Chloride ingress testing of concrete

Concrete is recognised as a durable material that can provide long-term protection to embedded carbon steel reinforcement. However, effective protection can only be achieved if the mechanisms of deterioration and the durability properties of the protective material involved are fully understood. A well-known phenomenon is the ingress of chloride ions into concrete, which takes place via the solution-filled pores. These ions, combined with optimum contents of air and moisture, result in reinforcement corrosion, and subsequently, loss in functionality of a reinforced concrete element. Currently, available literature suggests that measurement of chloride ion ingress into concrete can be misleading. Reasons for erroneous measurements include: (i) continuing formation of hydration products resulting in pore refinement/pore blocking and; (ii) chloride diffusion coefficients being commonly applied as the “effective” diffusivity, which does not take into account the effect of chemical binding on the chloride ion transport process. This paper reports the findings of an investigation of different chloride test methods for measuring chloride ingress of concrete, which are currently used. This was undertaken to establish their suitability to measure this intrinsic concrete durability property. Five test methods were selected, covering the two main test method types that currently finding application: (i) electrically accelerated short-term; and (ii) naturally accelerated long-term chloride test methods. Three concrete types of CEM I, PC/FA (20-55%) and PC/GGBS (25-75%) at varying water-cement (w/c) ratios of 0.35, 0.50 and 0.65 were utilised during the investigation. This work has established that whilst all the test methods demonstrated capacities to measure chloride ingress into concrete, operator accuracy is of significant importance.