Partial replacement of OPC with CSA cements – effects on hydration, fresh and hardened properties

Abstract

The effects of a partial replacement of Ordinary Portland cement (OPC) with three types of calcium sulfoaluminate (CSA) cements (40 wt% and 20 wt%) were investigated. The obtained results were generally in agreement with previously published data but with few interesting exceptions. Setting times were shortened due to the formation of ettringite. The maximum hydration temperature increased for concretes containing 40 wt% of CSA but decreased when 20 wt% replacement was used. The decrease was related to the deficiency of the available sulfates, which limited the formation of ettringite. The presence of extra anhydrite and calcium oxide was associated to the delayed establishment of the second temperature peak in contrast to OPC-based concretes. Their surplus delayed calcium aluminate and belite reactions, and triggered renewed formation of ettringite, C-S-H and portlandite. Effects of aluminum hydroxide were also indicated as possibly important, although not proved experimentally in this research. The slightly lower compressive strength measured for mixes containing 40 wt% of CSA were linked with more formed ettringite. The same factor was indicated as the key to the reduction of the total shrinkage in mixes containing 40 wt% of CSA and increased for the lower CSA replacement level. In that case, the insufficient amount of formed ettringite caused too small expansion, which could not efficiently mitigate or compensate the developed shrinkage.

Research on the Performance of Cement-Based Composite Borehole Sealing Material Based on Orthogonal Test

“…The cement specimens were made in accordance with the national standard GB/T17671-1999. In this work, a blend consisting of 60% polycarbonate (PC) and 40% calcium sulfate anhydrite (SAC) was selected. − The mass of the components was measured using a beaker and a precision balance with an accuracy of 0.01, following the proportions indicated in Table . The additives were incorporated into the mixed cement in proportion to its overall weight.…”

Early Age Performance of OPC-GGBFS-Concretes Containing Belite-CSA Cement Cured at Sub-Zero Temperatures

“…Mixes containing OPC:GGBFS (50:50 wt%) and 25 wt% of the AF showed a maximum slump of 20 cm, while the reference OPC concrete showed a minimum of 3 cm, see Figures 5 and 6. The workability was affected by the binder's fineness and incorporated chemical admixtures [49]. Fine binder, in conjunction with chemical admixtures, adheres more to As shown in Figure 4, the paste OPC:GGBFS:CSA (0:80:20) had a very low ultimate hydration peak despite the presence of the CSA cement.…”

“…The used belite-CSA cement contained 25 wt% of belite (C 2 S), Ye'elimite (C 4 A 3 Ŝ) content over 60 wt%, and calcium sulfate (C Ŝ) at 10 wt%. Consequently, the strength gain could be attributed to the formation of more C-S-H/C 2 ASH 8 and Portlandite but a limited formation of AFt phases [40,49]. Furthermore, relative to the CSA (100%) concrete, the binary blend OPC:CSA (80:20) showed lower strength at all ages except at 1 day.…”

“…The high early age strength was related to the rapid dissolution and accelerated hydration rate due to the co-existence of two types of cement and, consequently, the rapid formation of ettringite crystals [54]. However, these overlapping ettringite deposits on the C-S-H particles over time caused an adverse effect on the microstructure by the occurrence of microcracks [49,54].…”

“…The formed hexagonal-shaped thin ettringite plates filled the pore system, consumed excess pore moisture, prevented the large-size ice crystals, minimized the risk of frost damage, and further densified the binder matrix [11,47]. Furthermore, instead of C-S-H and portlandite, the presence of gibbsite in OPC-CSA systems promoted the synthesis of strätlingite (C 2 ASH 8 ) and portlandite via its interaction with alite (C 3 S) [48,49]. On the contrary, the belite-rich CSA as the sole binder promoted only the strätlingite (C 2 ASH 8 ), characterized as slow strength development on reaction with belite (C 2 S) and gibbsite (AH 3 ) [50].…”