Pergamon

PIhS0956-053X(96)00008-6

Waste Management, Vol. 15, No. 7, pp. 507-513, 1995 Copyright © 1996 Elsevier Science Ltd Printed in the USA. All rights reserved

0956-053X/95 $9.50 + 0.00

ORIGINAL CONTRIBUTION

QUALITY ANALYSIS/QUALITY CONTROL TESTS FOR FIELD STABILIZATION/SOLIDIFICATION ..... 2. UNTREATED WASTE, SODIUM SILICATE SOLUTION AND SOLIDIFIED WASTE

Caijun Shi, Julia A. Stegemann and Robert J. Caldwell Water Technology International Corporation. operator of the Wastewater Technology Centre and the Canadian Clean Technology Centre, 867 Lakeshore Road, P.O. Box 5068, Burlington, Ontario L7R 4L7, Canada

ABSTRACT. This paper reports on the efficacy of selected quality analysis/quality control testing procedures that were used during a full-scale stabilization/solidification trial of an arc furnace dust with high multiple contaminants. The qual- ity analysis/quality control test results of untreated waste, sodium silicate solution and solidified waste are discussed. Moisture content of the untreated waste was measured to control water addition. It was found that sodium silicate con- centration in solution was linearly related to its specific gravity. Thus, hydrometer measurement of specific gravity was used to control the silicate concentration in solution. Bulk density, moisture content, and cone and K-slump of freshly solidified wastes were measured. Laboratory measurement of bulk density and moisture content of freshly solidified wastes correlated well with water addition. It appeared from the field data that bulk density measurement underestimated the actual water-to-solid ratios, while moisture content measurement overestimated them. Cone slump and K-slump mea- surements fluctuated widely, the measurements were within the range normally observed from different types of concrete. Copyright © 1996 Elsevier Science Ltd

INTRODUCTION

Stabilization/solidification (s/s) of hazardous wastes by mixing with hydraulic binders, such as Portland cement and Portland blast furnace slag cement, usu- ally results in a strong, durable matrix of low perme- ability. Most heavy metals are precipitated as hydroxides of low solubility in the resulting alkaline environment. Thus, s/s can immobilize contaminants in two ways: (1) by chemically binding them in an insoluble form, and (2) by physically trapping them in a rigid, impermeable and durable matrix.

A variety of techniques have been developed for quality analysis/quality control of concrete mixes in

RECEIVED 23 MAY 1995; ACCEPTED 13 FEBRUARY 1996. Acknowledgements--Financial support for the field validation of test methods for solidified waste evaluation protocol is being pro- vided by Environment Canada's Demonstration and Evaluation of Site Remediation Technologies program, the United States Environmental Protection Agency, British Columbia Environment, and by the Ontario Ministry of the Environment and Energy.

The authors would also like to express their gratitude for expertise and in kind contributions to the project by Laidlaw Environmental Services Ltd, Shaw-Eurocan Environmental Inc., Standard Slag Cement and Lafarge Canada Inc., National Sili- cates Ltd, and Beachville Lime.

the cement and concrete industry, including titrimet- tic measurement of cement content, gravimetric or radiometric measurement of water content, bulk density measurement, air content measurement, and slump testing. However, no reliable quality control tests have been developed or proposed for field solidification processes. As part of a field validation study of their proposed protocol for solidified waste evaluation, j which will correlate laboratory test results with field behaviour, the Wastewater Tech- nology Centre (WTC) investigated the applicability of several rapid tests for quality analysis and control of the field solidified waste.

A pilot-scale landfill has been constructed by WTC and 63 m 3 of solidified arc furnace dust placed in it to correlate test results measured in the labora- tory with behaviour in the field. 2 The cementing additives were pre-blended and then transported to the field s/s site in a pneumatic trailer. At the time of solidified waste placement, a variety of rapid quality analysis and control tests were performed on pre-blended additives and solidified wastes. In Part 1 of this work, 2 quality analysis/quality control testing procedures and results for the pre-blended additives were reported. This paper deals with the quality

507

508 C. SHI ET AL.

analysis/quality control testing procedures and results for untreated wastes, sodium silicate solutions and solidified wastes.

The objectives of this work were to develop and validate quality analysis/quality control test methods for use during field stabilization/solidification.

A P P R O A C H

The selection of the arc furnace dust, solidification formulation development and additive pre-blending processes were described in detail in Part 1 of this work. 2 Only the preparation and test procedures related to the sodium silicate solution, the arc furnace dust and the field stabilization/solidification trials are described here.

Preparation and Addition of Sodium Silicate Laboratory development of the s/s formulation was conducted using solid sodium metasilicate dissolved in warm tap water. However, this anhydrous reagent is slow to dissolve, so a concentrated sodium silicate solution was prepared for use in the field s/s. The concentration of Na2SiO 3 in a solution can be deter- mined by chemical analysis, but this is an expensive and time-consuming process, and not practical for field quality analysis/quality control. Thus, a calibra- tion curve between specific gravity and concentra- tion of a sodium silicate solution was established in the laboratory and used to monitor the concentra- tion through specific gravity measurement of the sodium silicate solution used in the field test.

The concentrated sodium silicate solution was transported to the field site in a tanker truck. The properties of the concentrated solution are shown in Table 1. At the field site, water from a storage con- tainer was added to the concentrated silicate solu- tion in a 300 gallon (1130 1) fibreglass tank, until the desired concentration was achieved, based on mea- surement of the specific gravity of the diluted con- centrate using a hydrometer. Completed batches of sodium silicate solution were stored in a 500 gallon (1890 1) fibreglass tank, which provided the sodium silicate feed for the s/s process.

Untreated Arc Furnace Dust Characteristics The electric arc furnace dust was collected from the waste generator over a period of approximately 6 weeks, and stored in polypropylene supersacks under a tarpaulin prior to field solidification.

The total mass of dust used in the field experiment was 63 tonnes. Eighteen samples of arc furnace dust were collected by random sampling from the super- sacks after they had been transported to the field site. The moisture contents of 13 samples were deter- mined in situ using a Sartorius MA 30 electronic moisture analyzer at 65°C. Seven samples were sub- mitted for chemical analysis and the remaining 11 samples were archived.

Field Stabilization~Solidification A pilot-scale landfill was constructed in the 6 m compacted clay cover of the hazardous waste landfill operated by Laidlaw Environmental Services near Sarnia, Ontario, Canada. The experimental cell was designed as an inverted pyramid, with a maximum depth of 3 m at the centre, and an 18 × 18 m base. The solidified waste (63 m 3) w a s surrounded by a 0.5 m layer of silty sand, with a permeability of 1D 6 m/s. Full liner, leachate collection, and leak detection systems were installed, but no cover was provided, in order to allow free entry of precipitation.

Mixing of untreated waste, dry pre-blended addi- tive and silicate solution was performed using a mobile treatment system provided by Shaw-Eurocan Environmental Inc. (SHEEINC). The SHEEINC unit is composed of a central high-shear concrete mixer, surrounded by hoppers on load cells for each of the components of the mix. Mixing took place in batches with a total mixed volume of approximately 0 . 1 5 m 3 each. The components were mixed for approximately 3 min before being discharged to a positive displacement pump which transported the mixture a distance of approximately 50 m to the landfill cell. A pencil vibrator was used to compact the solidified waste upon discharge into the cell.

S/s of 414 batches took place between 2 October and 23 October 1993 to yield a total of approxi- mately 63 m 3 of solidified waste in the cell. The solidified waste from each day was observed to set by the following day, such that each day's work rep- resents a separate lift in the final solidified mass. During s/s, the mass of each component was recorded on a LOTUS 123 spreadsheet for each batch.

To assess the quality of the field solidified wastes, bulk density, moisture content, cone-slump and K- slump tests were performed. Excessive addition of mixing water will cause a porous solidified product which will have high contaminant leachability and poor durability, so the primary purpose of these

TABLE 1 Properties of Sodium Silicate Solution

Na20 SiO 2 Na20: SiO 2 Solid content (%) Specific gravity pH of solution (%) (%) (tool. ratio)

6.55 5.99 1.06 : 1 12.45 1.142 13.94

QA/QC TESTS FOR FIELD STABILIZATION/SOLIDIFICATION--2 509

tests was to minimize the water-to-solid ratio while maintaining adequate workability for pumping and placing. Thirteen samples of solidified waste were taken from the end of the discharge pipe for these tests. Specimens were also collected for curing and later testing in the WTC laboratory according to the WTC solidified waste evaluation protocol. 3 Bulk density. Bulk density measurement was chosen as a quality control test for the field because of its simplicity and reproducibility. The bulk density was measured by weighing cylinder vials 45 mm diam- eter and 75 mm high filled with solidified waste in the laboratory. Bulk density was reported as the ratio of the mass of filled solidified wastes to the vol- ume of the vials. A relationship between the bulk density of solidified wastes and water-to-solid ratio was established prior to the field solidification. Cylin- drical plastic moulds 76 mm in diameter and 152 mm high were used to measure bulk density during the field solidification. The solidified waste was placed in two layers and consolidated by manual vibration. Water content. In parallel with bulk density mea- surement, direct measurement of water content was chosen as a quality control test. The water content was determined using a Sartorius MA 30 electronic moisture analyzer. This measurement takes approxi- mately 15 min when drying the solidified wastes at 65°C. A relationship between the measured moisture content and calculated moisture content based on the water addition was also established in the labo- ratory before the field solidification. Slump. Two different types of slump tests were investigated for evaluating the workability of the field solidified product: 1. Cone slump testing is a standard test (ASTM

C143) 4 which is used to control the workability of fresh concrete in the concrete industry. The cone slump is measured by placing and compact- ing freshly mixed concrete in a mould in the shape of the frustum of a cone. The distance between the original and displaced position of the centre of the top surface of the concrete is reported as the slump of the concrete after the cone is raised. The cone slump test is also recom- mended for classification of "liquid wastes" by the Ontario Ministry of the Environment and Energy Government of Ontario, 5 and the method described in Ontario Regulation 347 was used in this study.

2. K-slump testing is a non-standard test, but it has the advantage that it can be performed in s i t u . 6

The results have been correlated with the cone slump of concrete mixtures, as shown in Fig. 1. The K-slump is measured by an apparatus called a "K-slump Tester" which consists of a porous hollow tube with external and internal diameters of 19 and 16 mm and a two-end plugged 13 mm

diameter hollow plastic measuring rod with scale. To measure K-slump, the measuring rod is raised first, then the tester is vertically inserted down into the concrete or solidified wastes to a certain depth without any rotation. After 60 s, the mea- suring rod is lowered slowly until it rests on the surface of the material that entered into the tube, and the K-slump is read directly on the scale of the measuring rod. 6 Because the lifts of solidified waste were not always thick enough to allow in situ K-slump measurement, some tests were per- formed in a 0.02 m s pail.

Depending on the application, the recommended cone slump for concrete can range from 25 to 150 mm. Using the correlation shown in Fig. l, this cor- responds to a K-slump of 0.5 to 69 mm.

In the construction industry, a slump is specified in order to ensure that concrete has appropriate workability for placement; the maximum slump cri- terion also limits the addition of water. In the case of solidified waste, workability is also important in production of a solid monolith with a low surface area for leaching. Because both slump tests need a large sample of solidified waste, few laboratory tests were performed and no relationship between work- ability and water addition for the solidified product was established in the laboratory. However, water addition in the field was adjusted, by trial mixing, to yield the stiffest possible product that could be pumped and placed uniformly in the cell using a pencil vibrator.

RESULTS AND DISCUSSION

Untreated Waste Characteristics Excluding one sample with a higher moisture con- tent, the average moisture content of the arc furnace dust was 0.8% and was ignored for the purpose of adjustment of water addition. The average contami- nant concentrations and coefficients of variation are summarized in Table 2. A stabilization/solidification formulation could be sensitive to the contaminant

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• . . . . . . . i . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . i . . . . . . .

. . . . . . . : . . . . . . . , ' . . . . . . . ' . . . . . 2 N . . . . ~ . . . . . . . : . . . . . . . ,~ . . . . . . . : . . . . . . . : . . . . . . .

: ' ~ ' T ! ....... . . . . . . i . . . . . . .

8 ~ . . . - . : . . . . . . ~ . . . . . . . i . . . . . . . - . . . . . . . ~ . . . . . . . ~ . . . . . . . i . . . . . . . - . . . . . . . il . . . . . . .

T ....... . . . . . . .

0 10 20 30 40 50 60 70 80 90 100 K-slump Testing (mrn)

FIGURE 1. Relationship between cone-slump and K-slump of concrete mixtures (data from ref. 7).

510 C. SHI ET AL.

T A B L E 2

Average Contaminant Concentrations in Elect r ic A r c Furnace Dust

Element Average concentration (mg/kg) ± coefficient of variation

B o r o n 783 + 6 .8%

C a d m i u m 131 ± 16%

C h r o m i u m 39,100 + 25%

C o p p e r 10,000 ± 14%

L e a d 15,000 + 8 .9%

M e r c u r y 1.5 + 55%

M o l y b d e n u m 3530 + 6 .0%

Nicke l 17,000 ± 11%

Z inc 66 ,000 ± 7 .4%

concentration and could need modification if there were a high variation in contaminant concentrations. Extensive laboratory optimization tests indicated that the formulation used in this field study could accom- modate the variation in contaminant concentration.

It should be noted that, while this testing verified bulk composition of the untreated waste, it did not verify speciation or leachability of the contaminants in either the untreated or solidified waste. A rapid leaching test developed by WTC may be able to address this issue, 8 but could not be field tested in this study because of the limitations of the mobile laboratory at the field site.

Addition of Sodium Silicate The relationships between solution specific gravity and sodium silicate concentration at 3°C and 23°C are shown in Fig. 2. It was found that if a 1.000- 1.220 hydrometer with a division of 0.002 was used, a change of one division corresponded to a change in concentration of 0.5%. A variation of half a divi- sion may be very clearly observed. Based on the design formulation, the required concentration of sodium silicate is 8%. Thus, the relative variance associated with using a hydrometer is approximately 4% of the silicate solution, which is accurate enough for the quality control of sodium silicate solution.

1.21 _ _ ~ ~ ~ ~ ~

1 . 1 ~ ~ i ............ i ........... .J" ........... ~ ............ i ........... i ............

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i . . . . . . . . . . . . . . . . . . ~ ,.,~ . . . . . . . . . . . i . . . . . . . . . . . . t c R = 0 . ~ I - ~ " i . . . . . . . . . . . .

, , ' . . . . . . . . . . . i . . . . . . . . . . . . ! . . . . . . . . . . . . . . . . . . . . . . .

1 08 . . . . . . . . . . . . . + . . . . . . . . . . . . " ' ~ - : ' ~ ' " " ~ " ' P ' " ' " " J i + . . . . . . . . . . . ~" . . . . . . " . . . . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1.02 . . . . . . . . ~ . . . . . . . . . . . ",, . . . . . . . . . . . .

1 2 4 6 8 10 12 14 Silicate ~ r a l k ~ n (%)

F I G U R E 2. Specific g r av i t y as a f u n c t i o n o f s o d i u m sil icate

c o n c e n t r a t i o n .

Figure 2 also indicates that temperature has an effect on the relationship between solution specific gravity and sodium silicate concentration.

Forty-five batches of sodium silicate solution were made during the field solidification. Table 3 summa- rizes the measured temperature, specific gravity and calculated concentration of the silicate solution. The effect of temperature on concentration was compen- sated for by interpolation based on the relationships between specific gravity and silicate concentration at 3 and 23°C, as shown in Fig. 2. Assuming a water- to-solid ratio of 0.26, the design concentration of sodium silicate in the solution was 8.0%, but the actual concentration used in solidification was varied from 2.49 to 10.55 based on the actual water-to- solid ratio, and the desired workability and setting characteristics of the mix. In particular, the sodium silicate concentration was increased to compensate for a higher than expected water consumption by the mix, and during cold weather, to avoid retardation of the set; it was decreased at the end of the day, to ensure that the solidified waste in the discharge pipe to the field cell would not set overnight.

Field Stabilization~Solidification Table 4 shows a summary of the additive dosages recorded in the field, in comparison with the design mix developed in the laboratory. It may be seen that the overall composition of the 63 m 3 of solidified waste corresponds closely to the design mix. Although the variation between batches, as indicated by the standard deviation, is small, there were occasional wide deviations from the design that were caused primarily by field equipment malfunctions. When- ever a malfunction occurred that could have been detrimental to the solidified waste, the equipment was shut down until the problem had been cor- rected. The data show that the water consumption by the field mix was higher than had been antici- pated in the laboratory. This, and the relatively cold atmospheric temperature, also resulted in a higher average concentration of sodium silicate than the design value, as described above.

QA/QC TESTS FOR FIELD STABILIZATION/SOLIDIFICATION--2

TABLE 3 Summary of Measured Temperature, Specific Gravity and Interpolated Concentration of 45 Batches of Silicate Solution

511

Item Temperature Specific gravity Silicate (°C) concentration (%)

Average 13.2 1.0928 7.96 Range 10.0-18.0 1.024-1.124 2,49-10.55

Standard deviation 1.74 0.021 1.70

TABLE 4 Summary of Field s/s Data

Mix component Waste Dry blend Silicate Water

Total quantity (tonnes) 63 41 2.8

Percentage of dry mix Average 58.9 38.5 2.6

Range* 53-62 3~44 0.5-3.1

Standard deviation* 0.8 0.8 0.5 2

57.4 40.4 2.1 26 Design formulation ( % )

33

31.1

14-38

* Expresses batch to batch variations.

Bulk density. As the density of pre-blended dry cementing materials and untreated arc furnace dust is much higher than that of water, bulk density mea- surements for a mixture were expected to provide a good indication of the water-to-solid ratio. This relationship was confirmed by measuring the bulk density of mixtures with different water-to-solid ratios in the laboratory. The data from this experi- ment have been plotted in Fig. 3, and show a good correlation with a correlation coefficient, R, of 0.998.

The average bulk density of the field quality con- trol samples was 2230 kg/m 3, with a range from 2150 to 2300. Using the regression equation in Fig. 3, these measurements indicate that the average water- to-solid ratio was 0.21, with a range from 0.14 to 0.30. The water-to-solid ratios based on the additive dosages ranged from 0.14 to 0.38, with an average of

2:300

2200

~ 21(73

200G

1700"

160( 2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Water-to-Solid Ratio

FIGURE 3. Relationship between bulk density and water-to-solid ratio of solidified arc furnace dust.

0.31. Thus, it appears that, in general, bulk density measurement resulted in estimation of lower water- to-solid ratios than indicated by the additive dosages. Moisture content. Although there was not the theo- retical 1 : 1 relationship, the measured moisture con- tent of solidified wastes in the laboratory correlated well with the calculated moisture content based on water addition, as shown in Fig. 4.

Table 5 shows the measured moisture contents of the fresh field solidified waste. The average measured moisture content of the quality control samples col- lected in the field was 24.2, with a range from 20.7 to 28.8. Using the regression equation in Fig. 4, these measurements indicate that the calculated moisture content ranged f rom 23.3 to 30, with an average of 26.1. The water-to-solid ratio is the quo- tient of the moisture content and the solids content,

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"~ 25"

~ 2 2 i i i - i i ', : ',

16. 16 19 22 25 28 31 34 37 40 43

Calculated Moisture Content (%)

FIGURE 4. Relationship between measured moisture content and calculated moisture content of solidified arc furnace dust.

512 C. S H I ET AL.

TABLE 5 Measured Moisture Content of Fresh Solidified Arc Furnace Dust

Batch no. Measured moisture content (% of wet solidified waste)

Rep 1 Rep 2 Rep 3 Average Standard deviation

2 22.2 23.27 23.08 22.85 0.57 3 25.39 22.85 23.62 23.95 1.30 4 21.39 22.06 21.96 21,8 0.36 5 25.78 26.31 27.92 26.67 1.11 6 24.37 23.99 24.18 0.26 7 29.41 27.19 26.48 27.69 1.53 8 25.83 24.31 24.08 24.74 0.95 9 31.21 28.48 26.8 28.83 2.23

10 23.73 23.42 22.41 23.19 0.69 11 23.92 25.17 24,19 24.43 0.66 12 19.23 21.54 21,35 20.71 1.28 13 23.67 26.11 23,02 24.27 1.63 14 20.63 22.52 20,49 21.21 1.13 Average 24.19 Range 20.71-28.83 Standard deviation 2.41

thus this corresponds to a water-to-solid ratio rang- ing from 0.30 to 0.43 with an average of 0.35. Thus, again comparing with the batch records, this tech- nique of moisture measurement appears to overesti- mate the water-to-solid ratio.

For comparison with Fig. 3, the bulk density mea- sured in the field was plotted in Fig. 5, as a function of the water-to-solid ratio calculated from the mois- ture content measured in the field. The regression equation is close to that determined in Fig. 2, but the correlation coefficient of 0.771. while adequate, shows more scatter than was evident in the labora- tory data. S l u m p . The cone slump measurements for the field solidified waste have been plotted against the K- slump measurements for the same samples in Fig. 6. There is no obvious relationship between the results from the two tests because of the limited number of points. However, comparison of Fig. 6 with Fig. 1 indicates that the results from the field solidified

I + / (R 0.7181)

0.20 0.25 030 0.3,5 0.4O 0.45 0.50 Water4o-.Solid Ralio

FIGURE 5. Field bulk density plotted as a function of field water-to-solid ratio.

waste are still within the range of results from con- crete. The cone slump test is known to exhibit large fluctuations, because it reflects minor changes in concrete composition. 9 For solidified waste, these fluctuations may be greater because the fresh solidified arc furnace dust is stickier than concrete, and tends to be drawn upwards as the cone is removed, i.e. a higher degree of operator skill is nec- essary to obtain reproducible measurements. On the other hand, K-slump testing can be performed in

s i tu and does not require particular skill on the part of the operator. There was no relationship between water content and slump measured for the field solidified waste.

C O N C L U S I O N S AND R E C O M M E N D A T I O N S

U n t r e a t e d W a s t e C h a r a c t e r i s t i c s

The moisture content of untreated wastes can be determined using a moisture analyzer to assess the

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i i i i i i i i i E 140" .................................................... ! i i ~ ~ " i *" ............................ i i i

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6 0 " . . . . . . . ~ . . . . . . . . ; . . . . . . . 4 . . . . . . . . ; . . . . . . . 4 . . . . . . . . ; . . . * - . . 4 - . . . . . . . ; . . . . . . . . " . . . . . . . .

+ ....... i ........ t ....... +,. ....... i ....... ....... t ....... ....... t ........ t ........ 20" . . . . . . . . "I . . . . . . . . l . . . . . . . . : " . . . . . . . I . . . . . . . 4 - . . . . . . . l . . . . . . . . ',- . . . . . . . ! . . . . . . . . I , . . . . . . .

o ; : : : : ; : : ; 0 10 20 30 40 50 60 70 80 90 100

K-Slump (ram)

FIGURE 6. Field cone slump measurements plotted against field K-slump measurements.

Q A / Q C T E S T S F O R FIELD S T A B I L I Z A T I O N / S O L I D I F I C A T I O N - - 2 513

requirement for adjustment of water addition during mixing. Contaminant concentrations should also be verified to ensure that the formulation is suitable for actual variations in contaminant concentrations. Although only bulk contaminant concentrations were analyzed in this study, a good quality control program for full-scale solidification operations should include examination of the leachability of the treated waste.

Sodium Silicate Concentration When sodium silicate is added in the form of a solu- tion, the concentration of the solution can be simply controlled by hydrometer measurement of specific gravity. This method is also suitable for processes that use sodium silicate solution.

FieM Solidification Quality Control Although laboratory tests showed that bulk density and moisture content of freshly solidified wastes cor- related well with water addition, it appeared from the field data that bulk density measurement under- estimated the actual water-to-solid ratios, while moisture content measurement overestimated them. However, the relationship between bulk density and moisture content found in the laboratory was con- firmed for field measurements. Thus, the measure- ments of bulk density and moisture content can be used as quality control indexes for field solidified wastes.

No simple relationship was found between cone- slump and K-slump measurements because of the limited amount of testing, but the measurements were within the range normally observed for differ-

ent types of concrete. Because solidified wastes are usually much more sticky than normal concrete, a higher degree of operator skill is needed for cone slump test. K-slump testing can be done in situ and does not require the same degree of operator skill.

REFERENCES

1. Stegemann, J. A., Caldwell, R. J. and Shi, C. Field Validation of Test Methods for Solidified Waste Evaluation, Draft Report, Wastewater Technology Centre, Burlington, Canada (1994).

2. Shi, C., Stegemann, J. A. and Caldwell, R. J. Quality Con- trol/Quality Assurance Tests for Field Solidification/Stabiliza- t ion-1. Dry Cem. Addit. 15, 265-270 (1995).

3. Wastewater Technology Centre. Proposed Evaluation Protocol for Cement-Based Stabilized~Solidified Wastes. Environment Canada Report EPS 3/HA/9 (1991).

4. American Society for Testing & Materials. ASTM C-143, Standard Test Method for Slump of Hydraulic Cement Con- crete, Annual Book of A S T M Standards, Iiol 04.01, Cement; Lime; Gypsum. ASTM, Philadelphia (1991).

5. Government of Ontario. Regulation 347. General- Waste Man- agement Regulation, Revised Regulations of Ontario, 1990 (as Amended), June 1993.

6. Nasser, K. W. and AI-Manaseer, A. A. New and simple test for slump of concrete. ACI J. Proc. 73, 561-565 (1976).

7. Nasser, K. W. and AI-Manaseer, A. A. Interoperator test program to determine the reliability of the K-slump tester. ACI Mat. J. 85, 197-201 (1988).

8. Caldwell, R. J. and Stegemann, J. A. Ultrasonic agitation method for accelerating batch leaching tests. In: Stabilization and Solidification of Hazardous, Radioactive, and Mixed Wastes, 3rd Volume, ASTM STP 1240. T. M. Gilliam and C. C. Wiles (Eds). American Society for Testing and Materials, Philadelphia ( 1995).

9. Popovics, S. The slump test is useless---or is it? Concr. Int. 16, 30-33 (1994).

Open for discussion until 27 September 1996