Freeze-thaw deterioration concrete

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. 

It can be concluded from the assessment of the data in this section that inclusion into a concrete mix of a water-reducing admixture of the lignosulfonate, hydroxycarboxylic acid and air-entraining type should not lead to any deterioration in the durability of that concrete to freeze-thaw cycling. Indeed there are strong indications that, when used either as a means of reducing the water-cement ratio or, alternatively, of reducing the cement content, more durable concrete may result. 

ABSTRACT This research project aims to use reactive powder concrete, RPC. as a new repair material and evaluate its bond strength and bond durability to existing concrete. One accelerated aging environment, namely a freeze-thaw cycle acceleration deterioration test, was selected for the evaluation of bond durability of the repair materials. Before and after aging, the samples were evaluated by the compressive strength, bond strength (slant shear test), steel pull out strength, and relative dynamic modulus NDT tests. 

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]. 

Concrete subjected to freeze-thaw cycling may suffer from micro cracks and surface scaling. Dynamic modulus of elasticity was measured to evaluate the degree of deterioration in the concrete cylinders. A decrease in dynamic modulus indicates that the concrete is internally deteriorating by micro cracks and/or surface scaling. 

In this chapter, only a few of the most common forms of physical and chemical deterioration of concrete wiU be mentioned (effects of freeze-thaw cycles, acid solutions, pure water, sulfates and aUcaH aggregate reactions). Other forms of deterioration, such as the action of certain aggressive liquids, while important in specific cases, wiU not be dealt with. For more details, the reader is referred to the classic Hterature on degradation of concrete, which has formed the source of usefiil information for many decades [1, 2]. Modern reference texts and standards rely for a large part on these classic sources [3, 4]. 

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. 

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. 

The decrease of freeze-thaw resistance with increasing rate of temperature changes, as well as a better freeze-thaw resistance tested in humid air than in water, was proved in laboratory experiments [98]. The concrete samples are deteriorated more rapidly when dried between the cycles of freezing and thawing. 

Jacobsen, S., Sellevold, E. J. (1996) Self healing of high strength concrete after deterioration by freeze/thaw. Cement and Concrete Research, 26(1) 55-62. 

Concrete itself can be destroyed by physical, mechanical, chemical or biological actions. Concrete deterioration can be the first step in corrosion of the reinforcement (e.g. when freeze-thaw processes induce cracking and spalling of the concrete cover). The chemical and physical attacks of concrete are described in detail in (Biczoc, 1986 Niirnberger, 1995). 

Concrete may deteriorate if adequate precautions are not exercised to protect it from adverse effects that could result from exposure to natural or artificial conditions. Several physical, chemical, and electrochemical processes are known to induce cracking of concrete. Concrete can have durability problems as a consequence of its exposure to seawater, sulfates, chlorides, freeze-thaw action, carbon dioxide, etc., or when it is attacked by artificially induced processes such as exposure to acids and salts in chemical plants or to fire. In recent years, a new type of durability problem was encountered that involved use of steam cured concrete products. The distress was caused by the formation of delayed ettringite. If the raw materials in concrete are not carefully controlled, there may be an eventual failure of concrete elements, eg., the presence of excess alkali in concrete that promotes alkali-aggregate expansion reaction, harmful impurities in the aggregates, or the presence of excess amounts of dead-burnt MgO. Thermal techniques in combination with others have been employed with success to examine the raw materials as well as the failed concrete. The knowledge gained from such work has been applied to produce more durable concrete. 

In sulphur concretes, the mechanism of deterioration caused by frost action has been attributed to entirely different causes to those above. The material has low permeability to moisture and as water is not used in mixing, it was not considered that water played a major role in deterioration. Sulphur has a very high coefficient of thermal expansion (a - 55 x 10 6/°C) and low thermal conductivity (0.27 W/m K). Hence the poor durability performance in cyclical freezing and thawing has been attributed to the development of high stresses due to thermal gradients (5,... 

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