What is Hydration?
Critical to the quality and integrity of any good concrete mix design is the complete hydration of cement in the formation of binding paste. Poorly hydrated cement will always result in an overall lack of structural integrity.
Hydration occurs in five specific stages. Enhance technology concentrates primarily on the first three stages where cement paste formation and related chemical reactions are critical to hydration and ultimately the quality of the hardened concrete. Proper understanding of hydration is equally important to all who will come in contact with the concrete in its’ mixing, placement, and finishing.
Hydration in short
Dr. K. Luke, Ph.D., researcher in cementing technology describes hydration as follows:
“On contact with water there is a rapid dissolution of cement grains and soluble alkalis giving rise to high concentrations of Ca2+, SO42- and OH ions in solution with a resultant increase in pH to 12-13. These ions react with the less soluble silicates and aluminates to form C-S-H gel and ettringite respectively, which then form a protective barrier around the unhydrated cement grains preventing further hydration and relates to the workability period where cement/concrete can be placed. During this period the Ca2+ ion concentration continues to increase from slow continuous hydration of cement grains behind the protective barrier. Super saturation in Ca2+ occurs and is followed by precipitation of Ca(OH)2 and further rapid hydration of cement grains to give C-S-H gel and ettringite. Formation of C-S-H gel and its’ interlocking of particles give rise to set and strength development.”
In order for an admixture to effectively enhance hydration the natural chemical and ionic transformations of Stage l (dissolution) must be extended for a period of time. Further, resulting incomplete particle hydration must be minimized.
Hydrate n (1802) 1. A compound or complex ion formed by the union of water with some other substance 2. HYDROXIDE (calcium~).
Broken down into identifiable stages below are those which fall into the initial mixing and workability period of ready mixed concrete:
- Stage I: C3S comes in contact with water and releases calcium and hydroxyl ions into the solution. Dissolution begins and a rapid evolution of heat occurs for a period of 15-20 minutes.
- Stage II: Dissolution continues but much more slowly and pH reaches 12 or more. Known as the dormant or induction period second stage reaction periods are very slow and the cement remains plastic, workable for a period of a few hours.
- Stage III: Active reaction restarts and accelerates with time. Initial set occurs as the reactions become vigorous. Final set occurs before the end of the third stage.
When a critical value of calcium and hydroxyl ions is reached there is a rapid crystallization of CH and CSH followed by a rapid reaction (hardening). The cementing action occurs through the interlocking crystalline structure of hydrated compounds. Cohesion results from the formation and subsequent desiccation of the gel (paste).
ENHANCE TECHNOLOGY: Natural Cement Chemistry
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