Freeze-thaw resistance is a key durability factor for concrete pavements. Recommendations for the air void system parameters are normally 6% ± 1% total air and spacing factor ≤ 0.20 mm (0.008 in.). However, it was observed that some concretes that did not possess these commonly accepted thresholds presented good freeze-thaw resistance in laboratory studies. A study evaluated the freeze-thaw resistance of several marginal air void mixes, with two different types of air-entraining admixtures: a Vinsol resin admixture and a synthetic admixture. The study used rapid cycles of freezing and thawing in plain water, in the absence of deicing salts. For specific materials and concrete mixture proportions used in this project, the marginal air mixes (concretes with fresh air contents of 3.5% or higher) presented an adequate freeze-thaw performance when Vinsol resin-based air-entraining admixture was used. The synthetic admixture used in the study did not show the same good performance as the Vinsol resin admixture did.
The coefficient of thermal expansion (CTE) of concrete is a property that can affect the performance of the pavement and its service life and is one of the most important inputs in the Mechanistic-Empirical Pavement Design Guide (MEPDG). The CTE can be either estimated or measured in the laboratory. The test method used to determine this property is AASHTO TP 60, still a provisional test method and not yet evaluated for its precision. CTEs of more than 1,800 concrete specimens were measured at the Turner-Fairbank Highway Research Center. The specimens included cylinders that were cast in the laboratory as well as field cores obtained from the Long-Term Pavement Performance pavement sections. Approximately 150 of the specimens were tested individually several times for assessment of repeatability of the test method. An analysis is presented of test differences observed, as is a sensitivity analysis of the CTE test variability on predicted performance based on the MEPDG. The differences in predicted international roughness index (IRI), percent slabs cracked, and faulting due to test variability were determined for concretes with CTEs ranging from 4 to 7 × 10−6 in./in./°F. It was observed that differences in test results may result in significant discrepancies in the predicted IRI, percent slabs cracked, and faulting. Thus, a single test result should not be used as representative of the CTE of a mixture due to the considerable impact of the test variability on the predicted pavement performance. Moreover, the specifications should state the minimum number of tests necessary for the CTE determination and the acceptable test variability.
Internal curing can reduce alkali-silica reaction (ASR) damage in concrete. Alkali reactions with chert in natural sand caused damaging ASR in plain concrete. However, ASR damage was minimal in companion internally cured (IC) concrete in which a portion of the sand was replaced with pre-wetted lightweight aggregate (LWA). IC improved paste quality through a quantitative reduction in paste porosity and unhydrated cement. This was assessed using quantitative paste characterization including image analysis of backscattered electron (BSE) images, quantitative fluorescent intensity assessment, resistivity measurements, and qualitative analyses using SEM-EDS and polarized light microscopy. In concretes with the same water-cement ratio (w/c), IC concrete has denser paste microstructure from increased hydration due to additional water from pre-wetted LWA. Less permeable paste reduced fluid ingress, ASR reaction, and crack propagation. This demonstrates the potential of internal curing as a mitigation tool in reducing damage from ASR when high cement content and potentially reactive aggregates are used.
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