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.