Computers and Geotechnics 64 (2015) 61–71

Contents lists available at ScienceDirect

Computers and Geotechnics

journal homepage: www.elsevier .com/locate /compgeo

CLSM bridge abutments – Finite element modeling and parametric study

http://dx.doi.org/10.1016/j.compgeo.2014.10.0150266-352X/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: 1000 River Rd., T-MU1-01, Teaneck, NJ 07666, UnitedStates. Tel.: +1 201 692 2122.

E-mail addresses: alizadeh@fdu.edu (V. Alizadeh), helwany@uwm.edu(S. Helwany), algh@uwm.edu (A. Ghorbanpoor), oliva@engr.wisc.edu (M. Oliva),rghaderi@uwm.edu (R. Ghaderi).

Vahid Alizadeh a,⇑, Sam Helwany b, Al Ghorbanpoor b, Michael Oliva c, Roonak Ghaderi b

a Fairleigh Dickinson University, United Statesb University of Wisconsin-Milwaukee, United Statesc University of Wisconsin-Madison, United States

a r t i c l e i n f o

Article history:Received 2 January 2014Received in revised form 31 October 2014Accepted 31 October 2014

Keywords:Bridge abutmentsControlled low strength material (CLSM)Finite elementsParametric studyBearing capacitySimulation

a b s t r a c t

Controlled low strength materials (CLSMs) are increasingly gaining importance in the construction indus-try. Among many applications, CLSMs can be used for rapid and sustainable construction of bridgeabutments. This paper describes the finite element analysis of a full-scale loading test of a bridgeabutment backfilled with the CLSM referred to as ‘‘CLSM bridge abutment’’. The finite element analysiswill help with the understanding of the behavior of CLSM bridge abutments, in terms of bearing capacity,displacements and the developed axial force in anchors. The accuracy of the finite element results for theresponse and failure behavior of a CLSM mass was evaluated by a comparison with the experimentalresults. The experimental program included both standard compressive strength testing on CLSMcylinders and a laboratory full-scale testing on a CLSM bridge abutment. The analysis shows that theperformance of a CLSM abutment while subject to a service load or a limiting failure load from a bridgesuperstructure can be simulated in a reasonably accurate manner.

In addition, a parametric study was conducted to better understand the performance of the CLSMbridge abutments in terms of bearing capacity and overall behavior. This study investigated theperformance of the CLSM bridge abutments as they are affected by material curing age, environmenttemperature and construction details. The results indicated that the CLSM bridge abutment is capableof carrying typical bridge loads with relatively after only one day from the placement. It was observedthat the bearing capacity increased with further curing of the CLSM material.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

In recent years, applications of controlled low strength materi-als (CLSMs) for construction have gained increasing attention.CLSM, also known as flowable fill, is a self-compacting cementi-tious material which is a mixture of aggregate, cement, fly ash,water and possibly chemical admixtures. CLSM is in a flowablestate at the time of placement. After placement, it hardens into amaterial with a higher strength than soil and normally has a spec-ified compressive strength of 8.3 MPa or less at 28 days. It is alsodefined as an excavatable material if the compressive strength is2.1 MPa or less at 28 days [1].

In actual construction, CLSMs have demonstrated a number ofdistinct advantages over conventional earthfill materials and beenused for a wide variety of applications including backfills,

structural fills, pavement bases, highway surface repair, conduitbedding, erosion prevention, void filling, and bridge rehabilitationthat are well documented in the literature [2]. A survey by Trejoet al. [3] indicated that 42 out of 44 state DOTs have specificationsto use CLSM as a construction material.

Successful application of CLSMs for rapid bridge constructionhas recently been reported by the authors through a full-scalelaboratory test [4]. As it is stated, construction duration of bridgesubstructures is one of the major obstacles facing rapid bridgeconstruction and this can be remedied by taking advantage ofthe CLSM properties for construction of bridge abutments. Use ofCLSM bridge abutments is best suited for rapid construction ofsingle-span bridges without intermediate piers. The CLSM bridgeabutment provides a load-bearing support for the bridge sill,eliminating the need for the more expensive pile foundations orspread footings. Since it is a self-compacting material, CLSMreduces the volume of labor intensive compacting operationneeded for the placement of backfills. Heavy machinery is notrequired for excavation, compaction, or pile placement. As such,construction of CLSM bridge abutments requires a shorter timecompared with conventional bridge abutments [4]. In addition to

62 V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71

the speedy construction, the ability to use by-product materials,such as fly ash and foundry sand, in CLSM backfill (thereby reduc-ing the demands on landfills, where these materials might other-wise be deposited) translates into greater economy and thepotential for a more sustainable design.

The CLSM bridge abutment examined here was assumed tohave full-height precast concrete exterior panels that are attachedto CLSM backfill via steel anchors. Fig. 1 shows a typical CLSMbridge abutment with different components including continuousprecast concrete panels, steel rebar anchors, the CLSM backfilland a bridge sill to support all relevant bridge loads.

This paper describes the finite element analysis of a full-scaleloading test of a CLSM bridge abutment. The objective is to estab-lish a rational procedure, via the finite element method, to simu-late the behavior of CLSM bridge abutments with increasingstatic loads up to failure. A plastic-damage model for quasi-brittlematerials which captures the material behavior using both classi-cal theory of elasto-plasticity and continuum damage mechanics,was chosen for this study. To show that the plastic-damage modelis appropriate for the analysis of a CLSM mass, a preliminary three-dimensional finite element model of standard compressivestrength testing on CLSM cylinders was analyzed.

The finite element analysis will help with the understanding ofthe behavior of CLSM bridge abutments, in terms of bearing capac-ity, displacements and the developed axial force in anchors. Thecapability of the finite element approach for the analysis of CLSMbridge abutments was evaluated by a comparison with the exper-imental results from the loading test of a laboratory CLSM bridgeabutment. The validated finite element approach was then usedto conduct a series of parametric studies to explore the effects ofCLSM curing age, environment temperature and constructiondetails on performance of the CLSM bridge abutments in terms ofbearing capacity and overall behavior.

2. Background

In a CLSM bridge abutment, the side-by-side interlocking full-height precast concrete panels serve as formwork that hold thenewly poured CLSM backfill in place until the setting of the backfillmaterial is complete. Since the steel anchors make the CLSM massand the concrete panels behave as one unit after curing, the abut-ment is analyzed as a large gravity wall for sliding and overturningstability.

The construction sequence of a CLSM bridge abutment is simpleand involves the following steps (see Fig. 2):

Step 1: Level the foundation soil and place a precast concreteleveling pad.

Fig. 1. CLSM brid

Step 2: Install interlocking full-height concrete panels withtemporary lateral supports.Step 3: Place the CLSM backfill (the entire abutment can bebackfilled in one continuous pour or in multiple layers bypumping of the CLSM material).Step 4: Install steel anchors (insert through the opening fromoutside). This may be done after the CLSM placement but beforeit is set since the guide holes in the concrete panels will keepthe anchors in a horizontal position.Step 5: Wait for the CLSM to set (one to seven days dependingon the mixture design) then remove the temporary lateralsupports.Step 6: Place the precast concrete bridge sill, place the approachfill behind the sill, and proceed with the construction of thebridge superstructure.

The bridge does not need to have an approach slab, but ratherroad base material can be compacted directly behind the bridge sillto form the approach way and to create a gradual transition fromthe roadway to the bridge. Asphalt pavement can then be placedon the bridge and approach without a conventional joint systemat the bridge ends. The intent is to allow the bridge and the adja-cent road to settle together, providing a smooth, bump-free ridefor drivers traveling on and off the bridge.

It is noteworthy that CLSM has been used by several state DOTsas self-leveling backfill behind conventional pile-supported bridgeabutments to alleviate the approach settlements at the end of thebridge. In the CLSM bridge abutment, however, the CLSM abutmentitself will provide the bearing mechanism for the bridge sill. Thisunique approach has never been attempted previously, but it hasthe potential to profoundly reduce the cost and construction timeof bridge abutments. A study of 177 bridges in Oklahoma com-pared different backfills behind conventional bridge abutments[5], and the results of the CLSM approaches showed very littlemovement prior to placement of the pavement. In addition, a Wis-DOT study [6] found that rideability over approaches with CLSMwas better than approaches with granular backfill. In another studyby ALDOT [7], use of CLSM for culvert-bridge rehabilitation hasdemonstrated important advantages including cost efficiency,expediency in returning traffic flow to normal, and enhanced struc-tural integrity and safety.

3. Experimental testing

Several CLSM mixtures were tested for flow consistency, com-pressive strength, and stress–strain response. A selected numberof suitable CLSM mixtures are proposed in Table 1 [8]. A poten-tial CLSM mixture to backfill a bridge abutment should have ade-

ge abutment.

Fig. 2. Construction sequence of the CLSM bridge abutment.

V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71 63

quate flowability (at least 200 mm according to ASTM D 6103)and relatively high early strength for rapid construction. Basedon ACI 229R [1], typical strength of CLSM as a replacement forcompacted backfill ranges from 0.3 to 0.7 MPa for mostapplications.

An instrumented laboratory bridge abutment with full-heightconcrete panels was constructed and backfilled with the CLSMmixture M3 (Table 1) to evaluate the performance in terms of loadcarrying capacity, deformations, lateral pressures behind the fac-ing panels and strain development in the anchors during loading[4]. The configuration of the CLSM bridge abutment experimentis depicted in Fig. 3. The abutment was 2.7 m � 2.7 m in plan,and 2.74 m in height and consisted of four identically prefabri-cated concrete panels at each side. Each concrete panel wasattached to the CLSM mass with the total of six anchors(12.7 mm diameter steel rebars) in three equally spaced rows(two in each row). As can be seen in Fig. 3, each panel had sixopenings to accommodate the installation of steel rebars. Verticalinterlocking connection (groove and tongue) was used betweenwall panels. The reinforced concrete bridge sill was 2.4 m �0.61 m with thickness of 0.25 m. This configuration was used asa base case for the FE modeling of the CLSM bridge abutmentand the parametric study. The constructed prototype CLSM bridgeabutment is shown in Fig. 4.

Table 1CLSM mixture proportions [8].

Mixture Mixture proportions (kg/m3) Flow (mm) Compressive strength (MPa)

Type I Portland cement Fly ash, Class F Sand Water Plasticizer 1-Day 7-Day 28-Day

M1 79 20 1458 452 – 241 – 0.16 0.38M2 76 497 1338 287 1.6 330 0.19 1.97 4.39M3 50 270 1569 245 – 210 0.16 0.21 0.4M4 58 331 1557 234 1 191 0.30 1.41 2.87M5 95 572 1240 267 1.9 305 0.42 3.68 8.20M6 56 319 1501 263 1.1 267 0.13 1.02 2.14M7 45 258 1516 303 – 356 0.08 0.38 0.85M8 123 31 1215 706 – 140 – 0.24 0.59M9 57 323 1521 266 1 330 0.16 0.94 1.88M10 87 299 1545 251 1 229 0.44 1.92 3.90

Note: 90-day compressive strength of mixture M7 was 1.03 MPa.

Fig. 3. Configuration of the full-scale CLSM bridge abutment [1].

Fig. 4. Full-scale laboratory CLSM bridge abutment.

64 V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71

4. Finite element analysis

4.1. Plastic-damage model and material parameters

In this study, a plastic-damage model proposed by Lubliner etal. [9] and modified by Lee and Fenves [10], available in the FE soft-ware Abaqus for quasi-brittle materials was chosen for the CLSMmass. In the plastic-damage model, stiffness degradation due todamage is embedded in the plasticity part of the model. An inde-pendent scalar (isotropic) damage variable d is used to describethe irreversible damage that occurs during the fracturing process.The initial undamaged state and total loss in strength of the mate-rial are indicated by d = 0 and d = 1, respectively. Any intermediatevalue indicates a partially damaged state. The material parametersrequired for the model are categorized into three types, namely

Fig. 5. Illustration of (a) yield surface an

elasticity, plasticity and damage. In the elastic zone, from theexperimental stress–strain response, Young’s modulus of46.1 MPa and yield stress of 274 kPa were determined and Pois-son’s ratio was assumed to be 0.19. Four parameters, rb0/rc0, Kc,w, and �, are required to define the yield surface and flow potentialfunction of the plasticity part.

The yield surface for this model as proposed by Lubliner et al.[9] is based on modifications of the classical Mohr–Coulomb plas-ticity (Fig. 5a):

F ¼ 11� a

ðq� 3apþ bð~eplÞhr̂maxi � ch�r̂maxiÞ � rcð~eplc Þ

with

a ¼ ðrb0=rc0Þ � 12ðrb0=rc0Þ � 1

; b ¼ rcð~eplc Þ

rtð~eplt Þð1� aÞ � ð1þ aÞ; c ¼ 3ð1� KcÞ

2Kc � 1

Here, r̂max – maximum principal stress, rc – uniaxial compressivestress, rt – uniaxial tensile stress, p – effective hydrostatic pressure,q – equivalent effective deviatoric stress, ~epl – equivalent plasticstrain.

rb0/rc0 is the ratio of initial equibiaxial compressive yield stressto initial uniaxial compressive yield stress (the typical value is1.16); Kc is the ratio of the second stress invariant on the tensilemeridian to that on the compressive meridian (the typical valueis 2=3) [11].

Assumption of the non-associated flow rule in the plastic-dam-age model requires a separate flow potential to determine thedirection of plastic flow. The flow potential G accepted for thismodel is the Drucker–Prager hyperbolic function:

G ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffið�rt0 tan wÞ2 þ q2

q� p tan w

where w is the dilation angle measured in the p–q plane and it con-trols the orientation of the flow potential function G, see Fig. 5b. It isnot possible to obtain w directly from the results of the experi-ments. It was set to 35� by applying the inverse modeling approachin comparing the simulated and the experimentally measuredstress–strain curves [12]. rt0 is the uniaxial tensile stress at failure,taken from the user-specified tension stiffening data; and � is theeccentricity of the flow potential, that defines the rate at whichthe function approaches the asymptote (the flow potential tendsto a straight line as the eccentricity tends to zero) (the default valueis 0.1), Fig. 5b. Parameters �p and �q are hydrostatic pressure and vonMises equivalent stress, respectively. The details of the mathemat-ical formulation of the plastic-damage model are given in the Aba-qus theory and analysis manual [11].

For plasticity and damage, the compressive and tensile behaviorof the material must be specified by strain softening and damageevolution functions. The strain softening curve is provided in the

d (b) dilation angle and eccentricity.

Fig. 6. Material input curves: strain softening and damage evolution.

Fig. 8. Simulation results and effect of dilation angle w and mesh size.

V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71 65

material model in the form of yield stress as a function of inelasticstrain. The inelastic strain is identified by subtracting the elasticstrain corresponding to the undamaged material from total strain.The damage evolution curve is given as damage parameter d andthe corresponding inelastic strain at certain points in the softeningzone of the experimental stress–strain curve. The correspondingdamage parameter d is determined from the varying slope (E)and the initial stiffness (E0) as d = 1 � E/E0. Accordingly, as illus-trated in Fig. 6, the strain softening and damage evolution curvesfor CLSM is determined from the experimental compressivestrength testing on mixture M7. Tensile behavior of the CLSMwas defined by a linear strain softening function which was esti-mated from uniaxial compressive strength. In general, the ratioof the direct tensile strength to compressive strength ranges fromabout 0.07 to 0.11 [13].

Fig. 7. Conical damage (a) at compressive strength, (b) at failure with fixed end conditionat failure with one unconstrained end, (f) at failure with capped end conditions, and (g)

The capability of the plastic-damage model with the identifiedmaterial parameters for the analysis of a CLSM mass was evaluatedby a comparison with the experimental results in compressivestrength testing on CLSM cylinders.

4.2. Finite element analysis of compressive strength test on CLSMcylinders

A preliminary three dimensional solid FE model was employedto simulate a 0.42 MPa CLSM cylinder (mixture M7) underunconfined compressive loading to evaluate the capability of the

s, (c) experimental conical failure, and shear damage (d) at compressive strength, (e)experimental shear failure.

Fig. 10. Comparison of experimental and numerical results, settlement of thebridge sill and maximum lateral deflection of a facing panel with the appliedpressure.

66 V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71

plastic-damage model to predict the stress–strain response andfailure of a CLSM mass. Similar to concrete, there are two mainmodes of failure commonly observed in the testing of CLSM cylin-ders, shear band failure and conical type shear failure. The cylin-ders were modeled by 8-node linear brick with reducedintegration hourglass control elements (C3D8R). In order to simu-late different modes of failure, different boundary conditions wereapplied to the CLSM cylinders. Fig. 7 shows the distribution of thestiffness degradation (damage) variable d at maximum compres-sive stress and at failure. This distribution is similar to the modesof failure frequently observed in the testing of CLSM cylinders.

As illustrated in Fig. 7a–c, cylinders with fixed ends (laterallyconstrained ends) exhibit a symmetrical conical type shear failuremode at the center of the cylinder. To stimulate the unsymmetricalshear failure, one end was set free for lateral displacements,Fig. 7d–g. Capped end conditions were also analyzed to determinethe effect of frictional lateral end constraints on cylinder’s failureresponse. Two caps with solid elements were modeled to contactthe two ends of the cylinder with friction coefficient of 0.3. As aresult of the simulation, the CLSM cylinder fails with unsymmetri-cal shear bands, see Fig. 7f. It was observed that the location of theshear band changes with the change of the friction between padsand the cylinder.

The simulation results and effect of mesh size and dilation angleon the stress–strain behavior are presented and compared with theexperimental results in Fig. 8. Due to the fracture energy criterionof Hilleborg in the plastic-damage model [11], the effect of meshsize on the simulated stress–strain behavior is negligible. The dila-tion angle of 35� shows quite good agreement with the experi-ment. It can be concluded that the plastic-damage model withthe identified material parameters is capable of simulating thestress–strain response and visualizing the failure of a CLSM mass.

4.3. Finite element analysis of the CLSM bridge abutment

Based on the achievement in FE modeling in the preceding sec-tion, a three dimensional FE analysis of the full-scale loading test ofthe CLSM bridge abutment (Fig. 4) was carried out using Abaqus.The geometry and boundary conditions of the FE model, as illus-trated in Fig. 9, match the conditions of the CLSM bridge abutmentpresented in Fig. 3. For symmetry, only half of the abutment wasconsidered. The FE mesh consists of C3D8R solid elements for theCLSM backfill, concrete panels and bridge sill. Steel rebar anchors

Fig. 9. Finite element simulation o

were modeled as 3-node quadratic beam elements (B32), assumedto be fully bonded and embedded inside the elements of the CLSMbackfill and concrete panels. The utilized embedded region tech-nique resulted in a significant reduction in the number of nodesneeded to account for the effect of bond-slip [11]. As in the exper-iment, a rigid foundation and the groove and tongue connectionbetween panels was considered.

The plastic-damage model, with the material parameters takenfrom the compressive stress–strain response of CLSM mixture M3,was implemented for the backfill. For nonlinear response of thesteel anchors, the linear elastic branch was defined by the Young’smodulus of 200 GPa and a Poisson’s ratio of 0.3, whereas the non-linear stage, assumed to be perfectly plastic, was only defined bythe yield strength of 345 MPa. For concrete panels, material

f the CLSM bridge abutment.

V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71 67

behavior was assumed to be linearly elastic, with Young’s modulusof 25 GPa and Poisson’s ratio of 0.2.

Loading was simulated by a prescribed displacement on thesurface of the bridge sill placed on the CLSM backfill. Betweenthe sill and CLSM, contact conditions are assumed, rough frictionas the tangential behavior and hard contact as the normal behaviorwhich does not allow separation after the contact. Since the expli-cit solver was used to model a static condition (quasi-static), theanalysis time was carefully chosen to avoid any dynamic effects.The gravity load was initially applied to the backfill material in asmooth step to develop initial stresses in all CLSM elements.

Behavior of the CLSM bridge abutment in terms of bearingcapacity, vertical and lateral displacements and the axial force inanchors from the FE model were compared with those experimen-tally measured in the full-scale laboratory test. As shown in Fig. 10,

Fig. 11. Prediction of the bearing pressure, with settlement and ma

the applied pressure versus settlement of the bridge sill in theexperiment agreed well with the numerical results up to the pres-sure of 483 kPa. Likewise, the predicted maximum lateral displace-ment of a facing panel (top of the panel) compared well with theexperimental data. In the experiment, it was not possible to applya failure load because of the capacity limit of the laboratory’s rigidfloor. With the aid of the FE simulation, the bearing capacity of theabutment can also be determined. Fig. 11 predicts the bearing pres-sure and values of settlement and maximum lateral deflection up tofailure of the CLSM abutment. From this numerical results, the bear-ing capacity of the CLSM bridge abutment (backfilled with the samemixture M3 as in the experiment) is about 1175 kPa. The allowablebearing pressure of a bridge sill over reinforced soil retaining wallshas been limited to 200 kPa in the NHI manual [14] without anyspecial provisions [15]. Bearing capacity of the CLSM bridge

ximum lateral deflection, and evolution of damage coefficient.

68 V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71

abutment backfilled with the 206 kPa mixture (M3) was predictedto be almost six times larger than the allowable bearing pressure ofa bridge sill over a reinforced soil retaining wall.

Fig. 11 also illustrates four stages of the predicted damage evo-lution where the failed zones are represented by red areas consist-ing of highly-damaged elements (with the damage index d P 0.93).At the pressure of 570 kPa (48% of the peak pressure), a longitudinalshear band initiated at the back of the bridge sill from the surface tothe depth of the CLSM mass (Fig. 11a). More pressure caused morelongitudinal shear bands to form (Fig. 11b). As the applied pressureapproached the peak, a splitting-mode failure zone initiated belowthe sill and propagated in the diagonal direction (Fig. 11c). Then thesplitting-mode failure zone propagated rapidly, leading to a drasticdecline on the pressure–settlement curve (Fig. 11d).

Fig. 12 is a typical behavior of a CLSM abutment with respect tothe lateral displacement (D). It shows that a facing panel deformsslightly as the pressure (q) on the bridge sill approaches to about70% of bearing capacity of a CLSM abutment (qf), thereafter lateraldeformations become more significant. 70% of the bearing capacityrelates to the Fig. 11b when a longitudinal shear band developsclose to the face.

Strain measurements were made with two strain gaugesbonded at opposite locations (top and bottom) on rebar anchorsnear their point of attachment with the facing panels. Based onthese measurements, the axial tensile force caused by the actionof the panels on the rebars were calculated and normalized bythe ultimate pullout force. In a large-scale experimental pullouttest, with the same rebar embedded in the same prototype CLSMabutment, the ultimate pullout force was measured to be about22 kN. Comparison of the measured axial anchor loads with thenumerical results in Fig. 13 shows a relatively satisfactory agree-ment considering the assumption of perfect bond.

5. Parametric study

The quasi-static analysis method presented in this study iscapable of predicting the bearing capacity, failure, and verticaland lateral displacement of the CLSM bridge abutment. It also

Fig. 12. Profile of lateral displacement (normalized by the wall height) of a facingpanel as a function of the applied pressure.

can predict the axial load developed in the anchors with an accept-able accuracy. The FE model was used for conducting a series ofparametric studies to evaluate the influence of CLSM curing age,environment temperature and some construction details on bear-ing capacity and performance of the abutment.

Since the construction duration of the CLSM abutment is dic-tated by the initial developed strength of the CLSM, the effect ofcuring age and so the influence of compressive strength of a CLSMmixture was studied. For this analysis, the mixture M7 with com-pressive strengths of 0.08, 0.38, 0.85, and 1.03 MPa at 1 day, 7 days,28 days, and 90 days, respectively, was considered. Fig. 14a showsthat the bearing pressure of the bridge abutment increases but theductility response decreases as the CLSM mixture cures. Bearingpressure of the abutment at 1 day is about 500 kPa and controlledby the bond failure of steel anchors located at top of the facing pan-els. As can been seen, the bearing pressure is significant after7 days.

The curing temperature is also an important factor that affectsthe strength gain of CLSM mixtures and so the bearing capacityand performance of the CLSM bridge abutment. This influencewas studied with a mixture (M7) cured for 7 days at 4 �C, 23 �Cand 38 �C that lead to compressive strengths of 0.24, 0.38, and1.38 MPa, respectively. Fig. 14b shows that bearing capacity ofthe CLSM abutment cured at a cold temperature of 4 �C is about30% less than if cured in the room temperature of 23 �C, whilethe abutment can gain almost twice strength at a high temperatureof 38 �C.

In another analysis, early strengths (1-day) and late strengths(28-day) of six different CLSM mixtures (from Table 1, mixturesM2, M4, M5, M7, M9, M10) were compared. Fig. 15a shows perfor-mance of the abutment due to early strength (at 1 day) of the CLSMmixtures and Fig. 15b shows the performance due to late strength(at 28 days). These results can be used as an initial guide for thedesign and selection of a CLSM mixture based on the desired earlyor late bearing capacity of the abutment. From Fig. 15 and Table 1,mixture M9 has the minimum compressive strength (0.16 MPa)which can provide adequate bearing capacity for the CLSM abut-ment after only one day from the CLSM placement.

Fig. 13. Comparison of the measured and computed axial anchor load at top,middle, and bottom of a facing panel.

Fig. 14. Performance of the bridge abutment with (a) CLSM curing time and (b)curing temperature.

Fig. 15. Performance of the CLSM abutment due to (a) early strength and (b) latestrength of different CLSM mixtures.

Fig. 16. Profile of lateral deformation at the maximum applied pressure withcompressive strength of CLSM mixtures.

Fig. 17. Effect of compressive strength of CLSM mixtures on developed axial stressin anchors.

V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71 69

The effect of CLSM compressive strength on lateral deformation(D) of the facing wall and the developed load in the anchors wasalso investigated. These values were normalized by the wall heightfor lateral deformation, and yield and bond strength for theanchors. Fig. 16 shows the profile of lateral deformation of a facepanel at maximum applied pressure for different CLSM mixtures.As can be seen in the figure, the maximum deformation relatesto the top of the panel. Mostly, as the mixture becomes stronger,

the panel undergoes more deformation before the failure. For thecase of the strongest mixture (8.2 MPa), the backfill behaves withmore rigidity and less deformation.

Fig. 17 compares the developed axial stress in anchors locatedat the top, middle and bottom of a face panel at the maximumapplied pressure and as a function of the compressive strength ofa CLSM mixture. Typically, more stress is mobilized at the topanchor, and a stronger mixture transfer less load to the anchors.Anchors embedded in a weaker CLSM mass are more susceptibleto failure due to bond strength and in a stronger mass, to yieldstrength of the steel rebar.

Fig. 18. Effect of some design modifications on performance of the CLSM abutment.

70 V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71

The FE model was also used to examine the effect of designmodifications on the performance of the CLSM bridge abutment.Four different cases were considered and compared with the basecase (in Figs. 3 and 9) as follow:

� Case 1: a backfill without the concrete panels and anchors.� Case 2: a backfill with the concrete panels and without the

anchors.� Case 3: three anchors in three equally spaced rows (one in

each row) was used to anchor panels at wing walls (in thebase case six anchors in three rows are used for all panelsas shown in Figs. 3 and 9).

� Case 4: vertical connection detail (groove and tongue) iseliminated between panels.

The first two cases reveal the effect of concrete panels andanchors on bearing capacity and displacements of the CLSM abut-ment. Case 3 was considered since it was observed that the anchorsused for wing walls are not taking considerable load. Case 4 was toexamine the value of contribution of the vertical connectionsbetween the panels. Fig. 18 compares the behavior of the abutmentin these cases (all have the same material backfill, mixture M3).Fig. 18a shows that the abutment loses half of its bearing capacitywithout the anchored panels to provide lateral support and confin-ing pressure. This also can be seen in Fig. 18b when these two casesshow large lateral deformations. Performance of the abutment incase 3 reveals that three anchors (one at the top, one at the middleand one at the bottom of a panel) would be enough to anchor thepanels of wing walls. Also case 4 demonstrates that the verticalconnection detail (groove and tongue connection) between panelsdoes not have a significant influence on bearing capacity of theabutment and it would be safe if it is eliminated. These two mod-ifications can lead to a faster and more economical constructiondesign for CLSM bridge abutments.

6. Conclusions

Controlled low strength materials (CLSMs) can be used for rapidand sustainable construction of bridge abutments. In this paper, a

finite element analysis was carried out to simulate the behavior ofa full-scale loading test of a bridge abutment backfilled with theCLSM referred to as ‘‘CLSM bridge abutment’’. The behavior ofthe CLSM was simulated using a plastic-damage model whichcaptures the material behavior using both classical theory of elas-to-plasticity and continuum damage mechanics. The FE modelingof the standard compressive strength tests demonstrated the capa-bility of the material model for a realistic prediction of the failurepatterns in the CLSM test cylinders and stress–strain response.

The numerical results were consistent with the measurementsobtained in a full-scale laboratory test on a CLSM bridge abutment.The analysis shows that the performance of a CLSM abutmentwhile subject to a service load or a limiting failure load from abridge superstructure can be simulated in a reasonably accuratemanner. The FE model showed that the CLSM abutment is capableof carrying typical bridge loads after one day with adequate mar-gins and with small deformations. It also indicated that the lateralmovement of the facing panels was negligible up to about 70% ofthe bearing capacity of the abutment when a longitudinal banddeveloped close to the face.

Finally, a parametric study was conducted to investigate theperformance of CLSM bridge abutments in terms of bearing capac-ity and overall behavior. This study showed that the performanceof CLSM bridge abutments is greatly affected by the CLSM curingage, environment temperature, and existence of anchored concretepanels. It was observed that the bearing capacity of the bridgeabutment increases as the CLSM mixture cures but the ductilityresponse decreases. Also, it was observed that higher curing tem-peratures promote the bearing capacity of the CLSM abutment.Performance of the abutment due to early (1 day) and late age(28 days) strength of different CLSM mixtures was also consideredto provide an initial guide for the selection of a mixture based onbearing capacity requirements.

References

[1] ACI Committee 229 (Reproved 2005). Controlled Low-Strength Materials.Farmington Hills (MI): American Concrete Institute (ACI); 1999.

[2] Folliard KJ, Du L, Trejo D, Halmen C, Sabol S, Leshchinsky D. Development of arecommended practice for use of controlled low-strength material in highwayconstruction. NCHRP Report 597. TRB, Washington DC; 2008.

V. Alizadeh et al. / Computers and Geotechnics 64 (2015) 61–71 71

[3] Trejo D, Folliard KJ, Du L. Sustainable development using controlled lowstrength material. In: Proc int workshop on sustainable development andconcrete technology, Iowa State Univ, Ames, IA; 2004. p. 231–50.

[4] Alizadeh V, Helwany S, Ghorbanpoor A, Oliva M. A rapid constructiontechnique for bridge abutments using controlled low strength materials.ASCE J Perform Constr Facil 2014;28(1):149–56.

[5] Snethen DR, Benson JM. Construction of CLSM approach embankment tominimize the bump at the end of the bridge. STP1331: The design andapplication of controlled low-strength materials (flowable fill), ASTM, WestConshohocken, PA; 1998. p. 165–79.

[6] Wilson J. Flowable fill as backfill for bridge abutments. Rep. No. WI-16-99,Wisconsin DOT, Madison, WI; 1999.

[7] Davidson J S, Copham B. Innovative use of flowable fill for short-span bridgerehabilitation. University Transportation Center for Alabama, Rep. No. 01218; 2002.

[8] Alizadeh V, Helwany S, Ghorbanpoor A, Sobolev K. Design and application ofcontrolled low strength materials as a structural fill. Constr Build Mater2014;53:425–31.

[9] Lubliner J, Oliver J, Oller S, Oñate E. A plastic-damage model for concrete. Int JSolids Struct 1989;25(3):299–329.

[10] Lee J, Fenves G. Plastic-damage model for cyclic loading of concrete structures.ASCE J Eng Mech 1998;124(8):892–900.

[11] Dassault Systèmes. Abaqus Analysis User’s Manual. Version 6.12; 2012.[12] Jankowiak T, Tomasz L. Identification of parameters of concrete damaged

plasticity constitutive model. Found Civ Environ Eng 2005;6:53–69.[13] Mindess S, Young JF, Darwin D. Concrete. Upper Saddle River (NJ): Pearson

Education, Inc.; 2003.[14] Elias V, Christopher BR, Berg RR. Mechanically stabilized earth walls and

reinforced soil slopes design and construction guidelines. National HighwayInstitute Course No. 132042, FHWA NHI-00-043, Washington, DC, 2001.

[15] Wu JTH, Lee KZZ, Pham T. Allowable bearing pressures of bridge sills on GRSabutments with flexible facing. ASCE J Geotech Geoenviron Eng2006;132(7):830–41.