Journal of Materials in Civil Engineering

It was found from field surveys that suspension bridge cables were under severe corrosion environments due to the water and high temperature inside the cable. Corrosion environments depended on the wire positions inside the cables. Wires were found to be continuously wet at the side, wet at night and dry during the day on the top, highly humid at the center, and soaked in the water at the bottom. Accelerated corrosion tests using galvanized steel wires showed that the side wires were most severely corroded, the bottom wires were also significantly corroded, but the upper and the center wires were rarely corroded. These phenomena agreed with the actual cable corrosion. The tests also showed that galvanized steel wires did not corrode when they were kept with a relative humidity below 60%, but became corrosive with the higher relative humidity. Larger amounts of sodium chloride increased corrosion considerably. The corrosion rate also exponentially increased with temperature. It was predicted that the zinc layer would be consumed within 10 years when wires were kept in the wet or soaked environments, 34 years with a relative humidity of 100%, and 211 years with a relative humidity below 60%.

In the present work the thermal conductivity of 29 samples of clay bricks was measured and the correlations of the thermal performance with the compositional, physical, and microstructural features of products were investigated. The results obtained directed our attention toward a better understanding of the role played by some parameters (i.e., mineralogical components and pore size distribution), other than bulk density, in improving or depressing the insulating properties of bricks. Among them, the unfavorable role of quartz, Ca-rich silicates, and amorphous phase came out, while the role of pore size and specific surface should be more accurately evaluated in the structural design of materials.

This paper investigates the use of fly ash as a replacement for sand in polymer concrete (PC). It is shown that a replacement of 15% by weight of sand with fly ash improves the compressive strength of unreinforced PC cylinders by about 30% and the flexural strength of steel-reinforced PC beams by about 15%. Other improvements in properties are relatively minor and include the tensile bond strength of PC under thermal cycling and the creep compliance of the PC under sustained loading. The replacement of sand with fly ash, however, does not seem to have an impact on the shear strength of PC. Potential applications of PC using fly ash are numerous, including thin overlays on bridges and floors, repairing concrete bridges and pavements, and the production of precast components such as wall panels, floor blocks, and underground vaults.

The effectiveness of several Class C and Class F fly ashes in controlling expansion due to alkali silica reactivity (ASR) was investigated based on a modified ASTM C 1260 test method. Three different strengths of NaOH solution (1N, 0.5N, and 0.25N) were used to test the reactivity of reactive and potentially reactive aggregate in mortars with 20 and 35% Class C and F fly ash replacements by mass of cement. The other variables included high and low alkali cement, extended curing time, and longer testing period of 28 days. Test results confirm that Class F fly ash is more effective than Class C fly ash in controlling expansion due to ASR, but that Class C fly ash can also be used under certain conditions.

Several statistical methods for controlling the quality of aggregate gradation are proposed, based on a multivariate model that describes compositional data. First, ternary quality control charts are developed to control a three-part gradation such as that given by the restricted zone method, with both hexagonal and elliptical acceptance regions. Second, multivariate quality control charts are developed with multiple category and $T^2$ acceptance regions. Hexagonal and multiple category regions use fixed lower and upper control limits for each category and are easier to interpret by a visual plot, whereas elliptical and $T^2$ regions account for the correlations among the categories and are more accurate and efficient. The control charts may be used to show the dynamic status of consecutive average values and can easily be applied with spreadsheet software such as Microsoft Excel.

This study was performed to investigate the development of restraint stress and strain in axially restrained concrete specimens at early ages. Axially restrained specimens, generally, well represent field conditions of actual structures. In this study, uniaxial restraint tests were performed with two levels of concrete strength, high- and normal-strength concrete, and three levels of restraint were applied, namely, high-restraint (H), low-restraint (L), and nonrestraint (N). It was revealed from the test results that a high tensile restraint stress was developed at an early age in high-strength concrete and that the inherent high tensile strength may not be utilized for the structural performance of high-strength concrete members. The tensile restraint stress was gradually reduced due to the creep effect with time. An analytical calculation considering creep under varying stresses and the time-dependent properties of concrete at early ages was compatible with the test results.

The paper presents the details of various investigations conducted for the laboratory evaluation of the performance of crumb–rubber modified asphalt mixes. Crumb rubber (CR) obtained from discarded truck and bus tires was used to modify 80/100 penetration grade asphalt cement. Fatigue and permanent deformation characteristics, temperature and moisture susceptibility, and oxidative aging are some of the performance indicators of mixes evaluated. A static indentation test was adopted for assessing the relative permanent deformation characteristics of different mixes. Three aggregate gradations: (1) superpave; (2) gradation specified by the Ministry of Surface Transport, India for asphalt concrete; and (3) one gap gradation, were considered in the investigation. Compared to normal mixes, CR modified mixes were found to have improved fatigue and permanent deformation characteristics. They also showed lower temperature susceptibility and greater resistance to moisture damage compared to normal mixes. Superpave mixes gave better overall performance compared to the mixes having other aggregate gradations.

The uniaxial compressive response of steel fiber-reinforced concrete (SFRC) subjected to high strain rate loading is presented. Details of an experimental investigation using a 75-mm-diameter split Hopkinson pressure bar (SHPB) are outlined. The investigation focuses on recorded data and results in distinguishing the strain rate that mobilizes ductility of steel fiber reinforced concrete. SFRC specimens with relatively high static compressive strength were tested at strain rates between about 20 and $100s^{-1}$ produced by impact from two specially designed striker bars on the SHPB facility; different impact load durations were produced using these striker bars. The reason for adopting this strategy is explained. Tests confirmed that the unconfined uniaxial compressive strength of SFRC increases with strain rate in the same way as plain concrete. Further, strain rate has a significant influence on the ductility of SFRC. At a high strain rate, the postpeak ductility is absent. This is in direct contrast to the behavior of the same material subjected to static loading. However, SFRC possesses good postpeak ductility at a strain rate below a specific value dictated by the entire loading process; a recommendation on the strain rate is proposed. A method for conducting approximate constant strain rate testing using the SHPB facility is also described in the paper.

One of the primary structural distress modes found in bituminous pavement layers is fatigue cracking, resulting from repeated application of traffic-induced stresses. The development of a four-point bending test arrangement to determine the dynamic mechanical properties of rectangular beam specimens $(305\times 45\times 50\mathrm{mm}$ dimensions) of bituminous mixtures is discussed. This novel system allows the crack-damaged surfaces of beam specimens to be inspected and monitored digitally in situ during fatigue tests. The test fixture, which was integrated with a closed-loop servo hydraulic feedback system, incorporates a constant clamping mechanism and uses a combined displacement and loading mode of control. A series of four-point bending fatigue tests were performed on specimens of two standard Irish mixtures: a hot rolled asphalt and dense base course macadam. The digitally imaged information on fatigue cracking was used to measure the extent of damage and to characterize a linear elastic fracture mechanics model.

The problem of aging water pipes manifesting leaks and breaks is common to municipalities throughout the North American continent and the world. The age distribution of the failing pipes is broad and the pipe material originates from periods when different manufacturing technologies were employed. Consequently, cast iron pipes exhibit a significant variability of material properties. In addition, these pipes are also in a more or less advanced state of deterioration as a result of corrosion phenomena. A general knowledge of the properties and state of deterioration of a water main network is needed to understand the failure mechanisms contributing to water pipe failure. Among them, knowledge of the mechanical properties of the pipe material itself is fundamental. To achieve this goal, an extensive pipe and soil sampling and testing program was undertaken on excavated pipes in Toronto, Ontario. The mechanical tests performed on pipes included tension, compression, and ring bearing tests as well as full-scale longitudinal bending tests. The outcome of this experimental investigation contributes towards a better understanding of the complex phenomena involved in the pipe failure process.

Achieving proper compaction of asphalt pavement is crucial to its longevity and acceptable performance. Laboratory compaction is an essential part of mix design. In order for the mix design process to be effective, laboratory compaction must adequately simulate field compaction. This study used mechanical properties measured with the Superpave shear tester to evaluate field compaction and laboratory compaction. The field compaction consisted of three test sections with different compaction patterns. The laboratory compaction used the Superpave gyratory compactor with adjustments to several parameters. Results of this study indicate that current gyratory protocol produces specimens with significantly different mechanical properties than field cores produced with the same material and compacted to the same air voids. Results also show that adjustments to certain parameters of the gyratory can produce specimens that better simulate the mechanical properties of pavement cores.

The effects of high temperature on the strength and stress-strain relationship of high strength concrete (HSC) were investigated. Stress-strain curve tests were conducted at various temperatures (20, 100, 200, 400, 600, and $800°C)$ for four types of HSC. The variables considered in the experimental study included concrete strength, type of aggregate, and the addition of steel fibers. Results from stress-strain curve tests show that plain HSC exhibits brittle properties below $600°C\text{,}$ and ductility above $600°C\text{.}$ HSC with steel fibers exhibits ductility for temperatures over $400°C\text{.}$ The compressive strength of HSC decreases by about a quarter of its room temperature strength within the range of $100-400°C\text{.}$ The strength further decreases with the increase of temperature and reaches about a quarter of its initial strength at $800°C\text{.}$ The strain at peak loading increases with temperature, from 0.003 at room temperature to 0.02 at $800°C\text{.}$ Further, the increase in strains for carbonate aggregate HSC is larger than that for siliceous aggregate HSC.

The potential of a concrete for carbonation can be assessed effectively by measuring its carbonation depth using an accelerated carbonation testing. This paper reports the findings of a laboratory study including compressive strength, accelerated carbonation depth, and porosity properties of concrete mixtures made with fly ash and normal portland cement. The study involves two replacement ratios of fly ash, various water-to-cement ratios, use of superplasticizer, two curing conditions, and four concrete ages. Statistical models that relate accelerated carbonation depth to strength and porosity are presented.

Many thousands of years after its development, unburnt earth block masonry continues to offer an environmentally sustainable and cost-effective alternative to other conventional wall building materials, such as concrete blocks and clay fired bricks, in both developing and developed countries. However, earth is a brittle building material with low tensile strength, and as a consequence tensile cracks in response to external actions or restrained shrinkage are often observed. Ductility and tensile strength may be improved by adding binders or natural fibers to the soil mixture. In this technical note, initial findings of an ongoing study of the tensile characteristics of compacted earth blocks reinforced with natural fibers is reported. The pre- and postcracking characteristics of compacted earth blocks in direct tension were determined using a test procedure developed for this work.