Journal of Materials in Civil Engineering

A condition survey method was developed to assess more than 1,000 footings in an old oil refinery in the Arabian gulf. A data collection sheet was used to record the exposure conditions during operation, the observed distresses, their degree, and the overall condition of the footings. A classification method was used to categorize the footings according to the observed distresses by applying a weighting system to each distress and degree of damage. The degree of confidence in this method was evaluated and was found to range between 85 and 91%. The results showed that 75% of the footings were exposed to cyclic wetting by seawater or combined attack from cyclic wetting with other pollutants. Footings exposed to water or water associated with pollutants suffered 75% of the total reported distresses. Cracking, delamination, and spalling were the most frequent distresses reported, and together they represented 60% of the total. Poor detailing of the joint between the concrete and the equipment chassis and the use of cement mortar with a high water to cement (w/c) ratio in sealing anchor bolts were found to be responsible for many of the steel corrosion distresses.

The complete stress-strain curves generated experimentally for high-strength plain and fiber concretes confined by transverse ties are reported in this paper. The test parameters include tie diameter, tie spacing, concrete core area, and casting direction of specimens. Test results indicate that the initial tangent modulus and initial Poisson's ratio of the concrete are not affected by confinement. However, confinement enhances both the peak stress and strain at peak stress. Vertically cast confined fiber concrete exhibits larger strain at peak stress and has higher postpeak ductility compared to the corresponding horizontally cast specimen. Vertically cast confined nonfiber concrete also has larger strain at peak stress, but ductility is hardly improved over horizontally cast specimens. Based on test data, an analytical model is proposed to generate the complete stress-strain curves of high-strength concrete confined by lateral ties. The proposed model has been found to agree well with the stress-strain curves generated experimentally.

Tests were carried out to study the influence of set accelerating admixtures on the properties of dry-mix shotcrete, especially its durability. A total of 27 mixtures were shot using two different types of cement (ASTM Type I with silica fume as partial cement replacement and ASTM Type III) and five different accelerators at various dosages. Half of these mixtures were shot with an air-entraining admixture. In addition to the determination of the setting time, the following properties were measured (on the hardened shotcrete): Air void characteristics, compressive strength, drying shrinkage, rapid freezing and thawing resistance and deicer salt scaling resistance. Results indicate that although all accelerators can reduce the initial and final setting times, some of them considerably decrease the durability, particularly the deicer salt scaling resistance. As a rule, better results were obtained with the mixtures containing the Type III cement than with those containing the Type I and silica fume. The tests confirm the importance of the use of an air-entraining admixture to obtain an adequate frost and deicer salt scaling resistance.

Due to their high strength-to-weight and stiffness-to-weight ratios; corrosion- and fatigue-resistance; and overall durability, fiber reinforced composites are increasingly being considered for use in jackets around deteriorating and understrength concrete columns. For this new technology to achieve widespread acceptance, there is a need to develop a solid engineering base for the design and prediction of response of such retrofit and repair schemes. The purpose of this investigation was to develop experimental data, based on a variety of reinforcing fiber types, orientations and jacket thickness, and to develop and/or verify simple design equations to estimate the response of composite confined concrete. Experimental results indicate that composite jackets significantly enhance the strength and pseudoductility of concrete. The proposed expressions for ultimate strength and strain are seen to compare well with experimental data, and a phenomenological model for confinement based on the composite behavior of the confined system is presented. The results of the use of a number of predictive equations are compared with the experimental data.

Slurry infiltrated mat concrete (SIMCON) is a new kind of fiber reinforced concrete with fibers preplaced in a mat form. It is shown in this paper that the mechanical properties of SIMCON such as flexural strength and toughness are improved significantly compared with conventional fiber reinforced concrete, due to the high fiber volume fraction and aspect ratio. Twelve series with a total 36 SIMCON specimens were tested under third-point bending. The effects of fiber volume fraction and fiber mat thickness on flexural behavior of SIMCON were studied in this experimental investigation. A special failure mode, consisting of a major vertical crack and horizontal branches, was observed and is analyzed in this paper.

Application of stress or changes in environmental conditions can cause a material such as concrete or rock to become damaged, thereby affecting the performance of the structure. Because damage processes produce microseismic events called acoustic emission (AE), the growth of damage and the onset of failure can be identified by monitoring AE. In particular, a probability density function of acoustic emission events was used to describe the development of damage. It was observed that more porous or cracked materials displayed a higher AE rate than less porous or cracked materials at the same percentage of the maximum stress prior to failure. This suggests that the AE technique may be applied to diagnose the level of damage in a brittle material and may be useful to select materials for certain applications. Also, the experimental results indicated that the average root-mean-square value from a number of AE signals could be used as a real-time monitoring tool to predict the onset of failure.

At Luleå University of Technology, Sweden, research has been carried out in the area of plate bonding, i.e., the problems that can arise when concrete members need to be strengthened using epoxy-bonded plates. Both comprehensive experimental and theoretical work have been done. In this paper a derivation of the shear and peeling stresses in the adhesive layer of a beam with a strengthening plate bonded to its soffit and loaded with an arbitrary point load are presented. The results from both theory and finite-element analysis show that the stresses are very large at the end of the plate, but they quickly diminish as we move nearer the center of the beam. The magnitude of the stresses is influenced not only by the geometrical and material parameters of the beam, but also by the adhesive and the strengthening material.

This paper presents a general stress-strain equation that expresses stress explicitly in terms of strain in a single continuous curve. It allows various features such as linear-elastic range, upper yield peak, plastic plateau, and smooth strain-hardening portion to be included. Any of these features can be excluded if desired. The shape of the curve described by the equation is identical, with positive and negative strains. The equation may be fitted to experimental data to represent the stress-strain behavior of a material and is therefore useful for describing experimental results in a succinct format. Comparison with experimental results shows that the equation can closely fit the stress-strain curves of steel at various temperatures—at temperatures where distinct yield peaks and plastic plateaus exit; as well as at temperatures where the stress-strain curves are smooth. Therefore the equation can be suitably extended to accurately model the temperature-dependent behavior of steel.