Prior to the construction of test sections utilizing PCR rocks and QB, a laboratory investigation was conducted to ascertain the optimized blend of the large PCR rocks and QB1 in a single lift and in two lifts. A customized compaction steel box (called the UIUC packing box) was built according to the ASTM size specifications to investigate the packing efficiency of the two materials. The steel box, shown in Figure 3.5(a), is 24 in. (610 mm) x 24 in. x 21 in. (530 mm) in height. One side of the box has
a removable steel door, which can be pulled up to expose the cross-section to a Plexiglass side after compaction. A high-resolution image of the cross-section was taken to further study the packing and percolation of QB1 through the large rocks. The goal was to obtain a consistent and meaningful qualitative assessment of QB1 blends to select the optimized QB1 percentage for field applications.
(a) (b)
Figure 3.5. (a) UIUC packing box; and (b) Cross-section of the tests with 25% of wet QB (w% = 2.5- 2.6%) two lifts (top) and in a single lift on top of soft compacted subgrade (bottom).
The test matrix studied in the laboratory consisted of conducting fourteen different tests using the UIUC packing box. Several variables were studied to examine factors that might affect the packing of the QB with the large rocks, and the maximum quantity of QB that could be intermixed by shaking from the top of the lift. Table 3.4 presents a summary of the variables studied using the test matrix. More details are presented in Appendix A and elsewhere (Qamhia et al., 2017). Vibration was
achieved using a laboratory-sized vibratory roller (VIBCO US-1600 model), at a vibration frequency of 9000 rpm, to simulate the field construction procedure.
As a first step, tests for the compaction of the large PCR rocks in a single lift and in two lifts were conducted to measure the void ratios or porosities. The bulk specific gravity of the CS02 PCR aggregate material was measured as per ASTM C127 Standard (ASTM, 2015) to be 2.67. Using this specific gravity and based on the packing arrangement of the large rocks in the box (with no particle crushing or breakage), void ratios of 77.5% and 83.1% were calculated (e = Vv/Vs) for the large rocks
compacted in two lifts and in one lift, respectively. These corresponded to porosity values (n = Vv/VT)
the maximum possible QB quantity to be used was determined to be approximately 40% of the weight of the dry large rocks.
Table 3.4. Summary of the Test Matrix for Tests Conducted Using the UIUC Packing Box
Test
No. Percentage of QB (%) No. of lifts
Moisture Content of QB (%) Support Condition Achieved Density pcf (kN/m3)
1 0 (PCR Only) 2 0 (oven-dried) Steel Bottom 93.8 (14.73)
2 0 2 0 Steel Bottom 93.9 (14.75) 3 0 1 0 Steel Bottom 90.1 (14.15) 4 0 1 0 Steel Bottom 91.9 (14.43) 5 20 2 0 Steel Bottom 113.3 (17.80) 6 40 2 0 Steel Bottom 124.6 (19.57) 7 30 2 0 Steel Bottom 120.6 (18.95) 8 30 1 0 Steel Bottom 119.0 (18.69) 9 30 2 0 Steel Bottom 121.4 (19.07) 10 40 2 0 Steel Bottom 129.1 (20.28)
11 35 1 0 Soft Loose Subgrade 118.3 (18.58)
12 30 2 2.6 Steel Bottom 120.4 (18.91)
13 25 2 2.5 Steel Bottom 116.6 (18.32)
14 25 1 2.6 Soft Compacted Subgrade 118.3 (18.58)
Following the determination of the void ratios, the effects of the following four study variables on the packing arrangements of QB were mainly investigated in the laboratory:
1. Number of lifts: A single 21-in. (530-mm) lift and two approximately equal 10.5-in. (265- mm) lifts with the QB1 were used. Appropriate amounts of QB1 were dropped and vibrated on top of each lift (either single lift or two-lift application) of the PCR rocks. 2. The quantity of the QB1: The quantity was varied from 20% all the way up to 40% of the
dry weight of the large rocks.
3. The moisture content (w %) of the QB1: Moisture content represents the dryness or wetness variability of the natural state of QBs obtained from a quarry source and used during pavement construction application. It varied from oven-dried QB1 (0%) to the as- received moisture content of the QB1 material from the source quarry (2.5±0.2%).
4. Reaction support in the experimental setup: The support conditions or foundation rigidity on top of which the samples are compacted need to address varying degrees of subgrade support. The support condition was varied from a rigid steel bottom to a very soft
subgrade soil placed at the bottom of the packing box and engineered to a CBR of less than 1% through moisture adjustment.
The heights of the loose large rocks, loose large rocks and QB1 on the surface, and the compacted mix were measured at nine locations (center, midpoint of each face, and each corner), and averaged for density calculations. To minimize variability, the same large aggregates were used for all tests. Laboratory experiments did not show significant differences in densities and characteristic trends of percolation between the single-lift and two-lift experiments with dry QB1. However, the results are expected to differ for wet QB as higher moisture contents reduce the ability of the QB1 to percolate and fill the voids at shallower depths with a single lift arrangement. For tests with varying QB1 content, 30% was found to be the optimum quantity of QB1 to be mixed with the PCR in the case of dry QB1. However, this same quantity was found to result in a relatively large amount of QB1 left on the surface for wet QB1 with a moisture content of 2.5%. Over the CBR=1% engineered subgrade, the optimum quantity of QB1 that could be packed was found to be 25% by dry weight of the large rocks for single lift arrangement. Moisture content was thus found to be the most dominant factor
governing the selection of the maximum allowable percentage of QB1 and optimum packing of inherent voids in PCR aggregates. Figure 3.5(b) showed the cross-section of the compacted large
rocks with 25% of QB by dry weight of the PCR aggregates, at a moisture content of 2.5-2.6% and (1) compacted in two lifts on top of a rigid steel foundation, and (2) compacted in one lift on top of compacted soft subgrade with CBR of 1%.
3.4 SUMMARY
This chapter provided a discussion of the materials selection criteria and the laboratory research components of this project. Laboratory tests described include grain size distibution, moisture- density tests, packing studies of QB with recycled coarse aggregates and with large aggregate subgrade rocks, and unconfined compressive strength testing of chemically stabilized QB applications.
The laboratory tests indicated that an optimum mixing ratio of QB with recycled coarse materials was 70% QB and 30% FRAP or FRCA by weight. Either 3% cement or 10% class C fly ash was found to provide appropriate compressive strength levels for chemically stabilized QB and QB blends with FRAP and cement achieving the highest strength; which was statistically different from chemically stabilized QB blends without coarse aggregates. The packing tests of QB into the voids of large aggregate subgrades indicated that 25% QB by the dry weight of the large rocks was approximately an optimum QB quantity to be used considering moist or wet conditions of QB delivery in the field. The next chapter will discuss the field designs and construction of the full-scale test sections based on the information from the laboratory studies.