Lightweight Concrete for High Strength - Expanded Shale & Clay

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Chapter 2. Analytical Investigation 2.1 General The potential advantages of using high-strength, high-performance concretes (HPC) for precast prestressed bridge girders may be lost if those girders are too heavy to be transported. The advantages presented by Kahn and Saber (2000) include spans up to 40% longer than when normal strength (6 ksi, 41.4 MPa) concrete is used, wider girder spacing and greater durability. A gauge of the transportation problem is the necessity to obtain hauling permits or “super permits.” When the gross vehicle weight (GVW, weight of girder plus tractor-trailer rig) exceeds 150-kips (68,200 kg), a “super permit” is required. This permit requires the hauler to obey certain additional restrictions that may include stopping before every bridge, proceeding over the bridge at a speed less than 5 mph (8 kmph) and that a police escort lead and follow the truck. Further, the state department of transportation must carefully review the route and evaluate the load capacity of each bridge. There may be no acceptable route. The slow rate of bridge crossing can significantly disrupt traffic. The purpose of this phase of the research was to investigate analytically if high-strength lightweight concrete (HSLWC) could be used to build pretensioned bridge girders with a length of 150-ft. (45.7 m) and girder spacing of 7-ft. (2.13 m) whose GVW did not exceed 150-kips (68,181 kg). Standard AASHTO (American Association of State Highway and Transportation Officials) and AASHTO-PCI (Precast/Prestressed Concrete Institute) sections are considered. The range of girder strengths was 8, 10 and 12 ksi (55.2, 69 and 82.8 MPa). The strength of the 7-in. (178 mm) thick composite deck was 3,500 psi (24 MPa). 2.2 Scope The scope of this study was limited to analytically investigating AASHTO Type II-V and AASHTO-PCI Bulb-Tee 54, 63 and 72 sections (Standard and Modified). For reference purposes, AASHTO-PCI Bulb-Tees will be listed as “Standard Bulb-Tees”. A Modified AASHTO-PCI Bulb-Tee will be listed as a “Modified Bulb-Tee.” The Modified Bulb-Tee sections consisted of a Standard Bulb-Tee with one additional row of 12 strands added to the 2-1
ottom flange. Prestressing strands were 0.6-in. (15 mm) diameter, 270 ksi (1862 MPa) low relaxation strands spaced at 2-in. (51 mm) centers. All girder designs in this research were based on the 16 th Edition of the AASHTO Bridge Design Specifications (1996) and used Georgia’s bridge design program PCPSBM1R with modifications to enable the use of HPLC. 2.3 Parametric Study A parametric study investigated the relation between concrete compressive strength, unit weight of the concrete, girder size and span length. One of the most important properties was the modulus of elasticity of the HPLC. In order to more accurately predict modulus values, a new equation was developed (Equation 2-1), similar in form to the Morales equation (Morales, 1982), but based on a “best fit” analysis of the experimental data from the thirteen expanded slate mixes. 0.9 ( 33,000⋅ fc ' + 4,000,000) ⋅( wc / 242) (2-1) The Georgia DOT bridge design program PCPSBM1R was modified to use lightweight concrete with λ factor of 0.75 and 0.85 for all-lightweight and for sand-lightweight concrete and to have densities less than 135 pcf. It was assumed that the concrete strength at release was 75% of the design strength. Design strengths of 8,000, 10,000 and 12,000 psi were used. Girder spacing was 7 ft, and the composite deck was taken as 7-in. thick with a strength of 3,500 psi. Unit weight given in Table 2-1 were used. Table 2.1 Slate high-strength lightweight concrete unit weight values. Concrete Strength, f c ’ psi (MPa) Low Unit Weight pcf (kg/m 3 ) Average Unit Weight pcf (kg/m 3 ) High Unit Weight pcf (kg/m 3 ) 8,000 (55.2) 113 (1810) 119 (1906) 126 (2019) 10,000 (69) 117 (1874) 124 (1986) 131 (2099) 12,000 (82.8) 122 (1954) 128 (2051) 135 (2163) 2-2
Page 1 and 2: School of Civil and Environmental E
Page 3 and 4: ACKNOWLEDGMENTS The research presen
Page 5 and 6: A statistical evaluation based on f
Page 7 and 8: 5.6 - Transfer Length 5-13 5.7 - Gi
Page 9 and 10: Report ACI 318- 99 AASHTO Standard
Page 11 and 12: Chapter 1. Introduction 1.1 Purpose
Page 13: Long term properties including pret
Page 17 and 18: 12500 12000 Concrete Strength, fc'
Page 19 and 20: Chapter 3. Mix Designs, Field Evalu
Page 21 and 22: Variation of coarse-to-fine aggrega
Page 23 and 24: 3.2.1 Compressive Strength Figure 3
Page 25 and 26: Table 3.5 Chloride Permeability --
Page 27 and 28: 12,000 11,500 11,000 Compressive St
Page 29 and 30: 1,400 1,300 1,200 1,100 Experimenta
Page 31 and 32: strength (10L made in the laborator
Page 33 and 34: The 50% and 90% of the 620-day cree
Page 35 and 36: 700 600 10,000-psi Measured Shams &
Page 37 and 38: a Creep Coefficient 3.0 2.5 2.0 1.5
Page 39 and 40: Chapter 5. Behavior of AASHTO Type
Page 41 and 42: Portion of Girder Damaged During Te
Page 43 and 44: 2” End Cover (Typ both ends) 4 Sp
Page 45 and 46: 5.3 Instrumentation The surface of
Page 47 and 48: Figure 5.7 Installation of stirrups
Page 49 and 50: Table 5.3 Girder concrete propertie
Page 51 and 52: 120 100 80 Stress (ksi) 60 40 20 0
Page 53 and 54: Table 5.5 -Transfer Length Results
Page 55 and 56: Figure 5.12 Typical flexural failur
Page 57 and 58: Since G2 girders had a higher concr
Page 59 and 60: V " pc cw− Pr ed = ft −Pr ed 1
Page 61 and 62: Test # Table 5.9 Predicted vs. Expe
Page 63 and 64: this research project, modification
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Chapter 6. Prestress Losses in HPLC
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losses in the 10,000-psi girders to
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Microstrains (in/inx10 -6 ) 0 500 1
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6.3 Conclusions Regarding Prestress
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7.3 Transfer Length An evaluation o
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Shrinkage after 620 days of drying
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More research is required to examin
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Appendix A. Background A.1 Introduc
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Raithby and Lydon described the use
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are normally recognized as being on
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aggregate must be saturated by pres
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A.7.2 Strength Ceiling Harmon discu
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compared to lower strength specimen
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A.8.8 Deatherage, Burdette and Chew
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3. Concrete compressive strength at
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findings were comments that the AAS
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including strand diameter, embedmen
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l d = l t + l fb = f si 3 d b + 1.5
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l d = l t + l fb ⎛ = ⎜ ⎝ f d
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Table A.1 Summary of Development Le
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strand release, the strand attempts
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Appendix B. Creep and Shrinkage B.1
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Changes in moisture migration: the
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t′: age of concrete at loading (d
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s: slump (in) γ ψ ⎧ 0.30 −1.4
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t: age of concrete (days) t 0 : age
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where ε sh ∞ ⎧ 510 µε for st
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left girder-end. The dimension L wa
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6” 85” 50” Segment of girder
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146” 89” 96” 137” Stirrups
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were added in a specific sequence f
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C.2.3 Formwork Removal, Detensionin
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Figure C.19 Mostafa Prestressing St
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Figure C.22 Ms. Lyn Clements (GDOT)
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If significant strand end slip over
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CSS at Level of Bottom Strands (µ
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Appendix D. Prestress Losses in HPL
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E ps : elastic modulus of prestress
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D.2.2. AASHTO-LRFD Refined Estimate
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∆f log(24 ⋅t) ⎛ f ⎜ ⎞ 55
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P i : initial prestressing force af
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References AASHTO (1996), Standard
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ASTM C 618, Standard Specification
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Guide for Structural Lightweight Ag
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Martin, L. D., Scott, N. L., “Dev
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Shahawy, M. A., Batchelor, B., “S
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Lightweight Concrete for High Strength - Expanded Shale & Clay

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