INTERIM FINAL TECHNICAL REPORT

September 1, 1996, through August 31, 1997

Project Title: FIELD STUDIES OF ILLINOIS PCC BOTTOM ASH FOR STRUCTURAL GRADE CONCRETE PAVEMENTS

ICCI Project Number: 96-1/3.1A-26

Principal Investigator: Nader Ghafoori, Southern Illinois University at Carbondale

Project Manager: Daniel Banerjee, ICCI

ABSTRACT

In the past four years, Southern Illinois University at Carbondale (SIUC), under the sponsorship of Materials Technology Center, has performed a series of laboratory research into engineering properties and long-term durability of vibratory-placed and roller compacted structural grade concretes containing bituminous pulverized coal combustion (PCC) bottom ash. These laboratory efforts have resulted in identification of a number of potentially viable commercial applications for PCC bottom ash by-product residues.

One potential and promising application of the Illinois PCC solid waste residues, which also accounts for the large utilization of coal-based by-product materials, is in pavement construction. The proposal presented herein is intended to embark on a new endeavor in order to bring the commercialization aspect of the initial laboratory project a step closer to reality by conducting a field demonstration of the optimized mixtures identified during the four-year laboratory investigation. Fourteen different pavement slabs (each 24 ft wide by 24 ft long) were constructed at an identified site located in the Illinois Coal Development Park, Carterville, by two construction contractors who are part of the industrial participants of the initial projects. All sections are subjected to an extensive engineering evaluation and monitored for approximately two years for short, medium, and long-term performance. The field results are compared to that of the equivalent laboratory-prepared mixes in order to ascertain the suitability of the proposed PCC bottom ash concretes for field paving applications. Field cores taken from paving slabs are also tested for leaching of solid waste to obtain an aqueous solution which are used to determine the materials that could leach into groundwater under the specific testing conditions. The results are then compared with the requirements of Class I and II of IEPA Groundwater Quality Standards. Moreover, an economical analysis of using PCC bottom ash versus natural fine aggregate for structural grade concrete pavements are conducted. Standard economic and productivity studies are used to develop a model from which the cost of building PCC bottom ash concrete pavements (per mile) are compared to that of the road constructed using traditional natural fine aggregates.

EXECUTIVE SUMMARY

Most modern pulverized-coal boilers have dry bottom furnaces; that is, the ash is intended to be removed as a dry solid before complete melting occurs. The PCC units operating within the state of Illinois are all dry boilers. These furnaces generally have open grates at their bases. Below the open grates there is generally a water-filled ash pit designed to receive the ash from the furnace. Although a small amount of molten slag will form on the internal walls of the boiler and find its way into the ash pit, a large portion of the dry bottom ash is collected in a dry state. By collecting the ash in a dry state, the physical properties of dry bottom ash are quite different from wet bottom slag. The dry bottom ash has the appearance of natural sand and, when examined under magnification, the spherical nature of these particles appear to be internally porous rather than externally porous. In addition, the predominant material is light in color and has a sand paper-like surface texture. The dry bottom ash is also lighter in weight than the slag bottom ash and, thus, generates a lighter product.

The objective of this program is to examine the performance of Illinois PCC bottom ash structural grade concrete pavements by conducting a demonstration project at a designated site in Carterville, Illinois. The major tasks assigned to this field study fully examine the engineering characteristics, long-term performance, and economical and environmental issues involved in large-scale utilization of Illinois PCC bottom ash surface course highway pavements.

During this reporting period, an experimental two-lane road, consisting of 14 different vibratory-placed concrete slab sections, was constructed. Each 24 x 24 ft slab was 8 inches deep. In addition to longitudinal joints, shrinkage/construction joints were provided at 24 ft intervals. Dowels were used to transfer loads between slabs. A portion of the experimental road consisted of nine solid slab sections. Three of them were made with 100% PCC bottom ash as a fine aggregate component of concrete. The other three solid slabs had their fine aggregate consisted of equal volumes of PCC bottom ash and natural siliceous fine aggregate (river sand). The remaining three solid sections were the control concretes made with 100% natural siliceous fine aggregate. There were five sandwich sections made with 4 in. deep of a richer concrete encased between 2 in. leaner mixtures. Cement factors of 550, 650, and 750 1b/yd3 were used. Concretes were prepared with a uniform consistency of 4 1/4 inches and an air-entrainment of 6 1%. All trial mixtures possessed an identical volume of solid particles and were prepared with a constant slump, water-cement ratio, and air content. However, to achieve these uniform characteristics, the amount of added water-reducing and air-entraining admixtures had to vary among mixes. The dry components and proportion of each field and laboratory mixture are shown in Tables 1 and 2, respectively, along with the actual water-cement ratio and the amount of admixtures utilized. Once consolidation and final finishing were completed, slab sections were sprayed with curing compound and covered with a plastic sheet for a period of 7 to 10 days prior to opening to vehicular traffic flow.

Tables 3 and 4 document the initial setting times of the field and laboratory mixtures. Test results reveal that inclusion of bottom ash improves initial and final setting times when compared to that of control concretes. When the fine aggregate portion contained 100% bottom ash, the initial and final setting time of the field and laboratory sample decreased, over those of the equivalent control mixes, by 17 and 18%; and 20 and 14%, respectively. The initial and final setting times of the combined bottom ash and natural fine aggregate mixtures were lower than that of the control concretes by 6 and 10%; and 8 and 5% for the field and laboratory specimens, respectively. Increases in cement content reduced the initial and final time of settings of both bottom ash and natural fine aggregate concretes in an approximately linear fashion.

For a uniform water-cement ratio and workability, the amount of bleeding of all laboratory and field mixes varied linearly with increases in cement content. For the range of cement factors used, the accumulated bleeding water for the bottom ash concretes were 1400 and 2350%, for field and laboratory mixtures, respectively, below that of the control mixes. Bleeding was still somewhat lower for the field and laboratory matrices containing equal dry volumes of natural fine aggregate and bottom ash when compared to that of the reference concretes (106 and 208%, respectively). By effect of filler the finer PCC bottom ash particles attached themselves to the cement particles, reducing the channels for bleeding and leaving very little free water available in fresh concrete for bleeding.

Table 4 also displays the peak adiabatic temperature rise and the corresponding elapsed time for both bottom ash and reference mixes. Test results indicate that all mixtures under consideration produced peak temperature at a rate similar to each other. The number of hours elapsed to reach the maximum temperature was also similar for PCC bottom ash concretes and reference mixtures.

As shown in Table 4 the unit weight of the PCC bottom ash concrete specimens were slightly below that of the reference mixes. However, they remained in the range typically expected for normal weight concrete.

Table 1:  Mixture Proportions of Field Paving Slabs

Mixture No.	Cement Content (lb/yd3)	Natural Fine Aggregate (lb/yd3)	PCC Bottom Ash (lb/yd3)	Limestone Coarse Aggregate (lb/yd3)	Actual Water (lb/yd3)	Water- Cement Ratio	Water- Reducer Admixture (oz/100# of cement)	Ari Entraining Admixture (oz/100# of cement	Air Content Designated (%)
100	550	0	1160	1878	258.0	0.470	10.0	2.0	6 +/- 1
200	650	0	1039	1878	272.35	0.419	10.0	2.0	6 +/- 1
300	750	0	906	1878	288.8	0.385	10.0	2.0	6 +/- 1
400	550	579	548	1936	254.6	0.463	5.0	1.50	6 +/- 1
500	650	520	492	1936	258.8	0.398	5.0	1.50	6 +/- 1
600	750	450	426	1936	277.5	0.370	5.0	1.50	6 +/- 1
700*	550	1157	0	1936	246.5	0.448	0.0	1.0	6 +/- 1
800*	650	1040	0	1936	243.4	0.375	0.0	1.0	6 +/- 1
900*	750	899	0	1936	280.0	0.373	0.0	1.0	6 +/- 1
S200, T or B S100, M	650 550	0 0	1039 1160	1878 1878	267.42 260.70	0.411 0.474	10.0 10.0	2.0 2.0	6 +/- 1
S300, T or B S100, M	750 550	0	906 1160	1878 1878	286.36 260.70	0.381 0.474	10.0 10.0	2.0 2.0	6 +/- 1
S500, T or B S400, M	650 550	0520 579	492 548	1936 1936	260.60 251.40	0.40 0.457	5.0 5.0	1.5 1.5	6 +/- 1
S600, T or B S400, M	750 550	450 579	426 548	1936 1936	277.23 251.40	0.370 0.457	5.0 5.0	1.5 1.5	6 +/- 1
S500, T or B S100, M	650 550	520 0	492 1160	1936 1878	260.60 260.70	0.400 0.474	5.0 10.0	1.5 2.0	6 +/- 1

Table 2:  Mixture Proportions of Laboratory Specimens

Mixture No.	Cement Content (lb/yd3)	Natural Fine Aggregate (lb/yd3)	PCC Bottom Ash (lb/yd3)	Liomestone Coarse Aggregate (lb/yd3)	Added Water (lb/yd3)	Water-Cement Ratio	Water-Reducer Admixture (oz/100# of cement)	Air Entraining Admixture (ox/100# of cement)	Air Content Designated (%)
100	550	0	1160	1878	247.5	.450	9.00	5.00	6 +/- 1
200	650	0	1039	1878	260	.400	9.00	5.00	6 +/- 1
300	750	0	906	1878	281.3	.375	8.00	5.00	6 +/- 1
400	550	579	548	1936	123.75	.450	5.00	3.00	6 +/- 1
500	650	520	492	1936	114.0	.400	5.00	3.00	6 +/- 1
600	750	450	426	1936	114.0	.375	5.00	5.00	6 +/- 1
700*	550	1157	0	1936	118.4	.450	0.00	1.00	6 +/- 1
800*	650	1040	0	1936	110.0	.400	0.00	1.00	6 +/- 1
900*	750	899	0	1936	110.6	.375	0.00	2.00	6 +/- 1

*Control Mixtures

Table 3:  Fresh Properties of Field Paving Slabs

Mixture No.	Slump (in.)	Air Content Measured (%)	Bleeding (%)	Initial Times of Setting (hrs)	Final Times of Setting (hrs)
100	4 +/- 1/4	6.25	0.010	4.02	5.27
200	4 +/- 1/4	5.70	0.010	3.43	4.43
300	4 +/- 1/4	7.25	0.042	3.03	3.77
400	4 +/- 1/4	7.25	0.089	4.37	5.50
500	4 +/- 1/4	7.0	0.090	3.93	4.87
600	4 +/- 1/4	7.0	0.120	3.48	4.30
700*	4 +/- 1/4	7.0	0.180	4.72	5.87
800*	4 +/- 1/4	6.4	0.210	4.02	5.43
900*	4 +/- 1/4	5.8	0.220	3.77	4.93
S200, T or B S100, M	4 +/- 1/4	7.0 6.0	0.023 0.01	4.10 4.39	4.94 5.53
S300, T or B S100, M	4 +/- 1/4	6.0 5.5	0.05 0.01	3.55 4.39	4.38 5.53
S500, T or B S400, M	4 +/- 1/4	5.5 5.0	0.105 0.092	3.42 4.10	4.45 5.31
S600,T or B S400,M	4 +/- 1/4	5.5 6.5	0.127 0.092	3.12 4.10	3.68 5.31
S500, T or B S100, M	4 +/- 1/4	5.25 5.0	0.105 0.01	3.42 4.39	4.45 5.53

*Control Pavements S = Sandwich sections T, B, and M = Top, bottom, and middle layers

Table 4:  Fresh Properties of Laboratory Specimens

Mixture No.	Slump (in.)	Air Content Measured (%)	Bleeding (%)	Initial Times of Setting (hrs)	Final Times of Setting (hrs)	Peak Adiabatic Temperature (degrees F)	Time to Reach Peak Adiabatic Temperature (hrs)	One-Day Demoled Unit Weight (lb/ft3)
100	4 +/- 1/4	6.5	0.00	3.12	4.52	125	11	142.30
200	4 +/- 1/4	5.5	0.01	2.73	3.93	131	10	143.10
300	4 +/- 1/4	5.5	0.047	2.55	3.77	140	11	143.80
400	4 +/- 1/4	6.0	0.086	3.55	4.68	116	12	145.0
500	4 +/- 1/4	6.0	0.094	3.05	4.40	127	12	145.60
600	4 +/- 1/4	6.0	0.157	3.03	4.32	140	11	146.05
700*	4 +/- 1/4	6.0	0.305	3.63	4.75	120	10	145.90
800*	4 +/- 1/4	6.0	0.324	3.58	4.70	126	12	146.50
900*	4 +/- 1/4	6.0	0.352	3.23	4.68	136	12	147.10

*Control Mixtures