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Method for determining the parameters of surfaceroughness by usage of a 3D scanner

M. Siewczynska

Poznan University of Technology, Piotrowo 5, 61-138 Poznan, Poland

a r t i c l e i n f o

Available online 23 March 2012

Keywords:

Surface roughness

3D scanner

Sandblasted concrete surface

RS

RL

nt matter & 2012 Politec.1016/j.acme.2012.03.007

Monika.Siewczynska@Pu

a b s t r a c t

Appropriate methods and parameters best describing the surface roughness are searched for.

Concrete is a heterogeneous material and various types of damage and surface cleaning cause

an increase of the roughness. Surface roughness depends i.a. on the quality and method of

cleaning used. Mapping the shape of the profile is usually performed using profilografs.

Description of surface roughness is usually expressed via standards parameters or fractografic

parameters that must be determined using the cycloid grid imposed on selected images of

surface profiles. This method is approximate. Described in this article is a new method for

measuring shapes which can be applied for any area (not just concrete), and most importantly,

gives information about the roughness of the entire surface in an accurate manner. The

calculations are made directly from geometric measurements of the whole surface, and not

based on averaging the results of the selected profiles. The method uses a 3D scanner and CAD

capabilities available in research centers or freeware programs.

& 2012 Politechnika Wrocławska. Published by Elsevier Urban & Partner Sp. z.o.o. All rights

reserved.

1. Introduction

Due to the increasing aggressiveness of the environment which

causes ageing of concrete and reinforced concrete—repair and

protection of these structures are more often needed. In order to

repair the surface, adhesion to the ground is most important and

the relationship between surface degree of development and

coating adhesion must be determined and so appropriate

methods for determining parameters of surface roughness are

searched for. Concrete is a heterogeneous material and various

types of damage or cleaning of its surface (before the application

of the repair materials) increase roughness [1,2]. Surface rough-

ness depends i.a. on the concrete grade and method of cleaning.

2. Concrete surface roughness

Roughness is a characteristic of the surface that identifies its

inequality (elevations and depressions) which is nothing less

hnika Wrocławska. Publis

t.Poznan.Pl

than the order of magnitude smaller than the size of the

element. There are two ways to describe the topography of

the surface: profile (flat—2D) and surface (spatial—3D) [3].

Mapping the shape of the profile is usually performed using

profilografs (mechanical or laser). Among the surface methods

used one can distinguish sand testing (quickest but approximate

which works only on horizontal surfaces) or analyzing the

surface topography of the spatial image, which is done in the

form of contour maps, gray or multicolor maps, isometric (3D)

performed by comparing the consecutive profile images.

Description of surface roughness is usually expressed through:

–

hed

standard parameters [4] designed for metal surfaces or

–

fractografic parameters, calculated on data obtained from

surfaces geometrical measurements of selected profiles [5].

Profile images are usually created by touch method (profilograf)

or by laser light which yields the roughness of the test profile. By

analyzing profile measurements an estimation of the roughness

by Elsevier Urban & Partner Sp. z.o.o. All rights reserved.

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 984

parameter, describing the entire surface is made. Furthermore

calculations of the surface roughness values (standards para-

meters) taken from the standards on metal surfaces are not

relevant to the concrete surfaces and have restrictions of use

[6,7]. Values of fractografic parameters are usually determined by

using a cycloid grid imposed on selected images of surface

profiles [8]. However this method is approximate and implies

that concrete surfaces can have fractal characteristics. Because of

this, determination of surface roughness by fractal theory is

burdened by three kinds of errors. The first approximation lies in

mapping of surface profiles, as any method e.g. mechanical or

laser profilometer is related to the accuracy of this device. The

second approximation results from methods of determining

factors to develop a profile of RL and RS to the surface of randomly

selected profiles. Third approximation stems from the applica-

tion of fractal theory to the concrete surface, for which the fractal

dimension D, according to information available, is located in

between 2 and 3. To qualify as a fractal shape, this value should

be between 1 and 2.

3. New method

The new method of shape measurement described in this article

not only gives accurate information about surface roughness but

also can be applied at surfaces different from concrete. The

calculations are made directly from geometric measurements of

the whole surface and not based on averaged results of selected

profiles. This is a non-invasive method, well suited in the trend of

diagnostic development that focuses on features other than

strength of elements and structures of concrete or reinforced

concrete [9].

During development an assumption was made that the

proposed method must be compatible with freeware pro-

grams or CAD software available in research centers. Further-

more the method would have to work on standard computer

configurations and not require any prior knowledge of

programming just program-specific one.

The new method consist of creating a virtual three-

dimensional image of the test surface by scanning it with a

3D optical scanner (using Moire’s effect of bend fringes)

(Fig. 1). The resulting image is a cloud of points with known

positions (named coordinates x, y, z in the adopted coordinate

system) on which (in a program that supports the scanner)

Fig. 1 – Comparison of images obtain

smallest possible triangles are drawn to create a dimensional

approximation of the scanned surface. This image approx-

imation accuracy is determined by the resolution of the

scanner and in this study it was 20 mm. Additionally separa-

tion of profiles was carried out in two perpendicular direc-

tions (x, z) and (y, z) at an interval of 1 mm.

Three-dimensional, virtual images and separate sections

are then imported into a CAD program. Calculations of

surface area and length are carried out to determine the

coefficients of the surface development:

–

ed

RS parameter Eq.:

RS ¼ S=A0 ð1Þ

where S is the specific surface area, and A0 is the area of

the orthogonal projection on the plane,

–

RL parameter Eq.:

RL ¼ L=L0 ð2Þ

where L is the length of the profile line, and L0 the length of

projection line profiling on a plane.

During method development the only measurement error

made was due to accuracy of the 3D scanner (0.20 mm); any

additional software was used only to change file formats and to

calculate parameter values needed to coordinate points located

on the analyzed surface and obtained during the scan. A detailed

statistical analysis was performed [6] during which an average

error of parameter RS was recorded at 8% of the parameter value

and RL at 10% of the parameter value. All the measurements

discussed in this study were carried out by a scanner of 1,400,000

dots points of measurement (ATOS II) but now, more sophisti-

cated equipment is available including scanners with over

4,000,000 points of measurement (ATOS SO 4M) [10,11]. Never-

theless the accuracy of the scanner used was assessed as

satisfactory due to the expected values but usage of scanners

with higher resolution would give a lower value of measurement

error resulting from the calculation of parameters.

4. Parameter calculation schedule

The result of a three-dimensional surface scan is a spatial

image, consisting of triangles with known coordinates of the

by 3D scanning with real ones.

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 9 85

vertices. For each surface file a �.stl export was created with

3D scanning software. Furthermore a set of coordinates can

be exported into a n.txt file. This data set contains consecutive

coordinates of points separated by space, for example:

2:088029 �32:265826 0:294061

23:653204 �59:483296 0:036868

19:770278 �18:440480 0:258670

2:277080 �31:906161 0:310550

One can also extract cross sections in a given distance from

each other, then the text file with the coordinates looks as

Fig. 2 – 3D view (Blender) of a sand

Fig. 3 – 3D view (Blender) of not sandblasted concrete surface

imperfections.

follows:

4:594258 0:013154 0:013154

4:697288 �66:000000 0:024115

4:893628 �66:000000 0:015943

4:973358 �66:000000 0:011526

The files were then imported into Blender, a freeware 3D

editing program, which allowed for editing of the images

spatial surface (Fig. 2). To ensure a more faithful representa-

tion of the concrete, a small area, located at the edges of the

cubes, was removed along with the markers stuck to stabilize

blasted concrete surface C8/10.

C12/15, doubling and flattening of the image, removal of

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 986

the image during the scan. Each surface was doubled and

flattened (Fig. 3) and then the spartial forms where exported

to a n.dxf file which is supported by CAD software (Figs. 4

and 5). Additionally, a program written in AutoLISP [12] was

used to calculate the area of all triangles. The specific surface

area and area of the orthogonal projection on the plane was

calculated for the whole surface of the scanned sample.

Moreover the calculation of the coefficient of the surface of

developing RS was performed.

In order to calculate the coefficient of the line profile—the

RL parameter in the editing program 3D rectangles perpendi-

cular to the plane of the mean were added. The lines of

Fig. 4 – 3D view (CAD) of not sandblasted concrete surfac

Fig. 5 – 3D view (CAD) of a sandblasted concrete surfac

Fig. 6 – 3D view (Blender) of selected profiles of not sandblasted

direction.

intersection of the planes profile were identified. Due to the

inability to import the CAD set of points and lines of zero

thickness profiling was performed to extend the line in a

perpendicular direction (Fig. 6), and then was made the export

to n.dxf format. Next the import of files n.dxf to CAD (Fig. 7)

program was done. The unnecessary points profile banner

stretched before were removed. In order to count the length of

all sections making up the surface profile a script written in

AutoLISP was used, which counts a total length of all selected

lines. The horizontal distance between the beginning and the

end of the profile was measured. Performed the calculation

factor to develop a profile RL.

e in C12/15 as a grid of triangles (a) and rendering (b).

e C8/10 as a grid of triangles (a) and rendering (b).

concrete surface C12/15, line extension in a perpendicular

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 9 87

5. Scope of research

Measurements of five different concrete surface classes

(before and after sandblasting) were performed using a 3D

scanner, after which the surface area and the profile

development rates (fractografic parameters) were calculated.

Measurement of surface shapes were made by a non-invasive

method in accordance with increased interest in these

studies which involve characteristics of construction materi-

als. Sample images of the surface are shown in Fig. 8.

Fig. 9 – Graph RS(fcm) for sandblasted (s) and not sandblasted

(n) surface.

6. Test results

Calculated values for RS and RL parameters are presented in

graphical form (Figs. 9 and 10). A trend of reducing the values

of RS and RL for sandblasted surface with increase of the

compressive strength of concrete was observed. The course of

the regression line falls within the error range of all points

and the points are located in the 95% confidence level. When

it comes to not sandblasted surfaces changes in the value of

the roughness parameters when changing the class of

concrete were not observed.

7. Test results analysis

Coefficients of surface and profile development are easy to fix

by the proposed method, and the RS parameter gives

information about the entire surface. Selected advantages

and disadvantages for the new method of calculating the

parameters RS, RL are discussed:

–

Fig

sur

Fig

Attention must be paid during the 3D surface scan, a beam

of light must reach the large cavities, otherwise there will

. 7 – 2D selected profile view (CAD) of sandblasted concrete

face C8/10.

. 8 – Exemplary view of scanned surfaces: concrete C12/15, not san

Fig

san

be a gap in the image area. The presence of such gaps will

not affect the methodology for determining the para-

meters, but their value can be reduced due to omission of

surface by a large cavity.

dblasted surface (a), concrete C8/10, sandblasted surface (b).

. 10 – Graph RL(fcm) for sandblasted (s) and not

dblasted (n) surface.

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 988

–

Fig

sa

In order to determine the fractografic parameters, knowl-

edge of complex norm methods to determine roughness is

not needed. One only needs basic competence with

software discussed in this study.

–

Calculation time is very short.

–

At any stage of determining the parameters, there is no

need to reduce the accuracy of calculations. None of the

programs reduce the accuracy and there is no danger in

confusion of reading by the person who carries out the

calculation.

–

Fig. 12 – Graph RS(RL) for different types of concrete, tests

conducted: 1—own research, 2—Czarnecki, 3—Coster,

Chermant, 4—Underwood, 5—Konkol, Prokopski (basalt

concrete), 6—Konkol, Prokopski (gravel concrete), 7—Wright,

Karlsson, 8—Gokhale, Uderwood.

Parameter values are the characteristics of the entire surface

with such accuracy as the 3D scanner. If necessary, one can

obtain information on the passage surface which, in the short

term performance, is not a labor-intensive calculation.

Developed method of calculating the parameters RS and RL

gives results without loss of measurement accuracy. Calcula-

tion of these values in accordance with the commonly used

theory of fractals is always approximate and depends on the

image magnification and the length of the selection step.

The relationship between RS and RL for the tested concrete

(Fig. 11) has a high correlation coefficient. For the sandblasted

surfaces it is r¼0.89, and for not sandblasted r¼0.83. The

regression lines have the form:

–

.

n

for sandblasted surface Eq.:

RS ¼ 131 � RL2029 ð3Þ

–

for not sandblasted surface Eq.:

RS ¼ 031 � RL þ 070 ð4Þ

The relationship RS(RL) for the sandblasted surface can be

compared with results of other tests conducted on concrete

breakthroughs. Fig. 12 presents a comparison of results obtained

according to the described studies done by Czarnecki, Costera,

Chermant, Underwood, Konkol and Prokopski, Wright and

Karlsson and Gokhale and Uderwood [8].

11 – Graph RS(RL) for sandblasted surfaces (p) and not

dblasted (n) obtained in the analysis of research.

The dependence discovered in this study falls within the

limits of Underwood, and Konkol and Prokopski and is almost

parallel to the line designated by Underwood and Czarnecki.

The regression line is consistent with the general trend for

various concretes. Moreover the change in the angle of

inclination is associated with different ways of preparing

concrete surfaces prior to the examination and their compo-

sition. In this research, areas have been sandblasted and

other studies have analyzed the surface concrete break-

throughs of different compositions.

8. Results

Analysis of tests carried out conclude that there is a

correlation between the strength of concrete under-surface

detachment and surface roughness subjected to sandblasting.

The higher the grade of concrete, the smaller the roughness

of sandblasted surfaces. For not sandblasted surfaces

roughness parameters are unaffected by varying grade of

concrete.

Coefficients of the surface and the profile development

reflect the nature of the surface roughness of concrete, this is

seen particularly with the parameter RS (spatial description).

Furthermore the value of using computer software can be

determined as the proposed method is much easier and it is

faster to obtain the results which are more accurate. Mean-

while, the proposed method of calculation using available

software, provides extra capabilities for process control and

analysis of surface roughness. It also gives a tool that can be

modified depending on need of analysis or the result sought.

Currently used values for determining surface roughness by

fractal theory are burdened with three kinds of errors. The new

method is developed only for measurement errors resulting from

the accuracy of the 3D scanner (in this study it was 0.20 mm).

However, further calculations of parameter values are carried out

without loss of accuracy. Additional software was present only to

change file formats and to calculate parameter values used to

coordinate points located on the analyzed surface and obtained

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 2 ( 2 0 1 2 ) 8 3 – 8 9 89

during the scan. This method does not require any prior

knowledge of programming just program-specific one. Measure-

ment of the reported studies were performed with a resolution of

the scanner of 1,400,000 dots/in., and scanners are now available

with a resolution of 4,000,000 dots/in. The described method can

be further simplified by preparing a computer program that will

calculate the parameters RL and RS directly from text files.

The new method of shape measurement described in this

article not only gives accurate information about surface rough-

ness but also can be applied at surfaces different from concrete.

This is a non-invasive method, well suited in the trend of

diagnostic development that focuses on features other than

strength of elements and structures of concrete or reinforced

concrete.

r e f e r e n c e s

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[2] Z. Kamaitis, Modelling of corrosion protection for reinforcedconcrete structures with surface coatings, Journal of CivilEngineering and Management 14 (4) (2008) 241–249 (s.).

[3] P. Paczynski, Technical Metrology, Wydawnictwo PolitechnikiPoznanskiej, Poznan, 2003 (in Polish).

[4] PN-87/M-04256/02 Geometrical Structure of the Surface,Surface Roughness, General Terminology (in Polish).

[5] G. Prokopski, Fracture Mechanics of Concrete Cement,Oficyna Wydawnicza Politechniki Rzeszowskiej, Rzeszow,2007 (in Polish).

[6] M. Siewczynska, Influence of selected parameters on theadhesion of concrete coatings, Dissertation, PolitechnikaPoznanska, Poznan, 2008 (in Polish).

[7] M. Siewczynska, New method of calculation of surfaceroughness parameters, in: M. Kaminski, J. Jasiczak, W.Buczkowski, T. Błaszczynski (Eds.), Modern Repair Methodsin Building and Constructions, Dolnoslaskie WydawnictwoEdukacyjne, Wrocław, 2009, pp. 77–86.

[8] A. Garbacz, Non-Destructive Investigations of Polymer–Concrete Composites with Stress Waves—Repair EfficiencyEvaluation, Oficyna Wydawnicza Politechniki Warszawskiej,Warszawa, 2007 (in Polish).

[9] J. Hoła, K. Schabowicz, State-of-the-art non-destructivemethods for diagnostic testing of building structures—

anticipated development trends, Archives of Civil andMechanical Engineering 10 (3) (2010) 5–18.

[10] Materials from webpage: /www.ita-polska.com.plS.[11] Materials from webpage: /www.gom.comS.[12] A. Pikon, AutoCAD 2002, Helion, Gliwice, 2001 (in Polish).