IGNIMBRITE POWDER AND SOME OTHER POZZOLANAS ADDITIONS TO AVOID CONCRETE EXPANSION CAUSED BY THE ALKALI SILICA REACTION Cement-Wapno-Beton, Vol. XVIII/LXXX, 2013, No 2, p. 100 Ignimbrite is a soft volcanic rock which was generally used in historical buildings and as an plaster of contemporary buildings. In this study the effect of ignimbrite, perlite, pumice and zeolite powders addition on the mortars expansion caused by the alkali-silica reaction was investigated. The accelerated mortar bars test was applied according to ASTM C 1260. Ordinary Portland cement was replaced by aforementioned powders in the quantity: 5, 10, 15, 20, 25, 30, 35, and 40%. The obtained results showed that the length change of mortar bars was decreasing with the increasing content of natural pozzolanas. It was determined that the ignimbrite powder replacing 30% of cement can control the ASR expansion. Moreover, it was found that zeolite powder is the most effective pozzolana to reduce the ASR expansion among other pozzolanas used in this study.