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OCR for page 48
48
aggregate sample, but it cannot be used for measuring angu- characteristics can be used to detect changes in these charac-
larity or texture. teristics and make appropriate adjustments. This will ensure
A methodology that uses direct measurements of shape the supply of aggregates with the desired characteristics,
(three dimensions), angularity, and texture was developed to thus leading to good performance and cost savings.
classify aggregates based on the distribution of their charac- · Evaluation of crushing methods: crushing methods can
teristics. It unifies the methods used to measure the charac- be evaluated by measuring aggregate shape characteristics
teristics of fine and coarse aggregates. The analysis methods produced using these methods. This evaluation will help
are simple, and the results have physical meanings that can be identify crushing methods that could produce aggregates
interpreted easily. The classification ranges were found to be with the desirable characteristics.
similar for the different aggregate sizes. This finding simplified · Evaluation of changes in aggregate texture: the proposed
the methodology, as one set of ranges is needed irrespective imaging systems can be used to measure the aggregate tex-
of aggregate sizes. This classification methodology is valuable ture and its change due to polishing which can be indicative
for the interpretation of the results and in order to facilitate of change in frictional characteristics.
implementation.
The classification results are presented in terms of the dis- The following research projects are recommended to enhance
tribution of shape properties within an aggregate sample. This the study findings and their implementation:
feature gives capabilities to (1) explore the influence of differ-
ent processes such as crushing and blending on aggregate 1. Research to further evaluate the ruggedness of the recom-
shape, (2) conduct quality control activities to detect changes in mended test methods. This work is essential to evaluate
the distribution of any of the aggregate characteristics, (3) relate the ability of each test method to provide repeatable and
the distribution of different characteristics to performance, reproducible results.
and (4) develop specifications based on the distribution of 2. Research to develop methods for incorporating aggregate
aggregate characteristics rather than average indices. physical properties in the design of pavement materials.
Generally, each of the paving mixtures (unbound aggregate
layers and layers bound and/or stabilized with asphalt,
Applicability and Suggested Research
hydraulic cement or other stabilizing material) does not
This study provides the pavement community with practical, consider aggregate characteristics, making it difficult to
reliable, and accurate methods for rapidly measuring aggregate relate aggregate characteristics on performance. Although
characteristics. The recommended methods can be used in the several studies have evaluated the relationship between
design of pavement layers, in Quality Control (QC) and Qual- physical characteristics and mixture performance, these
ity Assurance (QA) programs, and for problem diagnosis based studies have not developed adaptable specifications that
on understanding of the effects of aggregates on performance accommodate variations in aggregate characteristics.
of pavement structures. In addition, these methods will help the 3. Research to develop methods for optimizing the design of
industry set criteria for providing aggregates with the desired paving mixtures based on the physical properties of aggre-
characteristics. gates. This study did not specify performance-based limits
The recommended methods can be implemented in the for shape, angularity, and texture that should be used in the
following aspects of pavement engineering: mixtures of the different pavement layers. Such research will
provide means to allow highway agencies and the industry
· QA and QC procedures during aggregate production: to efficiently utilize the available sources of aggregates and
statistical parameters based on the distribution of aggregate reduce construction costs.
