Freeze-thaw durability tests upon concrete paving block specimens

Introduction CONCRETE block paving. in common with any other paving. must be of a quality sufficient to ensure an adequate resistance to damage by both vehicles and weather during the design life of the pavement. Surface and structural damage to pavements caused by alternate freezing and thawing can be a serious problem in many countries. This damage is exacerbated by the use of de-icing salts. Fortunately. in concrete pave­ments an excellent resistance to such damage is effected by incorporating the correct proportion of air in a properly proportioned and manu­factured concrete. In the UK, if it

T ABLE I: Mix details - Phases I and II

by A.J. Clark Cement and Concrete Association, UK

is to be considered adequately durable, a paving quality concrete must be air-entrained and contain 3 to 6% by volume of air; it must also have a minimum indirect tensile strength of 1.8 N / mm 2 at 28 days, a minimum cement content of 280 kg/ m' and a maximum water / cement ratio of 0.55'.

The manufacturing process used to produce paving blocks requires that the concrete used .shall be of a low moisture content. The stiff con­sistence of the fresh concrete inhibits the action of air-entraining agents and, also, makes the measurement of the air content extremely difficult. therefore. air-entrainment is not used

Specimen code

Aggregate Cement content (kg/ m')

Moisture Aggregate: Water/ content cement cement

(%) ratio ratio

PHASE I IjR+Gj5.2 IjR+Gj6.9 2jR+Gj5.0

2jR+Gj6.8 3jR+G/5.2 3/R+Gf7.0

I/G+Gj6.2 al/G+Gj6.1 al/G+Gf7.1 2/G+Gj6.0

b2/G+G/5.9

PS

IjR+Rj5.4 IjR+R/6.9 2/R+R/5.5 2/R+R/6.9 3/R+R/6.5 3/R+R/6.9

PHASE II A B D

R, +G, R, +G, R, +G, R, +G, R, +G, R,+G,

G, + G, G, + G, G, + GJ

G, + GJ

G, + G,

R, + L + G,

R, R, R, R, R, R,

R, + L + G, R, + L+G, R, +L+G,

570 570 456 456 380 380

570 570 570 456 456

estimated as 350

570 570 456 456 380 380

474 267 183

5.2 6.9 5.0 6.8 5.2 7.0

6.2 6.1 7.1 6.0 5.9

5.4 6.9 5.5

6.9 6.5 6.9

6.8 4.2 4.9

R, Mount Sorrel Granite (10 mm maximum size) G, North Notts Sand

3: I 3: I 4: I

4: I 5 : I

5: I

3: I 3: I 3: I 4: I 4: I

5.8: I

3 : I 3 : I 4 : I 4 : I 5 : I 5 : I

3.7: I

7.6: I 11.5 : I

G, Gravel (Sandy, Bedfordshire) (5 mm maximum size) G, Sand (Sandy, Bedfordshire) L Limestone (5 mm maximum size)

106

0.22 0.30 0.26 0.36 0.33 0.45

0.27 0.25 0.30 0.32 0.31

0.23 0.30 0.29 0.37 0.41 0.44

0.32 0.36 0.62

in concrete paving blocks. To ensure adequate durability under the com­bined action of frost and de-icing salts, it has been the practice in Europe to specify a level of paving block strength. This strength was derived from experience gained over many years of the performance of block paving when exposed to natural freeze-thaw cycles plus de­icing salts.

Five years ago. the Cement and Concrete Association, when produc­ing a specification for concrete paving blocks, followed this prece­dent, basing the level of strength specified upon European experience and upon some freeze-thaw tests carried out in the laboratory2.

Recently, more extensive tests have been carried out to evaluate this practice and to obtain a better understanding of the factors affect­ing the resistance of concrete paving blocks to damage by frost and de­icing salts.

It was originally intended that the specimens for the tests should be manufactured in the laboratory using a series of mixes that covered the aggregate types and mix proportions used in the production of the paving blOCks. However, following dis­cussions with paving block manu­facturers and representatives of the County Surveyors' Society, it was decided that the specimens would be more representative if they were produced on a standard production machine. A number of companies offered their services for this purpose and the specimens were eventually made by S Marshall & Sons Limited. using Sutcliffe Speakman plant.

Test details The test programme was carried out in two phases and Table I gives the mix details Df all the specimens tested. All paving block specimens were 200 x 100 x 65 mm thick, these being the same dimensions as one of the range of paving blocks produced by S Marshall & Sons Limited. In Phase J, aggregate types and mix proportions were selected, as pre­viously described, to cover the ranges used by all manufacturers. It was found, however. that the manufactur­ing process used to form the speci­mens (which was by the application of pressure alone unlike some other processes in which vibration is the

Concrete Block Paving

, FiI_ 1,' Ri"'''_loIp btl....,. "'",ily (. ~,~ .. <If' '1''''_"' """ _-.;,h , /""

' '''",' J: i/,J.li,,",hip bt,.· .. ... ", I<"'~'" ,.'iq """ _ ;p' /0 ..

"

, --,~ ' '1

0

, .. ,,- • -~'..,

0

--' •

-•

.. , . ~ ",. • .. • o ~

• • • .. --"."' ..... , .. ""0 • , .. _.-.. " • ..

, o.

'. " . .. o • • •

0 .. 0

•

0

..

ma in means .of cornpaClion ) had diffocul ly in prod uci n, I he ,rI"ci and .... tu ral sand (G + G ) Ir>«i mon. c'r>«ia lly wi.h lhe lowe.. a;mcn. COn" nl. A n a"cmp"o overcome . hi. difficul. y ""'" mado by dll n"n, '0. finor sand from. d,rre' enl IOU...,. bu • • hi. r.iled ligmficanlly 10 imp.o,.., ,h. 'i' '''''ion and ,h.",fo" no 813,..,1 ."".imens wt'" produud ... " h .h. lo"'esl cemen, eon'e nl.

The Pha s<: r " '" also inc luded 200 ~ 100 mm 'pecime ns CUI (rom p''''ing slabs mod. 10 8 S 368:1971'; Ih.s. , ,,,,eimons woro of a . j mil" r (h ie l< n." (0 (he other le,l specim en" T1I< ro arc ,<Iv rew. if any . '"poned il1 l1o ne." of jliIving slabs ma de to liS Jr.Il , u(fering from f.",! plu s de·icing sa h' a nd i( wu inten ded (hal lhes<: . pecimen. , hould be us<:d bOt h as a ba ,i. upon which to judge the ...... rily of the ,es' re"rne Ind .. a da tum wil b which lhe "".form.""" or block "r>«irnens could be compa red .

Phase II t .. IS ...... on s!>"; mcns · h ind . " • ow.r «rnenl conlenl • --~' 'o' ''' •. , _

o . ,.,-... ' .'-,6 • • _ ~ . ~ ... -

' ,,- ... , " 'M' __

, • " "."1 • o · • , •

• 0 •

i ' · 0 • • , ' . 0

• -. .. • .. ~"' ", .. - .. /-'

• "-... , .. G . ~ •• o_ c • ••• _

oO ... "'-, 1>- , 0"._ • , • .. ---o . .. _.-

0 • .. 0

-, .. • ~ <t . • • 0 o 0 '

0

• , • • / ..

• ' 0 o •

" "" .... , '00, _ .. 1_ ' .. •

••

TABLE 2: Surface damage rating

Raling

o No scaling

Very slight scaling (I mm depth, no coarse aggregate visible)

2 Slight to moderate scaling

3 Moderate scaling (some coarse aggregate visible)

4 Moderate to severe scaling

5 Severe scaling (coarse aggregate visible over entire surface)

specimens of a greater age than those tested previously. Normally, speci­mens were first exposed to the freeze-thaw regime at an age of approximately 35 days; in Phase II, however, some unused specimens from Phase I were tested to deter­mine what effect, if any, age had upon their durability. The specimens with lower cement contents were tested to obtain further information upon the effect of cement content on durability.

Freeze-thaw regime The paving block specimens were subjected to a freeze-thaw regime that complied with the RILEM Recommendation CDC 24. This recommendation requires that the specimens should be subjected to a temperature of -200 C ±2° C for a period of 16 to 17 hours before thaw­ing for 7 to 8 hours. The capacity of the freezer used for the tests must be such that the air temperature at 100 mm distant from any specimen shall be _18 0 C or cooler at 7 hours freezing.

The specimens are exposed to de­icing solutions by forming a dam on the surface of the specimen (see Figure I) within which a 2-3 mm deep, 3% concentration of de-icing solution (weight! volume in water) can be contained. A 3% solution is recommended because this has been shown to be a critical concentration in frost attack upon concrete. Rock salt, most commonly used -in the United Kingdom in de-icing public roads, was used to make up the solution used in these tests.

To assess the durabilitv of the specimens. the RI LEM - method recommends that at regular intervals throughout the test measurements shall be made of the weight of spa lied material. if any. and observations made of the severity of the spalling. i.e. depth. area and rating of the surface damage caused. The levels of assessment used in the rating of

108

5th cycle

0.

'I- 0.

o .... 25th cycle

0. MEAN 3

RATING VALUE 2

'I- -?-0 0." o , 50th cycle

3 0. 0 0" ~- •

• • 0.

to "

.., t~. ~-

to·,,·t B

~(j

t ~ 4Il W/C-O·S2

0

~ o w/c_ 0-62

~

t ~ (j

•

Agg/Cem

(j 3:14:15:1

.t ~ o • 1# R+G specimens D. G +G specimens o • ~ R1"R specimens

(9 monl~ age)-<?--.-+ R-+G specimens

L ~ha;e ~ specimer$

03 0-' WATER/CEMENT RATIO

0·5 0-6

Figure 4: Relationship between mean value raling and water/cement ralio

surface damage are shown in Table 2. It should be noted that, for the speci­mens tested, the maximum size of aggregate used was 10 mm. In this test programme, assessments of the damage, ifany, were made at the end of every fifth cycle to a maximum of 50 cycles unless the specimen was withdrawn through failure. Failure was defined, for this purpose, as the point at which the brine solution could not be retained by the dam due to excessive loss of surface material from the specimen.

Simultaneously with the exposure of speCimens for the first time to the freeze-thaw regime, a number of tests was also carried out upon other specimens taken from the same batches. These tests were compressive strength (as per the Cement and Concrete Association specificationS), absorption, dry density and initial surface absorption. It was hoped that the results from these tests, together with those obtained from the freeze­thaw tests, would identify parameters that could be used in the prediction of the durability of a paving block exposed to frost plus de-icing salts.

Results The relationship between the results obtained in the various tests carried out on the paving block specimens remained largely unchanged throughout the freeze-thaw tests. This is demonstrated in Figures 2, 3 and 4 at 5, 25 and 50 cycles. To help reduce the number of Figures, where the result pattern does not permit more than one set of results in a Figure, only those obtained at 25 cycles are given.

The cumulative average weight losses recorded at intervals of 5 cycles for the specimens tested in Phases I and II are shown in Figures 5 to 8. Five specimens were tested for each mix; where specimens failed to com­plete the full test programme, this is indicated in these Figures. A particu­lar example of this is in Figure 7

where two 3!R + R/6.5 specimens had to be withdrawn at 25 cycles and therefore the weight loss values from 30 cycles onwards are the average of three specimens only.

Generally. for a given water! cement ratio, the rate of weight loss was the same irrespective of the particular aggregate combination used in manufacture. Some of the results obtained for the gravel and natural sand specimens (G + G) were influenced by failure -of one or two pieces of the gravel aggregate in the freeze-thaw cycles. It has already been reported that, due to the method of manufacture, some diffi­culty was experienced in producing these specimens. This led to a rather exposed surface finish which prob­ably contributed to the attack upon some of the aggregate.

The first instances of spalling usually occurred where a larger piece of aggregate lay immediately below the surface. Depending upon the specimen, this spalling then tended to spread and, in extreme cases, led to loss of the larger aggregate. Although in some cases surface loss could not be detected visually, all block specimens suffered some degree of surface loss by the completion of five freeze-thaw cycles. The paving slab specimens, however, did not suffer any loss until the 25th cycle, when one of the specimens became slightly spalled. This was joined at 35 cycles by a second specimen but the remaining three specimens were unaffected by the freeze-thaw regime. This would appear to indicate that the laboratory tests were no more severe than natural conditions. How­ever, it is possible that the durability of the paving slab in relation to frost and de-icing salts is greater than is required for the natural conditions experienced in service and, therefore, the regime could be more severe than natural conditions.

Results obtained from the tests carried out in parallel with the freeze-

Concrete Block Paving

thaw tests are shown in Figures 2, 9, 10 and II plotted against the average cumulative weight loss values recorded for the freeze-thaw speci­mens. Despite the range of cement contents used in the PIlase I tests,

380-570 kg/m3, the range of block strengths obtained remained fairly narrow and no positive relationship was established between the strength of the specimens and their weight loss. In an attempt to widen the range

1o.------------------,--,

WEIGHT lOSS -mg/mm2

10

0·1

o 1/R+G/5-2 .1/R+G/6-9 o 2/R+G/5-0 .2/R+G/6·8 o 3/A+G/~'2 • 3/R+G/7-0

NUMBER OF CYCLES

WEIGHT LOSS­

mg/mm z

...

0-10

of block strengths, Phase II tests included specimens of a lower cement content than the lowest used in Phase I. The results obtained from these specimens (B and D) did fit the relationship that had been presumed

NUMBER OF CYCLES

o I/G+G/S-2 • al/G+ G/S-' o al/G +G/7-, .2/G+G/6-0 o b2/G.G/5·9 • P.S.

Figure 5: Relationship between average cumulalive weight loss (5 specimens) and number oj freeze.thaw cycle ..

Figure 6.- Relatiunship between average cumulative weight loss (5 specimens) and number aJJreeze·thaw cycles

WEIGHT lOSS­

mg/mm'2

10

1·0

01

o IIA +A/5-4 _ • 1/RiR/6-9 o 2/R +R/5'5 • 2/A t-R/S-9 o 3/R +A/6·5 • 3/R + R/S-9

O·Ol':.O--'~--,;20;-----c;;,---:;.\;-0---.\50'"--,,!60 NUMBER OF CYCLES

'Figure 7: Relationship between average cumulative weig (5 specimens) and number oj [reeze·thaw cycles

Concrete Block Paving

ass

WEIGHT lOSS -mg/mm 2

10,------------- -----,

10

0·1

eA •• .0 o 1/R -+ G/5·2 (9 months age) o 2/R -+G/5-0 (9 months age) o 3/R<t-G/5·2 (9 months age)

0.010!-----,L,---+--~,._--J,----50L,----J60

109

at the start of the programme but, overall, the correlation between strength and weight loss could not be said to have been proved.

Phase II tests upon nine-month old block specimens showed that although age had led to a significant increase in strength (19-45%) the

weight losses remained approxi­mately the same as those obtained for· specimens tested in Phase I. Only three mixes were tested in this way and further tests would be necessary in order to fully investigate this result. The rather large gain in strength between 35 days and 9

months is judged to be caused by the initially low level of hydration, due to the low moisture content of the concrete mix, being increased by moisture in the atmosphere surround­ing the specimens until the time of testing at 9 months.

Like compressive strength, the

90',-------------------------------------------------------------------,

110

80

70

MEAN COMPRESSIVE 60

STRENGTH - N/mm 2

50

40

5-1

4-9

47

ABSORPTION -I. 4·5

4-3

41

3-9

37

0-01

0·25

0-2

0-15

I.S.A.I. READINGS

- mt/sec

01

0·05

Aggjcem

3:1 4:1 5:1 o • 0

o • R i" G specimens

G ... G specimens -9-o • 0 R i" R specimens

5·9:1 t::. P.S. specimens

-¢- -~- -9- R + G specimens (9 months age) Phase n specimens

" '" 41

25th cycle

-,-0

0

~

0

'" 0

0, • -~-

0 • • ~

<01 •

0·' '-a WEIGHT lOSS - mg/mm 2

Agg/Cem 3:1 4:1 5: 1 o • Q A + G specimens

O. G +G specimens

o • ~ R ... R specimens

t::. P.S spe,cimens

-9- -~- -9- R-+G specimens (9 months age)

Phase n specimens

" OJ 41

25th cycle

-0-

o o

o

, .

• 0

0 • 0

0

• • <01

-i-

~

" •

0-1 ,-+ 3.55% 10

WEIGHT lOSS - mg/mm 2

~<OI

<01

'" ~

Agg/Cem 3:1 4:1 5:1

• * only one specimen lested

0 • 0 • 0 •

t:.

0 R + G spec.imens

G ... G specimens

0 R ... R specimens

5·8:1

'" P.S. speCimens

o

• o

•

·10

"

10

g~01~-------------------0~1--------------------~1~0~------------------~,0

WEiGHT LOSS - mg/mm 2

Figure 9: Relationship between mean compressive strength

(10 specimens) and weight loss

Figure 10: Relationship between absorption at 24 hours (average of5 specimens) and weight loss

Figure II: Relationship between [SA Tat [0 minutes (average oj 3 specimens) and weight loss at 25 cycles

Concrete Block Paving

-_ ..... - -. '-' --" ~[l rvl,n . .

"""''' . In r'l • w · - .. - • -. ., ... -. .. - • - .. - - -. .. __ n_ ... _ .'0<00<0.',

'_'_R ~- - .. ,- -, , -•

I _.

Lm • · , 0,",'"

I r'l ,-· - - - .. - - - - .. - , ...... - .. ""' .... absorplion. densny alKl ,nilial . urf ""~ a I»-orp' ion (I SA n al'" f. i led 10 exhibil a posi",. forrelalion wilh weighl 10 ... <C. Fi~uru 2, 10 aJ>d II. Ahhnugb. due 10 d,r/lcuhies wilb 'bo appar.,u •• not ali lSAT .esull, were oblained in Phase I aJ>d none al.1I in Ph.s. II . il i. I hough' 'h:lt. even ir.1I re,u l" had beon lI",h .. ed, " mOrt po,ili" relalionsh,p would nol ha"e b-een ob'aint<!. Th . lac\: of any definile rcla'ion~hip be,ween woighl I<>s< and .bsorption. den.ily or <U r· face. absorpli on would appeat to indicate ,halll>e\C 'tlU oould not be Ui"" .u.:=dully '0 predict the durabilily of plving bl<xh.

Wat~r/«",""n l .... , iOf (I« Table I)

M .. o.p,h: I .... a: ~ R.I,;"., :

Co .. _ 8""" 1"';"1

wcr~ derived fromHSp«dy~ mots,u," moa,uremon .. 'akell on the mix« u<cd in 'he p.od~flioll of 'he .p«i· mon •. Th...., ra.ios a .. ,hown in Figure J 10 ha" a dir«:1 correlalion with lhe weight loss of lhe f .. eze· Ihaw 'pecimenl. This ro lali on! hip i, a l,o demon.tr .. ed ill Fi~ur.s S to 8. Ceme nt COnton' i, iotr inS1ea ll y linked wilh water/conlen' rOlio; Figur. 3 al.o ,h<lw, Ihll impr<lved durab ililY in thc 'e'lS WI' generally providod by an incre ... in the cement oomenl.

The p.~in, .Iab <p«imen1 (om' pk,,,,, tbc f=,c'lhaw 1 •• I$COmpao, •• li"e1y undamaged (ven Ihough IlIeir cemenl con,e", W .. IM low.,,, oflhe Phase I sp«imens. II "'houghl th.,

, , , • , • • ,

the durabili'y of these specimen, i. produced by lhe rne.hod of manu· f.clUre. In Ihi. proc: .... Ihe cOllcrcle mi1 Juppl;.d forI M pav;ng sl.bs is of high W3ler oon,enl. Once plllc"" in lhe m<luld. pr .... u •• i$ applied l<ll he """"'ete by an hydraulic ram and a large pro"",rl;on of 'he W3'" in 'he mill i. oqUceZM <luI. A, lhe oom· pl.';On of lhe pr.",i"g operali<ln. I ho .lab is .je<'od from .1Ie mould ha.in~ ,"aincd <uffi."'nl slrenat h t<l be mechanically handle d. The p.~'agc of 'he water 'hrough 'he CO nere" during the producI i<ln proc.IS .u"ie. fi ne materi. l with i,. Los< of th i< mal<ri.l is prevented by f,lter p.1pcrs on ""th facel of ,h •• lab, .... hich produce a oonecntuI;on of tho fLn .'t panicles cemeno on ' lIelurf~«sof ,lie .Iab . Tllese $urfa«s. ,"erefo ... ha~. a high cemcnl eonl.nl and. beca~ ,lie "," 'er oo<>lenl has be.n considerably reduced. a low ",.te,/ «rnent "lio. fae'o .. which lhe Ie", have .11.0",·n prodU« a higher 1 .... 1 .... thaw durabilil j".

As was 10 be .. peel.d .• urface damage ralings p.oduced • simi]., c<l.",la,i<ln wilh ,,· ••• rl «melll r.lio' and «rnent conten .. 1'00 Tobl. 2). Thc Ph.", 11 low Cernent cOllt. nt ,pe<imen' s uffered i' sign ifICantly higher weigh l los. Ihan oth., SPOC L' me n,; h"",ever . a. Ihe I'ha so I speci· m.n, with a ferne nt C<lntC"' of J80 kgj m' had generally $uffef~"<l the higher w.i~h' I"'$e' in lhe ~!"$t $eri., <If I ..... III. .. ,""ease ,n dlmaSe was '0 be CXp«tM wilh • lIill funher r~duCli<ln in «menl cornen' .

Dioro",ion of , .. ,,11, The f«<",·tha ... ~Jim~ u$ed in 'he$e ,.". ' ''cmp'' '<l ,imullll. lhe oon· dili<l'" lbal can occur in • natural ,iwati<l". Fit"'. 12. whoch shows ,h. numbu n frcc·, c·lb.w cycle. npcr"'nccd in .hc wintc. <If 1978·79 at 'wo locati<ln ; in 'he Uniled King· dorn. indica"s Ihat thc number <If te," cycle, wa . realnnab le. The seve rity <If the teSI! hOI 01'0 been dis· cussed previou. ly in connect ion with 'he performance of the paving ' lab spe<:,men,. Although it il p-ossible ,~ .. paving ,lab> oomplying wtlh as 368 art"or grearerdurlb,lil Y rrum i$ re<juircd f<lr Ihc condili<l'" 10 which ' he~ areupOOCd in so!Vir;:(. ,lie minimal level <If damage t:au,cd '" ,lie .Iab .peeim .... , uUaur Ihal. "'"en if Ihis ""',. corrOOI. ,he: tr;$' rcgim. " 'as only ,Ii.htly mme 'eVc~ 'Mn nalural c<lDdi",," ,. Tile r~s"llI <lblain.d f""m the 1."1 can Ih.rd<ll"<: m.ke a useful contr ibut ion low.rd, <pccifyiog Iho frtt~e·thaw durability of concrete pav ing blocks.

From tho dala ob laillod lind beor· ing in mi nd th. SCQpe: <If Ihis invo" i· gation. Ihc rel ull, <lflhe IIlS I! did no! <how a very clear oorrel.,ion be'w<ocn C<lmr'e.,ive ."ellsth .nd

'"

f , .. ,,· th.~ ."'~"" 1 .. ", "I"''' '0""''' ~ ... nl "M •• p .... " " ""

"' ... ~P'h: l A"" "'l ROO;",:

" ,

"'". ~p'~. 1 At<a: 100 ,

, " ,

,.

, •

,. weighl I",,; therefore. II would 'pp-e"' ,h.,. by """If. ;lrcnglh i. nol on ido.1 m~.n< of pr.d icling dura­hilily. Ho"".'.r. mo," ,pocifi." wi ll prof. r 10 ha,c a ,implc lOll ,h.l oan he u«od 10 asse" compl iance. Absorplion. dCfl,ily and inili~1 sur_ f.ce at>.orp,ion all •• hibiled un C,'OIl

'"

, • •

, ,. •

•• " . ,

, .. ,. . •

lower COl rciatlon than mengl h wil h wei~ht toSl. If ~ ~impk "'" i. 10 be inclUd.d. it would "ppo.rlb., com­pr .. ,ivc Ilren~th i, 11>0 1><;" choic. f,om lhe varLou' p"r.l""'o" Ih., hove be~n e .. mined. From lh. dala ob(.ined in lh. Ie'" i, i, ,ugg<,,<d I hnl ~ ",i nimurn mean bloCK" r<ng(h

of 50 N I mm' could be u,ed in "cOm­pliance te,L Thi •• trtnglh tcvel i. ba.ed upon vatue, ohlained al J~ day< for Ion $pocimon. «Sled in accordance with Ihe Cement a nd CO""rclo A .. o<ialion .!'«'ir", .. io n' .

From the OOTrOlalion obl~i n.d betw..,n wate'/ coment ratio. cement conlenl and "",ighl 10... i1 i. "pp3rcn1 Ihol ..-alor {cemenl ra'io 0' oem.nl conlen1 can be .... d ">ensure a reasonabk du,abilily. Allhou ith wa tor/ umonl '.1io p,odu~od Iii. mo>l posi1 iveeffea upon weighl loss. Ih;' 1$ a fac ' or 1hal would be eXlremely difficull 10 check. should lhe s!'«'ir .. , wish to do so. Tl>orefo,e . ... 1110 .... nge of moisture COntents ust<l in 11>0 manufaC1ure of pavi"3 block. is fairly .... rrOw a nd La,,,,ly 5(' by ,110 produclion proo:: ... i, would a ppear Ihal seuing a minim um Umcnl conlon' i. a .ullablt method of en.u,ing du,ability. S!,«,imcns of ccmcnl conlcnl, below 380 k\(m' .u ffered con.iderabl. ; .. r a ce damage .nd. even a1 380 kglm', $Omo . pecimcn. "ill .uff'Il'd qu il' .ever. surface damage. II would app .... lherefor •. that 380 kg/ m' i. Ihe abwlute minimum level of oemenl Conlcn! ,h., can be pormitled and sli li oh,a in a rea.onabl. level of durability.

flofer.nco. I . D£PARTM£NT O F TItANSI'ORT.

SCOlTlSll DEVELOPMENT O f . PARTMU<T AN () W f.L~1{ OFFICE. Specijkolionlo , 'o~d and b'idg' ~·o,b. Fiflh <dilion. London. llMSO. 197~. 1'1'.194 .

2. Lltlf.Y. A.A. &slgn o/~o"crr" bi<X"k !><,v,mmlS I", \',hleu/o, naffir. ~lnl.l 18. Ninlh Inler­nalional CURve .. of 1110 Prtca.' Concre1.I n<lust'Y. Vionna.3-13 Soplombu 1979 . Repons. Lin>.. V«band O"e'rtiehisc:her 8e1on und Ferligteilwer ke. 1978. PI'. 11-174 - 11·180.

3. BRITISH STANDAIlDS [NSTI· TUTION. 8S )68,1971. Spuifi· ra'ion/o, P'ffO" ron,ulr /logs. London. pp.16.

4 . ISTERSAnONAL UNIO/< O f T ESTISG ASD RESEARCH LAB· ORATORIES FOR MATERIA LS AND STRUCTURE5. RILEM Recommendatio n C D C 2. Mnlro<ls 01 ,"""ying oul and rr{X)rling I"o .... ,ha~· I",. "" eon, .. U ~';Ih d, .. irinK clr"ni~als.

5. CU.IENT ANDCO~"CRETEASS<X"· 'AnO,", A 'fluljirmionlu' rOll­aere pal'i,,!! blork." Wexha m Spring,. 1978. pr.S. Publioation 46.025.