Effect of sodium sulfate and nano-SiO2 on hydration and microstructure of cementitious materials containing high volume fly ash under steam curing. (28th February 2018)

• Record Type: Journal Article
• Authors: Mei, Junpeng; Tan, Hongbo; Li, Hainan; Ma, Baoguo; Liu, Xiaohai; Jiang, Wenbin; Zhang, Ting; Li, Xin
• Is Part Of: Construction & building materials. Volume 163(2018)
• Page Start: 812
• Page End: 825
• Publication Date: 2018-02-28
• Subjects: Nano-SiO2 -- Sodium sulfate -- High volume fly ash -- Cement -- Hydration -- Pozzolanic reaction -- Pore structure -- Interfacial transition zone; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2017.12.159
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: The synergistic effect of NS and SS on hydration of CHVFA system is found. NS has much stronger effect on refining aperture and promoting the hydration of PC. SS exerts much stronger effect on accelerating the hydration of FA. NS and SS co-doped decrease the Ca/Si ratio and the enrichment degree of CH of ITZ. Abstract: Generally, high volume fly ash would considerably reduce the early strength of cement-based materials, and because of this disadvantage, the added amount of fly ash in steam-cured precast concrete is very limited. In this study, an attempt to enhance the early strength of steam-cured cement-high volume fly ash (40 wt%, CHVFA) system has been done with addition of nano-SiO2 (NS) and sodium sulfate (SS). Effect of these two chemicals on hydration, pore structure, and microstructure of interfacial transition zone (ITZ) were investigated. The results show that both NS and SS can improve the compressive strength, and the reason is mainly because these two chemicals can accelerate the hydration of cement minerals and can also hasten the pozzolanic reaction of fly ash. By contrast, because of the high activity of pozzolanic reaction and the filling and nucleation effects, NS has much stronger effect on refining pore structure and promoting the hydration of cement; while SS can exert much stronger effect on accelerating the hydration of fly ash than that of NS. An interesting thing can also be seen that with co-doped NS-SS, the enhancement in compressive strength is much stronger than that of the sum of these single systems with the same dosage, indicating that NS and SS can exert the synergistic effect; this effect is involved in the accelerated hydration of CHVFA, the refined pore structure, and the improved microstructure of ITZ. Such results would be expected to provide guidance on enhancing the early strength of steam-cured precast concrete with high volume fly ash in practical engineering.