Journal of Materials in Civil Engineering

Although the potential of continuous fiber reinforced polymers (FRPs) was recognized more than 50 years ago, bottlenecks such as vulnerability to static fatigue, ultraviolet radiation, alkaline environment, etc., continued to restrict their use as a construction material. Extensive research across the world during approximately the last 25 years has led to a better understanding of properties and behavior of the FRPs under different conditions. Given their lightweight, noncorrosive, and nonmagnetic nature and their high tensile strength, FRP composites are being used as reinforcement in concrete, especially in prestressed concrete construction, anchors for slope stabilization, and use in special structures such as high-speed linear motor railway tracks, MRI units of hospitals, and repair and rehabilitation works. An attempt has been made in this paper to comprehensively put together the various aspects of FRPs, including their structural and durability characteristics, the ongoing research in the areas related to their utilization as a reinforcing material for concrete structures, and the application of FRP sheets in rehabilitation of deteriorated concrete structures. Though issues related to the manufacture of FRP composites and design procedures have not been considered in detail, they have been included for information and completeness. The paper also presents the current thinking on the design and construction procedures using FRP material in conjunction with concrete and provides a brief discussion of some of the documented applications of FRP composites—rods and sheets—as reinforcement in concrete construction. It may also be mentioned that the paper is largely based on the case studies and research work carried out in Japan; appropriate references to related work in other parts of the world are also included, though in principle there is very little difference in the approaches being adopted across the world.

Dense friction course asphalt (DFC) has been used since the late 1980s as the premium surface course on the Ontario Ministry of Transportation’s (MTO) major highways. It was designed for a 12–15 year service life with minimum maintenance, primarily to resist excessive rutting problems associated with heavy commercial vehicles. However, in many cases, major rehabilitation of DFC highways was necessary within 4–7 years of paving. Failures occurred through abundant loss of fine aggregate, potholing, raveling, and occasionally delamination. MTO attempted to solve the problem by increasing the asphalt cement content of DFC, a procedure that proved costly and inefficient. This study used a $3^2$ factorial experimental plan to assess the effects of the asphalt cement content and the addition of either a liquid chemical or powdered antistripping agent on the durability of DFC mixtures. In addition, a field investigation on Highway 401 was conducted. It was found that stripping of aggregates due to the action of water is the major cause of DFC failures, and that the addition of an appropriate antistripping agent was effective in inhibiting the problem. Construction related problems, such as lift thickness variations, lack of compaction, and mix segregation, were also identified as additional causes of DFC failures. Although initial research on antistripping agents dates back around 40 years, the industry needs a fresh look at this issue.

Corrosion of steel cables and reinforcing steel in concrete structures is a major cause of structural deterioration. The current methods for corrosion detection suffer from several significant drawbacks. In this paper, a nondestructive evaluation technique is developed that is capable of determining the location and severity of corrosion of embedded or encased steel rebar and cables. This technique utilizes time domain reflectometry (TDR), which has been traditionally used to detect electrical discontinuities in transmission lines. By installing a sensor wire alongside the steel reinforcement, the reinforcement can be modeled as an asymmetric, twin-conductor transmission line. Physical defects of the reinforcement, such as abrupt pitting corrosion, general surface corrosion, and grouting voids, will change the electromagnetic properties of the line. They can be modeled analytically, and identified using TDR. TDR measurement results from several fabricated bridge cable sections with built-in defects are reported. Based on the initial results, the TDR corrosion detection method has proven to be more robust than the existing methods, because it allows one to detect, locate, and identify the extent of corrosion damage.

The styrene-butadiene-styrene (SBS) triblock copolymer was used to modify the asphalt binder. The morphology and engineering properties of the binders were investigated using transmission electron microscopy (TEM), rotational viscometer, and dynamic shear rheometer. The morphology of polymer-modified asphalt was described by the SBS concentration and the presence of microstructure of the copolymer. When the SBS concentration increased, the copolymer gradually became the dominant phase, and the transition was followed by a change in engineering properties of SBS-modified asphalt. Results from TEM showed that depending on the asphalt and copolymer source, a variety of morphology can be found. The SBS-modified binders might show a continuous asphalt phase with dispersed SBS particles, a continuous polymer phase with dispersed asphalt globules, or two interlocked continuous phases. The optimum SBS content was determined based on the formation of the critical network between asphalt and polymer. Because of this network formation, the binders showed a large increase in the complex modulus that indicates resistance to rutting. At low SBS concentrations, the Kerner model was found to be appropriate to estimate the rheological properties of SBS-modified asphalt. An adapted Kerner equation was proposed in this study to predict the complex modulus of modified asphalt at high SBS concentrations.

This paper discusses some important engineering properties of plain concrete for a wide range of compressive strength. A large volume of selected experimental data has been collected from existing literature and then analyzed. Particular emphasis has been given to studying the effects of concrete strength on the modulus of elasticity, tensile strength (flexural and splitting tensile), and Poisson’s ratio of concrete. Study on the effect of the size of specimens on the compressive strength and modulus of elasticity of concrete has also been included. The adequacy of some of the familiar relationships for predicting the modulus of elasticity and tensile strengths of concrete has been critically examined, and suitable expressions are suggested to cover concrete strength up to 120 MPa.

Pavement rehabilitation and reconstruction generates large quantities of reclaimed asphalt pavement (RAP) aggregate, and recycling into new asphalt paving mixtures is the predominant application. RAP acceptance in road bases and subbases has been limited, because of the lack of laboratory and field performance data. In the Sultanate of Oman, recycling of pavement materials is not practiced. A previous study conducted at Sultan Qaboos Univ. indicated that RAP-virgin aggregate mixtures could be utilized in the subbase layer rather than in the base course. This paper presents the results of a laboratory evaluation of cement stabilized RAP and RAP-virgin aggregate blends as base materials. Compaction and unconfined compressive strength tests were conducted on the following RAP/virgin aggregate mixtures: 100/0, 90/10, 80/20, 70/30, and 0/100%. Samples were prepared using 0, 3, 5, and 7% Type I portland cement and were cured for 3, 7, and 28 days in plastic bags at room temperature. A pavement design analysis of using various cement stabilized RAP-virgin aggregate mixtures as base materials was also undertaken. Results indicate that the optimum moisture content, maximum dry density, and strength of RAP will generally increase with the addition of virgin aggregate and cement. Longer curing periods will yield higher strength results. The ability of RAP aggregate to function as a structural component of the pavement is more pronounced when it is stabilized with cement rather than when blending with only virgin aggregate. A 100% RAP aggregate should not be recommended for use as a base material unless stabilized with cement. Cement stabilized RAP-virgin aggregate mixtures seem to be a viable alternative to dense-graded aggregate used in road base construction.

It has been indicated that the dynamic modulus for hot-mix asphalt will be included as a means of material characterization in the forthcoming AASHTO 2002 Guide for Design of Pavement Structures as well as the Superpave performance prediction system. One candidate model being considered for predicting the dynamic modulus includes an input for binder viscosity. In this model, the temperature susceptibility of the binder can be characterized using two parameters—viscosity-temperature susceptibility (VTS) and A (intercept). A simple method, given here to predict the parameters for a binder based on conventional test results, would allow the practicing engineer to derive the VTS and A parameters given any combination of penetration and viscosity tests for the respective binder. The first part of this method includes a derivation of a mechanistic-empirical method for predicting the viscosity of a binder as a function of the penetration value. The second part includes a least-squares method by which the user can enter their laboratory data to calculate the VTS and A parameters for the binder.

This paper presents an experimental study on the potential applications of the fiber-reinforced engineered cementitious composite (ECC) in concrete slabs, such as concrete bridge decks and pavements. It is recognized that cracking due to concrete shrinkage and temperature gradient in the transverse direction in concrete slabs strongly influences the fatigue service life of the slabs. In the present study, attempts at localizing cracks, especially shrinkage cracks, into designated strips, where ECC material with strain-hardening and high strain capacity (up to 5%) and high fatigue crack resistance behavior is used, were carried out. As a result, while microstructure damage exists in the ECC strip, the concrete remains intact. This is demonstrated by simulating the shrinkage in concrete under restrained conditions as tensile load acting on a specially designed specimen. Experimental results show that it is possible to achieve the targeted deformation mode with a certain design on the ECC/concrete interfaces and a certain curing period on the ECC-concrete composite slab. Due to the special material properties of ECC, the strain energy produced by shrinkage (under restrained conditions) of hardened cement and temperature changes can be released by the high strain ability of ECC material so that cracking in plain concrete can be avoided. Thus, the fatigue durability of concrete slabs can be improved, resulting in a longer service life. The proposed design concept may be implemented by placing ECC as periodic special joints or “ductile strip” between stretches of concrete slabs. By replacing standard joints, common deterioration (e.g., D-cracking) problems associated with joints may be also eliminated.

Tests on large diameter specimens using a split Hopkinson pressure bar (SHPB) facility are essential to obtain representative dynamic characteristics of engineering materials such as rocks, concrete, and steel fiber-reinforced concrete (SFRC). However, direct application of the conventional SHPB technique to measure the dynamic behavior of these materials has serious limitations, especially if the size of the specimen is relatively large. The background to material testing using the SHPB facility is explored in this paper. The experimental technique and analytical waveform analysis, together with their attendant problems, are presented. Waveform oscillations and nonhomogeneous deformation of brittle specimens are major problems in test data originating from the conventional SHPB technique. These problems are identified and addressed; techniques for circumventing such problems are described. The design and commissioning of a short-length 75 mm diameter SHPB is presented. To overcome a number of problems associated with such a large diameter short length facility, a novel loading method for eliminating oscillation and maintaining uniform deformation of specimens is proposed. Experimental waveforms are presented for brittle engineering materials to underscore the validity of the technique.

The effectiveness of time-delay artificial neural networks (TDANNs) as highly nonlinear mapping tools for simulation of hysteresis stress-strain (σ-ε) response of geomaterials under repeated reversal loading is investigated. A nonlinear recursive simulator containing the developed TDANNs was designed to enable forecasting of complete σ-ε curves from the knowledge of only the initial σ-ε condition of the tested material. Theoretically-obtained data were used to derive the TDANNs, and simulations were performed to validate the proposed approach. Advantages, limitations, and method of enhancement of the approach are presented.

In this work, the abrasion resistance of high volume fly ash concrete was investigated. Concrete mixtures containing a large amount of fly ash replacing the cement in mass basis at 50 and 70% were prepared with various water-cementitious material ratios. A specially selected superplasticizer was employed to maintain the workability of the concrete. Volume loss of the specimen was considered as the abrasion value measured using a Dorry abrasion machine. Comparisons were made between normal portland cement (NPC) concrete and fly ash concrete. Comparisons were also made between fly ash concretes with 50 and 70% replacement. Investigation results have shown that the abrasion resistance increased as compressive strength increased. Analysis of the results showed that, for high strength grades (>40 MPa), the abrasion resistance of high volume fly ash concrete with 70% replacement with cement was found to be higher than that of counterpart control NPC concrete and concrete made with 50% fly ash. Superplasticizer and curing conditions have no significant influence on the general trend of the abrasion of concrete studied.