Lightweight Concrete for High Strength - Expanded Shale & Clay

More documents

Recommendations

Info

normal weight aggregate does not creep at the stress levels present in concrete. However, in HSLC, the higher stress placed on the member might induce creep in the lightweight aggregate, due to its lower modulus and strength. Also, improvements in the interfacial transition zone, afforded by the use of ultra-fine pozzolanic particles and lightweight aggregate, can alter the mechanisms for creep. Particularly, they can alter mechanisms not only compared to normal strength concrete, but also compared to high strength concrete (due to improved compatibility between the aggregate and paste). Finally, the increased aggregate porosity and the effect of “internal curing” (when using saturated lightweight aggregate) can influence moisture movements during creep. These possible changes in expected behavior (as compared to normal concrete and high strength concrete) resulting from the use of high performance matrix and lightweight aggregate are described in further detail below. Aggregate mechanical properties: In normal weight concrete, creep is largely a phenomenon occurring in the paste, but its magnitude, and perhaps its temporal development, can be affected by the quantity and quality of the aggregate. The high porosity of lightweight aggregates may influence creep of concrete not only indirectly by reducing the elastic modulus and strength of the concrete, but also directly by participating in the moisture movements occurring during creep, as considered in the seepage theory. Improved interface characteristics: Micrographs of SLC (structural lightweight concrete) showed that the boundary between cementitious matrix and coarse aggregate was indistinguishable from the bulk paste (Holm and Bremner, 2000). This may result from: (1) improved physical bonding between the paste and aggregate (due to increased aggregate porosity); (2) improved chemical bonding between the paste and aggregate (due to pozzolanic activity); (3) reduced microcracking (due to elastic matching between aggregate and paste); and (4) reduced bleeding. In addition, “internal curing” may improve the strength and density of the interfacial transition zone (ITZ). This occurs when presoaked lightweight aggregate provides an internal reservoir of water maintaining favorable moisture conditions and extending the local hydration processes (ACI-213, 1987 -reapproved 1999; Holm and Bremner, 1990). These improvements to the ITZ could mitigate the “microcracking effect” on creep. Katz et al. (1999) postulated that an improved ITZ can be obtained by using dry lightweight aggregate. They concluded that the suction imposed by a dry lightweight aggregate can lead to a dense ITZ, with even some penetration of cement particles into the shell of the aggregate. B-2
Changes in moisture migration: the seepage theory views creep as a result of water movement under stress from micropores to the larger capillary pores. If water migration is the main factor in concrete creep, both the aggregate porosity (i.e., volume of pores, pore size, and pore distribution) and the permeability of the cementitious matrix become important factors. Several (ACI-213, 1999; Holm, 1995; Neville et al., 1983) have cited the importance of using lightweight aggregate in a saturated condition while mixing. If the aggregate is not saturated, a more rapid movement of water from the paste would be expected to lead to greater creep. On the other hand, the moisture conditions given by the saturated lightweight aggregate could replace the water lost under stress (seepage). B.2 Shrinkage of HPLC As occurs with creep of HPLC, there are only a few articles regarding shrinkage of HPLC. Besides, they usually do not report autogenous and drying shrinkage separately, but as overall shrinkage. Berra and Ferrada (1990) found that compared with HPC, HPLC had a lower shrinkage rate, but a higher ultimate value. According the authors, the lower rate was caused by the presence of water in the aggregate which delays drying. Holm and Bremner (1994) also observed that HSLC mix lagged behind at early ages, but one-year shrinkage was approximately 14% higher than the HPC counterpart. Holm and Bremner (1994) measured a higher shrinkage when they incorporated fly ash to the HSLC mix. Malhotra’s (1990) results, on the other hand, showed that fly ash particles in the HPLC helped to reduce shrinkage after one year. Leming (1990) reported one-year shrinkage of 4,000-psi and 8,000-psi lightweight concretes, made with saturated expanded slate, of 390 and 310 µε, respectively while the corresponding shrinkage of a 4,000-psi NWC was found to be 360 µε. Bilodeau et al. (1995) investigated HSLC with 28-day compressive strength ranging from 7,250 to 10,000 psi and found that the 450-day shrinkage was in the range 518 to 667 µε. Curcio et al. (1998) reported that one-year and ultimate shrinkage of HPLC with Type III cement and fly ash was 450 and 500 µε, respectively. Kohno et al. (1999) found out that autogenous shrinkage is reduced by the use of lightweight fine aggregate. They concluded that this is because water lost by self-desiccation of the cement paste is immediately replaced by moisture from lightweight aggregate. Aïtcin (1992) reported values of shrinkage of HPLC as low as 70 and 260 µε, after a 28-day curing. B-3
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 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: Appendix B. Creep and Shrinkage B.1
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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?