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FLAIR - DCA: FINE LIGHTWEIGHT AGGREGATES AS INTERNAL RESERVOIRS FOR THE DELIVERY OF CHEMICAL ADMIXTURES

IP.com Disclosure Number: IPCOM000030967D
Original Publication Date: 2004-Sep-02
Included in the Prior Art Database: 2004-Sep-02
Document File: 5 page(s) / 50K

Publishing Venue

National Institute of Standards and Technology

Related People

Dale P. Bentz: INVENTOR

Abstract

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.

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Summary of Experiments Performed to Reduce to Practice the Invention “FLAIR: Fine Lightweight Aggregates as Internal Reservoirs for the Delivery of Chemical Admixtures”

            During the summer of 2004, preliminary experiments have been conducted to demonstrate the viability of using saturated lightweight aggregates (LWA) as chemical admixture delivery vehicles in mortar and concrete.  Specifically, experiments were conducted to examine the efficiency of utilizing the LWA particles to deliver a shrinkage-reducing admixture to a hydrating mortar.  Previously, it has been conclusively demonstrated that the separate additions of either a shrinkage-reducing admixture or saturated LWA to a mortar result in substantial reductions in autogenous shrinkage [1].  Thus, for a preliminary evaluation of the FLAIR technology, three different mortar mixtures were prepared:

1)      a conventional mortar (mixture proportions are given in Table 1) with a low water-to-cement ratio (w/c) and no addition of either the chemical admixture or lightweight aggregates,

2)      a mortar with the same cement paste w/c, but with the addition of a fraction of saturated lightweight aggregates (1.18 to 2.36 mm in diameter) and the addition of a shrinkage-reducing admixture to the mortar mixing water (mixture proportions in Table 2), and

3)      a mortar with the same overall composition as mortar #2, but with the shrinkage-reducing admixture contained in the solution used to saturate the lightweight aggregates.

Table 1. Mixture proportions for control mortar #1

Ingredient

Mass (g)

CCRL Cement 152

1250.00

Water

365.40

Daracem 19

water reducer

16.00

F95 Sand

593.75

Graded Sand

451.25

20-30 Sand

451.25

S15 Sand

878.75

Table 2. Mixture proportions for mortars #2 and #3 with LWA and shrinkage-reducing admixture

Ingredient

Mass (g)

CCRL Cement 152

1250.00

Water

359.01

Daracem 19

water reducer

16.00

Eclipse shrinkage

reducing admixture

6.39

F95 sand

593.75

Graded sand

451.25

20-30 sand

451.25

S15 sand

279.65

SSD LWA

383.33

            The mortars were prepared in a Hobart blender following the standard practice and the following properties were evaluated (up to ages of about 28 days):

1)      air content of the fresh mixture,

2)      degree of cement hydration vs. time,

3)      compressive strength development,

4)      autogenous shrinkage, and

5)      drying shrinkage.

A comparison of these properties will demonstrate the viability of utilizing the FLAIR system for the delivery of chemical admixtures in mortars and concretes.

1)      Air content of fresh mortar mixtures:

The following air contents were measured for the three mixtures: 1- 3.4 %, 2- 5.1 %, and 3- 8.3 %.  Mixture 1 exhibits the lowest air content due to the overall low water content (dryness) of the mixture and the absence of any LWA particles.  The specific shrinkage-reducing admixture employed in mixtures 2 and 3 is known to have air detraining properties, so the increased air content of mixture 3 relative to mixture 2 indi...