Expansion Producers

These admixtures control settlement and provide expansion in the plastic state. In the plastic state, metallic Al, Mg, or Zn produce gases. Admixtures that produce expansion both in plastic and hardened states are calcium sulfoaluminate and lime based materials. Those which produce expansion only in the hardened state are granulated iron fdings and chemicals that promote the oxidation of iron and offset volume changes due to shrinkage. 

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Figure 5.9 The Joule-Thompson cycle (Linde cycle). The gas is first compressed and then cooled in a heat exchanger, before it passes through a throttle valve where it undergoes an isenthalpic Joule-Thomson expansion, producing some liquid. The cooled gas is separated from the liquid and returned to the compressor via the heat exchanger.

Since the expansion produced is dependent on the uniformity of particle distribution, longer than normal mixing times are required. However, prolonged mixing will result in a significant reduction of the expansive potential, especially at higher temperatures. 

Under conditions of internal restraint, the expansion produced is proportional to the ratio of steel to concrete and the dosage of the admixture. Special care should be taken to ensure that reinforcement is located in its proper position during placement and consolidation so that adequate restraint and good bond to steel is obtained. Restrained expansion increases the density of the matrix and produces concrete or mortar with a lower coefficient of permeability than that of corresponding Portland cement concretes and mortar. 

Compound 156 (prepared by reaction of tetrabromocyclopropene and 2,5-dimethylfuran) underwent dipolar cycloaddition with phenyl azide to produce the fused triazole 157. The reaction was carried out in dichloromethane at room temperature over 2 days. This lower reaction temperature allowed for the isolation of the adduct 157, which was established by X-ray crystallographic analysis to be the product of ct>-selective addition. Heating triazole 157 in benzene at reflux for 2 h resulted in ring expansion producing a 1 1 mixture of compounds 158 and 159 (Scheme 16) <2004JOC570>. 

The influence of the chain expansion produced by excluded volume on the mean-square optical anisotropy is studied in six types of polymers (PE, PVC, PVB, PS, polylp-chlorostyrene), polylp-bromostyrenel. RIS models are used for the configuration statistics of the unperturbed chains. The mean-square optical anisotropy of PE is found to be insensitive to excluded volume. The mean-square optical anisotropy of the five other polymers, on the other hand, is sensitive to the imposition of the excluded volume if the stereochemical composition is exclusively racemic. Much smaller effects are seen in meso chains and in chains with Bernoullian statistics and an equal probability for meso and racemic diads. 

Expansion of Liquids.—In liquids, the expansion produced by heat is much more marked than in Bolide they also differ among themselves in the amount of expansion produced by equal increments of heat. The most volatile liquids, or those of which the boiling point iB low, are found to be the most expansible under the influence of an increase of caloric, as may be observed from the appended table, showing the comparative increase in volume of several liquids when heated from 32° to 212°,—-... 

Mononitroglycerines are weak explosives. In consequence of a distinctively negative oxygen balance, only 434 kcal/kg are evolved on explosive decomposition (water in the form of vapour). Their sensitiveness to impact is extremely low. Indeed they are virtually insensitive. Their liability to detonate depends on their physical state. According to Naotim the lead block expansion produced by liquid mononitroglycerine is 75 cm3 only and products of incomplete decomposition, e.g. acrolein, are evolved. The crystalline product, on the other hand, detonates readily to produce an expansion amounting to 245 cm3. 

In physical properties and explosive parameters methyl glycol dinitrate resembles its isomer. The heat of detonation as 1110 kcal/kg (water as vapour). The expansion produced in the lead block with water tamping is 540 cm3 [4j. 

The substance is characterized by excellent chemical stability. Its explosive strength, as measured by the expansion produced in the lead block, is equivalent to about 75% of the explosive strength of nitroglycerine. 

The expansion produced by PETN in the lead block with sand tamping is 500 cm3 and with water tamping, 560 cm3. This is equivalent to about 93% of the strength of nitroglycerine or about 170% of that of picric acid. 

Nitromethoxy methanol nitrate produced a lead block expansion of 420 cm whereas the net expansion produced by nitroglycol in the same series of experiments was 450 cm3. 

Under normal condition it exists as a gas that it condensed at +10°C, and freezes at —76°C. In the condensed or solid state, chlorine dioxide explodes even while being poured from one vessel into another. The expansion produced in the lead block is 200 cm3. It was recently suggested as a component in liquid propellants for rockets. 

At what temperature do the competing effects of contraction and expansion produce the smallest volume for liquid water ... 

Does a real expansion produce more or less work than a reversible expansion Does a real compression require more or less work than a reversible compression ... 

The RCI expansion produces a relatively small number of additional terms and can be used for problematic cases to stabilize the energy obtained from Eq. (10). A wavefunction including these additional configurations for the example above would be denoted BOVB(41+S+RCI). 

The expansion produced in the lead block, as reported by various authors is 250-350 ml. Taking the value for TNT as 100, that for picric acid will be 102-120. 

Corrosion of reinforcement is probably the most widespread cause of deterioration in concrete. The expansion produced by rust formation causes the surrounding concrete to crack and spall. In a sound concrete, rusting is prevented by the high pH of the pore solution, which stabilizes an oxide film on the steel that inhibits further attack. This film is unstable at lower pH values, which can result from carbonation or leaching, or in the presence of Cl . Sources of the latter include sea water or salt spray, de-icing salts used on roads, certain aggregates, especially those available in desert climates, and CaClj used as an accelerator. Though now widely prohibited, this can... 

Fig. 12.6 Typical relations between expansion produced by ASR and age data arc for mortars with w/c = 0.41 and aggrcgate/ccment = 2, (A) with 6.7% of Beltane opal in the aggregate and a cement with Na O, = 1.24%, and (B) with 4.5% of Beltane opal in the aggregate and NajO = 0.8%. After Hobbs (H66).

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