Comparative Analysis of Mechanical Properties of Composite Walls Filled with Different Ecological Ma

Construction Engineering Volume 3, 2015 www.seipub.org/ce Doi: 10.14355/ce.2015.03.002

Comparative Analysis of Mechanical Properties of Composite Walls Filled with Different Ecological Materials M. Zhang*1, W. Huang 1, Z.K. Yang 1,2 College of Civil Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China College of Civil Engineering, Henan Polytechnic University, Jiaozuo 454000, China *1

mzhangsjz528@163.com; 266149154@qq.com; 394027203@qq.com

Abstract As a new system, eco‐composite wall structure is mainly constructed with pre‐cast eco‐composite wall, concealed frame and floor by means of assembling and casting. Since the existing filling materials are unable to meet the needs of research, various choices of ecological material filled in the ecological composite wall structure have become a key problem the group needs to solve. This paper mainly describes the preparation craft and the uniaxial compressive constitutive model of the building materials. Five kinds of materials filled within eco‐composite wall are analyzed and compared and the application range in the ecological composite wall structure system is given. Studies show that: ceramic blocks can be used in middle‐high rise buildings; aerated blocks and foam concrete blocks can be used in multi‐storey buildings; grass tiles can be used in low‐rise buildings; while the plaster, due to its poor ductility and durability, is not recommended for the structural system.

Keywords Aerated Concrete Block; Ceramic Block; Foam Concrete Block; Gypsum Block; Grass Brick; Twin Shear Unified Strength Theory; Constitutive Relationship

Introduction In order to adapt to the Chinaʹs basic conditions, and to satisfy the wall material innovation and building energy requirements, the group developed a new building structural system ‐ new composite wall structure which is characterized by low weight , energy‐saving, good seismic, ecological and environmental protection, energy dissipation damping, fast construction, and practically (shown as Fig.1). It is mainly constructed with precast eco‐ composite wall, concealed frame and floor by means of assembling and casting. As one of the main bearing components, the eco‐composite wall is made up of two parts, a concealed frame and a eco‐composite wall. Linking and restraining the eco‐composite wall, the concealed frame is composed of end frame columns and concealed beams. The eco‐composite wall is prefabricated with reinforced concrete frame grids and filler blocks. The beams and columns of reinforced concrete frame grids, which are called ribbed beams and ribbed columns, are small in section and reinforcement (shown as Fig.2).Along with the development of the new ecological material, the filling material of which has been changed to ecological blocks which are made by industry and agriculture wastes.

Concealed beam Floor End frame column Or Connecting column

Composite slab Connecting column

FIG.1 ECO‐COMPOSITE WALL STRUCTURE SYSTEM FIG.2 CONSTRUCTION DETAIL OF THE NEW COMPOSITE WALL

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The construction process of the precast eco‐composite wall is shown in Fig.3.

Based on early study, several kinds of ecological materials filled within composite wall have been developed and implicated [1]. But, due to the deepening and improvement of the subject, the existing fill materials have been unable to meet the needs of research. The diversified choices of materials filled in the ecological composite wall structure have become the key issue the group needs to solve. The paper mainly describes the preparation of their crafts, the uniaxial compressive constitutive model. Through the comparison of the five kinds of materials filled within composite wall, the application range in the ecological composite wall structure system is given.

(a) place the blocks (b) bind the steel bar (c) set up template (d) pouring concrete FIG.3 CONSTRUCTION PROCESS OF THE PRECAST ECO‐COMPOSITE WALL TAB.1 1M3 CONCRETE MIX PROPORTION (KG)

Intensity level LC30

Cement 340

Fly ash 50

Sand 525

Aggregate 975

Admixtures 5.9

Water 160

Experimental procedure Aerated Concrete Block The design mix of the material is shown in Tab.1.

The preparation process of aerated concrete block is shown in Fig. 4. The constitutive model of the aerated concrete block (bulk density of 5.8 KN/m3) is obtained [2, 3], shown as Fig. 5 .

1 .2

Preparation of siliceous material Preparation of calcium material





Conditioning agent, & Foaming agent

JQK-1 JQK-2 JQK-3 Fitting curve

1 .0 0 .8 0 .6

Mixing& Stirring

Casting& Foaming

Stand for a certain length of time & perform the cut

Steam with high temperature and high pressure

0 .4 0 .2 0 .0

0

1

2  3 

4

5

FIG.4 PREPARATION PROCESS OF AERATED CONCRETE BLOCK FIG.5 CONSTITUTIVE RELATION OF AERATED BLOCKS

The mathematical expression of stress‐strain relationship of aerated block is obtained:

   b [1.12(    0 [1.40(    0 [4.16  6.63(

 )  0.03] b

0     b (1)

 2  )  3.15( )  0.75] 0 0

 b     0 (2)

     )  4.91( ) 2  1.75( )3  0.30( ) 4  0.02( )5 ]  0     u (3) 0 0 0 0 0

where  b  0.75MPa ,  0  1.75MPa ,  b  0.0005 ,  0  0.0025 ,  u  0.004 ,  b ,  0 are scale limit stress and peak stress of aerated block respectively;  b ,  0 and  u are the size limit stress and peak stress of aerated block respectively.

Ceramsite Block The design mix of the material reference literature [4]and[5].

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The preparation process is shown as Fig.6. Experimental contrast analysis is done between ceramsite concrete block and ordinary concrete, and a corresponding adjustment of the descent stage of the LWAC constitutive model in Technical specification for lightweight aggregate concrete structures. Comparative analysis showed that ceramsite concrete and ordinary concrete were basic unanimously, except that the normal concrete was destroyed by the interface between coarse aggregate and mortar, while the ceramsite concrete was aggregate fracturing ceramsite concrete. The cause of this phenomenon is that the strength of the ceramsite is much lower than that of coarse aggregate [4].

Ceramsite block constitutive model of rising curve is based on the Technical specification for lightweight aggregate concrete structures (JGJ52‐2002) [5] while the expression of decline curve is based on literature [4].

   0 [1.5(   0   (

  )  0.5( ) 2 ] 0 0

   2 ) 1  b( )  ( ) 0 0 0

   0 (4)  0     u (5)

where  0  1.96MPa ,  0 =0.0022 ,  u =0.0038 ,  and b and can be obtained through experiments, and the higher the concrete strength grade is , the smaller the value  , b will be ;  0 ,  0 ,  u are the ceramsite block of peak stress, peak strain, ultimate compressive strain respectively.

Fig. 7 shows the comparison between the test fitting constitutive model and the standard model, in which we can see that two models match better in the rising period, but the standard model does not give a decline curve changes, which remains to be further perfect.

1.2

Fly ash & cement

Mixing & Balling

Test data Standard model

1.0



Into the mould



Slag

Binder

High-temperature roasting

Mold release and maintenance

0.8 0.6 0.4 0.2

Ceramsite

0.0

0

2  3 

1

4

5

FIG.6 PREPARATION PROCESS OF CERAMIC BLOCK FIG.7 COMPARISON OF EXPERIMENTAL MODEL AND STANDARD MODEL

Lightweight Foam Concrete Block The design mix of the material reference literature [6].

The preparation process of prefabricated foam mixing method is shown in Fig. 8. According to the test data uniaxial compressive stress‐strain fitting curve of foam concrete block can be obtained (shown as Fig. 9) [6].

1.2

P M -1 P M -2 F itting curve

Preparation of foaming agent Preparation of cement mortar





1.0

Mixing & Stirring

Concreting and vibrating

0.8 0.6

Mold release and maintenance

0.4 0.2 0.0

0

1

2  3 

4

5

FIG.8 PREPARATION PROCESS OF LIGHTWEIGHT FOAM CONCRETE BLOCK FIG.9 COMPRESSIVE STRESS –STRAIN CURVE OF FOAM CONCRETE

The compression stress‐strain mathematical expression of foam concrete is given:

 = 0 [2(

     )  1.1( ) 2  1.7( )3  3.8( ) 4  2( )5 ] 0 0 0 0 0

0     0 (6)

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   0 [5.2  3.7(

  )] [1  7.9( )]  0     u (7) 0 0

where  0  1.7 MPa ,  0  0.003 ,  u  0.006 ;  0 is the peak stress of the foam concrete;  0 ,  u ,are the peak strain and ultimate compressive strain of the foamed concrete respectively.

Gypsum Block The design mix of the material reference literature [7].

Different material mixture ratio and volume with different strength grade of gypsum block quality can be prepared, taking the quality volume of 650 kg/m3 of gypsum block [7]as an example: The preparation process is shown in Fig. 10. A reasonable constitutive model of gypsum and its mathematical expression are gotten [8~9].(shown as Fig.11) TAB.2 BASIC PHYSICAL AND MECHANICAL PROPERTIES OF THE GYPSUM BLOCK

Items

Bulk density (kg/m3)

Bending strength (MPa)

Compressive strength(MPa)

Tensile strength (MPa)

Softening coefficient

Performance indicators

650

4.0

9.0

2.0

≥0.5

Thermal Nail Sound insulation conductivity hanging performance (m3∙k/w) load 0.107

45.71

40

1.2 

1.0 0.8

Water Gypsum powder Additive

Mixing & Stirring

0.6

Casting & Molding

Mold release

0.4

Stoving and maintenance

0.2

0.0 0.0

0.5

1.0

1.5



2.0

2.5

FIG.10 PREPARATION PROCESS OF GYPSUM BLOCK FIG.11 STRESS‐STRAIN CURVE OF GYPSUM BLOCK

The fitting curve is :    0 [3.04(

 4    )  8.33( )3  7.31( ) 2  2.79( )] 0     u (8) 0 0 0 0

Where,  0  5.0 MPa ,  0  0.00166 ,  u  0.0025 ;  0 ,  0 ,  u are the peak stress, peak strain, ultimate compressive strain of the gypsum block respectively.

Grass brick The design mix of the material reference literature [10].

The preparation process is shown in Fig. 12. The uniaxial compression dimensionless constitutive relation curve of grass block is obtained as shown in Fig.13[10].

M G -1 M G -2 M G -3 Fitting curve

Crush cotton straw

Deal straw surface with glue

Mixing with fiber & Into the mold



1.2 1.0 0.8 0.6 0.4

Mold release and cut

Stand for 24 hours with pressure

0.2

Vibrating

0.0 0.0

0.5

1.0

1.5

 

2.0

2.5

FIG.12 PREPARATION PROCESS OF GRASS BRICK FIG.13 STRESS ‐ STRAIN CURVE OF GRASS BRICK

After getting the uniaxial compression dimensionless constitutive relation curve of grass block, the constitutive relation of the grass brick mathematical formula is obtained:

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   b [1.46(    0 [0.24(

 )  0.014] 0     b (9) b

 6      )  1.82( )5  5.23( ) 4  6.66( )3  2.62( )2  1.49( )]  b     u (10) 0 0 0 0 0 0

where  b  0.7 MPa ,  0  1.4MPa ,  b  0.025 ,  0  0.0573 ,  u  0.1154 ;  b and  0 are the proportion limit stress and peak stress of grass brick respectively;  b ,  0 and  u are the elastic limit of compressive strain, the peak strain and ultimate compressive strain of the block respectively.

Results and discussion Strength theory, under the complex stress state, generally refers to the regularity of plastic yield or brittle fracture theory, and twin shear stress unified strength theory, starting from the twin shearelement, which will consider the effect of intermediate stress on the material. Its practical significance lies in that the deepening unified strength theory can be applied to different types of materials while the old strength theory only could be applied to a single material strength theory in the past. Based on research, the group provides an effective unity solution for the ecological composite wall structure filled with different materials. Fig. 14 is twin shear element model proposed by Professor Yu Mao‐hong [11,12].

FIG.14 TWIN SHEAR ELEMENT MODEL

The mathematic expression of the unified strength theory is: F  1 

F 

 1 b

 b 2   3    t , when  2 

 1   3 , (1) 1 

   3 1 , (2) 1  b 2    3   t , when  2  1 1  1 b

where  1 ,  2 and  3 are the three principal stress respectively;    t /  c is the tension‐compression strength ratio;

 c and  t are the uniaxial compression strength and uniaxial tensile strength respectively; b reflects the material damage impacted by middle main shear stress and normal stress.

If the material strength parameters  and b is confirmed, then a suitable materialʹs yield criterion can be determined. The strength parameters  and b of the five kinds of materials is obtained, as shown in Tab.3.

TAB.3 STRENGTH PARAMETERS OF THE ECOLOGICAL BLOCKS

Parameters Blocks Aerated concrete block Ceramic block Foam concrete block Gypsum block Grass brick

fc

ft

/ MPa 4.0~5.0 5.3~8.1 2.5~7.5 8.8~10.0 2.5~3.8

/ MPa 0.4~0.55 0.5~0.85 0.2~0.8 0.6~2.0 0.2~0.35



b

0.1~0.11 0.09~0.1 0.08~0.11 0.06~0.2 0.09~0.1

0.25~0.5 0.25~0.6 0.3~0.5 0.5~0.8 0.3~0.5

Based on the early theory [1,13,14], if the uniaxial constitutive equation of materials is known, the material yield hardening function of expression is obtained, the incremental elastoplastic stress‐strain relationship corresponding to different yield function could be gotten and then the resulting incremental elastoplastic stiffness matrix could also be obtained. The multiaxial elastic‐plastic incremental stress‐strain relation is given:

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d{ }  [ D]ep d{ } (3)

where [ D]ep is incremental elastoplastic stiffness matrix, which can be represented as T  Q   F  [ D]  [ D] e           e     (4) [ D]  [ D]  ep T  F   Q  A   [ D]e            

where F or F ' is yield function; Q or Q ' is plastic potential function; A is a function of hardening parameter K ,and K can be represented as plastic deformation of plastic work:

dK   1d 1p   2 d  2p      d   p    d  T

A

T

F (5)   

F 1 F T   F  dK       (6) K d  K     

Under uniaxial stress state, A can be calculated by using the slope of uniaxial constitutive model that obtained before: A

d 1 ET   (7) d   d  e d  d  e 1  ET  E d d

Through the preceding analysis and derivation, after hardening function A , the corresponding incremental elastoplastic stress‐strain relationship can be gotten, then the elastoplastic stiffness matrix material can be obtained.

Nonlinear numerical analysis Tab.4 is the dimensions, reinforcement of the ABAQUS finite element model( as shown as Fig. 15), the concrete strenght of the frame and the rid grid is C30.

TAB.4 STRENGTH PARAMETERS OF THE ECOLOGICAL BLOCKS

dimensions /mm Length, height, thickness of wall Frame Frame Rid Rid /mm beam column beam column 1400×1440×200

100

100

50

Frame reinforcement

Rib grid reinforcement

Frame beam

Frame column

Stirrups

Rid beam

Rid column

Stirrups

4ф6

4ф6

ф4＠100

4ф4

4ф4

ф2＠100

50

Based on unified strength theory, by using ABAQUS UMAT subroutine, the P ‐ Δ curve of ecological composite wall filled with different material is obtained respectively by using finite element analysis. To facilitate the comparison and analysis, the five kinds of wall panels of P ‐ Δ curve are fitted under the same coordinate system (shown as Fig.16).

200 (kN)

Gypsum block Geramic block Foam block Aerated concrete block Grass brick

150

100

50

0

0

5

10

15

20

25

30 (mm)

FIG.15 ABAQUS FINITE ELEMENT MODEL FIG.16 P‐Δ CURVE COMPARISON OF COMPOSITE WALL

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Fig. 14 shows that: 1) The P ‐ Δ curve has no obvious turning point calculated by finite element method. It failed to simulate the decline part of the curve effectively due to the large number of cracking destruction in concrete and block in loading late.

2) The composite wall is regard as absolute rigid body in finite element model without taking damage factors in the actual situation , the flat‐fell seam between the blocks and bonding sash ‐ slip effect into consideration, therefore, calculated value tends to be greater than the relevant test value.

3) Having a moderate intensity, ceramsite block, and aerated block, foam concrete block can match the outer sash, and after the combination with outer sash the internal force, deformation development process of composite wall can be simulated truly. As the displacement increases gradually,the curve is more and more gentle, which shows that the stiffness degradation is in conformity with the previous experimental results.

According to the requirements of strength, ductility and durability, the applicability of various blocks filled in ecological composite wall structure is shown in Tab. 5.

TAB.5 APPLICATION SCOPE OF BLOCK

Materials

Ceramic block

Scope of application

middle‐high level

Aerated concrete block

Foam concrete block

multi‐storey

Grass brick

Gypsum block

low‐rise

—

Conclusions Based on the analytical and experimental investigations presented in this paper, the following conclusions may be made.

(1) With the properties of qualitative light, moderate intensity, and matching the outer frame structure performance, ceramic block can be used for middle‐high level ecological composite wall structure; (2) The aerated block and foam concrete block can be used in the multi‐layer ecological composite wall structure based on its strength and ductility requirements; (3) The grass brick, with its strength, durability and geographical limitations, is recommended for low‐rise ecological composite wall structure in villages and towns; (4) Gypsum block is not recommended in the ecological composite wall structure, because of its poor ductility and durability.

ACKNOWLEDGMENT

The authors gratefully acknowledge the financial support provided by the National Natural Science Foundation of China (51378416), National Twelfth 5‐year Scientific Support Program(2012BAJ16B02‐04)and Natural Science Foundation of Shaanxi Province of China(2013JK0986).

REFERENCES

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M.Zhang , born in Hebei Province on Nov. 6, 1988. She graduated from Huaqing College of Xiʹan University of Architecture and Tecnology, and get a bachelorʹs degree in civil engineering in July 2011; in June 2014, she graduated from Xiʹan University of Architecture and Tecnology, Disaster Prevention & Mitigation and Protection Engineering, received her Master degree. Now, she is Pursuing her Ph.D on Structural Engineering at Xiʹan University of Architecture and Tecnology. She’s current research is the new architecture and new materials.

W. Huang , born in Shaanxi Province on Dec. 1, 1975. He graduated from Xiʹan Jiaotong University School of industrial and civil construction force a bachelorʹs degree in engineering in june 1998;In June 2004, he graduated from Xiʹan University of Architecture & Civil Engineering, Structural Engineering, received his Ph.D. Prof.Huang, vice chairman of Shaanxi Province Earthquake Engineering Society of Civil Engineering Professional Committee, had been awarded for National Science and Technology Progress award in 2009 and provincial Science and Technology Progress award in 2008 and 2009.

Z.K. Yang , born in Henan Province on Jul. 24, 1983. In June 2006, she graduated from Henan University of Technology School of Civil Engineering Management, Bachelor of Engineering; in June 2009, graduated from Xiʹan University of Architecture and Civil Engineering, Civil Engineering Technology and Management, Master of Engineering; since2013 Sep, she is pursuing a Ph.D on Disaster Prevention & Mitigation and Protection Engineering in Xiʹan University of Architecture and Technology.

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