NMR-based Analysis on Pore Structure Characteristics Evolution of Alkali-activated Materials Subjected to Sulfate Environments
SONG Yi1, ZHANG Rongling1,2,*, SHI Yinliang1, YANG Yifan1, LIU Yilin1
1 School of Civil Engineering, LanzhouJiaotong University, Lanzhou 730070, China 2 Bridge Engineering National Local Joint Engineering Laboratory of Disaster Prevention and Control Technology, Lanzhou Jiaotong University, Lanzhou 730070, China
Abstract: In view of the reuse of large industrial solid waste and the damage and deterioration of concrete structure in the strong corrosive saline soil area ofNorthwest China, this paper took slag powder and fly ash as precursors, NaOH and sodium silicate as alkali activators to explore the macro-meso performance development and micro-pore structure of alkali-activated cementitious materials with different slag-cement ratios under the coupling effect of repetitive dry-wet alternations-sulfate erosion. Time-varying law based on low-field nuclear magnetic resonance T2 spectrum and fractal theory, and the pore fractal dimension of different pore size regions in the internal pores of alkali-activated cementitious materials were calculated. The change process of microscopic pore distribution of alkali-activated materials with the age of repetitive dry-wet alternations under the erosion environment of sodium sulfate was analyzed and studied. The results showed that the 28 d strengths of all the alkali-activated mate-rials designed in this paper were greater than 42.0 MPa, and exhibited a biphasic (increase → decrease) variation with the progress of repetitive dry-wet alternations-sulfate erosion. The strengths reached their maximum values when the repetitive dry-wet alternations lasted 45 d, and the highest strength (58.4 MPa) was achieved by the material with an ore-cement ratio of 8∶2. After 90 days of repetitive dry-wet alternations, the residual strength ratios of alkali-activated cementitious materials with different mineral ash ratios were greater than 0.95. The pore structures of the three groups of alkali-activated cementitious materials exhibited clear fractal characteristics. The fractal dimensions increased in the order of gel pores, transition pores, capillary pores, and macropores. With the aging of the materials under dry-wet alternations in sulfate erosion, the number of transition pores decreased while the number of capillary pores increased.
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2025, Vol. 39 
