Title: Durability of lkaline Portland Cement Concrete Made With Alkali-Reactive Aggregates

Author(s): P. V. Krivenko, N. M. Mhitaryan, V. V. Chirkova and E. P. Zgardan

Publication: Symposium Paper

Volume: 170

Issue:

Appears on pages(s): 587-596

Keywords: Alkalies; alkali-silica reactions; durability; microhardness; portland cement; rocks.

DOI: 10.14359/6843

Date: 7/1/1997

Abstract:
The paper presents the results of a study on the durability of alkaline portland cement concrete made with potentially alkali reactive aggregate. An alkaline portland cement, into which alkaline component was introduced by 3 methods, namely: - in a form of easily dissolvable active compounds of alkali metals creating an alkaline reaction in dissolving; -in a form of insoluble alkali-containing compounds that are themselves feldspar rocks containing 10-20 % by mass of alkali metal oxides (feldspar, nepheline, mariupolite), and - combined method (feldspar rock was ground with 25-50 % by mass clinker and a resultant blend was mixed with a solution of active alkaline compound), and andesite (alkali-reactive aggregate) and granite (reference) were used. The assessment of durability of the concrete was done by measuring variations in strength, volume, microhardness in a contact zone cement paste- aggregate and phase transformations. It was established, that corrosion of alkali-reactive aggregate while hardening of concrete is associated with structure forming processes in a contact zone that are directed at formation of alkaline and alkaline-alkali-earth aluminosilicate hydrate compounds. The formation of the latter initiates the binding of the alkaleis that were introduced into the cement and released during destruction of feldspar rocks and corrosion of aggregate. These processes take place at the highest rate when an alkaline component is introduced by the combined method. In this case, an active alkaline component introduced together with water initiates the destruction processes, and feldspar rocks are the crystallization centers of hydrate formations. These processes result in the formation of a dense shell around aggregate grains, this shell having width of 50 um and microhardness of up to 5200 MPa. A value of volumetric changes, when andesite aggregate is used, remains at a level of that of granite aggregate, and concrete strength increases with time testifying to its long-term durability.