Journal of Materials in Civil Engineering

The evaluation on the risk of thermal-induced cracking is among the key issues in the design and construction of the Three-Gorges Dam. The time-dependent thermomechanical behavior of the left guide-wall section of the dam is systematically studied. A series of laboratory tests on the concrete thermomechanical properties are conducted. A three-dimensional finite element code is developed for calculating the evolutionary temperature and stress field of the dam. The time-dependent thermomechanical properties of concrete, detailed construction procedures, variations of environmental temperature, and the effects of water cooling are taken into account in this code. The distribution and evolution of temperature and thermal stress of the dam are derived. The superimposed effects of thermal load, self-weight, and external water pressure are discussed. The results indicate that the thermal tensile stresses can be largely counteracted by the compressive stresses due to self-weight. There is very little cracking potential after reservoir filling. Nevertheless, during the construction, large tensile stresses can be locally caused; accordingly, some significant suggestions for the thermal stress and temperature control of the dam are presented.

The triaxial compressive response of bituminous mixes with volume fractions of aggregate in the range 52 to 85% was investigated over a wide range stresses and strain rates. The types of loadings considered include triaxial monotonic constant stress and constant applied strain rate, as well as creep recovery, continuous cyclic, and stress pulse train loadings. The mixes with a “fully dense” aggregate skeleton were found to dilate under all loading conditions and the creep response of the mixes was dependent on both the deviatoric and hydrostatic stresses. By contrast, recovery was found to occur under zero applied deviatoric stresses with the recovery rate only dependent on the “recoverable strain” and independent of any superimposed hydrostatic stress. Continuous and pulse loading cyclic stress-controlled tests showed that the response of the mixes was governed by the mean applied deviatoric stress in the continuous cyclic tests while strain recovery was important in the pulse loading tests. A phenomenological constitutive model was proposed to fit the measured triaxial response of the bituminous mixes and shown to capture the measurements over all the triaxial stress states and loading time histories investigated here. Furthermore, the model was extended to capture the temperature dependence of the mixtures which is governed by the temperature dependence of the bitumen binder.

The slant shear test highlighted by British Standard 6319 No. 4 was used to evaluate the bond strength between selected repair materials and parent concrete. Seven resinous and six cementitious repair materials were used to repair fractured specimens. Repaired test specimens were aged by subjecting them to heat-cool cycles that simulated repeated extreme summer day in the southern part of the United States (e.g., Mississippi). The results of thermal cycling showed a strong correlation between the difference in the coefficient of thermal expansions, as well as the difference in elastic moduli, between repair materials and concrete, and the reduction in bond strength. Although resinous materials possessed a higher bond strength to concrete, they showed higher reduction of bond strength than cementitious materials.

An investigation of various factors that can affect the fracture resistance of asphalt mixtures at low temperatures was conducted. The fracture resistance of 28 asphalt mixtures—which represent a combination of factors including binder type, binder modifier, aggregate type, asphalt content, and air voids—was evaluated by performing semi-circular bending fracture tests at three low temperatures. Two parameters, fracture energy and fracture toughness, were calculated from the experimental data. The statistical analysis indicated that fracture resistance is strongly dependent on temperature and significantly affected by the type of aggregate and air void content. The results of the analysis also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Asphalt content was also found to be significant for fracture energy but not a significant factor affecting fracture toughness.

There have been many studies investigating the properties of crumb rubber modified (CRM) binders, but few that have attempted to quantify the specific effects that the addition of crumb rubber has on asphalt binders. The writers previously identified two major effects that crumb rubber has on binders: interaction effect (IE) and particle effect (PE). The IE results from the diffusion of the light fractions of the binder into the rubber particles and the PE is due to the addition of particulate matter to the binder. This study focused on providing a further explanation of the IE by characterizing 36 CRM and three base binders using high-pressure gel permeation chromatography (HP-GPC). Comparison of the molecular size distributions of the different binders verified that the IE is, in fact, due to the diffusion of lighter binder fractions into the rubber particles. Additionally, the IE may provide a simple means to determine the compatibility of binders with crumb rubber.

Geofoam has the scientific name of expanded polystyrene (EPS). A block of EPS is made from particles of polystyrene through an expanding and melting process in an automatic mold machine by adding steam. The geofoam construction method employs large EPS blocks with unit weights between 12 and $30{\text{kg}}_{\text{force}}/{\text{m}}^3$ . In the 1970s, the use of EPS as a lightweight embankment in highway and earthwork developed concurrently in the United States and Norway. Most notably, in 1972, the Norwegian Road Research Laboratory placed geofoam in the approach fill of the Flom Bridge. The advantages of this construction method are that geofoam can be used not only to replace ground fill material but also to reduce the load applied to the foundation. This paper will introduce the following topics related to geofoam: the background and inspection conditions in Taiwan, United States, and Japan, the quality investigation of EPS production, and the experimental and analysis results of EPS manufacturing quality and homogenous test. This research illustrated that the quality control chart can analyze the stability of manufactured EPS. Meanwhile, the homogeneous testing method, which is put forth in this paper, can actually examine the stability of EPS manufacturing procedure. The results of this study can be used as the reference for quality control of geofoam. The issue of geofoam used for collision prevention, self-weight decreasing, and landslide resistance in geotechnical engineering will also be discussed.

Frost related damage in pavements is a major concern for highway engineers in cold regions. The existing methods for mitigating frost damage in flexible pavements are expensive; they require greater construction control and are not fully effective. This paper investigates an alternative approach for reducing frost penetration into the pavement layers by engineering a less conductive asphalt surface layer. It proposes a less conductive pavement by replacing conventional aggregate in the asphalt mix with lightweight aggregate (LWA). The paper discusses, in the context of the larger research program, the development of an optimized design of LWA-asphalt mix. It is has been demonstrated in work published elsewhere that because of its superior insulating behavior, LWA-asphalt mix can reduce frost penetration into the underlying pavement layers. Thus maintenance cost associated with frost damage can be reduced. This paper presents the physical properties of LWA, the lessons learned from the mix design process, as well as the preliminary thermal and mechanical properties of the optimized LWA-asphalt mix.

Toughened glass is often used in load carrying elements due to the relatively high tensile strength compared with float glass. The apparent tensile strength of toughened glass is a combination of the pure material strength and the residual stresses imposed by the toughening process. This paper is concerned with an experimental characterization of the residual stress state for toughened glass. Results for the variation of residual stresses within 32 square specimens with a side length of 300 mm are investigated. The specimens varied in thickness and one group was glass with low iron content. The photoelastic constant was estimated from a four-point bending test. The experimental results revealed large variations in the residual stress state within each specimen and between groups of different thicknesses. The results are compared with a nonstandard fragmentation test, showing that the fragment size does not seem to be dependent on the local variations of the residual stress state in a specimen.

A testing procedure was developed for determining thermal conductivity $k$ using the same cylindrical specimen geometry that is commonly used for standard mechanical property testing. An experimental test apparatus was constructed with a calculated systematic uncertainty of $\pm 0.021\text{W}{\text{m}}^{-1}°{\text{C}}^{-1}\left(\pm 5\%\right)$ for a $k=0.42\text{W}{\text{m}}^{-1}°{\text{C}}^{-1}$ . A cylindrical reference sample of ultrahigh molecular weight polyethylene resulted in a thermal conductivity of $0.441\pm 0.022\text{W}{\text{m}}^{-1}°{\text{C}}^{-1}\left(\pm 5.1\%\right)$ with 95% confidence. Conventional specimens of hot-mix asphalt and portland cement concrete mixtures were tested and yielded $k$ values of $0.896\pm 0.023\text{W}{\text{m}}^{-1}°{\text{C}}^{-1}\left(\pm 2.6\%\right)$ and $1.719\pm 0.048\text{W}{\text{m}}^{-1}°{\text{C}}^{-1}\left(\pm 2.8\%\right)$ , both at a 95% confidence interval. These results fall within common literature value ranges for these materials, and indicate an acceptable level of accuracy and repeatability for this new test method.

This paper presents a procedure to find the optimal balance between the consolidation properties and shape stability of fresh concrete mixtures to achieve a self-consolidating concrete applicable for the slip-form paving process. The investigations started with a conventional slip-form paving concrete mixture. Various types and amounts of supplementary cementitious materials (fly ash), admixtures (water reducers), and additives (clays, magnesium oxide, and fibers) were then gradually applied to modify flowability and maintain sufficient green strength. This approach has led to a successful mix design—the concrete mixture can be consolidated without internal or external vibration and also maintains its slab shape after the slip-form paving process. In the present paper, the step-by-step mix design approach is described, and the effects of admixtures and additives on concrete flowability and shape stability are explained.