镁离子对混凝土酸雨侵蚀破坏历程的影响

Influence of Magnesium Ion on Damage Process of Concrete by Acid Rain Attack

配制4种不同Mg^2+含量(0mol/L,0.005mol/L,0.015mol/L和0.025mol/L)的模拟酸雨溶液(pH=3.5),采用干湿循环加速腐蚀实验研究了酸雨中Mg^2+对混凝土轴心抗压强度和静压弹性模量在上述模拟酸雨环境下损伤退化规律的影响。结果表明:混凝土在酸雨侵蚀持续作用下,其轴心抗压强度和静压弹性模量损伤演化规律为短暂上升、缓慢下降、加速下降和临近破坏急速下降4个阶段。Mg^2+明显加速了混凝土酸雨侵蚀破坏进程,缩短了混凝土轴心抗压强度和静压弹性模量在酸雨侵蚀各阶段的保持时间,且Mg^2+含量越大越明显。微观测试分析表明Mg^2+加速混凝土酸雨侵蚀破坏主要源于酸雨中Mg^2+的侵入会进一步降低混凝土孔隙溶液的pH值,从而导致混凝土水泥水化产物C-S-H、C-A-H、AFt等进一步加速溶蚀分解破坏所致。

Four simulated acid rain solutions(pH=3.5)containing different Mg^2+ concentrations of 0 mol/L,0.015 mol/L,0.025 mol/L and 0.035 mol/L,respectively,were prepared.The influence of Mg^2+ content in acid rain on the damage evolution laws of axial compressive strength and static elastic modulus of concretes under the above-mentioned simulated acid rain solutions and were investigated through wetting-drying cycle accelerated corrosion tests.The results show that the axial compressive strength and static elastic modulus of concretes under the sustaining action of acid rain attack successively undergo transient rise stage,slow fall stage,accelerated fall stage and rapid fall stage.Mg^2+ in acid rain solutions obviously accelerates the damage processes of concrete due to acid rain attack and shortens the holding period in each phase of acid rain attack on concrete.Moreover,the effects become more obvious with the increase of Mg^2+ content in acid rain solutions.The results of microscopic tests analysis demonstrate that the damage degradation acceleration of concretes by Mg^2+ in acid rain is owing to that the invasion of Mg^2+ into concrete can lower concrete pore solutions alkalinity,resulting in the quicker decomposition damage of such as calcium silicate hydrate gel and ettringite on cement hydrates.