Chloride ion penetration

On the other hand, pit initiation which is the necessary precursor to propagation, is less well understood but is probably far more dependent on metallurgical structure. A detailed discussion of pit initiation is beyond the scope of this section. The two most widely accepted models are, however, as follows. Heine, etal. suggest that pit initiation on aluminium alloys occurs when chloride ions penetrate the passive oxide film by diffusion via lattice defects. McBee and Kruger indicate that this mechanism may also be applicable to pit initiation on iron. On the other hand, Evans has suggested that a pit initiates at a point on the surface where the rate of metal dissolution is momentarily high, with the result that more aggressive anions... 

Mixture series Batch no. W/C + S S/C + S Density at 1 day (kg ComfwessiVe strength (MPa) Flexure strength[ (MPa) Modulus of Elasticity (CPa) Chloride-ion penetration (Q... 

Fig. 7.5 Schematic representation of pit initiation by chloride ion penetration into passive film. Source Ref 6...

Mixed ethoxylate/propoxylates have also been prepared by the use firstly of ethylene oxide followed by that of propylene oxide. It has been claimed that the addition of such polycondensates to cement compositions extends their life through prevention of carbonation, and of both water and chloride ion penetration (ref. 23). 

M. A. Sanjuan, Several years Study on chloride ion penetration into concrete exposed to Atlantic ocean water , Proc. 2nd int. Rilem Workshop Testing and Modelling the Chloride Ingress into Concrete,... 

The alkaline nature of the environment surrounding the reinforcement steel rods embedded in the concrete matrix passivates the steel however, corrosion attack takes place when chloride ions penetrate into them from the seawater and other surroundings [64, 65]. The other ions like sulfate and carbonate ions also enhance the possibility of corrosion of the steel rods. Cathodic protection of such steel rods can be classified into two categories the surrounding of the steel rod is the only concrete environment and the other is any medium encountered by the structure. 

Method of test for chloride ion penetration depth of polymer-modified mortar... 

Figure 7.8 Polynicr-ccmcnt ratio vs. chloride ion penetration depth and carbonation depth of epoxy-modified mortars without and with hardener.

In another study, Ogawa et al. (2005) studied the chloride ion penetration resistance of beams made with ordinary concrete and HPFRCC. In their study, 8-mm-thick HPFRCC plates were cast. A 100 X 100 X 400 mm mold was built from the cut pieces of the 8-mm-thick HPFRCC plates. Ordinary concrete was poured into this mold. An ordinary concrete specimen of the same size was also prepared. Both specimens were cured under water for 38 days and were soaked in artificial seawater containing 1.8% chloride ion concentration for 30 and 60 days. Test results showed that... 

FGC beam specimen, FGC-2, lost an estimated 6.6% of its steel reinforcement. Specimen FGC-3 (the second FGC specimen), on the other hand, took about 141 days to reach the target 10% calculated steel loss. It was also observed that an FGC beam takes about 70% more time to achieve the same level of induced steel loss compared to an ordinary Portland cement concrete (OPCC) beam (Figure 6.16). The longer time required by specimen FGC-3 to reach the same level of calculated steel loss as ordinary concrete RC beam is probably due to the higher resistance of the DFRCC material to chloride ion penetration as well as the smaller width of the multiple cracks (or lower permeability) of DFRCC and the... 

ASTM C1202 (1991). Standard Test Method for Electrical Indication of Concrete s Ability to Resist Chloride Ion Penetration. American Society of Testing and Materials, West Conshohocken, PA. 

At variable conditions applied in the second method mentioned above, the samples in the form of elongated cylinders or cubes, immersed in the chloride solution are examined. All the surfaces of samples, beside of the one, ate sealed to prevent the chloride ions penetration. Only one surface is thus subjected to the penetration of chlorides. 

The lowering of w/c ratio and addition of silica fume are the most often applied methods in order to eliminate the negative effect of the interfacial transition zone. There is a common opinion that the high performance concretes have considerably reduced chloride ions penetration and higher resistance to the attack of corrosive solutions. 

In the presence of chloride ions passivation of steel needs higher pH value. Several hypotheses were proposed to explain the mechanism of passive film destmction in the presence of chlorides [342]. Possibility of chloride ions penetration to passive film, the effect of electric field generated around the adsorbed chloride ions, promoting of Fe " ions diffusion from the surface of metal are listed. Other factors will be discussed farther. 

However, one big implication of rubber in structural applications refers to the incorporation of waste tire rubber in concrete [156-161] this is also one of the most encountered applications of recycled rubber from tires to obtain building materials with improved properties, including high resistance to freeze-thaw, acid attack, and chloride ion penetration high strength and high resistance to sulfate, acid, and chloride environments [156],... 

Good resistance to freeze-thaw cycles and to chemical attack due to high density and very low permeability was also obtained. Carbonation and chloride ions penetration are strongly decreased. Layers of thickness over 12 mm exhibited sufficient strength and ductility to bridge and waterproof the substrate cracks. Increased adhesion to substrate material, that is, old concrete, was excellent provided that the surface was cleaned and wetted. The adhesion was tested using tensile and shear bond specimens. 

The primary cause is the chloride ion that results from the use of deicing salts on roadways or the presence of seawater. The chloride ion penetrates the concrete and attacks the carbon steel rebar forming rust, which expands the volume approximately 3-7 times causing the concrete to spall. 

Method of lew for chloride ion penetration deplh of polymer-modified moBir ... 

Latex-modified mortar and concrete have an excellent water impermeability as described in Sec. 2.4. Such good water impermeability also provides the high resistance of the latex-modified mortar and concrete to chloride ion (Cr) penetration, which is one of the most important factors affecting the corrosion of reinforcing bars in reinforced concrete structures. Table 4.12f °°l gives the apparent chloride ion diffusion coefficient of latex-modified mortars and concretes, which were estimated as a result of the chloride ion penetration kinetics examination in substitute seawater (NaCl content, 2.4%). The resistance to the chloride ion penetration of the latex-modified mortars and concretes tends to be improved with increasing polymer-cement ratio. 

Another major factor is chloride ion ingress to reinforcement. The ferric oxide (Fe203) or y-FeOOH film is resistant to chloride penetration, however ferrous oxide (Fe0 nH20) is sensitive to chloride ion penetration and reacts with it to... 

It was also found that a replacement of 1 wt% PC with CaCOa nanoparticles decreased the chloride ion permeability of PC concrete by approximately 20% and 50% at 28 and 90 days, respectively. In addition, the benefits of addition of CaCOa nanoparticles were also observed in HVFA concretes, in which approximately 19% and 12% reductions in the chloride ion penetration of HVFA concretes containing 39 and 59 wt% FA, respectively, were measured due to the addition of 1 wt% NC after 28 days of curing. However, no significant improvement in the above concretes was observed for 90 days of curing. 

The equilibrium is established at the silver/silver chloride boundary. It is therefore important that the silver chloride coat is porous so that the aqueous solution containing the chloride ions penetrates to the boundary and so permits the equilibrium in eqn (1.27) to be established. 

---