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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 most common test methods used to evaluate alkali-silica reaction (ASR) are the concrete prism test (CPT) and the accelerated mortar bar test (AMBT). However, these tests were not found to be entirely reliable in predicting the performance of concrete under field conditions, especially when supplementary cementitious materials (SCMs) are used. Recently, two new test methods, the miniature concrete prism test (MCPT) and the concrete cylinder test (CCT), have been proposed but still need to be benchmarked with results from outdoor exposed blocks. In this paper, the results from the MCPT, CCT, CPT and exposed blocks are compared and their ability to properly evaluate the expected behavior of these mixtures in service with regard to ASR is discussed. Here, the results of mixtures made with four reactive aggregates: Spratt, Placitas (coarse aggregates), Wright, and Jobe (fine aggregates) and SCMs (fly ashes Classes F or C, slag cement, or silica fume) at different levels of cement replacement or lithium nitrate are presented. For these mixtures, only the MCPT was capable of properly classifying the efficiency of the ASR preventive measures, as compared with the long-term results obtained from the exposed blocks.

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.

Pore solution expression is an established method to obtain samples of the liquid phase from cementitious systems. This experimental method applies pressure to a cementitious sample, forcing its liquid phase out of the pores. By collecting and studying the liquid phase in cementitious systems, it is possible to obtain information on its ionic concentrations. The ionic concentrations can be used for modeling calibrations and to estimate the resistivity of the pore solution. When the bulk resistivity of concrete is normalized by the pore solution resistivity, it is possible to determine the formation factor. The formation factor is related to the transport properties of the concrete and, as such, it can be used to estimate the rates of transport of ionic species within a concrete structure. The formation factor is currently being included in AASHTO PP84, Standard Practice for Developing Performance Engineered Concrete Pavement Mixtures, as an indicator of transport properties for quality control operations. Pore solution expression is included as one of the available procedures of AASHTO PP84-19 to determine the pore solution electrical resistivity. Previous studies on paste and mortar samples have demonstrated that increased loading pressure during the pore solution expression might impact the final ionic concentrations of the expressed solution. This study aims to verify if the pore solutions of concrete specimens are also influenced by the selected loading pressure and whether the potential consequent change in the measured ionic concentrations of the solution also has an impact on its resistivity. No appreciable trend in increased solubility was observed for the range of applied normal pressures between 600 and 985 MPa. Cyclic loading regimes increased the variability of alkali solubility. Sample preparation, in some cases, influenced the water content of the sample and induced unwanted alteration on the ionic concentrations of the mixtures under study.

In this paper, effects of nanomaterials on the hydration kinetics and rheology of ordinary Portland cement pastes were investigated. Three nanomaterials, nano-limestone, nano-silica, and nano-clay (a highly purified magnesium aluminosilicate), were added to a cement paste at the levels of 0.0 %, 0.5 %, 1.0 %, and 1.5 % (by mass) of cement. The heat of cement hydration of the paste was measured using isothermal calorimetry. Rheological behavior of the paste was characterized using a rotational rheometer. The rheology measurements were performed at 10, 30, 60, 90, and 120 min after the cement was mixed with water. Set times of the paste were measured according to ASTM C191 [Standard Test Methods for Time of Setting of Hydraulic Cement by Vicat Needle, Annual Book of ASTM Standards, ASTM International, West Conshohocken, PA]. The experimental results indicate that the addition of nano-limestone and nano-silica accelerated cement early hydration, the maximum heat flow increased, whereas the time to reach the heat-flow peaks decreased. The initial and final set times were also reduced. These effects were enhanced with increased nano-addition level. The addition of nano-clay also significantly increased the intensity of the heat flow peaks, and, especially, the peak corresponding to the renewed reaction of the aluminate phase. Addition of these nanomaterials generally increased yield stress and viscosity of the cement paste, especially after 60 min when cement hydration started to accelerate. Nano-clay considerably influenced the rheological behavior of the cement paste. Significantly higher shear stresses were required to initiate the flow.

While the influence of paste properties on concrete performance has been extensively studied and in many cases reduced to quantitative relationships (e.g., Abram's law), that between aggregate characteristics and concrete performance has not been investigated in detail. Based on previous research that demonstrated significant strength differences for two similar concrete mixtures, one prepared with limestone aggregates and the other with siliceous gravel, a joint study between the National Institute of Standards and Technology (NIST) and the Federal Highway Administration (FHWA) was initiated to explore in detail the influence of aggregate source, mineralogy, and material properties on concrete performance. Eleven aggregates of differing mineralogy were identified and obtained both for bulk characterization and for incorporation into two concrete mixtures. The first concrete mixture was based on a 100 % ordinary Type I/II portland cement (OPC), while the second consisted of a ternary 60:30:10 volumetric blend of this cement with 30 % of a Class C fly ash and 10 % of a fine limestone powder. This latter sustainable mixture had exhibited exemplary performance in a previous study. Aggregates were characterized with respect to mechanical and thermomechanical properties, geometrical characteristics, and surface energies. For the prepared concretes, mechanical, thermomechanical, and electrical properties were measured at different ages out to 91 d and microstructural examinations were conducted to examine the interfaces between aggregates and cement paste. Concrete performance varied widely amongst the different aggregates, with the (range/average) ratio for 28-d compressive strength being 0.32 for the OPC concretes and 0.37 for those based on the ternary blend binder. With the exceptions of relating concrete modulus to aggregate modulus and concrete coefficient of thermal expansion (CTE) to aggregate CTE, weak correlations were generally obtained between a single aggregate characteristic and concrete performance properties. Models to predict 28-d compressive strength based on the aggregates' CTE (and aggregate absorption in the case of the ternary blend mixtures) provided predictions with a relative standard error (standard error/mean) of about 7 %. It is suggested that aggregate and binder characteristics control the bond between aggregates and paste. Then, for most properties, concrete performance is primarily controlled by the level of this bonding, a characteristic that was only assessed in an indirect manner in the present study. Research using non-linear ultrasonic measurements to better assess this bonding in specimens remaining from the present study is currently underway.