Lightweight Concrete for High Strength - Expanded Shale & Clay

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Chapter 7. Conclusions and Recommendations 7.1. Analytical Investigation The use of HPLC has the potential to increase the length of simple span AASHTO Type IV and V sections up to four percent and Bulb-Tee sections up to three percent. However, AASHTO Type II and III sections do not benefit appreciably from the use of HPLC. The Modified Bulb-Tee section extended the length of a Standard Bulb-Tee by 10 feet using 8, 10 and 12 ksi HPLC or high-strength NWC. Bulb-Tee (Standard or Modified) sections provided longer spans at less weight for girders over 105 feet in length when compared to AASHTO sections. For spans between 125 feet and 155 feet, the use of HPLC can reduce the gross vehicle weight to less than 150 kips so that a super-load permit is not required for transport of long span girders in Georgia. 7.2 HPLC Mixes and Properties HPLC mixes were developed in the laboratory for 8,000 psi and 10,000 psi compressive strength using slate lightweight ½-in coarse aggregate and normal weight, natural sand. The dry unit weight of the concretes was approximately 117 and 119 pcf, respectively. A 12,000 psi design strength mix could not be developed. The strengths of mixes using lightweight fine aggregate could not be controlled; therefore no recommended mix used lightweight fines. The laboratory mixes were verified during field production. The field mixes yielded slightly higher strengths than found in the laboratory. Close monitoring of lightweight aggregate moisture was required. The HPLC, both 8,000 psi and 10,000 psi design strength continued to gain strength over the 100-day test period. Accelerated cured cylinders, which matched curing conditions of precast beams, showed about 25 percent higher one-day strength than ASTM cured cylinders; at 56 days, the ASTM cured cylinders were about 4% stronger than the accelerated cured cylinders. An equation was developed and provides a better estimate of the modulus of elasticity for slate HPLC than previous relations for normal strength concretes. 7-1
7.3 Transfer Length An evaluation of current code provisions using the 12 HPLC transfer lengths in this research and 8 normal weight HPC transfer lengths from Reutlinger (1999) showed the current AASHTO (1996) and ACI (2002) equations to be conservative. The AASHTO equation overestimated transfer lengths by 42% on average and never underestimated transfer lengths. The ACI equation using VWSG data to determine prestressing strand stress also overestimated transfer lengths by 46% and never underestimated transfer lengths. Use of either the AASHTO or ACI equations to predict transfer length for slate HPLC was conservative. Based on the concrete strength range addressed in this research project, modification of the current code specifications for transfer lengths was not necessary for slate HPLC. There was no indication throughout this analysis that a need existed to differentiate between slate HPLC and normal weight HPC with regard to transfer length. For initial concrete strengths, f ci ’, over 6,000 psi, the prediction of transfer length was the same for both slate lightweight and normal weight concrete. 7.4 Flexural Behavior The current prediction of cracking stress and cracking moment, when examined for slate HPLC, showed indications of becoming unconservative as concrete compressive strengths approached 11,000 psi. In some cases, the predicted cracking moments exceeded the experimental values. The use of a lambda factor (λ) of 0.85 for HPLC made with slate lightweight aggregate produced conservative results on average for compressive strengths below 11,000 psi. More research is required to examine a potential tension strength ceiling for HPLC and adjustments to lambda for concrete compressive strengths over 10,000 psi. The modulus of rupture test, ASTM C 78, did not accurately predict the cracking stress of HPLC girders. The current AASHTO procedure for ultimate moment calculation was conservative for slate HPLC girders with normal weight concrete decks having a compressive strength under 6,000 psi. 7.5 Shear Behavior The current AASHTO Standard specification provided a conservative prediction of concrete and ultimate shear capacity when shear steel capacity was capped at a yield strength of 7-2
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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
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
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: 6.3 Conclusions Regarding Prestress
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
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
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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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