Composite Pavement Systems, Volume 2: PCC/PCC Composite Pavements (2013) / Chapter Skim
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From page 47... ...
47 Introduction The analysis of laboratory and field data along with the development of models to better understand PCC/PCC design and behavior are detailed in this chapter. Although composite pavements generally are known to perform quite well, there has been little formal research into the performance of new PCC/PCC structures.
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48 Table 3.1. Modes of Failure, MEPDG Models Available, R21 Project Modifications for PCC/PCC Design Failure Mechanism MEPDG Model Available SHRP 2 R21 Model Modification Comment Bottom-up transverse cracking (fatigue)
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49 Figure 3.5. EAC flexural strength values for test sections constructed at MnROAD.
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50 Table 2.5 showed that LC had the highest modulus of elasticity of the three concretes, which confirms that it is not a low-quality concrete. The aggregates could have been used for conventional concrete, but it is considered as low cost because fly ash was substituted for 60% of its cement.
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51 and experts in construction materials, systems, and structures. The CIF test evaluates the capillary suction, surface scaling resistance, and internal damage of concrete samples exposed to 3% by volume sodium chloride solution, whereas AASHTO T161 evaluates the internal damage of concrete submerged in water from rapid freeze–thaw cycles and AASHTO T277 evaluates the scaling resistance of concrete exposed to 3% sodium chloride solution and freeze–thaw cycles.
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52 and average capillary pore size than did the field samples, as evidenced by the lower 7- and 28-day strengths. The average RCA laboratory sample's 28-day compressive strength was 50% that of the average RCA field sample.
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53 Figure 3.13 shows the cumulative mass of scaled material per unit area for both field and laboratory concrete samples as the number of freeze–thaw cycles increases. It is important to reiterate here that the test surfaces of the field RCA and EAC samples were submerged in pure water and the test surfaces of the laboratory RCA, LC, EAC, and Control samples were submerged in 3% sodium chloride solution.
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54 samples. For the PCC/PCC composite pavements constructed at MnROAD, the EAC was the only concrete that would have been subjected to deicing salt, and it proved to be an adequate concrete mixture for resisting deicing salt scaling.
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55 ratio and the quantity and spacing of entrained air bubbles (Setzer 1997)
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56 thermocouple depths are summarized in Table 3.9 for both cells. The depths available for the sensors, shown in Table 3.9, indicate that the sensors were installed at similar depths for each of the locations.
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57 not sufficient for characterizing the actual variation of the temperature throughout the depth. The nonlinearity of the temperature distribution should also be considered, which is done using ELTG.
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58 Ebot = elastic modulus of the lower layer, atop = coefficient of thermal expansion of the upper layer, abot = coefficient of thermal expansion of the lower layer, and heff = effective thickness of the pavement, which can be determined from Equation 3.2: h h E E h h x h eff top bot top bot top top = + + − 3 3 12 2 + + − 2 2 2 E E h h x hbot top top bot bot 3 3 2( .
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59 produces an upward warping of the slab (because the bottom of the slab is almost always saturated and the top typically goes through wet-dry cycles)
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60 Figure 3.25. Monthly average ambient relative humidity at MnROAD.
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61 the slab. The temperature gradient that is present in the slab at TZ is "locked" into the slab.
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62 in the slab at the TZ could be established relatively well, even with the limited data available. The slab WAT at TZ is another parameter that needs to be established.
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63 Source: FHWA 2000. Figure 3.32.
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64 cells were equal to or higher than 1.8 MPa. Thus, the composite pavement layers in Cell 71 and Cell 72 are well bonded to each other.
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65 reasonable to validate two-layer predictions against those of a structurally equivalent single-layer JPCP as predicted by MEPDG. To make this possible, modification to the EICM analysis in the two-layer PCC case were made, as detailed in the following sections, so that it would be more compatible with the single-layer design.
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66 MEPDG enhanced Integrated Climatic Model (eICM) for pCC/pCC In the original EICM thermal analysis (version 1.003 and versions before 1.014:9030A)
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68 Note: OL = overlay. Figure 3.38.
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69 compared with that of a structurally equivalent single layer JPCP. Table 3.16 shows the results of comparing MEPDG performance prediction of two structurally equivalent 9-in.
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70 Table 3.18. Comparison of Additional Structurally Equivalent 9-in.
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71 Table 3.19. Final Performance Predictions for R21 PCC/PCC Database Sections Using R21 Revised MEPDG Section, Location Climate Traffic PCC/PCC, Year Constructed, Joint Space, Dowels IRI (in./mi)
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72 Figure 3.40. PCC/PCC measured cracking versus MEPDG (v.
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73 specialized elements for fracture becomes a nontrivial problem. This problem is commonly solved using trial-and-error methods, with computationally expensive and cumbersome remeshing during the fracture process.
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74 Mixed-Mode Fracture Criteria A key feature of this model, as alluded to previously, is that it does not adopt a continuum approach for fracture. Rather, its discrete representation allows for the development of parameters governing fracture in the body, as suggested by Jagota and Bennison (1994)
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75 beam. Furthermore, each simulated beam was developed to accommodate nodes expressly to act as sites of forcing to accommodate three-point loading.
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76 Beginning with the case l2 = 330 mm, we observe that the nature of the fracture is mostly tensile; however, some events feature a shear component as high as ~0.1 MPa. As we continue clockwise, the shear component becomes more pronounced and reaches values as high as ~0.3 MPa at li = 950 mm.
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77 shearing) fracture situations, the shear strength weighs more heavily in predicting failure.
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78 constant temperature equivalent to the temperature at the bottom of the upper PCC layer. For this example, a half-slab with dimension 90 × 72 in.
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79 Table 3.21. Slab Properties for Two Lifts of PCC in Differential Strain Example E (psi)
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80 strain described in ISLAB2005 inputs: a -50°F temperature difference through the top layer and a -20°F temperature difference though the top layer. The -50°F is an extreme situation and is clearly unrealistic for an upper layer only 3 in.
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81 PCC pavement are constructed within a reasonable time frame there will be no debonding. Furthermore, the R21 2008 Survey of European Composite Pavements team was unable to locate field observations of PCC/PCC debonding with the assistance of project consultants in Europe.
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