Lightweight Concrete for High Strength - Expanded Shale & Clay

More documents

Recommendations

Info

All constructed in the 1960s, the bridge girders used LWC with a compressive strength between 5,000 and 6,000 psi. When the publication was issued in 1994, all the bridges were reported to be in excellent condition. Melby, Jordet and Hansvold described the use of HSLC for long-span bridges in Norway. The authors commented that LWC has been used for bridges in Norway since 1987. Their recommendations focused on testing mix designs thoroughly and ensuring excellent quality control to obtain consistent properties. They stated that the use of LWC was economical for long span bridges, but that bridge geometry would determine the amount of savings. Compressive strengths up to 8,700 psi with a unit weight of 125 pcf were successfully used to construct the Raftsundet Bridge. Holm and Bremner noted that LWC was a very promising alternative for the replacement of functionally obsolete bridges throughout the United States. In many cases, the use of LWC for deck replacement would allow upgrading bridge capacity based on lower deck dead load. The authors cited as an example the Woodrow Wilson Memorial Bridge in Washington, D. C. By replacing the bridge deck with LWC, engineers reduced the dead load on the structure and were able to add an additional lane of traffic without exceeding the load carrying capacity of the structure. 2.5 HSLC Mix Designs A.5.1 Coarse Aggregate Coarse aggregate is a primary factor in developing a mix design that is lightweight, highstrength, and cost effective. Manufactured lightweight coarse aggregates include expanded clays, expanded shales, expanded slates, expanded perlite, exfoliated vermiculite, and sintered fly ash. Lightweight coarse aggregates also occur naturally in the form of pumice and tuff. Depending on the source of the aggregate, the particle shape and surface texture vary significantly impacting all other aspects of the mix design and the placement characteristics of the concrete. Numerous authors commented on the need for specifications by particular aggregate manufacturer or source with respect to design characteristics. The raw material from which the LWA is produced determines the strength of the aggregate and thus the strength that can be achieved in the concrete. Expanded slate aggregates A-4
are normally recognized as being one of the LWA products able to produce the highest compressive strength and modulus of elasticity. The porosity of the LWA determines the degree to which the aggregate will absorb and release water and varies significantly between LWA types. Based on an absorption test using ASTM C 127 and ASTM C 128, the absorption of LWA can vary from 5 percent to over 25 percent moisture by mass of dry aggregate as compared to less than 2 percent for normal weight aggregate (Holm and Bremner 2000). Knowledge of the exact absorption characteristics of the chosen LWA is important in properly batching LWC. In addition, handling and quality control must be more exact when working with LWA. Bremner and Newman (1982) found that the internal microstructure of each type of LWA was independent of the source. A reduction in the maximum size of coarse aggregate can increase compressive strength without increasing the cement content or reducing the water-cement ratio. A.5.2 Fine Aggregate The addition of fine LWA to a mix design further lowers the unit weight of the concrete; however, other characteristics are impacted. In a study by Pfeifer, various amounts of the lightweight fine aggregate fraction were replaced with normal weight sand. The results showed that increasing the proportion of normal weight sand increased both compressive strength and modulus of elasticity. A.5.3 Portland Cement In HSLC mixes, the cement paste matrix must carry a higher portion of the load imposed on the concrete. As the strength limit of the cement paste matrix is reached, strength of the aggregate and interface between the aggregate and cement paste become the limiting factors. The type of cement used in the mix determined its curing characteristics. Use of a Type I/II cement results in lower initial strengths, but slightly higher strengths after 28 days. The use of Type III cement yields higher compressive strengths initially, which was desirable for prestressed construction, but results in slightly lower strengths at 28 days compared to Type I/II. A.5.4 Silica Fume The inclusion of silica fume in LWC mix designs was reported to significantly improve strength and other performance characteristics. Fujii et al. reported results of a study where they A-5
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 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: Raithby and Lydon described the use
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
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
Page 137 and 138:
Appendix D. Prestress Losses in HPL
Page 139 and 140:
E ps : elastic modulus of prestress
Page 141 and 142:
D.2.2. AASHTO-LRFD Refined Estimate
Page 143 and 144:
∆f log(24 ⋅t) ⎛ f ⎜ ⎞ 55
Page 145 and 146:
P i : initial prestressing force af
Page 147 and 148:
References AASHTO (1996), Standard
Page 149 and 150:
ASTM C 618, Standard Specification
Page 151 and 152:
Guide for Structural Lightweight Ag
Page 153 and 154:
Martin, L. D., Scott, N. L., “Dev
Page 155:
Shahawy, M. A., Batchelor, B., “S
show all

Lightweight Concrete for High Strength - Expanded Shale & Clay

Create successful ePaper yourself

Delete template?

Save as template?