Characterization of Cementitiously Stabilized Layers for Use in Pavement Design and Analysis (2014)

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26 C H A P T E R 5 Findings The study developed performance models for predict- ing shrinkage cracking and change of modulus of CSL due to growth, fatigue, freeze–thaw cycles, and wet–dry cycles. Incor- porating these models into the MEPDG would allow estimating CSL performance over time on a monthly basis for the prevail- ing traffic, climate, and materials. Developed Models and Inputs The three hierarchical levels adopted in the MEPDG are designated Levels 1, 2, and 3. Level 1 requires site- and/or material-specific inputs obtained through testing or measure- ments; Level 2 requires inputs estimated from correlations with other information; and Level 3 requires inputs defined by national or regional default values. Growth, durability, fatigue, and shrinkage cracking models developed in this research are listed in Table 5-1. The hierarchical levels of material proper- ties inputs associated with these models are listed in Table 5-2 and are described in the following paragraphs. Laboratory UCS values after 28-day curing at room tem- perature and 100% RH were collected from the literature. The range and typical values of the other material properties, including resilient modulus, MOR, flexural modulus, IDT strength, and IDT modulus, were estimated from the UCS values based on the correlations listed in Table 5-2. As noted in Chapter 2, a 7-day UCS of 200 psi was recommended as the criterion for distinguishing between heavily and lightly sta- bilized materials. This value corresponds to a 28-day UCS of 283 psi based on the strength growth model (Equation 3-4). Therefore, a heavily stabilized material would have a 28-day UCS ≥ 283 psi and a lightly stabilized material would have a 28-day UCS < 283 psi. Resilient modulus is recommended for lightly stabilized material only, and flexural modulus for heav- ily stabilized material only, based on their typical values from literatures and the criteria above. Equation 5-1 accounts for the growth, durability (wet–dry and freeze–thaw), and fatigue (bottom-up tensile-fatigue and top-down compressive-fatigue–erosion) effects on the strength or modulus. (5-1) 0A t A t N N D DW D F T B T T C( ) ( ) ( ) ( ) ( ) ( )= × α × β × λ × γ × η− − − − where A(t) = predicted strength or modulus in the field at time t A0 = measured saturated strength or modulus at 28 days at 100% RH curing at 68°F t = time in months Effect of Curing Time 1 1 1 1 0 2t p t t p( )α =     ( )− + −    where t0 = time in months corresponding to A0, equals to 28/30.5 p1, p2 = regression parameters, 1.59 and 1.61, respectively, as default values Effects of Wet–Dry Cycling N m e m W D n N ln UCS 1 1 ln UCS 2 1 28 1 28 1 ( ) ( ) ( )β = + + −  ( )− where UCS28 = 28-day UCS, psi N = number of wet–dry cycles m1, n1 = regression parameters for wet–dry durability, 2.58 and 0.62, respectively, as default values Findings and Recommendations for Research

27 esraoCeniFretemaraPnoitauqEledoMepyT Shrinkage Crack Shrinkage Crack Spacing in CSL UCS ∙ RH% l1 −1.19E−01 0 l2 5.98E−01 −1.39E−01 l3 −7.78E−01 −1.36E−04 l4 0 0 l5 0 −1.46E−01 l6 0 2.11E+00 l7 −2.20E−03 0 l8 −2.53E−01 0 l9 8.74E+00 3.85E+00 Shrinkage Crack Width in CSL ∙ ∙ UCS ∙ RH% w1 7.81E−03 0 w2 −1.20E+00 0 w3 7.67E−01 1.34E+00 w4 0 1.76E−05 w5 0 3.63E−02 w6 0 0 w7 6.69E−01 0 w8 4.71E−01 5.36E−02 w9 8.63E−04 1.78E−01 eulaVretemaraPnoitauqEledoMepyT Growth Growth p1 1.59 p2 1.61 Durability Wet–Dry UCS UCS UCS 2 m1 2.58 n1 0.62 Freeze–Thaw UCS UCS UCS 2 m2 6.68 n2 0.93 Fatigue Bottom-up Tensile Fatigue k1 1.07 k2 Table 3-6 k3 Table 3-6 Top-down Compressive Fatigue UCS k4 10.85 k5 1.47 Fatigue Damage (Bottom-up and Top-down) n/a n/a Bottom-up Tensile-Fatigue Modulus Reduction 2 m3 3.10 n3 3.99 Top-down Compressive- Fatigue Modulus Reduction m4 5.08 n4 2.01 2 Table 5-1. Model description.

28 Material Properties Level 1 Level 2 Level 3 (28-day curing at 68°F and 100% RH) Test Procedure Recommended Relationship Range Typical Value UCS Test protocol depends on binder and soil type (see notes) Same to Level 1 input See Table 5-3 Resilient Modulus Mixture design and testing protocol (MDTP) in conjunction with NCHRP 1-28A Mr = 0.12 × UCS + 9.98 where Mr = resilient modulus, ksi UCS = unconfined compressive strength, psi See Table 5-4 Modulus of Rupture Proposed test protocol (see Attachment) MOR = 0.14 × UCS MOR = SIDT/0.86 where MOR = modulus of rupture, psi UCS = unconfined compressive strength, psi SIDT = IDT strength, psi See Table 5-5 Flexural Modulus Proposed test protocol (see Attachment) Ef = 936.28 × MOR + 62382 Ef = 131.08 × UCS + 62382 where Ef = flexural modulus, psi MOR = modulus of rupture, psi UCS = unconfined compressive strength, psi See Table 5-6 IDT Strength Proposed test protocol (see Attachment) SIDT = 0.12 × UCS SIDT = 0.86 × MOR where SIDT = IDT strength, psi UCS = unconfined compressive strength, psi. MOR = modulus of rupture, psi See Table 5-7 IDT Modulus Proposed test protocol (see Attachment) Et = 7980.1 × SIDT Et= 957.61 × UCS where Et = IDT modulus, psi SIDT = IDT strength, psi UCS = unconfined compressive strength, psi See Table 5-8 Coefficient of Thermal Expansion Proposed test protocol (see Attachment) Not available 2 to 50 (10−6/°F) Clay 25.4 (10−6/°F) Silt 9.4 (10−6/°F) Gravel 8.5 (10−6/°F) Coefficient of Friction Proposed test protocol (see Attachment) µ = 156.48 × SIDT where µ = coefficient of friction, psi/in. SIDT = IDT strength, psi 22 to 14000 (psi/in.) Sublayer type Cement-stabilized, 13415 psi/in. Granular, 169 psi/in. Lime-treated clay, 146 psi/in. Clay, 22 psi/in. Notes: For cement-stabilized fine-grained materials (clay, silt and sand): ASTM D1633, Standard Test Method for Compressive Strength of Molded Soil–Cement Cylinders. For cement-stabilized granular materials: AASHTO T22, Standard Method of Test for Compressive Strength of Cylindrical Concrete Specimens. For lime-stabilized clay: ASTM D5102, Standard Test Method for Unconfined Compressive Strength of Compacted Soil–Lime Mixtures. For fly ash–stabilized soils: ASTM C593, Standard Specification for Fly Ash and Other Pozzolans for Use with Lime for Soil Stabilization. Table 5-2. Three levels of input for MEPDG. Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range 40 ~ 1015 88 ~ 900 80 ~ 843 392 ~ 1296 30 ~ 1088 Typical 263 363 350 763 653 Lime Range 19 ~ 522 78 ~ 510 Not applicable 64 ~ 91 Not applicable Typical 150 158 78 C fly ash Range 19 ~ 668 39 ~ 268 31 ~ 693 59 ~ 305 Not applicable Typical 181 115 174 214 Lime and F fly ash Range Not applicable 150 ~ 190 Not applicable Not applicable 120 ~ 200 Typical 170 190 Table 5-3. Level 3 input of UCS (psi).

29 Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range 15 ~ 136 Not applicable Not applicable Not applicable Not applicable Typical 43 Lime Range 12 ~ 75 20 ~ 73 Not applicable 18 ~ 21 Not applicable Typical 29 30 20 C fly ash Range 12 ~ 93 15 ~ 43 14 ~ 96 17 ~ 48 Not applicable Typical 32 24 32 37 Lime and F fly ash Range Not applicable 29 ~ 34 Not applicable Not applicable 25 ~ 35 Typical 31 34 Table 5-4. Level 3 input of resilient modulus of lightly stabilized materials (ksi). Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range 6 ~ 142 12 ~ 126 11 ~ 118 55 ~ 181 4 ~ 152 Typical 37 51 49 107 91 Lime Range 3 ~ 73 11 ~ 71 Not applicable 9 ~ 13 Not applicable Typical 21 25 11 C fly ash Range 3 ~ 94 5 ~ 38 4 ~ 97 8 ~ 43 Not applicable Typical 25 16 24 30 Lime and F fly ash Range Not applicable 21 ~ 27 Not applicable Not applicable 17 ~ 28 Typical 24 27 Table 5-5. Level 3 input of modulus of rupture (psi). Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range Not applicable 74 ~ 180 73 ~ 173 114 ~ 232 66 ~ 205 Typical 110 108 162 148 Lime Range Not applicable Not applicable Not applicable Not applicable Not applicable Typical C fly ash Range Not applicable Not applicable Not applicable Not applicable Not applicable Typical Lime and F fly ash Range Not applicable Not applicable Not applicable Not applicable Not applicable Typical Table 5-6. Level 3 input of flexural modulus of heavily stabilized materials (ksi). Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range 5 ~ 122 11 ~ 108 10 ~ 101 47 ~ 156 4 ~ 131 Typical 32 44 42 92 78 Lime Range 2 ~ 63 9 ~ 61 Not applicable 8 ~ 11 Not applicable Typical 18 19 9 C fly ash Range 2 ~ 80 5 ~ 32 4 ~ 83 7 ~ 37 Not applicable Typical 22 14 21 26 Lime and F fly ash Range Not applicable 18 ~ 23 Not applicable Not applicable 14 ~ 24 Typical 19 23 Table 5-7. Level 3 input of IDT strength (psi).

30 Table 5-8. Level 3 input of IDT modulus (ksi). Binder Values Soil Clay Silt Sand Gravel Recycled Materials Cement Range 38 ~ 972 77 ~ 807 77 ~ 807 375 ~ 1241 29 ~ 1042 Typical 252 335 335 731 625 Lime Range 18 ~ 500 75 ~ 488 Not applicable 61 ~ 87 Not applicable Typical 144 151 74 C fly ash Range 18 ~ 640 37 ~ 257 30 ~ 664 57 ~ 292 Not applicable Typical 173 110 167 205 Lime and F fly ash Range Not applicable 144 ~ 182 Not applicable Not applicable 115 ~ 192 Typical 155 182 Effects of Freeze–Thaw Cycling N m e m F T n N ln UCS 1 1 ln UCS 2 2 28 2 28 2 ( ) ( ) ( )λ = + + −  ( )− where UCS28 = 28-day UCS, psi N = number of freeze–thaw cycles m2, n2 = regression parameters for freeze–thaw durability, 6.68 and 0.93, respectively, as default values Effects of Bottom-up Tensile Fatigue D m e m B T n D ln UCS 1 1 ln UCS 2 3 28 sinh 3 28 3 ( ) ( ) ( )γ = + + −  [ ]( )− where D = accumulated damage due to bottom-up tensile fatigue UCS28 = 28-day UCS, psi m3, n3 = regression parameters for bottom-up tensile-fatigue damage, 3.10 and 3.99, respectively, as default values Effects of Top-down Compressive Fatigue–Erosion D m e m T C n D ln UCS 1 1 ln UCS 2 4 28 sinh 4 28 4 ( ) ( ) ( )η = + + −  [ ]( )− where D = accumulated damage due to top-down compres- sive fatigue–erosion UCS28 = 28-day UCS, psi m4, n4 = regression parameters for top-down compressive- fatigue–erosion damage, 5.08 and 2.01, respectively, as default values Quality Control and Quality Assurance The UCS is used directly in the models or correlated with other material properties in performance models. The 7-day UCS may be used as a QC/QA property. For lightly stabilized materials, such as clay–lime, curing at an accelerated tem- perature is needed. Recommendations for Future Research The following research topics are recommended for consideration: 1. Model validation—The models developed in this research were calibrated based on limited data. Further valida- tion using local field data, especially for the top-down compressive-fatigue–erosion model, would enhance pre- diction. Because of the errors associated with the FWD backcalculation of CSL, use of field cores of CSM in this validation is encouraged. The modulus of surface layer can be determined from tests on field cores and the modu- lus of unbound layers can be estimated from the dynamic cone penetrometer. 2. Reflective cracking model—Models are not currently available to predict reflective cracking in asphalt layers placed on CSL. Developing a reflective cracking model that considers shrinkage cracking would enhance performance prediction. 3. Calibration for concrete pavements—Limited data from asphalt pavements were used to calibrate the models devel- oped in this research. Further calibration using data from concrete pavements will enhance validity of these models. 4. Performance-based mix design—CSM mix design is empirical and largely based on trial and error. Developing a performance-based mix design will help better account for traffic levels and local climate.