Deicer Scaling Resistance of Concrete Mixtures Containing Slag Cement Phase 2: Evaluation of Different Laboratory Scaling Test Methods, TPF-5(100), 2012

With the use of supplementary cementing materials (SCMs) in concrete mixtures, salt scaling tests such as ASTM C672 have been found to be overly aggressive and do correlate well with field scaling performance. The reasons for this are thought to be because at high replacement levels, SCM mixtures can take longer to set and to develop their properties: neither of these factors is taken into account in the standard laboratory finishing and curing procedures. As a result, these variables were studied as well as a modified scaling test, based on the Quebec BNQ scaling test that had shown promise in other research. The experimental research focused on the evaluation of three scaling resistance tests, including the ASTM C672 test with normal curing as well as an accelerated curing regime used by VDOT for ASTM C1202 rapid chloride permeability tests and now included as an option in ASTM C1202. As well, several variations on the proposed draft ASTM WK9367 deicer scaling resistance test, based on the Quebec Ministry of Transportation BNQ test method, were evaluated for concretes containing varying amounts of slag cement. A total of 16 concrete mixtures were studied using both high alkali cement and low alkali cement, Grade 100 slag and Grade 120 slag with 0, 20, 35 and 50 percent slag replacement by mass of total cementing materials. Vinsol resin was used as the primary air entrainer and Micro Air® was used in two replicate mixes for comparison. Based on the results of this study, a draft alternative test method to ASTM C762 is proposed.

Examination of Curing Criteria for Cold In-Place Recycling Phase 2: Measuring Temperature, Moisture, Deflection and Distress from CIR Test Section, TR-590, 2009

The previous research performed laboratory experiments to measure the impacts of the curing on the indirect tensile strength of both CIR-foam and CIR-emulsion mixtures. However, a fundamental question was raised during the previous research regarding a relationship between the field moisture content and the laboratory moisture content. Therefore, during this research, both temperature and moisture conditions were measured in the field by embedding the sensors at a midpoint and a bottom of the CIR layer. The main objectives of the research are to: (1) measure the moisture levels throughout a CIR layer and (2) develop a moisture loss index to determine the optimum curing time of CIR layer before HMA overlay. To develop a set of moisture loss indices, the moisture contents and temperatures of CIR-foam and CIR-emulsion layers were monitored for five months. Based on the limited field experiment, the following conclusions are derived: 1. The moisture content of the CIR layer can be monitored accurately using the capacitance type moisture sensor. 2. The moisture loss index for CIR layers is a viable tool in determining the optimum timing for an overlay without measuring actual moisture contents. 3. The modulus back-calculated based on the deflection measured by FWD seemed to be in a good agreement with the stiffness measured by geo-gauge. 4. The geo-gauge should be considered for measuring the stiffness of CIR layer that can be used to determine the timing of an overlay. 5. The stiffness of CIR-foam layer increased as a curing time increased and it seemed to be more influenced by a temperature than moisture content. The developed sets of moisture loss indices based on the field measurements will help pavement engineers determine an optimum timing of an overlay without continually measuring moisture conditions in the field using a nuclear gauge.

Evaluation of Iowa’s 70 mph Speed Limit — 2.5 Year Update, 2009

On July 1, 2005, the State of Iowa implemented a 70 mile per hour (mph) speed limit on most rural Interstates. This document reports on a study of the safety effect of this change. Changes in speeds, traffic volume on and off the rural Interstate system (diversion), and safety (crashes) for on- and off-system roads were studied. After the change, mean and 85th percentile speeds increased by about 2 mph on rural Interstates, but speeding was reduced (the number of drivers exceeding the speed limit by 10 mph decreased from 20 per cent to about 8 per cent). Daytime and nighttime serious crashes were studied for a period of 14 and a half years prior to the change and 2 and a half years afterwards. Simple descriptive statistics reveal increases in all crash severity categories for the 2 and a half year period following the speed limit increase when compared to the most recent comparable 2 and a half year period prior to the increase. When compared to longer term trends, the increases were less pronounced in some severity levels and types, and for a few severity levels the average crash frequencies were observed to decrease. However, fatal and other serious cross-median crashes increased by relatively larger amounts as compared to expected random variation. The study also analyzed crash frequencies grouped into six-month periods, revealing similar findings.