Cold Weather Concreting

Transcription

1 Cold Weather Concreting January 9 & 10, 2019 Nebraska Concrete & Aggregate Association 2019 Quality Concrete Conference

2 Cold Weather Concrete Requires Experience

3 Cold Weather ACI 306R-16 Committee Definition Cold weather conditions exist when the air temperature has fallen to, or is expected to be 40ºF or less during the protection period

4 OK so what is the Protection Period? The protection period is defined as the time required to prevent concrete from being adversely affected by exposure to cold weather

5 ACI 306 Chapter 7 says 500 psi 1 freeze-thaw cycle Air entrained and not exposed to water saturation 3500 psi Repeated freeze thaw cycles Air entrained and not exposed to water saturation Rule of Thumb Concrete temperature above 50 F for 7 Days

6 Durability of Non-Air- Entrained Concrete

7 Overworked, Densified Surface Paste Trapped Moisture Layer Entrained Air Bubbles

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11 Effect of Freezing Fresh Concrete Up to 50% reduction of ultimate strength / durability can occur if frozen before reaching a strength of 500 psi (3.5 MPa) Frozen only once at an early age With curing nearly all strength can be restored Less resistance to weathering More permeable

12 Effect of Freezing Fresh Concrete It s a race between the concrete temperature and heat loss Includes the internal heat generated from the hydration of the cementitious At a point after hydration the concrete is strong enough to resist freezing Very little hydration takes place below 40 F

13 Relationship Between Initial Set and Casting Temperature

14 Setting Time of Concrete at Various Temperatures Concrete Construction, March 1990 Rule of Thumb For each 10 F reduction in in temperature, set time is increased by 1/3 Temperature Approximate Set Time 70 F 6 Hours 60 F 8 Hours 50 F 11 Hours 40 F 14 Hours 30 F 19 Hours 20 F Set Does Not Occur

15 Relationship Between Slump and Casting Temperature

16 Effect of Low Temperatures on Strength

17 Successful cold weather concrete projects depend on concrete that is properly Produced 3P s Placed Protected

18 What Can We Do? Goals for Cold Weather Concreting Practices Maintain curing conditions that foster normal strength development Prevent damage due to early freezing Limit rapid temperature changes that induce thermal stresses Assure development of concrete engineering properties to meet project requirements

19 Cold-Weather Concreting Methods to accelerate heat / strength gain: Type III or HE high-early-strength cement Additional portland cement 100 to 200 lb/yd 3 10 to 15 F gain in heat of hydration per 100 cwt Chemical accelerators

20 Typical Set Times with Chemical Accelerators POZZOLITH 122-HE TIME OF SET Chloride Based Time of Set POZZOLITH NC 534 TIME OF SET Non-Chloride Based Time of Set Penetration Resistance Penetration Resistance Time (Minutes) Time (Minutes) Control 16 oz./cwt 32 oz./cwt 48 oz./cwt 64 oz./cwt Control 10 oz./cwt 20 oz./cwt 30 oz./cwt 40 oz./cwt

21 ACI 306 Recommended Concrete Temperatures Air-Entrained Concrete Thickness of section Line Condition Less than to to 72 Over 72 1 Above 30 F 60 F 55 F 50 F 45 F 2 Min. temp. of fresh concrete 0 F to 30 F 65 F 60 F 55 F 50 F 3 Below 0 F 70 F 65 F 60 F 55 F 4 Min. temp. of fresh concrete as placed and maintained 55 F 50 F 45 F 40 F ASTM C 1622 offers more guidance for concrete temperatures

22 Effect of Temperature of Materials on Concrete Temperatures T = 0.22(T a M a + T c M c ) + T w M w + T wa M wa 0.22(M a + M c ) + M w + M wa T = temperature of the freshly mixed concrete, F ( C) T a, T c, T w, and T wa = temperature in F ( C) of aggregates, cement, added mixing water, and free water on aggregates, respectively M a, M c, M w, and M wa = mass, lbs (kg), of aggregates, cementing materials, added mixing water, and free water on aggregates, respectively

23 Concrete Temperature Prediction Model Concrete Temperature Analysis with Hot Water Input: Moisture Batch Temperature Material Content Weights F Cement lbs./cy 100 Fly Ash - 0 lbs./cy 75 Coarse Aggregate 1.0 % 1800 lbs./cy 60 Fine Aggregate 2.5 % 1300 lbs./cy 60 Water gals./cy 140 Concrete Temperature: 82.8 F Concrete Temperature Analysis with Ice Input: Moisture Batch Temperature Material Content Weights F Cement lbs./cy 100 Fly Ash - 0 lbs./cy 75 Coarse Aggregate 1.0 % 1800 lbs./cy 60 Fine Aggregate 2.5 % 1300 lbs./cy 60 Water - 30 gals/cy 140 Ice in lieu of water 80 lbs./cy Adjusted water 20.4 gals/cy Concrete Temperature: 64.4 F

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29 Gotta have a Plan!

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31 Cooling After Protection Maximum Allowable Temperature Drop During the First 24 Hours (ACI 306) Section size, minimum dimensions (in.) Less than to to 72 Over F 40 F 30 F 20 F

32 Checking Fresh Concrete Temperatures

33 Temperature of Test Cylinders ASTM C-31 states maintain temperature 60 F - 80 F at the jobsite for up to 48 hrs.

34 Retaining Heat of Hydration

35 Cold-Weather Insulation, Aboveground

36 Insulating Blankets Thermal resistance of mineral fiber blanket (2 to 2.75-in. thick) 1.2 (m 2 K)/ W 7 ( F hr ft 2 )/ Btu

37 Insulating Concrete Forms (ICF)

38 Insulated Column Forms High-density plywood Rigid polystyrene Rough plywood

39 Enclosures Wood Canvas Tarpaulins Polyethylene Film

40 Heated Enclosure

41 Direct-Fired Heater Caution! CO 2 can cause carbonation!

42 Indirect-Fired Heater

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44 Hydronic Systems

45 Maturity Concept Metric: M = (C + 10) t Inch-Pound: M = (F 14) t where M = maturity factor = summation C = concrete temperature, degrees Celsius F = concrete temperature, degrees Fahrenheit t = duration of curing at temperature C (F), usually in hours

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47 Concreting on Ground

48 Remember the 3 P s Produce, Place, & Protect And you will never spin your wheels

49 Thank You For Your Time Today!