Design of systems for time delayed activated internal release of chemicals in concrete from porous fibers, aggregates of prills, to improve durability

Abstract

Incorporation of chemicals into the internal matrix of cement or concrete, with later release occurring upon stimulation, alters the matrix parameters from those at the initial set. Permeability is reduced, for example, and therefore durability enhanced. The advantages of these designs would be the ability to reduce maintenance and repair costs in the initial building configuration and to delay the time of eventual repair. The components and the structure could take greater environmental abuse also.

Permeability is significantly reduced by release of a polymer from wax-coated porous fibers upon heating to temperature of polymerization. Freeze/thaw damage is somewhat reduced by the timed release of linseed oil or antifreeze from porous aggregates due to the freezing action itself. These example designs using timed release mostly gave improved durability performance when compared to conventional treatments for durability or environmental distress. Concerns that significant strength reduction would occur due to heating or fiber loading were shown to be unfounded by our test results; indeed, heating and fiber inclusion increased strength. An adequate amount of wetting of the samples could be obtained with 2.75% volume of fibers; however, above a 2.75% volume of fibers, fibers do reduce the strength. Results were analyzed by the method of comparing results in the samples with factors varied to results in samples without variable factors, that is, by comparing to the controls.

This research shows that timed internal release of chemicals into cement can be accomplished; it appears feasible and is potentially useful.

Long-term tests need to be performed on such factors as chloride ion intrusion/ corrosion tests. Filled fiber, aggregate or prill manufacture, storage, and placement need to be researched and assessed for cost. Design of components using only targeted areas for release in the component and the use of time released fibers in reinforced cement laminates should be evaluated.