Cl-渗透和碱集料反应作用下纳米混凝土的耐久性

Durability of concrete with nano-particles under the influence of both Cl- penetration and alkali aggregate reaction

摘要:

海洋环境下,氯离子(Cl^-)渗透和碱集料反应是影响混凝土耐久性的重要因素.为此,在普通海工混凝土中掺加适量纳米SiO₂或纳米Al₂O₃,研究纳米混凝土在Cl^-渗透和碱集料反应共同作用下的耐久性.结果表明:Cl^-渗透和碱集料反应两种因素对混凝土耐久性的影响是相互促进的.不同掺量的纳米SiO₂或纳米Al₂O₃可以不同程度地抑制混凝土的Cl^-渗透和碱集料反应,提高混凝土在两种因素共同作用下的耐久性,纳米SiO₂和纳米Al₂O₃在混凝土中的最优掺量均为2.0%.Cl^-总质量分数趋于平衡时,纳米SiO₂混凝土和纳米Al₂O₃混凝土的Cl^-总质量分数分别降低18.04%和11.60%；在第39周时,纳米SiO₂混凝土和纳米Al₂O₃混凝土的膨胀率分别降低28.75%和16.87%.纳米颗粒的加入能够改善混凝土的孔结构,提高混凝土的抗Cl^-渗透性,抑制Friedels盐的产生,从而减少混凝土的膨胀；此外,纳米颗粒能够促进水泥二次水化,降低过渡区Ca(OH)₂晶体的富集程度,阻碍CaCl₂的络合物产生和碱集料反应所需碱环境的形成.

Abstract:

In marine environment, chloride-ion (Cl^-) penetration and alkali aggregate reaction are important factors affecting the durability of concrete. In this paper, an appropriate amount of nano-SiO₂ or nano-Al₂O₃ was added to ordinary marine concrete to study the durability of concrete with nano-particles under the combined influence of Cl^- penetration and alkali aggregate reaction. The experimental results showed that Cl^- penetration and alkali aggregate reaction promoted the durability of the concrete mutually. Nano-SiO₂ or nano-Al₂O₃ of different amounts could inhibit the Cl^- penetration and alkali aggregate reaction of concrete to different degrees so that the durability of the concrete under the interaction of the two factors was improved. The optimum amount of nano-SiO₂ and nano-Al₂O₃ in concrete was both 2.0%. When the total content of Cl^- in concrete was basically stable, the total amount of Cl^- in concrete with nano-SiO₂ or nano-Al₂O₃ was decreased by 18.04% and 11.60%, respectively. In the 39th week, the expansion rate of concrete with nano-SiO₂ or nano-Al₂O₃ was reduced by 28.75% and 16.87%, respectively. The addition of nano-particles could improve the pore structure of concrete, enhance the Cl^- penetration resistance of concrete, inhibit the generation of Friedel’s salt, thereby mitigating the expansion of concrete. Additionally, nano-particles can promote secondary hydration of cement, reduce the aggregation degree of Ca(OH)₂ crystal in the transition zone, and restrain the formation of CaCl₂ complex compound and alkaline environment required for alkali aggregate reaction.