Journal of Materials in Civil Engineering

An experimental study was conducted to investigate the composite action of foamed and lightweight aggregate concrete. Thirty-six push-out tests were performed on concrete-filled steel hollow sections of square and circular shapes. Bond strength between steel and concrete in composite sections depends on several factors. The shape of the cross section, the age, and the type of concrete were considered in this study. The test results reported show that lightweight aggregate concrete offered higher bond strength than normal concrete, and the strength of bond in foamed-concrete–filled specimens was about 40 of the strength in normal-concrete–filled specimens. The experimental results also show that the load-slip behavior of foamed and lightweight aggregate concrete–filled specimens is similar to that of normal-concrete–filled specimens.

An experimental program was conducted to study the effect of temperature and galvanization on the mechanical properties of cold-formed steel members typically used in constructing hydroelectric transmission towers. Two types of steel were used in this program, ASTM A715 Grade 60 and CSA G40.21-300W. A series of 144 tension coupons was cut from steel members type ASTM A715 Grade 60 and another series of 48 tension coupons was cut from steel members type CSA G40.21-300W. Coupons cut from both ungalvanized and galvanized members were tested according to ASTM standards at temperatures ranging from −50°C to room temperature. In addition, semiguided bend tests were performed to check the ductility of the materials, and Charpy V-notch impact tests were conducted to study the effect of low temperature on toughness. The test results showed that the processes of hot-dip galvanizing and cold forming, coupled with low temperatures resulted in an increase of the yield and ultimate strengths, as well as in the modulus of elasticity of the materials. These processes, however, resulted in a reduction of their ductility. The degree to which these processes affected the mechanical properties depended on the type of steel. The mechanical properties of the CSA G40.21-300W steel were affected a lot more by these processes than were those of ASTM A715 Grade 60 steel.

The effect of reinforcement corrosion on the flexural strength of a uniformly loaded and simply supported one-way slab was investigated. In addition to the flexural strength, the effect of different degrees of reinforcement corrosion on the deformational behavior, ductility, and the mode of failure of the slabs were also evaluated. The critical level of reinforcement corrosion that renders the strength contribution of steel negligible was evaluated by comparing the strengths of slabs with highly corroded reinforcement with the strengths of plain concrete slabs. In order to induce different levels of reinforcement corrosion, a calibration curve establishing a relationship between the duration of the impressed current and reinforcement corrosion was prepared. The magnitude of reinforcement corrosion was measured as gravimetric loss in weight of the steel bars. The results indicate a sharp reduction in the ultimate flexural strength of slabs with an up to a 29 reinforcement corrosion; thereafter, the strength decreased at a somewhat reduced rate with further increase in reinforcement corrosion. The ultimate deflection of the slabs decreases with an increase in the magnitude of reinforcement corrosion, leading to a marked and progressive reduction in the ductility of the slabs. Furthermore, the strength of plain-concrete slabs and those reinforced with steel bars of less than 60 corrosion was almost similar.

A pilot study was undertaken on the use of lignite-based bottom ash as a fine aggregate in structural grade concrete. Bottom ash is combined with portland cement, crushed limestone coarse aggregate, and water to produce concretes with a uniform slump of 100 mm (4 ± 1/4 in.). Four different mixes with cement contents ranging from 297 to 475 kg/m ³ (500 to 800 lb/yd ³ ) are utilized. The bottom ash concretes are studied for fresh properties, hardened characteristics, and long-term durability. The engineering characteristics of mixtures made with bottom ash are compared with those of conventional concretes in order to evaluate the effectiveness and suitability of bottom ash as a viable fine aggregate in portland cement-based mixtures. Laboratory test results conclude that the inclusion of bottom ash increases the demand for mixing water in obtaining the required workability. As a consequence, both fresh and hardened properties are impacted, particularly for mixtures of low cement content. When a water-reducing admixture is used, the engineering properties of bottom ash concretes are similar, and in most cases superior, to those of control concretes.

The possibility of constructing a floating island using air/cement/water (ACW), a mixture of water glass solution and foamed cement paste, which shows a flash-setting property and is lighter than water, is studied. The following results obtained through a series of laboratory tests and model placement tests show a high applicability of ACW for floating island construction: (1) gel time of ACW can be controlled by the quantity ratio of water glass and cement; (2) seawater is also usable, however a larger amount of water glass is needed than for tap water for a given gel time ACW; (3) strength increases linearly with the logarithm of elapsed time, and depends on dry density; (4) viscosity of ACW before gelation is too low to prevent segregation, which can be controlled by bentonite addition; (5) permeability of ACW is dependent on dry density; (6) addition of coal fly ash lowers early strength but enhances long-term strength, and is usable as a partial substitution for the cement; (7) ACW can be directly placed on the water uniformly, and the placed mass on the water settles by its own weight; (8) this settlement ceases within 10 days; and (9) water intake of 30–40 takes place during the flotation, however, this is limited to the underwater part at the placement. This floating island construction is still at the experimental stage; however, the properties of ACW suggest a variety of actual usage such as for structural fills overlaying on very soft ground or embankments for emergency.

This study evaluated several promising laboratory aging methods for simulation of field aging of asphalts. The rheological properties of an asphalt binder after aging in the thin-film oven test (TFOT) and rolling thin-film oven test (RTFOT) processes performed at three different temperatures were compared with those after the California tilt oven, Strategic Highway Research Program (SHRP) pressure air vessel and actual field aging. Nine different modified asphalts made with five different types of polymer modifiers were also evaluated after being subjected to the TFOT and RTFOT at three different temperatures. The results indicate that the RTFOT aging process performed at a temperature of 185° can simulate a 1-yr field aging effect, and the California tilt oven process for a duration of 168 h can simulate 8-yr field aging under typical Florida conditions.

This study presents a state-of-the-art review of crumb-rubber modified (CRM) asphalt concrete technology and describes the results of viscosity measurements of CRM asphalt cements using a Brookfield viscometer. Literature was reviewed in relation to both the wet process (i.e., mixing of the crumb rubber with the binder prior to mixing with the aggregate) and the dry process (i.e., simultaneous mixing of the crumb rubber, the binder, and the aggregate). In wet processes, the reaction that takes place between rubber particles and asphalt binder is not chemical in nature, but rather a diffusion of the light aromatic components of the binder into the crumb rubber. This results in a reduction in the viscosity of the binder, which depends on the type of the binder, the type of the rubber, the mixing temperature, and the mixing energy (i.e., time). In dry processes, the crumb-rubber particles replace aggregate particles in the asphalt concrete mix, while due to the limited mixing time allowed, no significant reaction takes place between the crumb rubber and the binder. Brookfield viscometer testing of the CRM binder was conducted following a variation of the ASTM standards D2196-86 and D4402-87. Three binders were tested, namely AC-5, AC-10, and AC-20, with CRM percentages of 0, 3, 5, 7, 12, and 18. The CRM particle size was finer than sieve size No. 80. The viscosity of the CRM asphalt cement initially decreased in time, until the temperature of the crumb-rubber chips reached that of the binder. This took place in approximately 30–40 min, when a minimum viscosity value was reached, called the “stabilized” viscosity. The high-percentage CRM, however, experienced a linear increase in viscosity with time at a rate of approximately 180 cP/hr as mixing continued past the stabilized viscosity.

Results of experimental and theoretical studies of the micromechanical behavior of marble under compression are presented. A cylindrical marble specimen was submerged in a molten metal alloy under compression and the alloy was driven into voids and fractures by pore pressure. The alloy was solidified at a certain stage of the experiment in order to preserve the geometry of microcracks as they existed under load and to distinguish these cracks from those generated during sample polishing. With a surface tension of 400 mN/m, the alloy could penetrate into flat cracks with apertures as fine as 0.08 μm under a pore pressure of 10.3 MPa (1,500 psi). This technique also facilitated observation of the microcracks in three dimensions. A comprehensive image analysis was performed on the cracking pattern developed in the marble samples. The propagation of the cracking process was modeled using nonlinear discontinuous deformation analysis (DDA) with a finite-element meshed block system.

A building materials durability model (BMDM), developed in earlier work, is a framework that encompasses environmental stimuli, material damage relationships, performance criteria, and repair decision making to produce predictions of long-term performance of building materials. The framework of the model is able to accommodate a wide variety of building materials used in different applications. The current study applied the model to two cladding materials for buildings; aluminum and paint. Environmental stimuli included temperature, moisture, and impact of corrosive chemicals. The material damage models use environment as an input, and predict degradation of the cladding material. The rates of degradation in the mathematical models are tuned to fit existing data available in the literature. Quality of the cladding is calculated during the simulation, and repairs are triggered when quality falls below a predetermined threshold. Initial quality of the material and the repairs contribute to the overall cost. The results show that this general modeling tool gives the engineer a vehicle for assessing different materials, different environments, and the consequences of different repair strategies in making durability design decisions.