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International Conference on Infrastructure Development, UMS Surakarta, 1 – 3 Nov 2013 ISBN: 978-979-636-154-4
Page-266
Where high-strength concrete is not required, structural LWC can be used in the design of floor slabs in building and other structural members Hassoun, 2002. OPS LWC can be a good alternative. Due to the
low modulus of elasticity of OPS concrete, however, conventional crushed granite was added to OPS concrete mix, as 30 replacement to OPS, to produce concrete known as OPS hybrid concrete chiefly used
in precast flooring slabs fabrication. The optimum percentage of granite used was derived through trial mixes Ng et al., 2006.
In a typical modern building made of reinforced concrete, the conventional concrete floor slab system consumes the highest concrete volume up to 44 compared to other structural components. The floor
construction is the most time-consuming and costly activity particularly for a framed building, representing some 60-80 of the total in both cost and time Goodchild, 1997; Matthew and Bennett, 1990. The floor
slabs can be made of in-situ reinforced concrete or precast concrete. In the present, there are many types of precast concrete floors available in the markets such as flat slab, rib and timber infill floor, hollowcore,
single-T, double-T, beam and blocks, semi-precast slab, and channel slab. Each of these precast products has its own advantages and disadvantages. Generally, they are heavy in weight being made with normal
weight concrete NWC, and also, they require cast in-situ concrete topping which increase the cost of overall production. Prestressed elements which require jacking system is very costly. Therefore, the proper
selection of more efficient materials and improved design is essentially required to reduce the cost of precast floor production.
The Government has also started taking initiative years ago to promote sustainable construction of modular elements through precast technology to minimize wastage of building materials at the construction site. It
must be noted that though precast technology is no longer foreign to growing developers or big contractors for its proven work quality and achievements within a shorter construction period of time, small and
medium contractors would, however, still prefer conventional construction method due to lack of initial capital and exposure. Scarcity of aggregates and increasing building material costs are among two common
factors which have somehow discouraged them to venture further.
This paper presents the performance of the precast concrete floor panels namely C-Channels made with OPS concrete with regards to construction tolerances, stacking, and erecting. The result of the water leaking
tests revealed that C-Channel floor panels can act monolithically under load application.
2. MATERIALS
The ordinary Portland cement of ASTM Type I, river sand, OPS and crushed granite have been used. The OPS aggregates have been obtained from Desa Talisai Palm Oil mill, IJM Plantations, Sandakan, Sabah.
The properties of OPS, granite and river sand are shown in Table 1, where the aggregate was tested according to BS or ASTM. Table 2 shows the mix proportions of OPS hybrid concrete as investigated by
Ng et al., 2007, was used to cast the C-channel floor panels. The content of cement, water and river sand are kept constant. Free water cement wc ratio is 0.38. OPS aggregate used is in saturated surface dry
condition. Type-F naphthalene sulphonate formaldehyde condensed based super plasticizer in aqueous form conforming to ASTM C 494 has been used to increase the workability.
Table 1. Properties of OPS, crushed granite and river sand
Property of Aggregates Unit
Coarse aggregate Fine aggregate
OPS Granite
River sand Maximum Size
mm 12.00
19.00 1.18
Specific Gravity SSD ~
1.34 2.63
2.43 Water Absorption Capacity 24 hrs
21.30 2.04
3.89 Moisture Content as received
11.68 0.78
0.69 Los Angeles Abrasion Value
2.90 11.85
~ Bulk Density, compacted
kgm
3
646 1481
~ Fineness Modulus
~ 6.30
6.94 1.33
Aggregate Impact Value, AIV 6.60
12.60 ~
Aggregate Crushing Value, ACV 7.12
15.95 ~
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International Conference on Infrastructure Development, UMS Surakarta, 1 – 3 Nov 2013 ISBN: 978-979-636-154-4
Page-267 Table 2. Constituents of 1.0 m
3
OPS hybrid concrete
Constituent Unit
Quantity Cement
kg 450
Water kg
171 River Sand
kg 629
OPS kg
341 Crushed granite
kg 313
Super plasticizer liter
7.5
3. METHODOLOGY
Four nos of prototype C-channels were cast using OPS hybrid concrete into special steel-timber mould and cured for 7 days through water-spraying. After which, they were transported prior to
stacking and erecting to form the full-scale monolithic floor see Figure 1. The properties of C-channel designated as CH-1, CH-2, CH-3, and CH-4 used are presented in Table 3. The total length of the C-
channels is 5.2 m with the total rib depth 240 mm. The cross-section area was 0.106 m
2
which consumed concrete volume up to 0.551 m
3
per panel.
Table 3: Panel properties of C-channels
Properties per panel Panels
CH-1, CH-2, CH-3 and CH-4 Total length m
5.2 Total rib depth mm
240 Cross section area m
2
0.106 Total concrete volume m
3
0.551 Total weight kg
1,102 Modulus of elasticity of concrete, E
C
MPa 16,280
The four nos of C-channels were carefully transported to a location near the construction site where the lorry crane can erect the panels within reach and without the need of multiple handling.
These C-channels were placed side by side next to one another to form a flooring structure with a total area of approximately 21 m
2
supported by load-bearing walls made with solid concrete blocks. Each C-channel comes with two-edged grooves for the purpose of connection between panels when set up as floor structure.
The groove of two individual panels when placed together forms a longitudinal joint which is to be filled with mortar as shown in Figure 2. It must be noted that the mortar infill was only needed for in-situ casting
of joints between panel and panel.
Figure 1: Four nos. of C-channels forming a full-scale floor structure
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International Conference on Infrastructure Development, UMS Surakarta, 1 – 3 Nov 2013 ISBN: 978-979-636-154-4
Page-268 Figure 2: Support details of C-channels on load-bearing walls
The design and construction of joints is the most critical consideration in precast concrete construction. Seven days after infilling the joints between C-channels, testing was conducted to investigate the jointing
integrity using uniform distributed load and water ponding. The compressive strength of the companion cubes of the in-situ mortar infill was approximately 22.7 MPa at the age of 7-day.
4. RESULTS AND DISCUSSIONS
