Journal of Materials in Civil Engineering

The use of heat straightening to repair damaged steel structures has gained popularity in recent years. However, applications have been limited due to concerns related to degradation of material properties after repair. Most research has been limited to small undamaged plate specimens where only one to three heats were applied. The purpose of this paper is to report on a study in which structural members were damaged and completely repaired by heat straightening, after which material properties were investigated. The research data indicate that heat straightening does affect mechanical properties of steel. Yield stress may increase by as much as 20%, especially in the vicinity of the apex of vee heats. Tensile strength also increases but at only half the rate of yield stress. The ductility as measured by percent elongation may decrease by one-third, and the modulus of elasticity may decrease by over 25% in some heated regions. A portion of this study included the evaluation of the effect of degree of damage on material properties after heat straightening. Damage with maximum strains up to 100 times the yield strain were repaired, and material properties were compared to members damaged with much smaller strains. The degree of damage had a minimal effect on the material properties of heat-straightened steel. Some members were damaged and completely heat straightened more than once to evaluate the effect of repetitive damage on the material properties of heat-straightened steel. Changes in material properties are small after two cycles of damage and repair. However, additional cycles produced a more brittle material and, in some cases, resulted in fracture of the material. In summary, heat straightening is a viable alternative for the repair of damaged structural steel. However, the user should be aware that some material properties will be changed during the process.

A study has been conducted to evaluate the shear strength of 44 × 184 mm and 44 × 305 mm laminated veneer lumber and parallel strand lumber using ASTM shear block tests, center-point bending tests, and five-point bending tests. In the center-point bending tests of specimens with joist orientation, the specimens have been remanufactured into “I” shapes to promote longitudinal shear failures rather than bending failures. The ratio between the average apparent shear strength from the five-point and center-point loading tests ranges from 1.34 to 1.53. Similarly, the ratio between the average apparent shear strength from the five-point loading tests and the ASTM block shear tests ranges from 1.03 to 1.39.

Mound soils from some habitats of a common tropical species of termites were investigated with a view to the possibility of utilizing such soils for construction. The research program that comprises the evaluation of the geotechnical properties of the soil and a study of the compressive strength of mortar and concrete specimens containing mound soil showed that the soil could be used as an additive to enhance the strength of both mortar and concrete. Inclusion of mound soil in mortar matrix resulted in a compressive strength value of up to 40.08 N/mm², and addition of 5% of mound soil to a concrete mix of 1:2:4:0.56 (cement:sand:coarse aggregate:water) resulted in an increase of up to 20.35% in compressive strength.

Pumping of concrete is widely used in large highway projects due to convenience and economy of placement. The short-term effects of pumping on the durability of concrete is well documented, whereas the long-term effects on concrete durability is not known. Both types of effects were studied herein through collection and testing of 73 concrete samples from the Florida Department of Transportation bridge construction sites before and after pumping. The tests performed were air content, slump, unit weight, compressive strength, rapid chloride permeability, and water permeability. The air content and the slump of concrete decreased by about 1% and 13 mm (0.5 in.) on average, respectively, due to pumping. The unit weight and compressive strength of concrete were found to increase by about 24 kg/m³ (1.5 pcf) and 1.83 MPa (266 psi), respectively, due to pumping. Although test results are not statistically significant, pumping decreased the water and chloride ion permeabilities in the majority of tested samples. Results show that pumping does not have detrimental effects on concrete properties. In many cases, it results in stronger, denser, and more durable concrete. It is suggested that pumping be continued as a means of concrete placement in Florida Department of Transportation projects with confidence.

The corrosion condition of the galvanized reinforcement in Florida Department of Transportation (FDOT) Mechanically Stabilized Earth Walls (MSEW) was determined at selected sites. For this purpose, 10 MSEW structures were instrumented at 8 different Florida sites for measurements of soil resistivity, electrical potential, and corrosion rates of both galvanized steel and plain steel by polarization resistance tests. The FDOT design standards for soil chemistry and particle size distribution were met in virtually all the test locations and structures tested. The reinforcements in the structures investigated were typically in good condition and the apparent corrosion rate of galvanized elements was low (average about 1 μm/year). A deterioration model for service life forecasting was formulated using the field survey input.

A study was made of the use of pulverized fuel ash (PFA) mixtures to make a flowable material to backfill trenches. An optimum mix was designed to comply with current national specifications. The 4:8:1 (PFA:sand:cement) mix gave a compressive strength six times that of PFA:cement and 2.5 times that of sand:cement for the same (PFA + sand):cement ratio. Frost resistance was generally good. The material showed no expansion when tested in accordance with the freeze-thaw test procedure given in BS 812: Part 124. The use of calcium chloride to improve early strength was more effective than the two commercially available accelerators investigated. More work is needed to improve the early strength in cold weather and reduce cement content of the mix. A field trial showed that cementitious materials were better than conventional Type 1 granular subbase, both in terms of having less permanent deformation and elastic deflection. The cost of PFA:sand:cement trenchfill mixtures was within 10–15% of that of foamed concrete.

This investigation was carried out to study the volumetric and mechanical performance properties of the Superpave mixtures SP-1 and SP-2 and a typical Taiwan mixture (TTM). Both the Marshall and the Superpave mix design procedures were used to produce these mixtures, and the Superpave gyratory compactor was used for realistically compacting specimens to densities achieved under actual pavement conditions. These three mixtures were tested using the Superpave shear tester for conducting a simple shear test at constant height, frequency sweep test at constant height, and repeated shear test at constant height. Volumetric analyses of specimens showed that the TTM mixture hardly met the Superpave volumetric requirements and it contained less than 1% air voids at N_design, which strongly suggests that this mixture might be highly prone to rutting. The design asphalt content of each mixture was found very close to the peak of its compaction slope–asphalt content curve. Mechanical test results indicated that the Superpave mixtures were more resistant to permanent deformation than the TTM mixture.

The results of a metallographic study of gray cast-iron water pipes are reported. These pipes were installed between 1885 and 1973 in eight different water systems. Each pipe had been extracted during scheduled maintenance or failure repairs to provide data for a larger study to produce a methodology for determining the residual life of gray cast-iron pipes. This metallographic study was conducted to determine the causes of variations in the mechanical properties of these pipes. Pit-cast and spun-cast pipes were found to have distinctly different types of graphite flakes, flake sizes, and metallic matrices. These differences were directly responsible for the variations in the mechanical properties between the two types of pipes, with the larger flake sizes of the pit-cast pipes, in particular, producing weaker material. Examples of anomalous pipes that did not have the standard appearance of either type of manufacture were also found and the reasons for their appearance identified. The results of the study show that the metallurgy of the pipes may be a major contributing factor, along with external forces such as corrosion or poor installation practices. Metallographic analysis therefore can assist water utilities managers in making decisions on repairs, rehabilitation, and replacement.

The field of instrumentation is now going through new developments with the advent of fiber-optic strain gauges. Fabry-Pérot is one type of fiber-optic sensing technology that can be used for microstrain measurement of concrete. However, this new generation of strain gauges first needs laboratory investigation. The Fabry-Pérot type of sensor, specially designed for embedment in concrete, is evaluated. The sensor is protected by a steel sleeve that allows its installation in concrete elements. Laboratory experiments, including compressive and thermal loading, are performed on a high-performance concrete cylinder containing this new type of strain gauge. The fast response of these strain gauges allows monitoring of the dynamic load test up to 5 Hz. The strain gauge sleeve is made of steel, and numerical simulations using a finite-element method are performed to verify strain distribution in a concrete cylinder with an embedment fiber-optic strain gauge. Results show that this type of strain gauge performs well for strain measurement of concrete and seems not to be affected by temperature variations.

This paper contains details of uniaxial compression experiments on various idealized asphalt mixes with volume fractions of aggregate ranging from 40 to 85%. The compression experiments are performed over a wide range of temperatures, stresses, and strain rates. The steady-state axial behavior of the mixes has the same form as that of bitumen with the aggregate acting as a stiffener. However, the mixes with high volume fractions of aggregate dilate under a uniaxial compressive stress. The experimental results are compared with theoretical predictions of a modified version of Hashin's composite sphere model. Good agreement is observed.

The effect of fiber length on the mechanical properties of extruded cement-based polyvinyl alcohol fiber composites is strongly associated with the distribution of the fibers in the material. Statistical methods from the theory of point processes can be used to describe these patterns by straightforward and easily calculated statistics. The intensity of the fibers in different parts of a sample yields a general description of the fiber pattern, but the effects of length are expressed through second-moment measures that are found to be distinct for different fiber lengths and that are strongly associated with material properties.