Rohne, Ryan J.

This paper discusses the construction and early performance of a pervious concrete test cell at the MnROAD facility. The cell is subjected to daily loading of an 80-Kip 5-axle semi-trailer, two times a day, four days a week and 102-Kip 5-axle semi-trailer twice a day, one day a week. Performance was evaluated by comparing Falling Weight Deflectometer (FWD) deflection basins to those of normal concrete pavements of similar thickness design. Stress-strain response of the pavement system was computed from dynamic strain gauge data. Temperatures and freeze-thaw cycles at various pavement depths where monitored. An in-situ method for measuring time rate of flow was developed. Petrographic analysis reveled differences in porosity between the surface and bottom layers as well as drying shrinkage cracking. Normal sanding and salting operations during the winter do not appear to have impacted the pore structure within the pervious concrete after three years of service. Spalling and raveling were prevalent at the tooled joints and occurred in sections where the surface could have prematurely dried due to overworking. The test cell driveway showed superficial wear near the joints after its first season in service. Large 12x12 ft rectangular block cracking was observed after 2 ½ years as well as reflective cracking propagated from joints of the surrounding curb. Critical parameters including time rate of flow, raveling, and cracking will continue to be monitored. This paper was submitted to the Transportation Research Board for the 2009 Annual Meeting.

Developed by Magnetic Imaging Tools GmbH (Dresden, Germany), the MIT Scan-2 is a nondestructive testing device that uses magnetic imaging technology to measure the position of metal dowel bars embedded in concrete. It is very quick and easy to use. Less than five minutes are needed to scan each joint and reposition the device for the next joint. The hand held computer that controls the device allows the user to see the positions of the dowel bars in the joints immediately after scanning. It also has a very easy to use analysis program called MagnoProof that uses the specified dowel locations, along with allowable tolerances, to automatically identify misaligned dowels.

Mn/DOT demonstrated a porous pavement vacuuming process using equipment owned and operated by Reliakor, a Minnesota based Company at MnROAD on November 4, 2009. Pervious concrete test cells 85 and 89 and porous asphalt cells 86 and 88 were vacuumed. Representatives from Mn/DOT Metro District, Mn/DOT Research, Mn/DOT Tech Support, Mn/DOT Maintenance Research, the City of Minneapolis, DNR, and Reliakor Services Inc were in attendance. The test cells were approximately one year old at the time of the demonstration and were in good condition. The pervious concrete test cells had no surface raveling or joint distress and very few fine cracks. The porous asphalt test cells had isolated areas of surface raveling and light rutting. The voids in the pervious concrete and porous asphalt test cells appeared to be clean and free of debris. It is important to note that the brush on the vacuum was not used. The brush could pack debris further into the voids and increase clogging in the pervious/porous pavements.

With the construction of four new test cells in 2008, the Minnesota Department of Transportation (Mn/DOT) now has six unique pervious pavement test sections at the MnROAD test facility. Recorded temperatures in the pervious pavements and subgrades were compared to impervious Portland Cement Concrete (PCC) test sections over the same time interval. It was found that the subgrade in pervious PCC and Hot Mix Asphalt (HMA) was up to 4 °C warmer in the winter than impervious PCC pavements. The frost depth in an impervious PCC pavement was found to be 45.7 cm deeper than in a pervious PCC pavement of similar thickness. One pervious pavement test cell experienced 60% less freezing cycles over a three year interval than impervious PCC pavements of similar thickness. The air trapped in the pavement voids was suspected to be the main reason for the reduced number of freeze-thaw cycles by creating an insulating effect. In another pervious pavement, entrapped air within the base material may also insulate the pavement from the subgrade.

This report includes the test results on aggregates from four taconite strata from the Mesabi iron range of Minnesota for concrete qualities including Los Angeles Rattler (LAR), absorption, flatness and elongation, magnesium sulfate, ASTM C 1260, and ASTM C 1293. The strata are identified as LC-8 Bed from United Taconite, LC-5 Bed from Ispat Inland/Mittal Steel (Laurentian Pit), LS-2 Bed from Ispat Inland/Mittal Steel (Laurentian Pit), and LUC Bed from United Taconite. A granite source, known to have moderately low expansion characteristics was also tested for comparison. All ledges tested well for Los Angeles Rattler and magnesium sulfate soundness. Ledges LS-2, LC-8, and LS-2 had excellent results for ASTM C 1260 and ASTM C 1293 expansion, while the LC-5 ledge performed very poorly. The Coal Creek fly ash used in the ASTM C 1293 tests mitigated ASR expansions much better than the slag mixes. As with any natural aggregate source, the physical and chemical properties of the taconite ledges vary. Because of the high variation in expansion potential, each potential concrete strata should be tested within a mine using ASTM C 1293. A Quality Control plan should be developed for each source. Specific gravity may be used to screen out potential deleterious strata, and should be performed frequently, perhaps on each blast. ASTM C 1260 tests should also be used on a frequent basis.

Cell 54 was constructed in the fall of 2004 on the MnROAD low-volume loop. It is made up of eight inches of concrete underlain by Class 5 aggregate base and approximately three inches of compacted in-situ fill. Mn/DOT constructed this cell to study the properties of Mesabi-Select as coarse aggregate in concrete. This mineral aggregate that contains less iron than the ore, was obtained from overburdens in the iron ore ledges in northern Minnesota. There is no record of a previous cell constructed to study the suitability of Mesabi-Select in concrete. Cell 54 is in very good condition after five years. There are very few cracks of low severity. The types of distress found were spalling of transverse joints, longitudinal cracking, and transverse cracking. Very little joint faulting has occurred. In-situ concrete surface permeability measurements indicate that the concrete is good quality. Friction and ride quality measurements indicate that Cell 54 is in very good condition. Falling weight deflectometer (FWD) deflections at the surface and top of the base were of similar magnitude as in other doweled jointed plain concrete pavement (JPCP) test cells of similar design.

To determine whether the distress observed in MnROAD test sections was unique, researchers examined six other Minnesota concrete pavement projects of similar age and material. Similar types of distress were found but the extent of damage was not as severe and sections with base layers that adequately drained water within the joints performed significantly better.

This report analyzed the mix designs and permeability of 230 concrete mixes from Minnesota paving projects paved between 2004 and 2008. Concrete permeability was measured on cores according to ASTM C 1202, Standard Test Method for Electrical Indication of Concrete's Ability to Resist Chloride Ion Penetration. Previous studies showed that aggregate gradations conforming to the 8-18 gradation specification do not always produce denser graded aggregates or concrete with better properties (higher strength, better finishability, greater freeze-thaw durability) than gradations that do not meet the 8-18 specification. Based on box plots and descriptive statistics, granite produced concrete with lower permeability than limestone and gravel. According to the Student's T-test with a 95% significance level, 7-18 graded aggregate produced concrete with significantly lower permeability than 8-18 graded and cement source and contractor both also affected permeability. According to the Student's T-test with a 90% significance level, 7-18 graded aggregate produced concrete with significantly lower permeability than gap graded mixes.

The primary objective of this research study is to develop an improved service life prediction model for the Minnesota Department of Transportation's (Mn/DOT's) current 60-year concrete pavement designs. Secondary objectives include understanding the behavior of these pavements with regard to maturity, slab warp and curl, and thermal expansion. These objectives will be accomplished through extensive testing of materials during construction, and conducting seasonal load response testing under controlled loads of an instrumented concrete pavement test cell (Cell 53) built to Mn/DOT's current 60-year design standards. Load response testing of traditional designs constructed in MnROAD Phase I will be used in the development of the improved life prediction model. This construction report describes the construction and material testing done on MnROAD Low Volume Road test Cell 53. A summary of U.S. and international long-life concrete pavement designs is also included.

A maturity protocol will allow a more precise identification of the time when sufficient strength has been gained such that a pavement can be opened to traffic. This way traffic can be regulated to protect the integrity of the pavement while simultaneously streamlining construction operations by avoiding excessive initial cure periods. The overall goal of this research initiative is to develop maturity strength curves for the majority of the paving mixes used by Mn/DOT and test maturity meter implementation on several projects to observe potential difficulties/successes with their use. As such, Mn/DOT SP 6280-304, the TH-694/TH-35E interchange known as "Unweave the Weave" is one of the first Mn/DOT projects to test the implementation of maturity meters in a field setting. Based on the data from the pilot project and preliminary tasks, maturity curves are sensitive to small changes of 10 lb/yd 3 of cementitious material. It was also found that a maturity datum temperature of 0 °C was too high. Strength continued to increase even when the concrete fell below this temperature. Further studies of 15 projects over the next three years will further increase Mn/DOT's knowledge and experience with the maturity method. Included is an overview of the maturity function utilized by the data loggers.