NRMCA Reports on Transportation Research Board Annual Meeting

The 91st meeting of the Transportation Research Board (TRB) was held in late January in Washington, DC, with about 1,100 transportation professionals in attendance and more than 4,000 papers were presented. What follows is an update of the sessions and meetings attended by NRMCA:

• A half-day session on Internal Curing using Light Weight Aggregate Fines was held. Eight papers were presented discussing basic research to state highway department trials. During hydration these lightweight aggregate fines will slowly release water as needed. These materials will not replace traditional curing. It is primarily used to prevent autogeneous shrinkage and, to a lesser extent, thermal shrinkage. A future TRB Webinar is planned. NIST has tools for mixture proportioning, including an equation to calculate amount light weight aggregate fines needed to prevent shrinkage cracking. AFN40 Committee is working on a circular on internal curing. Louisiana DOT has developed a ternary concrete specification that allows up to 70% SCM and has no minimum cementitious content. This spec can be used only if external temperature is above 50°F. A mass concrete project has been completed successfully and a concrete pavement project is planned.
• There were several papers on surface resistivity. The test is more economical than the RCPT test (ASTM C1202). It is a lot easier and quicker and has excellent correlations with RCPT but with lower variability. AASHTO TP 95-11 is a provisional standard. A paper was presented on use of clean natural gas (CNG) instead of diesel for ready mixed concrete trucks. If CNG stations are widely available and natural gas has price differential with diesel, it will become cost effective. AZ state has an Excel spread sheet to compare costs.
• A paper was presented using lower discount rates for concrete vs. asphalt which showed significantly lower life cycle costs for concrete pavements as compared to asphalt pavements. There were a number of papers on recycled concrete aggregate and pervious concrete signifying continued interest in those subjects. TRB’s Properties of Concrete Committee is working on a circular on pervious concrete.
• IPRF Web site has fly ash type and dosage selection tool for concrete pavements based on performance requirements. Please see http://www.iprf.org/products/main.html. The National CP Tech Center has recently released "Sustainable Concrete Pavements: A Manual of Practice". PCA has developed a document "Guide to Cement Based Integrated Pavement Solution". It is a non-technical document discussing different types of pavement systems. Both documents can be downloaded at no cost from www.cptechcenter.org.
• Eight papers were presented over two sessions on Portland limestone blended cements (PLBC). Up to 15% limestone likely to be approved by ASTM C595/AASHTO M240 in 2012. Limestone fines may help with particle packing, providing additional nucleation sites for hydration products and formation of carbo-aluminates. PLBC has 580-600 m2/kg blaine as compared to about 380 m2/kg for portland cement. Typically, it is about 10 m2/kg higher blaine for every 1% limestone. Researchers stated that fly ash/slag cement can be added at the concrete plant to PLBC at the same rate as with ordinary portland cements with similar performance.

The theme for the 2013 TRB meeting is Deploying Transportation Infrastructure: Doing this faster, cheaper and better. TRB 2013 is likely to feature workshops on Cracking; and Ensuring Good Quality Concrete.

For more information, contact NRMCA's Karthik Obla at kobla@nrmca.org.

National Ready Mixed Concrete Association