Jussara Tanesi

Effect of Coefficient of Thermal Expansion Test Variability on Concrete Pavement Performance as Predicted by Mechanistic-Empirical Pavement Design Guide

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.

Freeze–Thaw Resistance of Concrete with Marginal Air Content

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.

Interlaboratory Study on Measuring Coefficient of Thermal Expansion of Concrete

Coefficient of thermal expansion (CTE) is one of the sensitive inputs in the new Mechanistic–Empirical Pavement Design Guide (MEPDG). The most widely used test method to measure CTE of concrete is outlined in AASHTO TP60-00, Coefficient of Thermal Expansion of Hydraulic Cement Concrete. Several state highway agency materials laboratories and university research centers have custom-built manually operated or automated CTE measuring devices based on recommendations from AASHTO TP60. Automated CTE devices are also commercially available. With many states in the process of implementing the MEPDG, it is important that the CTE measurements from the various devices provide accurate and comparable results. Results from a nationwide CTE interlaboratory study conducted by FHWA are presented. Eleven custom-built and seven commercially purchased CTE units were used in the study. The 18 CTE devices were divided into four groups, with each group testing one 410 stainless steel (SS) specimen and two concrete specimens with low and high CTE. Statistical analysis was performed to determine overall variability of the CTE measurements from the various devices. Additionally, variability was determined between custom-built and commercially available CTE units and between two CTE measuring methodologies (AASHTO TP60 and Texas test method). Accuracy of the CTE measurements from the interlaboratory study was determined from the CTE value of a 410 SS specimen measured according to ASTM E228-06, Standard Test Method for Linear Thermal Expansion of Solid Materials with a Push-Rod Dilatometer.

Enhancing High Volume Fly Ash Concretes Using Fine Limestone Powder

One of the primary approaches to producing more sustainable concretes consists of replacing 50% or more of the portland cement in a conventional concrete with fly ash, producing a so-called high volume fly ash (HVFA) concrete. While these mixtures typically perform admirably in the long term, they sometimes suffer from early-age performance issues including binder/admixture incompatibilities, delayed setting times, low early-age strengths, and a heightened sensitivity to curing conditions. Recent investigations have indicated that the replacement of a portion of the fly ash in these concrete mixtures by a suitably fine limestone powder can mitigate these early-age problems. The current study investigates the production of concrete mixtures where either 40% or 60% of the portland cement is replaced by fly ash (Class C or Class F) and limestone powder, on a volumetric basis. The mixtures are characterized based on measurement of their fresh properties, heat release, setting times, strength development, rapid chloride penetrability metrics and surface resistivity. The limestone powder not only accelerates the early age reactions of the cement and fly ash, but also provides significant benefits at ages of 28 d and beyond for both mechanical and transport properties.

New AASHTO T336-09 Coefficient of Thermal Expansion Test Method: How Will It Affect You?

Although many papers were published during the past decade on the coefficient of thermal expansion (CTE) and its impact on concrete pavement design, an error was recently discovered in the AASHTO TP60-00 about the calibration of the testing equipment and, consequently, determination of the concrete CTE. The new AASHTO T336-09, even though based on the TP60-00, rectifies this calibration issue. This paper presents differences between the two test methods and implications for the Long-Term Pavement Performance database and for the Mechanistic–Empirical Pavement Design Guide and for its implementation by state departments of transportation. Recommendations are provided for improvements to the AASHTO T336-09 test method.

Ruggedness Study on the AASHTO T 336 Coefficient of Thermal Expansion of Concrete Test Method

A ruggedness study on the AASHTO T 336 coefficient of thermal expansion of concrete test method was performed to evaluate the factors most likely to affect the test results. Seven factors were evaluated: time at temperature extremes, water level, position of the linear variable differential transformer, number of segments, saturation criterion, specimen length, and temperature of the first segment. Two concrete mixtures were used in this study, four laboratories participated, and five commercially made coefficient of thermal expansion devices from two manufacturers were used. On the basis of the results obtained, saturation criterion was found to be the most significant factor. The other factors were found not to have a significant impact on the test results, have already been addressed in the most current version of the test method, or, in the authors’ opinion, do not warrant being addressed.

Interlaboratory Study and Precision Statement for AASHTO T 336 Test Method

With the recent release of AASHTOWare Pavement ME Design software, there will be a greater emphasis on measuring the coefficient of thermal expansion (CTE) of concrete because of its significance on predicted distress and design life. The most widely used test method to measure the CTE of concrete is the AASHTO T 336 test method. Data are presented from an interlaboratory (round robin) study conducted by FHWA; this study included 20 CTE units and laboratories representing FHWA, state highway agencies, universities, commercial testing laboratories, and the concrete paving industry. As part of the study, each laboratory tested nine concrete specimens (three concrete mixtures 3 three specimens per mixture) that spanned the typical range of CTE values for concrete. On the basis of this interlaboratory study for the AASHTO T 336 test method, the within-laboratory single operator standard deviation was found to be 0.12 mstrain/°C and the between-laboratory standard deviation was found to be 0.28 mstrain/°C. Data from the study also showed that there was no statistically significant difference between custom-built CTE devices versus commercially available testing devices. This demonstrates the ruggedness of the current test method.

Isothermal Calorimetry as a Tool to Evaluate Early-Age Performance of Fly Ash Mixtures

This paper documents the use of an isothermal calorimeter as a scanning tool to evaluate early-age behavior of high-volume fly ash mixtures. A series of paste and mortar mixtures containing different fly ashes (one Class C fly ash and two Class F fly ashes) with replacement levels ranging from 20% to 60% and high- and low-alkali cement was evaluated. Materials testing included ASTM C109, compressive strength of mortar cubes at different ages; ASTM C1437, flow; ASTM C403, time of setting; and ASTM C1679, isothermal calorimetry. In most cases, for the same water–binder ratio (0.40) and replacement level, Class C fly ash mixtures exhibited higher strength but delayed setting compared with Class F fly ash mixtures. Isothermal calorimetry proved to be a good scanning tool for predicting setting time and early-age compressive strength and for identifying materials incompatibility.

The Effect of Nano Materials on HVFA Mixtures

The interest in more sustainable concrete mixtures with the supplementary cementitious materials like fly ash has increased significantly in the past few years. Nevertheless, the early age properties development (setting and strength gain) of these mixtures still remains a challenge and, in most cases, prevents their efficient use in practice. In this paper, nano-aluminosilicates were used to improve early age properties of high volume fly ash (HVFA) mixtures. This paper presents results of several different paste and mortar mixtures where 60 % (by volume) of the portland cement was replaced by fly ash (Class C or Class F) and 1 % of amorphous nano-aluminosilicates with different silicon-aluminum ratios. Paste mixtures were characterized by measuring heat release and setting times and the compressive strength was evaluated in mortar mixtures in order to determine the optimal silicon-aluminum ratio for the cementitious materials used in the study.

Reducing the Specimen Size of the AASHTO T 97 Concrete Flexural Strength Test for Safety and Ease of Handling

This study examined the feasibility of using smaller-size concrete beam specimens to conduct flexural strength tests of concrete with a simple beam with third-point loading according to the AASHTO T 97 procedure. Twenty-two mixtures containing four coarse aggregates (limestone, diabase, gravel, and granite) with maximum size varying from .75 to 1.5 in. were prepared. A total of 132 specimens measuring 4 × 4 × 14 in. and 132 standard-size specimens (6 × 6 × 21 in.) were tested. The 4- × 4-in. specimens yielded higher flexural strengths, as expected from the literature review. Analysis of the flexural strength test data revealed a very good correlation (R2 = .93) between the smaller- and standard-size beams. An equation is proposed to convert the flexural strength of the smaller-size specimen to the flexural strength of the standard-size specimen.