Exposure of concrete

Under other environmental conditions, Q can have different values. Bamforth [33] has reported on exposure of concrete blocks made with similar compositions and binders as described above along a motorway in the UK, subjected to de-icing salt application. The results (Table 6.1) show that Q increases over several years, taking values between 0.3 % and 0.6% chloride by mass of concrete (corresponding to 3 to 4% by mass of cement) after 9 y. These values are similar to those found after marine splash exposure and they depend in a similar way on the type of binder [23]. 

The exposure of concrete blocks made with different binders in the marine-splash zone or in a motorway environment described above show a wide range of apparent diffiision coefficients after 6 and 9 y, respectively, as shown in Table 6.1, ranging from 0.3 to 14 X 10 m /s, with lower values for fly ash and slag containing binders and higher values for pure Portland cement [23, 33]. 

It is difficult to determine a relationship between the results of accelerated tests and of the natural exposure of certain durations. However, many attempts are published in which a safe life cycle is estimated from the results of accelerated tests. For example, it has been proposed that exposure of concrete elements to pure CO2 over a period of 36 days with a ratio of concentration 3000 times higher may give the same carbonation of concrete as 300 years of service in natural atmosphere (Levy 1992). In the tests carried out by Sisomphon and Franke (2007) it has been derived on the basis of the second Fick s law that the carbonation in natural exposure with concentration CO2 of 0.03% is approximately 10 times slower than in the accelerated tests at concentration CO2 of 3%. 

Exposure of concrete to natural elements or to industrial chemicals may result in its deterioration. In many chemical industries the chemicals produced may react with concrete that is used as a construction material. For example, the influence of formic acid on concrete was studied by applying thermal techniques, DTA curves of samples showed that as Ihe exposure... 

Isolation of radioactive wastes for long periods to allow adequate decay is sought by the use of multiple barriers. These include the waste form itself, the primary containers made of resistant materials, overpacks as secondary layers, buffer materials, concrete vaults, and finally the host rock or sod. Barriers limit water access to the waste and minimize contamination of water suppHes. The length of time wastes must remain secure is dependent on the regulatory limit of the maximum radiation exposure of individuals in the vicinity of the disposal site. 

The sensitivity of Magnetic Resonance (MR) to the local concentration, molecular dynamics and molecular environment of these nuclei make it well suited for the study of deterioration processes in concrete materials. Hydrogen (water), lithium, sodium, chlorine and potassium are all MR sensitive nuclei and play an important role in cement chemistry. The ability of MRI to spatially resolve and non-destructively examine test samples as a function of treatment or exposure has the potential to provide new insight to better understand deterioration mechanisms and mass transport properties of concrete materials. 

The TCLP tests are performed by subjecting samples to a much harsher environment than would be encountered in natural surroundings. The samples of concrete are pulverized to maximize exposure to the acid used. Next, a particularly harsh solution of acetic acid is... 

Foundations. Concrete pads, base rings, and piers should show no signs of serious spilling, cracking, or uneven setding. Any such conditions, including uneven settlement and exposure of reinforcement, should be noted. 

Figure 19.29 shows the comparative shielding efficiency data for various materials. Rubber filled with lead oxides comes very close in performance to lead and is superior to concrete and aluminum. Exposure of these shields to radiation causes degradation of mechanical properties (hardness, in particular, is increased) but it does not affect shielding efficiency. 

In addition to the forms of attack already discussed, cracking and spalling of concrete due to acid-induced corrosion can also lead to and accelerate other forms of attack having other causes, most notably freeze-thaw deterioration. Prudil (30) found that concrete which normally withstood attack due to freeze-thaw cycling was subject to attack after exposure to acid solutions. 

Biczok (25) reports that although nitric acid is not as strong as sulfuric acid, it is more harmful to concrete on brief exposure as it transforms the Ca(0H>2 of concrete into highly soluble calcium nitrate. Nitric acid is destructive enough to bring about extensive deterioration even in highly diluted solutions. 

Calcite-cemented layers typically have thicknesses from around 10 cm to a metre or two, and vary widely in lateral extent. Minimum lateral extent is a matter of definition, as it is really determined by where one chooses to start talking of layers rather than of concretions. Maximum lateral extents are certainly greater than a few kilometres, as such extents can be observed in cliff exposures (Bryant et al., 1988 Walderhaug et al., 1989), and lateral extents of tens of kilometres cannot be excluded. Intermediate lateral extents of tens and hundreds of metres have also been observed (McBride et al., 1995 Walderhaug et al., 1995). 

The tests have shown that rubber polymer concrete (RubCon) is the composite with the highest water resistance. During the exposure of the RubCon samples in... 

Decisions regarding the method of preparation of concrete surfaces are complex and the application of surface coatings to a concrete floor should be made after carefully analyzing the geography of the site, the chemicals to be stored, the type of cement used, the potential exposure conditions and the life expectancy. 

Steel is noncombustible, but it is not classified as highly fire-resistant in structural design because of its reduction in ultimate strength with increasing temperature and its high coefficient of expansion this causes sagging and deformation after short-time, exposure to temperatures above 900 to llOO F created by inside fires. When required by code, an increase in fire resistance can be accomplished by use of a 2- to 4-in. -thick coating of concrete. 

From the viewpoint of prediction of service lives, the photochemical deterioration processes of polymers used as paints and finishes are theoretically analyzed based upon unsteady state dynamics. Theoretical results are compared with experimental data under natural and accelerated exposure. Infrared spectra and scanning micrographs show that the deterioration proceeds continuously inwards from the surface, but differently with the exposure conditions. Parabolic (/t ) law was derived approximately for the increase in the depth of the deteriorated layer of polymers with time. Paying attention to the influence of the deterioration of polymeric finishes, the parabolic law involving a constant term was also derived for the progress of carbonation of concrete. These parabolic laws well predict the progress of deterioration and explain the protective function of finishes on reinforced concrete. 

R. B. Polder, Simulated de-icing salt exposure of blended cement concrete - chloride penetration , Proc. 2nd International RILEM Workshop Testing and Modelling the Chloride Ingress into Concrete, C. Andrade,... 

Table 2.3 Resistivity [Cl m) of concrete made with Portland cement (OPC), blast furnace slag cement (GGBS), and Portland cement with addition of 5% silica fume (SF) iv/c = 0.45. lues were determined after 1.5—2.5 y exposure in a fog room or 20°C 80% R.H. climate [37]...

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