CIB TG 16, Suslainable Conslruclion , Tamp., F1orida, USA, November 6-9, 1994 .

NEWLY DEVELOPED REINFORCED MASONRY STRUCTURES SUITABLE FOR GLOBAL ENVIRONMENTAL REQUIREMENTS

Miho Makatayama*, Akio Baba*, Naoji Hasegawa*, and Osamu Senbu** * Building Research Institute, MOC(Govemment), Tsukuba, Ibaraki, 305 Japan **Hokkaido University, Sapporo, Hokkaido, 060 Japan

Introduction

Disposing of and reducing construction waste has become a serious problem. Because of environmental considerations, it is anticipated that plywood will not be able to be used as sheathing panels in formworks for reinforced concrete construction in Japan in the near future. As a substitute, a small modular permanent cast formwork system, using a new type of bond beam masonry units has been developed specifically for medium and low rise residential buildings. This type of building system, a combination of reinforccd concrete and masonry, has been developed and studied under a joint Japanese and American research project on earthquake resistant structures .

This paper introduces several new types of reinforced masonry structures. It also examines the positive environmental implications of these masonry construction methods due to the increased physical life time of the buildings, earth conscious materials, and decreased construction waste.

Reinforced Masonry Construction

1. RM structure system

RM structures are a kind of composite structure of masonry and reinforced concrete as shown in Figure 1. Walls and beams are composed of both concrete or ceramic masonry bond beam units and reinforced concrete. Floor and roof slabs are usually reinforced concrete. The RM construction system can be regarded as a newly developed method for reinforced concrete structures with standardized concrete or ceramic units with high quality, produced in factories . This construction method is similar to a conventional wall type reinforced concrete construction system. The newly developed masonry structures introduced herein have walls and beams constructed with ccmentitious grout and reinforcing bars. Slabs are of conventional reinforced concrete construction or new floor system utilizing thin steel or inorganic deck.

As a newly developed reinforced masonry construction system, that is to say RM construction compares favorably with conventional systems with plywood sheathing panels in the following items:

(1) aseismic fire resistance buildings equal to wall type reinforced concrete constructions (2) high durability equal to traditional clay brick and stone masonry (3) construction efficiency and reliability, and applicable to small areas without large crane

and scaffolding (4) fine exterior of buildings with dimensional preciseness and exccllent appearance (5) lower cost

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Figure 1. A Coucept or RM Construclion

2. A new construction system for alleviating environrnental problems

Wall type reinforced concrete structures are said to be suited for residential buildings in Japan. Unfortunately, this method involves the use of [arge amounts of plywood as sheathing panels for the reinforced conCrete. Using plywood causes environrnental degradation through deforestation of tropical rain forests while old discarded panels are a main factor in increased construction wastes. Therefore, it is imperative that a new construction system be developed to reduce plywood use and construction wastes. At the same time, it is necessary to increase the durability of buildings througb better construction methods to increase their physical lives.

The RM construction system is one of the most effective countermeasures for solving these problems. It is regarded as a newly developed reinforced concrete construction method with small size factory produced units, which is called RM units. It has merits for the following reasons;

(1) no use of plywood (2) reducing construction wastes (3) increasing durability

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3. Basic construction concepts

RM construction systems have originally been developed for construction rationalization. In order to improve construction efficiency, it was considered that the computer integrated systems shall be applied to design, material production and construction. Therefore, RM construction methods are systemized and standardized about designing, producing units, and construction. The characteristics mentioned above could be realized as shown in Table 1. RM construction systems are introduced in relation to environmental problems, reducing construction waste, and prolongation of the physical lifc time.

Table 1. Fundamental Requiremeots and Targets of Development for

Reinforced Masonry Construclion Systems

No. Items Requirements Presenl Target Reguired techniques

Conceming eondition

Materials All members are prefabricated Effedive palettlllg

precisel y in dimension, 01 systems, ami Self­

which connections are simple

devised in aceordance with o @ stabil ized joint

(Casting Joint)

robotics construetions

2 Wu rk ing

Proeedure

Lifting and installing are

perfonned by rabots x o Standardization, and

Developments of

constructiun robuts

3 Ditto Qual ity contral and adjustments Preparing const ruet tun

in installing are perfonned by x o manuals

labors

4 Working Clean working environments tu Nun suppnrL~ fur@Condition utilized robots effeL1ively fOlm wnrks

5

6

7

8

Preeiseness

Conslruction

Proeess

Ditto

Conditions

of site

Dimensional preciseness ur

structural bodics and a bes t

l:llndition can be kepl by robuls

Finishing ami equipments wurks can be set up early after a eyde

of strueturaJ construL1ion proL-eSS

One eyde of SlruL1urai construction

process can be perfonned in 5 days

Constructions can be perfonned

even in very much' populated area

without any disturbance to

x

o o

@

@

@

@

Casting juint with

inter rll<:king type

Non suppans tur

flllmwllrks

Opt imization of

COllstruction systems

neighbors and traftle

9 CunstruL1ion A multifunC1ionai group call eons1ruL1 @

throughout structural umsl ruelion

10 Wasle Reducing wasle and nOIl use plywood Computer integraledo @ manufaeturing

(Nole) @ : suffieienl, 0: enough, 6: insut'fieienl, X : impossibility

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Modular Coordination

RM structures are of systemized reinforced concrete construction with walls and beams constructed by using standardized RM masonry units. Masonry structures are the most popular construction system for residence in the U.5.A., N.Z. , and m<lny other countries. However, this type of system still has problems to be spread in rainy regions such as Japan. The major problem is preventing water leakage through the vertical joints of the units. Special honding panerns developed in Japan under the cooperative project are introduced herein to alleviate these problems.

The fundamentals of the newly developed bonding systems for reinforced masonry buildings are shown as folIows.

(1) Usage of open end units to avoid any web to web joints (2) Modular coordination in spacing between walls (3) Modular coordination in wall and opening sizes (4) Modular coordination in spacing between reinforcing bars (5) Running bonding in all the wall parts including wall connections (6) Minimum number of special units especially partially cut units

To satisfy the six items mentioned above, three shapes of RM units are proposed as shown in Figure 2. The most important point of this standard honding is to form square grids for vertical reinforcing as shown in Figure 3.

Conceming about the first item, standard shapes of RM units are designed with two open ends, and special corner RM units have one open and the other closed end as shown in Figure 2. This design provides waterproof in vertical joints by backing up the joint with grout. These are indispensable bonding principles for using masonry in rainy regions.

Standard Special B Special A

h~tjr-'-I( rt:d ~.:, T-j/Z T ]T-j/Z IT/Z I 3T/Z I

ZT-j 1 '/z 'I'L=ZT ,

Figure 2. A Typical Example of The Shape of Newly Developed RM Block

In order to satisfy the items, units shall be coordinated in three dimensions based on the fundamental unit module (MI). This unit module can be called the fundamental module length. Based on this unit module of RM, sizes of huildings and components can be designed easily and systematically. Table 2 shows the modular size of standard RM units in relation to the types of the fundamental module. Importantly, using this principle, the outer RM skin of buildings could be produced in factories. RM structures will be a kind of complete building system to improve the quality and reliability of the construction processes.

Many types of bonding panerns can he developed for thc specially shaped RM units for wall COrners and special wall parts such as windows, doors and other openings. To manuf<lcture RM units efficiently, the number of special RM units should he minimized. For

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the three systems deveJoped under the joint research project, one or two specially designed RM units generally are considered needed as shown in Figure 4.

II I

II

IFFU- -l!:f!l

- -

-

-

I II

Figure 3. An Example of Booding Patterns

Table 2. Size of Standard Units Spacing of Wall Type of Modular l1ückness Uni! Module for Uni! Module for

Bonding of walls, T (mm) LengUl of Walls Spacing of Re-bars,

Systems and Opellings. P (mm)

ML (mm)

121'ype 150,200.225,250,300 T T

23Type 150,200,266.6,300 3/4T 3/4T

C Type 150,200,225,250,300 T 3/4T

12 Type 23 Type CType

Figure 4. Shape of RM Blocks for New Bonding Systems

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Method for Prolonging the Physical Life of Buildings

The physical life time of reinforced masonry buildings is determined mainly hy the corrosion initiation of reinforcements. In normal circumstance, the carbonation of grout concrete and the protective function of face shells against this degradation are very important · for preventing reinforcements from rusting. Considering this, the carbonation coefficient and thickness of cover for reinforcements, including face shells, are important factors for the durability design of reinforced masonry buildings .

In the case of reinforced concrete buildings because of insufficient cu ring, the quality of surface concrete is sometimes so poor that the carbonat ion rate is consequently very high. Reinforced masonry buildings with good quality faces have great merits because of stahle quality made by factory. Unfortunately , the effect of face shells and their lJuality is not sufficiently considered in the Japanese construction specifications at present.

Carbonation of concrete is a chemical reaction of calcium hydroxide with carhon dioxide, The process can be considered as a complex diffusion due to hoth the inward diffusion of CO2 gas into the concrete from the surface, and the outward diffusion of Hp caused by the reaction. At present , it is difficult to explain this complicated process involving the effects on c1ay and concrete units.

/[\

1\

D=Afj'FFace Shell -------. ______ _

c _­.9 ,/ ~ ,.,/ C .,­o .,-

Grout --..... D=Acrr~ a

/---­"'- for non-cementitious Ls,~ Df Ij

0.. 1

es ~.Df'jr v- for cementitious f.s. "

Tl-Dfa2 fAf2 _R2

Exposure Time

Figure 5. A Theoretical Model of Clirbonation ror Grout Concrete or Masonry

lt is generally accepted that the rate of carbonat ion obeys the following equation: D=A xJT (1)

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where, 0 is the depth of carbonation A is the carbonation coefficient T is the exposure time

Using this equation, the simple model shown in Figure 5 was examined as part of this study. This model explains the carbonation of a concrete, such as grout, in masonry through a dissimilar surface layer such as face shells.

To examine the process of carbonation for inner concrete, two types of surface layers were considered:

Type 1. Surface concrete with different property (Concrete RM) Type 2. Non-cementitious face shells ~Ceramic RM)

Surface concrete with poor cu ring and concrete impregnated with various materials is contained in type 1. Face shells of grouted concrete units masonry buildings. Face shells of grouted day masonry buildings are contained in type 2.

In the case of types 1, inner concrete began to carbonate after the surface layer carbonated completely. In the case of carbonation of inner concrete through a surface layer, a plot of the carbonation depth versus exposure time (Off) falls on the same line as a plot of Off of the same concrete without any surface layer. According to previous studies using a time equivalent assumption, the Off line of carbonation of inner concrete through the surface layer beg ins at the time when the surface layer carbonates completely. The Off line of type 2 is considered parallel to the line for type 1, but showing an imaginary faster rate of carbonat ion. According to these results, the following equations can be proposed .

1) For type 1 T 1=(OfJAf)2 =R2 (2) T;;;;T1 :O=Af/F T;;:;T1 :Ac (,fF-R)+Ofo

2) For type 2 O=Ac (jftRT -R)+Ofo (3)

where, 0 is the Oepth of carbonation from the surface (mm) Ac is the Carbonation coefficient of inner concrete (mm/dai 12

) 2R=Dfo/Af (or Dfo IAn , R2 =T1

Af is the Carbonation coefficient of surface layer (mm/d ay J/2 )

Af*is the Imaginary carbonat ion coefficient of surface layer (mm/dai/2 ) R , which shall be named the carbonation resistance, can be determined by the

thickness of the material and quality of the surface layer. Using these values, the carbonat ion depth at any time can be ealculated.

Figure 6 shows the comparison of both the experimental results and the theoretical calculations based on Equation (2) and the effective thickness, Oe, of unit face shells can be determined as (Ac/Af)·Ofo. As shown in Figure 6, the carbonat ion depth of masonry which have various unit strength can be calculated rationally, the high strength masonry units would effectively prolong the physical life time. Therefore, using high quality units made in factories, durability of RM construction will improve remarkable.

Conclusion

Many difficult aspects of environmental problems are now under discussion. Recently,

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the newly developed RM construction system is introduced from the view point of environmental considerations. This paper suggests that RM construction is important in the three environmental aspects; The reduction of construction wastes, the reduction of plywood use during construction and the prolongation of physical life time due to the improvement in quality of units.

70 ,..--. 8 60E

'--' 0

.9 50 ~ 0

.0 0 40 .... Ü 30 4-< 0

.0 20P.. (l)

Cl 10

0 10 20 30 40

Akio Baba , el al. ,1987: Development of bondiug s)'slem for reinforced masonry buildings with open end units ,3rd

JTCCMR

Osamu Senbu , ct al. ,1988: Improving durability of reinforced masonry bui/dings by betler qu alily standards for groul

and ma50nry units, 8th lrlfemarianal BrickiBlack Masanry Canference

Akio Baba,1988: Acceleraled carbonalion and poss ible approach to prediclion of service life of concrele masonr)'. BRl Research Paper Na.} 26

\ \ \ \

\ ,,,,A ,

Thickness of Face shell 28mm

Compressive Strength of Graut 27.7MPa

A 150days • 60days

50 Compressive Strength of Face Materials(MPa) Ft

Figure 6. Relationship between carbonation depth and compressive strength of face shell

References

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