Method for the elimination of adverse swelling of sulfate bearing soils

Abstract

A method is shown for reducing the adverse swelling action of sulfates in clay bearing soils during lime stabilization by treating soils having high sulfate content with a soluble aluminum compound that can react with the sulfate ions in the soil to form ettringite or other swelling species during the initial reaction with lime stabilization prior to compaction and paving of the lime treated soil. The amount of soluble aluminum ions added to the soil is determined by the concentration of sulfate in the soil and the other soil parameters such as the soils PI, clay type, etc.

Claims

1. A method for reducing the delayed swelling action of soluble sulfates currently present in clay bearing soils comprising: In a first step, pretreating the clay soil by adding a sufficient amount of a soluble aluminum ion compound into the clay bearing soil, wherein the soluble aluminum ion compound rapidly reacts with the soluble sulfates present in the clay bearing soil; In a second step, further adding a calcium hydroxide ion compound to the clay bearing soil by a lime stabilization process; Wherein the soluble aluminum ion compound, the calcium hydroxide ion compound, and the soluble sulfates in the clay bearing soil immediately react to start the formation of ettringite or calcium alumina sulfate hydrate, prior to compacting and constructing on the soil; Wherein the immediate formation of said ettringite or calcium alumina sulfate hydrate reduces the delayed swelling action of soluble sulfate in the compacted clay bearing soil.

2. The method of claim 1, wherein the soluble aluminum ion compound is selected from the group consisting of aluminum chloride, aluminum nitrate, sodium aluminate.

Description

(4) DETAILED DESCRIPTION OF THE INVENTION

(1) The tests which follow were conducted to determine if reactions that form ettringite could be accelerated in sulfate bearing soils by pretreating them with soluble aluminum ions in an effort to rapidly remove the soluble sulfate ions during the initial mixing of the calcium hydroxide with the soil, thus eliminating the adverse sulfate swelling that can occur during compaction and paving.

(2) Three soils are included in the tests, Table 1:

(3) TABLE-US-00001 TABLE 1 Soil samples Typical garden soil Low PI soil 25 PI High PI soil 40 PI

(4) To insure that the soils had high levels of sulfate, gypsum, calcium sulfate, 10,000 PPM was added to each of the soils. Soils that contain over 2,000 PPM sulfate has historically been associated with adverse sulfate swell.

(5) The typical testing procedures were:

(6) Control:

(7) 500 grams of soil was placed in a plastic container

(8) 9 grams of gypsum (10,000 PPM) was added to the soil

(9) 150 gram of water was added to the soil

(10) 45 grams of hydrated lime (9% HL to soil) was added and the soil was mixed in the closed plastic container.

(11) An exact match of the control was prepared but the soluble aluminum ions were added and mixed with the lime treated high sulfate soil. Two different levels of aluminum ions were typically added to the high sulfate lime treated soil samples. Aluminum Chloride, Aluminum Nitrate, and Sodium Aluminate were utilized as sources of soluble aluminum ions, and Aluminum Trihydrate, and Meta Kaolin were also tested to determine if they could supply the fast reacting soluble aluminum ions.

(12) 65 gram of the treated soil (representing 10% of the sample) were removed from the closed plastic contain as a function of time, diluted with 500 gm of water, vacuumed filtered and then diluted to 1000 gram and tested for soluble sulfate ions.

(13) Table 2 shows that the addition of soluble aluminum ions, Aluminum Nitrate, during the initial treatment of the lime stabilized soil lead to a rapid reduction of the soluble sulfate ions in the soil.

(14) TABLE-US-00002 TABLE 2 Soluble Sulfate ions remaining in soil (PPM) Additive Time None Aluminum Nitrate Hours 0 1440 PPM 2880 PPM 0 9,200 9,200 9,200 1 5,200 3,400 2,000 5 5,400 2,800 1,060 26 4,200 70 3,000

(15) Within 5 hours after mixing the soluble aluminum ions into the high sulfate lime treated soil the concentration of soluble sulfate ions decreased to low safe levels of soluble sulfate. With increased concentration of soluble aluminum ions the more rapid the decrease in soluble sulfate. The decrease in soluble sulfate ions with the addition of soluble aluminum ions was the result of the rapid formation of ettringite or similar calcium alumina sulfate hydrate species.

(16) Table 3 shows similar results with the addition of Aluminum Chloride:

(17) TABLE-US-00003 TABLE 3 Soluble Sulfate ions remaining in soil (PPM) Additive Time None Aluminum Chloride Hours 0 1220 PPM 2440 PPM 0 9,200 9,200 9,200 1 5,200 2,800 2,800 5 5,400 2,600 1,040 26 4,200 70 3,000

(18) Table 4 with the addition of Sodium Aluminate confirms that the addition of any form of soluble aluminum ions can rapidly react with the soluble sulfate ions and thus eliminate the adverse delayed formation of ettringite.

(19) TABLE-US-00004 TABLE 4 Soluble Sulfate ions remaining in soil (PPM) Additive Time None Sodium Aluminate Hours 0 1700 PPM 3400 PPM 0 9,200 9,200 9,200 1 5,200 2,400 1,160 5 5,400 2,800 1,800 26 4,200 70 3,000 1,320 1,170

(20) Tables 5 and 6 show that the addition of Aluminum Trihydrate and Meta Kaolin do not have the rapid soluble aluminum ions in the initial phase of lime stabilization, and thus do not react with the soluble sulfate ions in the soil.

(21) TABLE-US-00005 TABLE 5 Soluble Sulfate ions remaining in soil (PPM) Additive Time None Alumina Trihydrate Hours 0 4,000 PPM 8,000 PPM 0 7,000 7,000 7,000 4 4,200 5,100 5,400 28 3,100 4,300 4,100 76 3,500 4,100 4,600

(22) TABLE-US-00006 TABLE 6 Soluble Sulfate ions remaining in soil (PPM) Additive Time None Metakaolin Hours 0 1460 PPM 2920 PPM 0 9,200 9,200 9,200 1 5,200 6,400 6,800 6 5,400 4,400 4,200 24 4,200 4,400 4,400 67 3,000 3,200 3,000

(23) Thus the addition of Aluminum Trihydrate or Meta Kaolin provide additional evidence that it is not the total amount of aluminum which slowly becomes soluble in the lime treated high sulfate soil, but the amount of highly reactive soluble aluminum ions that can eliminate the potential delayed adverse sulfate swell.

(24) Table 7 shows the results of the addition of Aluminum nitrate to a 25 PI soil. This soil was a reactive soil that had clay minerals that reacted with the calcium hydroxide to form soluble aluminum ions after 24 hours thus lowering the soluble sulfate concentration from 10000 to 2000 PPM. The addition of soluble aluminum ions accelerated the process to only 6 hours.

(25) TABLE-US-00007 TABLE 7 Soluble Sulfate ions remaining in soil (PPM) 25 PI Soil Additive Time None Aluminum Nitrate Hours 0 1440 PPM 0 10,000 10,000 1 7,400 4,200 6 6,000 1920 12 5,400 800 25 2000 400 96 760 200 264 240 115

(26) Table 8 details results for the 40 PI soil. This soil was less reactive initially to the lime treatment and showed the advantage of the treatment with the soluble aluminum ions.

(27) TABLE-US-00008 TABLE 8 Soluble Sulfate ions remaining in soil (PPM) 40 PI Soil Additive Time None AluminumNitrate Hours 0 1300 PPM 0 10,000 10,000 1 8,600 4,800 5 8,200 3400 22 7,400 1780 72 4400 420 122 3000 280

(28) During the lime stabilization process it may be advantageous to add the soluble aluminum ions to the lime slurry and thus eliminate the additional step of adding the soluble aluminum compound to the soil. Table 9 shows comparable results of either adding the soluble aluminum ions directly into the soil or with the lime slurry.

(29) TABLE-US-00009 TABLE 9 Soluble Sulfate ions remaining in soil (PPM) Additive Time Aluminum Nitrate 1440 PPM Hours None Added to soil Added to lime slurry 0 9200 9200 9200 1 5200 3400 5000 5 5400 2800 3200 26 4200 1680 70 3000 860 840