Chloride diffusion in alkali-activated fly ash/slag concretes: Role of slag content, water/binder ratio, alkali content and sand-aggregate ratio. (20th November 2020)

• Record Type: Journal Article
• Authors: Zhang, Jingxiao; Ma, Yuwei; Zheng, Jiazheng; Hu, Jie; Fu, Jiyang; Zhang, Zuhua; Wang, Hao
• Is Part Of: Construction & building materials. Volume 261(2020)
• Publication Date: 2020-11-20
• Subjects: Alkali-activated concrete -- Early age properties -- Natural chloride diffusion tests -- Chloride diffusion coefficient -- Pore structure; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2020.119940
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Chloride resistance was evaluated by natural chloride diffusion test. W/b and slag content significantly impacted chloride transport. Sand-aggregate ratio decided workability instead of Df . Df was related to the threshold pore diameter and pores > 5 nm. Abstract: The widespread application of alkali-activated fly ash/slag (AAFS) concrete requires the satisfaction of a series of performance criteria both from its early age properties (e.g. workability, strength) and long-term stability. In this study, long-term (till 180 days) natural chloride diffusion tests were conducted to evaluate the chloride diffusion in AAFS concretes prepared with different slag content, water/binder (w/b) ratio, alkali content, and sand-aggregate ratio. The results revealed that AAFS concretes obtained in this study were generally regarded as flow/high flow concretes (slump > 100 mm) with compressive strength > 50 MPa at 28 day. The free chloride diffusion coefficient (Df ) of AAFS concretes was between 0.4 and 1.8 × 10 -12 m 2 /s. The slag content and w/b were found as dominant parameters affecting the long-term chloride transport in AAFS concretes, while the sand-aggregate ratio presented a limited effect. The formation of more C-A-S-H gels (by increasing slag content ≥ 50%), and lower w/b (≤0.45) at Na2 O content of ∼ 5% was preferred for AAFS concretes with good workability, strength and durability. MIP results indicated that capillary pores in AAFS reached percolation and became disconnected after 180 days. The long-term chloride diffusivity of AAFS concretes was closely related to the threshold pore diameter and volume of pores > 5 nm. The more larger pores, the higher chloride diffusion coefficient was.