Calcium chloride concrete

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For concrete work in cold weather a specially rapid-hardening cement may be made by addition of calcium chloride to the cement. 

In concrete, triethanolamine accelerates set time and increases early set strength (41—43). These ate often formulated as admixtures (44), for later addition to the concrete mixtures. Compared to calcium chloride, another common set accelerator, triethanolamine is less corrosive to steel-reinforcing materials, and gives a concrete that is more resistant to creep under stress (45). Triethanolamine can also neutralize any acid in the concrete and forms a salt with chlorides. Improvement of mechanical properties, whiteness, and more even distribution of iron impurities in the mixture of portland cements, can be effected by addition of 2% triethanolamine (46). Triethanolamine bottoms and alkanolamine soaps can also be used in these type appUcations. Waterproofing or sealing concrete can be accompUshed by using formulations containing triethanolamine (47,48). 

Accelerator in Ready-Mix Concrete. Calcium chloride accelerates the set time of concrete giving it a high early strength development. It is not an antifreeze, but by using it duriag cold weather protection can proceed in a timely manner (31—34). In Russia, calcium chloride forms a component of several antifreeze admixtures (33). Reviews of the concerns and possible remedies of calcium chloride corrosion problems in concrete are available (21,35). There is no consensus on what the safe levels of calcium chloride in concrete are. 

Economic Aspects and Uses. Total production of calcium chloride in 1989 was 873,000 tons (31). Most of this was produced from Michigan brines. The principal use of calcium chloride is to melt snow and ice from roads. It is also used in dust control, concrete setting control, and various industrial uses. 

Calcium chloride May cause steel corrosion if concrete is porous/c racked... 

Galvanised steel provides increased corrosion resistance in carbonated concrete. In concrete with more than 0.4% chloride ion with respect to the cement content, there is an increased risk of corrosion and at high chloride contents the rate of corrosion approaches that of plain carbon steel. In test conditions the rate of corrosion is greater in the presence of sodium chloride than calcium chloride. Fusion-bonded epoxy-coated steel performs well in chloride-contaminated concrete up to about 3.9% chloride ion in content. 

Three other compounds of s-block elements—calcium oxide (CaO, known as lime ), sodium hydroxide (NaOH), and sodium carbonate (Na2 CO3)—are among the top 15 industrial chemicals in annual production. Lime is perennially in the top 10 because it is the key ingredient in construction materials such as concrete, cement, mortar, and plaster. Two other compounds, calcium chloride (CaCl2 ) and sodium sulfate (Na2 SO4 ), rank just below the top 50 in industrial importance. 

Calcium chloride (CaCy has many uses. It is used as a drying agent and to melt ice and snow on highways, to control dust, to thaw building materials (sand, gravel, concrete, and so on). It is also used in various food and pharmaceutical industries and as a fungicide. 

Uses of calcium chloride include road deicing (40%), where it competes with sodium chloride, road dust control and roadway base stabilization (20%), industrial processing (20%), oil and gas wells (10%), and concrete... 

Calcium chloride has several industrial applications. The major applications of this compound are in deicing of roads, dust control, imparting stability to roads and buildings, and to improve traction in tractor tires. It is mixed with ice to make freezing mixtures. Hexahydrate mixed with crushed ice can lower the temperature of the cooling bath to below -50°C. It also is used as a desiccant for dehydrating gases and liquids. It is added to cement in various proportions to manufacture different types of concrete. Other uses are in adhesives, to lower gel temperatures, and as a calcium source in liquid feed supplements for dairy cattle. Also, the compound is used to control particle size development and reduce coalescence in plastics. 

The action of an admixture in relation to attack on reinforcement can be considered either in direct chemical reaction with the steel or, alternatively, a breakdown of the passive layer imparted by concrete which normally prevents corrosion at the cement/steel interface. In this respect, any accelerating water-reducing admixtures containing calcium chloride can be considered hazardous as far as raising susceptibility of steel reinforcement to corrosion is concerned. It is particularly so at calcium chloride contents in the concrete at or above 1.5% by weight of cement as discussed in the section on accelerators. The use of such materials has been controlled by relevant codes of practice where embedded metal is present in the concrete. 

Direct addition of water-reducing admixture This increases the workability of the concrete. The effect of all types of water-reducing admixture under these conditions is invariably to increase the shrinkage and creep of the concrete. Some typical values are shown in Table 1.31. The considerable increases in both shrinkage and creep in the presence of admixtures containing calcium chloride and triethanolamine are clearly illustrated. 

Water-reducing admixtures containing calcium chloride should not be used in concrete containing embedded metal or where volume deformations are important. 

There has been controversy over the use of calcium chloride in concrete containing embedded metal in view of the possibility of corrosion, particularly where the concrete is of a porous nature. Many countries have made provision in the relevant codes of practice to prevent or limit its use where steel reinforcement is present. This has renewed interest in chloride-free accelerators as replacements for calcium chloride in reinforced concrete. However, calcium chloride remains a most effective material for use in unreinforced concrete for economic production under winter conditions and its effects on concrete, whether beneficial or undesirable, are well researched and quantified. In some areas the newer non-chloride materials, although shown to reduce the likelihood of reinforcement corrosion, have not been widely studied and their other effects on concrete are less known. 

The fact remains that calcium chloride has been widely used as an accelerator for plain umeinforced concrete and this area of application, which in accounts for over 60% of calcium chloride usage will continue in the future. 

The reactions between calcium chloride and the constituents and reaction products of Portland cement have been widely researched and are of importance in practice, since the risk of corrosion of reinforcement depends, at least in part, on the amount of chloride which is left in a free state in solution in the concrete [4]. 

Accelerating admixtures based on calcium chloride, formate, nitrate, and thiocyanate have no significant effect on the workability, air content, mix stability, or water-cement ratio of concretes into which they are incorporated. The only properties of plastic concrete which are affected are the heat evolution and setting time. 

The heat evolution of concrete mixes containing no admixture, 1.5% calcium chloride and 3.0% calcium formate is shown in Fig. 5.18. The heat evolution of calcium chloride and calcium formate are approximately equal at 24 h, which is reflected in similar compressive strengths at this age of 10.0 and 12.5 N mm i. 

Fig. 5.18 Heat evolution from insulated concrete cubes containing calcium chloride and formate. Table 5.1 The effect of calcium chloride and formate on mortar stiffening times...

The composition of the Portland cement in the concrete can also influence the effectiveness of both calcium chloride and calcium nitrate and a regression analysis [26] for data for 10 cements produced the equation... 

The permeability and porosity of concrete containing calcium chloride in relation to a plain concrete depends on two conflicting variables ... 

The degree of hydration of the concrete, which in the case of the calcium-chloride-containing concrete will initially be considerably increased, and the larger volume of hydration products will lead to a reduced permeability. 

Table 5.2 The increase in compressive strength of concrete containing calcium chloride is greater at lower temperatures...

The resistance of concrete containing calcium chloride to attack by aqueous sulfate is reduced [22, 31, 33], A comprehensive study of concrete over a 5-year period [24] using various cements and cement content stored in high-sulfate-containing water, gave the results shown in Figs 5.24 to 5.29, for which the following conclusions can be reached ... 

Concrete containing calcium chloride develops strength more rapidly and, therefore, has a greater resistance to damage by freezing at an early age, as shown in Fig. 5.30. There is some indication, however, that at later ages, the more mature concrete is less resistant to freeze-thaw cycling [22, 33]. 

The porosity of the concrete at an advanced state of maturity is increased in the presence of calcium chloride and, therefore, will allow a greater opportunity for air and moisture to come into contact with the steel reinforcement, encouraging corrosive effects. In practice, with reinforcement cover meeting the relevant codes of practice, this effect is regarded as of minimal significance. 

The presence of calcium chloride at concentrations greater than about 1.5% by weight of cement can lead to breakdown of the passive layer of Fe203 normally present at the steel/concrete interface, rendering the... 

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