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2v Slump loss under hot (concrete temperature 32°C or higher) and dry conditions
is more serious a problem in shrinkage-compensating concrete than in PCC. As a result of
slump loss, excessive retempering of concrete on the job site will not only reduce the strength
but also the expansion, which defeats the purpose for which the concrete is used.
2 Because of lack of bleeding and quicker stiffening and setting of concrete
under hot, dry, and windy conditions, plastic shrinkage cracking is another problems for
which extra precaution must be taken when using the shrinkage-compensating concrete. When
fresh concrete is likely to be in contact with an absorptive surface such as a dry soil or an old
concrete, the base should be thoroughly strutted by soaking it the evening before placement.
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The development of compressive, tensile, and flexural strength in shrinkage-
compensating concrete is generally influenced by the same factors as PCC. In the case of SCC,
a denser cement paste matrix and a stronger transition zone between the cement paste and
coarse aggregate are the factors responsible for strengths higher than those of PCC made with
an equivalent w/c ratio.
2g The drying shrinkage characteristics of a SCC are comparable to those of
a corresponding PCC; the rate and the magnitude of shrinkage in both the cases are affected by
the same factors, such as aggregate content and type, and water content. However, in the case
of SCC, the influence of the w/c ratio on expansion during the early moist curing period is
quite important. Since the degree of needed pre-compression in SCC may reduce considerably
with w/c ratio above 0.6, it is recommended that low w/c ratios be used even when this is not
needed from the standpoint of strength.
h For several reasons, such as the restrained expansion of concrete, lack of bleeding,
and little or no micro-cracking by drying shrinkage, the SCC provides a more dense and
essentially impermeable mass than does PCC of an equivalent w/c ratio in the range of 0.4 to 0.6.