It is interesting to note that while fly ash cement mortar (without CNTs) is lower in density compared to the control PC mortar at all ages, the fly ash mortar with CNTs was found to be significantly denser (2.29 g/cm3 at 28 day) than the corresponding fly ash mix without CNTs (2.19 g/cm3 at 28 day) and is also higher than that of PC control (2.23 g/cm3 at 28 day).