Freeze-thaw attack

When the temperature reaches values below 0 °C, water contained in the pores of concrete can freeze, causing an increase in volume by about 9 %. The tensile stresses generated may result in scaling, cracking or spalling of the concrete and, eventually, to its complete disintegration. 

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Freeze-thaw attack with or without de-idng agents... 

The European Standard EN 206 [4] distinguishes four classes of severity of freeze-thaw attack with or without de-icing agents and with moderate or high water saturation (XEl through XE4, Table 3.1). It further recommends a maximum wjc, a minimum cement content and minimum strength for each of these classes (Table 3.2). Eor XE2 and higher, at least 4% air is recommended. 

Other special requirements for specific environments are, for example, a minimum content of entrained air in concrete exposed to freeze-thaw attack or specific types of cement for concrete exposed to sulfate attack (see Chapter 3). 

The pure presence of biofilms alone may already cause detrimental effects on constructional materials. They may cause clogging of porous systems or form a slimy layer on the surface. The high water content retained in the EPS matrix of biohlms may increase the water content of porous materials resulting in an increased risk of a freeze-thaw attack. 

Fourier transform, impedance spectroscopy 297 fracture, environment sensitive 207-263 fracture toughness, oxide scales 97 Franck-Read sources 257 Free-Wilson method 530 freeze-thaw attack 196... 

Microorganisms tend to adhere to surfaces [27,41-43]. It is believed that more than 90% of all microorganisms grow in this way [12]. Concomitantly, exopolymeric substances are excreted. This may result in a slimy superficial layer on materials and/or, in the case of porous materials, in total clogging of the free pore volume [44]. The exopolymers are usually hydrated and may contain ionic groups favoring water inclusion. Thus, one result may be an increase in water content in the case of porous materials (a consequence is freeze-thaw attack see the following). 

These monomers provide a means for introducing carboxyl groups into copolymers. In copolymers these acids can improve adhesion properties, improve freeze-thaw and mechanical stability of polymer dispersions, provide stability in alkalies (including ammonia), increase resistance to attack by oils, and provide reactive centers for cross-linking by divalent metal ions, diamines, or epoxides. 

U) Special problems arise in drying photographs. Mass drying via freeze-thaw vacuum drying is possible if the emulsion has not been degraded by microbiological attack. 

The bathtub effect occurs, in part, because most wastes have much higher hydraulic conductivities than the natural material into which they are placed they may also have very different unsaturated soil—moisture characteristics. The hydraulic conductivity of some wastes can be reduced by compaction. The bathtub effect also occurs because more infiltration enters the disposal excavation than would under normal undisturbed conditions. Trench covers may be constructed to achieve the desired hydraulic conductivity and to limit infiltration for the required period of containment or until compaction of the wastes occurs however, it is difficult to maintain the trench covers. The covers must withstand attack by plants, weather (freeze—thaw, wet—dry), erosion, and strains caused by consolidation within the trench. Most trench covers are not capable of meeting these demanding requirements without costly long-term maintenance programs. The cover should be designed to allow for expected consolidation and to utilize hydro-geological concepts of saturated and unsaturated flow systems present at the site. 

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. 

Soundness of a egate is its resistance to chemical attack, or to repeated physical changes, such as freeze-thaw cycles. 

Freeze-thaw Alkali-aggregate reactions Fire Acid attack... 

Table 3.1 Exposure dasses for freeze-thaw and chemical attack, according to EN 206 [4]...

Where concrete is exposed to significant attack by freeze-thaw cycles whilst wet, the exposure shall be classified as follows ... 

XO For concrete without reinforcement or embedded metal all exposures except where there is freeze-thaw, abrasion or chemical attack. For concrete with reinforcement or Concrete inside buildings with very low... 

Interaction between durability and strength requirements is not limited to the iv/c ratio. For instance. Figure 12.4 shows that the air entrained to increase the resistance to freeze-thaw cycles reduces the strength of concrete and thus a lower w/c ratio is required to obtain the required strength. The prescription of a specific cement, for instance to increase the resistance to sulfate attack or chloride penetration, may affect the rate of development of strength and thus influence the w/c ratio required to fulfil the strength requirement. 

A preliminary assessment of the condition of the structure is required. Techniques described in Chapter 16 may be used to diagnose the causes of deterioration and the extent of damage. Degradation processes that may indirectly contribute to corrosion of the reinforcement (freeze-thaw, sulfate attack, etc.) should also be considered. Distinction should be made between different parts of the structure where ... 

The repair material should also be able to resist other types of attack that could occur in the specific environment (sulfate, freeze-thaw, etc.). 

Latex-modified mortar and concrete have improved resistance to freezing and thawing, i.e., frost attack, over conventional mortar and concrete. This is due to the reduction of porosity as a result of decreased water-cement ratio and filling of pores by polymers, and the air entrainment introduced by polymers and surfactants. Figures 4.66 and 4.67 represent the freeze-thaw durability in water (-18 to 4°C) of combined water and dry-cured SBR-, PAE-, and EVA-modified mortars.The frost resistance of SBR-, PAE-, and EVA-modified mortars is improved markedly at polymer-cement ratios of 5% or more. As the degree of expansion by frost (calculated... 

Corrosion is not the only deterioration mechanism in reinforced concrete. Alkali-silica reactivity (ASR), sulphate attack, thurmasite attack, delayed ettringite formation, freeze thaw, thermal movement, settlement and other movement can all lead to concrete damage and their assessment must be included in the surveys. 

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