Curing, concrete

The properties of cured Pordand cement are affected by these four constituents of the manufactured Pordand cement. Tricalcium siHcate hydrates and hardens rapidly, giving rise to the initial set and eady strength. Increased concentrations of tricalcium siHcate causes an increase in the eady strength of Pordand cement concretes. Dicalcium siHcate hydrates and hardens more slowly, giving the cured concrete its strength increases beyond one week. 

Tetracalcium aluminoferrite acts as a processing aid by reducing the clinkering temperature. It hydrates rapidly but does Htde for any performance property of the cured concrete. It does, however, cause most of the color effects in the cured concrete. 

Calcium hydroxide leached from incompletely cured concrete causes serious corrosion of lead (see Section 9.3). This is because carbon dioxide reacts with the lime solution to form calcium carbonate, which is practically insoluble. Carbonate ions are therefore not available to form a passive film on the surface of the lead . Typically, thick layers of PbO are formed, which may show seasonal rings of litharge (tetragonal PbO) and massicot (orthorhombic PbO) . 

NOTE Apart from the standard packaged, horizontal and vertical boilers discussed previously, other designs of packaged, direct-fired, LP steam generators are commonly available but designed for special industrial applications, such as curing concrete. 

ASTM D98-87, AASHTO2 M144-86 road conditioning/maintenance curing concrete solution unspecified concentrations dry three grades based on 77%, 90%, and 94% minimum assay 14,15... 

Cured concrete can be bonded to cured concrete, as in the installation of precast buttons to a highway surface. Steel bridge railings can also be bonded to the concrete surface of a bridge sidewalk. In the case of deteriorated concrete, the adhesive can be used to rebuild the structure to its former line and grade. Epoxy adhesives are also commonly used on other roadway materials, such as asphalt and brick however, the predominant application is concrete substrates. The most frequent combinations of substrates that are bonded with adhesives in this market segment are... 

In the bonding of cured concrete to cured concrete, the adhesive is applied directly to the substrates. In the case of new concrete, the bonding agent may be incorporated into the concrete formulation, or the adhesive may be applied to the nonconcrete surface. 

Once it is cured, concrete has several surface characteristics that are problems for bonding or sealing. The concrete surface is extremely alkaline and will destroy any hydrolysis-sensitive materials that are present at the interface. It often has a weak, porous surface layer that must be penetrated or removed before being bonded. Thus, sealers and primers are commonly used to moisture-proof and strengthen the concrete surface prior to bonding. 

A 5-m-vvide, 4-m-high, and 40-ra-long kiln used to cure concrete pipes is made of 20-cm-thick concrete walls and ceiling (k 0.9 W/m - °C). The kiln is maintained at 40 C by injecting hot steam into it. The two ends of the kiln, 4 in X 5 m in size, are made of a 3-tnm-thick sheet melal covered with 2-cm-thick Styrofoam k = 0.033 W/ra - °C). The convection heat transfer coefficients on the inner and the outer surface.s of the kiln arc 3000 W/m C and 25 W/m °C, respectively. Dl.srcgaiding any heat loss through llie floor, determine the rate of heat loss from the kiln when the ambient air is at — 4°C. 

Strength is based on 6 x 12 in. cylinders moist-cured 28 days at 73.4 3 F (23 1.7C) in accordance with Section 9(b) of ASTM C 31 for Making and Curing Concrete Compression and Flexure Test Specimens in the Field. 

When a monolithic surfacing is applied to a concrete substrate, in most cases much of the cure shrinkage of the concrete has already taken place. However, the concrete contractor will have, perhaps, installed expansion joints in the slab, and should have cut in or formed control joints as well, so that any future shrinkage will occur at these intentionally weakened parts of the slab rather than in random locations. In addition, there will be "cold seams"—locations where a concrete pour was completed one afternoon and another pour made a day or so later, or fresh concrete was poured against dry, partly cured concrete. This joint is also weak, and with shrinkage of concrete over the years will probably also crack. 

Use Paints, rubber plasticizers, curing concrete, impregnating paper, adhesives, hot-melt coatings, pressure-sensitive tapes. 

The rate of reaction of blast furnace slag and fly ash differs strongly To show this. Figure 1.8 compares electrical resistivity measurements of wet cured concrete with a water/cement ratio of 0.45 made with Portland, Portland fly ash and blast furnace slag cements. The development of resistivity of concrete at an early age... 

According to the data of Solomatovfi i on latex-modified concrete using a copolymer of vinyl acetate and didutyl maleate, the wet-cured conaete is more liable to affected by freeze-thaw cycles than the dry-cured concrete. 

A theoretical model to study chloride diffusion in concrete has been developed by Arora and Popov [77]. Two different coordinate systems are considered to model structure geometry. A chloride ion adsorption and diffusion schematic in a one-dimensional concrete cylinder is shown in Fig. 12.6, comparable to a planar slab with one-dimensional chloride diffusion. Chloride ingress follows Pick s law of diffusion for cured concretes [77]. 

The chloride ingress into concrete follows Pick s law of difiusion for cured concretes. Concrete mixtures and admixtures affect the diffusivity of chloride ions. Figure 12.7 shows the transport of chloride ions through the concrete deck under moderate corrosion environment. The surface chloride concentration is assumed to be equal to 3.56 kg/m, which corresponds to moderate corrosive conditions. Chloride diffusion follows an exponential decay into the concrete. Chloride concentration at the rebar surface increases with time. 

In the Middle East the severe conditions of warm marine climate, especially in the more heavily populated areas, with saline ground waters, increases all corrosion problems. This is made worse by the difficnlty of curing concrete that has led to very short lifetimes for reinforced concrete structures (Rasheeduzzafar et al., 1992). 

Many factors influence the ability of reinforced concrete to resist carbonation induced corrosion. As the carbonation rate is a function of thickness, good cover is essential to resist carbonation. As the process is one of neutralizing the alkalinity of the concrete, good reserves of alkali are needed, that is, a high cement content. The diffusion process is made easier if the concrete has an open pore structure. On the macroscopic scale this means that there should be good compaction. On a microscopic scale well cured concrete has small pores and lower connectivity of pores to the CO2 has a harder job moving through the concrete. Microsilica and other additives can block pores or reduce pores sizes. 

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