r .:f$o , .9- ~ I

- 39 -

LIGHT REFLECTION BY CONCRETE BLOCKS':

r F. Burghout, N.V. KEMA, Arnhem, The Netherlands

1. INTRODUCTION

Figure I shows one particular type of lighting installation in combina-tion with four different asphalt concrete road surfaces. In all fourcases the illuminance on the road surface is the same, both regardingmean level and distribution of light. Yet the appearance of the roadsurfaces is quite different, both with regard to the mean level oflightness - officially the mean road surface luminance - as with regardto the brightness distribution or patchyness - officially the unifor-mity of luminance. The explanation of this phenomenon obviously is,that the road surfaces reflect the incident light in different mannerstowards the observer. Hence the reflection properties of road surfacesare an important factor in street lighting. This of course also holdsfor concrete block pavements. Reflection properties of road surfaceshave been studied a lot in the past. One may say, however, exclusivelyfor bituminous mixes and for cement concrete road surfaces. Recently,the Study Centre for Road Construction took the initiative to extendthe investigation to the much used concrete blocks. The aim of thisshort contribution is to report on the first results in this respect,and in particular to see how concrete blocks compare with bituminous

mixes, and above all with cement concrete road surfaces.

2. FUNDAMENTALS OF LIGHT REFLECTION

The basic notions regarding reflection properties of road surfaces mayeasily be explained with the help of figure 2. Here A denotes a lanternwhich emits light towards road surface element dS. This causes on dS ahorizontal illuminance EH and consequently dS obtains a luminance L per-ceived by observer o. Obviously L is proportional to EH' so one maywrite:

L=q.EH

in which q is called luminance coefficient and is expressed ind -2 I -Ic.m . ux .

q is not a mere material property of the road surface. It is to a largeextent dependent upon the angle of illumination (y), the angle of ob-servation (a) and the angle (8) between the vertical planes containingthe directions of respectively illumination and observation. In publiclighting a may be taken as a constant (1°9'), and so one gets:

q = q (y,8)

For public lighting purpose q-values need be known at a large number of

combinations of y and 8 in order to have sufficient information aboutthe reflection properties of the road surface under consideration. Away of handling such a set of q-values is to plot q at each direction

.~,c of light incidence as a vector from dS as origin against the direction"

I ",;,

:~~""'"

I~:

",",

, ~

- 40 -

-~a

0,..4~cu

~~cu~rn~

0,..4

00~

0,..4~.c00

-,..4~

~a

0)p.>.~

1-1cu

~~(J

0,..4~1-1cup.

0)~a

>..0

~-,..4~

rn0)(Jcu

~1-1~rn

-0cua1-1

00~

-,..4~(J0)

~~0)1-1

>.~~~0)1-10)

~~0,..4-0

1-1~a

~

-

0)1-1~00

0,..4~

;'

- 4] -

II

i

3. CHARACTERIZATION OF LIGHT REFLECTION'c c

Research carried out on behalf of Working Group"E'z 1.1Rdad"tighting andsurface texture" of the Study Centre for Road Construction has shownthat the reflection indicatrix of a road surface is fully characterizedby the measurement of only three luminance co,efficients. Figure 4 showsat which three directions of light incidence the'luminance coefficientsmust be measured.

(,,., ..',~;.:".:.",~ j

,.","'"

- 42 -

~if

Figure 3. Reflection indicatrix.

From these luminance coefficients - denoted by q - two parameters may

be derived, viz. P(2;0) and P(1;90). Their definition also follows fromfigure 4. They are characteristic of the shape of the indicatrix. Thesize of the indicatrix may be accounted for by q as scale factor.

p4. CLASSIFICATION OF ROAD SURFACES

With regard to light reflection road surfaces may be represented in aP(2;0) - qp diagram. Figure 5 shows such a diagram for bituminous mixes,

e.g. cold asphalt and asphalt concrete, and cement concrete road surfa-ces. It appears that these road surfaces lie in a parabolic band withinthe diagram.

Research carried out for the afore-mentioned Working Group has shownthat two classes of road surfaces may be distinguished. These are deno-ted by CI and CII. Their boundary lies at P(2;0) = 0.4.

Road surfaces within CI are preferred over those in CII, because theirlevel of reflection is on the whole 25-50% higher, whilst their unifor-mity of luminance in street lighting, again on the whole, is at leastas good as the uniformity of the road surfaces which belong to CII.The qQ-values of the road surfaces within CI show a normal distributionaround a mean value of 0.08 cd.m-2.lux-l.Since in street lighting the mean road surface luminance is proportio-nal to qp' it is obvious that a preferred area may be distinguished inthe parameter diagram.This is defined as follows:

P(2;0) ~ 0.4

qp ~ 0.08 cd.m-2.lux-l

~

-Jf

iL'",-, 43",.' - -rI"'"

!~

fl Ii'

i

; :

,~!

,

! A":, '!

J Figure 4. Schematic representation of the directions of light incidenceII I, 2 and 3 for the measurement of resp. qp ' q (tan y = I, 13 = 900), °

and q (tan y = 2, 13 = 0 ).: Note: From these measurements the characterizing parameters

are calculated in the following manner:

P(2;0) =8.95 x 10-2xq(tanY=2, 13=0°); qp

fj P(I;90) =3.54 x 10-1 xq(tany= 1,13=90°)'i qpt:c

.[; qn = scalefactort; t'

I:,

O.

CI I CIII

00 6

~ P(2;O)Figure 5. P(2;O) - qp diagram for bituminous m1.xes and cement coi:crete

road surfaces.

- 44 -

Cement concrete road surfaces were found to belong to CI where they liearound the lower border of the preferred area. An analysis of the rela-tionship between the composition of bituminous mixes and reflection is

summarized in the Appendix.

5. LIGHT REFLECTION BY CONCRETE BLOCKS

The afore-mentioned luminance coefficients have been measured on con-crete blocks in order to learn how light reflection by these blockscompares with the reflection by bituminous mixes and concrete road

surfaces.Two types of concrete blocks were available, viz. grey ones and red co-loured ones. Of each type there were 10 new blocks and 10 blocks whichhad been in use. The used blocks had been in use long enough to justi-fy the expectation that they would no longer change with time. The newblocks - grey and red - were of one manufacturer, and the used blocks- also grey and red - were of another manufacturer. Therefore it is

not possible to draw definite conclusions about ageing.Figure 6 shows a representative block from each of the four categories.

~

above left: red used above r,ight: grey usedbelow left: red new below right: grey new

Figure 6. Examples of the four types of concrete blocks.

Table 1 contains the mean values of the parameters P(2;0) and P(I;90),a~d of the luminance coefficient qp toget'her with the standard devia-

t10ns.

_i

,,"~~"C--'

r _I~"I "", - 45 -

!I

1.1

Ii Manufac- Type qp P(2;0) P(I ;90)l~ turer ( d -2 1 -1 )il c.m . UXi~II I red used 0.055 0.64 0.39}~ (0.003) (0.09) (0.01)l~I'l I grey used 0.050 I .31 0.39\~ (0.002) (0. II) (0.00)

.."

t,! 2 red new 0.054 0.89 0.41~$ (0.001) (0.008) (0.00)fti:

11 2 grey new 0.066 0.68 0.38r"I\;~ (0.002) (0.10) (0.01)",'1'"

tl Note: data between brackets are standard deviations0:;2':0

'@ Table I. Photometric data measured on concrete blocks.1~

:i! The c~ncr:te blo~ks have also been plotted in the P (2; 0) -:- qp diagramIi for b1tum1nous m1xes and cement concrete road surfaces (f1gure 7). Thej data have been plotted together with the 2s-limits, i.e. in 95% of therl cases the qp and P(2;0) values of the type of blocks concrened will liei~ within the rectangles about the data points.

I

1, 008 -I;~ .

I 0. grey 8 used

I ::,\!OC I I C "T1"

j ig; .4.1.

~ III ai'" 6I~ a Q.2 0.4 . . . . . ."ill ~ P(2;0),,'"

f:

l Note: new blocks and used blocks are of different manufacturers.11

ii:i Figure 7. Plot of concrete blocks in the diagram of figure 5 togetherto with 2s-limits.

1 Figure 7 shows that concrete blocks by and large conform to the bandIi' which was found for the road surfaces investigated earlier. It may bej remarked, however, that the concrete blocks are on the whole more.II'c ,

'i;\ l:

:~

I i -CCA"

",.

- 46 -

specular than the other road surfaces owing to their relatively large

P(2;0) values.For practical purposes it is more interesting to take a look at theused blocks. Here one sees that the particular type of grey blocks isnot well suited for public lighting because of its high P(2;0) valuewhich would lead to too shiny road surfaces.The particular type of red blocks, however, behaves fairly well and apavement of such blocks may be compared with some of the bituminousmixes one may come across. It must be remembered that the used greyand red blocks are of different manufacturers, therefore it may not beconcluded that red blocks are better than grey ones.It is not possible to draw any conclusions regarding the effect of age-ing since the grey new and grey used blocks are of different manufac-turers. The same holds for the red blocks. Neglecting this, the greyblocks show increasing specularity with time as one would expect. Thered blocks, however, show the contrary effect. But here the rectanglesoverlap so the difference between old and new is relatively small.

From the present random samples it must be concluded that from a lightreflection point of view concrete blocks behave less favourably thanbituminous mixes and - which is here more relevant - cement concrete

road surfaces. It may be held well possible, however, that means can befound to shift concrete blocks into CI and possibly to raise their q -

value. One of the means to this end would be to provide the blocks w~th

a textured surface.

APPENDIX

Summary of the analysis of the relationship between reflection andcomposition of bituminous mixes

The investigation of the Working Group has led to the following conclu-sions with regard to bituminous mixes:

AI. As far as bituminous mixes are concerned no systematic relationshipcould be found between P(2;0) and qp on the one hand and the typeof bituminous mix - e.g. cold asphalt or concrete - on the other.

It may therefore be concluded that the relationship between reflec-tion and composition is determined only by the applied chippings.

A2. Bituminous mixes which contain the usual chippings may appear any-where in the diagram: as well in CI as in CII, however, not in thepreferred area.

A3. With bituminous mixes in which usual chippings have been replacedby white chippings, e.g. Luxovite or Synopal, it has been foundthat, if 30% or more of the total mineral aggregate consists ofwhite chippings, the surfaces fall within the preferred area. Sur-faces containing less than 30% white chippings will. belong toclass CII.

A4. Also in case of surface dressings or surfaces containing pre coatedchippings (e.g. hot rolled asphalt, topeca), the application ofwhite chippings leads to surfaces within the preferred area.

,

Ji

.,~

-

ro' 71,

t - 47 -f

t:, CONCLUSIONS

I In th: ~ymposium it was empha~ized that internal production contro~ has, a pos~t~ve effect on the qual~ty of the blocks and that therefore ~n-

ternal production control is necessary to present high-quality blocksi to .the user. Many developments will be co-determined by the demand, the; availability of proper raw-materials, the need for exactness in size-

i tolerances and the need for mechanisation of block laying.By further improvements in automation production volumes may well be

I significantly increased.

t, In view of the applications of concrete paving blocks it is desirable1. to aim at uniformity in block shape and block dimensions, on the othert hand variation in block shape will stay with us if only with an eye on'1 the visual aspect.j Of course for developing countries the consequences of production, qua-I, lity and laying techniques will be different.

; The results based on the papers presented during the Conference can be1 suIlUllarized as follows:

1 DESIGNj! Four types of design methods can be distinguished, namely:\ I. Design methods based on full scale testing of block pavements.I] 2. Modified asphalt design methods, based on CBR design philosophy.

3. Design methods based on linear-elastic multi-layer calculations,using elastic moduli for the various pavement layers.

4. Design methods based on finite element calculations.This approach has the best potential to analyse what is really hap-pening in a block pavement under loading conditions.

" On this Conference the theoretical design methods were emphasized,

I i which might have been a bit.disappoin~ing for the pra~tical engine7r~.l In the next conference spec~al attent~on should be pa~d to the ver~f~-; cation of the theoretical design methods.'. However, it became clear that the behaviour of block pavements ('pro-

: gressive stiffening') is different from that of asphalt and concrete; pavements.;~ CONSIDERATIONS ON THE CHOICE OF CONCRETE BLOCK PAVING" - -- ~

f It was made clear that there are two main applications of concrete,) b~ock pav~ng, namely built-up areas and heavily loaded industrial areasy l~ke term~nals.i However, adequate physical properties of the blocks are required to bef sure that the durability of the pavement structure is sufficient.i, CONSTRUCTION PRACTICE

In this Conference much attention was paid to mechanical block laying,

which is gaining ground because of costs and, in some countries, for

~fE,t: protecting the health of the paviors.

~~~'1c, ,

i

jii

"'",

- 48 -

Mechanical laying has its influence on the concrete block manufacturing.Furthermore it should be noted that the performance of the pavement un-der traffic in the case of mechanical laying is not always as good aswhen the blocks are laid by hand. One of the reasons for this is thaton this moment by machine not every laying pattern can be realized.

PAVEMENT MANAGEMENT

In the Conference low attention was paid to block pavement management.

However, experience in this field with asphalt and concrete pavementsis coming to block pavements.Condition rating is only possible and useful if we appropriate a modi-fied detection system.It became clear that there is no unique performance standard, for exam-ple the acceptable rut depth, because subgrade conditions and mainte-nance costs are different in the various countries.

MATERIALS

With respect to materials, it is felt that an increase of the abrasionresistance is the most important condition for an increasing applica-tion of concrete blocks. Possible the use of waste materials and by-products can be increased.

STANDARDS, SPECIFICATIONS AND TEST METHODS

It was shown that world-wide there is no uniformity in the judgementof concrete blocks.However, it is to be wished that some day there will be one strengthtest procedure for comparison of test results. ---

The strength requirements are dependent on local conditions, like frost-thaw regime, if any, and the magnitude of the loads.

~

I.

II

-

[.c

- 49 -

RECOMMENDATIONS

1. Judging from the papers offered for this Conference, it is felt thatthere are some 'blank areas' with respect to the application of con-crete block paving and that some kind of information is lacking.It is clear that the themes deserving emphasis in a next conferenceare: test methods related to concrete block pavements, performance

models, verification of design methods and pavement management and

maintenance.! The next figure, showing the deterioration of a pavement structure

as a function of time, summarizes the foregoing: which curve is va-" lid for the block pavement under consideration and where is it at

present?

quality

.-- ""

"'\m-""' '\"""""". :Ir. \

"'. \" \'" \

I "" \

1 time

Deterioration as a function of time for three different pavementstructures

i 2. The main developments in a wide area of applied research and quali-

ty control of 'open' pavements are found in the countries that pro-vided the strongest response at this Conference: Japan, Australia,I South Africa, United Kingdom, United States of America and The Ne-

,:.'; therlands.,~ :

?~c f 3. The broad participation and attention in this Conference on Concrete;: Block Paving (technical sessions, exhibition, manufacturing sympo-

I sium, excursion) indicates that it is a proper basis for a benefi-' cial exchange of know-how between principals, users, road authori-

ties, researchers and manufacturers.It should be considered, however, to widen the title to 'Internatio-nal Conference on Small Element Paving'.

, Therefore it may be desirable to set up an international 'Steering

Committee' with representatives from Asia, Australia, Europe, South

j

, -..IV

Africa and North America. The objectives of this Committee could be:- formulation of the scope of the international conference in rela-

tion to small element paving- stimulation of developments for test methods (streagth, durabili-

ty) and standardisation- pavement management and verification of design methods.

A general conclusion of this Conference might be that it has been shownthat the construction of adequately performing concrete block pavementsis a reality, noting that quality and performance are strongly influ-enced by the quality and construction of the underlying materials.Concrete block paving has proven itself as a structure with many possi-bilities for application.

See you all at the next Conference (in 1988?).There will always be a 'concrete' reason to remain 'locked.."up' in contact.

Prof. Wim van Dijk

4

A remaining memory to the Second International Conference on ConcreteBlock Paving 1984 near the entrance of the Main Auditorium of the DelftUniversity of Technology

,

-

r

- 51 -

BU TWEEDE BETONSTF ~~IIII~,r ""00 .~..(°.IJ: '~Q4CONGRES IN DELFT ./)~ J:". ,.,. 1J. rsl~ ~""'8

..- v~qt~;., ~ ~~~ ~~, <it . ~I lqql./)~ 'l ~~" 0:1 t~ tt.- 8t~ ~ ~S" i} ""'l ~~c' ~'.{-~/'8 ~~ .:;': tr a o~:tll}q~O~t~ "'cI~ V" ql qq~ ~/'8 'I] 4. '#.. Il}ql. Vq 1]" C'l;l

I~t "I~/, 'I} 1} Il} ~/'Pr 0 l~/'I{;; I~ ~t ~~t~1] tt.-o/'C1~

.olt qq:~C1~ ~~ <: ~~/' 'I}.~~ Q~ I; ~/q I~/. *~.... t ~I't "I] 'I},-J "It,(j~ ~, ~~ r. '" .

~ Il]t, ~ "Vp

j :tege ~~'9 ~stra -,pdrachtgevers. vaakn~m'

overheidslichamen en 0, ./It werpers - worden bij het, . 0, treden van de aula d

oJ : :t: FNV'ers staande gehou(S J!!. :S ~ <Z>.~ -' om een stencil in ontvangs

.I '" '"-'.I"" <Z> 0)'" ~- .C:.So' fI1 c: .. nemen.D,EL"~.&, ~ 0, f:? ;;; -E iii ~ du t ,.U doet nu net of hier bimmet,'; ~ ~ ~.S 0 ~ 0 ~ M . iets heel kwa1ijks gebeutig 0- E! -!!7 ~ ~ <Z>() ;fj 8: <Z> ~ ba Ii meent it. C. Heegstra. ho~ (j 0, c:' 6';C::: q; <Z> 0 "c:';;.t ~ wegen en verkeer van de J:6J § ~.S?>.o "",t:: c: ~ ~.c: ... ); vinciale waterstaat in Dr... ().5 if <Z> 8 .So ~ '" <Z> .f:1.:E.. q the en lid van het organisaI' - i::" 'tj 0- fI1 if fI1 :;, .So c: s'l , camire. Hij vindt dat,~;:: <Z> (j o,i::".:::::; cZI cZI g <Z> 1 Z., bouw- en houtbond even]

.'10 ,9:S C:.S ~ ~::::: ~ :;, () 3 ce. ~ moeten zeggen dat ze een,~'"-' O~"'V"o<Z> c:-- - ~ () ~ :;, '" ' ,t:: to. e str I; drage zou hebben voor"' ." 0 .- - <Z> :0f "s'.8 0- () ~ ~,t:: 0, 1 ou ... congres, maar dat is bet1 <Z> fI1 <Z> <z>' £: 8> .So <Z> 8 . er '" nou juist de bond werd() <Z> ().f.? 0" § 8> ~ () -ie ~, weigerd. want er stand 0fj 8' ~ -.;; c: £: ~ '" fI1 . io dit onderwerp al iemandt ~ tfi l! if § Q. cZI ~ .S gr.s is' de sprekerslijst, it. E. :c.So ;:: fI1 ~ ~ S '" ~ :.::; 4,1 v I-c ningsveld van de Bedrijf~§ -co:- '" g>~ ~ 0- C5 f §.. zondheidsdienst voorf £: ~ -q;- 6' -8 <Z> ~ -'r5i J I) Bouwnijverheid.'tj -0::::: fI1 ~ !Ith,,-.- -0 °..s> .~ 8 "j!f rdt It 0 ' ql'~ : Geopereerd

()fI1oe ec'fff"'eette J h: K'l'Oat 1I.1a ~all It Het vierkante fysiek van

, ~tollst~ llterllat.2 Jll e ~"strant Egbert Kamstrjedaa Ciatste lOll 'r ...tse Nieuw-Buil ~1) &"Se COllllell C . - -I~ dertig j

ordell ~1I11ell 13K'l'es ( . -- 1(S

II J/:epreSe PaPe~Ilell: Jell",.2; llteerd

&"er~~lcStatell~e~ll~ a ~

lrdell ~ ~all Ste alla q1s de all "'e llellSill&" it'eg ll;:ell is ltof ~ ~all cellJ r ItOllJ

Oard . elltl.-e dat Je st ueto, lIllJ ellell .

tll derti' i!Jaar be Jellsch &" Jaar ~ 8

erh apPel.'. reee A-' ats-- ardell ljlc °lld,

111 ~qell 'f:lle llJet eet t", Op gall II echte e

[OIlK'l'esee ~all d: gelc°llJe1" Pas e \\\3.\\'JoJt[.J. lioProl ~rgallisa ll. E:.ell~ Ilhell I.-. ~ ~ torell'deJj,,_!P- J'er".:.ueide;' _.~ ./)/"- J': t5