Moisture in Concrete Floors, Testing, Analysis and Prevention

Moisture in
Concrete Floors,
Testing, Analysis
and Prevention
Kevin MacDonald, P.E., Ph.D., FACI

Water in the Environment
3 phases
Solid
Liquid
Vapour

Psychrometrics

Definition of Humidity
Relative Humidity RH =
Vapour Pressure
Saturation vapour pressure

1
3 4
2
5
6

Water and air in equilibrium at
20 o C
Vapour pressure =
2kPa
Saturation vapour
pressure = 2kPa
Relative Humidity
(RH) = 100%
Air at atmospheric pressure
(100 kPa) made up of nitrogen
(approx 70kPa), oxygen and
other gases and water vapour
(approx 2kPa) 100% RH
Water

Half of the gas is replaced with dry
air
Vapour pressure =
1kPa
Saturation vapour
pressure = 2kPa
Relative Humidity
(RH) = 50% (typical
for inside a building)
Air at atmospheric pressure (100
kPa)
water vapour pressure 1kPa
(This will increase to 2kPa with
time)
Water

The temperature is increased rapidly to
near 100 o C (pressure held constant)
Vapour pressure = 1kPa
Saturation vapour pressure
= 90kPa (reaches
atmospheric pressure
at 100 o C)
Relative Humidity (RH)
= 1.1%
To get over 100 o C without
boiling the pressure must be
raised (as for autoclaved
concrete)
Air at atmospheric pressure
(100 kPa)
water vapour pressure 1kPa
(this will increase to 90kPa
with time)
Water

The temperature is decreased below
20 o C (total pressure held constant)
Vapour pressure =
1kPa
Saturation vapour
pressure = 0.5kPa
Relative Humidity
(RH) = 100%
(cannot go above
this. Will cause
condensation or fog)
Air at atmospheric pressure
(100 kPa)
water vapour pressure 1kPa
Water

Relative
Humidity
RH
≈
Massof
Massof
water
water perunitmassof air
perunitmassof airat saturation
Example A shows air at
100% RH and 20 o C
heated to 40 o C to give
31% RH
Example B shows air
at 50% RH and 20 o C
heated to 40 o C to give
15% RH

Dry-bulb temperature (DBT) is that of an air sample, as determined by an ordinary thermometer. It
is typically plotted as the abscissa (horizontal axis) of the graph. The SI units for temperature are
kelvins or degrees Celsius; other units are degrees Fahrenheit and degrees Rankine.
Wet-bulb temperature (WBT) is that of an air sample after it has passed through a constantpressure,
ideal, adiabatic saturation process, that is, after the air has passed over a large surface
of liquid water in an insulated channel. In practice this is the reading of a thermometer whose
sensing bulb is covered with a wet sock evaporating into a rapid stream of the sample air (see
Hygrometer). When the air sample is saturated with water, the WBT will read the same as the DBT.
The slope of the line of constant WBT reflects the heat of vaporization of the water required to
saturate the air of a given relative humidity.
Dew point temperature (DPT) is the temperature at which a moist air sample at the same pressure
would reach water vapor “saturation.” At this point further removal of heat would result in water
vapor condensing into liquid water fog or, if below freezing point, solid hoarfrost. The dew point
temperature is measured easily and provides useful information, but is normally not considered an
independent property of the air sample as it duplicates information available via other humidity
properties and the saturation curve.
Relative humidity (RH) is the ratio of the mole fraction of water vapor to the mole fraction of
saturated moist air at the same temperature and pressure. RH is dimensionless, and is usually
expressed as a percentage. Lines of constant RH reflect the physics of air and water: they are
determined via experimental measurement. The concept that air "holds" moisture, or that
moisture “dissolves” in dry air and saturates the solution at some proportion, is erroneous (albeit
widespread); see relative humidity for further details.
Humidity ratio is the proportion of mass of water vapor per unit mass of dry air at the given
conditions (DBT, WBT, DPT, RH, etc.). Also known as moisture content or mixing ratio. It is
typically plotted as the ordinate (vertical axis) of the graph. For a given DBT there will be a
particular humidity ratio for which the air sample is at 100% relative humidity: the relationship
reflects the physics of water and air and must be determined by measurement. The dimensionless
humidity ratio is typically expressed as grams of water per kilogram of dry air, or grains of water
per pound of air (7000 grains equal 1 pound

Ideal Solution Behaviour
Dalton’s Law
• The pressure of each constituent is proportional
to the mole fraction and the total pressure
Raoult’s Law
• The pressure above a solution is proportional to
the mole fraction of the component in the
solution

Colligative Properties of
Nonelectrolyte Solutions
Vapor-Pressure Lowering; The vapor pressure of a
Solution is lower than pure solute.
P 1 0 = vapor pressure of pure solvent
Raoult’s law
X 1 = mole fraction of the solvent
P 1 = X 1 P 0 1
Mole Fraction (X 1 )
moles of 1
sum of moles of all components

If the solution contains only one solute:
X 1 + X 2 =1
X 1 = 1 – X 2
X 2 = mole fraction of the solute
X 1 = mole fraction of the solvent
P 1 = X 1 P 1 0
P 1 = (1-X 2 ) P 1 0
P 1 = P 0 1-P 0 1X 2
P 1 0 - P 1 = ∆P = X 2 P 1 0

The presence of a non-volatile solute means that
fewer solvent particles are at the solution’s
surface, so less solvent evaporates!

Describe what is happening in the pictures below.
Use the concept of vapor pressure lowering to
explain this phenomenon.

Impacts on Project & Owner
Vapor Emission
Delayed flooring installations
• Delayed project completion
• Time
Mold / mildew and alkali damage
Short/long-term adhesive bonding
• Repair Costs
Voided Warranties
Downstream Client Costs
• LOST PROPERTY USE
• LOST WORKER PRODUCTIVITY
• LOST OWNER INCOME
Its estimated that vapor emission related flooring failures
cost industry in the U.S. billions of dollars annually in
damage, downtime, repair and replacement.
21

Epoxy system in Airport Hanger
Vinyl Tile in Retail Store
Rubberized Floor in Health Center

Mold/mildew
Mold flourishes in moist environments and
organic compounds found in construction
materials
Sick building syndrome
- Chemical/Biological contamination
- Toxic mold

Related ASTM Procedures
C 109/C 109M Test Method for Compressive Strength of Hydraulic Cement
Mortars
C 309 Specification for Liquid Membrane-Forming Compounds for Curing
Concrete
C 472 Test Method for Compressive Strength of Gypsum Cement
D 4259 Practice for Abrading Concrete
E 1155 Test Method for Determining FF/FL (Floor Flatness and Floor
Levelness)
E 1486 Test Method for Determining Floor Tolerances Using Waviness,
Wheel Path, and Levelness Criteria
E 1745 Specification for Plastic Water Vapor Retarders Used In Contact
With Soil or Granular Fill Under Concrete Slabs
F 141 Terminology Relating to Resilient Floor Coverings
F 1869 Test Method for Measuring Moisture Vapor Emission Rate of
Concrete Subfloor Using Anhydrous Calcium Chloride
F 2170 Test Method for Determining Relative Humidity in Concrete
Floor Slabs Using In Situ Probes

Porosity
The porosity (p) is defined as:
p = volume of pores × 100 %
Bulk volume
The bulk volume is measured by measuring the
dimensions of the solid and multiplying height
× width × depth.

Modified Pore Structure
Gel pores
Capillary Pores
OPC
60 %
Hydration
Intruded Volume
OPC +
GGBFS
0.001 0.01 0.1 1
10
Pore diameter, μm

Drying of materials
The rate of evaporation will depend on
temperature, the relative humidity near
the surface, the chemistry of the pore
solution, and the exposed surface area.
The relative humidity near the surface
will be controlled by air movement (wind
or convection).
Materials with salt in the pores will tend
to attract moisture and are described as
"hygroscopic".
The exposed surface area will be the
porosity × the area.

Condensation in pores
The conditions under which water will sustain a
meniscus in small pores are given by:
r Ln(RH) = - 2 m s
ρ R T
where: r is the pore radius in m
Ln(RH) is the natural log of the relative humidity
m is the molecular weight of water = 0.018 kg/mol
s is the surface tension of water = 0.073 N/m
ρ is the density of water = 1000 kg/m 3
R is the gas constant = 8.3 J/mol/ o K
T is the temperature = 290 o K (at 20 o C)

Water in Concrete
A pore of radius 3 × 10 -9 m will fill with water
at humidities over 70%. Thus in a moist
atmosphere concrete will absorb a large
amount of water.

Drying of Concrete
Water to Cement
ration (w/c) is the
main driver for
concrete drying

Water Cement Ratio
Low
High

ASTM F 710 – Industry Standard
• Establishes recommendations of MVER (ASTM F 1869)
• Establishes internal relative humidity testing recommendations
(ASTM F 2170)
• Establishes procedures for preparing floors
• Establishes pH test
Hardened cement paste reacts with atmospheric CO 2 which reduces the pH of
the surface to approximately 8.5

Using ASTM F 710….
Quantitative Test
ASTM F 1869
• Calcium Chloride (MVER)
ASTM F 2170
• Internal Relative Humidity

Moisture Vapor Emission Rate
Measures moisture absorbed by
CaCl 2
Most accurate in a building
environment under “expected
normal use” conditions
Target F 710 recommendations
Some flooring installers won’t
use this test

Advantages
It is Quantitative
Determines moisture being
emitted at one area of the
surface
Relatively easy test to perform
Gives a quantitative results
Disadvantages
Not totally accurate MVER
Chloride draws water out of surface
(can be misleading)
Only measures the top surface of the
concrete
Affected by ambient temp and dew
point conditions

MVER Test
Test Run at 73F and 50% RH

MVER Test
Test Run at 73F and 50% RH

ASTM F 2170
• Measurement for the internal
relative humidity of concrete
• Taken at 40 % of the slab
depth if one-way drying
• Target from F 710
recommendations

ASTM F 2170
Advantages
Disadvantages
Quantitative
BEST predictor of “true”
moisture within a slab
Relatively easy to run
Considers moisture gradient in
a slab
Measures moisture expected to
equalize at the surface of
concrete
Accuracy of probes can be a
question
Leapfrogging probes could give
bad results
Requires recalibration

Relative Humidity Test
Test Run at 73F and 50% RH

Relative Humidity Test

Conventional Floor Slab, w/c = 0.50
≈ 150 pounds/yard of water of convenience
If a internal relative humidity is not tested,
future moisture related problems are likely from:
1. Moisture Vapor Migration
2. pH > – Controlled with rapid-drying concrete

General Guidelines of ASTM F-710
Dry, clean, smooth and structurally sound…
Surface cracks and control joints should be
filled…and provide a minimum of 3000 psi
compressive strength in 28 days
Expansion joints shall not be filled…
Surface must be cleaned…
No asphaltic adhesive residues…
Shall be smooth and flat…within 3/16” in
10ft.

Testing a Slab per ASTM F-710
Removal of sealers, curing agents, bond
breakers otherwise known as the “water drop
test”
Moisture Testing
• Moisture Vapor Emissions Rate (MVER)
• In Situ RH (Relative Humidity)
pH Testing

Concrete Moisture Basics
Understanding how water moves through
hardened concrete is important in
determining:
• Consequences of the moisture movement;
• Effectiveness of moisture testing methods; and
• Validity of flooring manufacturers’ warranty
recommendations

Moisture Sources
Water of Hydration
• Water required to complete chemical reaction
Typically considered ~25% of cement by weight
Water of Convenience
• Water used for ease of workability and
placement
Usually another 25% to 40% of cement by weight
Moisture Vapor Transmission (MVT)
• Water of convenience evaporating
4” slab poured at .50 W/C evaporates >½ gallon per sq ft.
• Water coming up through the concrete from
under slab

Wetting Drying Hysteresis
Moisture Content
Wetting
Dryingg
Time

Effects of Secondary Moisture
Exposure
Concrete slabs,
properly prepared
and under functional
HVAC control typically
take 50-90 days to
reach moisture levels
suitable for “normal”
floor covering
installation
• Rewetting resets
the dry time clock
my several weeks

Reported by ACI Committee 302 -2006
Guide for Concrete Slabs that
Receive Moisture-Sensitive
Flooring Materials

Concrete Curing/Drying
After curing and before drying
begins, the moisture distribution
in a hardened concrete slab is
reasonably uniform throughout
the member thickness (Hanson
1968). As concrete dries, the
amount and distribution of
moisture changes (Hedenblad
1997).

Surface Shrinkage (Curl)
Grind it to make it flat
Only to have it invert after covering

Curing/Drying of Lightweight &
Normal Concrete

Moisture Movement

Moisture Movement
Both phases
Capillary Rise
Diffusion
Absorption / Desorption
Flow

Water Movement - Diffusion
J = −D ∂∂
∂∂

What can we do?

It depends when
Before Construction
• Install a Vapour Barrier
• Eliminate vapour sensitive coverings
• Use a low permeability Concrete
• Use a self –desiccating concrete
After Construction
• Wait
• Apply a topical protection

T, H
T, H

T, H
T, H

T, H
T, H

T, H
T, H

Deep Slab Relative Humidity

It Also Dries throughout the Depth
Conventional Concrete
Drying to this depth could take
years
Rapid-Drying Concrete
Drying throughout the depth will
take roughly 30 days

Questions?
Thanks for the time and attention