Alkaline mortar

The anodically produced acid is neutralized by the alkaline mortar (CaO). Corrosion is then possible only if the supply of alkali at the steel surface is consumed and the steel becomes active. This process is possible only under certain circumstances after a very long incubation period. Apparently in steel-concrete foundations the possible current densities are so small that this case never arises. The possibility of danger has to be verified with thin outer coatings where deliming has been noticed on the steel surface. 

In architectural work, particular care must be taken to avoid destructive attack of the anodic film by alkaline mortar or cement during erection, and temporary coatings of spirit-soluble waxes, or acetate-butyrate lacquers are frequently applied to window frames and the like to protect against mortar splashes, which in any event should be removed at the earliest possible moment. 

The important point to note is that these bacteria require oxygen and a source of reduced sulfur. The end product is sulfuric acid. The problem of septic sewage systems in hot climates starts with growth of anaerobic SRB in the sewage, producing H2S. This gas migrates to the air space at the top of the line, where it is oxidized into sulfuric acid in the water droplets at the crown of the pipe by Thiobacillus. The corrosion problem is due to the combination of the bacterial action that results in dissolution of the alkaline mortar by the acid, followed by corrosion of the ductile iron. (Stott)5... 

The soiling of paints by various particulates has been documented. These particulates include sulfates and chlorides of iron, calcium, and zinc (8) as well as dust from alkaline mortar (9). 

Conventional repair. The most utilised method consists in the removal of carbonated concrete and its replacement with alkaline mortar or concrete. This method is convenient when the corrosion attack is limited to zones of small extent (for example when the thickness of the concrete cover is reduced locally). In that case it is usually called patch repair. Conversely, it may be rather expensive when repair is required on large surfaces. In fact, concrete must be removed in all the zones where carbonation and subsequent corrosion of steel are expected to damage the structure within the design life of the repair. Even structurally sound concrete must be removed where the corrosion rate of the embedded steel is expected to... 

Repassivation with alkaline mortar or concrete. Repassivation of steel can be obtained by replacing the chloride-contaminated concrete with chloride-free and alkaline mortar or concrete. Because of the mechanism of chloride-induced corrosion, it is not sufficient to repair the concrete in the area where the reinforcement is de-passivated. The concrete must be removed in all areas where the chloride threshold has reached the depth of the reinforcement or is expected to reach it during the design Hfe of the repair. In fact, the concrete that surrounds the zones of corrosion usually has a chloride content higher than the chloride threshold, even though the steel remains passive because it is protected by the corroding site. In fact, a macrocell forms (Figure 18.6a) that provides cathodic polarization to adjacent steel and... 

Zinc disks in a proprietary high alkaline mortar jacket embedded in patch repairs to prevent the ring anode or incipient anode effect discussed earlier in this section (Fig. 13.22). 

Zinc plugs in a cylinder of a proprietary high alkaline mortar for installation in cored holes in the concrete (Fig. 13.23). 

There are different concrete replacement systems available for renovating reinforced concrete structures. They range from sprayed concrete without polymer additions to systems containing conducting polymers (PCC-mortar). Since with the latter alkalinity is lower, more rapid carbonization occurs on weathering [59] and the increased electrical resistivity has to be taken into account, so that with cathodic protection only sprayed concrete should be used as a repair mortar. 

Phenolic mortars have excellent resistance to acids, particularly for dilute nitric acid (up to 50%) and sulfuric acid (60-90%) but can only tolerate very dilute alkaline solutions at low temperatures. 

Maximum chemical resistance of polyester mortars is obtained from cements made from isophthalic or biphenol resins. The biphenolic resins are preferred for alkaline and hypochlorite solutions. 

Surface bonding mortar or cement is mentioned in some building codes as an approved dampproofing treatment, but not as a waterproofing treatment. A number of manufacturers produce cements and mortars impregnated with fibrous glass or other fibers. Some of these may be chemically unstable in the alkaline environment of Portland cement. 

Environment and health-related problems Water-soluble chrome(VI) compounds in the wet cement or mortar have a highly sensitising effect and are up to 90% the cause of allergic cement dermatitis (cement eczema, bricklayer s itch ). The high alkalinity (pH = 13) of cement aids the development of this contact eczema. Bricklayer s itch is one of the most frequent professional diseases in the construction industry. 

CH20N02 raw 239-15, N 17.57% liq, d 1.443 at 20° nD 1.4734 at 20° (Ref 3) it withstands 82-2° Heat Test for 5 mins power by ballistic mortar test 92% of Blasting Gelatin was prepd by condensing formaldehyde with l-nitropropane in an alkaline medium, and nitrating the product. It was reported to be a poor gelatinizer for soluble NC used in blasting compns... 

Dimethyl tellurium dihydroxide,2 (CH3)2Te(OH)2, is prepared by the action of silver hydroxide on the foregoing iodide, either by boiling the components in water or grinding them together with a little water in a mortar. The base forms a strongly alkaline solution which yields salts on treatment with halogen acids. 

The alkaline earth metal hydroxides M(OH)2 (M = Mg, Ca, Sr, or Ba) are also strong bases ( 100% dissociated), but they give lower OH- concentrations because they are less soluble. Their solubility at room temperature varies from 38 g/L for the relatively soluble Ba(OH)2 to 10-2 g/L for the relatively insoluble Mg(OH)2. Aqueous suspensions of Mg(OH)2, called milk of magnesia, are used as an antacid. The most common and least expensive alkaline earth hydroxide is Ca(OH)2, which is used in making mortars and cements. It is called slaked lime because it is made by treating lime (CaO) with water. Aqueous solutions of the slightly soluble Ca(OH)2 (solubility 1.3g/L) are known as limewater. 

Benzoic Acid.—250-500 c.c. of the beer, rendered alkaline with baryta water and mixed with about 50 grams of sand, are evaporated to dryness, the residue being treated in-a mortar repeatedly with alcohol and a little dilute sulphuric acid. The alcoholic liquid, decanted off or filtered, is again rendered alkaline with baryta and the alcohol distilled off, the syrupy residue being acidified with sulphuric acid and extracted with ether. The ether is evaporated and the residue tested for benzoic acid by the following reactions ... 

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