Alkali activated composite mineral binders. Interfacial transition zone steel-hardened cement paste
Marek Petri
Quarterly No. 3, 2010 pages 276-281
DOI:
keywords: fly ash, granulated blast-furnace slag, alkaline activation, solid, composite mineral binders interfacial transition zone, pull-out effect
abstract Alkaline activation of blended cements containing of slag or/and fly ash is one of the new methods of special binders production. Similarly as in the case of traditional concrete, the interfacial transition zone (ITZ) between cement paste and aggregate or steel strongly influences the mechanical and transport properties of mortar and concrete. This paper presents the results of a mechanical investigation (pull-out test) and microscopic observation of steel-hardened alkali activated cement paste (AAHCP) zone contact. In presented investigation, composite mineral binder consists of: 15% Portland cements CEM I 42, 5, 15% granulated blast furnace slag and 70% fly ash. As alkaline activator, sodium water glass with silicate modulus SiO2/Na2O = 1.5 were used. The two type of samples were prepared, the first for microscopic analyses of ITZ (AAHCP containing commercial steel fibers), and the second (for pull - out test) - concrete cubes (100x100x100) with steel rods (= 6.15 mm, a slight surface) anchorage in matrix. The steel rods were pulled out from concrete matrix with a displace constants displacement velocity 0.5 mm/min. Backscattered electron images (BSE) obtained by scanning electron microscope and EDS microanalyses were used to characterize the ITZ microstructure. Results obtained for the sodium water glass activated mineral composite binder shows, that in the opposite to steel-portland cement paste system, the zone of increased porosity and crystalline Ca(OH)2 layer was no observed. On the point of contact (steel-AAHCP) the dense mixed phase, C-S-H and N-A-S-H were identified. Also were observed the increase of amounts a Fe ions in described contact zone, especially on the binder hydration products side. It can suggest that connection of steel-AAHCP have a chemical character. The analyzing of stress-strain curves in the pulling out process of steel rods, from a concrete made of alkaline activated binder and compared PC concrete matrix confirms this thesis. In the case where AASC were used, the shear strength of the steel AAHCP bond were about twice more high than in the case of compared portland cement concrete.