{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,30]],"date-time":"2026-09-30T19:38:35Z","timestamp":1790797115734,"version":"4.1.0"},"reference-count":42,"publisher":"MDPI AG","issue":"2","license":[{"start":{"date-parts":[[2026,1,7]],"date-time":"2026-01-07T00:00:00Z","timestamp":1767744000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["201938"],"award-info":[{"award-number":["201938"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Science and Technology Progress and Innovation Program Project of the Hunan Provincial De-partment of Transportation","award":["201938"],"award-info":[{"award-number":["201938"]}]},{"name":"Scientific Research Project of the Hunan Provincial Department of Education","award":["20B010"],"award-info":[{"award-number":["20B010"]}]},{"name":"Open Fund for Changsha University of Science and Technology Bridge Engineering","award":["15KC03"],"award-info":[{"award-number":["15KC03"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Alkali-activated cementitious materials are environmentally friendly alternatives to traditional cement. The structure of their core product, sodium aluminosilicate hydrate (N-A-S-H) gel, is regulated by the silicon-to-aluminum (Si\/Al) ratio; however, the atomic-scale mechanism underlying this influence remains unclear. Integrating reactive force field molecular dynamics simulations and experiments, this study systematically reveals the regulation mechanism of the Si\/Al ratio (1.0\u20132.0) on the microstructure and macroscopic properties of N-A-S-H gels. Starting from well-defined PS and PSS oligomers, the simulation results demonstrate that the Si\/Al ratio governs the polymerization pathway, aluminum coordination environment (especially the content of pentacoordinate aluminum), and evolution of nanoporosity. When the Si\/Al ratio is approximately 1.8, the system exhibits the highest silicate polymerization degree, lowest nanoporosity, and densest three-dimensional (3D) network structure; deviation from this ratio leads to structural degradation due to charge imbalance or excessive polymerization. These computational findings are validated by experiments on fly ash-based geopolymers: the material achieves the highest compressive strength at a Si\/Al ratio of 1.8. The consistency between simulations and experiments collectively reveals a cross-scale action mechanism: the Si\/Al ratio determines the macroscopic mechanical properties by regulating the nanoscale packing density and defect distribution of the gel. This study provides critical atomic-scale insights for the rational design of high-performance geopolymers.<\/jats:p>","DOI":"10.3390\/ma19020246","type":"journal-article","created":{"date-parts":[[2026,1,7]],"date-time":"2026-01-07T14:02:51Z","timestamp":1767794571000},"page":"246","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":9,"title":["The Governing Role of Si\/Al Ratio in the Structural Evolution and Mechanical Properties of N-A-S-H Gel"],"prefix":"10.3390","volume":"19","author":[{"given":"Min","family":"Hu","sequence":"first","affiliation":[{"name":"School of Civil and Environmental Engineering, Changsha University of Science and Technology, Changsha 410114, China"},{"name":"Hunan Provincial Engineering Research Center for Bridge Engineering Safety Control Technology and Equipment, Changsha 410114, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jiayun","family":"Chen","sequence":"additional","affiliation":[{"name":"School of Civil and Environmental Engineering, Changsha University of Science and Technology, Changsha 410114, China"},{"name":"Hunan Provincial Engineering Research Center for Bridge Engineering Safety Control Technology and Equipment, Changsha 410114, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Bo","family":"Xia","sequence":"additional","affiliation":[{"name":"School of Hydraulic and Ocean Engineering, Changsha University of Science and Technology, Changsha 410114, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jiejin","family":"Chen","sequence":"additional","affiliation":[{"name":"School of Civil and Environmental Engineering, Changsha University of Science and Technology, Changsha 410114, China"},{"name":"Hunan Provincial Engineering Research Center for Bridge Engineering Safety Control Technology and Equipment, Changsha 410114, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,1,7]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Qaidi, S., Najm, H.M., Abed, S.M., \u00d6zk\u0131l\u0131\u00e7, Y.O., Al Dughaishi, H., Alosta, M., Sabri, M.M.S., Alkhatib, F., and Milad, A. 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