Class C Fly Ash As a Full Or Partial Replacement for Portland Cement Or Lime

68 TRANSPORTATION R ESEARCH RECORD 1219

Class C Fly Ash as a Full or Partial Replacement for Portland Cement or Lime

KENNETH L. McMANrs AND ARA ARMAN

A study was undertaken to evaluate the stabilization or mod Designation C 207, Type N) and a Type I portland cement ification of sands and clays using ASTM Class C fly ash as a (AASHTO Designation M85) were used in the study. full or partial replacement for hydraulic cement or hydrated A base or subbase material is usually evaluated with respect lime. Strength and durability tests demonstrated that the Class to its strength and durability. Louisiana Department of Trans C fly ashes of the study could be substituted for cement in portation and Development (DOTD) criteria (TR 432-82) some sands. Improvement of the sands was provided by the were used to evaluate the performance of the sand specimens matrix formed with fly ash acting as a filler and as a cementing (i.e., sand plus fly ash alone, sand plus fly ash and lime, sand agent. The test results indicate the importance of the gradation plus fly ash and cement, and sand plus cement alone). This characteristics of the materials and the effects on matrix quality due to the presence of fines in the natural sands. Also, improve specification required the minimum cement content to cor ments in the plastic properties and gains in soil support with respond to a strength of 250 psi with a 7-day curing period at the addition of fly ash and/or lime were evaluated for two clays. a temperature of 73° ± 3° F. The strength and durability of However, test results and analyses demonstrated that the Class the specimens were tested using ASTM C 593 procedures, C fly ash does not effectively compete as a substitute for lime except that the curing temperature was modified to agree with in the treatment of clays. DOTD TR 432-82. Class C fly ash used as a clay modifier was also studied. Electrical power plants in Louisiana use western coals and Both clays were evaluated with respect to changes in their are producing ASTM Class C fly ash. In addition to being plastic properties, strength index, and curing time. Atterberg pozzolanic, many Class C fly ashes have been shown to exhibit limit tests were conducted on the clays to evaluate the effects cementitious properties similar to portland cement. In recent of the additives on the soil plasticity. R-value tests were per years, an increasing number of stabilization projects has been formed to measure resistance to deformation and change in performed using Class C fly ash alone (1). Class C fly ash soil support values. with calcium oxide contents of 20 percent or more has report The standard Proctor (ASTM D 698) procedure was used edly adequately stabilized fine-grained plastic soils, as well as in molding the mixtures into sets of three specimens. In com coarse-grained soils, without the use of lime (1-4). The objec pacting the specimens, moisture contents were not allowed tives of this research were (a) to evaluate ASTM Class C fly to vary beyond ± 1 percent of optimum; and dry densities ash as a lone or partial replacement for portland cement in were maintained to within ± 3 lb of the theoretical dry weight sands and lime in clays and (b) to identify the manner in density. Those specimens not meeting these criteria were which improvements to the soils occur and the important remolded. characteristics of the materials. The molded specimens were extruded and cured for 7, 28, and 56 days at a temperature of 73° ± 3° F and at a relative humidity of 90 percent or greater. At the end of each curing TEST METHODOLOGY period, the mixtures were tested for compressive strength and durability. The average compressive strength of the three The testing program included two sands commonly used in specimen groups was used for comparison purposes. The coef base construction and two clays: a nonplastic A-3-0 sand, a ficient of variance of the individual group test values was slightly plastic A-2-4 silty sand (liquid limit = 21, plastic index computed and compared as a measure of the relative test = 7), an A-6(9) silty clay, and an A-7-6(20) clay. Ta dispersion. The coefficient of variance ranged from 5 to 14 ble 1 gives the engineering properties of the natural soils. percent with an overall value of 9 percent. Three fly ashes produced in Louisiana's Big Cajun, Nelson, DOTD TR 433-81 criteria for lime treatment of soils used and Rademacher power plants were included in the testing in Louisiana highways were used to determine the minimum program. The physical and chemical properties were analyzed amount of lime required. This requires that the liquid limit according to ASTM C 311 (Table 2). All the fly ashes were (LL) and plastic index (PI) after lime treatment cannot exceed ASTM Class C. The calcium oxide content ranged from 21.5 40 and 10, respectively, for soils used as a base course and percent to 27.2 percent. A hydrated, high-calcium lime (ASTM 40 and 15, respectively, when soils are used as a subbase. These criteria were also applied when fly ash was evaluated K. L. McManis, Civil Engineering Department, University of New Orleans, New Orleans, La. 70148. A. Annan, Louisiana Transpor as a replacement for lime with the clays. Both the A-3 sand tation Research Center, Louisiana State University, 4101 Gourrier, and the A-2-4 silty sand met this requirement without Baton Rouge, La. 70804-9245. treatment. McManis and Arman 69

TABLE 1 SOIL PROPERTIES Soil Variable A-3 A-2-4 A-7-6(20) A-6(9) Coarse sand (Ret #40) (%) 40 3 0 1 Fine sand (Ret #200) (%) 52 62 14 3 Clay and colloids (%) 3 17 55 34 Liquid limit(%) NP 21 60 31 Plastic index (%) NP 7 40 13 Max. dry wt. den . (pcf) 109.7 119.7 98.8 104.9 Optimum moisture(%) 13.0 12.l 23.1 19 .0 R-value < 5 30

NOTE: NP = nonplastic.

TABLE 2 CHEMICAL AND PHYSICAL ANALYSES OF FLY ASHES Fly Ash Source Variable Cajun Rademacher Nelson Retained #325 (%) 9.2-7.6 12.0-11.0 13 .9-18.3 Loss on ignition (%) 1.3-0.5 0.5-1.9 0.7-1.0 Total oxides• (%) 65.8-66.5 62.3-64.7 51.5-62.9 Calcium oxide (%) 21.5-24.5 27.20-24.0 25.2-25.8 Magnesium oxide (%) 4.4-4.7 4.9-4.5 4.9-2.9 Sulfur trioxide ( % ) 2.8-2.8 2.7-2.9 3.1-3.3 Alkalies(%) 1.34-0.66 1.49-1.06 1.45-1.74

NOTE: Materials were tested according to ASTM Designation C 311. 0 Si02 + Al 20 3 + Fe,0 3 •

As a measure of performance of the two treated clays in sands are shown in Figure 1. All three fly ashes gave similar an embankment or subbase, the R-value test (resistance value results. The addition of fly ash to the A-3 sand significantly ASTM D 2844) was used. A few specimen sets were subjected increased the maximum dry density and decreased the opti to an R-value retest with an additional 7 days to observe any mum moisture content throughout the range of fly ash per increase that may have occurred. centages tested. The reduction in optimum moisture content is attributed to the spherical shape of the fly ash particles in the sand voids, which lubricates the mix and aids in the den sification efforts. EVALUATION OF TEST RESULTS WITH The addition of the fly ash to the A-2-4 silty sand produced SANDS a small increase in dry density between 3.3 and 6.9 pcf with the different fly ashes. The maximum density occurred at fly To satisfy the stated acceptance criteria (250 psi compressive ash percentages of 15 to 20 percent for all three fly ashes. strength with a 7-day cure), the following minimum propor Additional fly ash beyond 20 percent produced a decrease in tions of stabilizing agents were required with the sands: density. The fly ash percentage corresponding to the maxi Stabilizing Agent A-3 Sand(%) A-2-4 Silty Sand mum density of the A-2-4 silty sand also seemed to coincide Fly ash 20-25 None meeting with the minimum value of the optimum moisture content. criteria Other mix combinations of cement plus fly ash and lime Lime + fly ash 4-6 lime+ None meeting plus fly ash with the A-3 sand also produced gains in density. 15 fly ash criteria Both lime and cement increased the density at different per All acceptable Cement + fly ash All centage levels. The resulting increase proportions or decrease varied among acceptable the different fly ashes. This was not the case for the A-2-4 except 4 silty sand. A decrease in density, below that of the raw soil, cement + 5 occurred with the addition of lime and was attributed to the fly ash effects of the fines present. Cement 8 All acceptable The aggregate gradation had a significant effect on the den The test results were evaluated in an attempt to identify or sity, strength, and durability of the mix (2,6). Using Talbot's explain the behavior of the fly ash mixtures. relationship for computing the ideal gradation necessary for maximum density, a grain size analysis was made for each sand.

Moisture Density p = (dfD)O 5 (1) where The density of the mixture has a major effect on the strength and durability of cement- and lime-fly ash stabilized materials P = percent finer by weight for grain size, (5,6). The curves for maximum dry density and optimum d = grain size being considered, and moisture content versus the percent fly ash additive for both D = maximum grain size. 70 TRANSPORTATION RESEARCH RECORD 1219

11'

14 0 13 1l IL --i 0 CL 12 s:: c 130 11 s:: >- I- 10 s:: 0 (/) z 1 21' II (/) w -I 0 !I c ::u I- 1 20 7 rri I (.'.) () !I 0 w ,, ,, z ~ -I " rri >- 4 z (t'. • SAND: OPTIMUM MOISTURE CONTENT -I 0 11 0 3 •SAND: A-3 MAXIMUM DENSITY II 2

1 01' 0 10 1 1' 20 21' 30 40 FLY ASH ADDITIVE , " (CAJUN)

1 40 1 1'

14 0 131' 13 1l IL -I 0 CL 12 s:: c 1 30 11 s:: >- I- 1 0 s:: 0 (/) z 121' 9 (/) w -I D !I c ::u I- 120 7 rri I 0 () II 0 w z ~ 11 1' -I " rri • SANDY-SILT: (A-2-'1) DENSITY >- 4 z 0:: -I • SANDY-SILT: OPTIMUM MOISTURE D 110 ;, II 2

101' 0 10 11' 20 21' 30 4 0 " FLY ASH ADDITIVE, " ( C AJUN) FIGURE 1 Dry density/optimum moisture content versus fly ash additive.

Figure 2 shows the original gradation curves for Rade providing a matrix for the sand particles. The maximum dry macher fly ash, the two sands, and the resulting gradation density was increased from 109.1 to 132.8 pcf with 25 percent curves for the soils blended with different percentages of fly ash. Rademacher fly ash. Note that the additional fly ash brings Figure 2 indicates that the addition of approximately 15 the resulting gradation curves closer to the ideal curve for percent fly ash would maximize the dry density of the A-2-4 maximum density of the A-3 sand (i.e., maximum density is silty sand compacted with the Rademacher fly ash. Test results achieved at 25 percent fly ash). With the absence of fines in demonstrated that 20 percent fly ash actually provided the the A-3 sand, the addition of the silt-size fly ash fills the voids, maximum dry density. The increase in maximum dry density McManis and Arman 71

100

I- lilO I (.'.) w 1!10 <> RODEMACHER FLY ASH ~ 0 RAW SOIL

LL 30 I- z w 20 u O'. w 10 0..

0 , . 00 0.00 0.01 0. 10 GRAIN SIZE, MM

100

I- lilO I (.'.) w 1!10 . ~ (> RODEMACH FLY ASH r- 70 m 0 RAW SOIL (A-2-4 SANDY LOAMl 'f:l. IDEAL_ GRADAl ION CURVE z eo

I- ~o • SOIL + 20% FLY ASH • SOIL + 15% FLY ASH O'. w z 40

LL 30 I- z w 20 u O'. w 10 0..

0 0 . 00 0.01 0 . 10 1. 00 GRAIN SIZE , MM FIGURE 2 Comparison of the gradation curves for the A-3 and A-2-4 sands with and without Rodemacher fly ash.

with the addition of fly ash was modest-increasing from of a secondary structure of silt and fly ash with clay particles 119.1 pcf to values ranging from 120.5 pcf to 124.8 pcf for the between. different fly ashes. The A-2-4 silty sand contained 35 percent fines (18 percent silt size and 17 percent clay size) for the natural soil. The addition of 20 percent fly ash to the natural Unconfined Compressive Strength silt and clay constituents of the A-2-4 soil gives 48 percent fines. It would appear that the small gain in density occurs Strength variation with increasing fly ash reflects the changes with a suspension of the sand particles in a matrix consisting observed in density for both of the sands (Figure 3). Large 72 TRANSPORTATIO N RESEARCH RECORD 121 9

140 700 • SAND: A-3 DEl~SITY • SAND:? DAY STRENGTH 0 SAND Y-SILT: (A -2-4) DENSITY 0 SANDY-SILT: (A - 2-4) 7 DAY STRENGTH 135 600

130 500 c: z 0 0 LI.... u z: o_ .., z rri >- 0 I- 125 400 0 (/) 0 z ~ LJ..J -0 0

I- ti) :r: -; ~ 120 300 ;;o rri w z: 3:: C) >- -; D::'. :r:: 0 -0 ti) 115 200

110 100

0 0 5 10 15 20 25 30 35 FLY ASH ADDITIVE, 7. FIGURE 3 Strength/dry density versus percent Cajun fly ash additive.

gains in strengths were developed in the A-3 sand with each and clay (25 percent CaO content x 20 percent fly ash/48 increment of increased fly ash. The strength variation of the percent fly ash, silt, and clay). The performance of the sta A-2-4 silty sand with fly ash also paralleled that of its variation bilized sands, as measured by their strength and durability in dry density. The fly ashes contained approximately 25 per tests, is closely related to the quality of the cementitious matrix cent calcium oxide (Table 2). Several investigators (7-10) of the mixture. In comparing the strength gain between mix have shown that much of the CaO in some Class C fly ash is tures of fly ash and the A-3 sand and A-2-4 silty sand, the combined with silicates and aluminates similar to that found difference can be seen. in portland cement. In comparing the performance of the There was an additional gain in strength corresponding to A-3 sand and the A-2-4 silty sand with the addition of 20 the addition of lime or portland cement with tly ash and the percent fly ash, the maximum cementing CaO constituents two sands. The strength gain with the addition of lime was possibly available would be 5 percent of the total mixture (25 not as significant in the A-2-4 silty sand as that occurring in percent CaO content x 20 percent fly ash). This would be the A-3 sand. Also, the A-2-4 soil seemed to produce more true for both sands. However, the A-3 sand would have a 25 erratic test measurements than did the A-3 sand. The clay percent CaO concentration in its fly ash matrix as opposed and silt-size fraction of the A-2-4 sand did not appear to have to 10.4 percent for the A-2-4 silty sand matrix of fly ash, silt, strong pozzolanic characteristics. The fines of the natural soil McManis and Arman 73

2200 A-3 SAND Ill 2000 0. 0 PORTLAND CEMENT J: 1800 I- • RODEMACHER FLY ASH Cl z 1800 4% CEMENT + FLY ASH llJ • 0: A I- 6% CEMENT + FLY ASH Ill 1400 8% CEMENT + FLY ASH 0. * ~ 0 1200 0

0 1000 llJz ... 1!100 z 0 0z 800 :::> >- 400 < 0 co 200 N

0 0 2 4 8 8 10 12 14 111 1 e 20 2 2 24 28 2a N PORTLAND CEMENT/RODEMACHER FLY ASH

1300

(/) 1200 D. 1100 I I- 1000 Clz w 0:: goo t- (/) 800 D. ~ 0 700 A-2-4 SAND 0 0 eoo PORTLAND CEMENT w z NELSON FLY ASH ... eoo 4% CEMENT + FLY ASH z + 0 400 6% CEMENT FLY ASH 0z 8% CEMENT + FLY ASH :::> 300 >- < 200 0

II) 100 N

0 0 2 4 e a 10 12 14 18 1a 20 22 24 28 2a 30 32 34 3e x PORTLAND CEMENT/NELSON FLY ASH FIGURE 4 Unconfined compressive strength versus percent portland cement/fly ash. may interfere with and produce discontinuities in the cement the additives for the cement-fly ash combinations appears to formed within the matrix by the fly ash and fly ash combi take the shape formed by shifting and combining the strength nations of additives. In the A-3 sand; the density (i.e., increased curves for cement and fly ash used alone (Figure 4). The percentages of fly ash) seemed to be more critical for strength cement- fly-ash strength of the A-3 sand demonstrates that gain than did the added lime. combining portland cement and fly ash contributes signifi A plot of the relationship between the 28-day strength and cantly to the cementing properties of the matrix. Similar trends 1000 • 25% CAJUN FLY ASH Ill 1100 n. • 20% CAJUN FLY ASH I 15% CAJUN FLY ASH t- 1100 • Cl z 1t' 10% CAJUN FLY ASH w 0: 700 t- Ill z 800 0 Ill soo Ill w 0: n. 400 l 0 0 300 Cl w z 200 ILz 0 0z 100 :::> 0 0 7 14 21 211 3~ 42 411 se 83 70 77 84 fil1 fill! CURING TIME, DAYS

1100 0 4% CEMENT Ill 1000 n. 6% CEMENT

:r 1100 * t- • 8% CEMENT Clz • 10% CEMENT w 1100 0: 201. RODEMACHER FLY ASH t- • Ill 700 25% RODEMACHER FLY ASH z *' 0 800 Ill Ill w soo 0: n. l 0 400 0 Cl 300 w z 200 ILz 0 0 100 z :::> 0 0 7 1 2 2 3 4 4 s 8 7 7 II II 1 4 1 II ~ 2 Iii 8 3 0 7 2 1 II 0 ~ J CURING TIME, DAYS FIGURE 5 Strength gain versus curing time for the A-3 sand with fly ash and cement. McManis and Arman 75 occurred in the cement-fly-ash mixtures of the A-2-4 Some reports have indicated that a portion of the calcium silty sand. However, the magnitude of the strength gain with oxide in some fly ashes exists as free lime, making it possible additional fly ash was much less, and the values were more for flocculation and agglomeration of clay minerals to occur erratic. and reduce the soil's plasticity (1,4). However, other inves tigators (7-10) report that the CaO (lime) present in the Class C fly ash is not in a free (available) state and, as a soil sta Curing Time bilizing agent, will not modify the plastic behavior of fine grained soils. The tests performed on the two clays in this In Figure 5, the initial slope of the strength-time curve is study were reviewed and analyzed in an attempt to examine indicative of the early self-hardening characteristics of the fly the role of the CaO in the fly ash. ashes. The initial set times of Class C fly ash have been reported to occur very rapidly in other studies (8,11). Laboratory tests conducted with slurries of sand mixed with Cajun, Nelson, Soil Plasticity and Rademacher fly ashes measured short initial set times ranging from 21 min to 3 hr 20 min. Thus, to get the full The Atterberg test results for the two clays, treated and advantage of Class C fly ash, the soil should be quickly mixed untreated, are shown in Figure 7. Lime added to the A-7-6 and compacted (11). clay reduced the liquid limit and greatly increased the plastic Comparisons of the A-3 sand with cement alone and with limit-resulting in a much-reduced plastic index. The lime the Rademacher fly ash alone are shown in Figure 5. The 25 fixation for this soil (i.e., the amount of lime required to percent fly ash mixture compared well with the 8 percent produce a constant value of the plastic index) is 4 percent cement and provided a denser mixture that may be more lime. This corresponds to a PI of 4 (raw soil PI = 40) and a durable. Using the current Louisiana DOTD strength/curing liquid limit of 38 (raw soil LL = 60). The A-6 clay was criteria and using the current local costs of cement and fly somewhat lime-reactive, and modifications to the plastic prop ash, the fly ash appeared to be competitive as a replacement erties of the soil occurred with the addition of lime. The PI for cement in a clean sand. was reduced from 13 to 7 with 2 percent lime and to 4 with 5 percent lime. Adding fly ash to the clays also produced changes in the Durability plasticity. These changes were greater in the A-7-6 clay (Fig ure 8). However, these changes occurring in the plastic prop Specimens were conditioned in a vacuum saturation chamber erties can be attributed to the effects of diluting the clay and tested for compressive strength according to ASTM C constituents with a nonplastic material (i .e., the fly ash). The 593 specifications, with the exception that they were cured in oretical relationships between the liquid and plastic limits and a humidity room at 73° ± 3° F rather than the 100° F specified the clay content were developed by Seed et al. (12). It was in the ASTM procedure. A comparison of the differences in shown that the variation of the liquid limit with the clay con strength between specimens subjected to this procedure and tent can be expressed as those not subjected provided a relative measure or indication WLL (C/100) WcLL (2) of the durability of all sand mixtures (Figure 6). There did = not seem to be any consistent loss of strength with the A-3 where sand beyond what might be expected as experimental varia tion. However, the A-2-4 silty sand demonstrated a consistent w LL = liquid limit of the soil mixture, loss in strength in the vacuum saturation test. WcLL = liquid limit of clay fraction, and C = percent of clay particles. A similar relationship for the plastic limit (14) is EVALUATION OF TEST RESULTS WITH CLAYS WPL = (C/100) WcPL (3)

where wPL is the plastic limit of soil mixture, and w c PL is DOTD TR 433-81 was used as the criterion to evaluate attempts plastic limit of clay fraction; or wPL = 0.5C (for C > 40). to modify the clay's plasticity (i.e., maximum LL of 40 and Assuming that the fly ash consists of particle sizes in the maximum PI of 10 and 15 for bases and subbases, respec fine sand-to-silt range (2) (Table 2) and that the only source tively). The Atterberg limits of the untreated A-6(9) silty clay of clay-size particles is from the A-7-6 clay alone, then satisfied the subbase criteria. The results of modification efforts on the plasticity of both soils produced the following C = [1 - (FA/100)] (% clay in raw soil) (4) proportions: where FA equals percent fly ash. Stabilizing Agent A-6(9) Clay (%) A-7-6(20) Clay (% ) Table 3 compares the liquid and plastic limits measured in Fly ash 20 (base 30 (base criteria, laboratory tests using the three fly ashes with those limits requirements) Rademacher only) predicted on the basis of variations in the clay content as 25-30 (subbase shown above. Average values of the percent clay in the raw criteria) soil were assumed to vary between 55 and 60 percent, and Lime 2 3 (base and the mean values tested for the liquid and plastic limits of the subbase criteria) Lime + fly ash <2 lime + fly ash Varies, raw soil were used. The outcome of the laboratory Atterberg approximately 2 tests did not vary greatly from what would be expected by lime with 10 fly ash blending a fine-grained, nonplastic soil with the A-7-6 clay. Ul D..

:r I- ~ 1500 w Ir 1- Ul w > •

~ 1000 w Ir D.. :l 0 0 0 w 500 z A-3 SAND IL • FLY ASH: 28 DAY STRENGTH z 0 • CEMENT / CEMENT + FLY ASH 0 z & LIME + FLY ASH :J

0 500 1000 1500 2000 2500 VACUUM SATURATION STRENGTH, PSI

Ul 1200 0. 1100 • • • :r I- C> 1000 z w Ir 1100 • I- ••• I/) •• eoo w > 700 • l/) l/) w eoo Ir D.. :l 500 0 () 400 0 • w A-2-4 SIL TY SAND z 300 • FLY ASH: 28 DAY STRENGTH LL • z 200 • CEMENT/CEMENT + FLY ASH 0 () z 100 "" LIME + FLY ASH :J

0 500 1000 1500 VACUUM SATURATION STRENGTH, PSI FIGURE 6 Unconfined versus vacuum-saturated strength for the A-3 and A-2-4 sands. 0 RAW A-?-6 SOIL: LL 110 D RAW A- 7-6 SOIL: PL o LIME: LL o LIME: PL •CAJUN FLY ASH: LL t- eo • CAJUN FLY ASH: PL z A RODEMACHER FLY ASH: LL w A RODEMACHER FLY ASH: PL t- 4e z •NELSON FLY ASH: LL 0 • NCLSON FLY ASI I: PL {) 40 w 0::: 3!5 :::> t- Ul 30 0 ~ 2!5

0 2 4 II 8 , , , , , 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 e 0 2 4 II 8 0 2 4 11 B 0 2 4 e B 0 2 4 8 8 0 PERCENT ADDITIVE

D RAW A-6 SOIL: LL D RAW A-6 SOIL: PL o LIME: LL o LIME: PL eo • CAJUN FLY ASH: LL • CAJUN FLY ASH: PL A RODEMACHER FLY ASH: LL tz • RODEMACHER FLY ASH: PL w • NELSON FLY ASH: LL t- 40 • NELSON FLY ASH: PL z 0 {) 3e w 0::: 30 :::> t- Ul 2!5 0 ~ 20 ~------:-= ie

PERCENT STABILIZER FIGURE 7 Atterberg tests versus percent additive for the A-7-6 and A-6 clays.

McManis and Arman 79

TABLE 3 ATTERBERG LIMITS: PREDICTED AND OBSERVED

Percent A-7-6 Fly Ash

FA c Raw Soil Cajun Nelson Rademacher Predicted

Liquid Limit

0 55 60

1 5 47 47 44 41 47-51

20 44 42 43 39 44-47

25 41 35 41 37 41 - 4 4

30 39 34 39 31 39-43

Plastic Limit

0 55 20

1 5 47 23 1 8 1 8 16-24

20 44 23 24 21 15-22

25 41 20 23 1 9 1 4-21

30 39 21 27 21 13-20

FA - fly ash percentage

C - clay fraction percentage

Thus, it appeared that the changes in plastic properties of Soil Support Resistance Value the fly ash-soil mixtures for these Class C fly ashes could be credited more to a decrease in the clay fraction than to chem The resistance or R-values of the A-7-6 and A-6 silty clays ical alteration of the clays. This is not to say that there was were greatly improved with additions of lime, fly ash, and not some effect or change due to whatever percentage of free lime-fly ash combination (Figure 8). However, the addition lime was available. However, there did not appear to be enough of lime or lime in combination with fly ash produced the free lime to provide substantial changes. greatest gain in the measured R-values for both soils . The testing procedure hould be con idered in evaluating the results. In this procedure, the test specimens were com Dry Density pacted after being mixed with the stabilizing agents and slaked with water for a 72-hr period. Within the ensuing 24 hr, they As expected, the addition of lime to the compacted clays were tested for exudation pressure followed by determination produced a density less than that for the raw soil. Although of expansion pressures. The R-values were measured approx the fly ash-soil density values varied, they seemed to produce imately 24 hr after compaction or 4 days after being initially densities that were approximately equal to those obtained mixed with the stabilit ing agents and slaking water. This is with the untreated soil. However, combining the lime and fly not enough time to assess the pozzolanic gain in strength. ash with the A-6 soil further reduced the density of the mix. There are also the effects of the slaking period on the Class The pronounced effect that the addition of lime had on the C fly ashes. Mixing the fly ash, soil, and water with the 72- density of both clays, with and without fly ash, and the Jack hr slake period in the R-value test procedure is probably of change (reduction) in density with the soil plus fly ash are counterproductive with respect to the fast initial set of the further indications of the absence of free lime in the fly ash. Class C fly ashes. 80 TRANSPORTATION RESEARCH RECORD 1219

100 31. LIME + FLY ASH 0 CAJUN FLY ASH • CAJUN - 7 DAY RETEST D RODEMACHER FLY ASH 95 ROD. - 7 DAY RElEST NELSON FLY ASH NELSON - 7 DAY RETEST

l.J..J =:) ~ 85 > I 0:::

12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 PERCENT: 3r. LIME + FLY ASH FIGURE 9 R-value gain with 7-day retests of A-7-6 clay with lime plus tly ash.

The uncured lime-soil and fly ash-soil mixtures immediately the test results of one set. The results varied but consistently improved the strength and deformation properties of both showed a significant gain in a relatively short time. Because soils with the most dramatic gai n occurring in the A-7-6 clay these test specimens were previously subjected to loading in (Figure ). Treating the A-7-6 ·oil wi th the lime or with the the stabilometer in the initial R-value test, the second R-value li me-fly ash p.rodu ed final R-valuc aim r as high a those determined at the end of an additional 7-day curing included of the 1-reated A-6 silty clay (R-va lues of 77 versu 5)-the some autogeneous healing in addition to further development A-7-6 being the mo t lime-reactive of the two soils. Lime was of their pozzolanic strength. them st effective tabilizing agent, although some small gains in the R-values were achieved in some cases by combining the lime and fly ash. Large quantities (30 percent) of fly ash CONCLUSIONS added to the lime showed no improvement over the smaller proportions (10 percent). The test results of this study demonstrate that ASTM Class Some of the A-7-6 specimens were retested for their R C fly ash could be u ed as a lone or partial replacement of values after an additional 7-day curing period. Figure 9 shows portland cement in and , depending n their gradati on char- McManis and Arman 81 acteristics. The improvement of the sands with the Class C REFERENCES fly ash tested is credited to its dual role as a matrix filler and cementing agent. The engineering and physical properties of 1. A. M. Digioia, R. J. McLaren, D. L. Burns, and D. E. Miller. the sand-fly-ash mixtures varied with changes in the fly ash Fly Ash Design Manual for Road and Site Applications, Vol ume 1: Dry or Conditioned Placement. Electric Power Research source. However, the general behavior was consistent for all. Institute, Palo Alto, Calif., Feb. 1986. Proportioning the A-3 sand and fly ash for maximum den 2. R. Pachowski et al. Brown Coal Fly Ash in Soil Stabilization. sity produced a correspondingly large gain in strength. How Interim Report FHWA/RD-84/072. U .S. Department of Trans ever, large quantities of fly ash (20 to 25 percent) were required portation, Federal Highway Administration, Oct. 1984. to maximize the density. Fly ash alone and the A-2-4 silty 3. M. Mateos. Stabilization of Soils with Fly A h Alone. Hlgltway Researclt Record 52, HRB, National Research Council , Wash sand did not fare well. Success in stabilizing a silty sand or ington, D.C., 1964. sandy silt with Class C fly ash will depend on the quantity 4. R. C. Joshi, D. M. Duncan, and H. McMaster. New and Con and reactive properties of the fine-grained material ( < #200 ventional Engineering Uses of Fly Ash. Transportation Engi sieve), that is, the matrix quality. The importance of the matrix neeri11g Jo11m11/, ASCE, Vol. 101, No. TE4, Nov. 1975. 5. B. J. Dempsey and M. R. Thompson. Vacuum Saturation Method materials with respect to durability was also reflected in a for Predicting Freeze-Thaw Durability of Stabilized Materials. greater loss of strength for the A-2-4 silty sand in the vacuum Highway Research Record 442, HRB, National Research Council, saturation tests. Washington, D.C., 1973. Alterations of the plastic properties of the clays with the 6. R. Andres, R. Giballa, and E. J. Barenberg. Some Factors Class C fly ashes used alone are attributed to an overall reduc Affecting the Durability of Lime-Fly Ash-Aggregate Mixtures. In Transportarion Research Record 560, TRB, National Research tion in the percentage of clay content corresponding to the Council, Washington, D.C., 1976. high percentages of fly ash used. The amount of free lime 7. W. C. McKcrnll , W. B. Ledbetter, and D. J. Teague. Analysis available in the fly ashes for cation exchange and flocculation of Fly Ashes Produced in 1e:ais. Research Rep n 240-1. Tcxa.~ agglomeration reactions is insufficient to compete effectively Transportation Research Institute, Texas A&M University, Jan. as a lime substitute. 1981. 8. W. B. Ledbetter. ls Lime in Fly Ash Available for Soil Stabili The soil support resistance of both clays as measured by zation? Civil Engineering Department, Texas A&M University, the stabilometer test was greatly improved with the addition April 1981. of lime or fly ash, or both. The greatest improvements occurred 9. M. L. Mings, S. M. Schlorholtz, J. M. Pitt, and T. Demirel. in the poorest soil [the A-7-6(20) clay]. As a lone additive, Characterization of Fly Ash by X-Ray Analysis Methods. In Transportation Research Record 941, TRB, National Research lime provided the greatest improvement in soil support. A Council, Washington, D.C., 1983, pp. 5-11. small gain in the R-values resulted when fly ash was added 10. J. M. Pitt, M. L. Mings, and T. Demirel. Characterization and to the lime. However, lime alone performed almost as well Techniques for Rapid Evaluation of Iowa Fly Ashes. In Trans without the fly ash. Unless proven economical to do so, there portation Research Record 941, TRB, National Research Council, does not appear to be any advantage to using a Class C fly Washington, D.C., 1983, pp. 12-17. 11. S. I. Tbornlon and D. G. Parker. Self-Hardening Fly Ash. AHTD ash over lime in the treatment of clays. Report H-52. Arkansas Highway and Trnnsp nation Depart ment, Little Rock, Oct. 1975. 12. H . B. Seed, R. J. Woodward, and R. Lundgren. Fundamental ACKNOWLEDGMENTS Aspects of the Atterberg Limits. Journal of the Soil Mechanics and Foundation Division, ASCE, Vol. 90, No. SM6, Nov. 1974. This study was sponsored by and conducted in cooperation with the Louisiana Department of Transportation and Devel opment and the Federal Highway Administration, U.S. Department of Transportation. The testing program was per Publication of this paper sponsored by Commiuee on Lime and Lime formed by the Louisiana Transportation Research Center. Fly Ash Stabilization.