[wirher]

Curing in cold weather will be different as in this case the biggest concern will be the maintaining of an adequate and conducive temperature for hydration. For massive members, the heat generated by the concrete during hydration will be adequate to provide a satisfactory curing temperature. For non-massive members, a good alternative is steam curing, which provides both moisture and heat. In any case, a minimum favorable temperature in the range of 10 - 21º C must be maintained in the concrete for the minimum required curing period (see below). Where moist curing is not done, very low temperatures may be avoided by insulating the member appropriately. here

[N5DWI]

Curing period and temperature
The curing period depends upon the type of cement used, mixture proportions, required strength, size and shape of member, ambient weather, future exposure conditions, and method of curing. Since all desirable properties are improved with curing, the period should be as long as practical. For most concrete structures, the curing period at temperatures above 5º C (40º F) should be a minimum of 7 days or until 70% of the specified compressive or flexural strength is attained. The period can be reduced to 3 days if high early strength concrete is used and the temperature is above 10º C (50º F). here

[marieellis444]

Michael Mamlouk & John Zaniewski (1999): Materials for Civil and Construction Engineers, Addison Wesley Longman, Inc.,

[Minsc]

Hydration is an exothermic chemical process, increasing the ambient temperature will increase the rate of hydration, and hence of strength development, while lowering it will have the opposite effect. Too much heat reduces the final concrete strength. Selecting an appropriate curing process helps in temperature control during hydration more

[Veltas]

Under hot weather conditions, the high temperatures are likely to result in excessive moisture loss. Maintaining mixing water in the concrete is the major concern. Continuous moist curing should be done for the entire curing period. If this is not possible, the concrete surfaces should be protected from drying out using any of the previously mentioned methods and the surfaces kept damp. Surfaces should dry out slowly after curing to reduce possibility of surface cracking. here

[diven]

Retardation of setting time is influenced by the type of admixtures used. The chart below illustrates the effect of various lignosufonates (1 and 2) and carboxylic (3 and 4) admixtures on setting time. here

[qay]

Figure 2 Effect of Various Admixtures on Concrete Setting Time here

[r4king]

Dosage Effect on Retardation of Initial Setting Time

[grrrl]

The effect of concrete temperature and retardation of setting time is given by PCA in the chart below. It is concluded from the chart that the retardation effect is more pronounced when a higher concrete temperature is used. more

[gem]

Figure 1 Effect of Concrete Temperature and Retarder on Setting Time here

[Marlo]

Temperatures for placement and protecting concrete in cold weather are established and mandated under ACI 306. The objective of the ACI 306 is to keep concrete warm, over 5 degrees Celsius, for the first 48 hours, where concrete strength development is critical.

[Etherael]

Cold weather concrete can be classified as a period of more than three days where some specific conditions occur under certain temperatures. The American Concrete Institute under ACI 306 defines that concrete will be exposed to cold weather "when the air temperature has fallen to, or is expected to fall, below 40°F (5°C) during the protection period. The protection period is defined as the time required to prevent concrete from being affected by exposure to cold weather."

[YeahR]

When concrete is being managed under cold weather, it must be protected from freezing shortly after being poured. Also concrete must be able to develop the required strength for the safe removal of forms while reducing the circumstances where excessive heat must be applied to help concrete develop the required strength. Other important factors that must be considered are the proper curing conditions that prevent cracking and provide the intended serviceability of the structure.

[vermonthotels545]

Follow these recommended steps to assure that concrete in cold weather will obtain the required design strength and that you don't have any other issues while the concrete is setting.

[neolith2099]

When concrete is being placed below 5 degrees but is not below freezing point, concrete will take longer to develop the required strength. Note that removing formwork when concrete is too cold or hasn’t reached desired strength, could damage concrete strength and surfaces and concrete might collapse. Using frost blankets and insulated formwork could be necessary to protect concrete. Insulated forms or temporary covers could provide sufficient insulation in beams, columns, and walls.

[Anaxagoras]

[lobo235]

For the posts -
If the remps are in the 40's and the ground is not frozen, just mix the concrete without additives. Backfill and cover for a day or so. You really do not need a lot of early strength since your concrete will be many times stonger than the soil in a few hours. Keep the concrete slightly (1-2") above grade and slope the top away if you are using wood posts.

[rosszapin96]

1. We're replacing part of a fence and need to install 11 posts with concrete securing them. The temps are going to be in the 40's. I have a bunch of bags of regular strength gravel mix. Can I use them or do I need additives or something else entirely?

[bart27newton]

2. I have to replace a basement window and will have to mortar around the outside of the frame. What cold weather considerations are there for that too?

[Hariposter]

For the window -
Normal mortar and keep if from freezing for a few days. This time of the year you foundation will probably provide enoigh heat, so just cover the masonry. Around here they build basements at temps as low a zero.

[strania]

[Pieter Wuille]