Freeze-thaw damage

Repair. Repairs for damaged bonded structure can be either mechanical or adhesively bonded. Mechanical repairs are metallic doublers on one or both sides of a damaged component, held on by fasteners. The fasteners transfer the load through the doubler around the damaged site and restore part functionality. Although common for metal-to-metal bonded structure, mechanical repair of sandwich structure is rare because of the risk of further delamination. Unless the doubler and fasteners are perfectly sealed, water can travel into the honeycomb core eventually causing freeze-thaw damage and delamination. 

Occasional in-service delaminations occurred at the aft tip of the wedge. Because there was no metal-to-metal closeout bond at the aft tip, any slight incidental damage could easily crack the bond slightly and allow moisture to enter the core. Eventually, freeze-thaw damage and delamination would occur. 

Cracking can be caused by numerous physical and chemical phenomena in Portland cement materials. For example, freeze-thaw damage and ASR manifest themselves through crack development that may be studied using MRI. In addi-... 

Depending on the material type and construction method, the saturated hydraulic conductivities for these barrier layers are typically between 1 x 10-5 and 1 x 10-9 cm/s. In addition, conventional cover systems generally include additional layers, such as surface layers to prevent erosion protection layers to minimize freeze/thaw damage internal drainage layers and gas collection layers.6 22... 

Hincha, D.K., Heber, U. Schmitt, J.M. (1990). Proteins from frost-hardy leaves protect thylakoids against mechanical freeze-thaw damage in vitro. Planta 180, 416-19. 

Figure 3. Temperature zone of freeze-thaw damage to catalase. Half-milliliter aliquots of the enzyme (1.7 fig/ml) were frozen at 900°C/min without seeding...

For concrete, deterioration due to freeze-thaw is caused bj freezing of pore water inside the concrete. If the pores are too small, then the expansion caused by freezing can exert stresses on the concrete that crack the concrete and thus cause deterioration. Air entrainment of 7-8 %, depending on the aggregate size, can essentially eliminate this freeze-thaw damage [3]. 

The measured strength of the concrete cubes was controlled by the interaction and combination of the above mechanisms. Strength reduction was noted after 600 and/or 1000 freeze-thaw cycles due to freeze-thaw damage. 

While corrosion of steel in concrete is a major cause of deterioration it is not the only one. Out in the real world we must not become blinkered to other problems like alkali-silica reactivity, freeze thaw damage and the structural implications of the damage done and of repairs. In this setting, however, we will concentrate on the corrosion issue although there will be passing references to other problems where relevant. 

Because freezing and thawing increase the permeability of clay, newly constructed liners must be protected from freeze-thaw damage using four feet of solid waste or other frost protection material dining winter months. Both the base liner and the lower 10 feet of the inside slopes are required to be protected from freeze-thaw damage. 

Petrographic examination. Petrographic examination is a microscopic analysis of concrete, performed on core samples removed from the structure. Further details may be foimd in the ASTM C856 standard. It yields information such as the depth of carbonation, density of the cement paste, air content, freeze-thaw damage, and direct attack of the concrete. 

Besides corrosion-induced rebar damage, there are three other commonly cited forms of concrete degradation, namely, alkali-aggregate reaction, freeze-thaw damage, and sulfate attack. 

Freeze-thaw damage. Freeze-thaw damage is related to the porous nature of concrete. If the solution trapped in the pores freezes, a volume expansion occurs, which results in tensile stresses. When the hydraulic pressure exceeds the strength of the cement paste, cracking and spalling of the concrete results. Concrete with a high moisture content is most susceptible to this damage mechanism. 

In cold climates, where this form of damage is a problem, the use of air-entrained concrete is specified. Such concrete has demonstrated its ability to provide durable long-term service. Essentially, additives create air voids entrained in the concrete. The freezing pore solution can then expand into this interconnected system of air voids. Usually the air content of this type of concrete is between 3 and 8 volume percent. However, the total air content alone is not necessarily adequate to assure resistance to freeze-thaw damage. The distribution and size of the entrained air voids are also of major importance. A tradeoff exists between air content and strength. 

---