Sulfate-bearing subgrade soils treated with calcium-based stabilizers often experience heaving problems (three-dimensional swell) caused by chemical reactions with the sulfate or sulfide minerals. Two research questions were addressed: ( a) what sulfate content results in deleterious chemical reactions using traditional (no mellowing) lime stabilization and ( b) how effective mellowing, double lime application and increased moisture content are at reducing swell in high-sulfate soils. To determine what concentrations of sulfate are too high for stabilization with lime in Texas, a soil from the Vertisol order was selected for three-dimensional swell measurements. This soil did not contain any detectable sulfates. Two different compounds were added to the soil: sodium sulfate (Na2SO4) and gypsum (CaSO4.2H2O). The sulfates were added to individual samples at concentrations of 0; 1,000; 2,000; 3,000; 5,000; 7,000; and 12,000 parts per million (ppm). The samples were then subjected to a three-dimensional swell test for a minimum of 45 days. Results of systematic swell experiments revealed that sulfate contents up to 3,000 ppm could safely be treated with traditional lime stabilization. Coarse-grained sulfates take longer to swell, but still swell and form deleterious reaction products. Mellowing is effective at treating sulfate concentrations up to at least 7,000 ppm, higher molding moisture contents (2% above optimum moisture) reduce swell better than optimum moisture, and single application of lime reduces swell better than double application. With systematic laboratory experiments, empirical field observations of sulfate limits presented by other investigators were confirmed.

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Shrinkage cracking occurs in cement-treated bases because of desiccation and cement hydration; eventually these cracks start to reflect through the pavement surfacing. Although initially considered cosmetic, these cracks open the pavement to water infiltration and increase the likelihood of accelerated pavement distress. Numerous options exist for minimizing the amount of reflective cracks that appear; microcracking is a promising approach. The microcracking concept can be defined as the application of several vibratory roller passes to the cement-treated base at a short curing stage, typically after 1 to 3 days, to create a fine network of cracks. In addition to the microcracked test sites, the contractor constructed moist-cured, dry-cured, and asphalt membrane–cured sites for comparison. Researchers used falling weight deflectometer (FWD) tests to control the microcracking process, periodic crack surveys to monitor crack performance, and FWD tests through time to track base moduli. Microcracking proved quite effective at reducing shrinkage cracking problems in the base; applying the procedure with three passes of the roller after 2 to 3 days of curing resulted in the best performance. In addition, researchers observed that, without microcracking, excessively high cement contents resulted in problematic cracking in the base even if they were cured according to good construction practice. Microcracking did not result in pavement damage or diminished inservice modulus; thus, microcracking should be considered a viable and inexpensive option to incorporate shrinkage crack control into the construction of cement-treated bases.

In an effort to construct roads more quickly, high-plasticity index soils stabilized with lime are now routinely compacted the day after mixing. With this practice has come an increasing number of heaves due to soluble sulfates reacting with the lime to form ettringite. Soils with sulfate concentrations below 7,000 to 8,000 parts per million (ppm) can generally be treated with lime. This research was performed to identify stabilizers that can be used with sulfate concentrations above 10,000 ppm. The effectiveness of the stabilizers was determined by the measurement of three-dimensional (3-D) swell reduction and unconfined compressive strength. The researchers evaluated 12 stabilizers, including enzymes, polymers, acids, emulsions, fly ash, and ground granulated blastfurnace slag (GGBFS). Three stabilizers significantly reduced volumetric swell. A polymer and an acid reduced swell by about 8%. GGBFS plus lime reduced swell by 10%. GGBFS plus lime was the only stabilizer that reduced swell, increased strength, and was cost-effective enough for the Texas Department of Transportation to consider as an alternative to lime in high-sulfate soils.

Segregation is a serious problem in hot-mix asphalt and typically results in poor performance, poor durability, a shorter life, and higher maintenance costs for the pavement. A summary of the results and recommendations from three projects in Texas in which infrared imaging and ground-penetrating radar were used to examine the uniformity of the pavement mat is presented. Both techniques have significant advantages over currently used nuclear density techniques in that they provide virtually 100% coverage of the new surface. The effectiveness of both the infrared and radar techniques was evaluated by taking measurements on new overlays at the time of placement, coring, and then identifying relationships between changes in the infrared and radar data with changes in the measured volumetric and engineering properties of the cores. Analyses of the results showed that changes in both infrared and radar data are significantly related to changes in hot-mix asphalt properties such as air void content and gradation. On the basis of current Texas Department of Transportation specifications, significant changes in the hot-mix asphalt are expected if temperature differentials of greater than 25°F (13.9°C) are measured after placement but before rolling. If the surface dielectric of the in-place mat changes by more than 0.8 for coarse-graded mixes and 0.4 for dense-graded materials, significant changes in mix properties are expected. Given the promising results from this work, agencies should consider implementing both the infrared and ground-penetrating radar technologies.