AAC-concrete light weight precast composite floor slab
Yavuz Yardim a ,⇑,A.M.T.Waleed b ,Mohd.Saleh Jaafar c ,Saleh Laima c
a
Engineering Faculty,Epoka University,Albania b
Engineering Faculty,University of Nizwa,Oman c
Engineering Faculty,UPM,Malaysia
h i g h l i g h t s
"We test nine different full scale slabs to find optimum solution for AAC precast slabs."We examine changes in the layout of precast floor and amount of AAC.
"The dead load of the slab can be reduced by using propod composite slab 32-23%compeered to solid RC.
"Bad on strain monitoring of the test specimens,structures perform in a fully composite manner until the ultimate load."Ductility and maximum deflection of the all tested slabs are well enough to give warning before failure.
a r t i c l e i n f o Article history:
Received 27August 2012
Received in revid form 20September 2012Accepted 12October 2012
Available online 12December 2012Keywords:Composite
Light weight slab Aerated concrete Ferrocement
a b s t r a c t
In this study,the u of Autoclaved Aerated Concrete (AAC)as an in fill material for mi precast panel is investigated experimentally.The effectiveness of propod light weight slab is reached by comparing the behavior of specimens with that of conventional solid precast slab.The comparisons were bad on struc-tural performance and total weight reduction.The composite AAC slabs ction chon are one way slabs with a size of 1m Â3m Â0.130m (Width ÂLength ÂDepth).The specimens vary in the AAC blocks lay-outs and total weight reduction ratio.The test results showed that the AAC composite precast panel pro-vides reasonable weight reduction without sacrificing the structural capacity.
Ó2012Elvier Ltd.All rights rerved.
1.Introduction时间长
A slab structure occupies the biggest percentage of total dead load and volume for an ordinary residential structure.A simple load calculation for a residential building shows that approxi-mately 40–60%of dead load is lf weight of slab structure [1].Thus approximately 10%of lf weight reduction from floor slab may lead to 5%of lf weight reduction of entire building.More-over,it directl
y faces the live load and transfers the load to beam and columns.Clearly,more mass means higher inertia force.There-fore,lighter buildings sustain the earthquake shaking better.Under horizontal shaking of the ground,horizontal inertia forces are gen-erated at level of the mass of the structure,usually this situated at the floor levels [2].The duties increa floor slab significance and complexity.The traditional solid precast slab is found to be chal-lenging for large scale projects becau of its heavy lf weight which leads to dependency on heavier equipment,transportation difficulties,expensive connections and joints solution.In addition,heavy precast slabs needs extra temporary supports during con-struction and larger beam and column size which result in the escalation of the overall cost [3,4].
In terms of better structural performance and lower cost,the development of varieties of light weight slab has become a crucial need.The u of mi precast panels is increasing rapidly due to it is versatile solution for transportation,handling and effective joint practice.In the recent past,a large number of mi precast panel have been developed using either ferrocement or composite cold steel deck with different type of toping concrete [5–9].Insulating and light weight core panels were then developed which greatly incread the desirability of this type of construction.The panel consists of two thin skins high strength layers and elastic moduli parated by a core thick layer of n
ormally much weaker and lower material density [10–13].More than 15different types of precast slab are being ud successfully in construction market.Five gen-eral criteria has to be considered for the capacity of flooring units;bearing capacity,shear capacity,flexure;capacity,deflection lim-its,handling restriction [3].There is no system fulfilling all of the
0950-0618/$-e front matter Ó2012Elvier Ltd.All rights rerved.dx.doi/10.buildmat.2012.10.011
Corresponding author.Tel.:+355672069729;fax:+3552222117.
E-mail address:yyardim@epoka.edu.al (Y.Yardim).
above mentioned criteria.Nevertheless rearches are going on to achieve the best fit slab system for different environments and projects.
The composite slab systems were found structurally effective with thin layer of precast member taking into account of the ben-efits which include:shorter construction time,less dependent on heaver equipment on job site,less wastage of material,high quality smooth surface finish,in situ structural concrete topping and in-fill forming monolithic structures,eliminates or greatly reduces props,eliminate convention formworks [14–18].
Thinner precast structure of the composite slab could be achieved with ferrocement technology.Ferrocement provides con-siderable reduction in cracks number and their spacing (64–84%)was obrved.Additionally,it enhances the ductility and energy absorption properties [1].Ferrocement is not only an extension of reinforced concrete but also is now considered a member of the family of laminated composites,it can be reinforced with steel,or non-metallic meshes such as fiber reinforced polymeric (FRP)meshes [16].The addition of fibers or micro-fibers as condary reinforcement in the cement matrix,to improve performance,makes ferrocement a hybrid composite.Light weight mi precast composite slab systems have been practicing mostly for roof panel.Weight reduction is achieved by replacing the core of panel with low density concrete and some other type of light weight infill blocks [19,20].Different types of composite roof panel with low density infill as core element have been prac-ticed [21,22].Composition of light weight aerated concrete and fer-rocement in sandwich structure shows effective load carrying performance in some applications [23].Compared to other conven-tional wall and roof systems,AAC composite panels reduce energy consumption of buildings significantly with its excellent insulation qualities.It is considered as environmental friendly,no pollutants or toxic by AAC products are relead that could affect indoor air quality [24,25].Moreover,AAC can be obtained in any dimension,it is easy to handle which increa the construction speed,and it is widely practicing and available in construction marked.鱼多久换一次水
However,there is no significant experimental works has been recorded for mi precast slab with ferrocement precast layer and AAC as in fill material where ferrocement work as precast layer and AAC as efficient thermal insulator and light weight core element.Therefore,this paper prents one of the attempts to develop a light weight composite floor system to address the
Precast Slab
Precast Slab
In situ Concrete AAC
Precast Beam
Precast Slab Wire mesh
Steel Bar for connection
Tie Steel
Projecting steel from Beam
Steel
Reinforcement
Fig.1.Ferrocement–AAC composite Slab.
b
a
b ≥ a
a ≥ 6x or 6y
L ≥ 3a or 150mm whichever is larger
y
x
of wire–mesh.
406Y.Yardim et al./Construction and Building Materials 40(2013)405–410
requirements.This study introduces a mi-precastfloor slab sys-tem;ferrocement–AAC composite slab to address some of the above listed shortcomings in existing systems.The new system consists of a bottom ferrocement skin,AAC masonry and in situ mortar ribs(Fig.1).The ferrocement layer is the precast part of the composite slab,which consists of a wire mesh and steel rein-forcement,required to resist the tensile stress.The thickness and reinforcement of this layer will depend mainly on the span of the slab.The AAC layer and the in situ ribs provide the necessary resistance to the compressive forces developed due to bending.The two layers are interconnected using interlocking and rough surface between precast and cast in situ layers.The advantages of this sys-tem,amongst others,are its relatively lighter weight compared to R.C which will reduce the load transferred to the beams/walls.The masonry AAC act as light,effective insulation material and at the same time resisting partially the compression forces developed due to bending of the composite.On site,the construction of the composite slab does not require heavy equipments to handle the ferrocement layer.Furthermore,the construction does not need any formwork since the bottom layer of ferrocement is a precast unit that can be easilyfixed in position,using simple crane,to pro-vide a platform that acts as a formwork for the brick layer and the in situ concrete ribs.This experimental stu
dy is limited to investi-gate the structural performance of one way ferrocement–AAC com-posite slab subjected to two-lines loading.The study highlights the effects of AAC layout on its overall structural respon in terms of load–deflection characteristic,ductility,strain distribution,com-posite action and failure load.
Fig.3.Stages of construction in cross-ction view.
Y.Yardim et al./Construction and Building Materials40(2013)405–410407
2.Material
For both topping and ferrocement layer,Ordinary Portland cement in accor-dance with Type I and natural sand(10mm maximum size)were ud for concrete in the ratio1:3with water/cement ratio of0.5.The mortar mix was designed to give 28-day cube strength of30N/mm2.
Welded steel wire mesh of opening size12.7mmÂ12.7mm with an average wire diameter of1.1mm was ud.Tension test on the specimens were carried out on the Universal Testing Machine Zwick/Roell Amsler HB1000.Load was ap-plied in increments of10N.Tests were performed for direct tension on the wire mesh and embedding a rectangular coupon of mesh in mortar.Dimensions of the
tensile test specimen of wire meshes were designed bad on ACI549recommen-dation(Fig.2.).The tensile strength of the mesh and steel bar were found250N/ mm2.
Bad on specifications in BS8110for quality control of AAC(BS8110-21998 clau6.4.2),twelve100Â100Â100mm were tested to determine compressive strength of AAC.The density of aerated autoclaved concrete was found as5.8kN/ m3and saturated compressive strength of from12specimens is6N/mm2
.
Fig.4.Test t up for simply supported two line load test ries.
Load-Deflection
Load-Deflection
2.1.Specimen preparation and testing
In order to determine the behavior of composite slab under flexural,one way slab specimens with size of 1m Â3m Â0.130m (W ÂL ÂD)have been chon for investigation.Precast layouts are designed bad on,previous experimental and literature investigation.[26–28].Table 1contains dimension description and weight reductions percentages of flexural specimens.
The constructions of the specimens can be summarized in three stages:prepa-ration of precast layer,placing of AAC blocks and filling of cast-in situ topping (Fig.3).
The slab specimens have been cast on the level floor of the heavy testing struc-tural laboratory.Flexural tests were carried out on simply supported 2800mm clear span under two line loads (Fig.4).
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During flexural test,strains on the specimen were carefully studied to obrve the composite behavior of the slab panel.The electrical strain gauges and demec points were installed along the depth,at the bottom and top surface of the speci-mens on critical locations to monitor the strain throughout the experiment.The points on top of the specimens were placed in such way that relative strain or dis-placement could be monitored.Strain gage were placed on main steel bars at mid span to obrve yielding stage.
3.Result and discussions
In the experiments,ultimate flexural capacity of the propod system with different AAC layout and amount,therefore different weight reduction,was investigated.Moreover,composite action between concrete and AAC,and ductility of the specimens were studied.The crack pattern shows that the system gives enough warning before fail.Full composite behavior was obrved for the propod system until ultimate load.The specimens show classical reinforced concrete slab flexural failure characteristics and cracks were obrved between two line rods.
Load deflection curves of specimens which are having the same number of transfer ribs but different numbers of longitudinal ribs,
are shown in Fig.5.The effect of longitudinal ribs could be en clearly in the figure.Reductions of weight as compared to solid RC slab for AS (22)and AS (42)are 32%and 23%respectively,how-ever ultimate load capacities were 23kN and 33kN respectively.Therefore,30%of the ultimate load capacity of the propod slab could be upgraded with considerably small increa of weight by adding more longitudinal ribs.
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Table 2summarizes the deflections measured at the yielding and ultimate load and the ductility of each specimen.The ductility (defined as the ratio of deflection at ultimate load to the deflection at yielding load)of each precast specimen is calculated and pre-nted in the same table.All the specimens show satisfactory duc-tility above 2.4.The number of the longitudinal ribs has a significant effect on the ductility as the specimens with four longi-tudinal ribs show 61%and 29.5%increa in ductility compared to the slab specimens with two and three longitudinal ribs respectively.
The propod structure contains three layers:ferrocement,ma-sonry and concrete.Therefore,the strain depth relationship is one of the important indicators of the structure behavior.The compres-sion zone of the composite slab is combination of AAC and toping concrete.Careful strain inspection proves that the strain at the top surface of the composite slab is equal for both the toping concrete a
nd masonry unit.
Strain measurements of all the slabs were carried out.Similar results were obtained for the all specimens;only one specimen’s (AS32)strain results were prented to illustrate the behavior.Due to the load caring capacity a stronger structure bears more load with same strain.The top strains of the specimens were found to be same (Fig.6).AAC composite structures’strain along the depth relation is recorded as in Fig.7.The result were found similar
Table 2
Ultimate moment,deflection and ductility of the specimens.ID
Ultimate load (P ULT )(kN)Ultimate moment,M U (k Nm/m)M U ðExpt ÞM U ðTheor Þ
Yielding deflection o y (mm)Ultimate load
deflection o u (mm)Ductility (o u/o y)Mode of failure
Theor.
Exper.Theor.Exper.AS2124.3720.511.399.570.849.623.74 2.48Flexural AS2224.3723.011.3910.730.947.620.63 2.71Flexural AS2324.3724.011.3911.200.98 6.518.55 2.85Flexural AS3125.2325.211.7911.76 1.09.127.68 3.04Flexural AS3225.2326.511.7912.37 1.057.926.68 3.38Flexural AS3325.2327.411.7912.79 1.087.124.53 3.45Flexural AS4125.7431.212.0314.56 1.218.133.51 4.14Flexural AS4225.7433.012.0315.40 1.287.331.7 4.34Flexural AS43
25.74
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12.03
15.96
1.33
14.8
29.53
4.61Flexural
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-0.0005
0.0005
Strain
Fig.6.Load-top fiber strain diagram for AS32.
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0.005-0.004Y.Yardim et al./Construction and Building Materials 40(2013)405–410
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