Utilisation of Poplar Lane Quarry (PLQ) basecourse aggregate as a suitable source for roading material.

Type of content
Theses / Dissertations
Publisher's DOI/URI
Thesis discipline
Engineering Geology
Degree name
Master of Science
Publisher
University of Canterbury
Journal Title
Journal ISSN
Volume Title
Language
English
Date
2016
Authors
Dring, Clare Louise
Abstract

The scope of this research was to assess the utilisation of Poplar Lane Quarry (PLQ) basecourse aggregate as a suitable source for roading material. Poplar Lane Quarry (PLQ) basecourse aggregate generally, but not consistently, meets the current M/4 specifications, and the effect of proposed revisions to M/4 on consistently satisfying required properties of M/4 is unknown.

In the past there have been some premature pavement failures when using PLQ aggregate which were at times unexplained as the aggregate met and exceeded the TNZ M/4 specification. Smectite clays were known to be present in the rock and may have been an influencing factor into the aggregate breakdown.

The objective of this research was to thoroughly investigate the properties and production processes of PLQ basecourse material in relation to the TNZ/NZTA specifications and relevant tests, in an effort to improve the correlation between the tests and the actual performance of the material. This included analysing historic M/4 test results as well as collecting material to conduct a full range of M/4 test. Additional analysis included the NZTA T20 Accelerated Weathering test, stabilising and strength testing, mineralogy analysis and failure plane analysis.

The results of the M/4 speciation testing and review indicated that the Plasticity Index and Clay index showed variable results over the years and at times did not meet the specification. The Clay Index values are accepted in the industry as identifying the presence of expansive clays where in fact this is not the case. Further clay analysis was conducted and it was found that no expansive clays such as smectite were present, instead the non-expansive clay halloysite was found. The variability in the Plasticity Index can be attributed to a number of factors, one being the variability of clays within the quarry and the competency of the laboratory technicians.

Following these initial tests and analysis further investigation were conducted. The NZTA T20 Accelerated Weathering test, which was not yet finalised for all regions when this thesis was completed, was found to provide inconclusive results. The PLQ aggregate and greywacke control stone failed to meet the proposed limit; these findings were passed onto the external authors of the test method for consideration. SEM analysis was conducted on the samples to aid in the identification of the clay type and content, this was inconclusive as no clays could be identified, but extensive alteration was found throughout. The expected failure planes of the aggregate was investigated using quarry wall mapping, hand sample analysis, thin section analysis and SEM. Joints and faults were found on the macro scale and micro-veins that pinched and swelled were found in the hand sections. Fracturing was observed in and around many minerals.

In conclusion, the PLQ aggregate continues to meet the requirements of the TNZ M/4 and draft NZTA M/4 Specification. The Clay Index test does not give an accurate identification of deleterious clays and may not be fit for purpose. The Plasticity Index has variable results related to either the clay type and content of the aggregate or the competency of the technicians. The clay found within the aggregate was halloysite which is non-expansive and will not cause aggregate breakdown from swelling. The NZTA Ethylene Glycol Accelerated Weathering test needs further review and testing to determine the appropriate limits. Failure planes, such as joints and micro-veins within the rock may decrease the structural integrity of the aggregate, but this can be combated by stabilising with 1% cement.

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Citation
Keywords
Ngā upoko tukutuku/Māori subject headings
ANZSRC fields of research
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All Rights Reserved