The impact of a calcined clay (CC) rich in meta kaolin (~50 wt%) present in composite cements at 0–40% substitution rate for the clinker was studied relative to the dispersing force of different PCE superplasticizers. It was found that CC increases the water demand of the blended cements considerably (+85% for the 60:40 blend vs. neat OPC). Furthermore, PCEs which fluidize OPC best also provide optimal performance in CC blended cements, but require much higher dosages (in OPC/CC 60:40, 4–6 times as compared to neat OPC). In all systems, HPEG-PCE produced superior dispersing performance over anionic MPEG-PCEs. A mechanistic study involving zeta potential measurements revealed that the initially negatively charged calcined clay surface adsorbs huge amounts of Ca2+ ions from the pore solution, thus facilitating adsorption of anionic PCE superplasticizers. The results signify that commercially available PCE products can effectively fluidize OPC/CC blended cements. •Cements containing 0–40 wt% of a calcined clay rich in meta kaolin were studied.•The calcined clay decreases fluidity of the blended cements considerably.•In cement, the calcined clay adsorbs a large amount of Ca2+ ions.•A common HPEG polycarboxylate superplasticizer fluidizes OPC/CC blends best.•A zwitterionic PCE also fluidizes well and adsorbs in similar amounts as HPEG.