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5

Accelerating Admixtures

1.0 INTRODUCTION

Admixtures can influence the properties of concrete from the
moment water comes into contact with the concrete ingredients. In the fresh
state, the water requirement, workability, bleeding, segregation, rate of
hydration, setting time, air content, pumpability, etc., and in the hardened
state, compressive, flexural and tensile strengths, creep, shrinkage, perme-
ability, and durability are affected to different extents, depending on the
type and amount of admixture added. The general types of admixtures used
in concrete and their applications have already been described in Ch. 4 of
this book.
Thermal analysis techniques have been applied widely for the
investigation of the role of admixtures, especially that related to the
hydration of cement and cement components. Application of thermal
analysis permits determination of the heat of reaction, mechanism of
reaction, kinetics of reactions, compatibility of admixtures with cements,
prediction of some properties, durability problems, material characteriza-
tion and selection, development of new admixtures, quick assessment of
some physical properties, etc. In some instances, they yield results that are
not possible to obtain with the use of other techniques.

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