Journal of Materials in Civil Engineering

A very high-strength microconcrete $\left(f_c=125\text{MPa}\right)$ containing polymeric fibers and quartzitic aggregates, but no silica fume, has been investigated both at high temperature and after cooling, in order to evaluate the thermal diffusivity and the mechanical decay as a function of the temperature, since there is still scanty information in the literature on the high-temperature behavior of this family of materials. The very high-strength concrete (VHSC) investigated turned out to be very efficient, since (1) its compressive strength exhibits a decay very close to that of normal-strength concrete, with no sizable differences between the “hot” and “residual” properties $\left(250–750°\text{C}\right)$ ; (2) its specific fracture energy increases very much indeed with the temperature; and (3) its rather low thermal diffusivity guarantees good insulation properties. As an application of this material, the parking apron of an airport and its two-layered pavement subjected to a hot spot $\left(T\le 400°\text{C}\right)$ have been considered, in order to investigate whether delamination at the interface between the top VHSC layer and the bottom normal strength concrete layer and/or cracking in the bottom layer may occur. The performance of the pavement was analyzed for different values of the thickness of the top VHSC layer and also for different values of its thermal properties, and proved to be very satisfactory in terms of tensile behavior. However, the critical factor remains the initial heating rate.

Drainability is one of the main characteristics of permeable friction course (PFC) mixtures and is the primary reason for using these mixtures as the surface course in asphalt pavements in the United States. Current approaches suggested for PFC mix design to evaluate drainability (using gyratory-compacted specimens) include: (1) achieving a target total air void (AV) content as an indirect indication of permeability and (2) direct measurement of permeability in the laboratory. The assessment conducted in this study suggested that these approaches are not effective in ensuring adequate drainability in field-compacted mixtures. Thus, different alternatives were evaluated to improve this assessment. Corresponding analysis suggested that: (1) the water-accessible AV content can be used as a surrogate of the total AV content to indirectly assess permeability and (2) the water flow value (outflow time) can be applied to evaluate the field drainability of PFC mixtures. The expected value of permeability, determined using a modified version of the Kozeny-Carman equation, was recommended to analytically predict permeability for mix design and evaluation purposes.

This study used high fineness of fly ash as a cement replacement to improve recycled aggregate concrete properties. The mixture proportions of recycled aggregate concretes were first prepared using 100% recycled coarse aggregate, and then river sand was replaced with recycled fine aggregate at 0, 50, and 100% by weight of the fine aggregate (river sand plus recycled fine aggregate). Results indicated that use of 35–50% fly ash (with respect to total cementitious content) of high fineness could improve slump loss behavior in recycled aggregate concretes. Greater proportions of recycled fine aggregates decreased the compressive strength of concrete. However, use of high fineness of fly ash (1.2% retained on a No. 325 sieve) in recycled aggregate concrete could produce greater compressive strength than that of the recycled aggregate concrete alone. The splitting tensile strength of the recycled aggregate concretes containing high fineness of fly ash was 8.2% of its compressive strength, slightly lower than that of the normal aggregate concrete. The modulus of elasticity of recycled aggregate concrete, with or without high fineness of fly ash, was lower than that of the normal aggregate concrete and about 5.9% lower than the value predicted by ACI 318. The results suggest that high fineness of fly ash can be used to improve various properties of recycled aggregate concrete.

In recent years, advanced fiber-reinforced polymer (FRP) composites have been steadily developed and used in a wide spectrum of infrastructure applications. It is, however, recognized that many polymer resins soften rapidly when heated above $82°\text{C}$ $\left(180°\text{F}\right)$ . Hence fire vulnerability may become a future obstacle with the widespread use of FRP materials. In this paper, initial findings from an on-going project, aimed at developing temperature-resistant cement-based composite sheets for structural retrofit, were reported. Following a similar installation procedure to that of FRP sheets, it is essential to examine the effect of mix compositions on the rheological properties of the cement slurry and to develop suitable cement slurries for making thin fiber-reinforced cement sheets on the job sites. Retrofit efficiency of using both epoxy-based and cement-based thin sheets is investigated. Preliminary results are presented and discussed in this paper. It is confirmed that cement sheets could be very likely made in situ and provide a similar retrofit capacity to their FRP counterparts.

Styrene-butadiene-styrene (SBS) and starch (ST) have been used by many to modify asphalt cement and to improve the properties of asphalt concrete. In this investigation, SBS and ST were used to modify asphalt cement. The basic properties of modified asphalt binders and stone mastic asphalt concrete (SMAC) containing such asphalt binders were studied and compared with those of asphalt cement. Marshall stability, Marshall Quotient, tensile strength, tensile strength ratio, rutting resistance, flexural strength, and resilient modulus were carried out on the SMAC. A mechanistic-empirical design approach was used for estimating the improvement in service life of the pavement or reduction in thickness of SMAC and base layer for the same service life due to modification the SMAC. In addition, an optimization table was prepared to select the type of SMAC for any field applications. The analyzes of test results show that the performance of SBS-modified SMAC is slightly better when compared to ST-modified SMAC. The temperature susceptibility can be reduced by the inclusion of SBS and ST in the SMAC. The results of multilayer elastic analysis presented herein indicate that the pavement consisting of SBS and ST-modified SMAC as a surface layer is beneficial in reducing the construction materials. Actual savings would depend upon the option exercised by the designer for reducing the thickness of an individual layer.

Moisture damage in asphalt mixtures is defined as the gradual loss of structural integrity caused by the presence of moisture. A simple experimental procedure was developed in this study to measure water vapor diffusion coefficients in coarse aggregates, fine aggregate mixture (blend of the fine portion of the aggregates with the asphalt binder), and hot-mix asphalt. The procedure is based on periodic weight measurements of specimen-container ensembles subjected to a controlled temperature and relative humidity environment. Fick’s first law was used to estimate the diffusion coefficients of the materials. The results show that the proposed experimental method is an economic and efficient tool to quantify water vapor diffusion coefficients. Determining these material properties is fundamental to develop numerical models to study the deleterious effects of moisture vapor on the mechanical performance of asphalt mixtures. In order to exemplify the significance of the experimental measurements, a numerical simulation of transient moisture diffusion within the cross section microstructure of an asphalt mixture was conducted. The results of the simulations suggest that diffusion coefficients are fundamental for tracking the potential of a mixture to develop moisture-related degradation processes. Furthermore, it was observed that under the same environmental conditions, moisture damage in an asphalt mixture is highly influenced by the moisture diffusion coefficient of its constitutive phases.

This research aimed to investigate the engineering and dynamic properties, such as unit weight, stiffness, natural frequency and damping ratio, of lightweight aggregate concrete (LWAC) beams made with sedimentary lightweight aggregate (LWA) and to compare with companion normal weight concrete (NWC) beams. The primary design variables included compressive strengths of 20, 40, and 60 MPa and reinforcement ratios of 0%, 1.03%, and 2.32%, respectively. A total of 62 beams were made and tested. Test results showed that the unit weight of LWAC beams was about 16–23% lower than that of NWC beams for the same strength level. In addition, the reduced modulus of elasticity of LWAC resulted in a stiffness decrease of reinforced lightweight concrete (RLC) beams of 5–15% related to the reinforced NWC (RC) beams. Nevertheless, the natural frequency of RLC was still higher by about 1–10% than that of RC. In contrast, it was also found that the porous LWA with high damping capacity enhanced the damping ratio of RLC beams by 13–30% for concrete strength in the range from 20 to 60 MPa. As a whole, the lower the concrete strength is (e.g., 20 MPa), the more effective will be for the lightness of LWAC beam and the damping ratio, which in turn is more favorable to the seismic resistant efficiency of LWAC beam.

A research study was conducted to evaluate the use of light weight aggregate (LWA) material produced from the manufacturing of expanded clay and shale (ECS) for potential use as a roadway approach embankment material. The use of such LWAs is expected to reduce stresses on subgrade foundation, which in turn could lead to less or no approach settlements. The test site was constructed on the south end of a new bridge overpass on State Highway 360 in Arlington, Texas and a control section was constructed on the north end of the same bridge. In the control section, a low plastic borrow soil (normal fill) was used as an embankment fill material. This paper presents both laboratory and field evaluations of the utilization of both ECS material and conventional borrow soil as embankments fill material. Shear strength and consolidation tests were performed to evaluate strength and compressibility characteristics. The embankment section was instrumented with vertical inclinometers to monitor the fill movements due to field loading conditions. Pavement surface profiling of both ends of the bridge was also performed at regular time intervals. Numerical simulations of test sections were also attempted. Based on the data obtained from experimental, field monitoring and numerical studies, it can be mentioned that the utilization of ECS LWAs are efficient in minimizing the bridge approach embankment settlements and reduced bump problems at the entry and departure of the bridges.

This paper presents a micromechanical finite-element (FE) model for predicting the viscoelastic properties (dynamic modulus and phase angle) of asphalt mixtures, typical stone-based composites. The two-dimensional (2D) microstructure of asphalt mixtures was captured by optically scanning the surface image of sectioned specimens. FE mesh of image samples was generated within each aggregate and asphalt mastic. Along the aggregate boundary, the FEs share the nodes to connect the deformation. The micromechanical FE model was accomplished by incorporating specimen microstructure and ingredient properties (viscoelastic asphalt mastic and elastic aggregates). The generalized Maxwell model was applied for viscoelastic asphalt mastic with calibrated parameters from nonlinear regression analysis of the mastic test data on dynamic modulus and phase angle. The displacement-based FE simulations were conducted on the numerical samples under sinusoidal cyclic loading. The predicted dynamic modulus and phase angle were compared favorably with the mixture test data over a frequency range. The simulation results of the asphalt mixture samples have good correlations with the numerical calibration of asphalt mastic specimens. These results indicate that the developed micromechanical FE model can provide a computational tool for predicting the global viscoelastic properties of asphalt mixtures with captured microstructure and ingredient properties. Additionally, this study can increase the mechanistic understanding of global viscoelastic properties of asphalt mixtures by linking their microstructure.

This paper describes the use of a fluidized soil-cement mix to fill a former gypsum-anhydrite mine located in the village of Santa Brigida in Northen Italy. The mine was excavated with the chamber-pillar method on four different levels and it was abandoned several tens of years ago. Two lower levels are flooded and the dissolution of gypsum and anhydrite, consequent to the flow of water inside the tunnels, puts under serious hydrogeological risk the area above the mine. Geological and geotechnical studies found as the most adequate solution to the problem the complete filling of the tunnels with a material with mechanical and physical properties comparable to common properties of soils. Nevertheless, the presence of water with significant concentration of sulfate ions inside the tunnels has required a specific study in order to define both an appropriate filling material and the technology to introduce it in the tunnels. The results of laboratory studies to develop and characterize the flowable soil-cement are summarized and a pilot work is described.

This study was concerned with vibrations induced during drilled shaft construction on green concrete in adjacent drilled shafts. To characterize the types of vibrations, a full-scale field test was conducted using a 0.9-m (3-ft)-diameter steel casing vibrated at a peak particle velocity (ppv) of 250 mm/s (10 in./s) to various depths in a sandy soil layer. In addition to the steel casing, the peak particle velocities were recorded at different distances and depths from the vibration source. Empirical relationships from measurements were developed to predict the velocity values on the surface and in the ground along the penetration depth of the steel casing. Laboratory tests were conducted on two groups of green concrete samples to determine the effect of ppv and curing time on concrete properties. These tests showed a 10% reduction in the 28-day compressive strength for samples subjected to continuous vibration at ppv of 50 mm/s (2 in./s) for a duration ranging from the initial to the final setting time. On the other hand, when samples were continuously vibrated until the final setting time, the 28-day compressive strength of the concrete increased by 10%. If vibrations with ppv of 50 mm/s are unavoidable, curing caissons shall be kept at a distance of more than two shaft diameters from the source of vibration.

This paper presents the physical properties of recycled asphalt pavement (RAP) and its influence on the mechanical performance of a binder course asphalt pavement mix. A series of binder course mixes were designed containing varying percentages of RAP. A mix made from only virgin material was selected as the control mix for the investigation. The effect of introducing RAP into the binder course mix was evaluated through a series of laboratory tests including the Marshall test, the indirect tensile stiffness modulus test, the indirect tensile fatigue test and the water sensitivity test. A circular wheel track (CWT) was developed in order to study the dynamic effects of a rolling wheel traveling over an asphalt pavement. The CWT was commissioned within a temperature controlled room along with a customized data acquisition system. The system involves the testing of rectangular slabs and allows for the investigation of dynamic tensile strain. The laboratory tests have shown that the introduction of RAP to the binder course mix resulted in an improvement in all mechanical properties. In particular, it was found that the mix containing up to 30% RAP, displayed improved fatigue resistance relative to the control mix manufactured from virgin materials.