significance of recent research on specifications and standards for soil-lime pavement layers --the need to reationalise the design procedure, The

Road & Transport Research, Jun 2000 by Holt, C C, Freer-Hewish, R J

CONCLUSIONS

1. An extensive global review of pavement specifications for soil-time treatments reveal that the use of a mellowing period before the treated layer is finally compacted is usually included in construction advice. The advice for mellowing periods, however, is not compatible with that used in the current standards for laboratory testing.

2. The recent work at the University of Birmingham highlighted that the physical and chemical properties of lime-treated materials are constantly changing during the mellowing process. The changes to the OMC and the take up of lime during mellowing is particularly significant. If mellowing durations are significantly longer than those used in the laboratory testing programme, there is a likelihood that the material on site may be compacted drier than designed for and that insufficient lime is available for stabilisation. This can reduce the design life of the highway in both the short and long term.

3. A laboratory design procedure has been suggested that takes into account the anticipated mellowing period to be used on site. The effects of the average daily ground temperature and moisture content of the host material is also allowed for. This proposed testing programme enables the engineer to have a far better understanding of how the lime-treated material is likely to behave and whether a mellowing period is necessary.

On-going work on low-temperature modification and stabilisation is necessary to support the practice of some treatments at low temperatures.

GLOSSARY OF TERMS

Average daily ground temperature: The average ground temperature during a 24 hour period. For example, in the UK, an average daily ground temperature of 10 deg C would be representative of early Spring/late Autumn.

Received/retrieval moisture content: The moisture content at which the soil is sampled.

Expected moisture content:The likely moisture content of the in situ material that is tobe treated with lime. Soil Investigation data should be used to determine this.

Immediate OMC:This isthe optimum moisture content determined immediately after the addition of lime.

Modified compaction characteristics: The compaction characteristics of a soil-lime mix alters with mellowing duration. The modified compaction characteristics are those determined after a specified time after lime addition.

REFERENCES

AMERICAN STANDARD TESTING METHOD (1990) Standard Practice for Laboratory Preparation of Soil-Lime Mixtures Using a Mechanical Mixture, Designation: D 3551-90. AUSTRALIAN STABILISATION INDUSTRY ASSOCIATION LIMITED (1998) Model Specification for Insitu Stabilisation of Local Government Roads Using Cementitious Binders Including Lime - Version B, Australian Stabilisation Industry Association (AustStab), Sydney.

BRITISH STANDARDS INSTITUTION (1990) Methods of Test for Stabilised Soils, London, BS 1924.

COMMITTEE OF STATE ROAD AUTHORITIES (1987) Standard Specification for Road and Bridge Works, Department of Transport, Pretoria.

DEPARTMENT OF TRANSPORT (1991) Specification for Highway Works, Seventh Edition (including August 1993 amendments), HMSO London.