TACA Conveyor - Summer 2008 - (Page 17)

At TxDOT, Aggregates Rock By Caroline Herrera, P.E. C ontractors utilized more than 15 million cubic yards of aggregates in 2007 on T i Texas D Department of T t t f Transportation t ti (Department) construction projects to produce concrete, surface treatments, seal coats, porous friction courses, and hot mix asphalt concrete. Each of these products is composed of an aggregate skeleton held together by a specified binder, and with aggregate being the largest component, the aggregate quality plays a critical role in their life expectancy and performance. The level of aggregate quality required varies depending on the product and intended use. For this reason, the Department specifies different requirements in the relevant Items published in the 2004 Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges. Approximately two hundred quarries provide aggregates for use on Department construction projects. The quality of the aggregates can vary widely both between quarries and within a quarry and is dependent on the geologic formations and layers within a quarry. Other properties such as gradation, shape, and cleanliness are dependent on the crushing, washing, and grading processes used to produce the ﬁnal product. Managing these aggregates can be challenging and time intensive, so the Department created the Aggregate Quality Monitoring Program (AQMP) to improve efﬁciency of Department operations while providing continuous quality assurance of aggregate products. The AQMP allows districts to use aggregates from rated sources without project speciﬁc testing by the Construction Division, Materials and Pavements Section (CST/M&P) for the tests listed in the AQMP producer catalogs, when the published ratings meet the project speciﬁcations. The AQMP, described in test method Tex-499-A, provides the requirements and procedures for CST/M&P to accept aggregate products that have demonstrated continuing quality and uniformity without performing project speciﬁc testing for speciﬁed tests. CST/M&P publishes the statistical ratings for the quality tests covered by AQMP in the ‘Bituminous Rated Source Quality Catalog’ (ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/ mpl/brsqc.pdf) and the ‘Concrete Rated Source Quality Catalog’ (ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/mpl/crsqc.pdf). The catalogs are updated in June and December, as well as when a source is added or removed. The program includes: • Monitoring of the mineralogy and durability of aggregate products representing normal production at a single source; • Statistical evaluation of recent aggregate quality test histories; • Expediency in aggregate quality acceptance; and Figure 1. AQMP Aggregate Sources • Optimized resource utilization by reducing aggregate acceptance on a test-prior-to-use basis. The map in Figure 1 shows the approximate locations of quarries monitored on the AQMP. Tex-499-A (ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/ TMS/400-A_series/pdfs/cnn499.pdf) was revised effective Dec. 1, 2007. Signiﬁcant revisions include requiring aggregate producers to: • maintain legible stockpile identiﬁcation in all stockpiles, • submit a mining plan annually to TxDOT, • submit quarry global positioning coordinates, • notify TxDOT of changes in quarry operations and • notify TxDOT if they want to split samples when the Department takes a sample. CONTINUED ON PAGE 22 TACA Conveyor • Summer 2008 17 ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/TMS/400-A_series/pdfs/cnn499.pdf ftp://ftp.dot.state.tx.us/pub/txdot-info/cst/TMS/400-A_series/pdfs/cnn499.pdf ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/mpl/brsqc.pdf ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/mpl/brsqc.pdf ftp://ftp.dot.state.tx.us/pub/txdot-info/cmd/mpl/crsqc.pdf

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TACA Conveyor - Summer 2008 Contents The Final Frontier And The Winner Is... Diagnosis: The Leadership Death Spiral Aggregates Rock Accident Investigation Training TXI Roadeo NRMCA Promoter of the Year Harold Hubbard NRMCA Driver of the Year Finalist Fort Worth Freightliner Changes at Cherry Crushed Concrete Index of Advertisers

TACA Conveyor - Summer 2008

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