Long term carbonation depth assessment of clinker-reduced binder mortars and its relation to water-binder ratio

The study comprehensively describes the impact of limestone addition on key durability performance indicators of binary and ternary clinker-reduced binder (CRB) in mixtures made from ordinary Portland cement (C), ground limestone (L) and ground granulated blast furnace slag (S). They were exposed to carbonation under CO2 concentrations of 0.04 vol% and 2 vol% at two different water/binder ratios. Finally, it is proved that limestone as a clinker substitute may be considered as an effective part of the multi-component binder and defined by an adjusted water to effective binder ratio (w/beff, with a k-factor of kL=0.15). The relationships obtained between w/beff and key performance indicators such as compressive strength, capillary porosity, air permeability and carbonation-related parameters are elucidated. Carbonation is found to be primarily governed by the degree of clinker replacement, the CO2 buffer capacity (w/CaOr) and capillary porosity, which can be correlated very accurately with w/beff. In addition, the minimum cover thickness (XCmin) of each mortar mix is estimated using the fib model code 2010, where the corrosion rate of steel after depassivation by carbonation is considered by partial safety factors (PSF) in relation to the environmental exposure classes (XC3 and XC4). XCmin assessment of investigated mortar mixtures shows the new way of predicting long-term carbonation depth by w/beff. The w/beff ratio with a k-value of kL= 0.15 for L proves to be an appropriate design criterion for assessing the carbonation resistance of CRB mixtures.