Cold-Weather Concreting

1. NMRMCAA Meeting November 7, 2007 Albuquerque, NM Ken Wylie Principal Materials Engineer AMEC Earth & Environmental Cold-Weather Concreting

2. Cold Weather(ACI 306 Definition) • Average daily temperature <5ºC (40ºF) for 3 successive days • Stays <10ºC (50ºF) for more than ½ of any 24h period

3. Concrete Components • Cement • Water • Fine Aggregate • Coarse Aggregate

4. Hydration Basics Cement Particle Early Stage of Hydration

5. Hydration Stages (73 ºF)

6. Setting Times at Different Temperatures

7. Rule of Thumb • “For every 10°C (18°F) reduction in concrete temperature, the times of setting of the concrete double...”

8. Effect of Temperature on Strength Development

9. Effect of Low Temperatures on Strength

10. Hydration Ceases at… 14 ºF

11. Whoops!!!

12. Effect of Casting Temperature on Slump

13. Relationship Between Temperature, Slump and Air Content

14. Rule of Thumb • “For every 10°C (18°F) reduction in concrete temperature, the times of setting of the concrete double, thus increasing the amount of time that the concrete is vulnerable to damage due to freezing.”

15. Effect of Freezing Fresh Concrete • Up to 50% reduction of ultimate strength can occur if frozen — • Within a few hours • Before reaching a strength of 3.5 MPa (500 psi) • Frozen only once at an early age — • With curing nearly all strength can be restored • Less resistance to weathering • More permeable

16. Evaporation of Surface Moisture from Concrete Inch-Pound

18. Air Entrainment for Safety Concrete considered to ultimately be “unexposed” may well be exposed during construction.

19. Surface Temperature Limitations(ACI 306) • Above freezing (at least 35°F) • No more than 10 °F higher than minimum placement temp.

20. Cold-Weather Concreting Methods to accelerate strength gain: • Type III or HE high-early-strength cement • Additional portland cement (60 to 120 kg/m3 or 100 to 200 lb/yd3) • Chemical accelerators

21. Early-Age Strength

22. Accelerating Admixtures ASTM C 494 or AASHTO M 194, Type C Accelerate the rate of: • Hydration (setting) • Early-age strength gain Calcium chloride accelerators: • Increase drying shrinkage, potential reinforcement corrosion, potential scaling • Darken concrete

23. Example of Non-Chloride Accelerator Effect on Set Time

24. Non-Chloride Accelerator Caution Quote from typical accelerator literature • “… the concrete producer should account for the water contained in the (accelerator). Each Liter of (accelerator) added to a concrete mix will contribute 0.78 kg (6.5 lbs/gal) of water to that mix.”

25. Recommended Concrete Temperatures—Air-Entrained Concrete (ACI 306)

26. Effect of Temperature of Materials on Concrete Temperatures T = 0.22(TaMa + TcMc) + TwMw + TwaMwa 0.22(Ma + Mc) + Mw + Mwa T = temperature of the freshly mixed concrete, °C (°F) Ta, Tc, Tw, and Twa = temperature in °C (°F) of aggregates, cement, added mixing water, and free water on aggregates, respectively Ma, Mc, Mw, and Mwa = mass, kg (lb), of aggregates, cementing materials, added mixing water, and free water on aggregates, respectively

27. Heating Materials • Water • Aggregates

28. Heating Mix Water

29. NRMCA Heating Criteria • For plants seeking certification to supply concrete in subfreezing weather i.e., where concrete is placed regularly during sub-freezing weather, minimum heating capacity for water and/or aggregate of 15 boiler output horsepower per 100 cubic yard average daily cold weather production. (May be reduced to 10 bph if storage capacity permits round-the-clock operation of heating equipment.) One boiler horsepower = 33,500 BTU per hour transferred to the water.

30. Admixtures • Protect from freezing • Agitate if necessary

31. Recommended Duration of Temperature Air-entrained concrete

32. Recommended Duration of Temperature Fully stressed, exposed, air-entrained concrete

33. Retaining Heat of Hydration

34. Cold-Weather Insulation, Aboveground

35. Insulating Blankets

36. Thermal Resistance, R, for (10-mm [1-in.] Thick) Insulating Materials

37. Enclosures • Wood • Canvas • Tarpaulins • Polyethylene Film

38. Heated Enclosure

39. Direct-Fired Heater

40. Indirect-Fired Heater

41. Hydronic Systems

42. Protect from Thermal Shock

43. Cooling After Protection Maximum Temperature Drop in 24 Hours

44. 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 Maturity Concept

46. Thank You!