# Presentation: 080936

## Capitalizing on Self-Desiccation for Autogenous Distribution of Chemical Admixtures

**Dale P. Bentz**
**4****th**** International Seminar on Self-Desiccation in Concrete**
**June 20, 2005**

## Background

- Self-desiccation due to chemical shrinkage results in:
- Reduction in internal RH
- Creation of capillary stresses in the pore solution
- Reduction in achieved degree of hydration relative to saturated curing
- Measurable autogenous deformation
- Possible (micro)cracking at early (and later) ages

## Example: Detrimental Influence

- Sealed curing and self-desiccation can lead to repercolation of originally depercolated capillary porosity in hydrating cement pastes as indicated by low temperature calorimetry (LTC) results

***Sealed/***
***resaturated ***
***specimens***
***w/c*****=0.35**
**20 ****o****C**

## Some Possible Benefits of Self-Desiccation

- Earlier application of flooring materials (Persson, 2002)
- Increased frost resistance (Powers, 1947)
- Offsetting thermal expansion at early ages (Swayze, 1942)
- Earlier depercolation of capillary porosity for intermediate *w/c* ratios (0.40 to 0.45)
***Autogenous distribution of chemical admixtures***

## Earlier Depercolation of Capillary Pores

***w/c*****=0.45, 40 ****o****C, 14 d curing**

## Earlier Depercolation of Capillary Pores

**saturated**

**sealed**

**- For intermediate *****w/*****c (0.4 to 0.45), sealed curing may be more effective at depercolating capillary porosity, as it concentrates hydration in smaller pores and pore entryways (not in empty larger pores)**

## Autogenous Distribution of Chemical Admixtures

- Concept is an extension of internal curing from delivering “curing” water to delivering solutions of chemical admixtures
- Fine lightweight aggregates are saturated with chemical admixture solutions
**FLAIR** (Fine Lightweight Aggregates as Internal Reservoirs)
- Potential advantages over conventional delivery
- Avoidance of detrimental interactions in fresh concrete
- More efficient delivery of admixtures that are partially absorbed by cement and hydration products

## Materials

- Cement and Concrete Reference Laboratory (CCRL) proficiency cement sample 152
- C3S: 73.4 %, C2S: 9.4 %, C3A: 13.1 %, C4AF: 4.1 %
- Blaine fineness of 408 m2/kg
- Mixing water-cement mass ratio (*w/c*) of 0.3
- Lightweight aggregates (LWA)
- Passing a #8 sieve, but retained on a #16
- SSD specific gravity of 1.67
- Water absorption of 20 % per unit dry mass LWA
- Saturated with either water or a 10 % shrinkage-reducing admixture (SRA)/water solution
- “Clarissa’s” mixture of four sands for a “high-performance” mortar

## Mortar Mixture Proportions

| Material | CONTROL | FLAIR | CONVENTIONAL |
| --- | --- | --- | --- |
| Cement | 1250 g | 1250 g | 1250 g |
| Water | 365.4  | 365.4  | 359.01  |
| Water reducer | 16.0  | 16.0  | 16.0 |
| SRA | --- | --- | 6.39 |
| F95 sand | 593.75 | 593.75 | 593.75 |
| Graded sand | 451.25 | 451.25 | 451.25 |
| 20-30 sand | 451.25 | 451.25 | 451.25 |
| S15 sand | 878.75 | 279.65 | 279.65 |
| Prewetted LWA | --- | 383.33 | 383.33 |
| Water for LWA | --- | --- | 63.89 |
| 10 % SRA solution | --- | 63.89 | --- |

## Measurements

- Air content of fresh mortar via unit mass
- Compressive strength of 50 mm cubes after 7 d, 28 d, and 91 d of sealed curing at 23 oC
- Degree of hydration at same ages via loss-on-ignition (LOI) analysis
- Drying shrinkage: 25 mm x 25 mm x 285 mm prisms exposed to 23 oC and 50 % RH after 3 d of sealed curing at 23 oC
- Autogenous shrinkage of 25 mm x 400 mm cylindrical corrugated tubes cured at 23 oC
- Jensen and Hansen method (Denmark)

## Mortar Properties

| Property | CONTROL | FLAIR | CONVENTIONAL |
| --- | --- | --- | --- |
| Air content | 3.4 % (0.6 %) | 8.3 % (0.4 %) | 5.1 % (0.4 %) |
| 7 d strength (MPa) | 38.8 (2.8 %) | 36.5 (4.6 %) | 40.4 (6.0 %) |
| 28 d strength | 42.1 (6.7 %) | 41.0 (3.7 %) | 41.0 (4.5 %) |
| 91 d strength | 43.7 (4.5 %) | 42.6 (9.9 %) | 42.7 (11.4 %) |
| 7 d hydration | 0.53 (0.01) | 0.57 (0.01) | 0.59 (0.01) |
| 28 d hydration | 0.57 (0.01) | 0.66 (0.01) | 0.66 (0.01) |
| 91 d hydration | 0.59 (0.01) | 0.68 (0.01) | 0.68 (0.01) |

**Higher air content in FLAIR system (SRA an air detrainer)**
**Equivalent performance in terms of strength**
**Enhanced hydration in the two systems with internal curing**

## Autogenous Deformation

**-FLAIR and conventional delivery provide equivalent**
**reductions in measured autogenous shrinkage**

## Drying Shrinkage (1)

**-Even with a higher water content, internal curing **
**mixtures exhibit less drying shrinkage due to the**
**presence of the SRA**

## Drying Shrinkage (2)

## Summary

- In this preliminary study contrasting FLAIR vs. conventional delivery of chemical admixtures:
- FLAIR system exhibited a significantly higher fresh air content (avoidance of SRA air detraining action)
- FLAIR and conventional delivery of the SRA, along with internal curing, provided basically equivalent improvements in both autogenous and drying shrinkage
- Further studies are underway for a variety of chemical admixtures and two LWA sources:
- Shrinkage-reducing admixtures
- Corrosion inhibitors
- Admixtures for mitigating alkali-silica reaction (ASR)

## Acknowledgements

- FLAIR collaborators
- Mr. Max Peltz (NIST)
- Mr. John W. Roberts (Northeast Solite)
- Mr. Thomas A. Holm (ESCSI)
- Dr. Neal Berke (W.R. Grace)
- Dr. Aiping Lu (Sika)
- Dr. Daniel Constantiner (Degussa)
- Ms. Caroline Talbot (Euclid Chemical)