Journal of Materials in Civil Engineering

Adhesives are increasingly being used in civil engineering applications as a means of bonding together similar or dissimilar materials. The prediction of the strength of bonded components is therefore vitally important and different methods are being used to investigate and predict the durability of adhesive joints when they are exposed to hostile environments. The present work reports the results obtained using adhesive joints made from mild steel and two epoxide based adhesives, a model adhesive and a specially devised adhesive formulation, that bonded to steel underwater. These joints were tested using custom designed, accelerated aging test equipment based on the double-torsion joint design and the application of fracture mechanics. The joints were subjected to various constant loads in the presence of water at room temperature. A graphite-gauge technique was also developed to monitor the incubation time for a crack to form and measure its subsequent velocity as a function of the applied fracture energy. Scanning electron microscopy and X-ray photoelectron spectroscopy were also employed to identify the locus of joint failure and assess the performance of the underwater made adhesive joints.

Waste tire rubber constitute a serious worldwide problem due to the lack of landfills and the health hazards associated with these landfills. In addition to the environmental motivation for providing a means of recycling large quantities of waste tire rubbers, the use of tire rubber particles provides a new type of concrete that has unique mechanical and fracture criteria. This paper presents the results of recent experimental investigations on rubber concrete. Chipped and crumbed tire rubber particles were used to replace coarse and fine aggregate with different volume replacement levels. The mechanical and fracture properties of rubber concrete were examined. Quasi-brittle fracture mechanics models are used to determine the effect of incorporating tire rubber particles on the fracture performance of rubber concrete. Finally, some microstructural features of rubber concrete are also reported. It is concluded that the choice of the optimal replacement ratio of the tire rubber particles can yield concretes with desirable strength and fracture toughness criteria for different applications.

In concrete pavements, steel dowels are exposed to a particularly aggressive environment that leads to depassivation and greatly reduces the corrosion initiation stage. Aggressive agents such as chlorides and $\mathrm{C}{\mathrm{O}}_2$ have easy access to the dowels through pavement joints and, consequently, the corrosion performance of the system depends largely on the properties of the steel dowel being used. This study investigates the corrosion performance of several types of steel dowels embedded in concrete and subjected to accelerated corrosion by exposure to 3.5% NaCl solution for $18\text{months}$ . Seven types of dowels were tested: bare carbon steel, stainless steel clad, grout-filled hollow stainless steel, microcomposite steel, carbon steel coated with bendable epoxy, and carbon steel coated with nonbendable epoxies. Half-cell potential, polarization resistance, visual inspections, and microscopic investigations by scanning electron microscopy were carried out to evaluate their corrosion performance. Results show that microcomposite steel dowels exhibit greater resistance to corrosion propagation than carbon steel dowels, but lesser than stainless clad and stainless hollow bars. In epoxy-coated bars, corrosion occurred at a few localized defective areas, generally at holidays and edges of bar ends. No significant difference was observed between nonbendable and bendable epoxy-coated dowels.

This study presents an approach to help understand moisture damage mechanisms and to evaluate the effects of hydrated lime as moisture damage resisting agents. To this end, various performance testing of hot mix asphalt (HMA) samples induced by moisture damage and several fundamental property measurements (stiffness, strength, toughness, and bonding energy) of mixture components were conducted. Testing data and analyses demonstrated that hydrated lime contributed to moisture damage resistance due to synergistic effects of mastic stiffening, toughening, and advanced bonding characteristics at mastic-aggregate interfaces. However, a well-controlled lime treatment is required to maximize distribution and dispersion of lime particles on aggregate surfaces. In addition to the clear effects of hydrated lime, mineral filler in the HMA samples showed its effects on damage resistance in an early stage of moisture damage due to substantial stiffening-toughening effects from filler addition. Properties and damage characteristics of mixture components measured in this study were related to macroscopic performance behavior of asphalt concrete samples, which infers that the approach herein based on the mixture components can be effectively used to evaluate (or predict) moisture damage of asphalt mixtures and pavements with much less effort.

This paper presents the results of a multiobjective laboratory study on scaling resistance of ternary concrete containing Class C fly ash (FA) and silica fume (SF). Several experimental variables were included in the research and statistical analysis was performed to examine specific effects of each of the variables on the amount of scaling. The first variable studied was the relative amount of FA (20 or 30% by mass of total cementitious materials) and SF (5 or 7% by mass of total cementitious materials) used in the ternary cementitious system. The second variable evaluated was the type of initial curing regime. The curing regimes compared included air drying, $3\text{days}$ under wet burlap, $7\text{days}$ under wet burlap, and application of curing compound for $7\text{days}$ . The last variable assessed was the time of exposure to freeze-thaw (F-T) cycles in the presence of deicing salt, which included testing at either early age (14, 17, or $21\text{days}$ depending on the initial curing regime) or at late age $\left(90\text{days}\right)$ . The major finding from the research conducted was that the ternary mixtures containing 20% FA are much less prone to scaling than the mixtures with 30% FA. The mixtures with 20% FA were also found to be less sensitive (in terms of scaling resistance) to the initial curing conditions than mixtures with 30% FA. The late exposure to F-T cycles in the presence of deicing salt did not significantly improve the scaling resistance of any of the evaluated mixtures, most probably due to differences in scaling mode associated with the exposure times evaluated.

The current understanding of the mechanics of bond resistance at the interface between concrete and plain and deformed steel bars is reviewed briefly along with the influence of corrosion on the phenomenon. Some of the available research on analytical models in both corroded and uncorroded steel bars is also reviewed. The influence of some of the significant parameters influencing the behavior of corroded bars, such as the concrete strength, crack width, extent of rebar corrosion (measured by mass loss), concrete cover thickness, bar diameter, and the loss of rebar lugs is reviewed. In addition, a preliminary framework is presented for design of reinforced concrete for durability against deterioration of bond due to steel rebar corrosion. A framework for design of structural concrete for durability against deterioration of bond at the steel-concrete interface due to corrosion of rebars is proposed. The technical note also stresses the need for more research on the above and other parameters influencing the deterioration of bond due to corrosion, before establishing a reliable design method using a semiprobabilistic approach in the design of structural concrete for other phenomena.