Rock Products

MAR 2013

Rock Products is the aggregates industry's leading source for market analysis and technology solutions, delivering critical content focusing on aggregates-processing equipment; operational efficiencies; management best practices; comprehensive market

Issue link: https://rock.epubxp.com/i/113289

Contents of this Issue

Navigation

Page 27 of 99

SPECIAL REPORT crusher fines and to blend open graded RCA with virgin aggregates to reduce precipitate formation. The existence of hazardous materials, such as lead and asbestos, is possible when the concrete is from commercial sources. Some states address this pos��� sibility by requiring a certification from the supplier indicating that the mate��� rial is in compliance with appropriate state and EPA requirements. The Maryland Department of Trans��� portation presented a Special Provi��� sion added to Section 900.03 of their Standard Specifications with such a requirement. The Texas Department of Transportation also has a specifica��� tion that addresses how nonhaz��� ardous recyclable materials, such as RCA, are addressed from an environ��� mental regulatory perspective. The determination about allowable uses of RCA by individual state Department of Environmental Protection (DEP) agen��� cies also varies from state to state. For example, in one state RCA has been defined by legislation to not be subject to review or permitting from the state DEP, another state developed a compliance agreement addressing the use of RCA, and another state had RCA exempted from solid waste regu��� lation as long as it remained on the project site. (FHWA, 2004) Consis��� tency in regulatory procedures be��� tween states is certainly desirable and could have an impact on both avail��� ability and cost of RCA. The majority of the state specifications for the material properties and grada��� tions for RCA are the same as for virgin aggregates. Because of the existence of cement paste and concrete mortar on the aggregates, RCA has a lower spe��� cific gravity and higher absorption than virgin aggregates. Most states allow up to five percent brick and five percent bituminous pavement by weight in RCA recogniz��� ing the realities involved with remov��� ing and demolishing existing concrete structures. AASHTO M 319 includes a note and Appendix X4 that provides for using excess bituminous pavement or brick in RCA. It presents three different 26 ROCKproducts ��� MARCH 2013 means to address performance criteria that can be used when considering in��� creasing the allowable percentages. The options include validation by (1) the use of CBR testing (AASHTO T 193); (2) the use of Resilient Modulus testing (AASHTO T 307); or (3) the use of a field validation using test strips or historical data. A similar approach could also be used to consider gradations differing from the agency���s normal requirements. When testing the durability of RCA with sodium sulfate (AASHTO T 104), some materials exhibit high soundness values that may not accurately reflect the quality. Note 5 of AASHTO M 319 cautions about this and provides dis��� cussion about alternatives in both Sec��� tion 6.3 and Appendix X3. The appendix offers options that include not testing along with three alternative test methods to evaluate freeze���thaw characteristics. In addition to not testing, AASHTO T 103 (freeze���thaw in water), New York State DOT method NY703���08 (sodium chloride brine solution), and Ontario Ministry of Transportation Test Method LS���614 (sodium chloride brine solution with five freeze���thaw cycles), are listed as acceptable alternative ap��� proaches to sodium sulfate. Some states require concrete from their own DOT furnished sources, such as existing pavements and structures, while others allow the concrete to orig��� inate from contractor provided sources, such as building demolition or commercial recyclers. Some states have different testing and stockpile management requirements depending on the source of the concrete and oth��� ers do not differentiate. If a particular state has good quality aggregates throughout, it is reasonable to assume that any concrete used to produce RCA would produce a durable and quality material. On the other hand, additional testing of concrete from unknown sources would seem reasonable for a state having high variability in the quality of available aggregates. Concrete that has exhibited alkali���silica reactivity (ASR) is acceptable for use for unbound base course using RCA, ac��� cording to the Michigan Department of Transportation Manual of Practice ad��� dressing RCA. (Van Dam, 2011) Sulfate attack may be an issue with some com��� bination of materials. Because of this, testing for sulfates in both the soils in contact with the RCA base as well as nearby surface water may be war��� ranted. (Cooley, 2007) Knowledge about local conditions and past experi��� ence should dictate whether or not such testing is advisable. The U.S. Geological Survey (USGS) has estimated that 1.2 billion tons of aggre��� gates were produced in 2011. (Willett, Mineral Commodity Summaries, Janu��� ary, 2012) Although this is below the record high of 2 billion tons produced in 2006, it still represents a significant quantity of aggregates. The Construc��� tion Materials Recycling Association es��� timates that 140 million tons of concrete are recycled annually in the United States. (CMRA, 2012) It is rea��� sonable to expect that the demand for aggregates will increase at some point in the future, although past predictions have not materialized due to recent economic trends. The permitting and opening of new ag��� gregate sources is time consuming, ex��� pensive and difficult to accomplish, especially in urban areas. The availabil��� ity of concrete capable of allowing the consistent production of RCA in large quantities is more likely in urban areas. As the aging infrastructure reaches the point of needing replacement, the recy��� cling of existing concrete accomplishes the ability to provide quality aggregate while not adding to diminishing landfill space. In that regard, the use of RCA should be considered a sustainable op��� tion for use as a base course by provid��� ing a quality choice without either adding to landfill space or exerting en��� ergy and resources to the mining and production of new aggregates. In a re��� cent Transportation Research Board paper the use of RCA as a replacement for virgin aggregate base in Florida was deemed sustainable and displayed lim��� ited impacts in the environmental, so��� cial and economic categories. (Donaldson, 2011) A RMRC user guideline reports that the www.rockproducts.com

Articles in this issue

Links on this page

Archives of this issue

view archives of Rock Products - MAR 2013