This paper reports a systematic attempt of preparing concentrated aqueous suspensions (up to 0.3 wt.%) of different types of carbon nanotubes (CNTs) using Pluronic F-127 for developing ductile cementitious composites. Single-walled and multi-walled nanotubes, both pristine and functionalized, were dispersed in water using a short (1 h) and medium energy (80 W) ultrasonication process using pluronic at high concentrations (above critical micelle concentration, 1–5 wt.%) and also using sodium dodecylbenzene sulphonate (SDBS) for comparison purpose. The CNT suspensions were characterized for agglomerate area, particle size, zeta potential, extractability and long-term storage stability for a period over 4 years. The optimum suspensions were used to fabricate cementitious composites and their fracture behavior was characterized. Experimental results suggested that the optimum pluronic concentrations (1% for 0.1% CNT, 5% for 0.2% and 0.3% CNT, all in weight percent) provided highly homogeneous CNT dispersion with very low area of agglomerates. The best dispersion quality was obtained with f-SWCNT/pluronic system, which provided very low agglomerate area (< 0.5%), lower CNT bundle size, good quantity of well dispersed nanotubes (up to 50%) and excellent long term storage stability. Cementitious composites fabricated using SWCNT and f-SWCNT suspensions showed ductile fracture behavior and improvement in fracture energy up to 164%.