Microstructure of Concretes Cast in the Canadian Arctic: Role of Cacl 2 Used as an Anti-Freezing Agent
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MICROSTRUCTURE OF CONCRETES CAST IN THE CANADIAN ARCTIC: ROLE OF CaC1 2 USED AS AN ANTI-FREEZING AGENT
"M.REGOURD*,
H. HORNAIN* AND PrC. AITCIN**
* CERILH, 23 rue Je Cronstadt 75015, Paris, FRANCE ** Universite de Sherbrooke, Faculte des Sciences Appliquees,
Sherbrooke,
Quebec JIK 2RI,
CANADA
ABSTRACT
Two concretes were made in the Canadian Arctic at sub-freezing temperature using an unusually high amount of calcium chloride, about 9% of the cement mass. Calcium chloride in such a high dosage was mainly used as an antifreezing admixture, because it was impossible to heat the cement and the aggregates prior to the batching and cure the concrete properly after its pouring. One of these two concretes was cast inside a mine, where the temperature is about -10°C all year round. After one year of service, the strength of this concrete was determined to be 39 MPa at room temperature. The second one was cast outside the mine at -30°C during winter and was exposed to temperatures above 0°C the following summer. After one winter of service the strength of this was 5 MPa. These two concretes were examined under the SEM and show quite a dense microstructures containing chloroaluminates.
INTRODUCTION
Cold weather concreting no longer represents a major technical achievement. In temperate climates during winter, when the temperature approaches the freezing point,
concrete producers
can use Type III
cement,
heat the mixing water and the aggregates, and also add up to 2% calcium chloride (when permitted) so that concrete at 150 to 20*C can be delivered when the outside temperature is down to -20°C. In addition concrete can either be cast in insulated forms to prevent heat losses, or it can be protected by temporary heated enclosures. All these techniques are well documented in ACI Standard on cold weather concreting [1]. It is not always possible to work and use concrete in such favorable conditions in the Arctic. Most of the time, the only concrete material that can be used hot is water; aggregates and cement are stored outside and must be used at the ambient temperature. Moreover,- it is not economical considered either heating the concrete or using insulated forms in such remote places. Quite recently, some information about the use of antifreezing admixtures in Soviet Union and Finland was reported in the literature [2,3]. It appears that in some parts of Soviet Union it is a current practice to use antifreezing admixtures in the ready-mix industry. The most common anti-freezing admixture used is calcium chloride at a dosage well above the 2% limit generally permitted. Calcium chloride is said to be used in conjunction such other calcium or sodium salts such as sodium chloride, calcium nitrite or nitrate, and urea. Very few scientific reports are available on the effect of such a high dosage of calcium chloride on the compressive strength and on the microstructure of concretes. It is the purpose of this paper to present experimental field data on this subject.
Mat. Res. Soc. Symp. Proc. Vol. 85. 11987 Materials
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