Novelties in Material Development for Massive Concrete Structures: Reduction in Heat of Hydration Observed in Ternary Replacement Mixtures

Abstract

As the size of modern infrastructure increases, novelties related to mass concrete mixtures including supplementary cementitious materials (SCMs) become critical. The effects of binary and ternary cement replacement mixtures including metakaolin, silica fume, ground calcium carbonate, granulated blast furnace slag, and fly ash on the rate and amount of heat generated in concrete mixtures are investigated. Twenty three binary and ternary mixtures with a water-to-cementitious binder ratio of 0.43 are evaluated. Between 15% and 45% cement replacement by weight is considered. Results indicate that binary mixtures containing metakaolin or silica fume offer no advantage in reducing the amount of heat but increase compressive strength by 20%. On contrary, ternary mixtures, including two pozzolanic materials, provide 15% reduction in the amount of heat evolution without compromising strength. This reduction is observed regardless of alumina (Al) or silica (Si) content in pozzolanic materials when 45% cement is replaced with a combination of slag and metakaolin, or slag and silica fume. Furthermore, the effect of increased calcium (Ca) content is investigated. It is concluded that ternary mixtures with decreased Ca/(Al+Si) ratio reduce internal temperature in mass concrete structures and are less likely to be exposed to the threshold temperature for delayed ettringite formation.

Characterizing the Performance of Ternary Concrete Mixtures Involving Slag and Metakaolin

“…A time history of the CTEs should be studied if ternary mixtures are to be used in mass concrete placements. A previous study [9] has reported the reduced heat of hydration in these ternary mixtures. The relationship between CTE and the extent of temperature-induced cracking should be of future interest.…”

“…To control the dilution effect, ternary SCM combinations shall also replace a portion of cement equaling 45%. Literature indicates that the heat of hydration is minimized at a 45% replacement when replacements by metakaolin and slag are 15% and 30% of the cement content, respectively [9]. Therefore, all combinations of metakaolin and slag in this study shall be 15% and 30% of the cement content, respectively.…”

“…Ternary mixtures including metakaolin have the potential of reducing the heat of hydration while maintaining mechanical strength, increasing the durability, and improving dimensional stability. While research has been conducted demonstrating the ability of ternary blends of metakaolin and slag to reduce the heat of hydration [9,10], comprehensive studies evaluating the mechanical properties, durability, and dimensional stability of these mixtures have not been conducted. Moreover, studies have not yet been conducted comparing the performance using various commercially-available metakaolin and blast furnace slag products.…”

“…This effect is characterized by the reduction in heat associated with decreased hydraulic activity. By virtue of dilution, ternary blends of SCMs have also been proven to reduce the heat of hydration when replacing large amounts of cement [7][8][9][10][11][12]. In practice, however, binary replacements of cement by SCMs are typically used to combat this problem.…”

“…Recent research demonstrated the reduced heat liberation of ternary cementitious blends incorporating metakaolin and slags [8,9]. Studies have also shown increased performance of these mixtures in mechanical tests [13,14] and improved pore properties [15,16].…”