The strong early hydration reaction and short setting time of alkali-activated slag composites limit its practical engineering application. Compared with traditional chemical admixture, organic phosphates show higher efficiency in delaying the hydration rate of alkali-activated slag system. However, there is limited research on the performance of alkali-activated materials modified by different organic phosphonate type, and their modification mechanism is also unclear. In this study, three typical organic phosphonates, hydroxyethylidene diphosphonic acid Tetrasodium (HEDP-4Na), aminotris (methylene phosphonic acid) tetrasodium (ATMP-4Na), and diethylenetriamine penta (methylene phosphonic acid) pentasodium (DTPMP-5Na), were selected to clarify the effect of organic phosphonate type on the properties of alkali-activated slag materials (AASM) and its mechanism under different dosage and alkali content. The results indicate that DTPMP-5Na has the most significant effect on the improvement of fresh properties of AASM, compared to other two types of organic phosphonates. Using 0.3 % DTPMP-5Na can delay the initial and final setting time of AASM by 240 % and 190 % respectively, increase the slump flow by 20 %, and reduce yield stress and plastic viscosity by 57 % and 65 % respectively. This was because DTPMP-5Na has the largest number of monomolecular phosphonic acid groups, which can chelate Ca in AASM, form stable complex and cover the surface of slag particles to prevent further hydration reaction. The phosphonate reduced the hydration rate and increased the surface negative potential of slag particles. The use of phosphonates and the increase in alkali content can significantly enhance the mechanical properties of AASM. Using 0.3 % of ATMP-4Na increased the 28-day compressive and flexural strengths of AASM made with 5 % alkali content by 155 % and 53 %, respectively, compared to the reference AASM with 3 % alkali content. Additionally, the 28-day compressive and flexural strengths of reference at 7 % alkali content increased by 115 % and 12 %, respectively, compared to that at 3 % alkali content. This improvement was mainly attributed to the consumption of organic phosphonates at the early stage, which provides more activation channels for slag later, resulting in a denser structure and improved pore structure of AASM, thus enhancing its long-term mechanical properties. However, with the increase of alkali content, the effect of organic phosphonates in strengthening fresh and hardened properties of AASM decreased. The use of 0.3 % HEDP-4Na increased 28-day compressive and flexural strengths of AASM with 3 % alkali contents increased by 25 % and 27 %, respectively, compared to the reference AASM. Such improvement was limited to 4 % and 19 % for AASM made with 5 % alkali content. This can be attributed to the significant promotion of OH concentration in the system, increasing the yield of hydration products at early age on the surface of slag, and reduced activation channels for slag over the long term. In summary, the use of ATMP-4Na is recommended in AASM, as it can significantly improve the fresh properties of AASM and provide excellent mechanical properties.

中文翻译：

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有机膦酸盐类型对碱激活矿渣基材料性能的影响及其机理


碱激活矿渣复合材料早期水化反应强、凝结时间短限制了其实际工程应用。与传统的化学外加剂相比，有机磷酸盐在延迟碱激活渣体系的水化速率方面表现出更高的效率。然而，对于不同类型有机膦酸酯改性的碱激活材料的性能研究有限，其改性机理也不清楚。本研究选择了三种典型的有机膦酸盐：羟基亚乙基二膦酸四钠（HEDP-4Na）、氨基三（亚甲基膦酸）四钠（ATMP-4Na）和二亚乙基三胺五（亚甲基膦酸）五钠（DTPMP-5Na），阐明了不同用量和碱含量下有机膦酸盐类型对碱激活渣材料（AASM）性能的影响及其机理。结果表明，与其他两类有机膦酸盐相比，DTPMP-5Na对AASM新鲜特性的改善效果最为显着。使用0.3%DTPMP-5Na可使AASM的初凝和终凝时间分别延迟240%和190%，坍落流动度提高20%，屈服应力和塑性粘度分别降低57%和65%。这是因为DTPMP-5Na具有最多数量的单分子膦酸基团，可以螯合AASM中的Ca，形成稳定的络合物并覆盖炉渣颗粒表面，阻止进一步的水化反应。膦酸盐降低了水化速率并增加了炉渣颗粒的表面负电势。膦酸盐的使用和碱含量的增加可以显着增强AASM的机械性能。使用 0。与碱含量为 3% 的参考 AASM 相比，3% ATMP-4Na 使碱含量为 5% 的 AASM 的 28 天抗压强度和弯曲强度分别提高了 155% 和 53%。此外，与 3% 碱含量相比，7% 碱含量的参考品的 28 天抗压强度和弯曲强度分别增加了 115% 和 12%。这种改善主要归因于早期有机膦酸盐的消耗，为后期炉渣提供了更多的活化通道，导致AASM的结构更加致密，孔结构得到改善，从而增强了其长期力学性能。然而，随着碱含量的增加，有机膦酸盐对AASM新鲜和硬化性能的增强作用减弱。与参考 AASM 相比，使用 0.3% HEDP-4Na 使碱含量为 3% 的 AASM 的 28 天抗压强度和弯曲强度分别增加了 25% 和 27%。对于碱含量为 5% 的 AASM，这种改进仅限于 4% 和 19%。这可归因于系统中 OH 浓度的显着提升，增加了炉渣表面早期水化产物的产率，并减少了炉渣长期的活化通道。综上所述，推荐在 AASM 中使用 ATMP-4Na，因为它可以显着提高 AASM 的新鲜性能并提供优异的机械性能。