Auckland Basalts as a Source of Alkali in Concrete

Chemical leaching techniques based on alkaline complexing solvents were used to determine alkali release from basalts in experimental mortars. Various aggregate grain size fractions from 1 mm to 0.063 mm were incorporated into the experimental mortars. Dissolution kinetics for various cement and aggregate phases in these solvents have been described elsewhere. To allow prediction of the levels of alkali release of a given basalt sample in concrete, a rapid technique of direct leaching of the aggregate, based on the use of 0.3 M lithium hydroxide (LiOH) and 0.3 M tetramethylammonium-hydroxide (TMA-OH), was developed. The basalts were analyzed using hydrofluoric-perchloric acid dissolution and atomic spectrometry (atomic absorption, flame emission, and inductively coupled plasma (ICP) emission spectrometry). X-ray diffraction spectrometry and optical microscopy were used to investigate phase and textural variations between the basalt samples.