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OCR for page 80
80
Laboratory mixture
Sample #6, 01:49 AM
35 Sample #5, 12:33 AM 5000
Sample #4, 10:43 PM
30 Sample #3, 12:54 AM
Penetration resistance (MPa)
4000
Penetration resistance (psi)
Sample #2, 12:34 AM
25 Sample #1, 12:05 AM
20 3000
15 2000
10
1000
5
0 0
0 50 100 150 200 250 300
Time (hours)
Note: Samples 1 through 3 were from one night's construction, and samples 4 through 6 were from
construction one week later, also at night.
Figure 4.17. Needle penetration values (ASTM C 403) for
rapid-setting CLSM used in bridge approach repair.
quite severe for CLSM due to the 13.62 kg mass of the steel section was due to the massive volume of the backfill. These
ball. When the CLSM was deemed to be strong enough to sup- high temperatures were not detected in the 150 × 300 mm
port heavy equipment, the asphalt paving commenced. cylinders prepared in the laboratory.
The two bridge approach backfills were instrumented with
temperature-measuring devices (i-buttons) to monitor the
Monitoring of Backfill Materials
temperature history on the second observation night. The
i-buttons were placed near the center of the backfill. The read- As previously described, compressive cylinders (75 × 150 mm
ing was taken every 5 minutes for 7 days. The results are plot- and 150 × 300 mm) were cast during the placement of the
ted in Figure 4.19. The southbound bridge approach reached rapid-setting CLSM. Because of logistical challenges in secur-
its peak of 47°C 24 hours after placement, while the north- ing and storing the cylinders in the field, they were transported
bound peak temperature of 54°C was reached about 2 days back to the laboratory after an age of at least 3 hours, by which
after placement. The measured temperature rise for each field time the cylinders were strong enough to resist damage due to
transport. The cylinders were then stored in a standard curing
room (23°C and 100 percent RH) until the time of testing. The
75 × 150 mm cylinders were tested using unbonded pads
(based on recommendations from Chapter 3) at ages of 1, 3, 7,
28, 90, and 180 days.
Figure 4.20 shows the strength development of cylinders
sampled from different batches at the jobsite. The variation of
strengths was relatively high, up to 20 percent, which can be at-
tributed to the cylinders being obtained from different batches,
variations in moisture content in sand, and inherent variabil-
ity in site-cast mixtures. In addition, visual inspection of
several cylinders after being tested to failure in compression
revealed the presence of deposits or lumps of white powder in
the mixture. This white powder was not analyzed, but the pres-
ence of this impurity, which may have been lime, likely had
some effect on the setting and hardening properties of the mix-
tures. Two of the sampled CLSM batches exhibited strengths
Figure 4.18. Use of Kelly ball to determine the proper greater than 5.0 MPa at an age of 6 months, which may make
timing of hot-mix asphalt paving. future excavation quite difficult. However, the intention of this
