碱-白云石反应机理与预防

MECHANISM AND PREVENTION OF ALKALI DOLOMITE REACTION

根据颗粒堆积原理计算了碱白云石反应引起的固相框架体积的变化，并用图象分析技术研究了反应产物间的孔隙体积。研究了碱白云石反应机理，从热力学和通过实验分析了溶液ｐＨ值对碱白云石反应程度与速率的影响。通过监测白云岩粉末样压实体和基本不含粘土及石英的白云质灰岩在碱溶液中的膨胀行为，研究了碱白云石反应本身的膨胀性。评估了低碱度的硫铝酸盐水泥对碱白云石反应的抑制作用。结果表明：球形产物如呈最紧密堆积，则固体产物的孔隙率为２５．９５％，碱白云石反应后固相框架体积将增加２９．２３％。实际上，固体产物的孔隙率为１５％，反应后固相框架体积将增加１２．５％，这为反应产生膨胀提供了前提条件。白云石与碱作用生成水镁石、方解石和碳酸碱，该过程能直接引起膨胀。反应和膨胀的速率取决于溶液的ｐＨ值，ｐＨ值越高，反应和膨胀越快，当ｐＨ值低于某一值后，碱白云石反应将不发生，相应地，岩石不产生膨胀。碱白云石反应膨胀的驱动力为去白云化反应生成的方解石和水镁石晶体在受限空间生长产生的结晶压力。硫铝酸盐水泥能有效地抑制碱白云石反应膨胀，从而能防止混凝土的开裂破坏。

The mechanism of alkali dolomite reaction (ADR) was investigated. Dolomite reacts with hydroxyl to form CO 3 2- ions, brucite and calcite. The absolute solid volume of the products of ADR is less than that of the reactant, while the relative volume is larger because there are many voids enclosed in the fine particles of products, resulting in the expansion of concrete containing reactive dolomitic aggregates. The driving force of expansion seems to be the crystallization pressure caused by growth of calcite and brucite crystals formed in a confined space, rather than the swelling of clay minerals within rocks. The increment of relative volume of ADR was evaluated by the principle of the tightest pile of particles and confirmed by using image analytic method. The influences of pH value of solution on the degree and rate of dedolomitization as well as the expansion of reactive dolomitic rock prisms were examined. The results show that the higher the pH value, the larger the degree and the expansion are. It is interested that sulfoaluminate cements instead of Portland cements can effectively suppress the expansion of concrete due to ADR and prevent concrete from cracking in a long period.