Using Low-Temperature Differential Scanning Calorimetry to Quantify Calcium Oxychloride Formation for Cementitious Materials in the Presence of Calcium Chloride

Abstract

Whereas many concrete pavements have exhibited service lives of 30 to 50 years, a portion of these pavements in regions that are exposed to snow, ice, and salt have shown premature distress at the joints. This distress has been observed to occur between 5 and 20 years and requires extensive repair of an otherwise well-functioning pavement. Although there are several potential mechanisms that can lead to this deterioration, a reaction can occur between calcium chloride coming from deicing salt (CaCl2) and the tricalcium aluminate (C3A) and/or calcium hydroxide (CH) in the cementitious matrix. This paper describes the development of a test method that can be used to evaluate the potential for a cementitious binder to react with the calcium chloride deicing salts to form calcium oxychloride (the reaction between CaCl2 and CH). The test method enables the quantity of calcium oxychloride to be determined for each binder system. The results indicate that the amount of calcium oxychloride can be reduced with the replacement of cement with supplementary cementitious materials (fly ash, slag, silica fume, etc.). It is anticipated that the proposed test method could be used to better understand the role of binder chemistry on the calcium oxide formation and to optimize the binder composition to reduce the calcium chloride formation to an acceptable level and ultimately reduce the risk for deterioration.

Calcium Oxychloride Formation Potential in Cementitious Pastes Exposed to Blends of Deicing Salt

“…17,19 A more detailed description of the effect different temperature regimes have on CAOXY formation is presented elsewhere. 30 The latent heat associated with the melting can be measured between the two temperature steps of the transition, and by comparing the latent heat with that measured for pure CAOXY (186 J/g), 19 the amount of CAOXY formed in any chosen mixture can be quantified. CAOXY amounts are presented here as g/100 g paste (oz/100 oz paste), where paste refers to the original weight of the ground paste sample.…”

Reducing Damage Due to Chemical Reactions in Concrete Exposed to Sodium Chloride: Quantification of a Deleterious Chemical Phase Change Formation

“…The sample was then placed in the LT-DSC and the following temperature cycle was applied: equilibrating at 25 o C; cooling to -90 o C at 2 o C /min; isothermal at -90 o C for 5 min; heating to 30 o C with 1 o C /min. It should be mentioned herein that heating/cooling rates were selected to provide a reasonable quantification of the chemical phase change for the purpose of general comparison between different mixtures although other heating/cooling rates can be used for this testing method [23].…”

Calcium oxychloride formation in pastes containing supplementary cementitious materials: Thoughts on the role of cement and supplementary cementitious materials reactivity

“…Three techniques were used to study the amount of CH and potential for CAOXY formation: 1) thermogravimetric analysis (TGA) [21,24], 2) low-temperature differential scanning calorimetry (LT-DSC), [19,20,25], and 3) thermodynamic modeling using the Gibbs Energy Minimization Software (GEMS) [26].…”

“…As the mixture was heated, CAOXY melts (at around 30 °C under these conditions); the amount of CAOXY was found by normalizing the heat release on melting with that of pure CAOXY. Additional details of the LT-DSC testing are presented elsewhere [20,25]. The tested samples of plain cement paste had a coefficient of variation of approximately 5% for LT-DSC.…”