Journal of Materials in Civil Engineering

Although several techniques have been introduced to reduce reflective cracking, one of the primary forms of distress in hot-mix asphalt (HMA) overlays of flexible and rigid pavements, the underlying mechanism and causes of reflective cracking are not yet well understood. Fracture mechanics is used to understand the stable and progressive crack growth that often occurs in engineering components under varying applied stress. The stress intensity factor (SIF) is its basis and describes the stress state at the crack tip. This can be used with the appropriate material properties to calculate the rate at which the crack will propagate in a linear elastic manner. Unfortunately, the SIF is difficult to compute or measure, particularly if the crack is situated in a complex three-dimensional (3D) geometry or subjected to a non-simple stress state. In this study, the neural networks (NN) methodology is successfully used to model the SIF as cracks grow upward through a HMA overlay as a result of both load and thermal effects with and without reinforcing interlayers. Nearly 100,000 runs of a finite-element program were conducted to calculate the SIFs at the tip of the reflection crack for a wide variety of crack lengths and pavement structures. The coefficient of determination ($R^2$) of all the developed NN models except one was above 0.99. Owing to the rapid prediction of SIFs using developed NN models, the overall computer run time for a 20-year reflection cracking prediction of a typical overlay was significantly reduced.

Measurement of deformation history during a high-speed mechanical test plays an important role in establishing the dynamic behavior of materials. Traditional strain measuring techniques such as extensometers and strain gauges have limitations such as frequency response and range of strain. Kevlar 49 fabrics were tested in tension within a strain-rate range of 25 to $170{\mathrm{s}}^{-1}$ using a high-speed servohydraulic testing system. Results show that the dynamic material properties in terms of Young’s modulus, tensile strength, maximum strain, and toughness increase with increasing strain rate. The woven nature of Kevlar 49 fabric results in large displacements and shape changes during tests. Noncontacting strain measuring technique is therefore highly preferred. A technique was developed using image analysis to obtain the deformation of Kevlar 49 fabrics at the tested strain rates. Using image analysis results, the stress-strain curves of Kevlar 49 fabrics at different strain rates were constructed and compared with those based on stroke measurement. Good agreement was obtained between these two methods.

A rammed-earth wall is a monolithic construction made by compacting processed soil in progressive layers in a rigid formwork. There is a growing interest in using this low-embodied-carbon building material in buildings. The paper investigates the strength and structural behavior of story-high cement-stabilized rammed-earth (CSRE) walls, reviews literature on the strength of CSRE, and discusses results of the compressive strength of CSRE prisms, wallettes, and story-high walls. The strength of the story-high wall was compared with the strength of wallettes and prisms. There is a nearly 30% reduction in strength as the height-to-thickness ratio increases from about 5 to 20. The ultimate compressive strength of CSRE walls predicted using the tangent modulus theory is in close agreement with the experimental values. The shear failures noticed in the story-high walls resemble the shear failures of short-height prism and wallette specimens. The paper ends with a discussion of structural design and characteristic compressive strength of CSRE walls.

Rutting has been considered the most serious distress in flexible pavements for many years. Flow number is an explanatory index for the evaluation of the rutting potential of asphalt mixtures. In this study, a promising variant of genetic programming, namely, gene expression programming (GEP), is utilized to predict the flow number of dense asphalt-aggregate mixtures. The proposed constitutive models relate the flow number of Marshall specimens to the coarse and fine aggregate contents, percentage of air voids, percentage of voids in mineral aggregate, Marshall stability, and Marshall flow. Different correlations were developed using different combinations of the influencing parameters. The comprehensive experimental database used for the development of the correlations was established on the basis of a series of uniaxial dynamic-creep tests conducted in this study. Relative importance values of various predictor variables were calculated to determine their contributions to the flow number prediction. A multiple-least-squares-regression (MLSR) analysis was performed to benchmark the GEP models. For more verification, a subsequent parametric study was carried out, and the trends of the results were confirmed with the results of previous studies. The results indicate that the proposed correlations are effectively capable of evaluating the flow number of asphalt mixtures. The GEP-based formulas are simple, straightforward, and particularly valuable for providing an analysis tool accessible to practicing engineers.

In this paper, the synthesis of high-strength geopolymer using fine high-calcium fly ash was studied. The effect of fineness of fly ash on the setting time of geopolymer paste, workability, strength development, and drying shrinkage of geopolymer mortars made from classified fine high-calcium fly ash was investigated. Air-classified fly ash with three different finenesses—coarse original fly ash (CFA), medium-fineness fly ash (MFA), and fine fly ash (FFA)—from the Mae Moh Power Station was used for this study. The heat-cured geopolymers were activated with sodium hydroxide (NaOH) and sodium silicate. A small amount of water was incorporated for workability. The results indicate that the setting time of paste decreases with an increase in fly-ash fineness. The flow, strength, and drying-shrinkage characteristics of mortars were improved using fine fly ash. Geopolymer mortars with high 28-day compressive strength of 86.0 MPa were obtained.

While the effectiveness of corrosion-inhibiting admixtures in new concrete has been well documented, there is little research on their surface-applied counterparts for existing structures. This study was undertaken to assess whether surface-applied products can delay, slow, or stop the corrosion process in contaminated concrete. A total of 348 specimens were tested using six commercially available corrosion inhibitors, at six levels of initial chloride content, and under two accelerated corrosive environments of salt-water spray and wet-dry cycles. Half of the specimens were intentionally cracked before applying the inhibitors, while the others were cracked afterward. Corrosion current and half-cell potential readings were taken weekly during the environmental exposure. Corroded bars were then assessed visually for surface rust and rib loss; and their mass loss and strength reduction were measured. Progression of chloride content over time was measured using companion concrete cubes. The inhibitors generally delayed the onset of corrosion and slowed the process, up to an initial chloride content of 0.5% by weight of cement. Each product seemed effective up to an extent in exposure time and the chloride content. However, no product stopped the corrosion process, and none purged chloride ions. The products may be most effective as preventive measures for fully hardened “virgin” concrete with initial chloride content below those specified to induce corrosion.

Using waste materials for new products is a global trend undergoing rapid development. Recycling materials allows for a more efficient life cycle and contributes to environmental protection. In the construction field, this trend has gained importance because of the shortage of natural resources and because of environmental problems caused by storing building-demolition wastes. This situation has led to the search for new applications for these wastes, and their use as aggregates in concrete is an interesting alternative. In this paper, some characteristics of recycled coarse aggregates obtained by crushing waste ready-mix concrete, as well as the mechanical and durability properties of recycled concretes made by using 25, 50, and 75% of these aggregates, are presented. Recycled concretes show lower compressive strength than conventional concrete for the higher strength level, whereas the durability properties of the two are similar.

Silicone foam was investigated as a sealant for small movement expansion joints in bridge decks. This paper presents results from the laboratory assessment of a model foam sealant subjected to thermal aging (exposure to high and low temperatures and temperature cycling), fatigue conditions, and outdoor weathering. Parallel tests were performed on a commercial solid-silicone bridge-joint sealant. Test results showed that the solid sealant recovered faster than the foam sealant after being subjected to prolonged compression at elevated temperature. When subjected to a constant tensile force, both the foam and solid sealants exhibited high initial creep rates (rate of elongation), but appeared to reach an equilibrium level of elongation at longer times. The foam sealant creeps at a slower rate and takes more time to get to the equilibrium elongation, whereas the solid sealant creeps much faster initially and reaches equilibrium faster. Thermal aging was found to have significant effects on the sealant modulus (increases with temperature); however, the effects on ultimate stress and strain were not apparent for both types of sealants. Temperature cycling between 24 and $-29°\mathrm{C}$ was observed to diminish the ultimate stress and strain of both the sealants by roughly 25%; however, no significant changes in modulus were found. Results from the tests on a limited number of outdoor-weathered sealant specimens showed that weathering appeared to produce an increase in sealant tensile and shear moduli (i.e., hardening effects because of weathering) and a decrease in ultimate strain. The weathered samples show tension loading-unloading behavior similar to the unaged samples. The tensile stress relaxation rate of the outdoor-weathered sealants could not be distinguished from those laboratory-cured (unweathered) counterparts.

Microstructures of calcium carbide residue (CCR) and CCR–ground fly ash (CCR-GFA) pastes were examined. A ratio of CCR to GFA of 30 to 70 by weight was used as a binder without portland cement. CCR-GFA pastes with three different water-to-binder (W/B) ratios of 0.3, 0.4, and 0.5 were prepared. Scanning electron microscopy (SEM) was used to study the morphology of the CCR-GFA pastes. X-ray diffractometry (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to provide fundamental information about the specimens. Microstructures of CCR-GFA pastes were studied at 60 days. The compressive strengths of CCR-GFA pastes were determined at 7, 14, 28, 42, and 60 days. The morphology of CCR-GFA paste was composed of gelatinous particles of different sizes. The fracture surface was inhomogeneous with rough textures. Calcium silicate hydrate (CSH) product as ${\mathrm{Ca}}_5({\mathrm{SiO}}_4{)}_2(\mathrm{OH}{)}_2$ was found in all CCR-GFA pastes. This new compound was also found by FTIR analysis at wavelengths of 435 and $970{\mathrm{cm}}^{-1}$. Results from this work illustrate that the formation of CSH products is most likely the reaction of ${\mathrm{SiO}}_2$ from GFA, and $\mathrm{Ca}(\mathrm{OH}{)}_2$ from CCR. This chemical reaction is possibly similar to the pozzolanic reaction. The compressive strengths of all samples increased with age and were almost constant after 42 days.

Chloride-induced corrosion is the most important durability issue in a reinforced-concrete structure. In this paper, the multispecies model was used to describe the chloride transport in saturated concrete. The model was solved by using the finite-difference method by inputting parameters such as porosity, density, chemical composition of pore solution, diffusion coefficient, and chloride-binding isotherm. A depth-dependent diffusion coefficient, instead of a fixed diffusion coefficient, was used in this model. The chloride-binding isotherm was directly obtained from the diffusion test. Finally, the numerical simulation results were validated with experimental results. It was found that the numerical simulation results were in good agreement with the experimental results.

The magnitude of the shrinkage strain is normally proportional to the amount of moisture lost caused by drying or cement hydration. In this study, the development of internal relative humidity and autogenous shrinkage in early age samples of normal- and high-strength concrete were experimentally measured starting from the time of concrete casting. The experimental results show that the development of the internal relative humidity of concrete first follows a vapor saturated stage ($\mathrm{RH}=100\%$, Stage I), followed by a gradually reducing stage ($\mathrm{RH}<100\%$, Stage II). Shrinkage strain developed in Stage I and Stage II may be correlated with chemical shrinkage and interior humidity reduction, respectively. An autogenous shrinkage model based on aforementioned mechanisms is developed. The model predictions agree well with experimental measurements on the development of autogenous shrinkage in early age normal- and high-strength concrete.

The present research investigates how the addition of processed carbon materials affects the mechanical properties of cement mortars. Five types of oxidation treatments (air at 250°C, air at 410°C, ozone, ${\mathrm{H}}_2{\mathrm{O}}_2$, and ${\mathrm{HNO}}_3$) were applied to graphite powder, powdered carbon fiber, and short carbon fiber to assess the influence of the modification of the carbon material surface in the interaction between cement paste and carbon material. The best oxidation treatment in terms of mechanical strength improvement was oxidation by air at 410°C because this procedure yielded the highest amount of oxygen surface functional groups, thus producing a better interaction with cement paste. Ozone treatment has also been shown to produce a high level of improvement in mechanical properties, but in this case the properties are improved because of the rough surface of the carbon materials.

The accelerated life test of concrete in a chloride environment was carried out with chloride ion migration equipment. The time that elapsed before critical chloride concentration led to reinforcement corrosion was defined in this paper as the service life of concrete. The negative logarithm of chloride ion concentration was linear with the electrochemical potential. The chloride concentration in the anode chamber was an approximate linear relationship and increased with the testing time after a different stage. The service life of concrete in a natural diffusion test could be predicted by the accelerated curve. The results show that the service life of 10 mm concrete cover in the chloride environment is between 11.89 and 12.45 years. The experimental value is in good agreement with the Life-365 prediction.

Open-graded friction course (OGFC) mixture is a special purpose mixture that is being increasingly used in pavement surfacing around the world. OGFC mixtures consist of an open gradation, mostly of coarse size aggregate with little fines. Asphalt contents for OGFC mixtures are generally slightly higher than for dense-graded mixtures. This paper deals with the viability of using reclaimed polyethylene (PE) fibers derived from low-density polyethylene (LDPE) tote bags collected from domestic waste as an additive in OGFC mixtures. Draindown test results indicated that OGFC mixtures with PE fibers can be effectively used to retard draindown of the binder and mineral filler. Mixture designs were performed for a range of 4.5–6.0% asphalt content. Laboratory tests were carried out on OGFC mixtures to determine the resistance to fatigue damage, unaged and aged abrasion, tensile strength, moisture-induced damage, and plastic deformation. The test results indicated that OGFC mixtures with reclaimed PE fibers showed improvement in tensile strength and improved resistance to permanent deformation, fatigue-induced damage, and moisture susceptibility when compared with mixtures without fibers.

The purpose of this study was first to present the laboratory mix design results for porous asphalt concrete (PAC) mixtures blended with high-viscosity-graded cement (AR-80) and asphalt rubber (AR). In addition, the master curves of dynamic modulus were determined for both the unconfined and confined conditions to evaluate the rutting behavior of both PAC mixtures. The mix design results showed that the PAC open-graded mixture consisted of a relatively large percentage of coarse aggregate, with less than 15% of the material passing through a 2.36-mm (No. 8) sieve, which created a sufficient space for water drainage. The target air voids of approximately 20%, as well as the coefficient of permeability greater than ${10}^{-2}\mathrm{cm}/\mathrm{s}$, were established. Comparing the master curves of dynamic modulus between these two types of PAC mixtures indicated that the asphalt-rubber mixtures exhibited higher dynamic modulus at longer reduced times for both the unconfined and confined conditions. The experimental results of repeated triaxial-loaded and wheel tracking permanent deformation tests confirmed that the asphalt-rubber mixtures have superior performance against rutting. Furthermore, the high void of both PAC mixtures illustrated the validity of the principles of time-temperature superposition in the large strain of the viscoplastic stage during repeated triaxial-loaded permanent deformation tests.