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Proceeding the 6th Civil Engineering Conference in Asia Region: Embracing the Future through

Sustainability

ISBN 978-602-8605-08-3

SEMI PRECAST SLAB AS AN ALTERNATIVEMETHOD TO PROMOTE GREEN CONSTRUCTION IN

RESIDENTIAL HOUSE PROJECT

Suprapto Siswosukarto

Structural Laboratory, Civil and Environmental Engineering Department,

Engineering Faculty, Gadjah Mada University

E-mail: dhomase@yahoo.com

ABSTRACT

The increasing trend on residential house built as two storey floors or more means the need for a more

efficient of slab construction method. The conventional wooden formwork is considered uneconomical

for its expensive cost of materials and labor, longer construction time, and most importantly for producing

significant amount waste of wooden formwork. As an alternative method for slab construction onresidential houses, semi-precast slab is introduced. The slab concreting work is divided into two stages,namely half slab thickness concrete precast and in-situ concrete works. The semi-precast component is

made into panels of similar width provided with two equally spaced longitudinal bars. The semi-precast

method is designed as such so that all the construction sequences can be carried out by common labour.

The methods have been successfully implemented in many residential houses projects. Well performance

of slab structural behavior was observed both in the site projects and laboratory work. In addition, lesserwooden formwork was needed and relatively shorter slab construction time was achieved.

Keywords: Concrete, Construction, Semi-Precast, Slab, Panel.

PRELIMINARY

There is an increase in trend on residential house built as two storey floors or more. This means that there

is a need of a more efficient of slab construction method. The application of conventional constructionmethod elaborating wooden formwork can be considered uneconomical due to the following reasons. The

construction of wooden formwork requires wood, bamboo, wooden panel, etc. at certain quantitiesdepending the area of the floor to be constructed. The larger the floor area the more materials will be

needed. The construction also demands the involvement of some wooden skills labor and take time for the

construction to be completed. These means that traditional concrete floor construction method need more

cash for materials and labors. Another disadvantages of this construction method is the production of

significant wooden formwork waste when construction completed. When more multistory residential

house are built there will be in need of more wood and bamboo and, hence more wooden waste formworkto be produced. This situation might be in contrast with the wood preservation program to combat global

warming.

As an attempt to solve this problem, the semi-precast slab construction method is introduced. Semi-

precast concrete slab is not a new system in concrete construction slab method. This system has been

extensively developed in the world of construction buildings and bridges. However, its application onconstruction of multistory residential house has not been as widespread as that in building construction.

Even so, some developers have introduced and implemented semi-precast system on the housing project.

One of them is the lantai keraton flooring system that consists of continuation of composite concrete

ceramics floor (http://lantaikeraton.com/). The flooring system consists of an array of ceramic panels and

is reinforced with steel bars and concrete mortar. This slab system is claimed to have equivalent strength

to that of monolithic concrete floor. Another semi precast concrete slab product is called baliton thatconsists of an arranged of concrete panels, each panel having dimension of 20 cm wide and 12 cm thick

(http://infiniti.indo-network.co.id/497571/balok-lantai-instan-beton.htm ). There is also a precast concrete

flooring products where the concrete slab system is divided into short segments

(http://natapersada.indonetwork.co.id/1493443/lantai-beton-pracetak.htm). There are many others precast

concrete products available, however, it seems that, in general, the precast concrete flooring system has

not gained enough popularity among people in society. The general public seems still to be reluctant to

adopt the precast system in the construction of their house. One reasons for this might be due to the

http://infiniti.indo-network.co.id/497571http://infiniti.indo-network.co.id/497571

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understanding that concrete precast system is always associated with a complex construction system, the

need of heavy construction machinery as well as high construction cost. For that reason, a semi precast

concrete slab system is introduced. The construction system is easy and can be carried out entirely bylocal labor without the need of heavy equipments.

SEMI-PRECAST CONCRETE SLAB CONCEPT

In general, the semi-precast concrete slab system consists of two components, namely 1) precast concrete

slab panel, also serve as formwork and 2) cast in place (in-situ) concrete component. The size of precast

panels is determined taking into account the capability of the workforce in the field. Since no heavy

machinery involved in the construction, the dimension of each precast panels will be dictated by the limit

weight of concrete panel the masons capable to lift. Therefore, the dimension of the precast panel is set to

have width of 200mm and 60mm thick, the panel length follows the width of slab. On the basis of this

dimension, the calculations show that for panel span of 3m - 3.5m, the precast concrete panel would gain

self-weight for 90kg -100kg. This slab panel weight is still within the capacity limits of weight that the

masons can lift in a group of 2 to 4 people. Figure 1 illustrates the semi-precast concrete slab components.

Fig. 1: Semi-precast concrete slab components

Each precast concrete panel is reinforced with two 8mm reinforcing plain bars which is extended at eachpanel ends to provide anchorages system. The number of precast concrete panel depends on the size of

the concrete floor to be made, for larger floor, more precast concrete panels will be needed. When the

arranged of precast concrete panels is already in place, in situ concreting will be carried out on top of its

surfaces. To maintain composite action between precast concrete panel and in-situ concrete component,

a system of shear connector is provided in the precast panels. To determine the reliability of the semi-

precast concrete slab system, a series of static load test was conducted in the laboratory. Testing was

conducted to simulate the field conditions of the semi-precast concrete slab. The test aims to investigatethe mechanical behavior of semi precast system in comparison to monolithic slab actions under loading.

The slab capacity to support load and its stiffness behavior under loading would be of interest parameters.

LABORATORY TESTING

The laboratory tests were conducted on full scale specimens of concrete slab model that could be divided

into two groups of slab model, namely monolithic model (PM) and semi-precast model (PK). The clean

length of the specimens is 3,000 mm and total slab thickness of 120 mm. The dimension of each precast

concrete slab panels was 60x200x3.000mm. Each precast concrete panel was reinforced with 2

longitudinal bar of 8 mm diameter placed in the middle section and 100mm distance apart. BJ37 steel

reinforcing bar withfyof 240 MPa and concrete strength of 15MPa were adopted in research. Low quality

of concrete was used in order to simulate the common concreting practice of in society.

Fig. 2: Schematic illustration of concrete panel and its bars reinforcement

Components of semi precast slab

1.

Support beams2. Precast concrete panel3. In situ concrete

3D illustration concrete panel

Arrangement of steel bars in panel

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Once precast concrete panels installed at its placed, the top reinforcing steel bars of 8mm diameter were

mounted on the surface of the precast panels. The steel bars spacing was 200mm. After completion of

arranging the steel bars, in-situ concreting followed. Figure 2 presents the schematic illustration ofconcrete panel and arrangement of its steel reinforcement. Meanwhile, Figure 3 illustrates the condition

of semi-precast slab and monolithic slab. Testing was performed after the in-situ concrete component

reached the age of 28 days. Loading system was carried out in two stages, namely 1) repetitive elasticloading followed by 2) loading that lead to collapsing the concrete slab specimens. Repetitive elastic

loading is carried out to simulate the action of live load on the floor. The magnitude of the repetitive

elastic load was limited to less than 30% f'c. The slab performance is measured based on the characteristic

of slab stiffness at each loading cycle. After completion of repetitive elastic testing, similar specimen is

loaded further until its collapsed. This later test was intended to determine the maximum capacity of the

concrete slab specimens. Schematic arrangement of testing for slab specimens is presented in Figure 4.

Fig. 3: Illustration of slab condition for semi-precast slab (left) and monolithic slab

(right)

Fig. 4: Schematic arrangement of testing frame and instrumentation

TEST EXECUTION

Tests conducted in the Structural Laboratory, Civil and Environmental Engineering Department, Faculty

of Engineering, Gadjah Mada University. The slab specimen was treated to have fixed support at bothends. This was elaborated by placing tension bar connecting both supports that was equipped with

adjustment bolt. As previously mentioned, the testing was carried out in two stages of loading. The load

was applied through hydraulic jack and recorded by load cell connected to data logger. Specimen

deformation under loading was monitored through series of LVDT mounted in the testing frame and also

connected to data logger. The first stage of repeated static loading, the load was gradually applied up to

about 15% of ultimate load and then the load was released. After a few minutes pause, the load was again

gradually applied until it reaches 15% of ultimate load and then being removed. Similar testing procedure

specimen

Pin

support

Roller support

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0

200

400

600

800

1000

1200

1400

0 0.5 1 1.5 2 2.5

Lendutan (mm)

Beban(N)

;

was repeated for 10 times. Following the completion of the first stages of testing, the second stage test

was performed where loading was gradually applied until the specimen reached its maximum capacity

and collapsed. Figure 5 shows the preparation of test on slab model width of 600mm.

Fig. 5: Test preparation on slab model width of 600mm

RESULTS AND DISCUSSION

From the results of repeated elastic load testing on concrete slab model, the relationship between appliedforced and deformation for each load cycle is obtained. From this relationship the magnitude of stiffness

of concrete slab model at every cycle can be determined. The result of the calculated stiffness of concrete

slab width of 200mm for both monolithic and semi-precast is presented in Figure 6 for monolithic slab

(left) and for semi-precast slab (right). Different specimen width of 400mm and 600mm were also tested,

but due to limited space for presenting data only one series of specimen width of 200mm is available.

0

200

400

600

800

1000

1200

1400

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Lendutan (mm)

Beban(N)

Fig. 6: The calculated stiffness of each cycle for monolithic slab (left) and semi-

precast slab (right)

Figure 6 indicates that there is no significant difference in the magnitude of stiffness for monolithic andsemi-precast slab. Similar behavior was observed in another series of specimen width of 400mm and600mm. This finding strongly suggests that there is no significant different in behavior of monolithic

concrete slab and semi-precast slab. This means that semi-precast slab will be able to closely behave

structurally as that of monolithic slab. Another finding reveals that the differences in magnitude of

stiffness between monolithic and semi-precast slab tend to diminish as the number of concrete panel

increases. This finding suggests when all concrete panels already installed the behavior of semi-precast

concrete slab would be similar to that of monolithic slab. Hence it can be concluded that semi-precast slabwill have similar flexural stiffness characteristic to that of monolithic slab.

Another result of testing concerns with the structural characteristic of specimen under loading up to

failure. Similarly, many testing were conducted on series of slab specimens, and the results is presented

Figure 7. The figure depicts the results of testing for specimen width of 200mm, 400mm and 600mm.

Figure 7 shows the relationship between load and deformation of specimen width of 200mm, 400mm and

600mm loading up to collapse for both monolithic and semi-precast. The figure suggests that the load

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capacity of semi-precast slab and monolithic slab is nearly similar, especially during the early stage of

loading or in the elastic range of materials. When loading continued, semi-precast slab tends to give lower

load capacity. The differences in load capacity tend to increase with the increasing number of concretepanels. In terms of deformation, semi-precast slab tends to have shorter deformation than that of

monolithic as shown for specimen width 400mm and 600mm, but for specimen width 200m the result is

on the way around. It is suggested that the differences in magnitude of load capacity between semi-precast and monolithic slabs might be attributed to the differences in tensioning level of tension bar in

each specimen. Higher tensioning level of the bar will result in higher load capacity. From load-failure

loading results, it can be concluded that the load capacity of semi-precast slab will be sufficient to support

actual loading in structures. Therefore, overall conclusion can be drawn that semi-precast slab method is

structurally reliable to be applied in concrete slab construction system.

Fig. 7: Result of load-failure test on specimen width of 200mm, 400mm and

600mm

a) Concrete Slab with of 200mm

b) Concrete slab width of 400mm

c) concrete slab width of 600mm

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FIELD APPLICATIONS

Semi-precast slab system has been applied in several places as shown in Figure 8 and Figure 9. Based on

the implementation of the semi-precast method in concrete floor construction, there are several note can

be taken, 1) the construction system is quite easy to learn, 2) faster construction time, 3) less number of

wooden panel needed, 4) less number of bamboo required, and all of these yield significant amount ofcost saving. When little amount of wood and bamboo were used for the slab formwork hence there will be

a few of those that will be discarded as waste. Based on these aspects, it is expected that the method will

be able to contribute to the environmental quality improvement program and can be considered as one

form of green construction method to combat global warming.

Fig. 8: Arrangement of precast concrete panels supported by light shoring.

Fig. 9: Arrangement of top steel reinforcement on top of concrete panel surfaces

The precast panel issupported by light

arrangement of

support from

bamboo.

Precast panel serve asformwork, hence no

wooden panel is

needed for flooring

construction.

Arranging top steel

reinforcing bars on

top surfaces of

concrete panels.

The steel placed with

spacing of 200mm.

Top steel is arrangedfor both directions,long and short

directions.

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CONCLUSIONS AND SUGGESTIONS

From the results of experiments and observation from field application, some conclusions can be drawn,

as follows:

1. The structural characteristic of semi-precast slab tend to be close to that of the behavior of monolithic

concrete slab, hence the system is potential to be applied in floor construction system.2. Field applications show ease construction method, faster construction time, much less need of

wooden panels as well as bamboo and, hence, there is significant reduction amount of waste wooden

formwork.

3. This study is limited by the slab width of only up to 3 concrete panels, therefore further research

needs necessary to study the behavior of semi-precast slab panels for full panels floor as well as

another aspects related to semi-precast panel behavior.

REFERENCES

SNI 03-2847-2002 (2007). Tata Cara Perhitungan Struktur Beton Untuk Bangunan Gedung, Surabaya,

Badan Standarisasi Nasional.

http://lantaikeraton.com/, accessed on 5 Mei 2013.

(http://infiniti.indonetwork.co.id/497571/balok-lantai-instan-beton.htm, accessed on Mei 2013

(http://natapersada.indonetwork.co.id/1493443/lantai-beton-pracetak.htm, accessed on 5 Mei 2013