Lightweight Concrete for High Strength - Expanded Shale & Clay

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f c ’ = concrete compressive strength (psi) w c = unit weight of concrete (lb/ft 3 ) An equation by Morales (Equation A.2) was suggested for use with lightweight concrete. E c = (40,000 f ' c ⎛ wc ⎞ + 1,000,000) ⎜ ⎟ ⎝145 ⎠ 1.5 ( A.2) Table A.1 lists compressive strengths, dry (equilibrium) unit weights and modulus values reported by various authors for slate HSLC mix designs having compressive strengths between 6,000 and 12,000 psi. Table A.1 Reported Strength, Weight and Elasticity Modulus Values for Slate HSLC Author(s) or Source Compressive Strength f c ’ (psi) Dry Unit Weight w (pcf) Modulus of Elasticity E c (million psi) Brown Davis 6,500 120 3.90 Leming 7,180 116.4 3.58 FIP Committee 7,500 118.6 3.55 Harmon 8,170 111.7 3.27 Bilodeau Chevrier Malhotra Hoff 9,090 119.2 4.06 Valum Nilsskog 9,550 123.0 3.41 Mor 9,650 130.0 3.91 Holm Bremner 9,856 117.0 3.50 Carolina Stalite Company 10,281 126.0 4.10 Harmon 10,980 119.2 3.95 Harmon 11,500 134.0 4.40 Carolina Stalite Company 11,588 132.0 4.40 Harmon 11,850 122.0 4.56 A-8
A.7.2 Strength Ceiling Harmon discussed a strength ceiling for HSLC being in the region of 12,000 to 13,000 psi based on the limiting strength of the slate LWA. Holm also discussed the strength ceiling with respect to smaller maximum size of aggregate. As the maximum size of aggregate is reduced, strength increases to some upper limit determined by the strength ceiling. Beyond the strength ceiling, additional binder does not increase the concrete’s strength. Bremner and Holm addressed the elastic mismatch between LWA and the high-strength cement paste matrix. As the HSLC strength increases, the difference between the elasticity modulus values becomes more pronounced. Under load, the “elastic mismatch” results in fracture that begins as transverse splitting of the LWA. This splitting action is indirectly responsible for the strength ceiling of HSLC. Holm also reported a tensile strength ceiling for LWC. Since the LWA is approximately one half voids, its tensile strength will be reduced in comparison to NWA. Holm suggested the LWA tensile strength ceiling might also be responsible for compression strength limitations. A.7.3 Internal Curing Internal curing results when absorbed water in the LWA provides an internal reservoir to enhance cement hydration and extend the curing process. Several authors have commented on this phenomenon as related to LWC and HSLC. Bremner, Holm and Ries performed a study in which LWA was added to NWC mixes to provide additional internal cure water in mixes having strengths from 6,400 psi to 8,700 psi. The internal curing is reported to not only add in strength gain, but positively impacts durability characteristics by providing a higher quality and denser matrix. A.8 Transfer Length Transfer length (l t ) is defined as the distance required to transfer the effective prestressing force from the strand to the surrounding concrete. The transfer length is developed when the pretensioning strands are released by flame cutting or other method from the restraining abutments. Numerous factors are thought to contribute to determining the transfer length including size and surface condition of the prestressing strand, concrete strength and modulus of elasticity at time of strand release, level of prestressing in the strand, and the amount of confining A-9
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School of Civil and Environmental E
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ACKNOWLEDGMENTS The research presen
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A statistical evaluation based on f
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5.6 - Transfer Length 5-13 5.7 - Gi
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Report ACI 318- 99 AASHTO Standard
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Chapter 1. Introduction 1.1 Purpose
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Long term properties including pret
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ottom flange. Prestressing strands
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12500 12000 Concrete Strength, fc'
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Chapter 3. Mix Designs, Field Evalu
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Variation of coarse-to-fine aggrega
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3.2.1 Compressive Strength Figure 3
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Table 3.5 Chloride Permeability --
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12,000 11,500 11,000 Compressive St
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1,400 1,300 1,200 1,100 Experimenta
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strength (10L made in the laborator
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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
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: aggregate must be saturated by pres
Page 89 and 90: compared to lower strength specimen
Page 91 and 92: A.8.8 Deatherage, Burdette and Chew
Page 93 and 94: 3. Concrete compressive strength at
Page 95 and 96: findings were comments that the AAS
Page 97 and 98: including strand diameter, embedmen
Page 99 and 100: l d = l t + l fb = f si 3 d b + 1.5
Page 101 and 102: l d = l t + l fb ⎛ = ⎜ ⎝ f d
Page 103 and 104: Table A.1 Summary of Development Le
Page 105 and 106: strand release, the strand attempts
Page 107 and 108: Appendix B. Creep and Shrinkage B.1
Page 109 and 110: Changes in moisture migration: the
Page 111 and 112: t′: age of concrete at loading (d
Page 113 and 114: s: slump (in) γ ψ ⎧ 0.30 −1.4
Page 115 and 116: t: age of concrete (days) t 0 : age
Page 117 and 118: where ε sh ∞ ⎧ 510 µε for st
Page 119 and 120: left girder-end. The dimension L wa
Page 121 and 122: 6” 85” 50” Segment of girder
Page 123 and 124: 146” 89” 96” 137” Stirrups
Page 125 and 126: were added in a specific sequence f
Page 127 and 128: C.2.3 Formwork Removal, Detensionin
Page 129 and 130: Figure C.19 Mostafa Prestressing St
Page 131 and 132: Figure C.22 Ms. Lyn Clements (GDOT)
Page 133 and 134: If significant strand end slip over
Page 135 and 136: 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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