LIGHTWEIGHT CONCRETE MATERIAL PROPERTIES FOR STRUCTURAL DESIGN. Henry G. Russell, Henry G. Russell, Inc., Glenview, IL

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1 LIGHTWEIGHT CONCRETE MATERIAL PROPERTIES FOR STRUCTURAL DESIGN Henry G. Russell, Henry G. Russell, In., Glenview, IL ABSTRACT This paper ontains a ompilation and synthesis of researh relating to lightweight onrete and its use in highway bridges as designed using the AASHTO LRFD Bridge Design Speifiations. Speifi topis inlude reep, shrinkage, modulus of elastiity, modulus of rupture, flexural and axial fore design, shear design, loss of prestress, and development length. For these topis, the existing LRFD provisions are generally adequate for the design of lightweight onrete members with onrete ompressive strength up to 10.0 ksi. Refinement of some provisions would improve their onsisteny and auray. Keywords: Axial Fore Design, Creep, Development Length, Flexural Design, Lightweight Conrete, Loss of Prestress, Material Properties, Modulus of Elastiity, Modulus of Rupture, Shear Design, Shrinkage, Splitting Tensile Strength, and Strutural Design. NOTE: This paper was first presented at the ESCSI Speial Workshop on Lightweight Aggregate Conrete Bridges that was held May 7, 2008, in St. Louis, MO. The workshop was held in onjuntion with the 2008 Conrete Bridge Conferene. This paper appeared as Paper 141 in the proeedings for the onferene. 1

2 INTRODUCTION Signifiant researh efforts are urrently being performed under the National Cooperative Highway Researh Program (NCHRP) and others to update and modify the AASHTO LRFD Bridge Design Speifiations for use with higher onrete ompressive strengths. This inludes the use of lightweight onrete. As part of this effort, a ompilation and synthesis of researh relating to lightweight onrete and its use in highway bridges as related to the AASHTO LRFD Bridge Design Speifiations was developed (Russell, 2007). This paper ontains a omparison of the AASHTO LRFD design provisions with available researh data for those provisions with the most available data. For details of all the provisions affeted by lightweight onrete and those provisions for whih researh data with lightweight onrete are laking, the reader is referred to the original report (Russell, 2007). Those provisions are not addressed in this paper. For purposes of this paper, lightweight onrete is assumed to have a density between about kf and that of normal weight onrete. The paper does not differentiate between alllightweight and sand-lightweight onrete. The literature searh onentrated on publiations onerning North Amerian materials and design praties. The researh results are presented as a omparison with the AASHTO LRFD Bridge Design Speifiations. Consequently, the units of the LRFD Speifiations are generally used throughout the paper. ARTICLE 5.4 MATERIAL PROPERTIES CREEP A omparison of speifi reep versus time for data by Harmon (2005), HDR (1998), Hoff (1992), Lopez et al. (2004), Pfeifer (1968), and Shideler (1957) is shown in Fig. 1. The data are plotted as speifi reep versus onrete age. Speifi reep, defined as reep strain divided by applied stress, is used beause it does not depend on the initial elasti strain or modulus of elastiity of the onrete. The data in Fig. 1 are for a variety of onrete unit weights, ompressive strengths, stress levels, aggregate soures, and loading ages. All of the reep data exept those by Lopez et al. are based on 6x12-in. ylinders stored at approximately 73 F and 50 perent relative humidity during the tests. Lopez et al. used 4x15- in. ylinders. The effet of stress level an be taken into aount by using reep strain per unit stress or speifi reep as plotted in Fig. 1. It is generally assumed that total reep strain is proportional to stress level up to a stress level of at least 40 perent of the onrete ompressive strength at the age of loading. In addition to the data shown in Fig. 1, Vinent et al. (2004) performed reep tests on four bathes of onrete. However, it is diffiult to determine the ages of loading and the applied stress level from their report. It also appears that the load was inreased during the test. 2

3 Speifi Creep, millionths/psi LRFD Harmon HDR Hoff Lopez Pfeifer Shideler Conrete Age, days Fig. 1 Creep Data For omparison with the measured values, reep alulated using Eq of the LRFD Speifiations is also shown in Fig. 1. The upper line is for a onrete ompressive strength of 4.0 ksi and a modulus of elastiity of 2000 ksi at a loading age of 7 days. The lower line is based on onrete ompressive strength of 8.0 ksi and a modulus of elastiity of 3.75 ksi at a loading age of 7 days. These lines orrespond to unit weights of about 110 and 130 pf aording to the revised equation for modulus of elastiity disussed in ARTICLE Both lines are based on 6x12-in. ylinders. The two lines orrespond to a wide range of reep properties but enompass most of the data exept those of Pfeifer (1968). In many ases, the ompressive strength of his onrete at the loading age of 7 days was less than 2.0 ksi and the ratio of stress to strength exeeded The ommentary to Artile states that without speifi physial tests or prior experiene with the materials, the use of the empirial methods referened in the speifiations annot be expeted to yield results with errors less than ±50 perent. A more detailed analysis is needed to determine if the separate variables in Eq represent the true behavior of lightweight onrete sine the equation was based on normal weight onrete (Tadros et al., 2003) SHRINKAGE A omparison of shrinkage versus drying time for data by Hanson (1968), Hoff (1992), Holm (1980), Leming (1990), Lopez et al. (2004), Malhotra (1990), Ozyildirim and Gomez (2005), Pfeifer (1968), Rogers (1957), Shideler (1957), and Vinent et al. (2004) is shown in Fig. 2. 3

4 Shrinkage, millionths LRFD Hanson Hoff Holm Leming Lopez Malhotra Ozyildirim Pfeifer Rogers Shideler Vinent Drying Time, days Fig. 2 Shrinkage Data These data are for a variety of onrete unit weights, ompressive strengths, aggregate soures, uring onditions, and speimen sizes. These variations may ontribute to the satter in the data. For omparison with the measured values, the shrinkage alulated using Eq of the LRFD Speifiations is also shown. The upper line is based on a 3x3-in. prism using a onrete ompressive strength of 4.0 ksi at the start of shrinkage measurements. The lower line is based on a 6x12-in. ylinder using a onrete ompressive strength of 9.0 ksi. The equations for shrinkage and reep were developed based on normal weight onretes (Tadros et al., 2003). Nevertheless, the upper and lower limits do enompass most of the range for lightweight onrete MODULUS OF ELASTICITY The existing equation ( ) for alulating modulus of elastiity is 1.5 ' E = 33,000 K1w f (1) where: K 1 = orretion fator for soure of aggregate to be taken as 1.0 unless determined by physial test, and as approved by the authority of jurisdition w = unit weight of onrete (kf) 4

5 f' = speified ompressive strength of onrete (ksi) The NCHRP Projet No titled "Appliation of the LRFD Bridge Design Speifiations to High-Strength Strutural Conrete: Flexure and Compression Provisions" (Rizkalla, 2007) ompiled 4388 data points for onrete unit weights ranging from to kf, onrete ompressive strengths from 0.4 to 24.0 ksi, and onrete modulus of elastiity from 710 to 10,780 ksi. Based on these data, the following equation was reommended to replae Eq : 2.5 ' ,000 K1w f E = (2) Comparisons of the measured data with values predited using Eq and the proposed equation are shown in Figs. 3 and 4, respetively. The proposed equation improves the overall agreement between measured and predited values and results in lower predited values for lightweight onrete ompared to values alulated using the existing equation. It should be noted that the spread of data is about ± 25 perent of the predited values. 10 R 2 = % 8 Predited Modulus of Elastiity, million psi % Measured Modulus of Elastiity, million psi 0.90 < w < kf < w < kf < w < kf < w < kf < w < kf w > kf Fig. 3 Comparison of Predited and Measured Modulus of Elastiity for Eq MODULUS OF RUPTURE A omparison of modulus of rupture versus onrete ompressive strength is shown in Fig. 5 for data by Harmon (2005), Heffington (2000), Hoff (1992), Malhotra (1990), Meyer (2002), 5

6 10 +25% R 2 = Predited Modulus of Elastiity, million psi % Measured Modulus of Elastiity, million psi 0.90 < w < kf < w < kf < w < kf < w < kf < w < kf w > kf Fig. 4 Comparison of Predited and Measured Modulus of Elastiity for Proposed Equation Modulus of 0.75 Rupture, ksi LRFD Harmon Heffington Hoff Malhotra Meyer Ozyildirim Ramirez Shideler Tasillo Compressive Strength, ksi Fig. 5 Modulus of Rupture Versus Conrete Compressive Strength 6

7 Ozyildirim and Gomez (2005), Ramirez et al. (2000), Shideler (1957), and Tasillo et al. (2004). These data are for a variety of onrete unit weights, aggregate soures, uring onditions, and speimen sizes. Slate et al. (1986) reommended a modulus of rupture of ' 0.21 f for ompressive strengths from 3.0 to 9.0 ksi for moist ured lightweight onretes. No satisfatory orrelation was found for dry-ured lightweight onrete. The measured modulus of rupture is sensitive to the uring onditions beause speimens that are allowed to dry develop tensile stresses near the surfaes. This in turn results in a redued measured value of the modulus of rupture. Speimens that are moist ured until test age have a higher measured modulus of rupture ompared to speimens that are allowed to dry out. This differene is often larger than would be expeted from the hange in ompressive strength. For omparison purposes, the two red lines in Fig. 5 show the modulus of rupture alulated using the provisions of Artile for sand-lightweight and all-lightweight onrete. The variation of splitting tensile strength with onrete ompressive strength is presented later in ARTICLE 5.8 SHEAR AND TORSION. ARTICLE 5.7 DESIGN FOR FLEXURAL AND AXIAL FORCE EFFECTS A omparison of maximum usable onrete ompressive strain versus onrete ompressive strength is shown in Fig. 6 for lightweight onrete data by Ahmad and Barker (1991), Ahmad and Batts (1991), Hoff (1992), Kaar et al. (1978), and Thather et al. (2002). For most of the data, the urrent assumed maximum usable strain of for unonfined onrete is a onservative value for lightweight onrete Maximum Strain LRFD Ahmad, Barker Ahmad, Batts Hoff Kaar Thather Conrete Strength, ksi Fig. 6 Maximum Strain Versus Conrete Compressive Strength 7

8 RECTANGULAR STRESS DISTRIBUTION The equivalent retangular stress blok assumes a uniform ompressive stress equal to 0.85f'. The 0.85 multiplier is sometimes alled the α 1 fator. Values of α 1 versus onrete ompressive strengths are shown in Fig. 7 for lightweight onrete data by Hoff (1992) and Kaar et al. (1978). In addition, there were 15 tests by Hanson reported by Hognestad et al. (1956) but speifi values were not reported α LRFD NCHRP Hoff Kaar Conrete Strength, ksi Fig. 7 Variation of α 1 Fator with Conrete Compressive Strength For omparison purposes, the value of 0.85 used in the LRFD Speifiations is also shown in Fig. 7 as the solid red line. Based on test data for normal weight onrete, NCHRP Projet has proposed that for onrete ompressive strengths greater than 10.0 ksi, the value of α 1 shall be redued by 0.02 for eah 1.0 ksi in exess of 10.0 ksi but shall not be less than This proposed relationship is also shown in Fig. 7 as the broken red line. Based on the limited data, it would seem that the existing and proposed relationships overestimate the value of α 1 for lightweight onrete. Kaar et al. (1978) suggested that α 1 should be taken as 0.65 for all strengths of lightweight onrete. The value of α 1 has little effet on the alulated flexural strength of under-reinfored setions but does affet the alulated axial load apaity where onrete ompression ontrols. The equivalent retangular stress blok assumes that the uniform ompressive stress ats over a depth of β 1, where is the depth of the neutral axis from the extreme ompression fiber. Values of β 1 for different onrete ompressive strengths are shown in Fig. 8 for data by Hoff (1992) and Kaar et al. (1978). For omparison purposes, the value of β 1 used in the LRFD Speifiations is also shown. For all values exept one, the measured values exeed the LRFD values. 8

9 β LRFD Hoff Kaar Conrete Strength, ksi Fig. 8 Variations of β 1 Fator with Conrete Compressive Strength FLEXURAL RESISTANCE Comparison of measured and alulated flexural strengths have been reported by Ahmad and Barker (1991), Ahmad and Batts (1991), Meyer (2002), Peterman et al. (1999), and Thather et al. (2002). In some ases, the flexural strengths were measured as part of a program to determine development length. A graph of measured strength divided by alulated strength versus onrete ompressive strength is shown in Fig. 9. In all ases, the alulated flexural strengths were determined using the proedures of the Standard Speifiations (AASHTO, 1996) or the ACI Building Code (ACI Committee 318, 1983). However, sine the proedures of the LRFD Speifiations result in similar flexural strengths to those alulated using the Standard Speifiations and the ACI Building Code, the ratios of measured to alulated strengths should not be too different using the LRFD Speifiations. Further analysis of the test results using the LRFD Speifiations may be warranted FACTORED AXIAL RESISTANCE Pfeifer (1969) tested twenty 6-in. diameter lightweight onrete olumns with onrete ompressive strengths ranging from 4.42 to 7.60 ksi, steel yield strengths ranging from 50.0 to 92.5 ksi, and perentage of reinforement ranging from 0 to 8.38 perent. Measured strengths were ompared with the equivalent of Eq The measured strengths were slightly less than predited in most ases and signifiantly less than predited when the steel yield strength was 92.5 ksi. 9

10 Ahmad, Barker Ahmad, Batts Meyer Peterman Thather 1.25 Flexural Strength, Measured/ 1.00 Calulated Conrete Strength, ksi Fig. 9 Comparison of the Ratio of Measured to Calulated Flexural Strength with Conrete Compressive Strength ARTICLE 5.8 SHEAR AND TORSION MODIFICATIONS FOR LIGHTWEIGHT CONCRETE Artile states that modifiations shall apply in determining resistane to torsion and shear of lightweight onrete. Where the average splitting tensile strength of lightweight onrete, f t, is speified, the term ' f may be replaed by 4.7 f t ' f. The use of f t in plae of ' f is based on the researh by Hanson (1961), who developed a orrelation between the shear raking strength of beams and the splitting tensile strength of ylinders. Where f t, is not speified, the term 0.75 sand-lightweight onrete shall be substituted for ' f for all lightweight onrete and 0.85 ' f ' f for. The origin of 0.75 and 0.85 fators appear to have been developed by ACI Committee 213 Lightweight Conrete and reommended to ACI Committee 318 (Ivey and Buth, 1967). A waiver to allow higher shear stresses when justified by splitting tensile tests was also inluded. Ivey and Buth (1967) ompared the results of tests at the Texas Transportation Institute, Portland Cement Assoiation, and the University of Texas with the ACI shear strength equations modified by the 0.75 and 0.85 fators and found reasonable onservatism. Although the shear design 10

11 approah has hanged from that used when the fators were developed, the modifiation fators remain the same. Data on the measured splitting tensile strength from 14 reports are shown in Fig. 10 (Hanson, 1961, 1965, 1968; Heffington, 2000; Hoff, 1992; Ivey and Buth, 1966; Khaloo and Nakseok, 1999; Malhotra, 1990; Mattok et al., 1976; Ozyildirim and Gomez, 2005; Pfeifer, 1967; Ramirez et al., 2000, 2004; and Vinent et al., 2004). The LRFD lines represent the above modifiations for lightweight onrete. The line labeled "LRFD at 0.23" applies to normal weight onrete. The LRFD lines for lightweight onrete tend to overestimate the measured strengths. Splitting Tensile Strength, ksi LRFD at 0.23 LRFD with speified strength LRFD with sand-lightweight LRFD with all-lightweight Hanson Heffington Hoff Ivey Khaloo Malhotra Mattok Ozyildirim Pfeifer Ramirez Vinent Compressive Strength, ksi Fig. 10 Splitting Tensile Strength Versus Conrete Compressive Strength Moore (1982) ompared the shear strength and response of short olumns made with lightweight and normal weight onrete subjet to yli loading. He onluded that for olumns with no axial load, the 15 perent redution for shear speified in Chapter 11 of ACI (ACI Committee 318, 1977) for lightweight onrete was adequate but for olumns with axial ompression, the 15 perent redution was not adequate. The 15 perent redution refers to the use of ' NOMINAL SHEAR RESISTANCE f for sand-lightweight onrete in Artile The shear design provisions of the LRFD Speifiations have been evolving sine their introdution in the first edition. The fourth edition (AASHTO, 2007) now inludes a new simplified proedure for prestressed and nonprestressed setions in addition to the general proedure (Artile ) and the simplified proedure for nonprestressed setions 11

12 (Artile ). As a result of NCHRP Projet titled "Appliations of LRFD Bridge Design Speifiations to High-Strength Strutural Conrete: Shear Provisions" (Hawkins et al., 2007), some additional hanges may also our in the future. Salandra and Ahmad (1989) tested eight reinfored lightweight onrete beams with shear reinforement but only two failed due to diagonal tension raking with the rest failing in flexure due to rushing of onrete in the onstant moment region. Ramirez et al. (2004) tested five reinfored and four prestressed lightweight onrete beams. Measured strengths were ompared with strengths alulated using the general and simplified methods of the LRFD Speifiations (AASHTO, 1998) through the 2001 Interim Revisions. Meyer (2002) tested six prestressed lightweight onrete beams that failed primarily due to shear. Measured strengths were ompared with strengths alulated using the 1998 LRFD Speifiations (AASHTO, 1998). Meyer (2002) onluded that the 1998 Speifiations provided a onservative predition of shear strength. A omparison of the ratio of measured to alulated strengths versus onrete ompressive strength for the tests by Meyer (2002) and Ramirez et al. (2004) is shown in Fig. 11. All measured strengths were greater than the alulated strengths. Although measured shear apaities exeeded alulated values, Ramirez et al. (2000) autioned that the degree of onservatism was less with high-strength lightweight onrete. They reommended more researh in the area of high-strength prestressed lightweight onrete beams espeially with regard to the requirements for minimum transverse reinforement Meyer Ramirez Shear Strength, 2.0 Measured/ Calulated Conrete Strength, ksi Fig. 11 Comparison of the Ratio of Measured to Calulated Shear Strengths with Conrete Compressive Strength 12

13 ARTICLE 5.9 PRESTRESSING AND PARTIAL PRESTRESSING LOSS OF PRESTRESS The provisions of Artile for prestress losses were revised to a great extent based on NCHRP Projet (Tadros et al., 2003), whih only investigated normal weight onrete. The ommentary C larifies that for lightweight onrete onstrution, an alternative method should be used. However, Artile allows the use of the losses in Table for lightweight onrete members other than those with omposite slabs. Hanson (1964) measured the effet of type of uring on prestress losses of onretes made using two different lightweight aggregates. Prestressed onrete members were simulated using short post-tensioned members of two different sizes. Companion reep and shrinkage tests were made on 6x12-in. ylinders. Cousins (2005) reported on the measurement of prestress losses in three lightweight onrete girders of the Chikahominy River Bridge, Virginia. The bridge is a three-span struture made ontinuous for live load with two end spans of 81 ft 10 in. and a enter span of 82 ft 10 in. Eah span onsists of five AASHTO Type IV girders at 10 ft enters with an 8.5-in. thik lightweight onrete dek. Measured values of prestress losses were ompared with those predited using the proedures of the LRFD Speifiations, NCHRP Report No. 469 (Tadros et al., 2003), and several other methods. Cousins (2005) onluded that the refined and approximate methods of the NCHRP report were suitable for a onservative estimate of total losses. Meyer (2002) monitored the prestress losses at three loations in eah of six girders on beams being used to determine transfer and development lengths. Measured values were ompared with alulated losses using the AASHTO Standard Speifiations (AASHTO, 1996). All measured values were less than the alulated values as shown in Figure 12. Kahn et al. (2005) reported prestress losses in four girders using two different onrete strengths. They ompared the measured values with alulated values using the refined method and the lump sum methods of the LRFD Speifiations (AASHTO, 1998). Their results are inluded in Fig. 12. In general, the refined method overestimated the losses, whereas the lump sum losses underestimated the losses for one of the mixes. ARTICLE 5.11 DEVELOPMENT AND SPLICES OF REINFORCEMENT Artile inludes modifiation fators for development length and splies of 1.3 and 1.2 for all-lightweight onrete and sand-lightweight onrete, respetively. In the 1989 edition of the ACI Building Code Requirements for Reinfored Conrete (ACI Committee 318, 1989), the fator for lightweight aggregate onretes was made equal to 1.3 for all types of aggregates when f t is not speified. Aording to the ACI Commentary, researh 13

14 60 50 Equality Meyer Kahn 40 Calulated Losses, ksi Measured Losses, ksi Fig. 12 Comparison of Calulated and Measured Prestress Losses on hooked bar anhorages did not support the variations speified in previous odes for alllightweight and sand-lightweight onrete. Similar hanges were not made in the AASHTO LRFD Speifiations. The ACI ommentary does not identify the speifi researh on whih the hanges were based or the researh for the original fators that are used in Artile Mithell and Marzouk (2007) tested 72 pull-out and push-in speimens to evaluate the bond behavior under monotoni and yli loading using No. 8 and No. 11 deformed reinforement embedded in lightweight onrete with a ompressive strength of 11.6 ksi. They onluded that high-strength, lightweight onrete behaves in a manner similar to highstrength, normal weight onrete and that the 30 perent inrease in development length required by ACI (ACI Committee 318, 2005) is not justified for high-strength lightweight onrete. The 30 perent inrease in ACI orresponds to the 1.3 fator in Artile Aording to ACI Committee 408 (2003) and ACI Committee 213 (2003), design provisions generally require longer development lengths for lightweight onrete although test results from previous researh are ontraditory. The report states that early researh by Lyse (1934), Peterson (1948), and Shideler (1957), and more reent researh by Martin (1982) and Clarke and Birjandi (1993) onluded that the bond behavior of reinforing steel in lightweight onrete was omparable to that in normal weight onrete. In ontrast, Baldwin (1965), Robins and Standish (1982), and Mor (1992) reported bond strengths in lightweight onrete that were less than bond strengths in normal weight onrete. Overall, the data indiate that the use of lightweight onrete an result in bond strengths that range from 14

15 nearly equal to 65 perent of the values obtained with normal weight onrete (ACI Committee 408, 2003) DEVELOPMENT OF PRESTRESSING STRAND Transfer Length Measurements of strand transfer length in lightweight onrete have been reported by Kozlos (2000), Thather et al. (2002), and Ozyildirim and Gomez (2005) for 0.5-in. diameter strand; Peterman et al. (1999, 2000) for 0.5-in. speial strand; and Meyer (2002) for 0.6-in. diameter strand. A graph of the ratio of measured to alulated transfer lengths versus onrete ompressive strength is shown in Fig. 13. All of the data for Meyer and Ozyildirim had measured lengths less than the alulated length of 60 strand diameters. The data of Thather et al. has measured lengths less than and greater than the alulated length. Peterman et al. did not report atual values but onluded that the measured lengths were less than 50 strand diameters the value used in the Standard Speifiations Kozlos Meyer Ozyildirim Thather 1.4 Transfer 1.2 Length, 1.0 Measured/ Calulated Conrete Strength at Transfer, ksi Fig. 13 Comparison of the Ratio of Measured to Calulated Transfer Length with Conrete Compressive Strength Thather et al. (2002) and Sylva III et al. (2002) reported on transfer lengths of 3/8-in. diameter strand in two 4-in. thik lightweight onrete panels. They onluded that the measured length was less than alulated using the 60 strand diameters of the LRFD Speifiations. 15

16 Development Length Aording to Artile , the development length of strand shall be alulated using Eq as follows: 2 l d κ f ps f pe db (3) 3 where: d b = nominal strand diameter (in.) f ps = average stress in prestressing steel at the time for whih the nominal resistane of the member is required (ksi) f pe = effetive stress in the prestressing steel after losses (ksi) κ = 1.0 for pretensioned panels, piling, and other pretensioned members with a depth of less than or equal to 24.0 in. κ = 1.6 for pretensioned members with a depth greater than 24.0 in. Equation without the κ fator was based largely on data from tests onduted by Hanson and Kaar (1959), whih did not inlude lightweight onrete. The history of the development length equation was desribed by Tabatabai and Dikson (1993). Peterman et al. (1999, 2000) onduted 12 development length tests on retangular singlestrand beams made with lightweight onrete and strand from two different manufaturers. The results indiated that the development length alulated using Eq provided suffiient embedment to develop the full apaity of a single strand. When the same ombinations of strands and onrete were tested in multi-strand T-beams, the results were mixed. For one strand, flexural failures ourred indiating that the development length per Eq was adequate. For the other strand, bond, flexure, and a ombination of bond and web shear failures ourred in different beams. Based on his tests, Meyer (2002) onluded that there was no need to differentiate between normal weight onrete and lightweight onrete made with a slate aggregate for onrete ompressive strengths greater than 8.0 ksi. Thather et al (2002) performed 10 tests of lightweight onrete beams with 1/2-in. diameter strands and embedment lengths of 80, 70, and 60 in. They onluded that the embedment length was less than 60 in. as all speimens failed in flexure. The alulated embedment length per Eq with κ = 1.0 was 86 in. Ozyildirim and Gomez (2005) determined that the measured development length of 1/2-in. diameter strand was less than alulated using Eq with κ =

17 CONCLUSIONS For the artiles of the AASHTO LRFD Bridge Design Speifiations disussed in this paper, the existing provisions are generally adequate for the design of lightweight onrete members with onrete ompressive strength up to 10.0 ksi. Refinement of some provisions would improve their onsisteny and auray. REFERENCES AASHTO, 1996, Standard Speifiations for Highway Bridges, Sixteenth Edition, Amerian Assoiation of State Highway and Transportation Offiials, Washington, D.C. AASHTO, 1998, AASHTO LRFD Bridge Design Speifiations, Seond Edition, Amerian Assoiation of State Highway and Transportation Offiials, Washington, D.C. AASHTO, 2007, AASHTO LRFD Bridge Design Speifiations, Fourth Edition, Amerian Assoiation of State Highway and Transportation Offiials, Washington, D.C. ACI Committee 213, 2003, "Guide for Strutural Lightweight-Aggregate Conrete," (ACI 213R-03) Amerian Conrete Institute, Farmington Hills, MI, 38 pp. ACI Committee 318, 1977, Building Code Requirements for Reinfored Conrete (ACI ), Amerian Conrete Institute, Farmington Hills, MI, 102 pp. ACI Committee 318, 1983, Building Code Requirements for Reinfored Conrete (ACI ), Amerian Conrete Institute, Farmington Hills, MI, 111 pp. ACI Committee 318, 1989, Building Code Requirements for Reinfored Conrete (ACI ) and Commentary (ACI 318R-89), Amerian Conrete Institute, Farmington Hills, MI, 353 pp. ACI Committee 318, 2005, Building Code Requirements for Strutural Conrete (ACI ) and Commentary (ACI 318R-05), Amerian Conrete Institute, Farmington Hills, MI, 430 pp. ACI Committee 408, 2003, "Bond and Development of Straight Reinforing Bars in Tension," Amerian Conrete Institute, Farmington Hills, MI, 49 pp. Ahmad, S. H. and Barker, R., 1991, "Flexural Behavior of Reinfored High-Strength Lightweight Conrete Beams," ACI Strutural Journal, Vol. 88, No. 1, January-February, pp Ahmad, S. H. and Batts, J., 1991, "Flexural Behavior of Doubly Reinfored High-Strength Lightweight Conrete Beams with Web Reinforement" ACI Strutural Journal, Vol. 88, No. 3, May-June, pp Baldwin, J. W., 1965, "Bond of Reinforement in Lightweight Aggregate Conrete," Preliminary Report, University of Missouri, Marh, 10 pp. Clarke, J. L. and Birjandi, F. K., 1993, "Bond Strength Tests For Ribbed Bars in Lightweight Aggregate Conrete," Magazine of Conrete Researh, Vol. 45, No. 163, pp

18 Cousins, T. E., 2005, "Investigation of Long-Term Prestress Losses in Pretensioned High Performane Conrete Girders," Final Contrat Report No. VTRC 05-CR20, Virginia Transportation Researh Counil, June, 70 pp. Hanson, N. W. and Kaar, P. H., 1959, "Flexural Bond Tests of Pretensioned Prestressed Beams," ACI Journal, Proeedings, Vol. 55, No. 7, January, pp Hanson, J. A., 1961, "Tensile Strength and Diagonal Tension Resistane of Strutural Lightweight Conrete," ACI Journal, Proeedings, Vol. 58, No. 1, July, pp Hanson. J. A., 1964, "Prestress Loss as Affeted by Type of Curing," PCI Journal, Vol. 9, No. 2, April, pp Hanson. J. A., 1965, "Optimum Steam Curing Proedures for Strutural Lightweight Conrete," ACI Journal, Proeedings, Vol. 62, No. 6, June, pp Hanson. J. A., 1968, "Effets of Curing and Drying Environments on Splitting Tensile Strength of Conrete," ACI Journal, Proeedings, Vol. 68, No. 7, July, pp Harmon, K. S., 2005, "Reent Researh Projets to Investigate Mehanial Properties of High Performane Lightweight Conrete," Seventh International Symposium on the Utilization of High-Strength/High-Performane Conrete, Publiation SP-228, Amerian Conrete Institute, Farmington Hills, MI, pp Hawkins, N. M. and Kuhma, D. A., "Appliation of LRFD Bridge Design Speifiations to High-Strength Strutural Conrete: Shear Provisions," Transportation Researh Board, NCHRP Report 579, Washington, D.C., 2007, 197 pp. HDR Engineering, 1998, "Amerian River Bridge at Lake Natoma Lightweight Conrete, Loading at 7, 28, and 90 Days." Heffington, J. A., 2000, "Development of High Performane Lightweight Conrete Mixes for Prestressed Bridge Girders," Masters Thesis, The University of Texas, Austin, May. Hoff, G. C., 1992, "High Strength Lightweight Aggregate Conrete for Arti Appliations, Parts 1, 2, and 3," Strutural Lightweight Aggregate Conrete Performane, Publiation SP- 136, Amerian Conrete Institute, Farmington Hills, MI, pp Hognestad E., Hanson, N. W., and MHenry, D., 1956, Disussion of "Conrete Stress Distribution in Ultimate Strength Design," ACI Journal, Proeedings, Vol. 28, No. 6, Deember, pp Holm, T. A., 1980, "Physial Properties of High Strength Lightweight Conretes," Seond International Congress on Lightweight Conrete, London, April. Ivey, D. L. and Buth, E., 1966, "Splitting Tension Test of Strutural Lightweight Conrete," Journal of Materials, ASTM, Vol. 1, No. 4, Deember, pp Ivey, D. L. and Buth, E., 1967, "Shear Capaity of Lightweight Conrete Beams," ACI Journal, Proeedings, Vol. 64, No. 10, Otober, pp Kaar, P. H., Hanson, N. W., and Capell, H. T., 1978, "Stress-Strain Charateristis of High- Strength Conrete," Douglas MHenry International Symposium on Conrete and Conrete 18

19 Strutures, Publiation SP-55, Amerian Conrete Institute, Farmington Hills, MI, pp Kahn, L. F., and Lopez, M., 2005, "Prestress Losses in High Performane Lightweight Conrete Pretensioned Bridge Girders," PCI Journal, Vol. 50, No. 5, September/Otober, pp Khaloo, A. R., and Nakseok, K., 1999, "Effet of Curing Condition on Strength and Elasti Modulus of Lightweight High Strength Conrete," ACI Materials Journal, Amerian Conrete Institute, Vol. 96, No. 4, pp Kolozs, R. T., 2000, "Transfer and Development Lengths of Fully Bonded 1/2-Inh Prestressing Strand in Standard AASHTO Type I Pretensioned High Performane Lightweight Conrete (HPLC) Beams," Masters Thesis, The University of Texas at Austin, May, 155 pp. Leming, M. L., 1990, Creep and Shrinkage of Lightweight Conrete, Report to Carolina Stalite Company, North Carolina State University, 4 pp. Lopez, M., Kahn, L. F., and Kurtis, K. E., 2004, "Creep and Shrinkage of High Performane Lightweight Conrete," ACI Materials Journal, Amerian Conrete Institute, Vol. 101, No. 5, September/Otober, pp Lyse, I., 1934, "Lightweight Slag Conrete," ACI Journal, Proeedings, Vol. 31, No. 1, pp Malhotra, V. M., 1990, "Properties of High-Strength Lightweight Conrete Inorporating Fly Ash and Silia Fume," High-Strength Conrete, Seond International Symposium, Publiation SP-21, Amerian Conrete Institute, Farmington Hills, MI, pp Martin, H., 1982, "Bond Performane of Ribbed Bars," Bond in Conrete Proeedings of the International Conferene on Bond in Conrete, Paisley, Applied Siene Publishers, London, pp Mattok, A. H., Li, W. K., and Wang, T. C., 1976, "Shear Transfer in Lightweight Reinfored Conrete," PCI Journal, Vol. 21, No. 1, January/February, pp Meyer, K. F., 2002, "Transfer and Development Length of 0.6-inh Diameter Prestressing Strand in High Strength Lightweight Conrete," A thesis presented to the Aademi Faulty in partial fulfillment of the requirements for the Degree of Dotor of Philosophy in Civil Engineering, Georgia Institute of Tehnology, May. Mithell, D. W., and Marzouk, H., 2007, "Bond Charateristis of High-Strength Lightweight Conrete," ACI Strutural Journal, Vol. 104, No. 1, January-February, pp Mor, A., 1992, "Steel-Conrete Bond in High-Strength Lightweight Conrete," ACI Materials Journal, Vol. 89, No. 1, January-February, pp Moore, M. E., 1982, "Shear Strength and Deterioration of Short Lightweight Reinfored Conrete Columns under Cyli Deformations," Thesis presented to The University of Texas at Austin in partial fulfillment of the requirements for the Degree of Master of Siene in Engineering. 19

20 Ozyildirim, C. and Gomez, J. P., 2005, "First Bridge Struture with Lightweight Conrete Beams and Dek in Virginia," Final Report No. VTR 06-R12, Virginia Transportation Researh Counil, Deember, 23 pp. Peterman, R. J., Ramirez, J. A., and Olek, J., 1999, "Evaluation of Strand Transfer and Development Lengths in Pretensioned Girders with Semi-Lightweight Conrete," Final Report, Report No. FHWA/IN/JTRP-99/3, Purdue University, August, 183 pp. Peterman, R. J., Ramirez, J. A., and Olek, J., 2000, "Influene of Flexure Shear Craking on Strand Development Length in Prestressed Conrete Members," PCI Journal, Vol. 45, No. 5, September/Otober, pp Peterson, P. H., 1948, "Properties of Some Lightweight Aggregate Conretes with and without an Air-Entraining Admixture," Building Materials and Strutures Report, BMS112, U.S. Department of Commere, National Bureau of Standards, August, 7 pp. Pfeifer, D. W., 1967, "Sand Replaement in Strutural Lightweight Conrete," ACI Journal, Proeedings, Vol. 64, No. 7, July, pp Pfeifer, D. W., 1968, "Sand Replaement in Strutural Lightweight Conrete Creep and Shrinkage Studies," ACI Journal, Proeedings, Vol. 65, No. 2, February, pp Pfeifer D. W., 1969, "Reinfored Lightweight Conrete Columns," Journal of the Strutural Division, ASCE, Vol. 95, No. ST1, January, pp Ramirez, J., Olek, J., Rolle, E., and Malone, B., 2000, "Performane of Bridge Deks and Girders with Lightweight Aggregate Conrete," Final Report, No. FHWA/IN/JTRP-98/17, Purdue University, 616 pp. Ramirez, J. A., Olek, J., and Malone, B. J., 2004, "Shear Strength of Lightweight Reinfored Conrete Beams," High-Performane Strutural Lightweight Conrete, Publiation SP-218, Amerian Conrete Institute, Farmington Hills, MI, pp Rizkalla, S., Mirmiran, A., Zia, P., Russell, H., and Mast, R., "Appliation of the LRFD Bridge Design Speifiations to High-Strength Strutural Conrete: Flexure and Compression Provisions," Transportation Researh Board, NCHRP Report 595, Washington, D.C., 2007, 28 pp. Robins, P. J. and Standish I. G., 1982, "Effets of Lateral Pressure on Bond of Reinforing Bars in Conrete," Bond in Conrete Proeedings of the International Conferene on Bond in Conrete, Paisley, Applied Siene Publishers, London, pp Russell, H. G., 2007, "Synthesis of Researh and Provisions Regarding the Use of Lightweight Conrete in Highway Bridges," FHWA, Offie of Infrastruture Researh and Development, Report No. FHWA-HRT , August, 114 pp. NTIS Aession No. PB Rogers, G. L., 1957, "On the Creep and Shrinkage Charateristis of Solite Conretes," Proeedings, World Conferene on Prestressed Conrete, July, San Franiso, CA. Salandra, M. A. and Ahmad, S. H., 1989, "Shear Capaity of Reinfored Lightweight High- Strength Conrete Beams," ACI Strutural Journal, Vol. 86, No. 6, November-Deember, pp

21 Shideler, J. J., 1957, "Lightweight-Aggregate Conrete for Strutural Use," ACI Journal, Proeedings, Vol. 54, No. 10, Otober, pp Sylva III, G. S., Breen, J. E., and Burns, N. H., 2002, "Feasibility of Utilizing High- Performane Lightweight Conrete in Pretensioned Bridge Girders and Panels," Report No. FHWA/TX-03/1852-2, Center for Transportation Researh, The University of Texas at Austin, 74 pp. Tabatabai, H. and Dikson, T. J., 1993, "The History of the Pretensioning Strand Development Length Equation," PCI Journal, Vol. 38, No. 6, November/Deember, pp Tadros, M. K., Al-Omaishi, N., Seguirant, S. J., and Gallt, J. G., 2003, "Prestress Losses in Pretensioned High-Strength Conrete Bridge Girders," NCHRP Report 496, Transportation Researh Board, Washington DC, 64 pp. Tasillo, C. L., Neeley, B. D., and Bombih, A. A., 2004, "Lightweight Conrete Makes a Dam Float," High-Performane Strutural Lightweight Conrete, Publiation SP-218, Amerian Conrete Institute, Farmington Hills, MI, pp Thather, D. B., Heffington, J. A., Kolozs, R. T., Sylva III, G. S., Breen, J. E., and Burns, N. H., 2002, "Strutural Lightweight Conrete Prestressed Girders and Panels," Report No. FHWA/TX-02/1852-1, Center for Transportation Researh, The University of Texas at Austin, 208 pp. Vinent, E. C., Townsend, B. D., Weyers, R. E., and Via, Jr., C. E., 2004, "Creep of High- Strength Normal and Lightweight Conrete," Final Contrat Report No. VTRC 04-CR8, Virginia Transportation Researh Counil, May. 21