Use of Seawater in Slurry of Cape Seal - CSIR

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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
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Use of Seawater in Slurry of Cape Seal - CSIR

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