Development of a Recommended Practice for Use of Controlled Low-Strength Material in Highway Construction (2008) / Chapter Skim
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Pages 61-88
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From page 61... ...
Unless otherwise noted, the test methods, specifications, and guidelines developed under this project were implemented in the various field tests. The researchers recognized from the onset of this field testing program that not all of the long-term data (e.g., corrosion)
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From page 62... ...
EBMUDd Texas DOT TAMU e Technical Issue Long-term strength gain/excavatability Short-term strength gain/constructibility Corrosion of metals in CLSM Productivity and cost Resistance to freezing and thawing Construction issues (i.e., pipe floating) Settlement Use of by-product materials Environmental issues Permeability/leak detection CLSM Application Backfill Utility bedding Void fill Bridge approach aInformation on productivity and cost was also obtained from the New York DOT but is not included herein (for conciseness)
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From page 63... ...
The fresh properties of CLSM mixtures were measured at the site, including flow, density, air content, and mixture temperature. A needle penetrometer (ASTM C 403)
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From page 64... ...
For CLSM mixtures containing fly ash, specimens cured at the site had much higher strengths than those in the fog room during the first 3 months. Ultimately, strengths of specimens cured in the fog room approached those of specimens cured on site at later ages (e.g., 10 months)
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From page 65... ...
The cores from Paste were actually slightly higher than those cured adjacent to the trench, confirming that the higher temperatures experienced within the trench resulted in higher strength values. This exercise shows that coring is feasible for certain CLSM mixtures, provided they are strong enough to handle the coring action.
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From page 66... ...
also yielded low compressive strength values (for the site-cured specimens tested on the day of excavation) well below the 1 MPa value that is sometimes used in the field as a rough index of excavatability.
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From page 67... ...
can profoundly impact excavatability. As reported in Chapter 3, the splitting tensile strength of CLSM might be a better indicator of excavatability than compressive strength, because the actual excavation of CLSM mimics a tensile failure in the material.
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From page 68... ...
One interesting observation from the NW trench was the significant difference in the DCP values (and calculated 68 Method NE Trench NW Trench Square-head shovel Easy Nearly impossible: only shallow dents were made on the surface Round-head shovel Easy Very difficult: small pieces were removed Pick Easy Difficult: pick could penetrate into the mixture Kelly ball (ASTM D 6024) Average diameter 95 mm Average diameter 87 mm; C.O.V.
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From page 69... ...
The third mixture, designated as FF1, is a fast-setting mixture typically used for backfill applications when setting time is a critical issue. Flow and temperature were measured following ASTM D 6103, "Flow Consistency of Controlled Low Strength Material (CLSM)
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From page 70... ...
) was the standard practice as just described; each of the three CLSM mixtures was placed into a trench on top of sand (row A in Figure 4.6)
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From page 71... ...
1A 1B 2A 2B 3A 3B CLSM CLSM 6'' ductile iron pipe6'' ductile iron pipe (a)
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From page 72... ...
In addition to the potential difference study, metal coupons were fabricated from a ductile iron pipe and these samples were also buried in the trenches in row B to evaluate their mass loss due to corrosion. It is anticipated that their mass loss will be determined based on ASTM G 1, "Preparing, Cleaning, and Evaluating Corrosion Test Specimens." Ductile iron coupons were attached to 0.3 m long sample holders in groups of four and placed in the CLSM when it was still in fluid state.
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From page 73... ...
Test Results Fresh Properties The flow and air content of the three CLSM mixtures are shown in Table 4.11, along with the ambient temperature and relative humidity at time of placement. The flow values for the three mixtures were adequate for the trench filling (some water was added to mixture A to obtain the desired flow)
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From page 74... ...
Compressive Strength Compressive strength test results of the three CLSM mixtures are shown in Table 4.12. For each mixture, tests were conducted on cylinders stored adjacent to the trenches and in a fog room (standard curing)
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From page 75... ...
After significant evaluation, the fine aggregate used in the initial, unsuccessful bridge approach application was determined to be a dredged sand with most of the particles falling between 0.1 and 1 mm in size and a resultant fineness modulus of 1.33, well below the typical values for sands used in conventional concrete and many CLSM mixtures. Based on this investigation, it is quite possible that the use of the fine aggregate required such an increase in the water content in the field to get the desired fluidity that the early setting and hardening behavior was greatly affected.
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From page 76... ...
The fly ash had a CaO content of 27.9 percent and was effective because of its rapid hardening in CLSM mixtures of this type. The research team believed that by specifying the actual materials to be used in the field trial, a higher level of quality assurance could be attained, and the true benefits of using CLSM for bridge approaches could be realized.
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From page 77... ...
The unconfined compressive strength of the various rapidsetting CLSM mixtures is plotted in Figure 4.15. For almost every mixture, the strength values were mainly determined by 77 Mixture Sand(part by mass)
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From page 78... ...
Repair of Bridge Approaches The two candidate CLSM mixtures selected by the research team were approved by TxDOT for the repair of the bridge approaches on Loop 1604. However, the contractor opted to use only one of the mixtures for the actual repair.
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From page 79... ...
shows the placing of the rapid-setting CLSM mixture into the bridge approach area. Note that the backfill was built up as thin layers.
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From page 80... ...
The two bridge approach backfills were instrumented with temperature-measuring devices (i-buttons) to monitor the temperature history on the second observation night.
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From page 81... ...
This observation agrees with the measured variations in compressive strength quite well and supports the empirical relation typically used for conventional concrete, whereby the 81 Southbound Northbound Time after placement (h:m) Diameter of Kelly ball indentation (mm)
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From page 82... ...
The objective of the field testing was to investigate the CLSM strength gain, excavatability of CLSM, and the longterm corrosion performance of ductile iron pipes and galvanized corrugated steel culverts backfilled with CLSM. It was recognized from the onset that because of the long-term nature of corrosion, long-term field data would be needed.
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From page 83... ...
Wiring of ductile iron pipes and corrugated steel culverts.
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From page 84... ...
Four ductile iron pipe samples and four corrugated steel culvert samples, including one of each with limited exposure areas, were placed in each trench. The pipe pieces were placed on steel chairs to allow free flow of CLSM mixture underneath the pipes.
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From page 85... ...
Compressive strength testing was performed using neoprene pads and displacementcontrolled testing equipment. The setting times of the CLSM mixture in the condition I trenches were measured using a needle penetrometer with a 6.45 mm2 needle tip.
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From page 86... ...
Figure 4.30 shows the compressive strength of the CLSM mixtures sampled from the two trucks at 4, 7, and 28 days. 86 PVC box 2% slope 20 ft 100 ft 40 ft1.5 ft Chloride Section Condition I Condition II Condition III Figure 4.28.
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From page 87... ...
These tables show the average half-cell potential measurement against the Cu-CuSO4 reference electrode of the four galvanized steel or the four ductile iron pipes exposed to the same conditions. The half-cell potentials shown are timeweighted averages for the conditions shown.
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From page 88... ...
This disconnect appears to be greatest when fly ash is used, and as such, users should be aware of this issue when considering long-term excavatability. • There is no single property of CLSM (e.g., compressive strength)
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