Journal of Materials in Civil Engineering

This research investigates the oxidative aging levels of polymer-modified asphalt (PMA) mixes using gel permeable chromatography (GPC), which can help to simplify the quantification of asphalt aging. Warm-mix asphalt (WMA) technologies, namely, Aspha-min and Sasobit, were especially adapted to the PMA mixes for the purpose of the aging reduction. A short-term oven aging (STOA) procedure was used under 135 and 154°C for 2 and 4 h, respectively, to simulate the asphalt binders aged during the field operations (i.e., production, hauling, and paving construction). The aging levels were analyzed based on large molecular size (LMS) of the binders extracted from the mixes. A rolling thin-film oven (RTFO) method was also utilized using PMA binders containing those WMA additives under 135 and 163°C for 85 minutes for comparison purposes. The results showed that (1) aging time and temperature were important parameters to influence the aging; (2) the STOA procedure had a higher aging level than the RTFO method, which could be influenced by thin film thickness on aggregates; (3) the use of WMA technologies was effective to reduce the aging level of PMA mixes; and (4) it was possible to quantify the oxidative aging of PMA mixes [both hot-mix asphalt (HMA) and WMA] using the GPC technique.

Knowledge about concrete properties is of utmost importance in engineering materials, and elastic modulus is one of concrete’s most important properties that is used in the calculation of deformation of structures. For this reason, many researchers have attempted to introduce various correlations between this property and the compressive strength. In this paper, support vector committee (SVC) is used for prediction of elastic modulus of normal strength (NSC) and high-strength concrete (HSC). The SVC is based on learning theory, and deploys the technique by introducing accuracy insensitive loss function. The comparison between concrete elastic modulus predicted by the SVC method with the experimental data and those from other methods like support vector machine (SVM), artificial neural networks (ANN), fuzzy logic, and other conventional methods show marked improvement in relation to the best of prediction methods with error indices constantly less than 1%. It is therefore concluded that the SVC model is a greatly more effective method of prediction for elastic modulus of all grades of concrete.

The primary objective of this research effort was to conduct a rutting performance–based comparison between limestone and basalt Superpave asphalt mixtures using dynamic creep rutting tests. Two sets of mixtures were prepared using limestone and basalt aggregate, mixed with one asphalt binder having a Superpave performance grade of PG 64-10. To overcome the stripping potential of the Superpave basalt asphalt mixtures, 1% by total weight of the basalt aggregate was replaced by hydrated lime for the filler portion of the aggregate. Rutting was evaluated at four different temperatures (40, 50, 60, and 65°C) and one loading frequency of 8 Hz. Rutting test results indicated that the basalt Superpave asphalt mixtures exhibited superior performance relative to the limestone Superpave asphalt mixtures. The difference in the rut depth at 19,200 loading cycles between the limestone and basalt asphalt mixtures was statistically significant at levels of $\alpha =1$, 5, 1, and 0.5% for the temperatures 40, 50, 60, and 65°C, respectively. The difference in the rut depth at 200,000 loading cycles between the two asphalt mixtures was statistically significant at levels of $\alpha =1$, 5, 0.1, and 0.1% for the temperatures 40, 50, 60, and 65°C, respectively. In addition, the difference in the number of loading cycles to rutting failure between limestone and basalt asphalt mixtures was also statistically significant at a level of $\alpha =0.1\%$ for all temperatures.

In this research, the relationship between the compressive strength, $f_c$, and the dynamic shear modulus, $G_d$, of normal concrete at an early age was studied. To investigate the correlation between $f_c$ and $G_d$ at an early age, different types of mixtures, including mortar and concrete, were prepared, and the corresponding $f_c$ and $G_d$ values were measured every 12 h after initial mixing up to 72 h after casting. The influences of hydration age, water-to-cement ($\mathrm{w}/\mathrm{c}$) ratio, curing temperature, aggregate volume content, and maximum aggregate size on the $G_d-f_c$ relationship of concrete were studied. The $G_d-f_c$ relationship was then mathematically modeled by using multivariable power laws. The developed model is reasonably accurate to predict the early age compressive strength of concrete with variations in hydration age, aggregate content, and sizes. This type of model can be used directly in the field for the estimation of concrete strength when nondestructive testing (NDT) techniques are employed.

The deterioration mechanisms of sulfate attack on concrete under sustained loading and wet-dry cycling were investigated based on micro and macroobservations. The mass fraction of sodium sulfate solution was 6.9%. Three loading levels of 20, 40, and 60% of ultimate flexural load were considered, and the load was mechanically applied to the specimens under four-point bending. Microobservations included the analysis of the chemical products formed using thermal analysis and the determination of the sulfate-ion content profile using the modified barium sulfate gravimetric method (chemical titration). Macroobservations primarily included visual observations and flexural strength changes. Test results showed that under alternate action of wet-dry cycling, concretes are attacked by expansive products such as ettringite and gypsum during the wetting cycle, and crystallization damage, induced by evaporation, is superposed during the drying cycle. Results also showed that the tensile stresses can increase diffusivity by initiating or developing microcracks; the compressive stresses are small compared with the concrete compressive strength, so any effect on ion transport properties is not obvious. Under simultaneous sulfate attack and flexural loading, deterioration is aggravated as the loading level increases, and this is characterized on the macroscale by the increased strength degradation. This research can provide some references for the assessment method of concrete structures under combined sulfate attack and loading action.

Most studies addressing the use of recycled asphalt materials in asphalt paving mixtures are based on experimental tests and performance evaluation. Investigating the effect of adding recycled materials to the microstructure of asphalt mixtures has received little consideration. For example, higher-order microstructural information can be used in place of simple volumetric information as input in micromechanical models that can more accurately predict the effective properties of asphalt mixtures. In this paper, the influence of adding three different recycled materials, reclaimed asphalt pavement (RAP), manufacturer waste scrap shingles (MWSS), and tear-off scrap shingles (TOSS), on the microstructural distribution of the aggregate phase is investigated using digitally processed images of asphalt mixtures and numerical evaluations of two- and three-point correlation functions. No significant variations are found among the gradation curves, and minimal differences were observed for two- and three-point correlation functions. This indicates that the addition of the recycled materials does not significantly affect the aggregate spatial distribution of asphalt mixtures. However, an increase in autocorrelation length was found for some of the mixtures containing recycled shingles.

Over the past few years, many regression-based and artificial neural network (ANN)-based models have been developed to estimate the dynamic modulus of hot mix asphalt (HMA). These models use the gradation of aggregates and the volumetric properties of compacted samples as input variables to the model. However, none of these models use aggregate shape parameters (i.e., angularity, texture, form, and sphericity) in the development of the model. Recently, researchers have expressed concerns that the shape parameters of aggregates need to be considered in the estimation of dynamic modulus. The primary objective of this study was to develop an ANN-based model for the estimation of dynamic modulus of HMA using aggregate shape parameters. The dynamic modulus of 20 different HMA mixes composed of various sources, sizes, types of aggregates, and different volumetric properties were measured in the laboratory. The shape parameters of different sizes of coarse and fine aggregates were measured with an automated aggregate image measurement system (AIMS). An ANN-based model was developed to consider the following input variables: aggregate shape parameters (i.e., angularity, texture, form, and sphericity), frequency, asphalt viscosity, and air voids of compacted samples. A sensitivity analysis of each model parameter was conducted by correlating these parameters with dynamic modulus. It is expected that this study will be helpful in predicting the dynamic modulus of HMA using aggregate shape parameters.

As a primary by-product of coal combustion produced in large quantities, coal fly ash is a material receiving considerable interest for potential large-scale engineering applications. However, the beneficial use of coal fly ash in concrete production and contaminant removal, which have divergent constraints to sorption capacity, requires a more complete understanding of the surface and sorptive characteristics of fly ash. A systematic analysis of fly ash particle size fractions established linkages between particle size, particle morphology, unburned carbon content, surface area, and sorption capacity. Unburned carbon was enriched in fly ash fractions of the largest particle sizes and associated with irregularly shaped particles. Further, most of the surface area and sorption capacity of fly ash could be attributed to unburned carbon. More importantly, unburned carbon content, specific surface area, and methylene blue sorption capacity were shown to strongly correlate to one another, providing a potentially quantitative basis for understanding the surface properties of fly ash and developing more effective process options to enhance the fly ash sorption behavior desirable for specific engineering applications.

Chemical compositions of approximately 5,500 fly ash samples from 36 power plants inside and outside Texas, compiled by the Texas Department of Transportation (TxDOT) over 18 years, were statistically analyzed in this study. The variations of oxide contents and their correlations were calculated and compared. Oxide contents of Class F fly ashes were found to be more variable than Class C fly ashes. In general, CaO and MgO contents were higher in Class C fly ashes than in Class F fly ashes, whereas the latter had higher ${\mathrm{SiO}}_2$ content. Other oxide contents of the two classes of fly ashes were comparable. Then, to demonstrate the potential beneficial use of chemical composition information of fly ash, an alkali-silica reaction (ASR) durability index was proposed to predict the comparative performance of fly ash in mitigating ASR in concrete. The index value was calculated using ${\mathrm{SiO}}_2$, ${\mathrm{Fe}}_2{\mathrm{O}}_3$, ${\mathrm{Al}}_2{\mathrm{O}}_3$, CaO, and equivalent alkali contents. Previously published research on the use of fly ash in mitigating ASR, using standardized tests, was utilized to validate the proposed index. The index was found capable of differentiating fly ashes in the same class. To verify the usefulness of the ASR durability index, tests were carried out in this study using an ASR reactive sand, two portland cements, four Class C fly ashes, and one Class F fly ash. The results were quite promising, and the use of the fly ash ASR durability index is proposed to screen fly ash for laboratory testing and construction.

This paper presents the findings from a study conducted to develop a simple quantitative test method to characterize the stability of asphalt emulsions. The proposed method uses electrokinetic techniques to determine the rate at which an asphalt emulsion breaks when subjected to an electric field. The test method was used with different types of emulsion as well as emulsions that were modified by further dilution or mechanical agitation. Results demonstrate that the parameters obtained from these tests were repeatable and different for different types of asphalt emulsions. Results also demonstrate that for a given type of emulsion the test method is sensitive to factors such as water content and partial breaking due to mechanical agitation. The proposed electrokinetics-based method and concomitant parameters provide a repeatable, rapid, and quantitative method by which to characterize asphalt emulsions.

To mitigate settlement problems associated with bridge approach embankments over soft soil, a newly-developed lightweight material was proposed in this study. This lightweight material consisted of expanded polystyrene beads, the hydraulic sand from the Yangtze River, and cement. The mechanical properties of the mixed lightweight material were determined through a series of laboratory tests, including standard Proctor tests, unconfined compression tests, California Bearing Ratio (CBR) tests, unconsolidated-undrained tests, and consolidated-undrained tests. The laboratory results showed the favorable properties of the lightweight material and that it can be used as a backfill material in highway embankment projects. A field study was also conducted to verify the performance of the embankment backfilled with this lightweight material, which resulted in a smaller settlement than the embankment backfilled with lime-stabilized soil (with and without any other ground improvement). Sand cone and CBR tests were performed in the field to verify the density and strength/stiffness of the lightweight fill.

The majority of tear-off roofing shingles and manufacturing shingle scraps are currently disposed of as solid waste in landfills. Landfills are also the end place for the majority of coal combustion byproducts like fly ash. In this study, geotechnical properties of recycled asphalt shingles (RAS) stabilized with a self-cementing fly ash (FA) for use as structural fill material were systematically evaluated. Compaction, hydraulic conductivity, compressibility, shear strength, and coefficient of lateral earth pressure at rest ($K_o$) of stabilized RAS were evaluated. The maximum dry unit weight (${\gamma }_{d\max }$) of RAS:FA mixtures varies between $11.3\mathrm{k}\mathrm{N}/{\mathrm{m}}^3$ and $13.8\mathrm{kN}/{\mathrm{m}}^3$ qualifying them as light-weight fill material and the compaction curves are not sensitive to water content. The hydraulic conductivity of RAS:FA varies between $2\times {10}^{-4}\mathrm{cm}/\mathrm{s}$ and $3\times {10}^{-5}\mathrm{cm}/\mathrm{s}$ for FA content varying between 0% and 20% resulting in a largely drainable material. RAS has a friction angle (${\phi }^{\prime }$) of 36° and cohesion ($c^{\prime }$) of 24 kPa. Addition of 20% FA reduces the ${\phi }^{\prime }$ to 33° but increases the $c^{\prime }$ to 100 kPa making it sufficiently strong as a fill material. However, compared to compacted sand, RAS is highly compressible. Stabilizing RAS with more than 10% of FA, keeps the long-term settlement of a typical highway embankment below the typical settlement limit. Stabilized RAS has a $K_o$ below 0.1 indicating lower lateral pressures behind retaining walls compared to typical soils. Overall results indicate that RAS stabilized with FA has potential as a lightweight material for use as highway embankment fill or retaining wall backfill.

The resistance to sulfate attack, compressive strength, sorptivity, and pore size of high-calcium bottom ash geopolymer mortars were studied. Ground lignite bottom ashes (BAs) with median particle sizes of 16, 25, and 32 μm were used. NaOH, sodium silicate, and temperature curing were used to activate the geopolymerization. Results showed that relatively high strengths of 40.0–54.5 MPa were obtained for the high-calcium bottom ash geopolymer mortars. The use of fine BA improved the strength and resistance to sulfate attack of mortars. The good performances were attributable to the high degree of reaction of fine BA and the associated low amount of large pores (0.05–100 μm) compared with those of coarse BA. The incorporation of water improved the workability of mixes, and the compressive strength, sorptivity, and resistance to sulfate attack decreased due to the increase in large pores.

In this study, a water-soluble aminosulfonate-phenol-salicylic acid-formaldehyde (AH) polymer was synthesized by the reaction between phenol, sodium sulfanilate, salicylic acid, and formaldehyde; the molecular structure of synthesized AH polymer under the optimum reaction conditions was characterized by Gel permeation chromatography (GPC) and infrared spectroscopy (IR); and the effect of AH polymer on the application properties of concrete, i.e., water reduction percentage, slump preservation, air content, wet density, setting times, the compressive strength, and the flexural strength, was compared with aminosulfonate-phenol-formaldehyde (AS) polymer. The test results indicated that the molecular weight of AH polymer has a narrower range distribution and a new function group ($-\mathrm{COOH}$) was bonded to the main chain of AH polymer molecule, the use of AH polymer in concrete resulted in an increase of the air content of concrete and a decrease of the wet density of fresh concrete, concrete with AH polymer exhibits a higher water-reduction percentage value and a lower slump loss, which cause a better retardation setting result and lower mechanical properties than concrete with AS polymer at the same dosage.

The effects of strain rate on the dynamic stress-strain behavior of cement mortar were investigated in split Hopkinson pressure bar (SHPB) tests; the resulting strain rates ranged from 20 to $280{\mathrm{s}}^{-1}$. A total of 39 specimens were subjected to static and dynamic axial compressive loadings. The results showed that cement mortar is a typical strain-rate dependent material. Both dynamic compressive strength and critical strain increased with strain-rate increases. However, there seemed to be no strain-rate effects on the initial elastic modulus of cement mortar. Based on the stress-strain curves of different strain rates, as well as the random statistical distribution hypothesis for strength, a dynamic damage constitutive model of cement model under compression was used. The relationships of the primary parameters for strain rate are also presented in this paper. The simulated stress-strain curves matched the experimental results well. The results showed that the strength of cement mortar obeyed a Weibull distribution.

This study reports the findings of an experimental investigation for alkali silica reaction (ASR) between reactive aggregates and the geopolymer matrix. Specimens were prepared using one Class C and two Class F fly ash stockpiles. Mechanical testing included potential reactivity of the aggregates via length change and compression test measurements, as per ASTM standards. Results suggest that the extent of ASR reaction due to the presence of reactive aggregates in fly ash-based geopolymer concretes is substantially lower than in the case of ordinary portland cement-based concrete, and well below the ASTM specified threshold. Furthermore, geopolymer concrete specimens appeared to undergo a densification process in the presence of alkali solutions, resulting in reduced permeability and increased mechanical strength. Utilizing ASR-vulnerable aggregates in the production of geopolymer concrete products could contribute to the economic appeal and sustainability of geopolymer binders in regions that suffer from insufficient local supply of high quality aggregates.

The method of testing asphalt mixtures including initial cracks appearing in pavements is presented in this paper. The main aim of the study was a determination of the durability of asphalt mixtures in regard to crack sizes. For this purpose, the four-point bending test was performed according to the technical standard PN-EN 12697-24. The test was conducted with selected asphalt mixtures under the controlled strain and with the application of different crack sizes. Specimens with cracks were analyzed. Moreover, a model based on finite-element method (FEM) calculations was worked out, which allowed for the verification of conditions of the asphalt mixtures’ response to strains and the assessment of the state of stresses and strains at the crack tip. The wide range of studied conditions helped to determine the fatigue criterion for the “cracked” beam in the fatigue tests. The presented fatigue condition is very useful in the estimation of fatigue durability of asphalt mixtures. The results of analyses clearly showed the influence of cracks on the decrease in stiffness modulus. This effect has a nonlinear behaviour in the case of larger cracks. The proposed FEM model of beam including cracks is very useful in studies of stresses and tensile strains concentrated at the crack tip.