THE INFLUENCE OF FLY ASH ADDITIONS ASSOCIATED WITH POLYCARBOXYLATE SUPERPASTICIZER ON THE MAIN PROPERTIES OF PORTLAND CEMENT PASTES AND MORTARS

The paper provides information regarding the influence of fly ash additions - alone or associated with polycarboxylate type superplasticizer - on the main physical and mechanical properties of pastes and mortars containing Portland cement CEM I 52.5 R. Fly-ash, from Govora plant, was used as addition in blended cements, in quantities of 10% up to 50%. The superplasticizer was of polycarboxylate type - CHRYSO Fluid Premia 180 (solution containing 21.5 +/- 1.0% active substance). The superplasticizer was dosed at a ratio of 0.9% (with reference to cement). Information of the influence of the fly ash addition, associated with superplasticizer, on the physical properties of cement pastes were obtained by the assesment of water for normal consistency and setting time. The hardening processes of cement mixed with different amounts of fly ash associated with polycarboxylate type superplasticizer, were evaluated by the assessment of mechanical strength, on the mortar specimens with binder/sand = 1/3 and water to binder ratios in order to ensure a similar workability for mortars without and with superplasticizer. The increase of fly-ash addition determines a continous increase of water for standard consistency (32.2%-37.6%). Polycarboxylate superplasticizer addition (0.9%) significantly reduced the values of the water for standard consistency, at levels between 22% and 28%, for cement containing 10 - 50% fly ash. The increase of fly ash amount increases the setting time, but for the pastes with 0.9% polycarboxylate additive this retarding effect is dimished. Mechanical strengths of the mortars based on cements with fly ash decreased, while the content of fly ash increased. The decrease of mechanical strengths was less important for the cements containing fly ash and 0.9% polycarboxylate superplasticizer, in correlation with the smaller water/binder ratio. Thus, for the binder with 30% fly ash and 0.9% superplasticizer, the compressive strengths were higher as compared with the ordinary Portland cement.