A pozzolanic composition for use in Portland cement-based concrete, said composition comprising coal ash combined with a natural pozzolan, wherein said natural pozzolan is present in a concentration of about 1 wt % to about 99 wt %, wherein said coal ash meets a specification for pozzolanic mixtures, pozzolan admixtures, or supplementary cementitious materials in concrete under ASTM and/or AASHTO, wherein said natural pozzolan meets a specification for pozzolanic mixtures, pozzolan admixtures, or supplementary cementitious materials in concrete under ASTM and/or AASHTO, and wherein said pozzolanic composition meets a specification under ASTM and/or AASHTO for pozzolanic mixtures, pozzolan admixtures, or supplementary cementitious materials in concrete.