B -- DEVELOPMENTS AT NIST

Researchers at the National Institute of Standards and Technology (NIST) are working on the following technologies. For further information, contact the: National Institute of Standards and Technology, Dale Bentz, 100 Bureau Drive, Stop 8615, Gaithersburg, Maryland 20899; Fax: +1 (555) 000-0000. This is not an announcement of a contract action or a grant. NIST DOCKET NUMBER: 04-022 Title: FLAIR-DCA - Fine Lightweight Aggregates as Internal Reservoirs for the Delivery of Chemical Admixtures Description: The invention consists of a unique method to control the distribution/delivery of chemical admixtures within a hardening concrete. Recently, the usage of saturated fine lightweight aggregates to provide internal curing water to promote cement hydration in hardening concrete with a low water to cementitious binder ratio (w/c <=0.42) has been demonstrated in the laboratory and the field. The novel aspect of this invention is to utilize these same internal reservoirs to supply chemical admixtures such as shrinkage-reducing admixtures, corrosion inhibitors, etc., to the concrete. As the cementitious components of the concrete react with the mix water, the hydration products occupy less volume than the starting materials. Thus, a concrete will imbibe water from its immediate surroundings or from internal sources to maintain a saturated capillary porosity. While to date, the internal reservoirs have been saturated only with water, they could equally be saturated with solutions of chemical admixtures. Admixture delivery via these internal reservoirs can offer several advantages over conventional delivery by direct addition to the mixing water. Some chemical admixtures such as shrinkage-reducing admixtures are partially absorbed by the cement hydration products. In this case, releasing the majority of the chemical admixture after some of the cement has already hydrated should result in a more efficient usage of the chemical. This would be the case should FLAIR be used to deliver the chemical admixture. Secondly, admixture combinations sometimes exhibit detrimental interactions. An example would be a shrinkage-reducing admixture which decreases the effectiveness of an air entraining admixture. By introducing the admixture that influences fresh concrete properties (air entrainment, rheology, setting) via conventional means and the admixture that influences hardened concrete properties (corrosion inhibition, shrinkage reduction, ASR mitigation) via the internal reservoirs, these detrimental interactions should be minimized.