The Utah Department of Transportation (UDOT) has fully implemented the Mechanistic-Empirical Pavement Design Guide for pavement design but has been using primarily level-three design inputs obtained from correlations to aggregate base materials developed at the national level. UDOT was interested in investigating correlations between laboratory measurements of resilient modulus, California bearing ratio (CBR), and other material properties specific to base materials commonly used in Utah; therefore, a statewide testing program was needed. The objectives of this research were to 1) determine the resilient modulus of several representative aggregate base materials in Utah and 2) investigate correlations between laboratory measurements of resilient modulus, CBR, and other properties of the tested materials. Two aggregate base materials were obtained from each of the four UDOT regions. Important material properties, including particle-size distribution, soil classification, and the moisture-density relationship, were investigated for each of the sampled aggregate base materials. The CBR and resilient modulus of each aggregate base material were determined in general accordance with American Society for Testing and Materials D1883 and American Association of State Highway and Transportation Officials T 307, respectively. After all of the data were collected, several existing models were evaluated to determine if one or more of them could be used to predict the resilient modulus values measured in this research. Statistical analyses were also performed to investigate correlations between measurements of resilient modulus, CBR, and other properties of the tested aggregate base materials, mainly including aspects of the particle-size distributions and moisture-density relationships. A set of independent predictor variables was analyzed using both stepwise regression and best subset analysis to develop a model for predicting resilient modulus. After a suitable model was developed, it was analyzed to determine the sensitivity of the model coefficients to the individual data points. For the aggregate base materials tested in this research, the average resilient modulus varied from 16.0 to 25.6 ksi. Regarding the correlation between resilient modulus and CBR, the test results show that resilient modulus and CBR are not correlated for the materials tested in this research. Therefore, a new model was developed to predict the resilient modulus based on the percent passing the No. 200 sieve, particle diameter corresponding to 30 percent finer, optimum moisture content, maximum dry density (MDD), and ratio of dry density to MDD. Although the equation may not be applicable for values outside the ranges of the predictor variables used to develop it, it is expected to provide UDOT with reasonable estimates of resilient modulus values for aggregate base materials similar to those tested in this research.

The objective of this research was to investigate the structural capacity of aggregate base materials stabilized with triaxial geogrid placed in a full-scale pavement involving control, or unstabilized, sections. Field testing was performed on a roadway in northeastern Utah that was 16 km (10 miles) long and included 10 test sections, seven stabilized sections and three control sections, each having five test locations. The pavement structure was comprised of a hot mix asphalt layer overlying an untreated aggregate base layer of varying thickness, depending on the test section. Except for the control sections, one or two layers of geogrid were incorporated into portions of the pavement structure at different locations. Falling-weight deflectometer testing and dynamic cone penetrometer testing were used to evaluate the structural capacity of the aggregate base layer in each pavement section. For data analysis, the Rohde's method was applied in conjunction with the 1993 American Association of State Highway and Transportation Officials pavement design guide methodology, and the Area under the Pavement Profile (AUPP) method was applied in conjunction with a mechanistic-empirical pavement analysis. Statistical analyses were then performed to enable comparisons of the test sections. Field results indicated that the asphalt layer thickness was consistently 140 mm (5.5 in.) at all 10 test sections, and the base layer thickness varied from 360 mm (14 in.) to 510 mm (20 in.). The results of the statistical analyses indicated that the majority of the 45 possible pairwise comparisons among the test sections were not statistically significant, meaning that variations in the presence and position of triaxial geogrid at those sections did not appear to affect the structural capacity. The remaining comparisons, however, were statistically significant and involved the test sections with the highest structural capacity. While one of these was unexpectedly an unstabilized control section, the others were constructed using one or two layers of geogrid in the base layer. In addition to being statistically significant, the observed differences were also practically important. Increases in the observed base layer coefficient from 0.12 to 0.18 correspond to an increase in the allowable number of equivalent single axle loads (ESALs) from 5.9 million to 19.2 million at the research site, while decreases in the observed AUPP value from 340 mm (13.37 in.) to 213 mm (8.38 in.) correspond to an increase in the allowable number of ESALs from 3.7 million to 17.3 million at the research site. These results indicate that, when geogrid reinforcement is compatible with the given aggregate base material and proper construction practices are followed, statistically significant and practically important increases in pavement design life can be achieved.

[pt] Este trabalho apresenta um estudo técnico experimental sobre a utilização de borracha moída de pneu (BMP) como adição, juntamente com cimento Portland à brita graduada simples (BGS), no intuito de avaliar a aplicabilidade desse material em camadas de base de pavimentos rodoviários. Como resultado obtémse uma BGTC - Brita graduada tratada com cimento, com adição de BMP. O principal objetivo da adição de borracha na BGTC é reduzir o fissuramento, que é um problema comum em bases cimentadas. Para melhor comparação dos resultados das misturas com adições de borracha foi realizada uma mistura de BGTC sem adições, a qual foi tratada como mistura padrão neste estudo, com 3 por cento, 4 por cento e 5 por cento de cimento. O agregado granítico selecionado para esta pesquisa é proveniente de jazida situada no município de Cariacica/ES e foi escolhido por ter apresentado bom desempenho nos ensaios de caracterização. A partir da análise granulométrica realizada na borracha, selecionou-se para esse estudo a fração passante na peneira de 2,38mm e retida na peneira de 1,19 mm. Foram estuadas as seguintes porcentagens de adição de BMP: 0,5 por cento, 1,0 por cento, 1,5 por cento, 2,5 por cento, 3,5 por cento e 4,5 por cento. As amostras foram submetidas a ensaios de compactação, compressão simples, compressão diametral, triaxial de cargas repetidas e microscopia eletrônica de varredura. Os ensaios de compressão simples foram realizados com tempos de cura de 7, 28 e 56 dias. Os ensaios de compressão diametral foram realizados com tempos de cura de 28 e 56 dias. Os ensaios triaxiais de carga repetida foram realizados com tempo de cura de 56 dias. Os resultados obtidos foram satisfatórios, sendo dependentes do teor de BMP utilizados e do tempo de cura. Dentre as composições de BMP estudadas, a que apresentou o melhor comportamento foi a que possuia adição de 1,5 por cento de borracha e 56 dias de cura. Esta adição apesar de reduzir a RCS e a RTCD em 30 por cento e 28 por cento respectivamente, proporcionou melhoria no comportamento resiliente e menor perda de resistência na região pós pico perante o ensaio de RCS. Tal fato ressalta o emprego positivo de borracha de pneu triturada em camadas de base de pavimentos rodoviários, tanto sob a ótica da engenharia de pavimentos quanto em relação a questões ambientais e econômicas. / [en] This work presents a technical and experimental study on the use of tire rubber as an addition, together with Portland cement, to a simple graded gravel, in order to evaluate the applicability of this material in the base layers of road pavements. As a result, cement-treated graded gravel with the addition of rubber is obtained. The main objective of the addition of rubber is to reduce cracking, which is a common problem in cemented bases. A standard mixture of cement-treated graded gravel was carried out for better comparison between the mixtures with additions of 3 percent, 4 percent and 5 percent of cement. The granitic aggregate selected for this research came from the municipality of Cariacica/ES and was selected because it presented an appropriate performance in the characterization tests. From the granulometric analysis performed on this material, the fraction passing the sieve 2,38 mm and retained in the sieve 1,19 mm, was selected for this study. In this study were selected 0,5 percent, 1,0 percent, 1,5 percent, 2,5 percent, 3,5 percent and 4,5 percent additions of rubber. The blends were subjected to compaction, direct compression, split tensile, cyclic triaxial and scanning electron microscope tests. Direct compression tests were performed with cure times of 7, 28 and 56 days. Split tensile tests were performed with curing time of 28 and 56 days. Cyclic triaxial tests were performed with curing time os 56 days. The results were satisfactory, being dependent on the content of rubber and the curing time. Among the blends that were analyzed, 1,5 percent of addition and 56 days of curing time leaded to the best results. Despite the reduction of 30 percent and 28 percent in the compression and tensile resistances, this amount of rubber addition provided a better resilient behavior and a higher post pick resistance in the compression test. This fact highlights the positive use of tire rubber in pavement base layers, not only from the standpoint of pavement engineering, but promoting gains of sustainability and economy as well.

The objectives of this research were to 1) measure the extent to which water vapor movement results in water accumulation in freezing base materials; 2) evaluate the effect of soil stabilization on water vapor movement in freezing base materials; 3) determine if the corresponding changes in water content are sufficient to cause frost heave during winter; 4) determine if the corresponding changes in water content are sufficient to cause reductions in stiffness during spring; 5) evaluate relationships between selected material properties, freezing conditions, and the occurrence and impact of water vapor movement; and 6) numerically simulate heat and water movement in selected pavement design scenarios. The research involved extensive laboratory and field testing, statistical analyses, and numerical modeling. The results of the laboratory testing, which included gradations, Atterberg limits, soil classifications, specific gravity and absorption values, electrical conductivity values, moisture-density relationships, soil-water characteristic curves, moisture-stiffness curves, hydraulic conductivity values, and frost susceptibility assessments, were used to characterize each material and enable subsequent statistical analyses. Testing of both treated and untreated materials enabled investigation of a wide variety of material properties. The results of the field testing, which included temperature, moisture content, water potential, elevation, and stiffness data over time, provided the basis for comparing pavement sections with and without capillary barriers and established the framework for numerical modeling. In a pavement section with a capillary barrier underlying the base layer, water vapor movement from the subgrade through the capillary barrier may be expected to increase the water content of the base layer by 1 to 3 percent during a typical winter season in northern Utah for base materials similar to those studied in this research. During winter, cold temperatures create an ideal environment for water vapor to travel upward from the warm subgrade soil below the frost line, through the capillary barrier, and into the base material. Soil stabilization can lead to increased or decreased amounts of water vapor movement in freezing base materials depending on the properties of the stabilized soil, which may be affected by gradation, mineralogy, and stabilizer type and concentration. Accumulation of water from long-term water vapor movement into frost-susceptible base materials underlain by a capillary barrier can lead to frost heave of the base layer as it approaches saturation, as water available in the layer can be redistributed upwards to create ice lenses upon freezing. However, the incremental increase in total water content that may occur exclusively from water vapor movement during a single winter season in northern Utah would not be expected to cause measurable increases in thaw weakening of the base layer during spring. Because water in a base layer overlying a capillary barrier cannot drain until nearly reaching positive pore pressures, the base layer will remain indefinitely saturated or nearly saturated as demonstrated in this research. For materials similar to those studied in this research, potentially important material properties related to the occurrence of water vapor movement during freezing include dry density, percent of material finer than the No. 200 sieve, percent of material finer than 0.02 mm, apparent specific gravity, absorption, initial water content, porosity, degree of saturation, hydraulic conductivity, and electrical conductivity. The rate at which water vapor movement occurs is also dependent on the thermal gradient within the given material, where higher thermal gradients are associated with higher amounts of water vapor movement. The numerical modeling supported the field observations that the capillary barrier effectively trapped moisture in the overlying base material, causing it to remain saturated or nearly saturated throughout the monitoring period. Only non-frost-susceptible aggregate base materials should be specified for use in cold climates in conjunction with capillary barriers, and the base material in this case should be assumed to remain in a saturated or nearly saturated condition during the entire service life of the pavement. Further study is recommended on water vapor movement in freezing aggregate base materials.

The objective of this research was to investigate the effects of thermal gradient and fines content and the interaction between these two factors on the frost heave characteristics of a typical Alaska base material. The laboratory frost heave testing involved one type of aggregate base material, three thermal gradients, and three fines contents in a full-factorial experimental design with two replicates. The aggregate was classified in the American Association of State Highway and Transportation Officials soil classification system as A-1-a; the thermal gradients were 0.15, 0.30, and 0.45 ºC/cm; and the fines contents were 6, 8, and 10 percent. After frost heave testing, a stepwise regression analysis was performed to identify significant independent variables for each of nine separate dependent variables, including frost heave, heave-uptake ratio, steady-state frost heave rate, gravimetric water ingress, and gravimetric water content in each of the five individual lifts tested following frost heave testing. Soil suction, specific gravity, salinity, and hydraulic conductivity testing were also performed on samples prepared at each of the three fines contents to support numerical modeling of the frost heave test results using the computer program ICE-1. The results of the stepwise regression analysis indicate that thermal gradient is a significant predictor of six of the nine dependent variables and that the square of thermal gradient is a significant predictor of five of these six dependent variables. As the thermal gradient increased, the samples experienced decreasing amounts of water ingress and frost heave. However, the data show that neither fines content nor the square of fines content is a significant predictor of any of the dependent variables. Thus, although previous research has shown that higher fines contents are generally associated with greater susceptibility to frost heave, this effect is not manifest in the comparatively small increases in fines contents evaluated in this research. The interaction between thermal gradient and fines content is a significant predictor of only one independent variable. Differences between the modeled and measured frost heave values ranged from 0.01 to 0.92 cm, with the larger differences typically associated with the lowest thermal gradient and the lowest fines content.