The influence of type and combination of polycarboxylate ether superplasticizer on the mechanical properties and microstructure of slag-silica fume ternary blended self-consolidating concrete

It is a common practice to blend various kinds of chemical admixtures during concrete fabrication in order to achieve desired properties of concretes. Nevertheless, there were limited experimental works reported on the influence of such activity on the properties of the concrete composite, particularly along with the blended cement concrete. Therefore, an experimental investigation was conducted to examine the effects of the type and combination of polycarboxylate-based (PCE) superplasticizer with different chemical structures on the properties of the high performance self-consolidating concrete (HPSCC) utilizing supplementary cementitious materials such as Ground Granulated Blast Furnace Slag (GGBS) and Densified Silica Fume (DSF). The drying shrinkage and mechanical performances in terms of mechanical strength, bulk density of the HPSCC were evaluated. Also, the influences of PCE on the morphology of hydrate products and the microstructure development of HPSCC were examined with the aid of the Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) technique. The results showed that the use of methoxy polyethylene glycols (MPEG) and isoprenyl polyethylene glycols (TPEG) PCE as a single chemical has a similar beneficial effect on most of the mechanical properties of the HPSCC, but increasing the drying shrinkage strain. On the other hand, the use of blended MPEG and TPEG PCE imposes an opposite effect on the mechanical properties and the drying shrinkage of the HPSCC compared to another two PCE series. This was due to the formation of both foil-like and fibril-like C-S-H bonds that weakens the C-S-H network's strength in the microstructure of concrete with such combination of PCE. Thus, the combination use of different types of PCE superplasticizers in the production of HPSCC was not encouraged due to the adverse results observed in terms of mechanical properties of concretes.