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Hot Cement
Impact of Hot Cement on the Concrete Mix
Hot cement describes clinker that has, through the process of grinding,
gained additional energy stored in the form of heat. Once the clinker
is ground, this “hot cement” is stockpiled in storage
silos where the elevated temperature, especially in warm climates,
is not readily abated.
 Summer
months exacerbate the situation since ambient temperatures are generally
high and cement consumption increases. The warmer temperatures reduce
the ability of the hot cement to release large quantities of heat
to the ambient air; and increased consumption means freshly ground
cement is not stored very long before being shipped to the ready-mixed
plants for use in batching.
Many attribute slump loss, strength reduction, or other concrete-related
problems to the temperature of the cement upon batching. However,
research has shown that cement’s ultimate effect on the concrete
mixture’s temperature is quite minimal.
 Initial
studies by Lerch, 1955, (see reference below) and duplicated research
has shown that to lower the temperature of normal concrete by 1°C,
the temperature of the cement must be reduced by 8.2°C, the
temperature of the water reduced by 4.9°C, and the temperature
of the aggregates lowered only 1.5°C. Thus the influence of
cement temperature on overall concrete batch temperature is less
than that of the other concrete ingredients. See Table 1 below,
adapted from Design
and Control of Concrete Mixtures, 2002, for a representation
of the effect between relative mass proportions and specific heat
capacity and temperature influence on a concrete mix.
The reason for this effect can be traced to the mix proportions
and the intrinsic thermal properties of the concrete ingredients.
Of the materials added to normal concrete, cement occupies only
7-15% of the concrete volume. Water and aggregates generally constitute
approximately 70-90% of the concrete volume. When compared to the
weight of the other constituents, cement’s potential influence
on temperature is diminished. In addition, cement has a very low
average specific heat capacity (0.92 kJ/kg•K) – meaning
that it gains and loses heat very readily when exposed
to high temperatures or when supplied with energy. Aggregates, on
average, have an equivalent specific heat capacity to that of cement,
but water’s specific heat is very high (4.184 kJ/kg•K)
– meaning it can store large amounts of heat.
 The
importance of controlling concrete temperature is well understood.
Temperature affects fresh and hardened properties of concrete as
well as the thermal cracking potential. Careful attention must be
paid to batch temperatures in hot and cold weather concreting. However,
as evidenced by the graph below, the relative effect of
“hot cement” on the batch temperature is negligible.
Note: This graph
represents the relative effect of each mix constituent
assuming the other temperatures are held constant at 20°C.
References (Click on title for more information
or to order)
Kosmatka, Kerkoff, and Panarese, Design
and Control of Concrete Mixtures,
EB001, 14th edition, Portland Cement Associaiton, Skokie, Illinois,
2002.
Lerch, W., Hot
Cement and Hot Weather Concrete Tests,
IS015, Portland Cement Association, Skokie, Illinois, 1955.
Wilson M.L., and Thomas, M.D.A., Hot
and Cold Weather Concreting,
CD057, Portland Cement Association, Skokie, Illinois, 2005.
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