F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

Shrinkage and its prediction 35
The aggregate content affects shrinkage partly because the aggregate
restrains the amount of shrinkage that can occur and partly because the
aggregate content determines the amount of cement paste, which causes
the shrinkage. However, the aggregate content is completely defined by
the cement-paste content; by allowing for the effect of the latter as
previously explained, the effect of the aggregate content is automatically
taken care of.
The cement-paste content and the w/c ratio completely define the water
content; for the purpose of practical design, it is only necessary to allow for
the effects of the cement-paste content and the w/c ratio as explained
above; the effect of the water content is then automatically taken care of.
Similarly, for practical design purposes, there is no need to allow specially
for the effects of the cement content, the aggregate/cement ratio or the
ratio of fine aggregate to coarse aggregate.
For ordinary and rapid-hardening Portland cements, the variations of
the chemical composition within the permitted ranges of BS 12 have
negligible effect on concrete shrinkage. Where the mix proportions are
kept constant, increasing the fineness of cement tends to increase shrinkage
slightly. Using a fineness of 225 000 mm 2 /g (which is the minimum specific
surface of ordinary Portland cement complying with BS 12) as the
reference, concrete shrinkage can be assumed to increase at the approximate
rate of ~% for each per cent increase in fineness. However, increasing
the fineness of cement reduces the amount of mixing water
required for a given workability and hence reduces the cement-paste
content and the w/c ratio, so that in practice the increase in shrinkage due
to the increase in cement fineness may be offset by the decrease due to the
reduction in the cement-paste content and the w/c ratio.
For concretes of the same mix proportions but made of different types of
cements, the shrinkages have the following approximate relative values:
ordinary Portland (100), rapid-hardening Portland (110), low-heat Portland
(115), high-alumina (100, but at a more rapid rate).
The relative shrinkage of concretes of the same mix proportions but
made with different types of aggregates are illustrated in Fig. 2.5-6.
Concretes having low shrinkages usually contain non-shrinking aggregates
such as quartzite gravel, mountain limestone, blast furnace slag, dolomite,
felspar, granite, etc.; high shrinkages will be caused by the use of
aggregates which exhibit appreciable volume changes on wetting and
drying, such as sandstone, slate, basalt and certain dolerites. Other
conditions being equal, the effect of using a shrinkable aggregate is to
increase the shrinkage of the concrete by an amount at least equal to the
shrinkage of the aggregate itself. Both coarse and fine aggregates influence
shrinkage but the influence of the coarse aggregate is more important. In
general, shrinkage of concrete is reduced by using aggregates of high
moduli of elasticity and which are hard and dense.
The grading, size, shape and surface texture do not have significant
direct effects on concrete shrinkage. Their effects are largely indirect and
due to their influence on the amount of mixing water required for a given
workability.
The size and shape of the concrete member affect concrete shrinkage
through their influence on the rate of loss of moisture; shrinkage varies