Mechanical and shrinkage characteristics of mortars with mixing water containing high NaCl concentrations

Abstract

In this paper, the mechanical and drying‐shrinkage behaviour of mortars with intentionally NaCl‐added mixing water (over 10 wt%) was examined. Mortars were mixed with tap water and artificial seawater containing NaCl up to 20 wt%, with and without 40 % replacement of cement by ground granulated blast‐furnace slag. Compressive strength was reduced at early ages by the addition of NaCl, but at 28 days the strength of seawater‐based mortars matched or exceeded that of the tap‐water reference, likely due to Friedel's salt and ettringite densifying the pore network. Drying shrinkage was non‐monotonic when NaCl was added to tap water: 3 wt% NaCl increased shrinkage owing to alkali enrichment, whereas at 10 and 20 wt% NaCl shrinkage decreased relative to the 3 wt% mix, attributed to humidity buffering by saturated NaCl precipitation and possibly additional ettringite formation. In seawater‐based mortars (with or without slag), shrinkage remained comparable to or smaller than the tap‐water reference at all NaCl levels.