ACI STRUCTURAL JOURNAL. '.. TECHNI.CAL PAPER.

Bond and Shear Behavior of Concrete Beams ContainingLightweight Synthetic Particlesby Matthew J. Heiser, Amr Hosny, Sami H. Rizkalla, and Paul Zia

This paper summarizes a comprehensive experimental programthat investigated the bond and shear behavior of concrete beamscontaining lightweight synthetic particles (LSP). LSP is a newconcrete additive that, when used, leads to reduced unit weight ofconcrete, enhances fiowability of the fresh concrete for pumpingpurposes, and produces durable concrete for freezing and thawingand deicing exposed conditions. It also reduces the thermalconductivity (increases R-value), thus reducing the energy requiredfor heating and cooling. The use of these specially formulatedparticles, in combination with normalweight aggregates, couldreduce the unit weigl:tl.9f concrete by IO to 20%, ranging from120 to /30 lblf~ (/920 to 2080 kg/m3), depending on the amountof LSP used in the concrete mixture. The experimental programincluded 27 large-scale specimens. Researchfindings indicate thatthe bond and shear behavior of beams with LSP additive is similarto the behavior of beams made with normalweight concrete. Testresults confirm that ACI 318-08 can be usedfor the design of LSPconcrete members for shear and the development length of steelreinforcement without the use of the reduction factor A requiredfor lightweight concrete.

Keywords: additive; beams; lightweight synthetic particles; reduced unitweight concrete; shear.

INTRODUCTIONACI 318-081 defines normalweight concrete as concrete

containing aggregates that conform to ASTM C33/C33M-082 with a unit weight between 135 and 160 Ib/ft3 (2160 and2560 kg/m3). ACI 318-081 also defines lightweight concrete asconcrete containing only lightweight aggregates conformingto ASTM C330-053 with a unit weight between 90 and115 Ib/ft3 (1440 and 1840 kg/m3). Lightweight syntheticparticles4 (LSP) are polymer spheres with a closed cellinner structure containing air. They are inert and hydro-phobic. They have a maximum sphere diameter of 0.25 in.(6.4 mm) and a specific gravity of 0.042. They are speciallyformulated for use with concrete with the ability to disperseuniformly in the concrete, resulting in a reduced concretedensity. In general, they are added to concrete as a partialreplacement for conventional fine or coarse aggregate. Thesespecially formulated particles are considered as an additivebecause they do not conform to either ASTM C33/C33M-08.or ASTM C330-05. Therefore, concrete made with normal-weight aggregates and LSP as an additive to reduce theunit weight is regarded as a normalweight concrete with"reduced" density.

This study summarizes the findings of an extensiveresearch program conducted to examine compliance withACI 318-08 for the bond and shear behavior of concretemembers containing LSP. A parallel st~dy by the authorsS toevaluate the material characteristics ofLSP concrete indicatesthat, for a given mixture design, as the amount of LSP isincreased in the concrete mixture to reduce the concretedensity, the compressive strength of concrete is reduced.

For example, when the concrete density was reducedfrom 145 Ib/ft3 (2320 kg/m3) without LSP to 130 Ib/ft3(2080 kg/m3) with LSP, the compressive strength of concretewas reduced by 30% from the original compressive strengthof 5740 psi (39.6 MPa). When the concrete density wasfurther reduced to 120 lb/ft3 (1920 kg/m3), the compressivestrength was reduced by 50%. In all cases, the tensile strengthand the modulus of elasticity of the LSP concrete correlatedwell with the predictions by the ACI 318-08 equations usingthe corresponding compressive strength and density. Itshould be noted that by adjusting the basic mixture design,one could achieve the desired structural strength after LSP isadded. The product is being used commercially for structuralconcrete ranging from 105 to 130 lb/ft3 (1680 to 2080 kg/m3)

unit weight with 28-day compressive strengths rangingfrom 3000 to 6000 psi (20 to 40 MPa).

The experimental program presented in this studyconsisted of 27 large-scale specimens, tested under staticloading up to failure. Research findings indicate that thedesign of concrete members containing LSP for bond andshear can use the provisions of ACI 318-08 for normal weightconcrete; and the modification factor A in the code, normallyassociated with lightweight concrete, is not applicable in thiscase for concrete with LSP additive.

The first phase of this study investigated the bond behaviorof 18 large-scale specimens consisting of both slabs andbeams. The second phase investigated the shear behavior ofnine large-scale beams--each end of a beam being testedto replicate the results-thus providing a total of 18 testedspecimens. The test results showed that the structuralbehavior of concrete containing LSP additive with a unitweight between 120 and 130 Ib/ft3 (1920 and 2080 kg/m3) wassimilar to that of normal weight concrete.

RESEARCH SIGNIFICANCEReduced unit weight concrete using LSP additive has

several structural and economical advantages in comparisonto normal- and lightweight concrete. The addition of LSP toa concrete mixture has been shown to reduce the pumpingpressures of fresh concrete; improve the thermal resistance,and reduce the unit weight for the hardened concrete. Theresearch presented in this paper provides the data anddemonstrates that, when the concrete unit weight is 120 lb/ft3(1920 kg/m3) or greater, the ACI 318-08 code provisionscan be used for the design of structural concrete members

ACI Structural Journal, V. J08, No.6, November·December 2011.MS No. S-2010-163.RI received September 23, 2010, and reviewed under Institute

publication policies. Copyright © 2011, American Concrete Institute. All rightsreserved, including the making of COpIeS unless penrusslOn IS obtamed from thecopyright proprietors. Pertinent discussion including author's closure, If any, WIll bepublished in the September-October 2012 ACI Structural Journal If the d,SCUSSIOnISreceived by May 1,2012.

D.&1at1member Matthew J. Heiser is a Structural Engineer at GE-Hitachi Nuclear• .l ergy. Wilmington, Ne. He received his BSCE In 2008 and hIs MSCE In 2010 from

rth Carolina State University, Raleigh, Ne.

':1member Amr Hosny is a Structural Engineer at BergerABAM Inc., Houston, TX., received his PhD in 20/0 from North Carolina State University.

Itaining Inti H. Rizkalla, FACI, is a Distinguished Professor of Civil and Construction19ineering in the Depanment a/Civil, Construction, and Environmental EngineeringNorth Carolina State University, where he also serves as the Director of the

mstructed Facilities Laboratory and NSF IIUCRC in Repair of Structures and'idges with Composite (RB'C).

~I Honorary Member Paul Zia is a Distinguished University Professor Emeritus atJrth Carolina State University. He served as ACl President in 1989 and is a member

nsity was redu several ACI committees, including ACI Commillee 363, High-Strellgth Conerete;: LSP to 130 Ib/int ACl-ASCE Commillees 423, Prestressed Conerete, and 445, Shear and TOrsion;

h f l Conerete Research Council; and the TAC Technology Transfer Commillee asstrengt .0 cOnCr~airof lTG-6.:ompressIve strenFJ.g _mcrete density \\(13), the compresSbntaining LSP additive and normal weight aggregates" the tensile stren~thout using the modification factor A associated with the) concrete correlabrmallightweight aggregate.~-08 equations usil~th and density. EXPERIMENTAL INVESTIGATIONasic mixture desi[ The overall experimental program consisted of 27 1arge-strength after LSF,ale reinforced concrete specimens tested under static~rcially for Structu!ading up to failure. The first phase of the program1680 to 2080 kg/I1cluded 12 beams and six slabs tested to evaluate the~ strengths rangi)nd characteristics of the LSP concrete. The second phase

cluded nine beams to evaluate the shear behavior of thelted in this stumcrete, with each beam being tested once at each end to, te~te~ under sta:plicate the test results. The steel reinforce~ent used hadgs mdlcate that tspecified minimum yield strength of 60 kSI (415 MPa),g LSP for bond a;cording to ASTM A615/A615M-09b6 specifications.·08 for normalwein the code, normahase 1: Bond behavior of LSP concrete membersnot applicable in tIThe bond behavior of concrete members with LSP additive

as evaluated using 12beams and six slabs. The beam specimensed the bond behavbre divided into three main groups using two targeted unitg of both slab~ "eights: 120 Ib/ft3 (1920 kg/m3) for Group 1 and 130 Ib/ft3he shear b~havlOr;080 kg/m3) for Group 2. The slab specimens had a targeteda beam bemg testit weight of 130 Ib/ft3 (2080 kg/m3) and were classified as~a total of 18 tesfoup 3. The targeted concrete compressive strength for th~

that the structl]ecimens within Group 1 was 2500 psi (20 MPa) and 4000 pSIadditive with a ~and 2080 kg/m3) ,

e. I;ANCEg LSP additiveItages in comparisIe addition of LSPreduce the pumpi.e thermal resistanl'dened concrete. 1lvides the data ait weight is 120 Ib:-08 code provisia1 concrete memb

(30 MPa) for the specimens in Groups 2 and 3, All tested beamshad cross-sectional dimensions of 12 x 18 in. (305 x 457 mm)and a total length of 16 ft (4877 mm), as shown in Fig. 1.All tested slabs had cross-sectional dimensions of 18 x 8 in.(457 x 203 mm) with a total length of 16 ft (4877 mm). Withineach group, the tension splice length of the reinforcementwas designed according to ACI 318-08 based on the targetedconcrete strengths of 2500 or 4000 psi (20 or 30 MPa). Thespecimens were constructed using splice lengths equal to0.75Ld, 1.0Ld, and 1.25Ld, where Ld is the splice lengthdetermined by ACI 318-08 requirements. For the beams, allthe transverse reinforcement consisted of No. 3 (No, 10) closedstirrups designed according to ACI 318-08 requirements, withan extension of six times the bar diameter past the 90-degreebend. Two specimens were fabricated and tested for each of theselected splice lengths for the repeatability of the test results.

The bond specimens given in Table 1 are identifiedusing three parameters: the first letter "B" stands for bondspecimens; the following number identifies the targeted unitweight of concrete in pounds per cubic feet (120 or 130).The second number identifies the specimen within eachgroup and ranges from 1 to 3. The letter "R" indicates thereplicate specimens, The letter "s" was used to designate theslab specimens.

The test setup and cross-sectional dimensions for thebeams and slabs are shown in Fig. 1. All beams and slabswere tested using a four-point bending setup to developa constant moment region at the location of the splicedbars. The length of the beams and slabs was kept constantat 16 ft (4877 mm). The test setup allowed a constantmoment region of 6 ft (1829 mm) with two outer shear spansof 4.5 ft (1372 mm) each. The beams were supported at bothends using composite steel sections restrained to the floor.A 150 kips (670 kN) load cell was placed at one end of thebeams to measure the reaction at the support, whereas theloads were applied using four hydraulic jacks-two at eachlocation-with a capacity of 120 kips (535 kN) each. Verticaldeflections were measured using string potentiometerslocated at the midspan of the test specimen,

The ready mixed concrete supplied by a local concreteproducer consisted of Type I cement, Class F fly ash,ASTM C33/C33M-08 natural sand, No. 78 granite, LSPconcrete additive,4 and standard high-range water reducer

192"(4877mm) I"" -54" (1372mm) -, --72" (1829mm)- --r--S4" (1372mm)----, I l12" (30sm~r=.15" (38mm),1 ' , ...l..: L ,-,'l Splice Length If 1 s· (38mml~ '" 1~--- r!!- I; (rto 29).:....- I tA::L ~ II I lB"(47mm)

JJIIJJJJ4IIJIOIOIIUJIITIIillI 11!.(Jo·f9lJ J"6 n••I/; =,=- 4-A =.:If:'; [I ,

1,1 ..fll9'~ l_~_" L.-.r!·1- I 1.s"(3Bmm)~ 5ectionA-A(No. 10@ lS2mm) , : I _... ..1 .. ..••. • .••• '. __ .4_. . __ •.. _ _ .. _.. __ ~ ..• _~

---------192" (4877mm)I--------""

I --54" (1372mm)---,---72"(1829mm)--e--54"(1372mm)-J.II'

i L '1- Splice ,Length IT, ~

---' La .8~ I

1--1B" (4s7mm)~ 1.5" (38mm)~ --.l.s· (3Bmm) I r

IB' (203min)

I-6 '5

(No. 16)

:ember 201 LI, and reviewed under lnst!:;oncrete Institute, All rinission is obtained fromlthor's closure, if any, wil-al Journal if the discussi(

-.J_, __ t[__c.B_:f_' __ 'L

Ratio of Predicted Maximum Yieldfc,psi j", Id,,-eqlfiN'd, ld.pro\·idt!d. ld.prol'ided to failure load, measured Measured-to- Mode of strain, lMaximum measured

BeamID (MPa) ksi (MPa) in. (mrn) in, (mm) ld.reqllired kip (kN) load, kip (kN) predicted load failure in.lin. strain, in.lin.

B-120-1 37.8 (168) 0.94 Splitting 0.003031.0 (787) 0.96

B-120-1-R 31.5 (140) 0,79 Splitting 0,0024

B-120-2 403 (179) 1.00 Flexural 0,00606000 (41.4) 74 (510) 32.3 (818) 41.0 (1041) 1.27 40.1 (178) 0,0026

B-120-2-R J 40.6 (181) 1.01 Flexural 0.0060

B-120-3 39,2 (174) 0.98 Flexural 0.006051.0 (1295) 1.58

B-120-3-R 39.5 (176) 0.99 Flexural 0.0060

B-130-1 31.8 (141) 0.80 Splitting 0.002226.0 (660) 0.77

B-130-1-R 34.8 (155) 0.87 Splitting 0.0023

B-130-2 38.2 (170) 0.96 Splitting 0,00275500 (37,9) 74 (510) 33.8 (859) 33.0 (838) 0.98 39.9 (177) 0,0026

B-130-2-R 38.4 (171) 0,96 Splitting 0,0026

B-130-3 39.8 (177) 1.00 Flexural 0,006041.0 (1041) 1.21

B-130-3-R 40.2 (179) 1.01 Flexural 0,0060

B-130-1-S 5,8 (26) 0,95 Splitting 0,002111.0 (279) 0.93

B-130-1-R-S 6.4 (28) 1.05 Splitting 0,0060

B-130-2-S 7.1 (32) 1.16 Splitting 0.00266000 (41.4) 61 (421) 11.8 (300) 15.0 (381) 1.27 6.1 (27) 0.0021

B-130-2-R-S 6.7 (30) 1.10 Splitting 0,0060

B-130-3-S 7,3 (32) 1.20 Flexural -18.0 (457) 1.52

B-130-3-R-S 7.8 (35) 1.28 Flexural 0,0060

By weight 130 (2082) 0.4 677 (402)Note: em is cementitious materials.

Specimens cast

Bond beamsTarget unit weight = 120 Ib/ft3 (1920 kg/m3)

Bond beamsTarget unit weight = 130 Ib/ft3 (2080 kg/m3)

Bond slabsTarget unit weight = 130 Ib/ft3 (2080 kg/m3)

Shear beamsTarget unit weight = 120 Ib/ft3(1920 kg/m3)

Shearbeams __ .Target unit weight = 130 Ib/ft3 (2080 kg/m3)

(HRWR). The compressive strength of the concrete wasdetermined by using 4 x 8 in. 002 x 204 mm) cylinderscured in the same environment as the test specimens, Table 2provides the mixture design of the two concrete mixtures,

Test resultsMaterial properties-Table 3 summarizes the measured

compressive strength of the concrete at 28 days and onthe day of testing for both the bond and shear studies, Itshould be noted that the concrete produced for the first cast

Compressive strength, psi (MPa)

Target Ie' Ie Day of Testing

2500 (20.0) 5660 (39.0) 6000 (41.4)

4000 (30,0) 5000 (34,S) 5500 (37.9)

4000 (30,0) 5470 (37.7) 6000 (41.4)

2500 (20.0) 3620 (25.0) 4120 (28.4)

4000 (30;0) . -5930 (40,9) 6890 (47,5)

according to the given mixture design resulted in both ahigher unit weight and highercompressive strength than thetargeted values. It is believed that the moisture content of thesand measured at the ready mixed concrete plant was higherthan the actual moisture content, making the total water lessthan designed, which led to a lower water-cement ratio (wlc)and, consequently, a higher concrete compressive strength.

Tension coupons from the Grade 60 steel reinforcementwere tested according to ASTM A370-097 to determine thematerial characteristics, The typical coupon length was 2 ft

(610 mm), taken from the same batches of the longitudinalreinforcement used in the beams. The No.9 (No. 29) bars usedas the longitudinal reinforcement and the No.3 (No. 16) barsused as the transverse reinforcement of the bond specimenshad yield strengths of 74 and 69 ksi (510 and 476 MPa),respectively. The yield strength of the No.5 (No. 16) barsused as the longitudinal reinforcement in the slabs for thebond tests was 61 ksi (421 MPa).

Load-deflection behavior-The load-deflection relationshipof the tested beams in the second group is shown in Fig. 2.The test results indicate that the beams with a splice lengthshorter than the required splice length failed before achievingtheir full design capacity. When the full splice length wasprovided, the beams were able to achieve their designcapacity but failed due to splitting without providing muchductility. When the provided splice length exceeded therequired splice length up to 1.58Ld, the beams achieved theflexural strength and a sufficient level of ductility. Similarbehavior was observed for the beams tested in Group 1 andthe slabs in Group 3.

Crack width-Crack width was measured by using PI-shaped mechanical gauges (hereafter called PI gauge)located at the ends of the splice and at the midspan of thespecimens. A crack comparator was also used to measurethe crack width at different load levels. It was observed thatin all cases, the first flexural cracks developed at the twoends of the splice zone-at the maximum moment and shearlocations. As the load was increased, the flexural crackspropagated toward the compression zone and increased innumber and width. A further increase in the applied load ledto the formation of splitting cracks parallel to the longitudinalbars (initially on the tension surface of the beam), followedby splitting cracks on the side of the beam. Measurementusing the crack comparator was discontinued after theyielding of the longitudinal reinforcement; however, PI gaugemeasurements showed that with adequate developmentlength according to ACI 318-08, the yield strength of thelongitudinal bar was fully developed and the beam achievedconsiderable ductility. Figure 3 shows the width of thesplitting crack and the applied loads for the first group ofbeams reinforced with No.9 (No. 29) bars. The test resultsindicate that the splitting cracks occurred at the same rangeof load level for all tested beams of the same group. Theinitiation of the splitting cracks occurs when the stresses inthe spliced bars induce forces in the concrete cover equal tothe tensile strength of the concrete. The figure also showsthat as the load was increased, the widths of the splittingcracks were larger for the shorter splice lengths. This wasdue to the higher stresses induced in the longitudinal barswith shorter splices in comparison to the bars with longersplice length at the same load--levels·. This in turn inducedhigher strains in the steel and the surrounding concrete,causing wider cracks.

Splice strength-Two different modes of failure wereobserved for the bond specimens. The first mode wassplitting failure, characterized by the formation andpropagation of splitting cracks parallel to the longitudinalbars along the splice length, as shown in Fig. 4. Such failureis generally sudden and brittle. The second mode of failurewas typical flexural failure initiated by the yielding of thereinforcement, followed by the final crushing of the concretein the compression zone. A summary of the test results forPhase I of the experimental program is presented in Table 1.

0.0

45

40

35

30

~ 2S~"~ 20

15

10

Deflection (mm)

38.1 76.2

200

178

156

133

111 ~

"89 ~.967

44

22

0

3.01.5Deflection (in)

111 ~

-g

89 ~

]:67 '"

The test results presented in Table 1 indicate that whenthe provided development length was equal to or morethan that required by ACI 318-08 using the measuredmaterial properties, the specimens were able to achieve theirrespective nominal flexural capacity after the yielding ofthe longitudinal reinforcement, as indicated by the strainmeasurements. When the provided development lengthwas less than the required value, the specimens showed

Ve Vs Vn

fe, Measured Measured MeasuredMaximum measured psi Measured, Predicted, versus Measured, Predicted, versus Predicted. versus

Beam shear, kip (kN) (MPa) kip (kN) kip (kN) predicted kip (kN) kip (kN) predicted kip (kN) oredicted

S-120-0% 35 (156) 36 0.97- - - (160)S-120-0%-R 43 (191) 1.18

Group S-120-0.25% 93 (414) 4150 39 36 54 (240) 31 1.73 67 1.381.08

1 S-120-0.25%-R 83 (369) (28.6) (173) (160) 44 (196) (138) 1.42 (298) 1.24

S-120-5% 126 (560) 87 (387) 62 1.39 99 1.28

S-120-0.5%-R 124 (552) 85 (378) (276) 1.36 (440) 1.26aid

= 3.0 S-130-0% 41 (182) 42 0.97- - - (187)S-130-0%-R 38 (169) 0.92

Group S-130-0.25% 97 (431) 6750 40 42 57 (254) 31 1.82 73 1.320.95

2 S-130-0.25%-R 104 (463) (46.5) (178) (187) 64 (285) (138) 2.05 (325) 1.42

S-130-0.5% 130 (578) 90 (400) 62 1.43 104 1.24

S-130-0.5%-R 132 (587) 92 (409) (276) 1.47 (463) 1.26

S-130-0%-1.5 153 (681)_ -- 42 3.61.. . .... .- .. - - - (187)S-130-0%-1.5-R 206 (916) 4.87

aid Group S-130-0.25%-1.5 194 (863) 6970 56 42 138 (614) 31 4.40 74 2.631.32= 1.5 3 S-130-0.25%-1.5-R 159 (707) (48.1) (249) (187) 103 (458) (138) 3.29 (329) 2.16

S-130-0.5%-1.5 214 (952) 158 (703) 62 2.53 105 2.04

S-130-0.5%-1.5-R 215 (956) 159 (707) (276) 2.54 (467) 2.05

tested in shear. Each beam specimen was identified by fourparameters: the first letter "S" stands for shear specimens;the following number identifies the targeted unit weight inpounds per cubic foot (120 or 130); and the third parameterdefines the transverse reinforcement ratio (0%, 0.25%, and0.5%) for the beams without transverse reinforcement, withminimum and maximum stirrups, respectively. The number"IS' following the transverse reinforcement ratio refers tothe aid of 1.5, which is different from the beams tested withan aid of 3.0 in the first two groups.

The test setup and cross-sectional dimensions for all sheartests are shown in Fig. 5. Two test setups were used--onefor each of the selected ald. The test setup was designed to

Phase II: Shear behavior of LSP concrete members allow each end of a beam to be tested so that the test could beThe shear behavior of reinforced concrete beams replicated. The first setup was used to test the first and second

containing LSP was evaluated using nine beams--each groups of beams with an aid of 3.0 by locating the appliedtested twice-for a total of 18 tests. The specimens were point load at a distance "a" of 43 in. (1092 mm) from thedivided into three main groups with two targeted unit left support, as -shown in Fig. 5. The second setup was usedweights of 120 and 130 Ib/ft3 (1920 and 2080 kg/m3). Similar to test the third group of beams with an aid of 1.5 and theto the bond investigation, target compressive strengths single applied load at a distance "a" of 22 in. (559 mm) fromof 2500 and 4000 psi (20 and 30MPa).weresele.ctedfQf. 1b~Jeftsupp()rt,.as sh0.'V'.l..~nFig ..5. The untested portion ofthe 120 and 130 Ib/ft3 (1920 and 2080 kg/m3) groups, each beam was cantilevered over the right support. Load wasrespectively. Two additional parameters considered in the applied by using a 440 kips (1960 kN) capacity hydraulicexperimental program were the shear span-depth ratio (aid) actuator supported by a steel frame that was securelyand the transverse reinforcement ratio Pt. The beams were anchored to the laboratory strong floor. The load provideddesigned according to ACI 318-08 provisions for shear and by the actuator was transferred by a single steel loading plateflexure, and the design ensured a shear-controlled failure that measured 1 in. (25 mm) thick by 8 in. (203 nun) wide.mode. Some of the beams were designed without transverse The beams were simply supported by a steel pin and a 1 in.reinforcement to evaluate the concrete contribution to (25 mm) thick bearing plate at the left end support and ashear strength, Ve, whereas others were designed with steel roller and a 1 in. (25 mm) thick bearing plate at the rightminimum and maximum allowable transverse reinforcement support. For each test setup, two 200 kips (890 kN) capacityratios as specified by ACI 318-08 to cover the two levels load cells were placed under the left support to measureof shear capacities. Table 4 provides details of the beams the reaction, which represented the maximum shear forces

bond failures with slightly less capacity in comparison tothe predicted nominal flexural strengths. The test resultsclearly confirm compliance of the LSP concrete to theACI 318-08 provisions for the development length of theflexural reinforcement. It should be noted that an increasein the splice length does not necessarily increase the load-carrying capacity of the beam due to the nonlinear stressdistribution along the splice lengthS and increase only theductility, as shown in Fig. 2. For example, in Table 3, althoughthe development length increased from 33 in. (838 mm) forBeam B-130-2-R to 41 in. (1041 mm) for Beam B-130-3-R,the load-carrying capacity increased by only 4%.

-10"-~-- a------- -----x----------y--(254mm)

______________pL- ~

.Id •5etIlp1~ 3.0 192" (~~mm) _~r 0092~) 86" (211Kmm) S3" (1316nwn)

Set\lp2 l.5 1Cl8"(2143mm)2l"{SS9mm)44"{1118mrn) 32" (813mm)--"'-A-~--- _:..L-_______ -~--- ·4·;~i(NO.32I_ -1.5" (38mm)

619 18" (457mm).(NO.29).

!!.. ~~J

''1,-.:..:... ~~-- ::.~ -·-:-:--.;..:.:rr·:,,:::;~-r--:,::::~::-::-~--=::-:-;-~--=-::--::;::::--~.. ;~:~-:.~ -

- ---_c--- -_::_--~._~~~--- __,,~=,_-=,!-~--~;:.l-;~-l~'_=~:,:~~",=~;o:.--. ~~--r;-o-- - ••.A --== ••.. ~.,.-.-:-----

#3 (No.10)/1.5" (38mm)'~ionA-A

within the short shear span under consideration. One linearvariable differential transducer (LVDT) was used at the topsurface of the beam at both supports to measure any possibledeflection at the support. Vertical beam deflections weremeasured by two string potentiometers placed directly underthe beam at the location of the actuator and 1.5 in. (38 mm)from the edge. The crack widths and strains in selectedstirrups were measured by using PI gauges and weldablestrain gauges, respectively. PI gauges were arranged in arosette configuration to capture most of the cracks within theshear span region. For the test specimens in Groups 1 and 2,three PI gauge rosettes were arranged diagonally betweenthe applied load and the left support reaction, as shown inFig. 6(a), whereas only two PI gauge rosettes were usedfor the shorter beams of Group 3. On the opposite face ofthe test specimen, PI gauges were arranged vertically atthe location of the selected stirrup located within the shearspan region, as shown in Fig. 6(b). The stirrup strains weremeasured using weldable strain gauges placed on someselected stirrups within each beam.

The same concrete mixture designs given in Table 2 wereused for the shear-speCimens: .Table' 3' aiso summanzes -the-measured concrete compressive strength at 28 days and atthe day of testing for the shear specimens. Tension couponsfor the Grade 60 reinforcing steel were tested according toASTM A370-09 using 2 ft (610 mm) coupons that were takenfrom the same batches of the transverse reinforcement usedin the beams and had a yield strength of 69 ksi (476 MPa).

Test resultsLoad-deflection behavior-The load-deflection behavior

of beams with LSP concrete was similar to that of beamsof normalweight concrete reported in the literature.9 Thebeams without transverse reinforcement failed shortly after

Oeflection(mm)

0.0 2.5 5.1 7.6 10.2 12.7 15.2 17.8 20.3 22.9 25.4

240 1,068

~ 160

~~~ 120

~~~ 80

1 $-130-max sup}_.I<'

o 0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Deflection (in)

Fig. 7~Shear load-deflection behavior for Group 2shear be~ms.

the initiation of the first diagonal cracks. Test beams withtrans-verse reinforcernent Were able to' sustain higher loadlevels, as shown in Fig. 7, for the beams of Group 2. Theload at the formation of the first critical diagonal crack formembers without shear reinforcement was taken as theconcrete contribution to shear resistance Vc for all beamswithin the same group. It can be observed from Fig. 7 thatby increasing the transverse reinforcement ratio from 0.25 to0.5%, the shear resistance of the beams was increased. Theshear at failure for the specimens with shear reinforcementwas taken as the nominal shear strength VII' The steelcontribution to the shear strength Vs was simply determinedas the difference of (VII - VcJ, The load-deflection behaviorof the beams in Group 3 is shown in Fig. 8. From this curve,

Deflection (mm)

0.0 2.5 5.1 7.6 10.2 12.7 15.2 17.8 20.3 22.9 25.4

240 .' 1,068

200 890

V> 160 712ZQ.

;R ~~ ~.2 120 534 .2~ ~~~ .c;;; 80 356 '"

40 178

Shear due to self load0 0

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

Deflection (in)

Fig. 8-Shear load-deflection behavior for Group 3shear beams.

Splitting Crackwidth (mm)

0.00 0.25 0.51 0.76 1.02 1.27 1.52 1.78

140 623

120 . 534

100 . - 445

0: Z;R 80 356 ~~ "-c -c!60 - 267 i« «

40 178

20 89

0

0.000 0.010 0.020 0.030 0.040 0.050 0.060 0.070Splitting Crack width (in)

it can be observed that the behavior of the specimens withinGroup 3 is quite different from those within Groups land 2,as shown in Fig. 7. This is due primarily to the small aid ofthis category of beams and the formation of a compressionstrut mechanism in resisting the applied shear. This archingaction mechanism is the cause of the significant increase in

the shear capacity of the beams within Group 3, especiallyfor those without transverse reinforcement.

Cracking behavior-Cracking on the side of the beamwas measured using PI gauge rosettes within the shear span,a, whereas cracking on the opposite side of the beam wasmeasured using the vertical PI gauges, as shown in Fig. 6.Crack width comparators were also used to measure thecrack width at different load levels. It was observed that theinitiation of the first flexural cracks occurred at the locationof the maximum bending moment directly under the appliedload. Flexural cracks propagated upwards and increased innumber and width as the load was increased.

The formation of shear cracks was dependent on thepresence of shear reinforcement and ald. For beams withshear reinforcement and an aid of 3.0, the first shear cracksappeared as an extension of the flexural shear cracks in thediagonal direction. When the applied load was increased,new diagonal shear cracks formed and were observedon both sides of the tested beam. In this study, failure ofthe beams was determined when the beam was no longerable to sustain any increase in the applied load. For thebeams without transverse reinforcement, once the firstshear crack appeared, it propagated diagonally throughthe shear span and suddenly increased in width by aslight increase in applied load before failure. For beamswith shear reinforcement, once the first diagonal tensioncrack occurred, measurements of the strain in the stirrups,using the weldable strain gauges, clearly indicated theparticipation of the stirrups in resisting the applied load. Thepresence of the stirrups controlled the increase in the widthof the diagonal tension crack, which led to the formationof multiple diagonal cracks within the shear span. Thecracking behavior for specimens with no stirrups, minimumstirrups, and maximum stirrups is shown in Fig. 9. Thefigure clearly indicates a single diagonal crack, spanningfrom the location of the applied load to the support for thebeams without stirrups and multiple diagonal cracks for thebeams with stirrups. Figure 10 shows the measured width ofthe diagonal shear crack using the crack comparators for thesecond group of beams with an aid of3.0. It should be notedthat the graph does not include the beams without transversereinforcement, as these beams failed suddenly after theinitiation of the diagonal crack. The graph also shows theeffect of the transverse reinforcement ratio in controllingthe crack width. It can be seen that for the same load level,the beams with the minimum transverse reinforcement ratiohad a wider crack width compared to the beams with themaximum transverse reinforcement ratio. An increase ofthe crack width is expected due to the high stresses inducedin the stirrups of the beams with the minimum transversereinforcement ratio in comparison to the beams with thehigher transverse reinforce'merit ratio at any given load. The .higher stress levels correspond to higher strains in the stirrupsand thus wider cracks in the concrete.

Failure mode-The failure mode of each group of test beamswas highly dependent on theal d. For Groups land 2 (specimenswith an aid of 3.0), the failure mode was also affected by theamount of transverse reinforcement used. For beams withouttransverse reinforcement, the failure mechanism occurred asa single shear crack that extended from the support to thelocation of the applied load. The typical failure observed forbeams with shear reinforcement was due to crushing of theconcrete at the nodal region of the diagonal compression strut

well after the formation of many diagonal cracks within theshear span.

The behavior of Group 3 specimens with an aid of1.5 was controlled, as expected, by stirrup spacing within themember. For the beams without transverse reinforcement,failure occurred at much higher-than-anticipated loadsdue to arching action within the short span. For the beamswith the minimum amount of transverse reinforcement,although arching action controlled the short shear span,flexural shear failure was observed in the longer shearspan at the uninstrumented side of the beam when theload-carrying capacity of that side was reached. When thetransverse reinforcement ratio was increased, the load-carrying capacity of the longer shear span was increasedand failure was due to arching action within the shortshear span of the beam. The measured ultimate loads aresignificantly higher than the predicted values according tothe ACI 318-08 design equations. When the strut-and-tiemethod is used as recommended by ACI 318-08 for low aid,however, the behavior is accurately predicted.

The results from the 18 shear tests are summarizedin Table 4, which shows the maximum measured shearforce in comparison to the ACI 318-08 predicted values.Because the beams were designed to have a shear failure,the longitudinal reinforcement was increased to avoidpremature flexural failure. To account for the increase ofthe flexural reinforcement, the concrete contribution to theshear strength, Vc, was predicted by using the followingACI 318-08 Eq. (11-5), which accounts for the effect of thelongitudinal reinforcement ratio pw.

where A is a reduction factor used with the lightweightconcrete and was assumed unity for the LSP concrete; Vu andMu are the ultimate shear force and moment, respectively, atthe section considered; bw is the width of the member; and d isthe depth from the centroid of the longitudinal reinforcementto the extreme compression fiber. For the beams with an aidof 3.0, Table 4 shows a very close correlation between themeasured and predicted shear force for the case withouttransverse reinforcement. With transverse reinforcement,the average measured-to-predicted ratio becomes 1.20 witha coefficient of variation of 0.14, which shows that theACI 318-08 provisions for shear can be safely used for thedesign of structural members with LSP additive. For thebeams with an aid of 1.5, the measured-to-predicted shearstrength according to ACI 318-08 was significantly higherdue to the arching action mechanism developed for thiscategory of beams.

CONCLUSIONS AND RECOMMENDATIONSBased on the test results of the experimental program and

the comparisons to the ACI 318-08 provisions for shear anddevelopment of reinforcement, the following conclusionsmay be drawn:

1. The concrete containing LSP additive used in thisstudy, with unit weights ranging between 120 and 130 Ib/ft3(1920 and 2080 kg/m3), achieved comparable compressivestrength to what is commonly used for structural applications.

2. Concrete containing LSP additive was flowable and hadgood workability.

3. The load-deflection characteristics and the crack patternof the beams and slabs tested in this experimental programwere similar to the expected behavior of beams and slabsusing normal weight concrete.

4. The cracked section analysis used to predict the behaviorof regular concrete could be used to predict the behavior ofconcrete members produced with LSP additive.

5. ACI 318-08 equations could be applied to the design ofthe tension splice required to develop the design strength ofthe reinforcement at a critical section.

6. The analysis of the bond specimens accurately predictedthe behavior of all tested beams. With sufficient splice length,the beams were capable of achieving their load-carryingcapacity. The results confirmed that the bond strength of beamscontaining LSP concrete additive met the bond requirementsspecified by ACI 318-08.

7. The beams with LSP concrete additive satisfy the sheardesign requirements of ACI 318-08.

8. The test results also confirmed that, for the structuraldesign ofLSP concrete containing normalweight aggregates,the reduction factor A normally used for lightweight concretedo not need to be applied for LSP concrete with a unit weightequal to or higher than 120 Ib/ft3 (1920 kg/m3).

Due to the limited number of bond and shear specimensused in this study, it is recommended that additional testsshould be conducted to include a wider range of concretedensities. In addition, whether the use of LSP in a concretemixture will affect the long-term bond and shear behavior ofconcrete members should also be investigated.

ACKNOWLEDGMENTSThe authors would like to thank NOVA Chemicals Inc. for their financial

assistance and for providing the concrete additive for the construction ofthe test specimens. The authors would also like to thank the Argos USAfor supplying the ready mixed concrete used in the research program.Special thanks go to the staff at the Constructed Facilities Laboratory,including J. Atkinson, J. McEntire, G. Lucier, and M. Dawood for theirinvaluable help.

REFERENCESI. ACI Committee 318, "Building Code Requirements for Structural

Concrete (ACI 318-08) and Commentary," American Concrete Institute,Farmington Hills, MI, 2008, 473 pp.

2. ASTM C33/C33M-08, "Standard Specification for ConcreteAggregates," ASTM International, West Conshohocken, PA, 2008, II pp.

3. ASTM C330-05, "Standard Specification for Lightweight Aggregatesfor Structural Concrete," ASTM International, West Conshohocken, PA,2005,4 pp.

4. NOVA Chemicals Inc., "Elemix Concrete Additive," 2008, http;//www.elemix.com/. (last accessed Feb. 19,2010)

5. Hosny, A., "Behavior of Concrete Members Containing LightweightSynthetic Particles," PhD dissertation, North Carolina State University,Raleigh, NC, 2010, 311 pp.

6. ASTM A615/A615M-09b, "Standard Specification for Deformed andPlain Carbon-Steel Bars for Concrete Reinforcement," ASTM International,West Conshohocken, PA, 2009, 6 pp.

7. ASTM A370-09, "Standard Test Methods and Definitions forMechanical Testing of Steel Products," ASTM International, WestConshohocken, PA, 2009,47 pp.

8. Canbay, E., and Frosch, R. J., "Bond Strength of Lap-Spliced Bars,"ACI Structural Journal, V. 102, No.4, July-Aug. 2005, pp. 605-614.

9. Wight, J. K., and MacGregor, J. G., Reinforced Concrete: Mechanicsand Design, fifth edition, Prentice Hall, Upper Saddle River, NJ, 2009,1126 pp.