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69 CBR combining the strength data from this field test with previously 1 10 100 1000 published data (Mullarky 1998), the short- and long-term 0 0 25 strength development can be plotted, as shown in Figure 4.5. 2 50 This graph emphasizes the long-term strength gain exhibited 75 by the CLSM in the NW trench, which ultimately resulted in DEPTH, mm difficulties in excavation. DEPTH, in. 4 100 125 150 6 Field Test at Hamilton County, Ohio 175 8 200 Introduction 225 250 Hamilton County (Ohio) has historically been one of the 10 1 10 100 1000 most innovative and advanced users of CLSM in the United States and was selected as a partner for a field test to tap into Figure 4.4. The CBR profile of NW trench. this experience. The objectives of this test were to investigate the constructability and early-age properties of CLSM and to CBR values) between the CLSM in the upper 80 to 100 mm of evaluate the long-term corrosion performance of ductile iron the trench and the CLSM below this point. To further evaluate pipes embedded in CLSM. This section briefly summarizes the this difference, the upper 80 to 100 mm portion of the trench main aspects of this field test; however, the key findings from was removed and found to be composed almost entirely of the corrosion study will ultimately be collected by long-term paste, without aggregates, clearly showing the effects of segre- monitoring of the site because of the long-term nature of cor- gation. This segregation may have occurred as a result of the rosion in field installations. inherent segregation susceptibility of this specific mixture or because of a hurricane that occurred shortly after trench Experimental Program placement. The calculation of RE was found to clearly differentiate the Three CLSM mixtures shown in Table 4.9 were chosen by excavatability of the two trenches. This RE value was calcu- Hamilton County engineers from a list of their approved CLSM lated based on strengths measured under the NRMCA proj- mixtures. Mixture S10 is commonly used for backfill applica- ect, and it is encouraging that the RE value was able to discern tions in the Hamilton County area. Mixture CDF1 is basically the removability of the two trenches, especially because the similar to S10, except the Class F fly ash used is high in carbon NW trench was originally designed to be excavatable. and is typically not allowed by state highway agencies for use in conventional concrete (mainly because of concerns with air entrainment) and sometimes not allowed by some agencies for Compressive and Splitting Tensile Strengths use in CLSM. This mixture was selected to demonstrate that Table 4.8 summarizes the strength tests performed on cylin- materials considered "off-spec" for some applications can be ders that had been stored in the fog room for about 6 years. suitable for use in CLSM. The third mixture, designated as FF1, Only a limited number of cylinders (four per mixture) were is a fast-setting mixture typically used for backfill applications available for testing; three were tested in compression and one when setting time is a critical issue. Flow and temperature were in tension from each set. The unbonded caps used for some of measured following ASTM D 6103, "Flow Consistency of the compression tests had a Shore A durometer of about 5. By Controlled Low Strength Material (CLSM)." Temperature was Table 4.8. Compressive and tensile strength of CLSM cylinders (stored in fog room for 6 years). Compressive Strength Splitting Tensile Strength Mixture Dimension Load Rate Capping Strength Dimension Load Rate Strength (mm) (kN/min) Method (kPa) (mm) (N/min) (kPa) 150 x 300 13.20 Sulfur 1779 NW 100 x 200 6.60 Sulfur 1864 154 304 6.60 170 100 x 200 6.60 Pads 1461a 150 x 300 1.32 Sulfur 408 NE 100 x 200 0.66 Sulfur 436 154 303 0.66 42 100 x 200 0.66 Pads 379b a The specimen was unintentionally crushed by sudden loading. b Large cavities were observed on the specimen surface.

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70 2 NE NW 1.5 Compressive strength (MPa) 1 0.5 0 1 10 100 1000 10+ Age (days) Figure 4.5. Compressive strength development of cylinders curing in the fog room. determined following ASTM C 1064, "Temperature of Freshly tance to allow CLSM to be used in direct contact with water Mixed Portland Cement Concrete." pipes. Therefore, in County projects involving water utilities, The test site, identified by Hamilton County engineers, was pipes are placed on sand beddings and backfilled with sand up adjacent to one of their ongoing project sites on Pontius Road, to 150 mm from the crown of the pipe. The rest of the trench Cincinnati. The site layout for the trenches is shown in Fig- is then typically backfilled with CLSM. The research team ure 4.6. Two rows of three trenches were excavated by Hamil- believes that backfilling the trenches completely with CLSM, ton County crews. The trenches were approximately 2.7 m as opposed to using primarily sand topped off with CLSM, long, 0.9 m wide, and 1.2 m deep. The 1.2 m depth was selected provides a faster construction method and potentially bet- because Cincinnati Water Works engineers require a depth of ter long-term corrosion performance of the pipe. To test 1.2 m for waterlines. this belief, the research team used and evaluated the two Hamilton County is a frequent user of CLSM for various backfill methods shown in Figure 4.7. The first method (Fig- applications and specifies it for backfill used in roadway cuts. ure 4.7(a)) was the standard practice as just described; each Hamilton County has had very good success in essentially of the three CLSM mixtures was placed into a trench on top eliminating problems with settlement often encountered of sand (row A in Figure 4.6). In the second method (Fig- when conventional backfill was used. However, the major util- ure 4.7(b)), ductile iron pipes were elevated on wood blocks ity in the area, Cincinnati Water Works, has expressed reluc- to allow CLSM to flow underneath the pipe and surround it Table 4.9. Mixture proportions of the CLSM mixtures. Cement Fly Ash Type Fly Ash Concrete Water Flow Temperature Mixture Content (ASTM Content Sand (kg/m3) (mm) (C) (kg/m3) C 618) (kg/m3) (kg/m3) S10 24 Class F 148 1727 273 305 26.7 Class F (high 28.3 CDF1 30 148 1727 273 127 carbon) Not FF1 None Class C 237 1721 a 305 30.0 specified a Water is added on jobsite to obtain the flow desired by the engineer.