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Cement Additives for Permeation Grouting - Blast Furnace Slag

Blast Furnace Slag

Figure 11: Blast furnace slag (Portland Cement Association)

Introduction

Ground-granulated blast furnace (GGBF) slag (ASTM C989) is a by-product of the production of iron. It requires an alkaline medium to initiate hydration. Slag does not require a high pH to activate, instead addition of portland cement will create formation of calcium silicate hydrate. Slag consists of silicates and aluminosilicates of calcium and other bases. Slag is classified into three grades. The properties can vary between sources, but are fairly consistent for a single source (Weaver, 2009).

Since use of slag in cement decreases the need to landfill large amounts of slag, up to 3 million tons of carbon dioxide emissions can be eliminated annually (Portland Cement Association).

Advantages

  • Increases strength, flowability/pumpability and cohesion

  • Decreases permeability

  • It does not react or absorb large amounts of water like fly ash.

  • Sulfate resistance

  • Delay setting time and rate gain but can be counteracted with additives. Therefore, there is controllable set time.

  • Provides corrosion resistance

  • Strong bond to rock masses

  • Ability to immobilize heavy metals and other harmful substances

  • Low cost

  • No harm to the environment (Weaver, 2009)

Disadvantages

  • Increased set time (Kaeck, 2009)

Applications

Ground granulated blastfurnace slag is being used in mining applications. Instead of disposing the large amounts of tailings (soils/waste removed from mines), this material can be made into a slurry and mixed with a small amount of cementitious material. This mixture can be used to fill parts of mines that are no longer in use. Slag is frequently used (mixed with Portland cement) as the cementitious binder in this mixture due to its ability to produce high strength, low permeability material as compared to Portland cement alone. The addition of slag can also increase homogeneity and increase strength gain of the mixture (Jefferis, 2012). Blast Furnace Slag has also been widely used in Poland on dam foundation treatment (Weaver, 2009).

Case Studies

Grouting of deep foundations at the Thames river bridge in Connecticut (Kaeck, 2009)

In 1918 a moveable bridge carrying carrying the Amtrak railroad over the Thames river was constructed. In 2006 work to expand the bridge caused significant movement of one of the piers when the new piles, located 20’ from the existing 40’ wide by 99’ long caisson, were driven below the depth of the caisson. To stabilize the caisson, compaction grouting was first implemented but inclinometer data, shown in Figure 12, revealed that movement of the sand layer beneath the caisson was still occurring. Instead of compacting the sporadically dense sand, the grout was escaping into the overlying layer of organic silt. After compaction grouting failed, permeation grouting was used to stabilize the underlying sands. Because of the variability of the sand and the great depth, a typical cement grout would require too many boreholes due to inadequate permeation. Therefore, a commercially available blast furnace slag based cement with a maximum particle size of 10 microns and a Blaine Fineness greater than 900 cm2/gr was used. Because blast furnace slag delays the set time, which is a disadvantage for this application, a diutan gum blend was utilized to stabilize the grout during the 24 hour set time. It required approximately 270,000 gal of grout to initially stabilize the pier followed by an additional 350,000 gal to further stabilize the influence zone.


Figure 12: Pier movement vs. grouting progress (Kaeck, 2009)

Long Distance Tunnel Grouting (Ryan, 2003)

A water intake tunnel below the Niagara River was contaminated with organic wastes from a landfill. Because of this, regulatory authorities requested that the tunnel be grouted closed. This project was complicated due to the depth of the tunnel, the amount of grout that needed to be applied and the fact that water would not be removed from the tunnel before grouting.

Since the grout needed to travel 25 meters below the ground and up to 1600 meters along the tunnel, the mix needed to have a set time of more than 24 hours to allow significant amounts of grout to be in place before it begins to set. The required grout also needed to be able to easily displace water and set in a saturated environment. It was also required that the grout have low viscosity, a 28 day compressive strength of 100-200 kPa or greater and a permeability of 10-6 cm/s or less.

Many different grout mixes were tested to find the best option for this project. Variations of bentonite clay, fly ash, foam and slag were tested with Portland cement. In the end, a mix of 75% slag with 25% Portland cement, among other additives (including bentonite) was used. This grout easily displaced water and set under water in tests. It also had the desired strength (200-800 kPa) and permeability (10-6-10-7 cm/s). Finally, with the addition of slag, the mix had low viscosity, low bleed, and low shrinkage.

 

 

 

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