Sulfate attack

Sulfate attack starts with penetration of sulfate ions into the concrete. Then mainly two detrimental reactions can occur sulfate can react with calcium hydroxide to form gypsum  

CjA + 3CaS04 + 32H2O 3CaO AI2O3 3CaS04 32H2O (2)  

The severity of the attack depends mainly on the concentration of the sulfates in the soil or in the water in contact with concrete and to a degree on the counter ion. 

For instance, magnesium sulfate has a more marked effect than other sulfates because it also leads to decomposition of the hydrated calcium silicates. Ammonium sulfate is especially aggressive, because the ammonia produced escapes as a gas. 

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Type V (High Sulfate Resistance). Type V Pordand cement is used in concrete exposed to severe sulfate attack of 1,500 to 10,000 ppm. Low concentrations of tricalcium aluminate [12042-78-3] give Type V its sulfate resistance. The sulfate resistance is improved with air entrainment and low water to cement ratios in the wet concrete. U.S. production of Type V Pordand cement in 1989 was 0.9% of the total Pordand cement production. 

Dimethyl sulfate attacks the sulfur atom in the benzodiazepinethionc 33 to form the 2-(methyl-sulfanyl)-3//-l,4-benzodiazepine 34 in high yield.228... 

Direct measurement of the effect of aggressive reagents on concrete durability appears to be confined to sea water and sulfate attack, where in both areas it is recognized that the lower the water-cement ratio, the greater will be the resistance to attack and the use of a water-reducing admixture will be obviously helpful. This is confirmed by work carried out in Holland [95] and Japan [84] and a general conclusion is that a reduction in the water- cement ratio from 0.5 to 0.40, would allow a reduction in thickness of cover of the reinforcement by about 50%. 

Research into the susceptibility of superplasticized concrete to sulfate attack has concluded that there is no significant difference between plain concrete and the admixture-containing concrete [71, 72]. Figure 2.22 presents some data for concretes containing an SNF superplasticizer exposed to a 3% magnesium sulfate solution. 

Fig. 5.24 CaCl2 decreases the resistance of concrete to sulfate attack (Shideler).

Only mixes containing 426 kg m 3 I0W-C3A cement showed unaffected resistance to sulfate attack over a 5-year period. 

The aluminate-based admixtures undoubtedly provide the best wet-mix shotcrete, making it possible to build thick linings even in overhead work. The high alkali content and the consequent health hazard are the main constraints to their more widespread use. Furthermore, there is concern that the admixture may promote the alkali-aggregate reaction in concretes containing reactive aggregates, as well as sulfate attack [117]. 

Copper is dissolved best by HNOy. nol atlacked by cold dilute HCI or HiSOj. but in hot HCI dissolves to yield cuprous chloride, in hoi concentrated 11 SO. to yield copper sulfate attacked by chlorine, especially when healed, to furm cuprous and cupric chlorides only slight action by H S or SO at ordinary temperatures in Ihe absence of air. 

Research into the susceptibility of superplasticized concrete to sulfate attack has... 

Jambor (42) has published a damage function describing sulfate attack in terms of the percent of SO3 bound in hardened cement paste, which he reports as being the prime cause of sulfate corrosion. The damage function (DC) which is expressed as... 

Even though the mechanisms are not fully understood, it has been fairly well established that SO2 accelerates the corrosion of carbon steel (14-16,49-51). This results in the creation of a layer of rust, i.e. iron oxides, on the surface of the steel, which occupies more than twice the volume of the iron from which it was produced. In addition, Haynie and Upham (15) report that iron oxides catalyze the oxidation of SO2 to SO3 as well as react with SO2 to form sulfates. Both conditions, i.e. the expansion of reinforcing steel due to corrosion and sulfate attack, have been shown to cause the deterioration of PCC. 

CACs were developed in response to the need for cements resistant to groundwater and seawater attack and are the only cements, other than Portland cement, that are in continuous long-term production [2], The property of CAC that was most important in their commercial development is the resistance to sulfate attack, which contrasted with the poor-sulfate resistance of contemporary Portland cements [2], and CAC was first patented in 1908 [2], Most early applications, in construction projects following the First World War, were in structures exposed to seawater, such as harbor pilings. Because CAC hardens rapidly, it was adopted for prestressed concrete beams in the post World War II construction boom, with some unfortunate results. Poor understanding of the material properties of CAC and incorrect water to cement ratios led to the collapse of several buildings, and the use of Portland cements, which are cheaper, has replaced CAC in prestressed concrete beams[2]. 

At ordinary temperatures it is entirely unaffected by air or water, but at elevated temperatures it oxidizes readily. Molten sulfur and phosphorus attack the metal slowly, while the vapors of these elements react with it vigorously. The metal is not attacked by alkaline solutions, but fused nitrates, peroxides, alkaline carbonates, hydroxides, and acid sulfates attack it... 

II2 Aids in providing moderate resistance to sulfate attack... 

Other types of cement than those of Table 1.3 are available for special uses. These are for instance low heat cements to be used when low heat of hydration is desired such as in massive structures, sulfate-resisting cements to be used to increase the resistance of concrete to sulfate attack, expansive cements, quick setting cements, white or coloured cements, etc. [2]. 

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