Abstract
It has been shown that sodium chloride can react with the tricalcium aluminate (C3A) and its hydrates, leading to a formation of a deleterious chemical phase change during thermal cycling. It is believed that this chemical phase change is implicated in the premature deterioration of concrete pavements in the cold regions. This work examines the potential formation of the deleterious chemical phase change in several cementitious pastes made using different types of portland cement and supplementary cementitious materials (SCMs). The amount of the chemical phase change was quantified using a low-temperature differential scanning calorimetry. The results indicated that the formation of the chemical phase change can be reduced by using cements with low C3A content. The addition of SCMs showed different effects on the chemical phase change formation. Slag and Class F fly ash could reduce the amount of the chemical phase change due to only the dilution effect whereas silica fume could significantly reduce the amount of the chemical phase change due to the dilution effect as well as pozzolanic reactions. Adversely, the addition of Class C fly ash showed a negative effect through increasing the formation of the chemical phase change.
Highlights
The weather conditions in the cold-regions are severe for concrete infrastructures due to the heavy use of deicing chemicals that are usually applied on the roads in order to maintain a normal traffic flow
The deleterious chemical phase change in pastes made with ordinary portland cement (OPC) I, OPC Type I (OPC I)/II and OPC Type V (OPC V), labeled as C1, C2 and C3 respectively in Figure 3, were calculated as 8.87, 6.25, and 2.38 J/gpowder respectively
OPC I sample (C1) shows the highest amount of the chemical phase change whereas OPC V sample (C3) shows the lowest. This implies that the formation of the chemical phase change is highly dependent on the cement chemistry (OPC V has typically low C3A content according to ASTM C150-07, see Table 1)
Summary
The weather conditions in the cold-regions are severe for concrete infrastructures due to the heavy use of deicing chemicals that are usually applied on the roads in order to maintain a normal traffic flow These chemicals are in the form of chloride-based salts such as sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2). The mechanisms of concrete deterioration in the presence of the deicing chemicals have been attributed to two main reasons; (i) classic freeze-thaw issues due to supersaturated concrete pores and (ii) deleterious chemical reactions between the deicing chemicals and the cementitious matrix [9-14] The former mechanism can be resolved through utilizing air-entrained admixtures which can establish an adequate void system to resist ice expansion pressures [10, 11]. The latter can be addressed through using proper supplementary cementitious materials (SCMs) as a partial replacement of ordinary portland cement (OPC) to improve the durability of concrete in the presence of deicing salts through dilution and/or pozzolanic reactions [15-21]
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