Journal of Materials in Civil Engineering

This paper presents experimental results obtained from tests conducted on remolded expansive soil specimens blended with rice-husk ash (RHA) and stabilized with lime and calcium chloride. The amounts of RHA, lime, and calcium chloride were varied from 0 to 16%, 0 to 5%, and 0 to 2%, respectively, by dry weight of the soil. The effect of additives on unconfined compressive strength (UCS) and California bearing ratio (CBR) is reported. It was found that the stress-strain behavior of expansive clay improved upon the addition of up to 5% lime or up to 1% calcium chloride. A maximum improvement in failure stress of 225 and 328% was observed at 4% lime and 1% calcium chloride, respectively. A RHA content of 12% was found to be the optimum with regard to both UCS and CBR in the presence of either lime or calcium chloride. An optimum content of 4% in the case of lime and 1% in the case of calcium chloride was observed even in clay-RHA mixes.

This research investigated the enhancement of polyethylene properties through the use of additives to make it suitable as a roofing material. To function as a roofing material, weatherability (resistance to photo-oxidation), low flammability, and good strength were identified as the key requirements that must be met by the polymer. The additives: carbon black, clay, and ammonium chloride were compounded with the polyethylene. Carbon black was used to protect against photo-oxidation; ammonium chloride was used as a flame retardant, and clay served as a flame retardant while also imparting hardness. ASTM D638-46T tensile test pieces were used to determine the strength of the mixtures, the horizontal UL 94 incipient regime flame test was used to determine flammability, and a simulated weathering test was developed to evaluate weatherability. Results indicated that at about 8.96% clay and 17.42% ammonium chloride, the polyethylene matrix has an average strength of $3.04\pm 0.42\mathrm{MPa}$ . The horizontal UL 94 fire test showed a marked improvement of flammability properties over that observed for virgin polyethylene. The simulated weathering test also showed an improvement in weatherability properties in polyethylene containing the additives.

Silica fume is a common addition to high-performance concrete mix designs. The use of silica fume in concrete leads to increased water demand. For this reason, Florida Department of Transportation (FDOT) allows only a 72-h continuous moist cure process for concrete containing silica fume. Accelerated curing has been shown to be effective in producing high-performance characteristics at early ages in silica-fume concrete. However, the heat greatly increases the moisture loss from exposed surfaces, which may cause shrinkage problems. An experimental study was undertaken to determine the feasibility of steam curing of FDOT concrete with silica fume in order to reduce precast turn around time. Various steam-curing durations were utilized with small laboratory specimens. The concrete compressive strength, surface resistivity, and shrinkage were determined for various durations of steam curing. Results indicate that steam cured silica-fume concrete met all FDOT requirements for the 12, 18, and $24\mathrm{h}$ of curing periods. All steam cured samples demonstrated excellent durability up to 1 year of age. It was recommended that FDOT allow $12\mathrm{h}$ steam curing for concrete with silica fume.

Dynamic modulus $(\mid E^{*}\mid )$ of hot-mix asphalt (HMA) mixtures is one of the fundamental engineering properties measured by the simple performance tester and has also been incorporated as a basic input into the American Association of State Highway and Transportation Officials Mechanistic-Empirical Design Guide for flexible pavements. Although direct laboratory testing and empirical equations (such as the Witczak model and the Hirsch model) provide two ways to obtain the values of dynamic modulus of HMA mixtures, a predictive model based on the microstructure of HMA mixtures is more desirable. This paper presents a viscoelastic micromechanical model to predict the dynamic modulus of HMA mixtures based on the elastic-viscoelastic correspondence principle. In this model, HMA mixtures are treated as a composite by embedding the mastic (or asphalt binder)-coated aggregate particles into the equivalent medium of HMA mixtures. Using the proposed model, a solution was obtained to predict the elastic modulus of HMA mixtures. Based on the elastic-viscoelastic correspondence principle, a viscoelastic equation was derived to predict the complex modulus and subsequently the dynamic modulus of HMA mixtures. The developed equations had the capability of taking into account both aggregate gradation and air void size distribution. Laboratory experiments were conducted to verify the developed model. The dynamic modulus values of mastics and HMA mixtures were obtained through direct laboratory testing. The dynamic modulus of mastic was then used to predict the dynamic modulus of laboratory-prepared HMA mixtures with the newly developed model. Laboratory test results showed that a discrepancy exists between the calculated and measured dynamic moduli. The reason for the discrepancy between measured and predicted dynamic moduli and the factors affecting the dynamic modulus were also explored in the paper.

In recent years, increased attention has been given to the identification of the origin of hydraulic cement clinker with trace element contents. Establishing a standard pattern of the trace element for each origin can facilitate this purpose. However, defining a standard pattern is difficult because each origin has various patterns in practice. Therefore, an effective supporting methodology to deal with the uncertain information is necessary. This paper integrates both concepts of gray number and gray relational analysis to develop a new gray model for qualitative identification of the origin of hydraulic cement clinker. In this proposed model, a detailed operation procedure using gray numbers is provided to effectively handle the uncertain information. Both a set of training data and a set of testing sample are adopted to demonstrate the feasibility and practicability of the proposed model. Results show that the proposed model can indeed efficiently identify the origin of clinker by its trace element contents.

This paper presents very recent results of an experimental program aimed at disclosing size and strain rate effects on the fracture behavior of reinforced concrete beams. Thirty-six reinforced beams made from two microconcretes with different Hillerborg’s characteristic length [one is $66\mathrm{mm}$ (material A), the other is $105\mathrm{mm}$ (material B)], of three sizes (75, 150, and $300\mathrm{mm}$ in depth), were tested under four strain rates ( $1.05\times {10}^{-5}$ , $1.25\times {10}^{-3}$ , $1.25\times {10}^{-2}$ , and $3.75\times {10}^{-2}{\mathrm{s}}^{-1}$ ). The results show that the peak loads increase with an increase in the strain rate; the rate dependence of the peak load is stronger for larger specimens than for smaller ones. Moreover, size effect is only shown under the nominal strain rate $1.05\times {10}^{-5}{\mathrm{s}}^{-1}$ ; under the higher strain rates, it is inconspicuous. These results seem to reveal an apparent physical inconsistency, since there is no obvious reason that the size effect disappears when the strain rate increases. The explanation to this is sought numerically using an explicit cohesive model.

With increasing traffic loads and changes in crude petroleum refining techniques, cracking in asphalt pavements continues to be a major cause of structural and functional deterioration of these systems, particularly in cold climates. Although modern design tools such as the AASHTO Mechanistic Empirical Pavement Design Guide have recognized the need to predict pavement cracking in pavement life cycle cost analyses, the development of true fracture tests and associated models is hampered by a lack of fundamental knowledge of the physical nature of cracking in asphalt concrete materials. A clustered discrete element method (DEM) was employed as a means to investigate fracture mechanisms in asphalt concrete at low temperatures. The DEM approach was first verified by comparing elastic continuum theory and the discontinuum approach using uniform axial compression and cantilever beam models. A bilinear cohesive zone model was implemented into the DEM framework to enable simulation of crack initiation and propagation in asphalt concrete. Verification of the cohesive zone fracture model was carried out using a double cantilever beam. The main advantage of the DEM approach was that a mesoscale representation of the morphology of the material could be easily incorporated into the model using high-resolution imaging, image analysis software, and by developing a relatively simple mesh generation code. The simulation results were shown to compare favorably with experimental results, and moreover, the simulations provide new insight into the mechanisms of fracture in asphalt concrete. The modeling technique can provide more details of the fracture process in laboratory fracture tests, the influence of heterogeneity on crack path, and the effects of local material strength and fracture energy on global fracture test response.