Supplementary cementing material (SCMs) of domestic resources was used for partial replacement of the Portland clinker in attempt to reduce CO2 emission in the cement production. Replacement of Portland clinker up to 20 wt.% with SCMs in the normal cement has reduced CO2 emission by 0.18 kg CO2/kg cement. Purpose of this research is to improve mechanical strength of portland blended cement made from Portland cement and trass, by mechanical and chemical activations. Portland blended cement were made in the mixture of Portland cement to trass in ratio of 80:20, 70:30 and 60:40%. Trass as natural pozzolan reacts with Ca(OH)2 from cement hydration to form additional calcium silicate hydrates. Study on mineralogy of trass however shows that most of trass contains more crystalline phase of SiO2 rather than the desirable amorphous silica or glassy phase of silica which is naturally reactive. In this research, trass were ground for fineness, represented by the specific surface area, Blaine of 2400 cm2/gr to 8000 cm2/gr or particle size between 10 to 45 um. Polyethylene glycol, PEG was introduced during milling to improve material's grindability as to obtain finer and more dispersed produc