EFFECTIVENESS OF POZZOLAN IN PREVENTING EXPANSION DUE TO ALKALI-AGGREGATE REACTION AND ITS MECHANISM

1.灰岩对碱硅膨胀的抑制作用在很大程度上取决于灰岩和活性骨料的类型、孔隙溶液的碱浓度和灰岩在砂浆中的含量。因此，所有火山灰对碱-硅膨胀的影响都不能用某种机制来完全解释。在以白烷蛋白石为反应骨料制成的砂浆中，如果用粉煤灰或日本高炉炉渣代替水泥的量分别大于25%或60%（重量比），则可以防止碱-硅膨胀。日本粉煤灰或高炉炉渣防止碱-硅膨胀的能力与它们的加入降低了孔溶液中的碱度有关。除降低孔隙溶液中的碱度外，还有一些因素似乎与掺入一些火山灰石来防止或减少碱-硅反应引起的膨胀有关。添加相对少量的硅灰有望防止碱硅膨胀，因为它的高火山灰活性被发现可以增强砂浆的膨胀。这种膨胀的增强是由于硅灰砂浆中形成的凝胶的软化延迟。

1.THE EFFECT OF POZZOLAN ON THE PREVENSION OF ALKALI-SILICA EXPANSION IS FOUND TO LARGELY DEPEND UPON THE TYPE OF POZZOLAN AND REACTIVE AGGREGATE, ALKALI CONCENTRATION OF THE PORE SOLUTION AND CONTENT OF POZZOLAN IN MORTARS. THEREFOR, THE EFFECTS OF ALL POZZOLANS ON ALKALI-SILICA EXPANSION CAN NOT BE TOTALLY EXPLAINED BY ONE OF SOME MECHANISMS.2.IN THE MORTARS MADE WITH BELTANE OPAL AS A REACTIVE AGGREGATE, IF THE AMOUNT OF CEMENT REPLACED BY FLY ASHES OR BLAST FURNACE SLAGS IN JAPAN IS MORE THAN 25% OR 60% BY WEIGHT, RESPECTIVELY, ALKALI-SILICA EXPANSION CAN BE PREVENTED.PREVENTIVE ABILITY OF FLY ASHES OR BLAST FURNACE SLAGS IN JAPAN AGAINST THE ALKALI-SILICA EXPANSION CORRELATES WITH THE REDUCED ALKALINITY IN PORE SOLUTION DUE TO THEIR ADDITION.3.SOME FACTORS OTHER THAN REDUCED ALKALINITY IN PORE SOLUTION ALSO APPEAR TO BE RELATED TO THE PREVENTION OR REDUCTION OF EXPANSION DUE TO ALKALI-SILICA REACTION BY INCORPORATION OF SOME POZZOLANS.4.ADDITION OF RELATIVELY SMALL AMOUNT OF SILICA FUME WHICH IS EXPECTED TO HAVE A POSSIBILITY OF PREVENTING ALKALI-SILICA EXPANSION FOR ITS HIGH POZZOLANIC ACTIVITY WAS FOUND TO ENHANCE EXPANSION OF MORTARS. THIS ENHANCEMENT OF EXPANSION IS ATTRIBUTABLE TO THE DELAY IN SOFTENING OF THE GELS FORMED IN THE SILICA FUME-BEARING MORTARS.