May_1967 — Page 37

ing, initial compaction of two or three passes of an 8 ton tandem roller fol- lowed by four passes of a 24 ton pneumatic roller were then sufficient to bring the mixture to a density above 95% B.S. heavy compaction. The cement-stabilized soil was then sealed with bitumen emulsion, as with the lime-stabilized soil.

A total of 380,000 sq. yd of 4% lime-stabilized soil and 84,000 sq. yd of 5% cement-stabilized soil was laid as the working course for aircraft pavements, and a total of 60,000 sq. yd of 6% lime-stabilized soil and 38,000 sq. yd of 6% cement-stabilized soil was laid as base course for roads and runway shoulders. Asphalt

The specification allowed the con- tractor complete freedom in the choice of aggregates used in the asphalt work, provided he designed mixes within the limits specified for the Marshall method of design and used granite coarse aggregate for the wear- ing course. All aggregates within economic range of the site were in- vestigated and 31 series of Marshall design tests were carried out on dif- ferent combinations of aggregates until mixes finally acceptable to both parties were evolved.

These mixes were henceforth called

the job standard mixes'. The job standard mixes were very economical, as approximately 50% of the agre gates were obtained on or close to the

site and required no working other than loading and transporting to the batching plant. Moreover, the optimum bitumen contents for the Marshall design were respectively 3.3%. 4.2% and 5.4% for the bitu- men-bound base course, binder or base course and wearing course. Evaluation of pavement strength

The method used for evaluating the strengths of the various pavements was the Air Ministry load classifica- tion number system as described in I.C.A.O. Aerodrome Manual, Pt

4 1960. However, it is considered that a pavement of deep asphaltic construction must reach a certain age before the tests give a true indication of the strength of this type of pave- ment, and that the value of the system as a means of control testing during construction of such a pavement is doubtful.

The writing of this Paper commenc- ed before the completion of the pro- ject and testing was still in progress. These tests however indicated that the

strength of the pavement was still increasing with age.

Acknowledgements

The authors wish to record their thanks to the Director of Public Works for permission to present this Paper, and to his staff who were engaged on this project and made the presentation of the Paper possible.

Thanks are also due to the British Road Research Laboratory and to Shell Bitumen Laboratory, London, for assistance and advice.

Finally, the authors would express their appreciation for the work done by the main contractor. Gammon (Malaya) Ltd. and the principal sub- contractor, Limmer Trinidad Interna- tional Asphalt Co. Ltd.

References

1. Burmister D. M. Theory of stresses and displacements in layered systems and applications to the design of air- port runways. 23rd Annual Meeting of U.S. Highway Research Board, 1943, 2. Webster J.D. and Sheary V.J. Stabilis- ation of clays and other fine grained materials. Australian Road Research Board First Biennial Conference. September 1962 (pp. 24-25). 3. Road Research Laboratory. The deter- mination of the cement or time con- tent of cement or lime stabilised soil, Road Note 28, 1960 (pp. 2-9).

APPENDIX I

The following equipment was used for constructing the lime-stabilized soil work- ing courses.

Pulverizing and mixing

2 Bros-5 P.R.M.-84 B. Rotomixer 2 Fordson Major tractors with Howard

Rotovators

1 Cement Spreader Rec-C 900 Spreading and compaction

1 Aveling Barford 8 ton tandem roller 1 Aveling Barford 21⁄2 ton three wheel

roller

1 Aveling Barford V.R. vibrating roller 1 Cat. 12 grader.

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TO PRESSURE GROUT A FOUNDATION

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Far East Architect & Builder May, 1967

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