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TECHNICAL NOTE ON THE USE OF TRINIDAD TAR/OIL SAND FOR ROAD FINISHING, PAVING AND MAINTENANCE By FRANCIS RAYMOND CHARLES, Lecturer - Transportation Division and WINSTON TADDIUS RAJPAULSINGH, Lecturer - Engineering Geology, Department of Civil Engineering, University of the West Indies, St. Augustine.

Origin, Location and Quality

Tar/Oil impregnated sands are found in the Southern Basin of Trinidad associated with oil seeps, a pitch lake (asphalt deposit) and sub surface producing oufields. In terms of their economic potential, thirteen separate tar/oil sand deposits were identified in the Southern Basin, Trinidad and are shown on the attached map (Figure 1). The table attached (Table 1) gives the weight percent of extracted tar/oil from representative samples of each deposit. These vary from 7.2% to 20.5%. Experimental work done by the German Agency for Technical Cooperation Ltd. (GTZ) in their secondary roads improvement project for the Trinidad Government indicates that an average bitumen content of approximately 14% by weight gives this material tremendous possibilities of an economic nature which would favour its use as a road building material. Furthermore, they have concluded with weight percent tar/oil of less than 14, the tar/oil sand should be mixed with coarse sand or quarry dust in a proportion of 60% oil sand to 40% quarry dust. This material can provide a good base course for secondary roads.


Chemical Properties
The fractional composition of the bitumen in the oil sands is 71.4% malthenes and 28.6%, asphaltenes. Table 2 gives the fractional composi­tions of several bitumens, including Trinidad lake asphalt and tar/oil sands. ldealy the fractions suggest the oil sands to be a sol structure with an index ­of colloidal instability of 0.88. This indicates very good micro-integrity of the bitumen in the oil sands, as well as, sound durability and performance for secondary and tertiary roads.

TABLE 1: WEIGHT PERCENT OF EXTRACTED TAR/OIL
FROM SAMPLES OF EACH SURFACE TAR/OIL DEPOSIT OF TRINIDAD

NUMBER DEPOSIT WT %TAR/OlL WT.%TAR/OIL WT % TAR/OIL
EXTRACT I EXTRACT 2 AVERAGE EXTRACT

1 Kapur Ridge 9.8 1 10.1
2 Goudron 17.2 16.6 16.9
3 Penal A 6.9 7.5 7.2
4 Penal B 6.9 8.7 7.8
5 Penal C 16.0 14.6 15.3
6 Apex 9.0 10.0 9.5
7 Fyzabad 9.7 10.4 10.1
8 F/Reserve 15.1 13.5 14.3
9 LosBajos 15.4 15.2 15.3
10 Erin 13.0 12.6 12.8
11 Parrylands 17.9 17.3 17.6
12 Lot 1 19.0 19.2 19.1
13 VanceRiver 18.1 15.1 16.6
14 Rousillac 17.0 17.6 17.3
15 Point Fortin 20.4 20.2 20.3
16 PointLigoure 16.2 14.0 15.1


Asphaltenes are generally regarded as the con­stituent which gives asphalt its "body' and play an important role in the structural response of the asphalt. The asphaltenes are hard brittle sub-micron particles which do not melt but intumesce on heating, yielding fixed carbon. Their presence in the oil sands combined with the colloidal stability suggest that in its early life the bitumen binder in the sands will be moderately sensitive to thermal changes.

The presence of saturates is to provide a con­tinuous phase for the asphaltenes. The quantity, 25.8% (as shown in Table 3), is a bit high when compared to refinery bitumen, but will not present a problem after spreading and placing of the oil sands as they would evaporate over a few days to produce a much lower content.

TABLE 2: COMPARATIVE ASPHALTFENES/MALTHNES CONTENT

Asphaltenes % Malthenes %
Kuwait, residual 0 100
Califomia,vacuum 11 89
Kuwait, vacuum 11.5 88.5
Venezuela, vacuum 23 77
Mexico, vacuum 31.7 68.3
Trinidad Lake Asphalt 34 66
TrinidadTar/OilSand 28.6 71.4
Wyoming, residual 38 62
Mexico, blown 41 59

Use in Road Building
At present, ojisand is used extensively as a surfacing material on road networks of Trinidad, particularly secondary roads.
Typically yellow limestone is compacted in a l50mm layer as sub-base. A base course of porcellanite 75mm thick is then installed, and a 50mm thick oilsand wearing course completes the roadway.
Hardening of an oilsand surface occurs in the course of time because of the solar effects. Owing to radiafion, the volatile binder components are heated and gradually evaporate causing hardness of the surface. Excessive hardening of the material through age hardening can cause the oilsand to become brittle and breakup under traffic, leading to deteriorafion of the roadway. However, this effect is common for most bituminous mixes, after long periods of exposure to sunlight.
Some oilsands contain a relatively high per­centage of volatile components. On the basis of the composifion and technical properties, these oilsands would be appropriate as a cold mix for provisional elimination of street damage such as break-off and potholes. However, this cold mix may not be cov­ered by hot asphalt since the volatile portion would not be able to escape and lead to bubble formation.
Bituminous surfaces may also be produced by mixing oilsand with mineral aggregates such as porcellanite, yellow limestone and any other compatible igneous rock. The manufacture of these mixes can be carried out at a modified asphalt batching plant. The modification of the mixing plant consists of a cooling air addition near to the oilsand filling hole in the middle of the mixing drum. The cooling air lowers the exhaust gas tem­perature so that thermic overstress ot the binder component is avoided. The heating process at the plant would accelerate the process of evaporation of the volafile components, thus resulting in a much more stable product.
The exorbitantly high humidity proportions in the oilsand would necessitate enormous energy requirements for drying of the oilsand, and subse­quently would reduce the mixing capacity of the plant. In addition, binder changes in the asphalt mixture by re-emulsification with the humidity surplus which remained in the mixture has the effect of producing rubber-like characteristics which be­come perceptible during the compaction procedure.
Other Considerations
l.The cost effectiveness in the use of oilsand with mineral aggregate (TT$346,500.00) per kilometre) as against asphaltic concrete (TT$444,500.00 per kilometre) in road building, (1989 prices).
2.Equipment and processing costs arc much lower than that for asphaltic concrete. For second­ary and tertiary roads these costs may be minimal.
3.Provides for labour intensive operation, as it can be applied manually as against mechanical application of asphaltic concrete, thus giving added socio-economic benefits.



References
Charles, F.R.: "Bitumen Modification with Trinidad Lake Asphalt", V. Congress Ibero -Latinamericano del Asfalto, (1989), pp.273-292.

Daniel, R.L.: Low Cost Road Strategies, Trinidad, MSc. Thesis in Construction Engineering and Management, Faculty of Engineering, The University of the West Indies, St. Augustine, Trinidad, (1989), 158 pp.

Rajpaulsingh, W.T:: An Evaluation of the Tar Sands of Trinidad, MPhil. Thesis in Petroleum Engineering, Faculty of Engineering, I'he Univer­sity of the West Indies, St. Augustine, (1989), 178 pp.

German Agency for Technical Cooperation Ltd. (GTZ): Secondary Roads Improvement Programme Phase I, for Ministry of Local Govern­ment, Government of Trinidad and Tobago, (1979), 40 pp.

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