Choosing a binder for reinforced concrete in a chloride environment raises a question that a strength result alone cannot settle. How does the cover concrete influence the steel’s exposure and electrochemical response over time? Wioletta Raczkiewicz, Kamil Bacharz and Albert Grajek addressed part of that question in a peer-reviewed laboratory study comparing two mixes at Kielce University of Technology.
What the authors tested
The researchers compared blast-furnace cement CEM III and composite cement CEM V while holding the other mix proportions constant. For the corrosion measurements they cast 24 reinforced prisms, 12 per mix. Each measured 100 × 100 × 280 mm, with one 8 mm reinforcing bar and 25 mm cover. The four exposure groups per mix contained three prisms each.
The groups comprised laboratory controls, full immersion in 3% sodium chloride for 37 days, and two groups subjected to 100 freeze–thaw cycles under full or partial immersion in the same solution. The team measured corrosion current density, stationary steel potential and concrete cover resistivity using the galvanostatic pulse method. Separate specimens were used to investigate properties including strength, shrinkage, water absorption and freeze–thaw performance.
What the measurements showed
In the immersion-only group at the second measurement stage, corrosion current density ranged from 1.94 to 3.79 µA/cm² for the CEM III mix and from 1.62 to 2.03 µA/cm² for the CEM V mix. The ranges overlap. The authors nevertheless found generally lower current densities for the CEM V mix across their programme and interpreted the results as evidence of better protection under the conditions tested.
The results also depended on when the specimens were measured. At the initial stage, CEM V readings were more variable and included higher values than those for CEM III. The authors discuss continuing hydration and young concrete’s moisture condition as factors that can affect the electrochemical response. They caution against taking cover resistivity measured at this age as a straightforward indicator of future performance.
The reported mean cube strengths were 46.3 MPa for CEM III and 53.7 MPa for CEM V. Separate shrinkage testing found about 32% lower mean shrinkage for CEM V at the end of the 130-day measurement period. These are results for the two formulations and test regimes in the paper. Strength and shrinkage provide context for the comparison, while corrosion measurements address a different aspect of performance.
How far the evidence transfers
Holding the other proportions fixed makes the comparison informative for these two formulations. Comparing the same mixes across several exposures also reveals why a single immersion result is an incomplete description. But with three prisms per mix in each exposure group, individual specimens can have a large influence on the reported range. Measurements at two points on each prism provide local information and do not double the number of independent specimens.
The current density is an electrochemical indicator. Turning it into a long-term prediction for a bridge deck, marine pile or retaining wall would require evidence about how the relevant material and exposure evolve over time. Actual structures have variable cover, curing and cracking. They can experience wetting and drying, different temperatures and salt deposition over years. A short accelerated exposure offers a controlled comparison and leaves those longer-term influences unresolved.
The specific cements are another important boundary. A cement designation describes a family of products. Results for the binders and aggregates selected in Poland do not establish how a locally sourced Australian mix with a similar binder description will behave. A different source of supplementary cementitious material, admixture or curing regime can change the comparison the project actually needs to make.
A practical use for the study
Civil Insight’s interpretation is that the paper supports a project-specific trial when a proposed binder change has consequences for exposure performance. Ask the supplier to identify the actual binder and mix proportions, and agree with the designer and asset owner on the properties, ages and exposure conditions that the trial needs to represent. Include the project’s early-age construction constraints as well as its durability objectives. Keep the acceptance decision tied to the applicable project specification and evidence for the mix under consideration.
Original research
Raczkiewicz, W., Bacharz, K. and Grajek, A. (2026). Assessment of the Influence of Environmental Conditions on the Corrosion Rate of Reinforcing Bars in Concrete Made with Two Different Cements. Materials, 19(18), 3998. Published online 20 September 2026. Original peer-reviewed paper, DOI 10.3390/ma19183998
Slump and air-content testing of the two concrete mixes in the study. Wioletta Raczkiewicz, Kamil Bacharz and Albert Grajek, Materials (2026), Figure 1 · CC BY 4.0.
