纳米二氧化硅改性磷酸镁水泥砂浆的性能优化与微观机理

Performance Optimization and Microscopic Mechanism of Nano-silica Modified Magnesium Phosphate Cement Mortar

摘要:

以纳米二氧化硅（NS）等质量取代过烧氧化镁（MgO），制备了不同NS掺量（0%~4%）的磷酸镁水泥（MPC）砂浆，系统研究了NS对砂浆性能的影响。结果表明：当NS掺量为4%时，MPC凝结时间较基准组缩短22.7%；在3%掺量下，砂浆标准养护28 d的抗压强度较未掺NS组提升29.9%；浸水养护（7 d标准+28 d浸水）后，掺3%NS的砂浆表现出最优耐水性，其抗压与抗折强度保留率分别达1.170和1.023。微观分析表明，NS通过双重机制优化MPC砂浆性能：其一，纳米颗粒有效填充材料孔隙，提升微观致密度；其二，NS参与二次水化反应生成M-S-H凝胶，在孔隙内部形成致密保护层，从而显著增强耐水性。本研究明确了NS改性MPC砂浆的作用机理，确定3%为最佳掺量，为开发高性能混凝土修补材料提供了理论依据与技术参考。

Abstract:

This study prepared magnesium phosphate cement-nano-silica （MPC-NS） composite mortars with different NS contents （0%-4%） by replacing dead-burned magnesium oxide （MgO） with nano-silica （NS） at equal mass， and systematically investigated the effect of NS on the properties of the mortars. The results showed that when the NS content was 4%， the setting time of the mortar was shortened by 22.7% compared with the reference group； at 3% NS content， the compressive strength after 28 days of standard curing was increased by 29.9% compared with the group without NS addition； after immersion curing （7 days of standard curing followed by 28 days of immersion）， MPC-3NS exhibited the optimal water resistance， with the retention rates of compressive and flexural strengths reaching 1.170 and 1.023， respectively. Microscopic analysis indicated that NS optimized the properties of MPC through a dual mechanism： first， the nanoparticles effectively filled the pores of the material and improved the micro-density； second， NS participated in the secondary hydration reaction to generate M-S-H gel， forming a dense protective layer inside the pores， thus significantly enhancing water resistance. This study clarified the modification mechanism of NS on MPC and confirmed that 3% is the optimal NS content， providing a theoretical basis and technical reference for the development of high-performance concrete repair materials.