A carbonation‐resistance study of LC ³ mortars ‐ implications of C‐S‐H nucleation seeding

Abstract

Carbonation threatens reinforced concrete durability by lowering pH, which may promote corrosion. Although clinker replacement with SCM reduces CO ₂ footprint, it may increase carbonation rate due to dilution and pozzolanic consumption of portlandite, reducing buffering capacity. Here, LC ³ mortars were formulated using three commercial calcined clays (two kaolinite‐based and one bentonite‐based). The binder consisted of 52 wt% PC, 30 wt% calcined clay, 15 wt% limestone, and 3 wt% gypsum. Two sets of mortars were prepared with water‐to‐binder mass ratios (w/b) of 0.50 and 0.40 and corresponding sand‐to‐binder (s/b) ratios of 3.00 and 1.78. Mortars were prepared without and with a C‐S‐H seeding admixture to evaluate its effect on strength developments and carbonation resistance performances. Compressive strength and carbonation depth were measured up to 132 days under accelerated carbonation conditions. Compressive strength results showed clear early‐age enhancement due to STE53 addition. After carbonation, strength development remained comparable between seeded and unseeded mortars, although a slight improvement was observed in bentonite‐containing mortars with C‐S‐H seeding. Carbonation depths were slightly lower in seeded samples at 70 days, with minor differences at later ages. As expected, mortars with w/b = 0.40 exhibited much higher carbonation resistance.