Joakim G. Laguros

Gradation and Moisture Effects on Resilient Moduli of Aggregate Bases

Resilient modulus (M R ) which properly characterizes the load-deformation response of pavement materials under traffic loading, is evaluated. The M R values due to three different gradations and three different moisture contents were investigated for the Richard Spur and the Sawyer aggregates, which are commonly used in Oklahoma as the subbase or base materials of roadway pavements. The three gradations were finer limit, median, and coarser limit, as specified by the Oklahoma Department of Transportation for Type A aggregate. The three moisture contents selected are optimum moisture content (OMC), 2 percent below OMC, and 2 percent above OMC. To investigate the variability of the test results, six duplicate M R tests under identical conditions were performed for each case by using the AASHTO T294-94 method. Furthermore, the material properties, K1 and K2, which are required input in the AASHTO pavement design equation, were evaluated for the M R values obtained. Finally, multiple linear regression models for predicting the M R values of the two aggregates were established.

Durability Effects on Resilient Moduli of Stabilized Aggregate Base

The effect of wetting/drying and freezing/thawing on the resilient modulus values of Meridian limestone aggregate stabilized with cement-kiln-dust is investigated. Freezing/thawing is found more detrimental than wetting/drying at low deviator stresses. In addition, the stabilized aggregate suffers greater strength reduction during the initial stages of the freeze/thaw test. On the other hand, wetting/drying produces greater strength reduction at high deviator stresses. The layer coefficients of the stabilized aggregate base, which are significantly higher than those of the raw aggregates, are reduced appreciably due to freezing/thawing and wetting/drying.

Finite element algorithm for jointed concrete pavements subjected to moving aircraft

Abstract An algorithm based on the finite element method is developed to analyze the dynamic response of multiple, jointed concrete pavements to moving aircraft loads. In the finite element idealization, the pavement-subgrade system is idealized by thin plate finite elements resting on Winkler-type viscoelastic foundation represented by a series of distributed springs and dashpots. The dowel bars at the transverse joints are represented by beam elements. It i assumed that the dowel bar is fully embedded into the pavement thus neglecting dowel-pavement interaction effects. The longitudinal keyed or aggregate interlock joints are modeled by vertical spring elements. The dynamic aircraft-pavement interaction effects are considered in the analysis by modeling the aircraft by masses supported by spring-dashpot systems representing the landing gear of the aircraft. It is assumed that the aircraft travels along a straight line with a specific initial velocity and acceleration. The aircraft-pavement interaction takes the form of two sets of coupled equations which result ina non-symmetric stiffness matrix. An approximate mixed iteration-direct elimination scheme is used to solve for the dynamic equations. The accuracy of the computer code is verified by the available experimental and analytical solutions. A parametric study is conducted to investigate the effects of various parameters on the dynamic response of pavements.

Characterization of Base/Subbase Materials under Repetitive Loading

Testing of granular materials for evaluation of Resilient Modulus (MR) suffers from the lack of a standardized test method. Although AASHTO over the past six years (1986 to 1992) has proposed three different testing procedures (T274-86, T292-91I, and T294-92I), some state transportation departments have adopted their own MR testing procedures. In this study, the factors affecting the measurement of MR such as the testing method used and stress applied and its sequence are investigated. In addition, the updated methodologies proposed by various agencies for MR of granular materials and the MR values obtained are reviewed and evaluated. It is found that the applied stress sequence has some effects on MR of granular materials. For the two aggregate types investigated in this study, with the same location of LVDT and dynamic waveform, the T294-92I testing procedure yields higher MR than that obtained by using the T292-91I testing procedure. The stress sequence in T294-92I infers a stiffening and strengthening effect on the specimen structure as the stress level increases from low to high. The variation of MR values due to testing procedure is found to be higher than those due to the aggregate source. The MR values obtained in this study are found to be lower than those reported in the literature. Furthermore, with the updated testing procedure for MR, the correlation between the structural layer coefficients and MR of granular base and subbase proposed by the AASHTO needs to be modified accordingly.

Similarities and Differences in Shale, Aggregate Mixes and Concrete Containing Fly Ash

Fly ash technology has been very effective in providing stability in roadway base courses composed either of shale or aggregate materials, and also in partly replacing Portland cement in concrete. X-ray diffractometry and scanning electron microscopy observations indicate that there are certain similarities among these three types of mixes concerning the hydration process; on the other hand, there is evidence of distinct differences in the hydration products which are found to act either as a filler, a chemical agent, or both. Fly ash suppresses the intensity of the clay minerals in shale, speeds up the hydration process in concrete and acts partly as a filler in aggregate mixes. The net practical result is strength development which varies not only in terms of the maximum level attained, but also in regard to its rate. The conversion of ettringite to monosulfoaluminate proceeds at a rate which is considered high in concrete, moderate in aggregate mixes, and moderate to low in shale. X-ray diffraction analyses help to identify other dissimilarities in the minerals produced. The modification which takes place in the fabric and the matrix of the mixes is morphologically the same; in contrast, the growth of crystallites at the “particle”/fly ash interface is explicitly different. Preliminary quantification of matrix changes resulting from new hydration products is also explored.

Performance of a Fly Ash Stabilized Pavement

An expansive shale roadbase, stabilized with a Class C (high-calcium) fly ash received an 11–inch full–depth asphaltic concrete surface layer and the highway was opened to traffic six years ago. Periodic sampling and visual observations indicate that the performance of the pavement test sections are above average. Analyses of field samples showed that fly ash was effective in ameliorating the texture and plasticity of the shale and imparting strength to it on a long term basis. Pavement deflections and the extent of cracking have not increased beyond acceptable levels during the six year period. X-ray diffraction studies show a reduction of the areas under the peaks and the SEM observations reveal a dense degree of packing and reduction of the void areas. These modifications occur during the first two years of service and any changes beyond that period appear to be minor.

Aluminum Sulfate Hydration Retarders for High-Calcium Fly Ash Used in Highway Construction

The rapid hydration and setting associated with the use of high-calcium fly ash as an additive in soil and aggregate base stabilization in highway construction imposes certain limitations in regards to operational time and volume of work executed. Aluminum sulfate and its ammonium salt were evaluated as hydration reaction retarders. Mixtures of Ottawa sand and Class C high lime fly ash in a 1:1 weight ratio were used for the evaluations. These additives minimized the adverse effects of delayed compaction by recovering some of the compressive strength lost to the rapid hydration, although in all cases the density of the mixes decreased. The recovery of strength was related to the heat of hydration, wherein the peak temperature was reduced from 90°F to the range of 86–78°F at 2 hours; further temperature decreases were observed as reaction time increased. The availability of the sulfate ions, as manifested by the presence of ettringite, helps the hydration process continue, minimizes the adverse effects of delayed compaction and assists positively in the reduction of the void area of mixes and in stratlingite formation, which contributes to a strong crystalline framework.

Fly Ash in Shale Stabilization for Highway Construction

The expansive shales used for roadbeds in Oklahoma are traditionally stabilized with lime. Stabilization with a Class C (high-calcium) fly ash was explored and compared to an optimum design utilizing the conjunctive use of fly ash, lime and cement, in the laboratory and in a field experimental project. Periodic visual observations indicated that the performance of test sections was excellent. Analyses of field samples showed that fly ash, either alone or mixed with lime and cement, was effective in ameliorating the texture and plasticity of the shale by reducing the amount of clay size particles and by imparting higher strength levels to the shale. Laboratory samples showed better stabilization than field samples, but the field samples performed at an acceptable level in measurements of compressive and beam strength, cohesion, angle of internal friction and resistance to deflection. The microstructure of stabilized shale was studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Nonbasal (hkl) reflections in stabilized oriented specimens suggest that the clay particles acquire high resistance to dispersive forces. The reduction of the areas under the peaks help explain the strength gain observed. The SEM observations indicated newly formed hydration products, possibly calcium aluminum silicate hydrate crystals, and a rather dense degree of packing as manifested by the substantial reduction of void areas as a result of stabilization.

Effect of Cement Kiln Dust and Rock Dust as Mineral Fillers on Bulk Specific Gravity of Fine Aggregates

The bulk specific gravity (Gsb) of aggregates is a critical parameter in the design of asphalt mixes. In the Superpave volumetric mix design, Gsb is used to determine the amount of asphalt binder absorbed by aggregates and the percentage of voids in the mineral aggregate. Problems with the current test methods of measuring the Gsb of fine aggregates, i.e., AASHTO T84 or ASTM C128, have been reported in some previous studies as well as in the current study. These standard test methods remain questionable under certain conditions: (1) When rough and angular as well as small and varying particle size distributions of fine aggregates are present and (2) when water reactive mineral fillers (passing No. 200 sieve) are added to fine aggregates. This study examined the addition of two selected mineral fillers, namely, Cement Kiln Dust (CKD) and rock dust, on the overall Gsb of fine aggregates by employing the AASHTO T84 and the CoreLok-Aggplus test procedures. When using the AASHTO T84 test method, the overall Gsb values reduce for both the additives. When using a newly developed CoreLok method, the Gsb values increased for rock dust up to 10 %, beyond which a reduction is observed. With CKD, the Gsb values show an increase for up to 6 % addition of it and then a decrease is observed. The data suggest that the AASHTO T84 test method may not be applicable in the presence of CKD due to the chemical reactions in the presence of water and the formation of cementitious products. A possibility of chemical reaction due to the presence of limestone in the rock dust and its fine gradation influence the results of the AASHTO T84 test method. Thus, use of the CoreLok method appears more appropriate in the presence of such reactive materials. To further analyze the problem, the specific surface area of fine aggregates and mineral fillers was measured using water vapor and nitrogen adsorption methods. This study also reveals that angular fine aggregates with a high angularity and rough surface texture pose significant difficulty in measuring Gsb by the AASHTO T84 test method.

Behavior of Stabilized Aggregate Bases Subjected to Cyclic Loading and Wet-Dry Cycles

A laboratory study was undertaken to investigate the effect of wet-dry (W-D) cycles on aggregate bases, namely, Meridian (M), Richard Spur (RS), and Sawyer (S), stabilized with cement kiln dust (CKD), class C fly ash (CFA), and fluidized bed ash (FBA). Cylindrical specimens were molded, cured, and subjected to W-D cycles prior to testing for resilient modulus (Mr). It was found that the Mr values for most of specimens decreased as W-D cycles increased. Sawyer aggregates stabilized with CKD, however, exhibited an increase with W-D cycles up to 8, beyond which a decrease in Mr occurred. It is believed that s uch a decrease/increase in Mr values may be attributed to the deceleration/acceleration of pozzolanic reactions. Laboratory observations revealed visual degradation of only Sawyer specimens stabilized with fluidized bed ash after 16 W-D cycles; no Mr tests were performed on the degraded