Lightweight Concrete for High Strength - Expanded Shale & Clay

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The two models that better estimate creep of HPLC, utilized the maturity of concrete at loading rather than age. Age of loading is an important factor in determining creep. For precast prestressed concrete members, the age of application of load can be as low as 16 hours, so creep becomes very dependant of concrete mechanical properties at the moment of loading. HPC usually includes high contents of cementitious materials which generate a high heat of hydration. This heat of hydration is responsible for raising concrete temperature to levels as high as 145 o F; this heat accelerates the hydration process. This self feeding reaction increases concrete mechanical properties above the expected values. Hence, maturity leads to more accurate estimate of concrete performance. The Shams and Kahn and AASHTO-LRFD models were able to better estimate creep because 8,000-psi and 10,000-psi HPLC had a maturity at 24 hours equivalent to 147 and 158 hours (6.1 and 6.6 days). The AASHTO-LRFD model gave the best shrinkage estimate for the 8.000 psi HPLC while the Shams and Kahn’s gave the best shrinkage estimate for the 10,000 psi HPLC. 4.4 Conclusions Regarding Creep and Shrinkage HPLC (10,000-psi HPLC) had a specific creep similar to that of an HPC of the same grade, but with less cement paste content, and it had significantly less creep than an HPC of the same grade and similar cement paste content. The shrinkage of the HPLC was about 20% greater than the HPC after 620 days. Therefore, the HPLC had less creep yet somewhat more shrinkage than comparable HPC. Altogether, the creep of HPLC is much less than that of normal weight, normal strength concrete, and the shrinkage of HPLC is somewhat less than that of normal weight, normal strength concrete. 4-9
Chapter 5. Behavior of AASHTO Type II HPLC Girders 5.1 Introduction The following objectives were established to serve as guidelines to prioritize and focus the experimental design and procedure. 1. To determine the transfer length, l t , for 0.6-inch diameter prestressing strand used with slate HPLC. 2. To determine the development length, l d , for 0.6-inch diameter prestressing strand used with slate HPLC. 3. To verify current code equations for l t and l d as appropriate for use with slate HPLC and suggest better equations if necessary. 4. To determine the effect of shear reinforcement spacing on strand slip, development length, and shear capacity of pretensioned slate HPLC girders. 5. To determine the shear strength, V c , of prestressed slate HPLC. 6. To verify current code equations for shear strength of slate HPLC. 7. To verify the current code-specified reduction factor, λ, for slate lightweight concrete as related to concrete tensile strength, and, suggest a more appropriate factor if necessary. In order to achieve the seven experimental objectives, the following variables were altered in order to observe the results. Concrete Compressive Strength, f c ’. Concrete design strengths of 8,000 and 10,000 psi were used for girder construction – Mixes 8F (termed G1) and 10F (termed G2) from Chapter 4. Shear Span to Depth Ratio, a/d. The “a” distance was varied from approximately 63 to 100 percent of the current code-specified l d value. Yield Strength of Shear Reinforcement Steel, f y . Only Grade 60 # 4 bar stirrups were used. Values of f y of 60 ksi (414 MPa) and the actual f y value were used to determine whether an upper limit was appropriate for use with HPLC. Spacing of Shear Reinforcement Steel, “s.” The “s” distance was varied to determine the impact of A v /s (stirrup area-to-spacing ratios)on l d , strand slip, and shear strength. Span Length of Tested Section, L 1 . In order to achieve three tests per girder, the span length was varied to focus on specific sections of the girder for each test. 5-1
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 and 14: Long term properties including pret
Page 15 and 16: ottom flange. Prestressing strands
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: a Creep Coefficient 3.0 2.5 2.0 1.5
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
Page 65 and 66: Chapter 6. Prestress Losses in HPLC
Page 67 and 68: losses in the 10,000-psi girders to
Page 69 and 70: Microstrains (in/inx10 -6 ) 0 500 1
Page 71 and 72: 6.3 Conclusions Regarding Prestress
Page 73 and 74: 7.3 Transfer Length An evaluation o
Page 75 and 76: Shrinkage after 620 days of drying
Page 77 and 78: More research is required to examin
Page 79 and 80: Appendix A. Background A.1 Introduc
Page 81 and 82: Raithby and Lydon described the use
Page 83 and 84: are normally recognized as being on
Page 85 and 86: aggregate must be saturated by pres
Page 87 and 88: A.7.2 Strength Ceiling Harmon discu
Page 89 and 90:
compared to lower strength specimen
Page 91 and 92:
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
Page 153 and 154:
Martin, L. D., Scott, N. L., “Dev
Page 155:
Shahawy, M. A., Batchelor, B., “S
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Lightweight Concrete for High Strength - Expanded Shale & Clay

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