Use of Seawater in Slurry of Cape Seal - CSIR

Use of Seawater in Slurry of Cape Seal - CSIR

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA0061/298 8: Langebaanweg) (Table 1) suggests that Thornthwaite's Moisture Index (Schulze,1958) of about - 40 for the site (which is slightly less arid than Langebaanweg) gives a moreaccurate picture of the relatively arid nature of the area than does Weinert’s (1980) N-value of 4,which seems misleadingly low. Most of the average of 274 mm of rain falls during the wintermonths of May to August and the least during January to March. The mean annual A-panequivalent potential evaporation of about 2 200 mm after allowance for rainfall is about eighttimes the mean annual rainfall.The site therefore possesses the warm, dry climate conducive to salt damage (Netterberg,1979; Woodbridge et al, 1994).Climatic classificationThornthwaite (1931) (1)Table 1. Climatic data.Parameter Units Langebaanweg (0061/298 8)(Lat. 32° 58' S; Long. 18° 10' E)Thornthwaite’s Moisture Index (2)cmWeinert’s N-value (3)-Mean annual rainfall mm/y 274 (4); 265 (5)-Borderline Semiarid Warm (DB’d) to Arid Warm(EB’d), Moisture Deficient in All Seasons- 414Mean annual potential evaporation mm/y 2 200 (6)(1) From a 1:5M map by F. Netterberg (1969) (NITRR/CSIR Map No. RM1-77) after B.R. Schulze (1947).(2) From a 1:2,5M map by S.J. Emery (1992)(NITRR/CSIR Map No. 940-0-4184/4).(3) From a 1:5M map by H.H. Weinert (NITRR/CSIR Map No. RM1-59A/3.(4) Weather Bureau data for 1973 – 1998 (pers. comm.).(5) Weather Bureau (1986) data for 1973 – 1984.(6) Estimated Class A-pan (from Schulze et al, 1997).4. RAINFALLThe monthly rainfall recorded at the site office during the construction period of October 1979 –April 1984 compared well with the actuals and means for Langebaanweg. The actual rainfallwas slightly less than the long-term average. The records for Langebaanweg show that therainfall over the first few years (the critical period for salt damage) was normal. Thereafter (from1984 onwards) it was higher for a few years, but the average for the 18 years of 274 mm wasnormal.Both the total of 59 mm which fell at the site office during the approximate period of constructionand the total of 201 mm for the year of October 1979 to September1980 were less than the longterm means for Langebaanweg of 79 and 254 mm, respectively. This means that the weatherduring construction and soon after opening to traffic was more rather than less favourable thanaverage towards salt damage. In other words, the weather conditions under which theexperiment was laid were not unusual, and even apparently conservative.The total of 4 - 12 mm (S. V. 11,0 - 11,1 km) or 11-12 mm (S. V. 3,9 - 4,0 km) of rain which fellbetween laying the bottom seawater slurries in Oct.-Nov. 1979 and covering them with the topslurry some 1 - 4 months later is considered to have been insufficient to have leached any saltfrom the bottom slurries. However, the 22 mm which fell on the top seawater slurry betweenS. V. 3,896 and 4,015 km after laying on the 3 rd April and opening to traffic on the 16 th April 1980might possibly have leached some salt out if it had not been well-rolled as soon as possible,especially as 13 mm fell the day after laying. The top slurries were apparently not rolled. Theperformance of the top seawater slurries may therefore have been slightly better than theywould have been had no rain fallen. On the other hand, early leaching out of salt might have leftvoids which would have tended to have had the opposite effect.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA5. PAVEMENT DESIGNThe pavement was a standard granular Class N3 Cape Provincial design with sealed shouldersintended for a total of 1-3 M E80 over its design life of 20 years:Surfacing : 19 mm Cape seal (7,40 m carriageways plus 2,40 m shoulders)Primer : MC-30 at hot gross rate of 0,66 - 0,69 l/m 2Base : 2 x 100mm G3 graded crushed stone (granite)Subbase : 150 mm G5 natural gravelThe Cape seal was of the split application type with two coats of slurry.6. TRAFFICThe seven available traffic counts show that the traffic increased from about 700 equivalentheavy vehicle units (e.v.u.) / day in 1983 to about 1 200 in 1989. In 1986 the AADT was 890v.p.d. including about 109 heavy vehicles, equivalent to 1 217 e.v.u./day and about65 E80 / day in both directions. In March 1999 the traffic was 850 lights and 138 heavies / day.The results of an axle mass survey carried out over a full week in March 1998 were as follows:LHS RHSAverage vehicles/day:light 357 361heavy 69 46total 425 407Average axles (0,2 - 15 tons)/day 864 1 008percent over 8 tons 2 5Average E80/day (n = 4,2) 62 131percent over 8 tons 60 87Average standard axle factor (E80/heavy vehicle) 0,9 2,9Using these figures of E80/day and assuming an annual growth rate of 6 %, it was estimatedthat the log left (Saldanha-bound) lane carried a cumulative total of about 0,25 and the log right(Langebaanweg-bound) lane about 0,5 M E80 over the approximately 18 years before resealingin 1998. Although the percentage of overloaded axles was quite small (≤ 5 % on average), theycontributed most (60 % in the log left and 87 % in the log right lanes) of the E80.The pavement and traffic are therefore fairly typical of a modern rural main road in the drier halfof South Africa. This amount of traffic is probably sufficient to knead and compact the slurry andto show up any tendency towards excessive wear, but not to prevent salt damage, especially onthe shoulders and outside the wheelpaths.7. MAINTENANCENo maintenance work of any kind had been carried out on the seal from opening to traffic inApril 1980 up to the time it was first resealed with a split application 13 mm single seal in March1998.8. MATERIALSThe 200 mm thick base course was a non-plastic, granite crusher-run with added crusher dustbinder compacted in two layers to at least 98 % MAASHO (98-101 % achieved in upper layerand 100-104 % in lower). The same “fresh” water source as used for the slurries was also usedfor the base course, resulting in saturated paste electrical conductivities (ECs) of the completedbase of up to 0,18 S/m before slushing with water from the same source. No damage to thePaper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAprimed surface occurred even though the current usual upper limit of 0,15 S/m was slightlyexceeded in places. The base course was therefore of good quality, well compacted and notweakened by salt crystallization. It thus provided a sound base for the surfacing, without anyexpectation of punching of chippings, absorption, bleeding, or salt blistering of the surfacing.The properties of the materials used are shown in Tables 2 - 4. Unless otherwise indicated, alltest methods used were those current at the time, i.e. essentially those now in TMH 1 (NationalInstitute for Transport and Road Research (NITRR), 1979; 1986).The slurry sand (Table 2) was a fairly angular, natural sand derived from decomposed granitefrom the farm Zoutzaksfontein 95. Visually, the sand had a brown colour and was composedmostly of quartz. However, no proper mineralogical analysis was carried out, and from the sandequivalents (SE) and fines contents it is likely that small quantities of other granitic minerals in aweathered state such as felspar were also present. However, the very good dry and soakedACVs and the adequate SE indicates that these were minimal. Apart from not being the productof an approved base course or surfacing aggregate quarry the material satisfied all the normalrequirements for a fine grade of slurry sand. However, the ACV of the sand showed that it wouldsatisfy the particle strength requirements for surfacing aggregate. Its adhesion to bitumen usingcationic emulsion in laboratory tests was also good. The very low EC of 0,01 S/m showed thatthe sand itself contained a negligible quantity of soluble salts. The grading of the sand wassatisfactory although the P075 was borderline.4,752,361,810,600,300,150,075Sand EquivalentNormal (SE)Extended (ESE)(1)Relative Density (2)ApparentBulkTable 2. Properties of the slurry sand used.Parameter Units Site controlsampleNITRR SEG8146sampleSpecifications(SABS 1083-1976)Sieve size (mm) % Cumulative passing by mass%%%%%%%--100927052372410ndnd100927253392512423310090 – 10065 - 9542 - 7223 - 4810 - 274 – 12- nd2,65-- nd2,62-Water absorption (2) % nd 0,39 -EC @ 25 ºC (3) S/m 0,01 Nd -Aggregate crushing value (ACV)(2)(4)DrySoaked% nd17% nd18Bitumen adhesion (2)(5)(7) % nd +95 -∃35-(# 30)(6)(# 38)(6)(1) CRB Method 370.2: ESE = SE after 10 min. shaking 2 /SE.(2) Fraction > 2,00 min.(3) Fraction < 6,7 mm.(4) Percentage passing 0,725 mm (otherwise according to BS 812, 78 mm cylinder, 100 kN).(5) ASTM D1664-69 (cationic emulsion).(6) Normally crusher dust from approved chips or base quarry, i.e. dry ACV of ≤ 21 or ≤ 30, respectively.(7) Other results on sand from the same Zoutzaksfontein source: Riedel & Weber 4-5 cationic,0-1 anionic; pH 6,8.(8) nd = Not determinedPaper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAThe seawater used (Table 3) was drawn from the jetty in Saldanha Bay. The results of chemicalanalysis show that with a total dissolved solids (TDS) content of 2,8 - 3,3 % it was slightly lesssaline than the 3,5 % of normal, open ocean seawater. This is common and is due to dilution byrunoff and underground water from the land. The “fresh” water came from borrow pit 101 onTR 77/1 and, with a TDS of about 0,4 % (about twice the recommended limit for human drinkingwater), was actually neither fresh nor potable. EC measurements were found very useful foron-site checking of the salinity of construction water as well as other materials.ParametersUnits(1)Table 3. Properties of the waters used.Fresh water (2) Seawater (3)Site controlsamplesNITRRsample8149 (4)Site controlsamplesNITRRsample8148 (4)EC @ 25 °C S/m 0,60 – 0,62 0,600 4,37 – 4,75 5,00 5,25APPROX. TDS (6) % 0,39 – 0,40 0,39 2,8 – 3,1 3,25 3,53Mean(Openocean) (5)PH - nd 7,8; 8,1 nd 7,3 7,8 – 8,3NaKCaMgSO 4 ²¯Cl¯TOTAL ALKALINITYas CaCO 3ppmppmppmppmppmppmppmndndndndndndnd950121501003001 590380Ndndndndndndnd11 1004303701 3002 60019 800nd10 8043894091 3022 71119 426143(1) Mass/volume basis unless otherwise stated.(2) From BP 101 on TR 77/1.(3) From BP 101 on TR 77/1.(4) Analyst: Nat. Inst. Water Research, Bellville.(5) Open ocean average seawater, calculated on a mass/volume basis where relevant from m/m data inMason and Moore (1982) and/or Riley and Skirrow (1965).(6) Inferred from EC.(7) nd = Not tested or not available.The emulsion used (Table 4) was of the cationic type because of doubts about the performanceof the more usual anionic type with the siliceous natural sand available. Initially it was thoughtthat the emulsion was actually nonionic because no deposit on either plate could be detectedeven using up to 30 mA. However, further tests by the Cape Provincial Central RoadsLaboratory on the same emulsion obtained a deposit on the cathode after 2 minutes at 40 mAand a pH of 1,7, proving the emulsion to be cationic in nature.9. SLURRIESThe mix used was the usual sand:cement:emulsion:water ratio of 100:1,5:20:10 (including the2-3 % moisture content of the sand) by mass. Check testing of three samples indicated that only14-18 parts of emulsion may have been used (Table 5). The slurries were therefore on the leanrather than the rich side of normal. This should have made them more rather than lesssusceptible to salt damage, although the salt would also have been more easily leached out byrainfall. The gradings were also found to be marginal in that the P150 and the P075 weremarginal to slightly excessive.Some crystallization of salt was noticed in laboratory mixes by the Provincial laboratory.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICASaybolt Furol ViscosityBinder contentFluxing agentResidue on sievingParticle chargeSedimentation (60 revs)Coagulation valueTable 4. Properties of the emulsion used.Property Units Cationic stable-mix type (1)secs% m/m% m/m binderg/100 ml--% m/mResults (2)13,260,0nd0,2Nil (3)nd (4)ndSpecificationSABS 548-197250 max.60-63Nil0,25 max.PositiveNil2,0 max.(1) Supplied by VIALIT (Pty) Ltd.(2) Tested by NITRR.(3) Nil by both standard and modified procedure, but later found to be positive by CPA laboratory.(4) Coagulated immediately on adding soap.(5) nd = Not determined.LayerwaterS.V.BinderEmulsion (calc.)Passing sieve size(mm)4,752,361,180,600,300,150,075Table 5. Properties of the slurries used.UnitsKm%PARTS/100 agg.%%%%%%%Firstsea4,009,518100927355402713(1)Tested by Cape Provincial Central Roads Laboratory.Secondfresh 4,039,618100947556402713Secondsea3,9-4,07,8 – 8,614 - 1698 – 10091 – 9471 – 7552 – 5538 – 4125 – 2811 – 16Specification(Contract & SABS1083)-2010090 – 10065 – 9542 – 7223 – 4810 – 274 – 1210. CONSTRUCTIONThe layout and construction details of the experimental sections are shown in Table 6. Thedesign and construction of the Cape seal surfacing was carried out in accordance with the1970/1972 specification for a chip and slurry surfacing (Cape Provincial Roads Department,1977). Among other aspects this specification placed restrictions on the quality of materials,mixing of the slurry, weather and temperature conditions, and method of working. A shoulder toshoulder chip spread rate and thorough rolling with a 13-15 ton pneumatic and two 5-8 tonsteel-wheeled rollers were required. The first (i.e. bottom) layer of slurry had to be spread overthe full width of the primed surface between 4 days and 4 weeks after the second spray(1-3 weeks achieved) after one pass of a 5-8 ton flat roller and a light sprinkle of water at such arate that the tops of the stone chippings were just exposed. The importance of hand work withsqueegees was emphasized. Thorough compaction with a pneumatic roller immediately aftercuring was required (three passes were given). The second (i.e. top) slurry was required to beapplied as soon as possible, but not later than 4 weeks after compaction of the final layer, but tothe width of the chippings only. In the event this delay was exceeded and varied from about 6weeks for the sections from S. V. 10,9 - 11,1 to 11 weeks for S. V. 4,0 - 4,1 and 20 weeks for3,9 - 4,0. The idea was to have the tops of the chippings just exposed. The second layer ofslurry on a Cape seal is not normally rolled, but opened to traffic as soon as it has set up. In thiscase the whole road was opened to traffic only on the 16th April 1986. This was about twoweeks after completing the top slurry from S. V. 3,9 to 4,0, 10 weeks after completion of thesection from 4,0 - 4,1 and 19 weeks after completion of the sections from S. V. 10,9 - 11,1.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICATable 6. Surfacing construction details.Section No. Units 1 2 3 4 5Stake value(1)Km 3,896 - 3,938 - 4,015 - 10,900 - 11,000 -3,938 4,015 4,100 11,000 11,100Approx. log km(1)Km 8,8 - 8,7 8,7 - 8,6 8,6 - 8,5 1,6 -1,5 1,5 - 1,4Purpose - Expt Expt Control Control ExptWater(2) : top slurry: bottom slurryTDS : sea: freshBinder rate(3) : top: bottom--% m/v% m/vl/m 2SeaFresh2,90,38SeaSea2,9-0,770,80FreshFresh-0,380,860,79FreshFresh-0,390,84(6)0,80(6)0,77l/m 2 0,80Chipping rate(4) m 2 /m 3 81 81 81 77 77Slurry rate(5) : top: bottomSlurry constr. Dates: bottom: topSlurry time delay: bottom - top: top – opening(7): bottom – openingSite rainfall: bottom - top slurry: top – opening(7): bottom - openingkg/m 2 2,22kg/m 2 7,68y-m-dy-m-dDaysDaysWeeksmmmmmm79-11-1580-04-0313913221122132,227,4879-11-1580-04-0313913222,217,6879-11-1580-01-317776222,137,4879-10-2379-12-013913625FreshSea3,20,390,84(6)0,80(6)2,137,6879-10-2379-12-01(1) S.V. 0,430 (log km 12,11) at int. with MR3; S.V. 3,815 at int. with railway line; log km 0 (~ S.V. 12,5)at int. with TR 77/1.(2) Seawater from Saldanha Bay, fresh water from BP 101 on TR 77/1.(3) Cationic 65% emulsion, cold net rates.(4) Granite: 19 mm, Treton 18 %, ALD 11,8 mm (S.V. 3,8 - 4,1), 11,6 mm (S.V. 10,9 -11,1) from PeakQuarries at Rondeberg (S.V. 52 on TR 77/1).(5) Aggregate only.(6) Right outer 0,88 l/m 2 top; 0,77 bottom.(7) Opened to traffic 1980-04-16.The maximum permitted delay of 4 weeks between the bottom and top slurries was thereforegreatly exceeded (6-20 weeks). However, during this period only 4-11 mm of rain fell. The delaybetween the top slurry and opening to traffic (2-19 weeks) was also longer than desirable.During this period 22-33 mm of rain fell, with 22 mm on the top seawater slurries(S. V. 3,896 -4,015). Whilst these delays were undesirable, it is considered that the 22 mm ofrain on the top seawater slurries, especially the 13 mm recorded on the 4 th April, was moreimportant and may have leached some of the salt from them.These delays should have rendered the slurries more rather than less permeable and thereforemore rather than less susceptible to salt damage. On the other hand, the presumed more opennature of the slurries should also have made them more susceptible to leaching of the salt byrainfall. Which of these effects was more important is not known, and they may even havecancelled each other out.Whilst the construction and weather were not ideal, it was nevertheless considered that theslurries were acceptable for experimental purposes and conditions in the arid or dry semiaridarea of southern Africa.1122138253343337391362543337Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA11. RESULTS AND DISCUSSIONThe Resident Engineer reported that there had been no problems in the mixing or laying of anyof the slurries, and no differences in workability and breaking or drying time. They could all betrafficked within a few hours of laying and no differences in performance were apparent at theend of the Contractor’s maintenance period in April 1981.The slurries were inspected visually at irregular intervals by the author together withrepresentatives of the former Cape Provincial Roads Department from soon after completion ofeach layer until 1986. During the early stages the Resident Engineer was also present. After1986 the inspections were carried out by the author alone up to the final inspection in January1998.Apart from a slight glitter and slightly lighter colour of the seawater sections (presumably due tosalt crystals) in the early stages no differences could be observed between these and the freshwater controls. It was considered that the bottom slurry on Sections 1 and 3 was laid a little toothick and there was a little early loss of the top slurry from part of the fresh water Section No. 3.Scattered “blow-holes” up to 3 mm in diameter, each containing an uncoated particle werenoticed on both layers of both the fresh and the seawater Sections 4 and 5 as well as on thefresh water slurries on the other side (S. V. 11,1 - 11,2) of the seawater Section 5. Such holeswere extremely rare on Sections 1 - 3. The Resident Engineer noticed damp patches aroundthese holes 6 days after laying, some salt around them 8 days after laying, and brown stainslater. Some of these holes were still present in 1998 between S. V. 10,9 and 11,2. The cause ofthe “blow-holes” was not investigated. As they occurred dominantly on the fresh water slurries,around S. V. 10,9 - 11,2, they were not due to the use of seawater. It is presumed that they weredue to the evaporation of excess water associated with poorer quality (coated, dusty orweathered) sand particles which then stripped. The extended sand equivalent result of 4 mm depth between stones, estimated texture depth>1,0 mm) in the lanes and inner shoulders by 1986. There was no significant further loss in thenext 10-12 years. In other words, the top slurry had largely worn off by about November 1986.The performance of the normal slurry (i.e. fresh water) in both layers from S. V. 11,100 onwardswas the same as that on Sections 4 (also fresh) and 5.Slight fatting occurred up to a maximum of Degree 2 in the outer wheelpaths of Sections 1 and2 and over the full width of the lanes and the inner halves of the shoulders of Section 3, butextending to at least S. V. 4,200 on the normal fresh water work. This was ascribed to thesesections being on the route of quarry trucks emerging at S. V. 3,865 before Section 1 and alsobeing on a slope. Negligible fatting up was apparent on Sections 4 - 6 on level ground and withslightly less traffic.In-situ air permeability tests in 1986 showed the surfacing on all sections to be impermeable toair.The condition of the binder in January 1998 in both the slurry and the sprays was stillgood:sticky and black in the slurry and also bright on the chips.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAAccording to the pavement management system (PMS) data the reseal condition indices wereas follows:Log km Pavement Reseal1996: 0 - 4,5 100 (very good) 68 ( C priority)12,11 95 (very good) 51 ( C priority)1997: 0 - 4,5 100 (very good) 80 ( C priority)12,11 100 (very good) 89 (none)Although the surfacing condition appeared to have inexplicably improved without maintenanceof any kind between 1996 and 1997, in essence the whole road including the surfacing was stillin a very good condition and not in urgent need of a reseal or any other work. The experimentalsections had not been assessed separately, but Sections 4 and 5 (log km 1,4 - 1,6) would havefallen in the first half of the road and Sections 1 - 3 (log km 8,5 - 8,8) in the second half.In July 1997 an Impulse Deflection Meter (IDM) survey yielded base layer indices (BLI) of 403and 288 at log kms 1,40 and 1,60 and 317 and 354 at log kms 8,60 and 8,80 respectively, incomparison with a mean of 288 for the whole 12,11 km surveyed, Whilst the exact positions ofthese measurements in relation to the sections are uncertain and they are also too few to be ofmuch use, all except the one at log km 1,60 (well onto the fresh water control Section 4), wereabove the average for the road.The PMS data were really too coarse to be of much use for evaluating such short experimentalsections. However, it would appear from this that the sections which utilised seawater were inno worse a condition than the rest of the road when resealed, thus supporting the detailedvisual inspections.Cracking, patching, potholes, ruts and shear failures were absent and bleeding and ravelling ofchippings insignificant. The only significant defect was therefore rather more wear of the slurrieson both the seawater and fresh water sections than might have been expected. Whether thiswas due to the salt, the siliceous natural sand, the apparently low charge on the emulsion, theapparently slightly lower binder contents in the slurries, or a combination of all of these factors,has not been determined. However, although high, the degree of wear after 19 years was stillacceptable and no worse on the seawater sections: almost no chippings had been lost and nomaintenance had to be carried out, and resealing after 19 years - especially on a C priority -represents an above-average life for a Cape seal. It is therefore concluded that the wear wasnot due to the use of seawater.With some reservations about binder content, construction delays and rain on the top seawaterslurries before trafficking, the records and results of 18 years of monitoring show that thenecessary experimental conditions were met, that there has been no significant difference in theperformance of the slurries, and that this performance has been satisfactory. It is thereforeconcluded that, under similar conditions and with similar materials, salt water of similarcomposition to and at least as saline as the seawater used (2,8 - 3,3 % TDS) can probably beused in slurry seals.12. CATIONIC VS ANIONIC EMULSION AND EFFECT OF CEMENTIt is uncertain whether the findings of this experiment can be extended to the more usual caseof anionic emulsion. Unfortunately, no laboratory work or road experiments have been carriedout using anionic emulsion and seawater.Ordinary portland cement (OPC) is usually added to slurries in the proportion of 1 - 2 parts ofcement to 100 parts by mass of aggregate. Since a cationic emulsion is acidic and cementhighly alkaline (pH about 12 -13) it would be expected that they would react and negate thereason for using the cationic emulsion in the first place, i.e. that of improved adhesion to aquartzitic aggregate.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAExperiments in the Cape Provincial Laboratory showed that the addition of 1,5 % cement to thepure sand (pH 6,8) raised the pH to 11,7 and the addition of 20 % VIALIT cationic emulsion(pH 1,7) to the sand-water-cement mix yielded a pH of 11,3. Particle charge tests (at 50 mA for2 minutes) showed that the addition of cement had neutralised the charge as no deposit couldbe obtained on either electrode. However, further laboratory work with both this sand as well asother quartzitic sands showed no difference in workability between slurries made with VIALITanionic and cationic emulsions. Riedel and Weber adhesion tests on slurries made with cementyielded high values of 6 - 7 regardless of the type of aggregate, but with the anionic emulsionstending to yield the slightly higher values. When the cement was omitted similar values wereobtained with dolomite, dolerite, hornfels and granite crusher dusts with either VIALIT emulsion.Slightly lower values were obtained with the anionic emulsion and a quartzite crusher dust(6 vs 7), much lower values with the angular Zoutzaksfontein granitic sand (0- vs 4 - 5), butsimilar values (0 vs 0-1) with a rounded quartzitic river sand. Similar tests with PETROCOLemulsions and the Zoutzaksfontein sand without cement yielded Riedel and Weber values of 2 -3 with both anionic and cationic emulsions.Investigations at the then NITRR by C. M. Mac Carron and C. P. Marais using an immersionwheel tracking test at 25 °C showed no significant differences between cationic and anionicslurries using Zoutzaksfontein quartzitic sand, a rounded quartzitic river sand and a granitecrusher dust, with or without cement - all were satisfactory. However, in the case of the roundedriver sand the cationic emulsion without cement was slightly better than that with it.In view of these uncertainties a road experiment was carried out near Wellington in whichslurries employing two quartzitic sands (including the Zoutzaksfontein sand) and a granitecrusher dust and both VIALIT cationic and anionic emulsions were compared. After about threeyears under traffic it was concluded that there was no difference in durability between the twotypes of emulsions. However, it was concluded that the anionic emulsion was preferred becauseit tended to give better workability, it was less sensitive to the amount of water added, it wasmore stable, and it was slightly cheaper. As cement had to be added in any event for workabilitythere was thus no advantage in using a cationic emulsion.It can therefore be concluded from this work that, although adding cement does not break orotherwise detrimentally affect a cationic emulsion, it does neutralise its positive charge,apparently converting it to a nonionic emulsion. However, although there is no difference inadhesion and durability in practice between slurries made with cationic or anionic emulsionsand quartzitic sands, as cement normally has to be added in any event, there is no point inusing a cationic emulsion in a slurry seal. (Acidic fillers should not have this effect and could beadvantageous in difficult cases.)The usual criterion for water for slurry seals is that it should be potable (i.e. fit to drink) and thisis also specified in the Cape Provincial Administration (CPA)(1993) materials manual and inmost other guides (e.g. Asphalt Institute, 1987) and specifications (e.g. ASTM, 1994). In somecases compatibility with the mix and freedom from harmful soluble salts are also required.In essence, ions in solution, a pH greatly differing from that of the emulsion, or the presence ofcolloidal suspended matter such as clay may alter the properties of the emulsion or even causeit to break prematurely. In the case of a cationic emulsion, a pH >7 or a high alkalinity(i.e. CO 3 2- , HCO 3 - ) would be of concern, whilst in the case of an anionic emulsion a pH

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICA13. CONCLUSIONSThe necessary experimental conditions were not totally met in that the fines contents of theslurries were slightly excessive, the binder contents were too low, the delays between thebottom and top slurries were greatly excessive, and that some rain fell during these delays.Whether the net effect of these deficiencies was to make the seawater slurries more or lesssusceptible to salt damage is uncertain. However, visual inspection after construction indicatedthat salt was still present.No significant differences in behaviour or performance during or after construction up to thenearly 18 years before resealing were noticed.It is therefore tentatively concluded that salt water at least up to the salinity of that used(2,8-3,3 %) can be used in cationic slurry seals provided that laboratory dilution, coagulation,mixing and adhesion tests with the proposed aggregate are satisfied.Seawater can probably also be used in anionic slurry seals provided that such tests aresatisfied.Natural sand similar to that used can be used in slurry seals under similar traffic conditionsprovided that the other modern specification requirements are also met.Laboratory dilution, coagulation, mixing, adhesion and immersion index tests should be carriedout before the use of any salt water is attempted on the road.14. ACKNOWLEDGEMENTSThis paper is based upon a report by Frank Netterberg to the Department of Transportation andWorks of the Provincial Administration of the Western Cape and is published with thepermission of the Deputy Director-General. However, the opinions expressed are those of theauthor and not necessarily those of the Department or any other persons. Some of the workdescribed was carried out whilst the author was employed by the former National Institute forTransport and Road Research of the CSIR. The Consulting Engineers were Jeffares and Green(Resident Engineer Mr J. G. Wilkinson) and the Contractor Savage and Lovemore. Messrs B. J.Alexander, W. J. Biesenbach, P. A. Myburgh, P. Neal, and I. Smit of the Department all assistedin various ways with the experiment during the first six years. The PMS data was supplied atvarious times by Mr D. Rose and Mr L. Wessels. Unpublished Weather Bureau data was madeavailable by Mrs G. Swart. The writer also benefited from discussions with Dr C. P. Marais andMessrs W, Babb, L. K. Davidson and J. G. Louw.15. REFERENCESCommittee of Land Transport Officials, 1996. Structural design of flexible pavements forinterurban and rural roads. Draft TRH4: 1996, COLTO, Department of Transport, Pretoria.Schulze, B.R., 1947. The Climates of South Africa according to the classification ofKöppen and Thornthwaite. S. Afr. Geog. J., Vol. 29, 32-42.Schulze, B.R., 1958. The Climate of South Africa according to Thornthwaite’s rationalclassification. S. Afr. Geog. J., Vol. 40, 31–53.Weinert, H.H., 1980. The natural road construction materials of southern Africa.Academica, Pretoria.Netterberg, F., 1979. Salt damage to roads - an interim guide to its diagnosis, preventionand repair. J. Instn. Mun. Engrs. S. Afr. Vol. 4. No. 9, 13-17.Paper 090

8 th CONFERENCE ON ASPHALT PAVEMENTS FOR SOUTHERN AFRICAWoodbridge, M.E., Obika, B., Freer-Hewish, R., and Newill, D., 1994. Salt damage tobituminous surfacings: results from road trials in Botswana. Proc. 6 th Conf. Asphaltpavements S. Afr., Cape Town, Vol. 1, II -149 to II-162.Netterberg, F., 1969. The geology and engineering properties of South African calcretes.PhD thesis, Univ. Witwatersrand Vol. 4, Johannesburg.Emery, S.J., 1992. The prediction of moisture content in untreated pavement layers andan application to design in southern Africa. CSIR Res. Rep. 644, Pretoria.Weather Bureau, 1986. Climate of South Africa. WB40, Govt Printer, Pretoria.Schulze, R.E., Maharaj, M., Lynch, S.D., Howe, B.J. and Melvil-Thomson, G.I.S., 1997. SouthAfrican atlas of agrohydrology and -climatology. Dept. Agric Engng, Univ. Natal,Pietermaritzburg.National Institute for Transport and Road Research, 1979, 1986. Standard methods of testingroad construction materials. TMH 1 (1st and 2nd edns), NITRR, CSIR, Pretoria.South African Bureau of Standards, 1976. Standard specification for aggregates fromnatural sources. SABS 1083-1976, Pretoria.Mason, B. and Moore, C.B., 1982. Principles of geochemistry. 4th Edn, Wiley, New York.Riley, J.P., and Skirrow, G. (eds), 1965. Chemical oceanography. Academic Press, London.Cape Provincial Roads Department, 1977. Section 23: Surface treatment using a splitapplication of bituminous binder, 19 or 13 millimetre stone chips and slurry seal. CapeProvincial Administration, Cape Town.National Institute for Transport and Road Research, 1985. Nomenclature and methods fordescribing the condition of Asphalt pavements. TRH 6: 1985, NITRR, CSIR, Pretoria.Cape Provincial Administration, 1993. Materials Manual. Vol. 2, Chapter 2, p. 2-65 to 2-66.Asphalt Institute, 1987. A basic asphalt emulsion manual. Asphalt Institute Manual Series No.9 (2 nd edn,), College Park.American Society for Testing and Materials, 1994. Standard practices for design, testing andconstruction of slurry seal. ASTM D 39 10-90 in 1994 annual book of ASTM standards, Vol.0.4, 399-406.Colas Southern Africa (Pty) Ltd, 1996. The road to success. Colas products and serviceshandbook. Sections 3.5.1 and 8.4.6. Colas Southern Africa (Pty) Ltd, Johannesburg.Paper 090

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