Journal of Materials in Civil Engineering

A new mechanistic-empirical pavement design guide to better predict the service life of pavement systems is in its final stages of validation. One of the new input parameters recommended for the design is the dynamic modulus of the asphalt concrete mixes. The developers of the design guide have developed a laboratory test setup that can provide this parameter. To verify the accuracy and precision of the proposed test setup, several synthetic specimens with known material properties and different length-to-diameter ratios were procured and tested. Since the new design guide advocates the use of specimens with length-to-diameter ratios of less than two, the utility of using end friction reducing layers between the specimen and the end platens were also evaluated. In the end, the hot mix asphalt concrete specimens were also prepared and tested. Overall, the test setup is precise and can be used for dynamic modulus measurement of asphalt concrete mixes. The results also suggest that the specimen geometry and the end friction reducing layers affect the accuracy and precision of estimated dynamic modulus.

This paper investigates the specimen size effect on the dynamic response of plain concrete. The report is based upon experimental data by the writers and others and considers results from creep tests on beams, beams under flexural impact, and cylinders under axial impact loading. Size effect is examined using Bažant’s size effect law and the multifractal scaling law, and both scaling models are able to capture the size effect on strength. For fracture energy, on the other hand, the size effect manifests itself only at impact rates. Under quasi-static loading, plain concrete in compression is less sensitive to the specimen size. But under impact, the compressive response appears to be more size dependent than flexure. However, upon accounting for the stress rate effects, the flexural response depicts a more significant size effect, similar to that seen at quasi-static rates.

Temperature is one of the most dominant factors that impact the variation in modulus of asphalt concrete (AC) layers. An accurate relationship between temperature and modulus is necessary to successfully characterize asphalt concrete pavements. The variation in modulus is typically related to the average temperature of a layer. However, the temperature gradient within a layer also plays a role in that relationship. The impact of temperature gradient on modulus of AC layers is reported in this paper. A test setup that can simulate the variation in temperature with time of day was developed and used. With the data obtained, a preliminary relationship between temperature gradient and modulus has been developed. The next step of this study is to develop a model that can be used in pavement analysis.

The alkali-silica reaction (ASR) is a chemical reaction that causes expansions and unexpected deformations of concrete structures. A methodology of assessment of ASR-damaged structures is required in order to evaluate their structural stability. Chemomechanical calculations have been performed in order to investigate the assumption of modeling ASR-induced expansions as imposed strains. The input data for the model comprises the moisture distribution in the damaged structures, ASR-induced potential strains, and the influence of ASR on the concrete mechanical properties. The results of calculations have been compared with experimental data obtained from ASR-damaged beam specimens. The role of water supply and reinforcement has been analyzed in comparing the deformations of plain and reinforced concrete beams subjected to a moisture gradient. Calculations show that cracking and compressive stresses (here induced by steel reinforcement) have a large influence on the anisotropy of the ASR swellings. This induced anisotropy is shown to be one of the main factors that should be considered while predicting the mechanical behavior of ASR-damaged structures.

It has been widely recognized that the behavior of confined concrete depends upon the level of confinement. Brittleness or ductility is a function of the state of compressive stresses, unconfined concrete strength, volumetric expansion, and concrete softening. Constitutive models for strength enhancement, concrete dilatation, and a new stress-strain relationship for concrete in triaxial compression are proposed. The load-carrying capacity of confined concrete is predicted by utilizing an Ottosen-type surface with newly developed coefficients that account for a wide range of confinement levels (lateral pressures up to 100% of the unconfined concrete strength) and unconfined concrete strengths from 20 to $130\mathrm{MPa}$ . Concrete dilatation is modeled as a function of the lateral pressure ratio and concrete strength and can reach values beyond the limit of uncompressibility. Experimental results are used to corroborate the new models at the material level, producing accurate agreement.

This paper provides the results of an experimental investigation into the use of crushed new clay brick as coarse aggregate in producing concrete. The present investigation is the first phase of a two-phase program to study the effects of using recycled masonry aggregate (predominately made of clay brick) with its impurities on the properties of fresh and hardened concrete. Four different types of new clay bricks with different compressive strengths were used in the investigation. Several physical and mechanical properties of fresh and hardened concrete produced from crushed clay brick aggregates were determined and compared to concrete produced using granite as a proven aggregate.

The strength and durability performance of concretes incorporating $0–40\%$ of finely ground pumice as cement replacement (by mass) subjected to high temperatures up to $800°\mathrm{C}$ is described. The strength properties were assessed by unstressed residual compressive strength, while durability was investigated by crack pattern observations, the rapid chloride permeability test (RCPT), mercury intrusion porosimetry, microhardness testing, and differential scanning calorimetry. The results of RCPT revealed that concrete durability deterioration commences at temperatures that are lower than those at which compressive strength deterioration commences. Such a loss of durability can be explained by a weakened interfacial transition zone between the hardened cement paste (hcp) and aggregate and by the concurrent coarsening of the hcp pore structure. When pumice is included, an improvement of fire resistance was observed, as characterized by the higher residual compressive strength and improved durability. Pumice concrete showed good performance with a higher residual strength, higher chloride resistance, and higher resistance against deterioration, particularly at temperatures below $600°\mathrm{C}$ as compared to the control normal Portland cement concrete. The improved performance of pumice concrete can be attributed to the substitution of pumice for cement, which leads to refinement of the pore structure and a lower quantity of calcium silicate hydrate. The deterioration of both strength and durability of pumice concrete increased with the increase of temperature up to $800°\mathrm{C}$ due to a substantial reduction in residual strength and increase in pore volume and pore diameter. The serviceability assessment of pumice concrete after a fire should therefore be based on both strength and durability considerations.

The nonlinear models of pavement base and subgrade were briefly reviewed. Subroutines of the three-dimensional finite-element analysis in the ABAQUS package were developed for nonlinear behavior of a coarse-grained base and subgrade. The programs were validated by comparing them with the theoretical-solution-based program BISAR and the 2D finite-element program ILLI-PAVE. Significant discrepancy was found between the 3D analysis and the 2D axisymmetric analysis, especially for the deformation results. It was also found that the stiffness matrices of the nonlinear materials were not symmetrical, which causes accuracy problems in those programs based on 2D axisymmetry formulations. The results of nonlinear analysis and linear analysis were also compared. It was concluded that the determinations of the resilient modulus for the linear models is critical to interpret the behaviors of nonlinear materials.

For many years, ASTM D 2493 has been used as a reference for determining mixing and compaction temperatures for asphalt binders. However, this method only applies to neat or unmodified binders. With the inception of modified binders, which incorporate various additives that stiffen binders, this method predicts unreasonably high mixing and compaction temperatures. The current study examined 50 commercially available binders. In this study, the viscosity values that are used for temperature selection were evaluated. Modified binders that are currently in industry are stiff, which makes it not possible to achieve reasonable temperatures using the current viscosity values. Therefore it was necessary to determine more appropriate viscosity ranges. Based on testing done with these binders, more reasonable viscosity ranges, centered on values of 0.275 and $0.550\mathrm{Pa}\mathrm{s}$ , were chosen. The new viscosity range, coupled with a higher shear rate of $500{\mathrm{s}}^{-1}$ , resulted in more reasonable mixing and compaction temperatures that were from $13\text{to}52°\mathrm{C}$ lower than the traditional method.

Colloidal nanoparticles were electrokinetically transported into hardened cement paste pores where they underwent chemical reactions resulting in reduced permeability. $20\mathrm{nm}$ silica and $2\mathrm{nm}$ alumina particles were combined with simulated pore fluids to assess precipitate production. One precipitate formed was $\mathrm{C}\text{-}\mathrm{S}\text{-}\mathrm{H}$ , the binder material native to Portland cement paste. Permeability tests were conducted to study the effect of these processes on hardened cement pastes of high water/cement ratio and of high and low alkali contents. It was observed that $5\min$ treatments using $5\mathrm{V}$ of potential applied over a span of $0.15\mathrm{m}$ is sufficient to drive nanoparticles into the pore system, enabling them to react and produce precipitates. The coefficient of permeability for each paste was reduced by 1–3 orders of magnitude. These findings indicate that reactive nanoparticles can be electrokinetically inserted to reduce the permeability of hardened cement paste, even in the presence of an opposing hydraulic flow.

The binder viscosity in a reclaimed asphalt pavement (RAP) is usually measured from the recovered binder. To recover the aged binder from RAP, there must be a series of laboratory process which takes at least a day or two. This study was initiated to determine the possibility of estimating absolute viscosity of aged binder (in RAP) within a short time $\left(2\mathrm{h}\right)$ by using gel-permeation chromatograph (GPC) technique. Many studies have shown that the GPC profile has a good correlation with physical properties of binder. To apply this concept, GPC tests were run on the samples from RAP mixtures without recovery. Statistical analysis indicated that absolute viscosity of the binder in an asphalt mixture could be reasonably estimated from the GPC test. The $R^2$ value of the absolute viscosity with large molecular size was as high as 0.95 for unmodified asphalt and 0.9 for polymer-modified asphalt binder.

The fiber composites reported herein comprise a particular class of multiphase materials in which the major volumetric phase, the binder, is a rapid-hardening cement-based material and the minor volumetric phase, the reinforcement, is a fibrous steel material. A further feature of these composites was that the proportion of fiber to binder was significantly high, up to 20% by volume. The work was limited to commercially available steel fibers and cements; the latter were a magnesium phosphate and an accelerated calcium aluminate. The objectives of this work were (1) to carry out a brief review on rapid-hardening cements; (2) to identify the influence of early-age temperature rise on the stability of cement grouts; and (3) to investigate their early-age strength development. The work established that both cements could be used as binders in fiber composites.

California Bearing Ratio (CBR) and static and cyclic triaxial tests were conducted on the four most frequently encountered local materials—fly ash, coarse sand, stone dust, and river bed material (RBM)—for their use in the subbase layer of a flexible pavement. The CBR of stone dust was the maximum value of all, but its behavior under dynamic load in triaxial tests was inferior to that of the other materials. Fly ash has low CBR, but better stress-strain behavior than stone dust. The results show that RBM is the best material for use in the subbase layer as it had good CBR, high E-value and resilient modulus, and low permanent strain values compared to other materials used in this study.

During the past 20-plus years, designs based on the post-tension segmental concrete box concept have evolved to become prominent in bridge construction. Critical to the safety and longevity of such structures is the integrity of post-tensioning tendons. However, during the past five years, several Florida bridges have suffered tendon deterioration and failure because of strand corrosion at grout voids in which bleed water had accumulated. In some cases, the high-density polyethylene (HDPE) ducts within which the grouted strands reside had cracked. Although none of the tendon failures to date have been related to the HDPE duct cracking, left unaddressed moisture, chlorides, and oxygen will invariably corrode strands in the long-term. In order to assess the cause(s) and mechanism(s) of HDPE duct cracking, fatigue tests were performed upon duct samples retrieved from representative bridges and the results were compared with those from (1) material property determinations of the corresponding ducts, (2) experiments on simulated tendons that were subjected to thermal cycling, and (3) finite element analyses. Based on the outcomes, a mechanism is proposed for the duct cracking and time-to-cracking projections are made for ducts that are still sound.

Alkali-silica reaction (ASR) is a concrete pathology due to chemical reactions involving reactive silica from reactive aggregates and the inner solution of concrete. Main effects are swelling, cracking, and reduction in the mechanical properties of affected concretes. Water is very important for ASR; the more available water, the more expansion and degradation. This article presents new laws for modeling of the influence of water upon ASR. They are based on experimental results and then used to simulate results taken out of the scientific literature.

This paper investigates the potential of using design of experiments and neural networks to determine the effect of fly ash replacements, from 0 to 50%, on early and late compressive strength, from 3 to $56\mathrm{days}$ , of low- and high-strength concrete, at water-cementitious material ratios in the range of 0.3–0.7. The research reported in this paper shows the following conclusions: (1) using a simplex-centroid mixture experiment design, a much smaller number of experiments need to be performed to obtain meaningful data; (2) high correlations between the compressive strength and the component composition of concrete can be developed using the generalization capabilities of the neural networks; (3) analyses of variance to test the effects of the variables and their interactions on concrete strength can be performed; (4) the strength ratio, i.e., the percentage of strength of concrete containing fly ash to strength of concrete without fly ash (pure-cement concrete) based on the same $w∕b$ and the same age, is significantly reduced as the fly ash replacement increases, is somewhat reduced as the water-binder ratio decreases, and is highly significantly reduced as the age decreases; and (5) the higher fly ash content mixes yielded lower strength ratios throughout, the difference being greater at early age and low water-binder ratio.

The enormous amount of wastes produced during wood processing operations in many countries provides challenging opportunities for the use of wood waste as a construction material. In this research, wood waste (sawdust and wood shaving) ash (WWA) of pretreated timber of 0, 5, 10, 15, 20, 25, and 30% by weight of cement was added as a supplement to a concrete of mix proportion 1:2:4:0.56 (cement:sand:coarse aggregate:water cement ratio), and the strengths and the water absorption of the matrix were evaluated. Also, the metal leachability of WWA was analyzed. The compressive and the flexural strengths of WWA concrete for the ages investigated ranged from $12.83\text{to}28.66\mathrm{N}∕{\mathrm{mm}}^2$ , and $3.65\text{to}5.57\mathrm{N}∕{\mathrm{mm}}^2$ , respectively, with the lowest values obtained at 30% additive level of ash. When compared with the strength of plain concrete (control), the compressive and flexural strengths of WWA concrete were between 62 and 91% and 65 and 98%, respectively, of the former. The trend of the water absorption of WWA concrete was a reversal of those of the strengths, that is, the highest water absorption values were recorded for concrete specimens with the highest additive level of ash. A batch leaching test also performed at an ash-leachant volumetric ratio of 20 produced leachate containing chromium, arsenic, iron, copper, and zinc at the following concentrations: 410, 6720, 150, 280, and $1690\mu \mathrm{g}∕\mathrm{L}$ , respectively, when leached at a pH of 4, and 400, 10,670, 0, 100, $1470\mu \mathrm{g}∕\mathrm{L}$ , respectively, when leached at a pH of 5. These concentration levels exceed the EPA fresh water acute criteria limits.

Recent research achieved on recycled railway ballasts issued that they were not properly assessed using European standard test methods. Indeed, other characteristics such as wear stage of particles have to be checked to assess their resistance to tracks vertical deformations. This paper introduces a new image processing based method and angularity criteria for the characterization of railway ballast wear stage. They have been implemented into the VDG40 videograder. Experimental design technique has been used to validate the method and criteria and to set up an efficient test procedure. Samples have been artificially worn away using a milling device. Then the wear stage of each sample was determined using the test procedure. Two main conclusions were drawn: first, two rock types showed similar angularity evolution with respect to wear stage, which puts the question whether they would resist similarly to tracks vertical deformation and second, this evolution is nonlinear.

Metakaolin is a pozzolanic material obtained through thermal activation of kaolinite. It has several important advantages when used as an extender for Portland cement. This note describes the strength enhancement observed in mortars containing metakaolin additions between 10 and 30%. It was found that compressive strengths increase with increased curing times and depended strongly on the activation temperature used. Strength enhancements did not depend significantly on the concentration of metakaolin addition. Significant improvements in compressive strengths of cement mortars, up to 80% or more, was found in selected cases.