碱硅酸反应与碱碳酸盐反应

Alkali-silica Reaction and Alkali-carbonate Reaction

碱集料反应(AAR)可分为两类,即碱硅酸反应(ASR)与碱碳酸盐反应(ACR)。二者的共同点是与碱发生的化学反应可导致混凝土中集料的体积增大,从而可能使混凝土甚至整个建筑物或构筑物发生膨胀开裂。文章着重从膨胀过程和机理以及岩石的结构特征探讨二者的特性与差异。ASR类型岩石具有碱活性的前提条件是较低的二氧化硅结晶完整度。只有隐晶质、微晶质、玻璃质或发生过应变的二氧化硅才会具有较高的化学活性,导致混凝土破坏。通过系统研究证实,对碱碳酸盐反应,虽然结晶的完整程度以及白云石(CaCO3·MgCO3)分子式中Ca/Mg比也将影响其与碱反应的速率,但起决定作用的是白云石晶体的尺寸及其在岩石中的分布状态和被基质包围的紧密程度。从微观结构得出的这些特征将有助于加深对碱集料反应膨胀机理的认识。文中还介绍了形成活性白云石的地质环境和碱硅酸反应与碱碳酸盐反应的区分方法。

Alkali\|aggregate reaction(AAR)may be divided into two kinds:alkali\|silica reaction (ASR) and alkali carbonate reaction (ACR).The chemical reaction between the reactive aggregate and alkali causes serious expansion and results in the deterioration of concrete structure,which is the common character of both.In this paper,the characteristics and differences between ASR and ACR were discussed in detail from expansive process,mechanism and the structural characteristics of rocks.For ASR,the prime essential is the crystallinity of silica,which causes the rocks to display alkali reactivity.Thus only cryptocrystalline,microcrystalline,glassy and strained silica,cristobalite,tridymite,etc.display high alkali reactivity.The criteria and methodology to determine the crystallinity of silica were described in more detail.Through systematically study,it was proved that for ACR,although the crystallinity of dolomite and the Ca/Mg ratio of dolomite may influence the rate of reaction,the decisive roles are the size of dolomite crystals and the distributions in the matrix and the compact degree of surrounding matrix.These results will help to deeply understand the essential of mechanism of AAR.In addition,the geological conditions of formation of reactive carbonate rock were studied,which will be very beneficial to confirm the distribution of reactive carbonate rocks in a region or in a country.Finally the method for distinguishing ASR and ACR was introduced. [