EXPERIMENTAL EVIDENCE ON WEAR BEHAVIOURS OF
FLOOR SURFACES AND AN APPLICATION FOR SLIP AND
FALL SAFETY ASSESSMENTS
In-Ju Kim and Anas Alduhishy
Department of Physical Therapy, College of Applied Medical Sciences
University of Dammam, Dammam 31451, Kingdom of Saudi Arabia

Flooring materials and floor coverings should retain continual slip resistancequalities throughout lifetime, but their slip-resistance properties could be changed
over time. Those variations seem to largely affect slip resistance performance.
Main aims of this study are to 1) determine if there are significant differences in
the measured slip-resistance properties of floor surfaces, 2) identify wear effects offloor surfaces on slip-resistance performance, and 3) formulate a clear concept on
wear phenomena of the floor surfaces. To approach the aims, dynamic friction tests
were conducted amongst3 different types of floor specimens with a similar range of
topographic characteristics and two shoes under a clean and dry condition.
Topographic changes and wear developments of each floor surface were
quantitatively and qualitatively measured by surface roughness parameters andmicroscopic observations. Findings from this study clearly showed that initial
surface features of the floor specimens were clearly modified during an early stageof dynamic friction tests and significantly affected slip-resistance properties.
Results also identified that various regimes of wear behaviours such as adhesive,
abrasive, ploughing, and fatigue were found as main wear behaviours and theresultant effects on slip resistance performance. This study suggests that future
research on slips and falls should pay a close attention to the issues on relevant
wear phenomena of the floor surfaces and their effects on slip-resistance
performance.

Introduction
Fall incidents resulting from slips are the major outcomes in surveys on serious occupational
incidents as well as one of the most common geriatric syndromes threatening the independenceof older people (Dias et al., 2011; Perez-Jara et al., 2012; Demura et al., 2013; Whitney et al.,2013). Although many factors contribute to slips and falls, underfoot surfaces and floors have amajor effect on the incidents. Floors and underfoot surfaces should be constructed to provide
comfortable walking environments and good protection against any slip potentials. With
continued walking activities, however, topographic changes and progressive wear of the floor
surfaces are unavoidable and they can substantially affect slip-resistance properties.
Changes of surface topographies of the floors during slip-resistance measurements havebeen reported in the recent literature. For example, extended wear on smooth floors could cause
polishing effects and considerable drops on coefficient of friction (COF) quantities (Manning etal., 1998; Kim & Smith, 2000, 2003; Kim et al., 2001; Kim, 2004a, 2004b). Those studies
showed strong relationships between surface roughness and slip-resistance properties, but
fundamental aspects on wear phenomena and associated tribological characteristics of the floor- 99 -

surfaces were not fully explored. In particular, it is scarce to find any definitive concepts andmethodical studies on wear behaviors of the floor surfaces and their effects on slip-resistance
performance. The present study aimed to:(1) perceive fundamental aspects of wear behaviors of the floor surfaces;(2) understand the nature of surface changes and wear developments of the floor surfaces; and(3) identify their effects on slip-resistance performance.
To validate such aims, topographic characteristics of new and rubbed floor specimens were
measured by a number of surface roughness parameters before and after slip-resistance tests forquantitative analyses. A series of micrographs were also taken by a scanning electron
microscope to monitor surface changes and wear growths of the floor specimens after the tests
for qualitative analyses.

Material and methods
Dynamic friction tester

A pendulum-type hydraulic dynamic friction tester was used to measure slip-resistanceproperties. The tester’s set up values could be adjusted to cover various parameters taken fromhuman walking trials such as a heel contact angle, vertical load and its rate of increase andsliding speed. The normal force was kept around 400 N and the sliding speed was controlled at
25 cm/sec based on gait studies (Kim et al., 2013). A heel contact angle of 9º was chosen by the
result of previous biomechanical studies (Kim et al., 2013).

Floor specimens

In order to objectively monitor changes on surface topographies of the floor specimens andanalyse their effects on slip-resistance performance, 3 different types of floor specimens: vinyl,
terracotta, and ceramic with a similar range of topographic characteristics were used (see, Table1). The floor specimens were thoroughly cleaned with demineralised water to remove any dirt
and dust, dried and kept in plastic containers during the tests.
Table 1. Summary of surface roughness parameters of floor specimens before (BFT) andafter the tests (AFT)
Surface
Vinyl
Terracotta
Ceramic
Roughness
BFT
AFT
BFT
AFT
BFT
AFT
Parameters
Ra
Rq
Rtm
Rpm
Rvm

2.330
3.121
16.8176.483-7.492

1.477
1.973
15.860
4.882-3.6452.788
3.767
19.00811.701-7.3072.727
3.355
10.5995.192-5.4073.933
4.935
19.50010.899-8.601

1.986
2.571
9.900
5.827
-4.073Shoes

New Nitrile Rubber (No. 1) and Polyurethane (No. 2) soled shoes were used. The shoes were
thoroughly cleaned with demineralised water to eliminate any dirt and dust, dried and kept inplastic containers during the tests.

Test conditions

Dynamic friction tests were conducted on clean and dry conditions in order to eliminate any
confounding effects of contaminants by agents other than shoe and floor specimens themselves.
The controlled test conditions were also intended to investigate the following two major goals:- 100 -

1) observe dominant effects of geometric characteristics and wear behaviours of the floor
specimens such as wear formation, growth and propagation; and2) investigate main roles of surface topographies of the floor surfaces and their effects on slipresistance properties.

Quantitative analysis

A laser scanning confocal microscope (MRC-600, Bio-Rad) which had 0.1 μm step size wasused to measure surface roughness of the floor specimens before and after the tests. Surface
profiles of the floor specimens were measured three times at five different locations along thesliding directions. Averages of the individual roughness measures were used for the analysis.
Peak height related roughness parameters such as Rtm, Rpm, and Rvm were measured withsurface height ones such as Ra and Rq before and after the tests. Details of the surface roughness
parameters are found in the literature (Kim & Smith, 2000; Chang et al., 2001).

Qualitative analysis

In order to validate surface roughness data and identify wear modes and developments, rubbed
surfaces of the floor specimens were comprehensively examined by a stereo scanning electron
microscope (SEM: XL 30, Philips). The SEM was operated at 10 kV setting to avoid radiation
damages to the transferred polymeric particles from the heel surface.

Results
Slip-resistance performancesFig. 1 shows the result of dynamic friction tests between the three floor specimens and two
shoes. Quantities of dynamic friction coefficient (DFC) were largely decreased after the tests. In
the case of the Polyurethane shoe (Shoe No. 2), the DFC values showed larger changes than the
Nitrile Rubber one (Shoe No. 1) rubbed against all the three floors.

(a) Vinyl floor(b) Terracotta and Ceramic floors
Figure 1. Results of dynamic friction tests amongst three floor specimens and two shoes
under clean and dry surface conditions: (a) Vinyl floor and (b) Terracotta and Ceramic

Surface analysis - Quantitative approach
Surface roughness parameters

Table 1 summarizes the measurement results of surface roughness parameters of each floor
specimen after the tests. As shown in Table 1, all the roughness parameters of the floor
specimens were largely changed after the dynamic friction tests. The detailed observations oneach roughness parameter are further discussed in the below:(1) Centre-line average (Ra) and root mean square (Rq) roughness parameters- 101 -

Ra and Rq parameters of each floor surface were largely decreased by about 36.61%, 2.19%, and49.50% in Ra, and 36.78%, 10.94%, and 47.90% in Rq, respectively after the tests. These
seemed to be caused by depositions of polymeric materials from heel surfaces into discrete
patches of the floor surfaces. As a result, modified roughness heights directly contributed to theroughness parameters.
(2) Maximum mean peak-to-valley (Rtm) and maximum mean peak height (Rpm) parameters
Rtm and Rpm parameters of each floor surface were also largely decreased by about 5.69%,
44.24%, and 49.23% in Rtm, and 24.70%, 55.63%, and 46.54% in Rpm, respectively after thetests. These findings showed a strong evidence of the flooring wear as a direct wear progress.
(3) Maximum mean depth (Rvm) parameter
Rvm parameter of each floor surface was significantly reduced by 51.35%, 26.00%, and 52.65%,
respectively after the tests. This reduction showed the largest changes amongst the measured
roughness parameters. This result identified that polymeric wear debris and particles from theheel surfaces were largely embedded into valley areas of the floor surfaces. This finding
suggests a clear evidence of the flooring wear as an indirect wear progress.

Surface analysis - Qualitative approach
Wear observations

Fig. 8 shows examples of micrographs of the floor surfaces rubbed against the two shoes after
the tests. Each floor experienced extensive wear events during the tests. A range of wear
particles and debris with different patterns, shapes and sizes were found on the floor surfaces.
Those findings provided visible evidences of the flooring wear as a function of directmaterial transfer. The greater the roughness of the floor surface the wider the ranges and shapesof wear particles. The main findings on wear modes of the floor surfaces are summarized in thefollowing:(a) Vinyl floor – BFT(b) Vinyl floor vs. Shoe No. 1(d) Terracotta – BFT(c) Vinyl floor vs. Shoe No. 2(e) Terracotta floor vs. Shoe No 1

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(f) Ceramic floor – BFT(g) Ceramic floor vs. Shoe No. 2
Figure 2. Micrographs of the floor surfaces rubbed against two different shoes –BFT and AFT(1) Large amount of wear debris and particles were observed on the surfaces of wear tracks,
depending upon the topographies of floor surfaces;(2) Different shapes, sizes, and types of wear debris were embedded into the valley areas of thefloor surfaces;(3) Wear evolutions were generally associated with the nominal contact areas between thefloor surfaces and the shoe heels; and(4) Irregular shaped fragments were commonly found in the wedge areas, but the transferred
wear particles did not heavily cover the peak asperities of the floor surfaces.

Limitations of the study
This study tested only a small selection of ooring materials within a limited number and rangeof surface roughness scales. Further research on the slip resistance properties of a range offlooring materials with different surface characteristics is needed to comprehensively understandflooring wear mechanics and mechanisms. Experimental design of this study involved only clean
and dry surface conditions. This limits the applicability of findings from the current study only
to this type of surface condition. Other surface conditions such as lubricants and contaminantswith different composition and viscosity may result in different phenomena of flooring wear.

Conclusion
This study aimed at understanding wear behaviors of the floor surfaces in an early stage ofsimulated slip resistance measurements and identifying their effects on slip-resistance properties.
A series of dynamic friction tests were conducted amongst three common types of floor
specimens and two shoes under clean and dry conditions. The rubbed surfaces of each floor
specimen were comprehensively analyzed by quantitative and qualitative methods. From theoverall results, the followings main findings were summarized:
1) There were significant changes in the topographic structures of the floor specimens after thetests. Topographic structures of the floor specimens were largely altered not only in theinitial stages, but also in the later stages of slip resistance tests by wear-induced sliding
friction processes.
2) Surface roughness parameters of each floor specimen showed large variations after the tests.
Amongst the measured surface roughness parameters, the maximum mean peak height(Rpm) and maximum mean depth (Rvm) of all the floor specimens underwent significant
changes (on average more than 42% for Rpm and 43% for Rvm, respectively) after the tests.
3) Wear developments of the floor specimens were caused by a combination of direct materialtransfer from the shoe heels and indirect abrasive wear evolutions of the floor specimens.

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4) Structural changes of the floor surfaces directly affected to DFC results.
Overall outcomes from this study clearly showed the importance of flooring wear
phenomena and their significance effects on slip-resistance properties. It is wished that the idea
explored in this study may not only provide a sound foundation for the understanding of wear
phenomena of the floor surfaces but also make a progress towards an account of the underlying
complex mechanisms of slip-resistance properties.

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