Journal of Materials in Civil Engineering

This study examines the effect of high-calcium fly ash in combination with finely ground limestone as cement replacement on cement’s hydration characteristics. Heat released by a hydration reaction was investigated using isothermal calorimetry. X-ray diffraction and thermogravimetric analysis were used to identify hydration products. In this work, fly ash and limestone were used to replace part of Portland cement at 30% by weight in terms of ternary blended cement. All pastes and mortars were cured in water at $23\pm 2°\mathrm{C}$. The compressive strength of mortars were examined for a period of 28 days. The results show that the hydration reaction of cement containing fly ash accelerated when limestone powder was incorporated. Thermogravimetric analysis of the samples hydrated at 28 days show similar hydration products such as ettringite, calcium silicate hydrate, portlandite, and calcite. However, the dehydration of monocarboaluminate was observed in ternary blended cements of Portland, fly ash, and limestone. From X-ray diffraction patterns, the hydration products of ternary blended cements were found to be mostly similar to that of plain Portland cement; however, monocarboaluminate has been detected. The compressive strength at early ages of ternary blended cements was higher than that of fly ash cement, which conforms to the heat of hydration and thermogravimetric results.

Viscoelastic materials exhibit rate- and temperature-dependant behavior in terms of stress-strain response and fracture. As a representative of this class of materials, rate-dependant fracture should be expected for the bituminous asphalt binders used in the construction of pavement. Preliminary results are reported regarding studies using atomic force microscopy (AFM) to determine rate- and temperature-dependent adhesive fracture in bitumen thin films. This AFM technique involves creating then fracturing a microadhesive contact joint between a bitumen thin film and a glass microbead tip affixed to a cantilever by application of a direct tensile force to the contact. The mechanical work required to fracture this contact is measured as a function of temperature and separation rate. Results of this study suggest that adherence fracture energy of bitumen films is rate and temperature dependant based on measures of energy dissipation at and below the temperature of 25°C. These materials also exhibit a viscoelastic to viscous transition in adhesive behavior above 25°C attributed to observed loss of energy dissipation.

Solid phases percolation and capillary pores depercolation in hydrating cement pastes show great influences on mechanical properties and durability. In this paper, two nondestructive apparatuses, ultrasonic wave measurement and noncontacting electrical resistivity device, were used to in situ continuously track solid phases percolation and capillary pores depercolation evolution in cement pastes, respectively. In parallel with experiments, a hydration model was employed to simulate the early age formation of microstructure. The results show that first percolation (first depercolation) time and fully percolation (fully depercolation) time for solid phases (capillary pores) are identified from velocity (resistivity) curves. On one hand, a correlation is found between the change in connected volume of solid phases simulated with model and the evolution of velocity tested by ultrasonic wave measurement. In contrast, the development of resistivity is a good indicator for evaluating the depercolation of capillary pores.

The effect of combining brass-coated steel microfiber and ground-granulated blast-furnace slag (GGBS) on the mitigation of deleterious expansion due to alkali-silica reaction (ASR) was investigated in this research. A potentially reactive basaltic aggregate was chosen as a reactive material. Two series of specimens containing different amounts of microfiber were prepared. One of them was cured in 1 M NaOH solution at 80°C to obtain a similar maturity; the other series was cured in 80°C water up to 120 days. ASR expansion, strength development, and toughness properties were observed for 120 days in NaOH solution and the results were compared with specimens kept in water. Test results indicate that the combination of GGBS and steel fibers reduced ASR expansion significantly. Furthermore, the combination was very effective at preventing the mechanical property loss due to ASR, such as flexural strength, compressive strength, and toughness. Microstructural investigations revealed that the reaction products had a different morphology (e.g., fibrous, network appearance) when the specimens were kept in NaOH solution.

Carbon (CFRP) and glass (GFRP) fiber-reinforced composites of epoxy matrix are considered in the study, with greater emphasis on GFRP. Accelerated conditioning was imposed in the form of salt fog cycles, hygrothermal cycles (tap water), and tidal-like cycles (aqueous solution of NaCl, $50\mathrm{g}/\mathrm{L}$), both on laminate composites and on beams externally reinforced with fiber-reinforced polymers (FRP) on their soffit. Freeze/thaw cycles were also applied to the study of degradation of the laminates. Mechanical tests showed degradation due to damage to the matrices, fiber-matrix linkage or bond between FRP and concrete. Several advanced techniques were used to interpret the results and enable better understanding of the phenomenological data. Changes on the glass transition temperature ($Tg$) of the epoxy matrix are reported as possible indicators of decrease of the tensile strength of the GFRP composite. Attention is given to the evolution of the relative values of the tensile strength of concrete and adhesive along time given their importance on the effectiveness of the FRP-adhesive-concrete joints. The results revealed, e.g., that the more severe decrease of the carrying capacity of the beams was due to the salt fog cycles in the beams strengthened with CFRP.

In order to explore the potential use of fly ash and plastic waste in bulk quantities in civil engineering applications, it is necessary to understand the behavior of fly ash and fly ash mixed with plastic waste. These materials are considered as wastes and in this study, it is shown that combination of fly ash and plastic waste is very useful. In this regard, various tests such as classification tests, unconfined compressive strength and compressibility tests, consolidated undrained tests, and California bearing ratio tests were conducted. The results indicated that the inclusion of plastic waste in fly ash is effective in improving the engineering properties of fly ash in terms of compressive strength, shear strength parameters, and CBR values. In order to understand the effect of sample size on the shear strength parameters of fly ash and fly ash mixed with plastic waste, consolidated undrained tests were conducted with sample sizes of $38\times 76\mathrm{mm}$ and $50\times 100\mathrm{mm}$. The results of the tests indicate that the shear strength increases with the increase in sample size. The implication of the use of fly ash mixed with plastic waste in unpaved roads is presented in terms of reduction of carbon print.

Microbial induced calcite precipitation (MICP) is one of the potential methods for improvement of engineering properties of soil. A laboratory study was conducted to investigate the influence of various factors on engineering properties of MICP-treated soil catalyzed by bacteria and ureases. Some of these factors include bacteria concentration, urease concentration, cementation media concentration, reaction time, type of sand, and curing conditions. The experiments of MICP catalyzed by Sporosarcina pasteurii and urease were conducted in similar conditions. The soil samples were prepared with full contact flexible molds (FCFMs). The results of unconfined compression test show that the experimental factors (bacteria/urease concentration, cementation media concentration, reaction time, and type of sand) have a significant impact on the MICP process and engineering properties of sand treated by both bacteria and urease, whereas the curing conditions has a small effect. The unconfined compression strength (approximately 1.76–2.04 MPa) of bacteria treated samples is almost $5\times$ (approximately 0.33–0.43 MPa) that of urease treated samples under similar urease activity. The MICP process catalyzed by bacteria is much more effective than the process catalyzed by urease in terms of engineering soil properties improvement.

In published literature, emphasis has been on appropriate mesh design covering element size and element aspect ratio for two-dimensional (2D) cup and cone fracture predictions. Appropriate mesh design for accurate predictions of fracture load and displacement at fracture, which are more important for design, quality assurance, and integrity assessment purposes, has not been published. This work revealed that 2D simulations generally employed in published literature for cup and cone fracture predictions cannot accurately predict the complete fracture behavior of wires used for civil engineering applications. The displacement at fracture of $12\times 5{\mathrm{mm}}^2$ and $12\times 7{\mathrm{mm}}^2$ wires is proportional to element dimension in tensile loading direction. Three-dimensional simulation with global $1\times 1\times 1\mathrm{mm}$ elements and $0.0625\text{-}{\mathrm{mm}}^3$ refined elements at the wire model’s middle with an aspect ratio of $2:1$ represents an appropriate element size and element aspect ratio for accurate prediction of the wires’ complete fracture behavior. Positioning the $0.0625\text{-}{\mathrm{mm}}^3$ refined elements with local length, width, and thickness in the wire model’s global width, length, and thickness is required for accurate prediction of the wires’ complete fracture behavior.

Performance of the engineering properties of paste manufactured with an eco-binder was evaluated. The eco-binder without cement, SCA, was made with slag (S) and fly ash (CA) that had been created by circulating fluidized bed combustion (CFBC). Experimental results show that the pure slag paste hardly sets and the pure CA paste gives very little strength. But when slag and CA are mixed together, the SCA paste not only has proper setting times but also has sufficient strength. The compressive and tensile strength of SCA paste can reach 80 MPa and 4.6 MPa, respectively, at 28 days and higher at longer ages. In addition, the early expansion of the SCA paste compensates for its later shrinkage so that the ultimate drying shrinkage of SCA paste is lower than that of ordinary portland cement paste. The hydration products of the SCA paste detected by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray (EDX) are ettringite, calcium silicate hydrate (C-S-H), and calcium silicate alumina hydrate (C-S-A-H). All of them are bonded together and generate self-cementitious properties in SCA paste.

A new adhesive strength test (AST) was developed to determine the adhesive strength of joint sealant. A series of sealant thicknesses, displacement rates, and curing times was tested to determine proper AST testing parameters using self-leveling (SL) and non-self-leveling (NS) silicone sealants. A series of tests was conducted under varying moisture conditions. The results appeared to indicate that moisture may reduce adhesive strength. Drying-time tests were conducted to determine the approximate appropriate wait time between joint washing and sealant installation for 3.2 mm ($1/8\mathrm{in.}$) and 9.5 mm ($3/8\mathrm{in.}$) joints. A series of tests was also conducted on artificially aged sealants, which appeared to indicate that oven aging reduces adhesive strength for SL sealant. Non-self-leveling sealant, on the other hand, appeared to be largely unaffected by oven aging. Hot-water aging and freeze-thaw aging appeared to reduce adhesive strengths for both sealant mixtures.

Wood-plastic composites (WPCs), commonly used in residential decks and railings, exhibit mechanical behavior that is bimodal, anisotropic, and nonlinear viscoelastic. They exhibit different stress-strain responses to tension and compression, both of which are nonlinear. Their mechanical properties vary with respect to extrusion direction, their deformation under sustained load is time-dependent (they experience creep), and the severity of creep is stress-dependent. Because of these complexities, it is beneficial to create a mechanics-based predictive model that will calculate the material’s response in situations that are too difficult or expensive to test experimentally. Such a model would also be valuable in designing and optimizing new structural shapes. Analysis and prediction of WPC members begins with the time-dependent characterization of the material’s axial and shear behaviors. The data must then be combined with a tool that can simulate mode-dependence, anisotropy, and nonlinear axial stress distributions that vary over the length of a member and evolve with time. Time-dependent finite-element (FE) modeling is the most practical way to satisfy all of these requirements. This paper presents an FE material model that was developed to predict the deflection of flexural members subjected to both quasi-static ramp loading and long-term creep. Predictions were made for six different WPC products, encompassing a variety of polymers and cross-sections. These predictions were compared with experimental testing and the model shows some success, particularly in the quasi-static response. Creep predictions were more accurate for solid polyethene-based materials than polypropylene-based hollow box sections.

Increasing traffic volumes, heavier loads, higher tire pressures, and performance problems with asphalt concrete mixtures under adverse conditions are leading state highway departments to using modified binders to enhance the physical properties of asphalt mix. This paper reports the advantages of modified nanoclays (NC) as asphalt modifiers. Dynamic mechanical analysis, flexural creep stiffness, and flexural tests were conducted on the NC-asphalt nanocomposite. In addition, Fourier transform infrared (FTIR) testing was conducted to evaluate the nature of the interactions between NC and asphalt. Increasing NC concentration in asphalt enhances temperature susceptibility of asphalt, as well as increasing the complex modulus in addition to decreasing phase angle. FTIR experiments indicate a significant change in $\mathrm{Si}─\mathrm{O}$ vibration from NC, indicating strong nonbonded interactions of $\mathrm{Si}─\mathrm{O}$ tetrahedra with asphalt. These changes in $\mathrm{Si}─\mathrm{O}$ vibrations suggest both distortion in $\mathrm{Si}─\mathrm{O}$ tetrahedra as well as stronger interactions between asphalt and NC. Further, X-ray diffraction (XRD) testing results show intercalation of asphalt in clay galleries indicated by an enlarged $d$-spacing of up to 43.17 Å. The $d$-spacing decreases with NC content. These experiments suggest that the addition of engineered nanoclays to asphalt has tremendous potential in tailoring the properties of asphalt based on type of application.

Unconfined compressive strength (UCS) of synthetic biochar mixed clays (BMC) treated with lime-GGBS has been investigated. Biochar utilized in this study was produced from the slow pyrolysis of green waste residue. Treated biochar mixed clays have also been tested for microstructural and mineralogical developments. Results of this study showed that a lime content of 2 wt%, which is much lower than the conventionally used 10 wt% lime for synthetic clay, can be effectively incorporated to improve BMCs. X-ray Diffraction analysis carried out on treated BMCs showed the development of cementitious minerals ($\mathrm{C}─\mathrm{S}─\mathrm{H}$, ettringite). Scanning Electron Microscopy with Energy Dispersive Spectrum (EDS) enabled identification of three separate types of microstructural interactions between biochar and soil particles, namely interface cementation, surface deposition and pore space filling by cementitious minerals, all of which are responsible for the enhancement of UCS with curing.