Early thermal contraction

Concrete structures often show cracks. There are several reasons for the formation of these cracks, including physical effects, drying shrinkage, crazing, thermal effects due to seasonal variations in external temperature, early thermal contraction, freeze-thaw cycles and structural effects such as overloading and impact (Concrete Society, 1982). 

Early thermal contraction G External restraint Thick walls Excess heat generation Rapid cooling 1 day to 2-3 weeks... 

Early thermal contraction cracking or thermal stress cracking... 

Early thermal contraction cracking, also known as thermal stress cracking or curling, is caused by excess temperature gradients (deferential) or moisture content between the top and bottom of a slab, attributed to rapid cooling when ambient temperature drops and, in the case of thick (mass) concrete elements, to excess heat generation during hydration of the cement. 

The early thermal contraction cracks are linear and formed in the slab s corners or edges. The cracks may be deep and of variable length depending on the size of the concrete element. The typical time of appearance is after 1 day to 2-4 weeks. 

Early thermal contraction cracking - occurs within a few days of casting. 

Many of the design features of the dielectric are governed by the necessity to operate the cable at a temperature suitable for the Nb3Sn superconductor (6 to 8 K). Extruded pol3rmer is not a viable mode of insulation application since the very large thermal contraction associated with extruded polyethylene would almost certainly lead to early mechanical failure of this dielectric. Instead, the choice was made to lap many layers of plastic tape and impregnate the butt-gaps with supercritical helium. The major dielectric, mechanical, and thermal specifications for the dielectric tapes are summarized in Table I. 

Early work (B-69MI51600) on 7V-substituted-l//-azepines revealed that they undergo photoinduced ring contraction to bicyclic valence tautomers as indicated in Scheme 1. Subsequently, it has been found that 3H- and 4H- azepines enter into analogous ring contractions, as do some of their oxo and benzo derivatives. These transformations, which parallel those undergone by cycloheptatriene, are often thermally reversible and occur by an orbital symmetry-controlled disrotatory electrocyclic process. 

Many, many types of cans were proposed, some as early as the summer of 1943. Szilard wanted to solder the can on the slug, with some alloy which contracted after cooling. Creutz proposed to replace that alloy by zinc which adheres well both to the uranium and the aluminium. Another proposition of Creutz s was to put all the slugs into one common tube which would have to be closed only at the two ends. Ohlinger proposed to draw the aluminium tube over the uranium in a drawbench and it was proved that the mechanical pressure which is created in the drawing process produces a sufficiently close thermal contact between the slug and the can. The duPont Company s plant at Cleveland made a proposition that was very similar to Creutz s except that the zinc was replaced by the alloy of aluminium and silicon. 

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