Effects of load-induced micro-cracks on chloride penetration resistance in different types of concrete

Abstract

Chloride penetration resistance of concrete is one of the key parameters for the durability design of reinforced concrete structures located in chloride-bearing environments. In all the current available durability models, service life is evaluated considering concrete in uncracked conditions, which is rarely found in practice. This work investigates chloride penetration resistance of concrete in uncracked and micro-cracked configurations, evaluated in terms of chloride migration coefficient through non-steady state migration test (Rapid Chloride Migration test). Prismatic specimens were manufactured considering six different concrete types and two different times of curing. In micro-cracked configuration, cracks were obtained with a specifically developed loading procedure. Micro-cracks were characterized at the end of the exposure test, in terms of crack width at the exposed surface and crack depth. Results showed that cracks were 5–70 μm wide and up to 40 mm deep, always causing an increase in chloride penetration, that should be evaluated considering both crack width and crack depth, with respect to sound conditions. The effects on the chloride penetration seemed to be more pronounced on the more impervious concretes.

Effects of cracks on chloride‐induced corrosion initiation and propagation of carbon and stainless steel rebar

“…This is because it depends on concrete cover thickness, on the apparent diffusion coefficient of chlorides through the concrete cover and on the critical chloride threshold ( Cl th ) of the specific steel type. Concrete cover in this study was kept constant, and the influence of the apparent diffusion coefficient was of minor extent, since tests performed on replicate unreinforced specimens characterized by the same geometry, to evaluate the resistance to chloride penetration, showed a good repeatability of results 4 . Cl th , on the other hand, is a statistical parameter characterized by a stochastic nature, and this can induce high variability in corrosion initiation time.…”

“…A displacement-controlled load was applied, to obtain a longitudinal crack in correspondence of the notch (for more info on cracking procedure see Ref. [4]). After demolding and after cracking procedure, all the specimens were moist cured for 7 days in a curing chamber at 20 C and R.H. > 95%.…”

“…The existing regulations and current structural design codes in chloride-contaminated environments provide limitations, only in terms of crack opening at the exposed surface, that are typically in the order of magnitude of several hundreds of microns (e.g., 0.2-0.4 mm in Italian national code 2 ). However, literature on the effects of cracks on chloride penetration in unreinforced concrete, either considering accelerated tests [3][4][5] or more conventional diffusion tests, 6,7 showed that chloride penetration resistance was affected even for small crack width, in the range of micro-cracks (width smaller than 100 μm). A further detrimental effect of cracks could be that corrosion preferentially initiates where crack tip reaches the steel reinforcement, 8 generating a small anode to large cathode ratio, greatly accelerating corrosion.…”

Innovative Calcium Carbonate-Based Products to Repair Cracked Cement Mortars

“…Hairline cracks (microcracks smaller than 0.3 mm) are usually left untreated in common practice due to the difficulty of injecting them with commercial epoxy resins [17]. Nonetheless, microcracks adversely influence the durability of reinforced concrete structures, for instance, the resistance to chloride penetration and related damage [44]. Therefore, compatible consolidants with concrete substrates and having good penetration into microcracks, and reconsolidation ability were tested in the present investigation.…”

Comparative study of probabilistic modeling approaches for chloride ingress in concrete structures with macro‐cracks

“…Experiments with bending cracks showed, that they offer a resistance to chloride penetration, which is directly proportional to d cr . For such cases, additionally, a series layout can be used to obtain composite diffusion coefficients as shown in Figure 10, which has been suggested by Russo et al 46 It must be emphasized that the determination of the diffusion coefficient concerning the composite approach with a parallel and series system is only a suitable predictor for the chloride ingress close to a crack and not for the whole structure. 47 In addition, it must be emphasized that D smeared from the composite approach (Equation ( 9)) is not exactly same as the analytical formula from the composite media theory of Gérard and Marchand 5 (Equation ( 6)).…”