Pumice concrete for structural wall panels

Engineering Structures 25 (2003) 115–125www.elsevier.com/locate/engstruct

Pumice concrete for structural wall panels

L. Cavaleri∗, N. Miraglia, M. PapiaDepartment of Structural and Geotechnical Engineering, University of Palermo, Viale delle Scienze, 90128 Palermo, Italy

Received 15 April 2002; accepted 22 July 2002

Abstract

Some properties of lightweight pumice stone concrete (LWPSC) are discussed, on account of a possible structural use of this material.Then the results of an experimental investigation are described, in order to show that pumice can really be considered an alternative tocommon artificial lightweight aggregates, taking into account the performance pointed out by loading tests carried out on structuralsystems made of LWPSC. Three different kinds of reinforced wall panels were made using LWPSC, lightweight expanded clay concreteand normal weight concrete; then their structural responses under horizontal cyclic and constant vertical forces were compared, aboveall with reference to lateral stiffness, cracking pattern, ultimate strength and associated plastic deformations. This comparison shows theeffectiveness of pumice as an aggregate in manufacturing concrete, at least for this type of structural element. 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Pumice aggregate; Structural lightweight concrete; Squat reinforced concrete walls

1. Introduction

Structural lightweight aggregate concrete (LWC) hasbeen used in many civil engineering applications as a veryconvenient alternative to conventional concrete. As a mat-ter of fact its lighter weight permits a saving in dead loadwith a reduction in the costs of both superstructures andfoundations. In addition, the better thermal insulation, thegreater fire resistance and the substantially equivalentsound-proofing properties (in spite of its minor mass com-pared to normal weight concrete (NWC) — see e.g. [1])make it preferable with respect to NWC itself for non-structural uses.

In the last five decades the use of LWC has beenextended to structural elements, thanks to the improvementin performances obtainable (in terms of stiffness, strengthand ductility) by means of appropriate ingredient mix pro-portions [2] and appropriate design of the reinforcement.

Naturally, the use of lightweight concrete has been con-fined to large structures (where the beneficial influences ofthe reduced weight are greater), and, more in particular, tostructures where a high dead load to live load ratio occurs.

∗ Corresponding author. Tel.:+39 091-6568457; fax:+39 091-6568407.

E-mail address: [email protected] (L. Cavaleri).

0141-0296/03/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0141-0296 (02)00123-2

Further, the reduced weight may make LWC preferable forstructures in seismic zones, because of the reduceddynamic actions, and for precast structures, because itmakes it easier to move the elements to be connected.

More recently, lightweight concrete was also applied inmarine structures (offshore structures and ships), and laterfor long span bridges, buildings and grandstands [1]. Refer-ring to buildings, LWC can be used in structural frames,but it proves to be more suitable for wall system structures,where the local ductility demand (in seismic zones) andthe required strength of the materials are reduced and thedead load to live load ratio is very high.

LWC is manufactured by using different kinds of light-weight aggregates, available in nature or artificially pro-duced, so that the properties of LWC depend on the proper-ties of the particular lightweight aggregate being used.

Natural lightweight aggregate sources can be found inregions characterized by volcanic activity, where porousrocks (known as pumices), are available. Artificial light-weight aggregates (like the expanded clay obtained bythermal treatment of argillaceous materials) are producedin many countries, the raw materials being very com-mon. They may exhibit higher resistance than naturallightweight aggregates, but this favourable result impliesa greater production cost.

Considering the availability of pumice in the worldand its usability as a natural aggregate for concrete, a

116 L. Cavaleri et al. / Engineering Structures 25 (2003) 115–125

research program has been carried out in order to verifythe mechanical properties of the pumice concrete inrelation to the mechanical standards requested bypresent-day codes for structural applications, and inorder to observe its behaviour when used for structuralelements. The main results at the actual stage of thisresearch are presented through the paper. Specifically,the results of the tests on lightweight pumice stone con-crete (LWPSC) wall panels subjected to vertical and lat-eral loads are shown and compared to those obtainedfrom similar NWC and lightweight expanded clay con-crete (LWECC) wall panels.

2. Pumice as an aggregate for structurallightweight concrete

Pumice is a natural sponge-like material of volcanic ori-gin composed principally of silica and produced frommolten lava rapidly cooling and trapping millions of tinyair bubbles. Volcanic pumice has been used as an aggregatein the production of lightweight concrete in many countriesof the world. In particular, it can be found in the Mediter-ranean area (Italy, Turkey, Greece, and Spain). In the USAit is mined mainly in the Rocky Mountains and PacificCoast States. From the commercial point of view, pumicecan be found as granulates characterized by different distri-bution curves. Production is mainly devoted to non-struc-tural concrete elements and today the material is not usedin structural elements although historically it has been usedsince ancient Roman times for structural applications (thedome of the Pantheon in Rome is a famous example). Withrespect to the components of reinforced concrete, pumiceis an inert material, i.e. it has no chemical reaction withcement paste or steel reinforcement.

It has been found that, by using volcanic pumice, satis-factory concrete, from 30 to 40% lighter than normal con-crete having good insulation and structural strength charac-teristics can be manufactured [3,4] in agreement with thestandards requested by Eurocode 2 [5] and ACI Code [6].

The pumice used in this research comes from Italy, onthe island of Lipari. It is not very different from the pumiceobtainable from other sources, and is commercially charac-terized by rounded particles with a size between 0 and 15mm and a dry loose bulk density of 750 kg/m3. The specificgravity of the single particles constituting the aggregatevaries with size, being higher for the fine particles andlower for the coarse ones. The surface texture is charac-terized by small exposed pores not communicating withthe internal ones; this circumstance reduces water absorp-tion during the manufacturing of concrete. In order todefine the optimal mix proportions for the concrete and toobtain good mechanical properties, commercial aggregateshave been distinguished into three different size ranges, thefirst characterized by particles whose size is smaller than3 mm, the second comprising particles with a size between

3 and 7 mm and the third comprising particles greater than7 mm. In the two last cases (used in LWPSC) the meandensity values of the particles are 940 and 1040 kg/m3,respectively.

The chemical composition of the pumice used in thisinvestigation is reported in Table 1, where the high percent-age of SiO2 characterizing this kind of material can beobserved.

3. LWPSC and structural walls

In structural wall systems the strength of the walls,whose thickness is often fixed in agreement with thetechnological minimum size, may be so large that a fullyelastic response can be expected even under accidentalloads, like a severe earthquake. For these structures theexpected stress level usually proves to be very low, andconsequently high material strength is not required,especially when squat wall systems are considered. Asa matter of fact in this case the flexural effects underhorizontal loads are reduced by the relatively large avail-able internal lever arm. In these connections the low duc-tility of this kind of structural systems is not likely tobe of great importance. On the other hand, the bearingwalls constitute a relevant part of the entire weight of abuilding of this kind, so a marked reduction in stressescan be obtained by reducing their weight. Under theseconditions the size of the foundation can be reduced too,and moving and mounting are made easier when precastelements are used.

LWPSC, in spite of the not optimal mechanicalproperties, may be used for structural walls; on the con-trary, the optimal thermal and acoustic properties of theLWPSC make its use a very appropriate solution. Forthis reason the structural behaviour of bearing walls ofLWPSC was investigated.

Table 1Chemical composition of Lipari pumice

Component % Mass

Silica (SiO2) 71.75Alumina (Al2O3) 12.33Ferric oxide (Fe2O3) 1.98Lime (CaO) 0.70Magnesia oxide(MgO) 0.12Natrium oxide (Na2O) 3.59Potassium oxide (K2O) 4.47Sulphuric oxide (SO3) 0.18Other 4.88

117L. Cavaleri et al. / Engineering Structures 25 (2003) 115–125

4. Experimental program

4.1. Test specimens

A vertical structural reinforced panel was selected asa prototype structure under vertical and horizontal loads.The nominal dimensions of each sample are 1250 mmin height, 1650 mm in length, and 100 mm in thickness.Every panel can be considered to represent a criticalstory scaled element of a structural wall system. Thepanels were constructed with top and bottom beams. Thetop beam (1650×400×300 mm) allowed the distributionof the axial and horizontal loads; the bottom beam(2450×800×250 mm) made it possible to clamp thespecimen to the laboratory strong floor.

Each specimen was reinforced with high tensile steelbars, having 8 mm diameter, placed in the middle layerof the element, in the form of a welded wire mesh fabric.The amount of the reinforcement was chosen referringto the minimum content of 0.25% indicated in the ACICode [7] for structural walls in seismic zones. As aconsequence a spacing of 200 mm was selected for verti-cal as well as for horizontal reinforcement bars. Such areinforcement arrangement, not usual in real walls wherea double plane is generally adopted, is not effective forthe concrete confinement. Nevertheless, it allows one toobserve the behaviour of the different kinds of concreteused with respect to the splitting phenomenon, the studyof the reinforcement confinement effect being delayedto successive tests.

Fig. 1 shows the test specimen with its nominaldimensions and the arrangement of the vertical and thehorizontal reinforcement.

The experimental work involved the testing of ninespecimens made of LWPSC (three), of LWECC (three)and NWC (three). A comparison between the three kinds

Fig. 1. Details of test specimens (measurements in mm).

of specimens showed the good mechanical properties ofthe LWPSC panels. The comparison between theLWECC and LWPSC panels validated the use of pumiceas an alternative to the more common lightweight arti-ficial aggregates, while the comparison with the NWCpanels showed the good mechanical properties comparedto conventional concrete.

In the following sections the wall panels made ofLWPSC are synthetically indicated with the letter P fol-lowed by the number of the specimen; the wall panelsmade of LWECC are indicated with the letter A and thepanels made of NWC are indicated with the letter C.

4.2. Material properties

The NWC and the LWC used in this study were pro-duced employing only conventional techniques and com-mercially available materials.

A preliminary investigation made it possible to definethe optimal mixture proportions for the LWPSC. A pro-per size distribution of the aggregates was chosen takinginto account the dependence on it of workability, cementcontent, optimum air content and drying shrinkage. Thefine particles of the pumice aggregates (those havingdiameter smaller than 3 mm) were replaced by normalweight sand. So a stiffer and stronger cement paste wasobtained than the one produced by using lightweightsand. Further, better workability and contained shrinkagewere obtained for the concrete.

The LWECC and the NWC used for the panels weremanufactured in a such a way as to obtain the same com-pressive strength class as for LWPSC. The final mixtureproportions and the unit weights of the three kinds ofconcrete are shown in Tables 2 and 3. Further, in Table4 the mechanic characteristics in terms of mean valuesare shown. Note that the compressive strength and the


Table 2Concrete mixture components (kg/m3)

(Pumice aggregate Expanded clay aggregate NormalCement Effective Absorption Normal sand aggregate (7–

Type Portland 425 water water (0–3 mm) 15 mm)

(3–7 mm) (7–15 mm) (3–7 mm) (7–15 mm)

NWC 300 180 – – – – – 630 1250LWECC 350 175 99 – – 237 304 615 –LWPSC 350 175 64 206 260 – – 615 –

Table 3Concrete unit weight

Total weight of the Weight after 28 daysType components (kg/m3) (kg/m3)

NWC 2360 2325LWECC 1780 1680LWPSC 1670 1600

elastic modulus were measured on cylindrical specimensof material (n=10 for each kind of concrete) havingdiameter 150 mm and height 300 mm, while the tensilestrength was measured by split tests on cylindricalsamples (n=10 for each kind of concrete) having diam-eter 100 mm and length 200 mm. Every test gave veryclose values of the mechanic characteristics investigated,and for this reason the results of each test are notreported in Table 4, while the mean data and the standarddeviations are shown. In Table 5, the standards in termsof maximum unit weight and minimum compressivestrength requested by American and European Codes forstructural LWC are shown. Those values suggest that theweight and the strength of the concrete with pumice usedin this research belong to the class of structural LWC.

The reinforcement consisted of steel bars with a meanyield strength of 375 N/mm2.

4.3. Test setup and instrumentation

Each panel was subjected to a combination of axialand horizontal loads using the testing apparatus shown

Table 4Mechanic characteristics of the concrete

Type Compressive strength (MPa) Elastic modulus (MPa) Tensile strength (split test) (MPa)

Mean Standard deviation Mean Standard deviation Mean Standard deviation

NWC 22.9 0.79 27015 74.5 2.6 0.11LWECC 21.0 0.61 15328 33.3 2.2 0.09LWPSC 20.5 0.81 13854 29.4 1.9 0.09

Table 5Properties of lightweight concrete in EC and ACI

MinimumMaximum weight compressive strength

Code (kg/m3) (MPa)

EC2 2050 16.00ACI 1850 17.24

in Fig. 2. Once the specimen was in the test location, arigid steel beam was connected to it for the transfer ofthe loads.

The vertical loads were applied by four manually con-trolled hydraulic jacks connected by means of four met-allic tendons to a horizontal rigid steel beam placed onthe rigid beam mentioned before; the forces were moni-tored by measuring the oil pressure. The upper steelbeam was constrained with respect to the horizontal dis-placements maintaining the verticality of the transmittedforces, while the lower steel beam, fixed to the specimen,could move horizontally allowing lateral displacementsof the head of the specimen. The lateral loads wereapplied by two single-effect horizontal jacks placed oneach side of the panel, and the forces were monitoredby proper load cells. Since a collapse lateral load of ca600 kN was predicted, horizontal jacks having 1000 kNcapacity were used. The friction force transmitted by thevertical loading device to the specimen was measuredby a load cell. The displacements of the specimen weremeasured by transducers located as in Fig. 3. Possiblehorizontal and vertical displacements of the foundation


Fig. 2. Test setup.

were measured in order to verify that the foundation wasfixed to the laboratory strong floor.

4.4. Loading patterns and history

Each specimen was subjected to different combi-nations of axial and lateral loading. The axial loads(vertical dead and live loads) were maintained constantduring each test. A total vertical force of 300 kN wasapplied, reproducing the load applied on a panel locatedat a low floor of a multi-story building. It correspondsnearly to 0.1 of the uniaxial compressive strength Pu ofthe wall cross section evaluated as Pu � 0.85fc’bl, fc’being the cylinder compressive strength and l and b thelength and the thickness of the panel, respectively.

The lateral load was cyclically applied with anincreasing maximum value at each semi-cycle. The loadwas applied with an incremental step of 20 kN. At eachincremental loading step the load was maintained con-

Fig. 3. Transducer location.

stant for a few seconds in order to measure and recordthe load and the displacement response of the head ofthe specimen. The lateral load history is depicted in Fig.4. Usually the tests were stopped when a suddenreduction of strength was observed with respect to themaximum value reached (ultimate load).

4.5. Expected behaviour for squat shear walls

The behaviour of shear walls has been investigated inseveral studies (e.g. [8–16]). When a height to lengthratio of less than 2 is maintained, walls generally exhibitshear collapse under a lateral load [10,16], except witha special amount and distribution of the reinforcementas specified by Paulay et al. [13]. The shear collapseshows limited ductility and dramatic degradation in bothstiffness and strength, all characteristics that should not

Fig. 4. Loading history.


be encouraged in seismic design. Nevertheless, the lowsteel reinforcement requirement, often satisfied by near-minimum steel content, provides sufficient energyabsorption in the post-elastic range, since squat shearwalls, generally designed in agreement with the mini-mum dimension requirements, in wall systems mayabsorb all or most of the seismic shock in the elasticrange, so they generally do not require a high plasticdeformation capacity.

Shear collapse may be originated by diagonal tensionfailure or diagonal compression failure. The former mayoccur after a corner-to-corner diagonal tension failureplane or a steeper one develops (Fig. 5). The collapse isassociated with a total (Fig. 5a) or a partial (Fig. 5b) lossof equilibrium that can be avoided by a proper amount ofhorizontal reinforcement.

If a high reinforcement ratio is used, failure may occurdue to compression stress along the diagonal direction(Fig. 6a) and under reversed cyclic loading the crushingof the concrete rapidly spreads over the entire length ofthe wall (Fig. 6b). The contribution of the concreteagainst shear is traditionally expressed in terms of trussaction, aggregate interlock, uncracked flexural com-pression zone of the wall and dowel action of the rein-forcing bars. These mechanisms depend on the featuresof the concrete-reinforcement system, namely on theconcrete compressive strength, the elastic properties ofthe mortar and the aggregate, involvement of the aggre-gate in the fracture path, and the bond condition betweenconcrete and reinforcement.

Fig. 5. Diagonal tension shear failure.

Fig. 6. Diagonal compression shear failure.

5. Test results

The tests, performed using the three kinds of concretementioned before, showed how the aggregates usedinfluenced the cracking mechanisms under shear loading.The main results are given in the following figures andtables. Figs. 7–8 contain the lateral load-lateral displace-ment cyclic curves referring to each of the nine panels.In Table 6 the values of the first macro-cracking load,of the ultimate load and of the stage of the loading pat-tern where they occurred are shown. Further, in Fig. 9the variation in the secant stiffness versus the maximumlateral load in each half cycle is depicted. Finally in Figs.10–13 the evolution of the cracking patterns and the col-lapse mechanism are shown.

5.1. Stiffness

For all specimens the stiffness in the elastic range wasapproximately constant, decreasing very much after thecracking process began (Fig. 9). The panels C exhibitedhigher initial stiffness than the panels P and A as aconsequence of the different elastic modulus of the con-crete (Table 4).

Panels A and P, as well as the panels C, were affectedby a reduction in stiffness when the lateral loadincreased. Panels P exhibited the smallest values of stiff-ness as shown in Fig. 8, in which the comparisonbetween the response of the different kinds of panels isinserted. Referring to the load peak in the first half cycle,the secant stiffness of panels A is significantly higherthan the secant stiffness of panels P, in spite of the not


Fig. 7. Lateral load versus top horizontal displacement.

relevant difference of the elastic modulus of thematerials (see Table 4 and Fig. 8). This occurrence wasdue to the early micro-cracking process that involved thepanels P.

As the lateral load exceeded the values correspondingto a severe cracked state, the difference in the stiffnessof each kind of specimen reduced. In this stage a trusssystem behaviour completely replaced the initial behav-iour.

The higher reduction in stiffness of the panels P andthe more diffused micro-cracking process evidenced amore uniform dissipation capacity, revealing more duc-tile behaviour.

5.2. Cracking

For panels P macro-cracks appeared along the diag-onal direction (Fig. 12) when at least 40% of the ultimateload was reached. The slope of the cracks was ca 45° ormore. Initially, few distributed cracks appeared, whoseextension and density increased with the load. Thecracks on the panels C (Fig. 10) and A (Fig. 11)appeared first near the diagonals and propagated differ-ently from the cracks in the panels P. With regard to thelatter, the localization of the cracks near the principaldiagonals of the walls was observed.

Referring to the panels A, when the first macro-cracks


Fig. 8. Lateral load versus top horizontal displacement: (a) panels Cand P; (b) panels C and A.

appeared, a similar percentage of the ultimate load wasrecorded with respect to the panels P. By contrast, onaverage panels C were subjected to 55% of their capacitywhen the first cracks appeared. The load values corre-sponding to the first cracks can be found in detail inTable 6. In each case the crack paths evidenced shearbehaviour prevailing over flexural, as was expectedbecause of the shape of the panels, the amount ofreinforcement adopted and the axial load applied. Forpanels P and panels A the reduced tensile strength ofthe material anticipated the cracking with respect topanels C.

Table 6Lateral loads at first cracking and at ultimate load

Axial load First cracking CollapseSpecimen (kN)

Lateral Lateralload (kN) Half cycle load (kN) Half cycle

C1 300 �400 5 �630 8C2 300 +330 5 �480 6C3 300 �300 4 �450 6A1 300 �190 4 �420 6A2 300 +210 3 �450 6A3 300 +240 5 �510 6P1 300 �160 4 +360 5P2 300 �185 4 �410 6P3 300 �175 4 +400 5

Fig. 9. Secant stiffness versus lateral load.

The cracks observed in the panels revealed the possi-bility of transfer of the shear load to the foundation aftera truss mechanism formed, involving the concrete diag-onal strut between the upper and the lower beams andthe reinforcement.

A micro-cracking process interested panels P for aload level lower than that observed in the other panels,as the stiffness measurement confirmed. This occurrenceproduced a more diffused crack pattern before thereinforcement reached the yielding stress.

In detail, Figs. 10–12 present the crack pattern evol-ution observed on one of each of the three kind of panels.Fig. 10 presents the crack evolution observed in thepanel C1, while Figs. 11 and 12 present the crack evol-ution observed in the panel A2 and P2, respectively.Analogous crack evolution was observed in the otherpanels varying the kind of concrete.

When the panels were near to collapse, splitting of theconcrete in compression was observed, due to theabsence of a reinforcement confining action. Neverthe-less, this effect can be drastically reduced if an adequateamount of reinforcement is distributed on each side ofthe panel, unlike what was done in the specimens tested.


Fig. 10. Significant stages of cracking process exhibited by the panel C1: (a) 400 kN, half-cycle 5; (b) �480 kN, half-cycle 6; (c) 560 kN, half-cycle 7; (d) �630 kN, half-cycle 8.

Fig. 11. Significant stages of cracking process exhibited by the panel A2: (a) �320 kN, half-cycle 4; (b) 300 kN, half-cycle 5; (c) 400 kN, half-cycle 5; (d) �450 kN, half-cycle 6.

The tests showed that the splitting occurred in a similarway in the normal concrete as well as in the concretewith pumice and expanded clay, evidencing no amplifi-cation of the phenomenon in the pumice concrete.

5.3. Cyclic response

The horizontal load versus the horizontal top displace-ment of all specimens, shown in Fig. 7, distinctly indi-cates a non-linear deformational response. After the firstcycles the curves are characterized by a pinched shapearound the origin, caused by opening and closing ofdiagonal cracks at each reversal of loading.

Examination of Fig. 8, where the load-displacement

curves are compared by overlapping, clearly indicatesthe difference between the load-displacement relation-ship of the three kinds of walls. After the first cycles,characterized by a quasi linear elastic behaviour, moresignificant pinching was experienced on the panels C andA in the following cycles.

Referring to the panels P, lateral permanent top dis-placements higher than those observed for the otherpanels were recorded.

The different shapes of the load-displacement curvesare immediately explained by considering the evolutionof the crack patterns described before: the gradual propa-gation of the cracks and their higher diffusion alloweda gradual transfer of the stresses from the concrete to


Fig. 12. Significant stages of cracking process exhibited by the panel P2: (a) �185 kN, half-cycle 4; (b) 200 kN, half-cycle 5; (c) 400 kN, half-cycle 5; (d) �410 kN, half-cycle 6.

Fig. 13. Typical collapse of the concrete in the compressive edge of the panels: (a) C; (b) A; (c) P.

the reinforcement and better distribution on eachreinforcement bar, avoiding any concentration ofstresses. Furthermore, the high diffusion of cracksreduced the increase in stiffness that generally followsthe closing of the cracks themselves when the loadincreases, producing a more rounded shape of the load-displacement cycle.

The observations mentioned before reveal bettercapacity of the panels P to dissipate energy and moreductile behaviour. Note that only the behaviour tendencyof the wall panels in terms of ductility and energy dissi-pation can be observed, because the tests themselves areperformed by controlling the forces.

5.4. Strength and collapse mode

Fig. 7 and Table 6 show that the mean horizontal ulti-mate loads of each type of wall tested are not very differ-ent. Nevertheless, such small differences in strength, inspite of the same conventional compressive strength ofthe concretes investigated, indicate that the strength and

deformational characteristics of the walls are influencedby the type of aggregate, which modifies the concretetensile strength, by the concrete-reinforcement bondstate, and by the shear load transfer mechanisms.

The maximum horizontal load sustained by the panelsC was the highest. The panels P exhibited a lateralstrength ca 10% lower than that of the panels A and ca20% lower than that of the panels C. It has to be noticedthat the prediction of the lateral bearing capacity of thepanels P, made in agreement with the ACI BuildingCode, leads to a conservative value with respect to theexperimental results.

As a consequence of the higher capacity of the panelsC, a higher number of lateral loading cycles were perfor-med compared to the panels A and P.

For the panels P the recorded ratio of the lateral andthe vertical forces at ultimate load was 1.3; this value isan index of good seismic capacity of the wall systems,where the design seismic forces are a low percentage ofthe vertical loads; the high value of the before mentionedratio makes one predict similar qualities even for high


floor panels (different from the case examined) wherethe vertical loads are lesser. However further tests, fea-tured by reduced level of the vertical loads, need to con-firm this remark.

The collapse mode for each kind of panel was seento depend mainly on diagonal crushing of the concretein the compressive zone at the base (Fig. 13). At thisstage a large diagonal crack width was reached, indicat-ing that high values of the tensile stress in the reinforce-ment were simultaneously reached.

The crushing of the concrete strut assumed by the trussmodel of the panel is compatible with the concrete com-pressive strength and the diagonal tensile stress state. Inthe panels P, in contrast to the panels A and C, the largenumber of diagonals cracks, spreading up to the edge ofthe panel for a high value of the lateral load, seems toreduce the strength of the concrete in compression. In thespecimens tested the crushing was immediately followedby the formation of a diagonal failure plane as in Fig. 5a,which indicated the immediate transfer of the total shearload to the horizontal reinforcement.

6. Conclusions

The use of pumice as an alternative aggregate formanufacturing structural lightweight concrete elementshas been discussed. After the evaluation of the mechan-ical and physical properties of this kind of concrete, itsapplicability for structural panels has been recognised asmuch effective as the LWC made of expanded clay andthe NWC. An experimental investigation has beenpresented to observe the behaviour of pumice concretepanels under constant vertical loads (of normalized valueapproximately equal to 0.1 with respect to the axial nom-inal bearing capacity) and cyclic horizontal loads, andto compare them to nominally equal panels made ofNWC and lightweight structural concrete with expandedclay, the latter being the most common lightweightaggregate. The three kinds of concrete were manufac-tured in such a way as to obtain more or less the samecompressive strength.

The following observations were made:

1. panels P, like panels A, exhibit lower initial stiffnessthan panels C;

2. the reduction in stiffness of the panels P with anincrease in the lateral load is associated with a morediffused micro and macro cracking process comparedto the panels A and C;

3. the difference in stiffness of the three kinds of panelsdecreases after cracking occurs, producing the classi-cal truss mechanism;

4. the lateral capacity of the lightweight concrete panelsis lower than that exhibited by panels C, and further-more the average strength of panels P is 10% lowerthan for panels A;

5. the ultimate deformation of the panels P is larger by

a factor of 1.5 with respect to the panels A whoseultimate deformation is close to that exhibited bypanels C;

6. before the collapse of the panels P, both materials(concrete and reinforcement) are interested by a moreuniform state of stress thanks to a very diffused crackpattern, producing higher energy dissipation due toyielding of the reinforcement and to friction along thefracture layers;

7. as a consequence of the previous points from 2 to 6,more ductile behaviour is exhibited by panels P.

The experimental results show that LWPSC is a goodalternative for use in construction, particularly in thosecountries where pumice is locally available and for kindsof structural systems composed by bearing elements thatdo not require high resistance against horizontal loadsand ductility/energy dissipation.

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Pumice concrete for structural wall panels

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