DIN 1164-10 defines the characteristic “low effective alkali content” in simplified form as the total alkali content and, if applicable, on the basis of the slag content. VDZ intends to develop a testing and assessment system based on a new approach to better reflect the cements’ material characteristics. Assessment criteria will be derived from pore solutions expressed from hardened cement paste as well as from the experiences gained with different concrete compositions stored in an outdoor exposure site and tested in ASR performance testing. In certain cases, concrete constructions with alkali-reactive aggregates can achieve sufficient resistance to alkali-silica reaction (ASR) by using cements with low effective alkali content (low-alkali cement). So far, the simplified classification of total alkali content does not fully, if at all, account for the effect of various blastfurnace slags and other cement main constituents like limestone (LL) having on the cement’s effective alkali content.
Aim of the research project
The IGF project 19295 N intends to devise a testing and assessment system that better reflects the cements’ material properties. To do so, assessment criteria will be derived for cements in various applications – with and without external alkali supply – and in combination with aggregates of various alkali reactivity (e.g. to include criteria for moderately alkali reactive aggregates, potentially class E II-S)
Derivation of assessment criteria
CEM I low-alkali cements, road pavement and laboratory cements of different composition will be examined by means of pore solution expression test and bleeding solution test. The result is reflected by the hydroxide ion concentration of the extracted pore solution and the bleeding solution above the hardened cement paste with a water/cement-ratio of 1.00; these are then used to assess the effective alkali content of the cement.
The hydroxide ion concentrations are compared with the results of laboratory concrete testing (ASR performance tests) and the concrete tests with outdoor exposure (see figure above) that have been conducted over the last forty years. Together, this forms the basis for proposals regarding assessment criteria for cement’s effective alkali content.