ALKALI-SILICA REACTION - PART-2 - THE EFFECT OF CHEMICAL ADMIXTURES

Many aggregates are susceptible to the alkali-silica reaction. Ar a re sult of this reaction, mortar bars and concrete elements containing po rtland cement expand. In order to limit this expansion, chemical admix tures that interfere with the alkali-silica reaction can be introduced into the mixing water: The research discussed below describes holy se veral of these chemical admixtures affect mortar-bar expansion. Mortar bars containing any of several chemical admixtures in the mixing wate r at initial molar-concentrations of 1 or 2 were subjected to ASTM C 1 260 tests. After the expansion rest, samples were prepared from each o f the mortar bars and examined in a scanning electron microscope with EDX capabilities. The following chloride salts and hydroxides were use d: NaOH, KOH, LiOH, NaCl, KCl, LiCl, CaCl2, MgCl2, and AlCl3. For a gi ven initial molar concentration, the expansion rest results indicated that the chlorine salts with monovalent cations were the most damaging , followed by those with divalent and trivalent cations. These results are in agreement with a theoretical model presented in a previous pap er that explains the volume change behavior of the reaction product ge ls. This model attributes the swelling of the reaction product gel to double-layer repulsion forces.