Calorimetry Study of the Influence of Portland Cement Content, Slag/Fly Ash Ratio, and Activator Type on the Early Hydration of Hybrid Cements

The influence of curing temperature on the strength and phase assemblage of hybrid cements based on GGBFS/FA blends

“…Cements were designed by varying the amount of Pc between 0 and 14.4 wt%, and the activator dosage in the range 2-4 wt%, at a constant GGBFS/FA mass ratio of 1:1.5. The activator (sodium sulfate) dosage range was specified based on previous studies, which indicate that this range yields optimum performance (Donatello et al, 2018;Mota et al, 2019;Fu et al, 2021;Gluth and Garel, 2021). All cements were mixed with deionized water at a water/cement (w/c) ratio of 0.35 by mass to obtain workable pastes (c comprises all solid components, including the sodium sulfate).…”

“…Figure 3 shows the XRD patterns in the range 5-25 °2θ to focus on the diagnostic reflections of hydration products other than C-N-A-S-H. Ettringite (PDF# 00-041-1451) was formed in all hybrid cements, indicated by its main reflection at 9.1 °2θ. The stability of ettringite is favored by the high amounts of fly ash and sodium sulfate (Taylor et al, 2001;Lothenbach et al, 2011;Gluth and Garel, 2021), as the high sulfate content suppresses the formation of monosulfoaluminate. In contrast to the other hybrid cements, C14S4 contained portlandite (PDF# 00-044-1481) and small amounts of a meixnerite-type phase (Mg-Al layered double hydroxide, LDH; PDF# 00-038-0478).…”

“…The main hydration product of hybrid cements is C-N-A-S-H, a compound related to calcium silicate hydrate (C-S-H) present in OPC, formed by substitution of silicon with aluminium in the tetrahedral bridging sites of the silica chains and associated uptake of alkali ions to balance the negative charge arising from Al 3+ in 4-fold coordination (Garcia-Lodeiro et al, 2016). As a result of the reduced amount of OPC and the high fraction of SCMs, hybrid cements usually exhibit significantly less heat of hydration than plain OPC, while maintaining sufficient high early compressive strength (Lee et al, 2003;Garcia-Lodeiro et al, 2013;Garcia-Lodeiro et al, 2016;Alahrache et al, 2017;Donatello et al, 2018;Mota et al, 2019;Fu et al, 2021;Gluth and Garel, 2021;Xue et al, 2021). In addition, there are chemical and mineralogical similarities between hybrid cements and the cements of ancient Roman concretes that have survived in a marine, i.e., strongly corrosive, saline, environment for several centuries (Jackson et al, 2013;Jackson et al, 2014;Jackson et al, 2018;Palomo et al, 2019), implying an excellent durability of concretes based on hybrid cements in salt-rich environments such as seawater (Palomo et al, 2019).…”

“…For example, the chemical compositions of ground granulated blast furnace slags (GGBFS) differ significantly between materials from different sources, especially regarding the amount of available silicon, alumina and magnesia, which influence the formation of hydration products of alkali-activated slags (Ben Haha et al, 2012;Bernal et al, 2014). As for hybrid cements, materials with fly ash as the sole SCM (Lee et al, 2003;Garcia-Lodeiro et al, 2013;Garcia-Lodeiro et al, 2016;Alahrache et al, 2017;Donatello et al, 2018) as well as materials with GGBFS as the sole SCM (Angulo-Ramírez et al, 2017;Mota et al, 2019;Fu et al, 2021;Gluth and Garel, 2021;Xue et al, 2021) have been studied in considerable detail. In contrast, studies of hybrid cements based on blends of GGBFS and fly ash (Gluth and Garel, 2021;Xue et al, 2021) are scarce, although a large amount of work on AAMs indicates that blending GGBFS with other SCMs can yield advantageous behavior and properties of the resulting materials, and previous experience shows that employment of such blends is a way to control the heat release and the setting times of hybrid cements (Gluth and Garel, 2021;Xue et al, 2021).…”

“…As for hybrid cements, materials with fly ash as the sole SCM (Lee et al, 2003;Garcia-Lodeiro et al, 2013;Garcia-Lodeiro et al, 2016;Alahrache et al, 2017;Donatello et al, 2018) as well as materials with GGBFS as the sole SCM (Angulo-Ramírez et al, 2017;Mota et al, 2019;Fu et al, 2021;Gluth and Garel, 2021;Xue et al, 2021) have been studied in considerable detail. In contrast, studies of hybrid cements based on blends of GGBFS and fly ash (Gluth and Garel, 2021;Xue et al, 2021) are scarce, although a large amount of work on AAMs indicates that blending GGBFS with other SCMs can yield advantageous behavior and properties of the resulting materials, and previous experience shows that employment of such blends is a way to control the heat release and the setting times of hybrid cements (Gluth and Garel, 2021;Xue et al, 2021). Thus, it is desirable and necessary to understand the behavior of hybrid cements based on GGBFS/fly ash blends in more detail than is hitherto available.…”