Journal of Materials in Civil Engineering

Cracks in concrete propagate preferentially along cement-aggregate interfaces. Therefore, these interfaces act like weak links. The fracture mechanical behavior of the interfaces can be described quantitatively by means of the specific fracture energy G _F , which is obtained from the load-displacement curve of the wedge-splitting test. The G _F values of the selected sandstone-matrix and limestone-matrix composites varied between 6 and 18 N/m, although the specific fracture energy of the matrix was about 80 N/m; this means that the resistance against crack propagation of interfaces between aggregate surfaces and matrix is only 1/6th of the cement-matrix resistance. This demonstrates the different behavior of the interfaces compared to the matrix. Testing composite specimens of different dimensions showed that there is only a small size effect in the fracture surface area range of 22.5–85 cm ² (ligament length approximately 4.8–8.4 cm). In the range of 22.5–45 cm ² (ligament length approximately 4.8 cm), an augmentation of the fracture surface area leads to an increase of the G _F value of the cement matrix. Above 45 cm ² (ligament length approximately 4.8 cm), G _F remains almost constant.

The water potential that controls moisture movement in concrete is a kind of stress that also causes concrete to shrink and to expand. An explicit equation that shows the relationships between water potential and drying shrinkage was derived through a mathematical process. In this study, only two micromechanisms that are valid when the relative humidity is over 50% are considered among the three shrinkage mechanisms. The theory developed shows that the magnitude and the shape of the drying-shrinkage curve depends on the compressibility of the ingredients, the amount of aggregate, and the pore structure of the cement. The relationship between drying shrinkage and water potential is found to be a logarithmic curve. Thermocouple psychrometers are embedded in a concrete slab to measure the water potential. The test results prove the validity of the theory, and show how to use the derived equation.

Laboratory investigations were performed to design four high-volume fly ash roller-compacted concrete mixtures. The amount of fly ash was fixed at 63% of the total cementitious material. Two mixtures (one air-entrained and one non-air-entrained) had a cementitious material content of 12% (as a proportion of the total mass of dry materials), and two mixtures (one air-entrained and one non-air-entrained) had a cementitious material content of 15%. The apparatus used to prepare the cylindrical specimens required for the tests was specifically designed for this purpose. In this apparatus, the concrete is placed in a cylindrical mold that is vibrated laterally while a longitudinal compressive force is applied to the concrete. Each mixture was tested for strength, absorption, permeability, determination of the air-void characteristics, and frost resistance. The frost resistance of air-entrained concretes (tested according to Procedure A of ASTM Standard C 666) was found to be very good, irrespective of the cementitious material content. These concretes contained only a small number of irregularly shaped compaction air voids. The value of the air-void spacing factor was 250 ± 5 μm for the air-entrained concretes, and only slightly higher at 309 μm and 393 μm for the non-air-entrained concretes. The latter concretes also showed adequate frost resistance. Notwithstanding these conditions, the use of air entrainment is recommended for roller-compacted, high-volume fly ash concretes.

Acoustic-emission (AE) technology is considered a potential new testing method to monitor the integrity of concrete materials. This study is devoted to the investigation of the AE Kaiser effect in fly-ash cement mortar (FACM) under uniaxial compression. The major experimental parameters include the amount of cement replaced by fly ash, curing time, compressive strain and stress, loading pattern, and loading rate. The test results showed that the AE Kaiser effect existed in FACM specimens up to 80% of its ultimate strength. Good correlation between the variation of the AE signals and the compressive strains was observed. In addition, the results indicated that the AE Kaiser effect existed in FACM specimen during different curing periods of three, seven, 14, and 28 days. These observations suggested that the AE Kaiser effect has good potential to be used as a new tool to monitor the loading history of concrete materials.

Cement kiln dust (CKD) is a waste by-product of portland cement manufacture. This material poses a health hazard, storage problem, and a potential pollution source. Consuming such material in civil engineering works to upgrade marginal materials would help solve some of these problems. Dune sand, an abundant marginal soil, was treated by varying amounts of CKD. In addition, 100% CKD was tested. Compacted specimens were tested for unconfined compression (UC) after seven-, 28, and 90-day curing periods at different temperature levels. Further testing was conducted for specimens with CKD percentages that gave satisfactory results for road subbases. These tests included durability, the California bearing ratio (CBR), and split tension. The test results indicated that on the basis of utilization, CKD between 12 and 50% may be satisfactory. Specimens of 75% and 100% CKD gave relatively high strengths but failed the durability requirements.

The use of fiber-reinforced composite materials for the construction and rehabilitation of civil engineering structures is relatively new. Structural members are routinely joined by bolted connections. Bolted connections are relatively easy to assemble and maintain, and are capable of transferring the high loads that typically occur in civil engineering structures. Currently there is a serious lack of knowledge on the behavior and design of bolted connections for fiber-reinforced composites. In light of this, a comprehensive experimental and analytical investigation was conducted at the University of Manitoba to study the behavior of bolted connections in composite materials appropriate for civil engineering applications. A total of 102 single-bolt connections were tested up to failure. The various parameters investigated were the width of the structural member, the edge distance, the thickness, and the direction of the fibers with respect to the applied load. The experimental program also included comprehensive material testing to determine the various in-plane material properties. This paper discusses the experimental program, test results, and various modes of failure as affected by the foregoing parameters. From the test results an analytical model and design procedure were developed as proposed in a companion paper.

The use of fiber-reinforced composite materials in civil structural applications is relatively new and there is a serious lack of information on the behavior and design of the bolted connections normally used for structural members. As a result, a comprehensive experimental and analytical investigation was conducted at the University of Manitoba to study and determine the behavior of bolted connections in composite materials used for civil engineering applications. Based on the research findings and observed behavior, a design procedure is introduced, which accounts for material orthotropy, pseudoyielding capability, and other factors that influence bolted-connection behavior. The proposed model is capable of predicting the ultimate capacity and the mode of failure of the connections. Because of the generic nature of the model, the design guidelines can be applied to a multitude of composite material systems. Due to the model's simplicity, the proposed design procedure is ideal for implementation in design codes.

The need to develop new materials and techniques capable of rapidly and cost-effectively rehabilitating infrastructure components motivated this study. Corrosion is a major cause of deterioration in civil infrastructure, especially steel bridges, with consequences ranging from the progressive weakening of structural elements due to cracking and loss of section, to sudden collapse. The high strength-to-weight and stiffness-to-weight ratios of composites make them attractive for use in infrastructure rehabilitation. In addition, composites have advantages such as high chemical and corrosion resistance, fatigue resistance, design flexibility, and ability to be tailored to match specific design requirements in different directions simultaneously. However, the ultimate success of the strategy depends on the durability of the bond between the composite and the base steel. Durability of the bond and the composite-steel system is investigated through the wedge test. It is shown that S-glass-based composites show the maximum durability, and it is proposed that a hybrid glass-carbon composite system be used to optimize durability and performance attributes.

To control the effect of concrete expansion or contraction on the integrity of concrete bridge structures, the thermal coefficient of expansion of concrete is often incorporated into design equations. Current practice is to use the value recommended by the Association of American State Highway and Transportation Officials of 11 parts per million per °C (6 parts per million per °F) change. Historically this has been used without considering the effect of local material properties on the overall expansion of concrete. This paper summarizes research findings on the thermal behavior of structural bridge concretes in Iowa. The thermal coefficient of expansion of limestone aggregates, gravel aggregates, mortar, corresponding limestone aggregate concretes, and gravel aggregate concretes were determined in the laboratory. Laboratory results were compared to actual bridge expansion data from field studies and the results from an empirical equation for determining concrete expansion. Results of the laboratory study compared very favorably to field data and results from the empirical equation. Results also indicated that the coefficients of expansion obtained in this study were lower than the Association of American State Highway and Transportation Officials suggested design value. These lower values of thermal coefficient of expansion affect the design length of integral abutment bridges in Iowa.

Corrosion of steel in concrete is a major concern. The use of alternate, noncorrosive reinforcement such as fiber-reinforced plastic (FRP) bars and tendons has, therefore, received much attention lately. There is limited information, however, with respect to the use of two-dimensional (2-D) FRP grids as reinforcement in concrete slabs. In the research reported here, the behavior of concrete slabs reinforced with FRP grids is compared to that of a slab reinforced with steel grid. Slabs were subjected to transverse loads and the load versus load point displacement plots were obtained. The influence of concrete strength and the use of fiber-reinforced concrete were investigated. Strains were recorded at various grid locations. The ultimate loads supported by slabs reinforced with FRP were equal to or higher than that supported by the companion slab reinforced with steel. It was observed, however, that because of the brittle nature of fracture in the FRP, slabs reinforced with such grids were less energy absorbing than one reinforced with steel. In this context, the use of fiber-reinforced concrete appears to be promising. The ultimate loads supported by slabs were compared to those predicted by the various code equations. It appears that not many changes are needed to these equations when applying them to slabs reinforced with FRP grids.

Polyurethane foams have been used for their shock-absorption properties in various packaging applications. In many lightweight structural applications, polyurethane foams are used as the core material in sandwich beams or in panel construction. The mechanical properties of these foams have come under increased scrutiny because of their application to nuclear-waste shipment packages, and their use as “bone simulants” in testing orthopedic implants. This paper describes a number of tests performed on polyurethane foams of various densities to understand their tensile fracture characteristics. Uniaxial tension, torsion, and Flexure tests were conducted to study size effect and other fracture-related phenomena. Nonlinear fracture phenomena were studied using optical microscopy and holographic interferometry at the microscopic and macroscopic level. Uniaxial tensile tests show linear elastic response leading to brittle failure. However, other experiments demonstrate nonlinear phenomena such as the existence of a fracture process zone and the demonstration of a size effect less than that predicted by linear elastic fracture mechanics. Factors affecting various mechanical properties were examined with the existing theories of solid mechanics.

In this paper, we evaluate the logistic differential equation as a mathematical method for representing changes in asphalt properties during pavement aging in the field. We chose the logistic function because it appears to be theoretically consistent with the micromolecular model of asphalt aging. This choice was validated, because we did find that the logistic function gave a close fit with experimental data from a variety of pavement-aging studies. The logistic function allows us to quantify two essential characteristics of asphalt aging: the rate of aging and the ultimate degree of change in asphalt properties due to aging. Therefore, we believe that the logistic equation is a potentially powerful tool for studying asphalt aging, because it provides a method for consolidating aging data in an accurate and useful format. The importance of such a tool lies in its use for studying the relative effects on the aging process of factors such as asphalt type, void level, and climate. An understanding of the role of asphalt type on the aging process is crucial if we are to develop more durable asphalt pavements.

Results from an experimental investigation of the compression-creep behavior of thermoset-pultruded fiberglass-reinforced-plastic angle sections are presented. Tests were carried out on three 152 mm (6 in.) angle stubs made of isophtalic polyester resin with 53–59% E-glass fibers in weight. Each stub was instrumented with twelve 5-mm-long gauges in order to assess the variability of the strain measurements on the faces of the shape. Coupon-creep and stub tests were carried out simultaneously, and results of the two series of tests were compared to validate the use of coupon tests to predict creep deformations of full-sized members. The total duration of the tests was 2,500 h in creep and 250 h in creep recovery. Average predictions using Findley's power law with creep parameters determined from the stub tests and coupon tests agree with one another and with the actual creep strain measurements on the stubs. This indicates that there is no real benefit in making detailed creep-strain measurements on stub angles. The creepocity (ratio of creep strain to initial strain) measured on angle stubs is relatively small (14.4% after 2,500 h at a stress level averaging 45% of the proportionality limit) and should not cause geometrical integrity problems at the stress level considered. Finally, Boltzman's superposition principle was used to compare the experimental creep-recovery results with predictions from Findley's model, and agreement was also observed.

Expansive alkali-aggregate reactions (AAR) are a frequent and worldwide cause of poor durability in Portland cement concrete. In plain concrete, deleterious AAR generally results in expansion and map-cracking, but in reinforced or prestressed concrete cracks may show a linear relationship to reinforcement. Expansion may lead to buckling, extrusion of joint filler, and displacement of equipment set in concrete. White deposits of silica gel, rims surrounding aggregate particles, pop outs, loss of strength, and decrease in modulus of elasticity may occur. Damage may be so severe that concrete has to be replaced, but less drastic remedial measures have been tried when the damage is less severe. Aggregates likely to cause expansive AAR may be identified by petrographic methods, length-change tests, and examination of deteriorated concrete made with similar materials and exposed to similar conditions. Potential expansion due to AAR may be minimized by reduction of the available supply of alkalies in concrete, use of mineral and chemical admixtures, design to limit wetting, and the beneficiation of aggregates. Classification of the types of reaction and mechanisms of expansion are reviewed.

When reinforcing cages for reinforced concrete structures are fabricated by robots using tack welds to improve productivity, the ductility and strength of the rebars are affected. This paper presents information on the effect of welds on the mechanical properties of rebars under uniaxial monotonic loads. It is found in the study that welding reduces the ductility and strength of rebars, but that annealing is not necessary from the standpoint of reinforced concrete design.

No-fines concrete is defined as a type of concrete from which the fine aggregate component of the matrix is entirely omitted. The aggregate is of a single size and the finished product is a cellular concrete of comparatively low strength and specific weight. The cellular nature eliminates capillary attraction and provides greater thermal insulation and water permeability than exists in conventional concrete. The advantages of no-fines concrete for different construction purposes have long been recognized. The post–World War II era has experienced the extensive use of no-fines concrete for load-bearing walls in single and multistory buildings, retaining walls, and ground-drainage slab systems. This paper traces the development and applications of no-fines concrete for building and other nonpavement purposes. The pavement applications are introduced in a companion article published in the ASCE Journal of Transportation Engineering .