Page 333 - Construction Waterproofing Handbook

CHAPTER 7

ADMIXTURES

INTRODUCTION

Admixtures are used with masonry and concrete materials to enhance and improve in-
place cementitious product performance. Admixtures are additions, other than normal
ingredients of aggregate, sand, water, and cement, which impart desirable qualities to in-
place concrete or masonry. These qualities might include:
● Color
● Workability
● Shrinkage reduction
● Improved hydration
● Reduction of porosity
● Faster setting times
● Faster curing
● Waterproofing
Admixtures added during mixing of the concrete or masonry slurries add qualities
throughout the in-place product. Surface-applied admixtures only disperse additional qual-
ities to the substrate surface and to the depth to which it penetrates. Admixtures are avail-
able in many forms, including:

● Dry form
● Liquid additive
● Premixed cementitious form
● Dry shake or troweled-on (added at finishing stage)
● Liquid mixtures (applied during curing stages)

HYDRATION

Water added to cement, sand, and aggregate forms a paste that cures, hardens, and shrinks
to create the finished concrete or masonry product. During curing, water leaves this paste
through a process called hydration, which causes formation of microscopic voids and
cracks in concrete. Once formed, these voids allow water absorption through the material.
7.1
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