.

Question 29Moisture in Concrete: Sources, Transport, and Effects

A floor slab shows a white crystalline deposit on its surface several months after construction, and the deposit reappears after cleaning. Which moisture-related process best explains this observation?

  1. Freeze-thaw cycling causing surface scaling of the paste
  2. Carbonation of calcium hydroxide within the surface layer
  3. Alkali-aggregate reaction producing a swelling gel at the surface
  4. Dissolved salts migrating to the drying surface and crystallizing there Correct answer.

Explanation

Efflorescence forms when water carries dissolved salts through the pore system to a surface where evaporation occurs. As the water evaporates, salt concentration rises until crystals precipitate on the surface. Because the salt source remains in the concrete, the deposit can recur after cleaning.

Question 30Moisture in Concrete: Sources, Transport, and Effects

Two concrete prisms of identical mix and dimensions are conditioned at 50 percent and 90 percent relative humidity, respectively, before a vapor transmission test. Which explanation best accounts for the much lower vapor flow measured in the 90 percent specimen when tested under the same imposed gradient?

  1. At high relative humidity the specimen temperature rises, which increases the vapor pressure gradient across it
  2. At high relative humidity hydration restarts and consumes the water that would otherwise diffuse through the specimen
  3. At high relative humidity the pore network holds more condensed water, blocking vapor pathways and lowering the effective vapor diffusion coefficient Correct answer.
  4. At high relative humidity the pores fill with water, and dissolved ions reduce the vapor pressure driving diffusion

Explanation

As relative humidity rises, progressively more pores become filled with condensed water, so the continuous air-filled pathway available for vapor diffusion is reduced. This lowers the effective vapor diffusion coefficient and the measured vapor flow. The effect is a function of the pore structure and the fraction of pores filled, not of ion content, renewed hydration, or temperature change.

Question 31ASTM F2170 In-Situ Relative Humidity Testing

Under ASTM F2170, what is the standard depth for placing in-situ relative humidity probes in a slab-on-grade concrete floor?

  1. 40% of the slab thickness
  2. 20% of the slab thickness Correct answer.
  3. 80% of the slab thickness
  4. 50% of the slab thickness

Explanation

ASTM F2170 requires probe holes drilled to a depth equal to 20 percent of the slab thickness, measured from the surface that will receive the floor covering. This depth is intended to represent the moisture condition in the upper portion of the slab where the flooring adhesive will bond.

Question 32ASTM F2170 In-Situ Relative Humidity Testing

According to ASTM F2170, how long must the in-situ probe remain in the drilled hole before the relative humidity reading is recorded?

  1. At least 72 hours
  2. At least 15 minutes
  3. At least 24 hours Correct answer.
  4. At least 1 hour

Explanation

ASTM F2170 requires the probe to equilibrate in the sealed hole for a minimum of 24 hours before the reading is taken. Shorter periods do not allow the humidity within the hole to reach equilibrium with the surrounding concrete.

Question 33ASTM F2170 In-Situ Relative Humidity Testing

What is the required minimum diameter for holes drilled for ASTM F2170 in-situ RH probes?

  1. 7/8 inch (22 mm)
  2. 5/8 inch (16 mm) Correct answer.
  3. 1/2 inch (13 mm)
  4. 3/4 inch (19 mm)

Explanation

ASTM F2170 specifies that probe holes be drilled to a nominal diameter of 5/8 inch (16 mm). The hole must be sized to accept the probe sleeve while leaving the specified clearance for the probe to seat properly.

Question 34ASTM F2170 In-Situ Relative Humidity Testing

Before placing a probe, how should the drilled hole be cleaned per ASTM F2170?

  1. Fill the hole with the drilling dust and tamp it
  2. Rinse the hole with clean water
  3. Wipe the hole with a damp cloth
  4. Blow the hole with oil-free compressed air and vacuum it Correct answer.

Explanation

ASTM F2170 requires the hole to be cleaned of drilling dust and debris, typically by vacuuming and using oil-free compressed air. Residual dust can absorb or release moisture and bias the reading.

Question 35ASTM F2170 In-Situ Relative Humidity Testing

Why does ASTM F2170 require the probe hole to be sealed at the surface during equilibration?

  1. To keep the concrete warm
  2. To protect the probe from physical damage
  3. To keep ambient air from exchanging with the hole atmosphere Correct answer.
  4. To prevent the probe from being removed

Explanation

Sealing the hole isolates the cavity from ambient air so the measured humidity reflects the concrete rather than the surrounding room. ASTM F2170 requires the seal to prevent air exchange during the 24-hour equilibration period.

Question 36ASTM F2170 In-Situ Relative Humidity Testing

Which condition is required of the concrete slab before ASTM F2170 testing begins?

  1. The slab must be at its in-service condition with the HVAC system operating Correct answer.
  2. The slab must be freshly placed and still curing
  3. The slab must be fully saturated
  4. The slab must have the finished floor already installed

Explanation

ASTM F2170 requires testing to occur when the building is at or near its normal service conditions, including the HVAC system operating as it will when occupied. Testing a slab in a different environment does not represent the final moisture condition.

Question 37ASTM F2170 In-Situ Relative Humidity Testing

What type of instrument does ASTM F2170 require for measuring relative humidity in the probe hole?

  1. A pin-type resistance meter
  2. A calibrated in-situ RH probe with a digital readout Correct answer.
  3. A surface-mounted moisture meter
  4. A calcium chloride test kit

Explanation

ASTM F2170 specifies an in-situ relative humidity probe that is inserted into the drilled hole and read with a calibrated instrument. The probe measures the humidity of the air within the sealed cavity.

Question 38ASTM F2170 In-Situ Relative Humidity Testing

How many in-situ RH probes does ASTM F2170 require for the first 1,000 square feet of slab area?

  1. Ten probes
  2. One probe
  3. Three probes Correct answer.
  4. Five probes

Explanation

ASTM F2170 requires a minimum of three probes for the first 1,000 square feet of floor area. Additional probes are required for each additional area increment, so the initial sampling density is set at three.

Question 39ASTM F2170 In-Situ Relative Humidity Testing

A 6-inch thick slab-on-grade is to be tested per ASTM F2170. At what depth below the surface should the probe hole terminate?

  1. 0.6 inch
  2. 3.0 inches
  3. 1.2 inches Correct answer.
  4. 4.8 inches

Explanation

The probe depth is 20 percent of slab thickness, so 20 percent of 6 inches equals 1.2 inches. The hole is drilled to this depth so the probe senses the humidity near the flooring interface.

Question 40ASTM F2170 In-Situ Relative Humidity Testing

A technician drills a probe hole, cleans it, inserts the probe, seals the surface, and reads the meter after 45 minutes. What is the primary deficiency in this procedure?

  1. The hole was cleaned before insertion
  2. The surface was sealed
  3. The meter was read too late
  4. The probe was not equilibrated for 24 hours Correct answer.

Explanation

ASTM F2170 requires at least 24 hours of equilibration before the reading is recorded. A 45-minute wait does not allow the sealed cavity to reach equilibrium, so the reading is unreliable.

Question 41ASTM F2170 In-Situ Relative Humidity Testing

A building has 4,000 square feet of concrete to be tested per ASTM F2170. What is the minimum number of probes required?

  1. 9 probes
  2. 6 probes Correct answer.
  3. 12 probes
  4. 3 probes

Explanation

ASTM F2170 requires three probes for the first 1,000 square feet plus one additional probe for each additional 1,000 square feet. For 4,000 square feet, that is three for the first 1,000 plus three more for the remaining 3,000, totaling six.

Question 42ASTM F2170 In-Situ Relative Humidity Testing

During equilibration, a probe seal is found to be loose and ambient air enters the hole. How does this affect the measured relative humidity?

  1. The reading will always be higher than the true concrete humidity
  2. The reading will reflect ambient conditions rather than concrete pore humidity Correct answer.
  3. The reading will always equal the slab's true humidity
  4. The reading will be unaffected because the probe is still in the hole

Explanation

The seal isolates the cavity so the probe measures concrete humidity. If ambient air enters, the cavity equilibrates with room air instead, and the reading no longer represents the slab.

Question 43ASTM F2170 In-Situ Relative Humidity Testing

Which factor most directly determines the equilibration time required before an ASTM F2170 reading is valid?

  1. The color of the concrete surface
  2. The brand of the RH meter
  3. The number of probes installed
  4. The time needed for the sealed cavity to reach equilibrium with the concrete Correct answer.

Explanation

The 24-hour minimum exists because the sealed cavity must equilibrate with the surrounding concrete pore humidity. The standard sets the minimum time based on this equilibration process, not on instrument branding or probe count.

Question 44ASTM F2170 In-Situ Relative Humidity Testing

A technician proposes testing a slab while the building is open to outside air with no HVAC running, on a humid summer day. What is the ASTM F2170 concern?

  1. The probe will not fit in the hole
  2. The test should be performed at in-service conditions, and uncontrolled ambient air can bias results Correct answer.
  3. The slab will dry faster and read low
  4. The concrete will not cure

Explanation

ASTM F2170 requires testing at or near normal service conditions, including HVAC operation. Uncontrolled humid ambient air can alter the cavity humidity and produce readings that do not represent the future service environment.

Question 45ASTM F2170 In-Situ Relative Humidity Testing

What is the purpose of the sleeve or liner used with ASTM F2170 probes?

  1. To add moisture to the hole
  2. To insulate the probe from temperature changes
  3. To make the hole larger than the drill bit
  4. To line the hole and provide a consistent sealed cavity for the probe Correct answer.

Explanation

The sleeve lines the drilled hole so the probe sits in a defined, sealed cavity of consistent dimensions. This helps ensure the probe measures the concrete atmosphere rather than the raw drilled surface.

Question 46ASTM F2170 In-Situ Relative Humidity Testing

A technician takes a reading immediately after inserting the probe and again after 24 hours. The 24-hour reading is lower. What is the most likely explanation?

  1. The concrete dried out completely in 24 hours
  2. The probe failed
  3. The seal was removed
  4. The immediate reading had not equilibrated with the concrete Correct answer.

Explanation

The immediate reading reflects the probe's starting condition and the disturbed air in the freshly drilled hole. Over 24 hours the cavity equilibrates with the concrete, so the later reading is the valid one under ASTM F2170.

Question 47ASTM F2170 In-Situ Relative Humidity Testing

How should the temperature of the probe and the concrete be considered when interpreting ASTM F2170 results?

  1. RH is temperature-dependent, so testing should occur at in-service temperatures Correct answer.
  2. The probe should be cooled before reading
  3. The concrete should be heated to accelerate drying
  4. Temperature has no effect on RH readings

Explanation

Relative humidity depends on temperature, and the slab's in-service temperature affects the equilibrium RH. ASTM F2170 therefore calls for testing at or near service conditions so the reading represents the final environment.

Question 48ASTM F2170 In-Situ Relative Humidity Testing

A floor covering installer asks whether a single probe reading of 78 percent RH is sufficient to approve a large warehouse slab. What is the ASTM F2170 response?

  1. No, because RH cannot be measured in warehouses
  2. Yes, one reading is sufficient if the probe was calibrated
  3. No, the standard requires multiple probes distributed across the area Correct answer.
  4. Yes, if the slab is thicker than 6 inches

Explanation

ASTM F2170 sets a minimum number of probes based on floor area, so a single reading does not represent a large slab. Multiple probes are needed to account for variability in thickness, curing, and exposure.

Question 49ASTM F2170 In-Situ Relative Humidity Testing

What does ASTM F2170 require regarding documentation of probe locations and readings?

  1. Only the average reading is required
  2. Only the highest reading must be recorded
  3. Documentation is optional
  4. Probe locations and readings should be recorded so results can be verified Correct answer.

Explanation

Good practice under ASTM F2170 includes recording probe locations, depths, and readings so the results can be verified and compared to the flooring manufacturer's limits. Documentation supports the decision to install the floor covering.

Question 50ASTM F2170 In-Situ Relative Humidity Testing

A 10-inch thick slab is tested per ASTM F2170. A technician drills to 2 inches. What is the error?

  1. The depth should be 8.0 inches
  2. The depth is correct Correct answer.
  3. The depth should be 2.0 inches, so no error
  4. The depth should be 5.0 inches

Explanation

Twenty percent of a 10-inch slab is 2.0 inches, so the technician's depth is correct. The probe depth scales with slab thickness rather than being a fixed value.