Use of Seawater in Slurry of Cape Seal - CSIR

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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
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Use of Seawater in Slurry of Cape Seal - CSIR

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