A fast testing method for discriminating hardened cement paste reactivity with external sulphate

Civil engineering structures exposed to external sulphate are widely encountered in the world. Usual laboratory experiments used to characterize sulphate attack require long periods of time (e.g., for months). We have adapted a test already available in the literature: ground compacted materials placed in an oedometric cell are flushed with a sodium sulphate solution. The test was optimized by injecting a stoichiometric amount of sulphate in a single injection, whose duration and flow rate are controlled. We first analyzed the testing method in terms of permeability before and after compaction, of expansion behavior after sulphate injection, and of sulphate uptake during injection. Experimental results showed that the amount of sulphates retained in the sample is correlated to the duration of the injection. Reactive transport calculations simulating the injection/expansion periods highlighted the significance of mechanisms occurring at different time scales: flow of water, sorption of sulphate on C-S-H, and formation of secondary ettringite and diffusion of sulphate within the compact. Eventually, expansions of various cement pastes (namely, CEM I, CEM I + 20% limestone filler and CEM-III/C) correlate with results obtained on stress-free concrete samples made of those same paste. This testing strategy is promising to discriminate the sensitivity of various cements to sulphates with a laboratory experiment lasting on the order of a week.