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Permeation Grouting Case Study

Cement Additives for Permeation Grouting

 

Cement Additives For Permiation Grouting 

(Foam, Fly Ash, Blast Furnace Slag and Silica Fume)

By: Olivia Marshall and David Quintal

April 7th, 2014

 


 

 


Introduction

There are many different additives that can be used in cement mixes which are used to improve certain properties of the mixture depending on the application. This project focuses on foam (cellular), fly ash, blast furnace slag, and silica fume as additives and partial replacement of cement grouts.

Grout is used to improve many inadequate or failed soils by injecting stabilizing materials. Cement grout is typically injected into granular soils to improve bearing capacity, reduce settlements and permeability and mitigate liquefaction (Akbulut, 2003). Grout is in general injected until the soil cannot accept any more grout however even small amounts of grout injected into soils can significantly improve soil characteristics (Ali, 1992).

 

Each additive has unique properties that contribute to improvement of certain properties of the grout. The specific changes in properties of a grout mixture can often be either an advantage, disadvantage or both depending on the application. The effects and applications of the cement additives or alternatives are given below for each of the additives.

 

 


 Foam (Cellular) Grout

Figure 1: Foam used for for grout mixture (Cellular Concrete, 2014)

Introduction

Foam or cellular grout is a cement grout mixture that contains foaming agents (surfactants) (Bruce, 2005). The foaming agents create many small air voids in the mix that reduce the unit weight and improve flow of the mixture. Foam grout density ranges from about 30-80 pcf (480-1300 kg/m3) which result in 28-day compressive strengths of 50-1200 psi (350-8300 kPa). The density and compressive strengths of the mix are tradeoffs: the higher the density, the higher the compressive strength. To achieve a specific compressive strength, different mix designs should be tested to find a minimum density to achieve the desired strength (Henn, 2003). Figure 2 shows the tradeoff between density and compressive strength for cellular grouts with varying degrees of foaming. With increased quantities of foam the density (unit weight) decreases resulting in a decrease in compressive strength.


Figure 2: Variation of compressive strength with unit weight and cure time for foam grouts (Vipulanandan, 2000)

Advantages

  • Easy to level

  • Free flowing (easy to pump vertically and horizontally, fills small voids)

  • Self-leveling

  • Does not require compaction (fills voids)

  • Frost resistance

  • Good thermal insulation

  • Good water absorption

  • Fast and inexpensive

  • Can pick desired density and strength (Barnes, 2009)

  • Good energy absorption (Vipulanandan, 2000)

  • Can endure deformations (Vipulanandan, 2000)

  • Requires low pump pressure (Midwest Mole)

Disadvantages

  • Low strength (McGillivray, 2012)

  • High compressibility (McGillivray, 2012)

  • If placed below the water table, the foam grout must be dense enough to displace the water (Henn, 2003).

Applications

Foam grout is typically used as a low cost option when strength is not a requirement (McGillivray, 2012). The air voids in foam grout allow the material to be somewhat compressible and therefore a good material for increased energy absorption. This property makes foam grout a good option for seismic areas, highways, and airport runways (Henn, 2003). It can also be used as backfill for tunnels and pipelines and fill material. It is also used to fill in the ring between the outside of a pipe and it’s surroundings (backpack grouting) (Vipulanandan, 2000).

Sliplining has been used with increasing popularity to replace existing concrete sewer pipes. In this process a new pipe is introduced within the existing pipe and the annular space between the pipes is filled with grout to support the new pipe and control infiltration. Poor grouting mixes and practices have resulted in many problems when it comes to sliplining including “unwanted buoyant uplift, excess deflection or collapse of the new liner pipe.” To avoid these problems it is very important to use a lightweight grout with good flow properties which is why foam grouts are typically used for these applications (Vipulanandan, 2000).

Although foam grout is generally used as a lightweight material to fill voids, it can also be used for stabilization purposes such as protecting slopes against earthquakes or preventing liquefaction. Typically, to stabilize a soil with grout the void space is completely filled with a particulate or chemical grout but often the same soil could be adequately stabilized by grouting the particle contacts without filling all the void space. Ali and Woods show how particle contact grouting can be accomplished with the use of a foam grout. By introducing bubbles through the foaming process, sand specimens were able to be grouted to various degrees of cementation. A micrograph showing cemented particles surrounded by void space can be seen below in Figure 3. For large scale remediation projects, the amount saved by not completely filling the void space can be significant (Ali, 2009).


Figure 3: Micrograph showing open pores and pendular elements formed between Ottawa 20-30 sand particles (Ali, 2009)

 

 

Case Study

Sinkhole remediation in Hillsborough Florida (McGillivray, 2012)

In 2003 a sand/cement/foam grout was used by McGillivray et al. to successfully treat sinkholes in Hillsborough Florida. The foam used for this project was a synthetic material which came in a concentrate form. Using a foam generator, shown in Figure 4, a foaming agent with small stable bubbles was created and dispensed directly into mixing trucks, shown in Figure 5. The mixing trucks, which originally contained a partial load of sand/cement/fly ash grout mixes the foaming agent with the grout mixture to create a pre-formed foam grout, shown in Figure 6. For this application, the grout was only required to be slightly stronger than the surrounding soil so a target strength of 3 MPa was used. Laboratory compressive strength tests of the foam grout used for the project had an average strength of 3 MPa with a standard deviation of 0.6 Mpa. Through experimentation it was shown that a 60% to 40% grout/foam mixture would result in a 20 to 25% savings on cost for a typical sinkhole remediation project compared to using traditional grouts.


Figure 4: Foam Generator Setup (McGillivray, 2012)

Figure 5: Foam being added to mixing truck (McGillivray, 2012)

Figure 6: Foam grout after pumping (McGillivray, 2012)

 

 

 


Fly Ash

Figure 7: Fly ash (Portland Cement Association)

Figure 8: Fly ash particles (University of Kentucky, 2014)

 

Introduction

Fly ash (ASTM C618) is a by-product of the combustion of coal in power plants. In cement mixes, a portion of the cement can be substituted with fly ash due to its pozzolanic properties. Fly ash is a electrically precipitated powder produced from crushed coal. The fine (10 micrometer) particles are made up of silicate glass spheres containing silica, alumina, iron and calcium. The particle gradation is slightly more coarse than portland cement. Since fly ash is a waste product, it’s properties can vary by source (Weaver, 2007).

Fly ash comes in two different types: Class C and Class F. Class F is rather inexpensive and has pozzolanic characteristics but cannot set without a source of calcium (lime or cement). Class F fly ash is produced from anthracite or bituminous coal and cures slowly. Class C has both cementitious and pozzolanic characteristics, so it can set by itself without cement. It is produced from subbituminous or lignite coal and can be pulverized to improve hydraulic properties. If more than 15% by weight of cement is Class C fly ash, the grout can deteriorate due to expansive tendencies of the Class C fly ash. There should be no more than 10% carbon used in grouts containing fly ash since more water will be required (Weaver, 2007).

Typically for a fly ash/cement grout, 15-20% of the cement is replaced by grout but due to economic and environmental pressure, high volume fly ash/cement grouts (grouts containing > 55% fly ash) are being used with greater regularity. A few important property changes that occur from the use of high volume fly ash use include a decrease in flow time for low water/cement ratios, significantly increased stability for high water/cement ratios, a decrease in setting time due to the slow reaction of fly ash (shown below in Figure 9) and a reduction in modulus of elasticity (Mirza, 1999).


Figure 9: Effect of 60% fly ash on the initial setting time of portland cement and portland cement/fly ash mixtures (Mirza, 1999)

Advantages

  • Often a cheap partial replacement for cement

Abstract

During summer 1996, low-pressure permeation grouting was performed inside portions of four unlined, shallow waste disposal trenches at a radioactive waste burial ground that was opened in 1951 at the Oak Ridge National Laboratory (ORNL). The objective was to selectively control sources that release about 25 percent of all strontium 90 (90Sr) discharged from the ORNL complex. A unique grouting methodology was adapted to control interaction of wastes with natural runoff at this humid site. Driven sleeve pipes were injected 4 to 5 times with multiple formulae of type III portland cement- based grouts, ultra fine cement-based grouts, and acrylamide grouts. Multiple-hole grout injection was monitored continuously using real time monitoring equipment. Apparent Lugeon values were calculated during grouting operations and grout formulae were continually adjusted during injection to maximize permeation, durability, and economy. Over 500 cubic meters of combined grout types were emplaced. At the completion of production grouting, the effectiveness of grout spread and in situ hydraulic conductivity of the grouted mass were assessed. The average residual hydraulic conductivity measured in more than 20 check pipes was less than I x 10` cm/sec. Hydrologic monitoring has been established to determine the overall effectiveness of the project for 9OSrmore » control.« less

Authors:
Long, J.D.; Huff, D.D. [1]; Naudts, A.A. [2]
  1. Lockheed Martin Energy Systems, Inc., Oak Ridge, TN (United States)
  2. ECO Grouting Specialists, Ltd, Cheltenham, Ontario, (Canada)
Publication Date:
Research Org.:
Oak Ridge National Lab., TN (United States)
Sponsoring Org.:
USDOE Office of Environmental Restoration and Waste Management, Washington, DC (United States)
OSTI Identifier:
459324
Report Number(s):
CONF-970208-7
ON: DE97003335; TRN: 97:006703
DOE Contract Number:
AC05-96OR22464
Resource Type:
Conference
Resource Relation:
Conference: International containment technology conference and exhibition, St. Petersburg, FL (United States), 9-12 Feb 1997; Other Information: PBD: [1997]
Country of Publication:
United States
Language:
English
Subject:
05 NUCLEAR FUELS; 54 ENVIRONMENTAL SCIENCES; STRONTIUM 90; GROUND DISPOSAL; CONTAINMENT; SOILS; REMEDIAL ACTION; RADIONUCLIDE MIGRATION; GROUTING; ORNL; PERMEABILITY; HYDRAULIC CONDUCTIVITY; MOISTURE; CONTAMINATION

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