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4

Introduction to Concrete

Admixtures

1.0 INTRODUCTION

Concrete admixtures are defined as materials other than hydraulic
cement, water, or aggregates that are added immediately before or during
mixing. Additives or additions such as grinding aids are added to cement
during manufacture. An addition is a material that is interground or blended
during the manufacture of cement. Most concrete used in North America
contains at least one admixture. The admixtures are added to improve the
quality of concrete in the fresh and hardened state. Publications and patents
on admixtures are voluminous. Interest in the development of admixtures
is evident from the number of patents taken every year. The total number
of patents reported in the years 1985, 1986, 1987, 1988, 1989, 1990, 1991,
and 1992 were respectively 44, 64, 99, 133, 242, 57, 53, and 149.
Categorization of admixtures into distinct groups is not easy as one
material may belong to more than one category. Broadly, however, they
could be divided into the following categories.

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