Journal of Materials in Civil Engineering

Three controlled low-strength material (CLSM) mixtures (100, 100S with sand, and 100SG with sand and stone) were made using 93, 32, and 22% high-carbon fly ash (12% loss on ignition) by mass of total solids, respectively. Three concrete mixtures [40, 50 with steel fibers, and 60 with taconite (an iron ore) pellets] were made, each containing high-carbon fly ash at 43% of total cementitious materials. The respective $28\text{-}\text{day}$ electrical resistivity values of water-cured, saturated CLSM mixtures 100, 100S, and 100SG were 0.5, 1.0, and $1.8\Omega \text{-}\mathrm{m}$ (ohm-m), and the corresponding values of water-cured, saturated concrete mixtures 40, 50, and 60 were 41, 15, and $17\Omega \text{-}\mathrm{m}$ . As the amount of cementitious paste (including high-carbon fly ash) increased, electrical resistivity of CLSM decreased. Electrical resistivity of concrete reduced by more than half upon inclusion of 3% steel fibers or upon replacement of natural crushed stone with taconite pellets. This study also shows that high-carbon fly ash can be used in manufacturing conductive CLSM and concrete. Such materials can be used for conducting electrical charge from lightening to the ground more safely.

An amorphous silica (AS) replacing up to 10% of the portland cement by mass in concrete behaved partly as a traditional pozzolan, partly crystallized to quartz and the rest underwent some (crystal) structural reorganization without morphological changes. The pozzolanic behavior was evident from a reduction in the calcium hydroxide content of AS-cement paste with time. A new crystalline phase was observed in the scanning electron microscope only when AS was present, and energy dispersive X-ray microanalysis coupled with X-ray absorption near edge structure spectroscopy confirmed that it was the most stable form of silica, quartz. The presence of AS changed the concrete’s microstructure, aggregate–paste interface, and pore size distribution.

Results are presented from experimental work on the high-temperature behavior of conventional vibrated high-strength concrete and self-compacting high-strength concrete. Concrete cylindrical specimens and prismatic specimens were subjected to a low heating rate of $0.5°\mathrm{C}∕\min$ (up to $400°\mathrm{C}$ ) and a high heating rate according to International Standard Organization 834 fire curve (up to $600°\mathrm{C}$ ). The experimental results show that the residual mechanical properties in reference to initial mechanical properties of self-compacting high-strength concretes were similar to that of conventional high-strength concrete. The risk of spalling for self-compacting high-strength concrete was greater than that of conventional high-strength concrete. As for the conventional vibrated high-strength concrete, the use of polypropylene fiber improved the thermal stability of self-compacting high-strength concrete. Adding polypropylene fiber modified thermal gradient (in consequence thermal stresses) in the tested concrete specimens during the heating–cooling cycles. This may contribute to explaining the difference in thermal stability.

The ability to quantify adhesion based on surface energies of the bitumen and aggregate components enables selection of compatible materials and quantitative assessment of moisture susceptibility. Reliable surface energy characterization is required in order to implement this technology successfully. One proven method to estimate bitumen surface energy is to calculate it using contact angles measured with various liquids. However, improper selection of probe liquids or interpretation of resulting data can easily mislead users into drawing inaccurate conclusions. This paper presents a refined test method and analysis procedure customized to estimate bitumen surface energy using contact angles measured by the Wilhelmy plate. Results for five neat and three modified bitumen are presented and results are interpreted to study the relationships between contact-angle based surface energies and damage in hot mix asphalt. In a separate study by Bhasin et al. in 2004, surface energy characteristics of bitumen determined using methods described in this paper were combined with surface energies of aggregates to successfully predict moisture susceptibility of mixes.

The carbonation behavior of six cementitious materials was examined (CSA Type 10 cement, CSA Type 30 cement, fly ash, ground granulated blast furnace (GGBF) slag, electric arc furnace (EAF) slag, and hydrated lime) for applicability to $\mathrm{C}{\mathrm{O}}_2$ sequestration applications. No-slump press-formed compacts and loose powders were subjected to 100% $\mathrm{C}{\mathrm{O}}_2$ at a constant pressure of $5\text{bar}$ for $2\mathrm{h}$ . The $\mathrm{C}{\mathrm{O}}_2$ contents of the as-received and the carbonated materials were measured. It was found that the cements, fly ash, and electric arc furnace slag could each show $\mathrm{C}{\mathrm{O}}_2$ uptake on the order of 12%, while the lime achieved nearly 40%. The blast furnace slag managed 7% uptake. The carbon uptakes achieved were significantly lower than the theoretical maximum as determined by chemistry. The $2\mathrm{h}$ carbonation produced high early age strength in cements and hydrated lime, which can be used as structural materials. The strength gain in fly ash, EAF slag, and GGBF slag was nevertheless not sufficient. X-ray diffraction analysis determined that the primary carbonation product formed was calcite, while ${\mathrm{C}}_3\mathrm{S}$ , ${\mathrm{C}}_2\mathrm{S}$ , and $\mathrm{Ca}{\left(\mathrm{O}\mathrm{H}\right)}_2$ were the phases consumed. Scanning electron microscopy observations considered the morphology of the carbonation products and the degree of reaction in terms of microstructure characteristics.

In the customary way of clay brick production by burning soil in Bangladesh and other developing countries, a good number of bricks (approximately 13%) are severely overburnt due to uncontrolled distribution of temperature in the kiln. These bricks are dark red in color, severely distorted, and swollen. These bricks are considered totally useless and are not allowed in any construction work. In this study, the feasibility of utilizing these overburnt bricks as coarse aggregates in highway pavement projects was explored. Routine laboratory tests such as the Los Angeles abrasion, water absorption, specific gravity, and unit weight, were used to compare the properties of the overburnt bricks with the best possible quality picked or pick-Jhama (Type A) bricks from the same stockyards in Bangladesh. It was found that overburnt brick aggregates are much stronger, less absorptive, and denser in general than the ones from the picked or pick-Jhama (Type A) bricks. Therefore, these bricks may be conveniently and economically used as highway pavement coarse aggregates. Manufacturers may also be encouraged to produce such high strength brick with adequate quality control measures.

An experimental program was undertaken to evaluate the effect of a mixture’s consistency on the lateral pressure that can be developed by highly flowable concrete. Six mixtures, with various contents of high-range water-reducing admixtures, were tested and had consistency levels varying between a slump of $220\mathrm{mm}$ and a slump flow of $750\mathrm{mm}$ . The mixtures had similar water-to-cementitious materials and sand-to-total aggregate ratios of 0.40 and 0.46, respectively. Depending on the mixture consistency, the maximum initial pressures varied between 75 and 98% of hydrostatic. Concretes with lower consistency were shown to exert lower initial lateral pressure and had faster rates of pressure drop with time. This can be attributed to the increased degree of shear strengths that enables the fresh concrete to further resist vertical stresses, hence precluding the development of high lateral pressure. Self-consolidating concrete mixtures made with standard CSA Type 10 cement exhibited higher initial pressure and lower rates of pressure drop compared to those of equal consistency prepared with ternary cement. At the end of the dormant period of cement hydration, the acceleration of formation of hydrates is shown to enable the concrete to be self-bearing—resulting in the cancellation of lateral pressure.

Ready-mixed soil material (RMSM) is a new range of soil material with physical properties lying between controlled low-strength material (CLSM) and soil cement. The design approach of RMSM combines the advantages of both CLSM and soil cement, yet it resolves the following deficiencies of the two materials. The production of CLSM uses large quantities of coarse aggregate, sand, and cement, and results in a high-density high-strength CLSM mix, which is difficult to reexcavate. Soil cement is not suited to site conditions where there is confined working space. The unconfined compressive strength of RMSM is 2 to 30 times greater than that of soil materials, and the flexural strength is about 5 to 10% greater than that of its unconfined compressive strength. The RMSM material developed in this research has adequate strength its intended purpose, yet it allows re-excavation at a later date.

One of the major causes of corrosion of reinforced concrete structures worldwide is chloride. With progressing corrosion, the integrity of the structure is at stake and repair measures are necessary. In recent years electrochemical repair methods such as chloride extraction or cathodic protection have become increasingly popular. Chloride extraction is less expensive as compared to traditional patch repair methods due to its short duration. It is accepted for application on ordinary concrete structures with mild steel reinforcement. Its application on prestressed concrete, however, has been ruled out because of the danger of hydrogen embrittlement. Contradicting results of research on the subject have suggested that chloride extraction might be a feasible repair option for prestressed concrete structures, thus leading to major cost savings for bridge owners. This study investigated the feasibility of chloride extraction on prestressed concrete structures. A distinction was made between hydrogen embrittlement, which temporarily reduces the ductility of steel, and hydrogen-induced stress corrosion cracking, which leads to sudden and unexpected collapse of the structure. The most commonly accepted test methods for hydrogen embrittlement are constant extension rate tests, but they give little indication of the performance of the prestressed tendons under serviceability conditions. In this study, along with constant extension rate tests, 22 prestressed concrete specimens were also tested using a fatigue test program. The fractured surfaces were carefully investigated to identify signs of hydrogen embrittlement and to rule out any other causes of failure. The results of the study suggest that chloride extraction temporarily reduces the fatigue life of prestressed steel. Although hydrogen-induced stress corrosion cracking was not observed for the type of steel investigated in the main study, it occurred for a different type of steel. Statistic analysis of the fatigue tests also suggested the possibility of hydrogen-induced stress corrosion cracking for the investigated steel; therefore, chloride extraction should not be applied to prestressed concrete structures.

Natural pozzolans, also known as trass, can be used in cement manufacturing due to their cementitious properties after reaction with calcium hydroxide. At different mixture proportions, the strength, setting time, workability, and soundness of the cement mortar made will differ. In this paper, cement mortars with six different natural pozzolan additions (ranging from 0 to 35%) were employed while using one type of natural pozzolan. As the experimental results show, increase in a natural pozzolan addition decreases the early age strength of cement significantly as expected and decreases the soundness of mortar by two-thirds. In addition, the workability conditions relatively improve and the settings delay for awhile.

Fracture energy represents the average total energy consumption during a complete crack propagation process. The use of one fracture property, the RILEM fracture energy, on its own is not sufficient to characterize the fracture behavior during crack stable and unstable propagation periods. In this paper, two fracture energy quantities, the stable fracture energy and unstable fracture energy, are introduced to predict energy consumption for those two crack extension periods. Wedge splitting tests were carried out on concrete specimens with different ligament length to identify all three fracture energy quantities. The experimental results show that the stable fracture energy remains almost a constant irrespective of specimen size, while the unstable fracture energy increases with increasing ligament length. A similar size dependency is observed in the RILEM fracture energy. An explanation is offered for this size dependency by considering the boundary effect of the specimen.

A study was carried out on the contact pressure and shear stress at the interface of a carbon-fiber-reinforced polymer (CFRP) rod in contact with aluminum alloy or copper sleeves of different hardness. The main objective was to investigate the effect of the sleeve material on the interfacial sliding behavior under high contact pressures required for the design of wedge anchor systems to grip CFRP rods in prestressed concrete applications. The shear stress increased with the contact pressure; aluminum alloy sleeves generated higher shear stresses than copper sleeves. For both sleeve materials, higher shear stresses resulted from softening sleeves, an effect attributed to the lower yield stress facilitating metal flow, which resulted in a larger contact area between the sleeve and the CFRP rod.

Cracking is an important aspect of concrete behavior that considerably affects the overall response of concrete structures. The initiation of cracks is governed by concrete tensile properties. The propagation of cracks is a complicated phenomenon that plays a significant role in the nonlinear analysis of concrete structures. The cracking process in tension starts at a relatively low tensile strain, causing plain concrete to exhibit a gradual softening behavior. This softening is augmented by the tension stiffening of reinforcing bars. The smeared crack approach is typically combined with nonlinear finite-element analysis to generate an accurate global response. The key to such representative accurate predictions relates to material parameters, especially those of tension stiffening effects. For a complete understanding of the crack development process, tests should be performed on concrete specimens at various load histories. However, due to the difficulty of testing concrete in uniaxial tension, only limited and often conflicting results are available. The present work develops an inverse approach combining nonlinear numerical analysis and global experimental response to develop the tension stiffening model parameters needed to simulate homogenized concrete behavior in tension. The results of the study provide good model parameters to use in the case of concrete beams reinforced with steel and fiber-reinforced polymer (FRP) bars.

The performance of an organic, penetrating corrosion inhibitor in reducing the rate of corrosion and delaying the onset of corrosion in carbonated concrete was investigated. Laboratory trials were undertaken on specimens treated with the corrosion inhibitor before and after accelerated carbonation. Corrosion monitoring was undertaken for 11 months measuring corrosion rate, rebar potential, and resistivity. Results indicate that the penetrating corrosion inhibitor is capable of reducing corrosion rates and delaying the onset of corrosion under carbonation conditions. The effectiveness of the inhibitor was also assessed on site structures exhibiting severe carbonation-induced corrosion. Corrosion monitoring on site was done for a period of nine months. Findings from site studies confirmed that surface application of the corrosion inhibitor significantly reduced the corrosion rate of reinforcement embedded in carbonated concrete when compared with untreated elements.

Nitinol superelastic materials (SEM) are mostly used for low-force/large displacements applications involving tensile or bending modes of loading. The paper describes experiments on the radial compression of superelastic wires and tubes between flat loading surfaces. Elastic (recoverable) deformations—up to 22.5% with high damping under loads in the kN/mm range for solid wires, and the 10– $100\mathrm{N}∕\mathrm{mm}$ range for tubes with an outer diameter of 0.4– $2\mathrm{mm}$ —have been observed. The recoverable deformation as great as 60% has been measured on a thin-walled SEM tube. This phenomenon was named a “giant superelasticity effect” (GSE). The experiments were performed in a broad range of loading rates. Stainless-steel specimens were also tested for comparison. A closed-form analysis for thin-wall tubes, and some realized and potential applications of GSE, are described.

The results of creep and pseudocreep tests, carried out on the masonry of an ancient structure, are presented and their interpretation by means of a probabilistic model is proposed, based on the definition of a random variable as a significant index of vulnerability, and on the solution of the classic problem of reliability in stochastic conditions. A comparison between vertical and horizontal strain rate is put forward and the application of the proposed procedure to the Tower of Monza is attempted. Aim of the research is to provide a mathematical model able to predict possible failures of heavy masonry structures due to long term damage, allowing preventive repair.

The Florida Department of Transportation (FDOT) specifications contain equations of concrete compressive strength to predict equivalent 28-day strengths based on core strengths at other times. The FDOT equations are many years old, and are not likely to represent current FDOT concrete mixes. Compressive strength testing at various ages, by using a typical FDOT concrete mix proportion, was performed in order to derive appropriate strength development models. Variation in the mixes was achieved through the substitution of cement types, slag for fly ash, and coarse aggregate type. Selected existing models from the literature were examined for statistical goodness-of-fit to the test data. The best performing models relating the 28-day compressive strength to strengths of concrete aged more than 42 day were recommended.