Journal of Materials in Civil Engineering

Microstructural changes that occur over time around fibers in the cement matrix, leading to an enhanced bond and stiffening of the interfacial transition zone, may result in a reduction in the mechanical properties of the composite. Micromechanical modeling of processes of this kind suggest that such aging trends may occur in microfiber reinforcement but not in macrofiber reinforcement. Degradation in mechanical properties of the composite will show up only when a “pessimum” combination of parameters exist, particularly brittle microfibers in a very dense matrix. Therefore, in the development of new cementitious composites, interfacial effects of this kind should be considered, because aging due to such mechanisms can be demonstrated to occur in practice. Thus, it is not sufficient to assess the durability of cementitious composites by considering only the chemical stability of the fiber in the alkaline cementitious matrix.

Impressed current cathodic protection (CP) has been shown to provide an effective means of restraining corrosion associated with the presence of chloride ions in reinforced concrete structures. Advances in extended anode systems and monitoring methods, together with improved understanding of how to minimize the risks of adverse side effects, have led to widespread acceptance of the approach for treating such problems. Interesting developments in recent years have included the use of very low current density CP for preventing the initiation of corrosion in new structures (cathodic prevention) and intermittent or temporary forms of CP for restoring the passivating character of contaminated cover concrete. Progress is also being made in the application of sacrificial anode CP, particularly as a means of enhancing the performance of patch repairs, which as yet have not been considered a durable method of restoring chloride-contaminated reinforced concrete.

This paper presents a critical analysis of the mechanisms of ice formation in high-performance materials. The process of ice formation in ordinary and high-performance concrete mixtures is first investigated by low-temperature calorimetry. Three concrete mixtures (with water-to-cement ratios of 0.25, 0.35, and 0.45) were prepared and tested. The mechanisms of ice formation were also studied from a theoretical point of view using a numerical model. In this analysis, special attention is placed on the phenomenon of solid/liquid interface propagation. Test results indicate that a reduction of the water-to-cement ratio contributes to refine the concrete pore structure and limit the amount of ice formed between 0 and −55°C. However, low-temperature measurements and theoretical calculations show that it is hardly possible to totally impede ice formation in cement-based materials. According to both types of analysis, ice formation in high-performance concrete mixtures is most certainly initiated by the propagation of a solid/liquid interface.

This paper introduces a study carried out to investigate sulfate attack caused by gypsum formation. The aim, specifically, was to study whether gypsum formation can be a factor leading to expansion in concrete exposed to solutions containing sulfate ions. It was found from the laboratory study that alite paste specimens (0.48 water-to-alite ratio) expanded and cracked significantly in 5% Na₂SO₄ solution after a “dormant” period of about 1 year. X-ray diffraction confirmed that gypsum was the main product—ettringite does not form in the system, because of the lack of aluminate. The detailed study of the mechanism for expansion and cracking is continuing. These findings confirm the long-term understanding that sulfate attack mechanism is a complicated process. A highlight of the study, therefore, reveals that expansion and cracking of portland cement concrete may not be attributed solely to ettringite formation. Gypsum formation may be a cause leading to expansion and subsequent cracking. More research is needed in this area.

The variation in cement type affects the performance of concrete in terms of durability and strength. Concretes made with different cement types are known to behave differently under similar conditions such as environmental conditions, mixture proportions, etc. In 1940, the Portland Cement Association initiated a long-time durability study to investigate the effects of the variation in cement type on different durability aspects. The United States Bureau of Reclamation agreed to place 28 different cement types on the parapet wall panels of the Green Mountain Dam. Each of the 28 cement types was used in 3 or 4 of the 104 panels of the parapet wall. The Green Mountain Dam is located on the Blue River, a tributary of the Colorado River, 13 mi southeast of Kremling, Colo. The dam itself is an earthfill structure. This particular paper investigates the influence of cement type, air-entrainment, and method of air-entrainment on the freezing and thawing resistance of concrete.

Suspension bridge cable inspections have revealed severely corroded and broken wires in some main cables. Accelerated, cyclic corrosion studies were conducted to assess the relative effect of general corrosion, corrosion cracking, and hydrogen embrittlement on the deterioration in material properties of high-strength steel bridge wire. Galvanized and ungalvanized wire samples were corroded in a cabinet that cyclically applied an acidic salt spray, dry conditions, and 100% relative humidity at elevated temperatures. Specimens under zero applied load, and under tensile loads of up to 22 kN (5,000 lb) were studied. Mass loss, hydrogen concentration, ultimate load, and elongation at failure were obtained from corroded and uncorroded samples. Elongation measurements indicate a significant embrittlement of the wires, a result supported by fracture surface morphology. Ultimate load was found to degrade at a rate in excess of that attributable to material loss by general corrosion. The hydrogen content of corroded wire was found to be greater than that of uncorroded wire, particularly for galvanized wire.

Investigations conducted on the strength and deformation characteristics of 23 concrete beams reinforced with babadua bars are reported in this paper. Different percentages by area of tensile reinforcement ranging from 2.87 to 12.13 were used in the beams, which measured 100 × 180 mm and 135 × 235 mm with spans of 1.5 m and 1.8 m, respectively. Stirrups formed from babadua bars approximately 8 mm in diameter were used in six of the beams. The beams were tested to failure generally under third-point loading. Collapse of the beams occurred through either flexural failure by crushing of concrete in compression or diagonal tension failure. The experimental failure loads for all beams averaged, respectively, 6.40 and 2.62 times the theoretical flexural strength and theoretical shear strength of the unreinforced concrete section. On the other hand, the experimental failure loads were only about 1.18 times the theoretical flexural strength of the reinforced concrete and 1.05 times the theoretical shear strength of the concrete sections, taking into consideration the resistance of the tension reinforcement.

Pavement surface texture significantly contributes to tire wear and tire-pavement friction. Currently available relationships quantify tire wear and tire-pavement friction simply in terms of empirical pavement texture parameters. The objective of this paper is to present correlations with which the tire wear rate and tire-pavement friction on smooth concrete pavements can be predicted using actual texture properties. Using a laboratory tire wear simulator and an aircraft tread-rubber block, a number of wear and friction tests are performed on pavement samples having different fine aggregate sizes. Frequency characteristics of the texture of the pavements are achieved by decomposing the profilometer measurements using the fast Fourier transform technique and constructing power spectral density plots of texture over surface spatial frequency. Then the tire wear rates as well as dry friction and wet friction of the tire-pavement interface are correlated to microtexture and macrotexture components of the texture power spectral density. The developed correlations indicate that both tire wear and dry friction are significantly affected by pavement microtexture. The developed wear correlations can be also useful for predicting the wear index of a pavement based on conventional Mu-meter and grease patch test results. This is illustrated by an example in which the wear index for a concrete runway pavement at Luke Air Force Base, Ariz., is computed using the new relations.

In this study, mechanical properties of fired clay and expanded perlite aggregate mixtures have been predicted by applying the composite materials approach. Models and analytical expressions of composition and property relations recorded in literature for the modulus of elasticity and compressive and flexural strengths are summarized and results of the experimental work are given. As a conclusion, a dependable approach has been obtained in which the effects of the phases are emphasized.

Tests on composite material from high-lime (ASTM class C) fly ash and recycled polyethylene terephthalate (RPET) were conducted to investigate the physiomechanical properties and microstructure features. Composite specimens with varying fly ash concentrations were tested in compression and tension, immersed in water to measure water absorption, and observed for shrinkage during manufacturing. Theoretical equations from modulus of elasticity and tensile strength were derived with values compared to portland cement concrete. Microstructural features associated with crack propagation during compression loading and the RPET binding mechanism were studied utilizing scanning electron and polarized reflective light microscopy and differential scanning calorimetry. The results of this investigation showed that the fly ash concentration contributed significantly to both the strength of composite material and the crystallinity of the RPET binder. Based on the evidence, it was concluded that the composite material is a value-added material with a variety of potential construction applications.

This paper presents an experimental study on crack bridging in steel-fiber-reinforced concrete (SFRC) materials under deformation-controlled uniaxial fatigue tension. Two types of commercially available steel fibers, straight steel fiber and hooked end steel fiber, were used separately in this experimental investigation. A total of six series of fatigue tensile tests with constant amplitude between maximum and minimum crack openings were conducted. The experimental results show that the bridging stress decreases with the number of load cycles, and this phenomenon is termed bridging degradation. The general behavior of the bridging degradation with the number of cycles in SFRCs is represented by a fast dropping stage (reduction in bridging stress within the first 10–15 cycles) with a decelerated degradation rate, followed by a stable stage with an almost constant degradation rate for straight SFRC, or by several periods with a decelerated rate in each period for hooked SFRC. Although fiber deformation, such as in hooked end fiber, can improve the monotonic crack bridging significantly, faster bridging degradation is found in hooked SFRC than in straight SFRC with the same maximum crack width (>0.1 mm) and minimum load condition.

One of the methods used to increase the bending and shear resistance of concrete structural elements consists of the addition of steel plates, which are bonded to the original concrete element with epoxy resin. The resulting bonds behave well under the structure's normal load conditions. Nevertheless, because the bonding material used in this method is an organic compound, its strength is sensitive to an increase in temperature and may fail in the event of a fire. In this work, the behavior of the different types of concrete bonded to steel plates by epoxy resin is studied under conditions of elevated temperature and shear loading.

As a result of excavation blasting, traffic, sudden ground movements, rock bursts, and seismic activity, shotcrete is often subjected to impact and other dynamic loads. Limited data exist, however, with regard to the resistance of shotcrete to such dynamic loads. Impact resistance of wet-mix shotcrete reinforced with 10 different types of fibers was investigated using instrumented drop weight impact tests. A direct comparison was made with the quasi-static response. Both beam and plate specimens were tested and the data were correlated. Fiber reinforcement was found to be highly effective in improving the fracture energy absorption and toughness under impact loading, but the improvements under impact loading were found to be substantially different than those seen in quasi-static tests, and were also highly dependent on the type of fiber used. When beams and plates were compared, the relative improvements between fiber types were found not necessarily in agreement.

The goal of the research presented here is to investigate the extent of healing of cracked concrete. A feedback-controlled test was used to generate a crack with a controlled width in concrete specimens. Then, water permeability was evaluated by a low-pressure water permeability test (WPT). Elastic wave signal transmission measurements were performed immediately after cracking and repeated after 100 days of WPT. Immediately after cracking, water permeability increased and the signal transmission decreased with increasing initial crack width. The water permeability of cracked specimens decreased significantly, whereas the signal transmission increased with time. Both permeability and transmission measurements suggest autogenous healing of the cracks. However, the recovery in signal transmission with crack healing is not as spectacular as changes in permeability, inferring only partial mechanical healing of the cracks.