Cold-weather concreting

Retarders and Accelerators. Materials that control hardening of cement may be either organic or inorganic. Retarders are often incorporated in oil well cementing and hot-weather concrete appHcations, whereas accelerators may be useful for cold-weather concrete appHcations in which higher rates of reactivity are desirable. In most cases, these admixtures are used in low concentrations, suggesting that they act by adsorption. 

Korhonen, C. J. and Smith, C.E. (1991). New Admixtures for Cold Weather Concreting, CRREL Special Report 90-32, 200-9. 

Other fine materials which tend to inhibit air entrainment include pigments, particularly carbon black. This is of concern to the ready-mixed operator supplying integrally colored concrete for exterior exposure [6]. Accelerating admixtures which are used to reduce down time and in cold weather concreting can be used successfully in air-entrained concrete, but should be added separately and in solution form to the mix. Direct contact of these admixtures with some types of air-entraining agents mixed in the same water phase may adversely affect both admixtures. 

The choice of a particular option or options is determined by the desired set time and rate strength development. Accelerated time of setting is usually achieved by increasing the heat of hydration of the concrete mixture. Selection of appropriate chemical admixtures enables the production of cold-weather concrete mixtures with both accelerated setting and early-age strength development characteristics, similar to that obtained with plain... 

A viable, economic alternative to other cold-weather concreting options (increased cement content (Fig. 7.39) and hot water). 

ACI Committee 306 (1988). Cold Weather Concreting, ACI 306.R-88, American Concrete Institute, Detroit, Michigan. 

Cold-weather concrete mixtures incorporating non-chloride antifreeze accelerating admixtures have been used in a number of projects. Two of these projects are profiled. All the concrete mixtures described below were treated with the sodium-thiocyanate-based CWA mentioned earlier. These projects illustrate the impact of this admixture on normal concrete mixtures containing Class C fly ash, since fly ash typically delays time of setting and, hence, would not be a logical choice for cold-weather concrete. 

American Concrete Institute, 2010. ACI306R Guide to Cold Weather Concreting. ... 

How can the damaging effect of cold weather concreting be minimized ... 

Concrete with a high early strength development is desirable for cold weather concreting. Reg Set cement concrete can be used for this application. Strength determinations for Reg Set concrete cured for one hour at 20°C and subsequently at -10°C for 28 days give similar strengths to those for Reg Set concrete cured continuously at 20°C for the same period. 

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