20. M = Σ (C + 10) ∆t
where
M = maturity factor
Σ = summation
C = concrete temperature, °C
∆t = duration of curing at temperature
°C, usually in hours
21. Even in the winter, an outdoor construction can
be done.
can be avoided by controlling the setting times
of the concrete.
Fig. 14-2. Close-up view of ice impressions in paste of frozen fresh concrete. The ice crystal formations occur as unhardened concrete freezes. They do not occur in adequately hardened concrete. The disruption of the paste matrix by freezing can cause reduced strength gain and increased porosity. (44047)
Fig. 14-3. Initial set characteristics as a function of casting temperature (Burg 1996).
Fig. 14-4 Slump characteristics as a function of casting temperature (Burg 1996).
Fig. 14-5. Effect of temperature conditions on the strength development of concrete. Concrete for the lower curve was cast at 4°C and placed immediately in a curing room at -4°C. Both concretes received 100% relative-humidity curing for first 28 days followed by 50% relative-humidity curing (Klieger 1958).
Fig. 14-8. Concrete footing pedestal being covered with a tarpaulin to retain the heat of hydration. (69870)
Fig. 14-11. Example of a concrete floor that was saturated with rain, snow, or water and then frozen, showing the need for air entrainment. (69869)
Fig. 14-13. A bimetallic pocket thermometer with a metal sensor suitable for checking fresh concrete temperatures. (69881, 69882)
Fig. 14-14. Scheme for measuring concrete temperatures below the surface with a glass thermometer.
Fig. 14-18. (top) Tarpaulin heated enclosure maintains an adequate temperature for proper curing and protection during severe and prolonged winter weather. (bottom) Polyethylene plastic sheets admitting daylight are used to fully enclose a building frame. The temperature inside is maintained at 10°C with space heaters. (69877, 69878)
Fig. 14-19. Stack of insulating blankets. These blankets trap heat and moisture in the concrete, providing beneficial curing. (43460)
Fig. 14-20. Insulating concrete forms (ICF) permit concreting in cold weather. (69699)
Fig. 14-21. With air temperatures down to -23°C, concrete was cast in this insulated column form made of 19-mm high-density plywood inside, 25-mm rigid polystyrene in the middle, and 13-mm rough plywood outside. RSI value: 1.0 m 2 · °C/W. (43461)
Fig. 14-24. A direct-fired heater installed through the enclosure, thus using a fresh air supply. (69875)
Fig. 14-23. An indirect-fired heater. Notice vent pipe that carries combustion gases outside the enclosure. (43459)
Fig. 14-25. Hydronic system showing hoses (left) laying on soil to defrost subgrade and (right) warming the forms while fresh concrete is pumped in. (68345, 68344)
The equation is based on the premise that concrete gains strength (that is , the cement continues to hydrate) at temperatures as low as -10°C. The Maturity Concept is based on the principle that strength gain in concrete is a function of curing time and temperature. The Maturity Concept can be found in ACI 306R-88 and ASTM 1074
The equation is based on the premise that concrete gains strength (that is , the cement continues to hydrate) at temperatures as low as -10°C. The Maturity Concept is based on the principle that strength gain in concrete is a function of curing time and temperature. The Maturity Concept can be found in ACI 306R-88 and ASTM 1074
