Published at the Proceedings of the X International Symposium on Ferrocement and Thin Reinforced Cement Composites (FERRO 10),held in Havana, Cuba in Oct. 2012

1. Fibre-reinforced and Ferrocement Car-park Pavers
Dr R. Sri Ravindrarajah
Centre for Built Infrastructure Research, University of Technology. Sydney, Australia
1-Introduction
Normal weight concrete is accepted as the suitable construction material for roads,
highways and airport pavements because of its ability to carry service loads and low
maintenance cost. Rainwater cannot infiltrate into the subsurface because of the low
permeability of the traditional concrete pavement. In addition, it is difficult for soil to
exchange heat and moisture with atmosphere, and consequently the temperature and
humidity of the air are affected, causing the phenomenon of heat islands around large cities.
The impermeability of pavement increases the storm-water runoff and overloads the
drainage system. This leads to flooding in many cities during heavy rainfall for a short
period of time. The intensity of flooding further increases when the existing drainage
system is either blocked or inadequate.
In order to reduce stormwater runoff from redeveloped properties, municipal councils in
Sydney, Australia adopted on-site stormwater detention (OSD) systems in the early 1990s
[1]. OSD systems consist of surface or underground storages with a control pit for water
discharge. Although OSD has been adopted in some larger country towns and in Canberra,
it was rejected as an option for the Central Business District of Sydney.
As an alternative, porous pavement can be easily considered as suitable solution in urban
cities to mitigate the storm-water runoff problems. The typical porous pavement systems
commonly consist of a matrix of concrete pavers with voids filled with sand, gravel or soil.
These voids allow storm-water to infiltrate through the pavement into the soil. In
Singapore, precast reinforced concrete pavers of different shapes and sizes, with opening,
are used for a number of years for the construction of open car parks, in the public housing
estates. This paper reports the results of a survey conducted in monitoring the condition of
these precast reinforced concrete pavers after a number years of service.
Ferrocement is known to have significant crack resistance and suitable to produce thin
structural elements [2-4]. Similarly, steel fibre reinforced slabs are also have significant
resistance to cracking [5]. In order to achieve improvement of the precast concrete car park
pavers, it is necessary to look for an alternative car park paver designs with improved
strength, ductility and cracking resistance. An experimental investigation was carried out
with voided steel fibre reinforced concrete and ferrocement pavers. These pavers were
tested under simple bending to determine their first crack and ultimate strengths, mid-span
deflection and cracking patterns. A comparative performance of these pavers with currently
used reinforced concrete pavers is reported.

2. 2-Survey of voided car park pavers
Voided reinforced concrete pavers are commonly used for the construction of open car
parks in many public housing estates in Singapore. The public policy of Singapore requires
all open car parks with trees for the protection of public from sun radiation heat and to
maintain greenness of Singapore. The tropical environment helps the growth of the trees in
Singapore. Conventional impervious pavements with either concrete or bitumen fail are not
completely suitable to provide moisture saturation to the soil, which is needed for the
growth of the trees and grass. The use of precast voided reinforced concrete pavers provide
car park with grass surface appearance and aesthetically pleasant aeration patterns. The
openings in the slabs allow percolation of surface water into subsoil, hence reducing
heaving problems. However, the use of voided pavers appears to be less superior to
convention concrete or bituminous pavement from the strength point of view.
2.1-Shapes of precast reinforced concrete aerated pavers
The main factors affecting the choice of a particular pattern of the precast reinforced
concrete pavers for car park construction are aesthetic and performance specification
requirements. The available shapes of these pavers with openings were rectangular, square
or hexagonal as shown in Figure 1. The thickness of the pavers varied between 60 to 75mm
and the shapes of the openings are rectangular, square or rounded. The void area content of
these pavers varied between 16.6% and 44.3% of the total area. The largest and heaviest
paver had the dimensions of 735mm by 735mm by 75mm with 8 rectangular openings of
245mm by 55mm (producing the void area content of 31.6% of the total area). The weight
of this type of paver is 66.5kg. At least two adults are needed to carry a single paver.
Fig. 1 -Shapes of precast reinforced concrete voided pavers

3. The most commonly used car park paver for open car park construction is rectangular in
shape (Figure 1(A)). The typical dimensions of such paver are 735mm by 375mm by 65mm
with four 240mm by 50mm voids, providing the void area content of 38.7%. The weight of
a single paver is 26.8kg and can be easily lifted by an adult worker.
Fig. 2 -Typical deterioration for reinforced concrete pavers in open car parks
2.2-Field performance of reinforced concrete car park pavers
A satisfactory performance of car park pavers requires crack-free condition during its
designed service life period. A field survey conducted at a typical open car park in
Singapore housing estate showed that a number of voided concrete pavers were cracked
and deteriorated. The main cause for cracking and deterioration is associated with the
unevenness of the base and structural weakness of the pavers. Unstable base led to tilting,
settling and rocking of the pavers. Some possible causes for base instability are lack of
interlocking between adjacent pavers, unsound base materials, uneven moisture distribution
and presence of compressive soil at the joint locations. The concrete pavers are not capable
of fully resisting the developed bending stresses. In addition, the steel reinforcing bars are
not sufficiently increasing the ductility of the concrete pavers.
A conditional survey was conducted at a typical open car park in Singapore housing estate
showed that 473 out of 1500 concrete pavers were cracked and deteriorated. Cracking in
some concrete pavers was very severe as shown in Figure 2 and endanger the car park
users. If no maintenance is performed, further deterioration of these cracked pavers could
be unavoidable with the increase of service time. In addition, labour shortage in Singapore
is not helping to maintain open car parks with concrete voided pavers without cracks.
In order to improve of the service performance of concrete pavers, suitable for open car
park construction, it is necessary to look for alternative concrete pavement designs with
improved first-crack strength, ductility and cracking characteristics. In this study
performance of voided rectangular steel fibre-reinforced mortar pavers and ferrocement
pavers, similar to the concrete pavers used in Singapore was investigated and compared
with those for the reinforced concrete pavers.

4. 3-Experimental investigation
Voided rectangular concrete pavers (635mm by 310mm) were made with three different
materials, namely reinforced concrete, steel fibre-reinforced mortar and ferrocement.
Ordinary Portland cement (OPC) was used in both mortar and concrete mixtures. The mix
composition of mortar used for both fibre-reinforced mortar and ferrocement was 1:2:0.50
(cement: fine sand: water), by weight. Dramic steel fibres, having the fibre length of 30mm
and 0.50mm diameter (l/d = 60), were used in fibre mortar mix with 2% fibre volume.
Fig. 3 -Reinforcement details for voided concrete and ferrocement pavers
Figure 3 shows the reinforcement details for the cast test specimens with reinforced
concrete and ferrocement voided pavers. The ferrocement pavers had the welded wire mesh
at the top and bottom with 7.5mm thickness. Three 5mm diameter mild steel bars were used
with lateral bars at the top and bottom of the ferrocement and steel fibre reinforced mortar
pavers. The reinforced concrete pavers had three 10mm diameter mild steel bars placed at
the centre with lateral bars. The composition of the concrete mixture was 1:2:2:0.50
(cement : fine sand : coarse aggregate : water), by weight. The maximum aggregate size of
the coarse aggregate was 10mm.
Fig. 4 -Test set-up for flexural testing of pavers

5. For each type of paver, six identical voided pavers were cast in wooden moulds. Full
compaction during casting of the test pavers was achieved by using a vibrating table. The
pavers were demoulded after 24 hours and stored in water at 28o
C for the next 13 days.
Three pavers for each type were tested under mid-point line loading over a simply-
supported span of 555mm using an Instron testing machine, as shown in Figure 4. The mid-
span deflection under the loading point was continuously monitored using an LVDT under
the increasing applied load. The first-crack load, ultimate load and load-deflection
characteristics were determined. The failed test pavers under bending were examined to
assess the cracking patterns.
Fig. 5-Strength development for plain and steel fibre mortars with age
Property Plain mortar Fibre mortar Concrete
Compressive strength (MPa) 34.2 34.1 42.5
Tensile strength (MPa) 2.50 3.45 -
Flexural strength (MPa) 5.51 16.0 5.80
Modulus of elasticity (GPa) 21.0 21.1 27.1
Toughness Index (I5) 1.0 5.9 -
Toughness Index (I10) 1.0 12.8 -
Toughness Index (I30) 1.0 41.5 -
Table 4.1. Properties of plain mortar and fibre mortar at 28 days
4.-Results and Discussion
4.1-Properties of materials
Figure 5 shows the development of plain and steel fibre reinforced mortar with age under
continuously water curing condition at 28o
C. Table 4.1 shows the mechanical properties of
plain and steel fibre mortar at 28 days. The presence of steel fibres showed no significant
improvement in the compressive strength until 90 days. At the age of 28 days, both
compressive strength and modulus of elasticity are not affected by the addition of steel
0
10
20
30
40
50
0 30 60 90 120 150 180
Compressivestrength(MPa)
Age (days)
Plain
2% Fibre

6. fibres. However, the results showed that both tensile and flexural strengths are significantly
increased by the presence of 2% steel fibres. Fibre mortar had the flexural strength of
16.7MPa is 2.6 times of that for the plain mortar. Toughness index of both plain and fibre
mortar was determined by testing (125mm by 25mm by 1000mm) specimens under simple
bending. The details of the testings are reported elsewhere [5]. Toughness indices of I5, I10
and I30 were 5.9, 12.6 and 41.5, respectively. Therefore, the ductility of steel fibre mortar
was remarkably increased over the plain mortar.
The compressive strength of concrete at 28 days was 42.5 MPa and the modulus of
elasticity was 27.1 GPa due to the presence of high modulus natural river granite coarse
aggregates. The flexural strength of concrete was 5.81 MPa which is comparable with that
for the plain mortar of 5.51 MPa.
Paver type First crack moment
N-m
Ultimate Moment
N-m
Ultimate/First Crack
Moment Ratio
Plain mortar 560 560 1.00
Plain concrete 575 575 1.00
Fibre mortar 640 1480 2.31
Reinforced concrete 530 1470 2.77
Ferrocement 625 1685 2.70
Table 4.2. First crack and ultimate mid-span moments for different paver types
Fig. 6-Moment-Deflection relationship for pavers under bending
0
400
800
1200
1600
2000
0 2 4 6 8 10 12
Mid-spanmoment(N-m)
Mid-span deflection (mm)
Reinforced
Steel fibre
Ferrocement

7. 4.2 –First crack and ultimate moment capacity
Table 4.2 summarises the first crack and ultimate moment at the mid-span location under
bending for plain mortar, plain concrete, steel fibre-reinforced mortar, reinforced concrete
and ferrocement pavers. The first-crack moment is the lowest for the reinforced concrete
slab and equal to 530 N-m which is similar to unreinforced plain concrete paver. Therefore,
the inclusion of 10mm diameter steel rebar at the centre of paver had failed to increase the
first crack moment due to rebar position at the neutral axis. Both ferrocement and fibre
mortar pavers showed improved first-crack moment compared to reinforced concrete paver.
The first-crack moment for steel fibre reinforced mortar paver was 640 N-m compared to
535 N-m for reinforced concrete paver. Similarly, ferrocement paver experience first-
cracking at nearly the same moment when compared with that for the fibre reinforced
mortar paver. Therefore, both fibre reinforced mortar and ferrocement pavers resisted
significant moment before developing the first crack than the reinforced concrete paver.
The highest ultimate mid-span moment of 1685 N-m was recorded with ferrocement paver
compared to 1480 N-m for fibre mortar paver and 1470 N-m for the reinforced concrete
paver. Ferrocement having increased crack resistance showed 2.70 times the first-crack
moment until the ultimate failure was occurred. The corresponding values for reinforced
concrete and fibre reinforced pavers are 2.77 and 2.31, respectively. The presence of 10mm
steel rebars in reinforced concrete paver had contributed to the improved ultimate moment
capacity.
Fig. 7-Cracking patterns in failed fibre reinforced mortar,
reinforced concrete and ferrocement pavers
4.3 –Ductility of the pavers
Figure 6 shows the typical moment-deflection characteristics at the mid-span location for
steel fibre mortar, ferrocement and reinforced concrete paver under simple bending. The
ferrocement paver showed highest fracture toughness (area under moment-deflection curve)

8. compared to fibre-reinforced and reinforced concrete pavers. Even though the first cracking
moment is important, from the point of view of energy required to develop cracking in the
pavers, the fracture toughness is equally important. Considering these two in addition to
deflection control, it can be said that ferrocement paver provide an effective alternative to
the currently used reinforced concrete paver.
4.4 –Failure pattern of the pavers
Figure 7 shows the crack patterns at failure for fibre reinforced, reinforced concrete and
ferrocement pavers under increasing flexural loading. The fibre reinforced and reinforced
concrete pavers had a clean single major crack after sustaining significant deflection under
flexure. However, ferrocement paver experienced multiple cracking and narrower crack
width compared to other two types of pavers.
Considering the performance of these three types of pavers, it can be said that the
ferrocement paver is the best alternative to reinforced concrete paver in controlling
cracking and inducing fracture toughness. The fibre mortar paver showed comparable
performance with reinforced concrete paver. Considering the possibility of corrosion of
steel fibres, this may not be a good alternative. In addition, steel fibres if exposed may
cause harm to the car tyres and car park users.
5. -Concluding Remarks
Voided pavers made from cement composites, namely seel fibre-reinforced mortar,
ferrocement and steel reinforced concrete pavers were tested under simple bending until
failure. The voids in the pavers allow the infiltration of storm-water. Traditional use of
reinforced concrete paver with nominal steel rebars experienced cracking and deterioration
due to the instability of the base of the pavers. Based on the current investigation,
ferrocement pavers have superior performance from the load carrying capacity, crack
resistance, deflection and cracking pattern. With proper adoption of production technology,
it is possible to produce precast ferrocement car park pavers without any difficulties.
6. References
1-O’Loughlin, G., Beecham, S., Lees, S., Rose, L. and Nicholas, D. On-site stormwater
detention systems in Sydney, Water Science and Technology, IAWQ, 32(1), 1997.
2-Sri Ravindrarajah, R. and Tam, C. T. Dimensional stability of ferrocement, J. of
Ferrocement, 13(1) 1983, 1-12.
3-Sri Ravindrarajah, R. and Tam, C. T. Watertightness in ferrocement, Journal of
Ferrocement, 14(1), 1984, 11-20.
4-Paramasivam, P. and Sri Ravindrarajah, R., Effect of arrangement of reinforcement on
ferrocement properties, ACI Structural J., 85, Jan-Feb. 1988, 3-11.
5-Sri Ravindrarajah, R., Behaviour of fibre-reinforced thin slabs under short and long-
term loading, Proc. of an Int. Symp. on Ferrocement and Thin Reinforced cement
Composites, 2006, Bangkok, Thailand