Influence of the Binder on the ASR Expansion of Mortar Bars Immersed in Saturated NaCl Solution

In Denmark, TI-B 51 is used to test the reactivity of sand containing porous flint, but it is also the reference test to document the ASR performance of binders that do not fulfil the requirements on the total alkali content, orto decide on the declared alkali content of a binder.

In TI-B 51, mortar bars are first cured in water for four weeks and then immersed in a saturated NaCl solution at 50 ℃. However, the type of binder affects different properties, such as the chemistry of the pore solution and the ingress resistance to external compounds. The present study investigated these two aspects and intended to address the following question: what is the most influential factor on the TI-B 51 outcome between the free alkali content and the resistance to NaCl ingress?

Three binders were used: 1) a low-alkali OPC, 2) the same OPC with 35 wt.% replacement by fly ash and 3) a composite cement with 35 wt.% clinker replacement by equal amounts of calcined clay and limestone (same clinker as the OPC). Investigations were carried out on mortar bars cast with a highly reactive sand containing porous opaline flint. The experimental program included: TI-B 51 expansions, penetration depths of chloride over time, thin sections and µXRF analyses. In parallel, corresponding paste samples were cast to determine the free alkali metal concentration in the pore solution by Cold Water Extraction.