Title no. 104-M43
Fast-Track Construction with Slag Cement Concrete:
Adiabatic Strength Development and Strength Prediction
by Stephanie J. Barnett, Marios N. Soutsos, John H. Bungey, and Steve G. Millard The early-age strength development of concrete containing slag cement has been investigated to give guidance for its use in fasttrack construction. Measurements of temperature rise under adiabatic conditions have shown that high levels of slag cement— for example, 70% of the total binder—are required to obtain a significant reduction in the peak temperature rise. Despite these temperature rises being lower than those for portland cement mixtures, however, the early-age strength under adiabatic conditions of slag cement concrete can be as high as 250% of the strength of companion cubes cured at 20 °C (68 °F). The maturity and, hence, strength development were calculated from the adiabatic temperature histories based on several maturity functions available in the literature. The predicted strength development with age was
compared with the experimental results. Maturity functions that take into account the lower ultimate strengths obtained at elevated curing temperatures were found to be better at predicting the strength development.
Keywords: early age; fast-track construction; slag cement; strength.
In recent years, fast-track construction has created a need
for early-age estimates of concrete strength. Fast-track
construction can have considerable economic benefits.
Accelerated construction schedules that put a new, repaired, or overlaid pavement into service require adequate concrete
strength to withstand traffic loads. Typical applications
include localized repairs, replacement of busy intersections, and major slipform paving. In structural components, the
early removal of forms or the application of post-tensioning and the termination of curing in cold weather have safety
implications as well as potential cost savings.1 Because fasttrack construction requires high early-age strengths, the factors affecting these properties must be considered.
Factors include the composition of the concrete mixture,
such as cement type and use of supplementary cementitious
materials, and the use of retarding or accelerating admixtures. The strength development of a concrete is also influenced by temperature, with strength gain more rapid at higher
temperatures and slower at lower temperatures. If the
temperature is too low, strength gain will cease. The temperature inside the concrete depends on the heat of hydration
produced by the reaction of cement, the size and shape of the structural element, the ambient temperature, and the use
Slag cement is commonly used in concrete in combination
with portland cement. It can improve the performance of
both fresh and hardened concrete, producing improved
workability, reduced heat of hydration, higher ultimate
strength, and enhanced durability.2-4 The strength development of slag cement concrete under standard curing conditions,
however, is slower than that of portland-cement concrete.
Slag cement, along with other supplementary cementitious
materials such as fly ash, is not therefore commonly used in applications where high early-age strength is required, for
example fast-track construction. There is evidence, however, that these materials are heavily penalized by standard 20 °C (68 °F) curing temperatures and can achieve significantly
improved early-age strength development under elevated curing temperatures. The higher early-age temperatures occurring
inside structural elements, due to heat of hydration of the binder, appear to be sufficient to produce a considerable improvement in the early-age strength of slag cement concrete.3,5,6
To provide guidance on the use of slag cement in fast-track
construction, it is necessary to model the strength development of the concrete under...