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26 Table 3.17. Overview of laboratory Hardened CLSM Test Methods testing program. Unconfined Compressive Strength CLSM Initial Study Additional Studies Because of the importance of the compressive strength of Characteristic Flow ASTM D 6103 CLSM in specifications, design, and construction, consider- Setting/ Soil pocket penetrometer hardening time ASTM C 403 Pocket torvane able effort was placed in developing a test method with im- Sample size effect proved accuracy and reliability, and upon developing this Small vs. large machine method, work was done to better understand the effects of Loading rate Compressive Effect of drying samples materials and mixture proportions on CLSM strength. This ASTM D 4832 strength Alternative capping section describes the basic procedures followed to test the un- materials Effects of drainage confined compressive strength of the initial 38 mixtures, in- Curing methods, conditions cluding methods of preparing test cylinders, curing, capping, CLSM vs. sand ASTM G 1 and testing. After describing this approach, information is ASTM G 1, Galvanic cells modified G 109 provided on the various modifications and improvements in- pH ASTM G 51 vestigated using the mixtures previously shown in Tables 3.7 Resistivity ASTM G 57 through 3.15. The results of the initial compressive strength Segregation, bleeding ASTM C 940 study, as well as the findings of the various follow-up studies, Subsidence No Standard were used to develop and recommend an improved uncon- Triaxial shear USACE EM fined compression test for CLSM, as presented in Appendix B. strength 1110-2-1906 California Because the strength of CLSM is relatively weak (compared AASHTO T 193 bearing ratio to concrete), careful handling of the test cylinders is necessary, Resilient modulus AASHTO T 292 especially when stripping the cylinders from the molds. There- Water fore, plastic cylinder molds were pre-cut down the sides (two ASTM D 5084 permeability vertical cuts from top to bottom on opposite sides of the cylin- Drying shrinkage No standard Excavatability No standard Splitting tensile strength der) and taped closed. After the CLSM was mixed, the cylin- Chloride ASTM C 1152 ders were filled, while being tapped lightly on the sides to re- diffusion move large entrapped air voids. Plastic lids were then placed Freezing and ASTM D 560 Effects on permeability firmly on the cylinders, and the specimens were moved im- thawing Direct shear None mediately to the moist-curing or "fog" room, which was strength Thermal maintained at 100 percent relative humidity (RH) and 23C. None For most of the mixtures tested, the cylinders were kept in the conductivity Air/gas molds for 7 days (or less for tests performed at earlier ages) None permeability Consolidation None and were then stripped by simply removing the tape and re- Leaching None Chemical and toxicity moving the CLSM specimens from the cylinders. Conven- analyses tional stripping tools were not used because of possible dam- age to the specimens. The cylinders were then kept outside of their molds in the fog room until testing. Some CLSM mix- used for determining the FM of the fine aggregate. As is the tures tend to leach and soften upon long-term fog-room ex- case with the normal treatment of FM, two different grada- posure. Further studies on this issue and other cylinder stor- tions can yield the same FM. Therefore, the overall grada- age issues are described later in this chapter. tion was also considered when the results were analyzed, as Moist curing was selected for this study so that test results described later. Details of this test method can be found in can be compared from one laboratory to another, even though Appendix B. CLSM is rarely, if ever, moist cured in the field. The same ar- gument can also be presented for concrete testing. That is, con- crete is rarely moist cured for more than 7 days (if at all) in field Subsidence applications, but standard curing in a fog room provides a The surface settlement of a 100 600 mm cylindrical benchmark for specification and construction acceptance. CLSM sample was monitored with time. The mold was pre- Although an ASTM method currently exists for measur- pared by stacking three 100 200 mm molds. A PVC pipe is ing the unconfined compressive strength of CLSM (ASTM D also a good alternative. A small device to facilitate accurate 4832), some modifications were made to the method for this measurement of the surface height changes was developed, as project, as described later. Most of the compression tests described in Appendix B. were performed on a relatively low-load capacity machine

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27 (100 kN Instron), but some testing was also performed on a in the molds (in the fog room) until the time of testing. This larger capacity machine (1780 kN Tinius Olson) to evaluate procedure is different from the normal concrete approach to the effects of machine capacity. When using the smaller ma- stripping the cylinders from their molds after about the first chine, displacement control was used. Additional testing was day of curing and then curing them in the fog room. ASTM performed to examine the effects of cylinder size (75 100 mm, D 4832 also specifies test cylinders must undergo a drying 100 200 mm, and 150 300 mm), using a constant appar- time of 4 to 8 hours after their moist-curing period ends and ent strain rate. For this testing, the crosshead displacement before they are tested in compression. Concrete cylinders, on was set at 0.38 mm/min for the 100 mm high specimen, the other hand, are specified to remain moist until the time 0.51 mm/min for the 200 mm high specimen, and 0.76 of testing, with no required drying time. Research was con- mm/min for the 300 mm high specimen. The objective was ducted to investigate the effects of cylinder storage (i.e., in or to produce failure in about the same amount of time for each out of molds) and specimen conditioning or drying prior to cylinder size for a given mixture. A floating, spherical head testing. was used to minimize eccentricities in loading. To evaluate the effects of different curing (or specimen For the larger capacity compression machine, load- storage) regimes, the 10 mixtures in Table 3.13 (mixtures controlled testing was employed, as is the case for concrete test- G-1 to G-10) were cast and test cylinders were prepared. This ing. The typical load rates used for concrete, 138 to 345 kPa/s, study aimed to identify possible differences in compressive would fail most CLSM specimens in a matter of seconds. Thus, strength when four different curing conditions were used, as a lower load rate was selected (6.9 kPa/s). This lower load rate summarized in Table 3.18. Curing condition A, described as was possible on the machine for this study but may not be "normal" in the table, was the method used most throughout available for many standard concrete compression machines. this project, and curing condition C was identical to the Sulfur capping was used for almost all of the cylinders, ex- method specified in ASTM D 4832. For curing condition D, cept for some weaker mixtures at early ages where use of sul- the cylinders were placed outside the laboratory and were ex- fur caps was not possible. For these mixtures, neoprene pads posed to the high summer temperature and dry atmosphere were used. As previously mentioned, several variations were of Austin, Texas. All cylinders were capped with sulfur cap- investigated for the unconfined compressive test, including ping compound and tested at a loading rate of 0.38 mm/min. cylinder size, machine capacity, capping method, load rate, The mixtures listed in Table 3.8 were used to study the ef- and curing. A description of these investigations is presented fects of drying time (0.5, 2, 4, and 8 hours) on strength val- next, and the findings are included later in this chapter. ues. Cylinders for this test were cured for various ages (7, 28, Effects of Loading Rate on Compressive Strength. ASTM and 91 days) in a fog room, and then dried for the different D 4832 gives little guidance regarding load rate, stating only to time periods. The cylinders were then sulfur capped and "Apply the load at a constant rate such that the cylinder will fail tested in a deflection-controlled machine (0.38 mm/min). in not less than 2 min." Because of the vagueness in defining Effects of Curing Temperature and Humidity on Com- the load rate, additional testing was performed to investigate pressive Strength. As already addressed, the temperature the effects of loading rate on compressive strength. Using the to which CLSM is exposed during its strength-gain process seven CLSM mixtures summarized in Table 3.7, the effects of may be very important, especially when mixtures containing displacement rate (cross-head displacement of small load- frame) on compressive strength and deformation at peak load were studied. The following loading rates (or more accurately, Table 3.18. Additional curing deflection rates) were evaluated: 0.13 mm/min, 0.25 mm/min, regimes evaluated. 0.38 mm/min, 0.51 mm/min, and 0.89 mm/min. The aim was to determine a suitable load rate range that produces repeat- Curing Curing Regime able compressive strength values and can be performed in a rel- Condition A (Normal) Keep sample in mold with cap on, atively short time. The latter concern was because several mix- for 7 days in fog room. Then strip tures from early research took a relatively long time (i.e., cylinder and keep cylinders in fog greater than 10 to 15 minutes) to fail in compression under dis- room until time of testing. B (Mold) Keep sample in mold, with cap on, placement control, which would not be ideal for a testing lab- for 7 days in fog room. Then oratory that must test many cylinders daily. remove cap and keep cylinder in mold in fog room until time of Cylinder Curing and Conditioning. Another possible testing. C (Cap) Keep sample in mold, with cap on, source of error and confusion in ASTM D 4832 involves the in the fog room until time of testing. curing conditions and the treatment of cylinders before test- D (Outside) Keep sample in mold, with cap off, ing. According to ASTM D 4832, CLSM cylinders are cured outdoors until time of testing.

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28 certain fly ashes are used. Because CLSM is used in many dif- drainage conditions. To simulate the condition of no water ferent environments in practice, the same mixture propor- loss, CLSM mixtures were cast in plastic molds without tions could exhibit different strength values. This study was holes and tight lids were placed on the cylinders (condition intended to identify factors affecting strength gain of CLSM "cap"). To simulate the condition that only surface water mixtures. This study was a follow-up to earlier testing that evaporation is possible, mixtures were cast in plastic molds suggested that temperature plays a major role in CLSM without holes and lids (condition "no cap"). To simulate strength development. moderate water seepage, mixtures were cast into molds Three curing temperatures (10C, 21C, and 38C) and six (without caps) with seven uniformly distributed 3.6 mm di- CLSM mixtures (H-1 to H-6 in Table 3.14) were selected to ameter holes on the bottom (condition "bottom holes"). To study the strength gain of CLSM across a range of practical simulate a more severe drainage condition, mixtures were construction conditions. CLSM was cast into standard cylin- cast into molds with holes not only on the bottom but also der molds (75 mm 150 mm) and moved to the appropriate on the side (condition "side holes"), again without caps temperature-controlled chamber until the date of testing. The being placed on the top of the cylinders. There were thirty- cylinders were stored in two different manners. Half the cylin- six holes on the walls and seven holes on the bottom per ders from each mixture were stripped after 3 days and returned mold. All drilled holes were 3.6 mm in diameter. To avoid to the same chamber until the time of testing (without control local effects, CLSM specimens from a given mixture were over relative humidity in the chamber). This condition is des- randomly placed throughout the test box. ignated later in this report as "dry" curing. Temperature and humidity were monitored throughout the test. The other half Alternative Capping Materials for Compression Testing. of the specimens from a given mixture were kept inside the In preliminary testing, as well as the testing of the initial molds with the caps firmly placed on top until the day of test- 38 mixtures included in this study, sulfur capping was found ing (designated as "wet" curing). These cylinders were placed to be an effective method of obtaining repeatable compressive directly next to the cylinders that had already been stripped. strength data. However, for early age samples and/or for par- Cylinders were tested for compressive strength at 7, 28, and ticularly low strength cylinders, it may not be possible to cap 91 days. The moisture contents of tested specimens were cylinders with sulfur because of the risk of specimen damage. measured to assess the effects of curing conditions on the Neoprene pads were used in these cases, but because only lim- moisture content (or evaporable water content) and strength ited testing was performed, the researchers decided to signifi- of CLSM. cantly expand the scope of the original work to investigate a range of neoprene (or other) pads with varying properties. Effects of Drainage Conditions on Compressive Strength. It is well established that higher strength concrete requires Unlike conventional concrete, CLSM is very rarely, if ever, higher neoprene durometer values, and vice versa. Thus, for cured. During the strength-gain process of CLSM, it is often CLSM, softer neoprene pads (much softer than those used continuously in contact with the surrounding soil and/or struc- for concrete) were expected to be needed. Other motiva- ture. Different environments may significantly affect the final tions for studying alternatives to sulfur capping are the po- strength of CLSM as the water-cement ratio may be affected by tential health concerns over the fumes generated from sulfur the seepage of water into surrounding materials or the loss of capping stations and the length of time needed to cap cylin- water through evaporation of bleed water. ders with sulfur. The effects of seepage and evaporation were investigated in To address these important capping-related issues, a com- a study using the mixtures detailed in Table 3.12 (F-1 to F-8). prehensive investigation of alternative capping materials was This study also investigated the effects of temperature on launched. Included in this study were sulfur caps, gypsum (or strength gain, using the fog room as a control and ambient hydrostone) caps, and neoprene pads with durometer values conditions (hot Texas summer weather) as a test condition. of 20, 40, 50, 60, and 70. In a previous study, Sauter and As described later in this report, the findings of this temper- Crouch (2000) used soft neoprene pads made of wet-suit rub- ature effects study were quite interesting, and subsequent ber to measure the compressive strengths of excavatable testing was performed using controlled-temperature envi- CLSM cylinders. This idea was extended under this project ronments to further elucidate the influence of temperature to examine soft non-neoprene rubber pads and two-layer on CLSM strength, especially for mixtures containing high systems. A commercially available sorbothane viscoelastic volumes of fly ash. polyurethane rubber material was identified and chosen for To simulate field conditions, plastic molds were buried this study. The Shore OO durometer hardness of this material in loose sand and CLSM mixtures were cast directly into the is 50, which is approximately a Shore A durometer hardness molds. Before the cylinders were cast, the plastic molds of 5, according to the producer. Pads were single-layer rubber were subjected to different treatments to simulate various sheets with a thickness of 12.7 mm. In the early stages of this

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29 study, the researchers were concerned that the polyurethane mixtures. The dynamic cone penetrometer (DCP) was also pads may be too soft to dissipate the stress concentrations. used to estimate the excavatability of CLSM mixtures. The DCP As a result, a two-layer pad system was also tested, which is a modified and simplified version of the penetrometer used consisted of polyurethane-neoprene (P-N) pads. Testing of by the Country Roads Board, Victoria, Australia. It is used by samples included glued and unglued systems. The glued sys- geotechnical engineers to obtain an index of in-situ CBR and tem used rubber cement to bond the polyurethane and neo- to estimate the strength of soil as a function of depth. The test- prene. For comparison, neoprene pads, 13 mm thick, with a ing consists of dropping a hammer (8 kg in weight) from a Shore A durometer hardness of 50 were also used in certain height of 575 mm, which forces a steel rod with a conical head tests. Table 3.19 summarizes the variables tested in this pro- into the CLSM or soil. The penetration depth per blow was gram. Nine mixtures (E-series) were used in this study, as recorded. The corresponding DCP index value was used to es- previously described in Table 3.11. timate a soil strength value (CBR). A second approach that was used in this study to predict Excavatability excavatability follows a procedure developed and used in Hamilton County, Ohio. This approach uses a removability The excavatability of CLSM was assessed for six of the orig- modulus (RE), as shown in Equation 3.1a: inal thirty-eight CLSM mixtures to gain an "order of magni- tude feel" for the relative ease of excavating various CLSM mix- W 1.5 104 C 0.5 tures. CLSM was cast into 450 450 300 mm plywood boxes RE = (3.1a) 106 and allowed to harden. Attempts were made to correlate "walk- ability" with soil penetrometer values as the CLSM gained strength in the first few hours. Long-term excavatability was where assessed at an age of approximately 9 months using typical W = In-situ unit weight (lb/ft3) hand tools, including a shovel and a pick for six selected mix- C = 28-day unconfined compressive strength (psi) tures. The compressive strength of laboratory-cured cylinders was also measured. In addition, a relatively new instrument, When SI units are used, as required by AASHTO, the equa- the Humboldt GeoGauge, was used at the time of excavation tion is rewritten as shown in Equation 3.1b: to attempt to correlate excavatability with the stiffness of CLSM, as measured by the GeoGauge. W 1.5 0.619 C 0.5 RE = (3.1b) After the initial excavation study, a more comprehensive 106 study on long-term strength gain and excavatability was launched. Nine CLSM mixtures (C-1 to C-9 in Table 3.9) were where included in the study. A field penetrometer (field version of W = In-situ unit weight (kg/m3) ASTM C 403) was used to evaluate the strength gain of CLSM C = 28-day unconfined compressive strength (kPa) Table 3.19. Summary of various capping systems used to test compressive strength of CLSM. Neoprene a b CLSM Curing Sulfur Cap Polyurethane Cap P-NU P-N Cap Mixture Condition 7 d 28 d 91 d 7 d 28 d 3 d 7 d 28 d 91 d 7 d 28 d 7 d 28 d E-9 E-10 E-11 E-12 E-13 Lab E-14 E-15 E-16 E-17 E-13 E-14 E-15 Field E-16 E-17 E-18 a P-N cap unbonded. b P-N cap bonded.