concrete moisture and ph testing what are we measuring?...ph testing • you are a chemist preparing...

Guidance to Concrete Solutions

NORTH S ETARRCONCRETE CONSULTING, P.C.

Scott M. Tarr, P.E. FACI

[email protected]


NORTH STARRCONCRETE CONSULTING, P.C.

November 9, 2017

Concrete Moisture and pH TestingWhat Are We Measuring?



What We Want to Avoid



Moisture 101

Moisture is Found Naturally in Three States

SolidLiquid

Gas



Moisture 101



Moisture 101

Sources of Liquid Moisture and Vapor• Concrete



How much free water ?



Moisture 101

Typical 4000 psi concrete

32 gal of water/cu yd = 267 lbs/cu yd

Water-to-cement ratio 0.50

Leaves 133.5 lbs free water/yd

= 1,650 lbs free-water/1,000 sq ft (4” slab)

Water needed for hydration w/c 0.25 = 133.5 lbs



Every truckload delivers over 100 gallonsof free water at no extra charge.

That’s Free Water!



Moisture 101

Sources of Liquid Moisture and Vapor• Concrete



Moisture 101

Sources of Liquid Moisture and Vapor• Concrete• Irrigation• Broken Pipes• Condensation (dewpoint or “adsorption”)



Moisture 101

80

90 %

77



Dewpoint Condensation

Dehumidified Air

Warm Humid Air



Warm Slab Above Dewpoint Temperature



Slab Surface Density



Moisture 101

Sources of Liquid Moisture and Vapor• Concrete• Irrigation• Broken Pipes• Condensation (dewpoint or “adsorption”)• Fill Course (cushion or blotter layer)



Moisture 101



Moisture 101

Sources of Liquid Moisture and Vapor• Concrete• Irrigation• Broken Pipes• Condensation (dewpoint or “adsorption”)• Fill Course (cushion or blotter layer)• Adhesives• Maintenance



Moisture 101

Groundwater Sources of Moisture• Hydrostatic Pressure• Capillary Action• Vapor Diffusion



Concrete Slab-on-Ground

Hydrostatic Pressure



Hydrostatic Pressure



Water

Narrow Glass Straw

Capillary Action



Water

Wide Glass Straw

Capillary Action



Capillary Action



Lower Vapor Pressure

Higher Vapor Pressure

Concrete

Vapor Diffusion



Vapor Diffusion



5555

100

70

30



Water Vapor Pressure Differential

55°F and 100% RH = 0.214 psi

70°F and 30% RH= 0.108 psi

- Vapor Diffusion



Vapor Barrier / Retarder

Water Vapor Pressure Differential

70°F and 30% RH= .108 psi

55°F and 100% RH = 0.214 psi



Note Condensed Water Droplets

Under VaporRetarder.

Vapor Retarder



Lower Vapor Pressure

Higher Vapor Pressure

Concrete

Vapor Diffusion



Vapor Diffusion



0

10

20

30

40

50

60

70

80

90

10050 55 60 65 70 75 80 85 90 95 100

RH%

Dep

th, m

m

concrete placed

(day zero)

9-days40-days70-days5 months

Slab with a vapor retarder immediately below

~10% RHGradient

Surface

Bottom

4 in. Thick

Slab Curling/Warping Moisture Gradient



Slab Relative Humidity Gradient

-2

0

2

4

6

8

10

0 20 40 60 80 100 120

Relative Humidity, Percent

Slab

Dep

th, i

n.

7-in.-thick slab

4-year old slab on draining base

9540

55% RHGradient

2

Slab Curling/Warping Moisture Gradient



What is Dry?

CaCl MeterRH

ResistanceMeter

MassLoss

What is a Triathlete?

Surface RH(Hood Test)

Plastic Sheet

MatBond



What Moisture is Measured?

CaClMeter



Sla

b D

epth

% RH ~100%

Initial Concrete PlacementAfter Surface Drying – Moisture Gradient

Moisture Equilibration After Covering

Basics of Slab Moisture



Sla

b D

epth

% RH ~100%




40% Slab DepthASTM F 2170



Discrepancy Between Manufacturers???



Sla

b D

epth

% RH ~100%




40% Slab DepthASTM F 2170

And If You Think Moisture is Tricky to Measure…What About pH???



In Las Vegas, they make a big deal about pH…



pHIs a measure of hydrogen ions in solution

But in Science…



pH Testing• You are a chemist

preparing a solution• Clean Surface• Distilled or

Deionized Water• Puddle 1 inch

Diameter• 60 Seconds +/- 5

Seconds• Wet Paper and

Immediately Compare to Chart



Don’t let moisture take a bite out of you or your business



Thank You!Scott M. Tarr, P.E. FACI

[email protected]

Concrete Moisture and pH Testing�What Are We Measuring?Slide Number 2What We Want to AvoidMoisture 101Moisture 101Moisture 101Slide Number 7Moisture 101Slide Number 9Moisture 101Moisture 101Moisture 101Slide Number 13Slide Number 14Slide Number 15Slide Number 16Moisture 101Moisture 101Slide Number 20Slide Number 21Moisture 101Moisture 101Hydrostatic PressureSlide Number 25Hydrostatic PressureCapillary ActionCapillary ActionCapillary ActionVapor DiffusionVapor DiffusionSlide Number 32Slide Number 33Slide Number 35Slide Number 36Vapor RetarderVapor DiffusionVapor DiffusionVapor DiffusionSlide Number 41Slide Number 42Slide Number 44Slide Number 45Slide Number 46Slide Number 47Slide Number 48Slide Number 49Slide Number 50Slide Number 51Slide Number 52Slide Number 53Slide Number 54Slide Number 55Slide Number 56Slide Number 57

concrete moisture and ph testing what are we measuring?...ph testing • you are a chemist preparing...

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