Meaning
Chemical compound added to concrete mixtures during batching reduces the surface tension of pore water to minimize drying shrinkage. The shrinkage reducing admixture lowers the internal stresses that develop as water evaporates from the capillary pores. This chemical mitigation helps maintain the structural integrity of large floor slabs without requiring additional reinforcement.
Surface Tension
Capillary tension develops as the meniscus of pore water pulls against the pore walls during drying. The shrinkage reducing admixture decreases this tension, resulting in less overall volume change for a given amount of water loss. This mechanism operates even in environments with low relative humidity.
Cracking Control
Restrained concrete is highly prone to cracking when it shrinks against rigid boundaries. Specifying a shrinkage reducing admixture reduces the width and frequency of cracks in bridge decks and containment walls. This chemical solution is often combined with fiber reinforcement to provide both initiation resistance and post-crack load transfer.
Contractors can increase the distance between expansion joints when this admixture is utilized, saving labor and material costs. In massive foundation slabs, reducing shrinkage stresses minimizes the risk of thermal and drying-induced fractures.
Strength Impact
Compressive strength can be slightly affected by the presence of organic compounds in the pore solution. Using a shrinkage reducing admixture requires careful evaluation of early-age strength development to ensure it meets structural requirements. The addition of this compound does not alter the workability of the fresh concrete.
