Page 33 - Masonry and Concrete

Understanding Concrete
32 CHAPTER TWO

EDGE BEFORE EDGE TO
REMOVING MATCH CONTROL
BULKHEAD JOINTS

1 / 4 T T
OR
1
1 / 2 "
MIN
COAT WITH OIL,
1
/ 10 T OR 2 LUMBER PAINT OR
3
/ 4 " MIN BULKHEAD CURING COMPOUND
TO PREVENT BOND
FIGURE 2-16
Construction joints.

2.6 Cement Hydration and Concrete Curing

Concrete curing is not simply a matter of the concrete hardening as it
dries out. In fact, it is just the opposite. Portland cement is a hydraulic
material. That is, it requires water for curing and can, in fact, fully cure
to a hardened state even if it is completely submerged in water. Port-
land cement is anhydrous—it contains no water or moisture at all. The
moment it comes in contact with water, a chemical reaction takes
place in which new compounds are formed. This reaction is called
cement hydration. The rate of hydration
varies with the composition of the cement,
the fineness of the cement particles, the
1 /2" RADIUS
1 /4" BELOW
amount of water present, the air tempera-
SURFACE
ture, and the presence of admixtures. If the
EDGE OF EXISTING mixing water dries out too rapidly before
BUILDING, SLAB, the cement has fully hydrated, the curing
WALK, DRIVE, ETC.
process will stop and the concrete will not
harden to its intended strength. Curing
1 /4" TO 1 /2"
PREMOLDED will resume if more water is introduced,
JOINT MATERIAL
but at a slower rate. Hydration occurs
FIGURE 2-17 more rapidly at higher air temperatures.
Isolation joints.

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