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)

Strength of concrete 21
- Ordinary Portland cement
-- - -- Rapid-hardening Portland
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Water/ cement ratio (by weight)
Hg. 2.5-2 Relation between water/cement ratio and mean compressive
strength-tOO mm cubes (after Road Note No.4: Reference 6)
called the evaporable water. The spaces left after the loss of the evaporable
water and the spaces occupied by any bubbles of air trapped in the concrete
mix are collectively known as the voids, the presence of which is a great
source of weakness. It is thus seen that the relation between the w/c ratio
and strength is intimately connected with the voids in the concrete and with
the degree of hydration of the cement. Further discussion of this aspect of
concrete strength would require a study of the physical structure and
porosity of the hardened cement paste. It is sufficient for our purpose to
note that concrete strength increases with the gel/space ratio, which is the
ratio of the volume of the gel to the sum of the solid volume of the cement
that has hydrated and the volume of the mixing water.
As stated in Section 2.3, the characteristics of the aggregate such as the
size, shape, surface texture, and grading, affect the strength of concrete