Journal of Materials in Civil Engineering

This study is aimed to utilize of the Golden Horn (GH) sediments in briquette production after they were conveyed to a stone quarry in Istanbul, Turkey. Two different types of mixtures were prepared for hydrothermal agglomeration. In the first type, GH sediment and lime and in the second type GH sediment, lime, and quartz were mixed. For thermal agglomeration, GH sediment was used alone. First, physical, chemical, and mineralogical properties of the GH sediments were determined. Then, the prepared briquette samples were agglomerated under 0.5, 1.0, and $1.5\mathrm{MPa}$ water vapor pressure for $4\mathrm{h}$ with the hydrothermal method in the autoclave and then under ${\mathrm{1,273}}^{\circ }\mathrm{K}$ constant temperature for $2\mathrm{h}$ in a thermal agglomeration oven. Density change of the briquettes as a result of agglomeration compressive strength were measured and the results of the mechanical data and x-ray analysis of sediments subjected to thermal and hydrothermal treatment are presented. Calcium silicate hydrate peaks were observed only at $1.0\mathrm{MPa}$ between 423 and $473\mathrm{K}$ in the first type of mixture and the highest compressive strength value $\left(27\mathrm{MPa}\right)$ was observed in briquettes prepared without quartz in the hydrothermal method at $1.5\mathrm{MPa}$ . This study showed that it is possible to produce briquettes from GH sediments and this will reduce environmental pollution.

This paper examines the fracture energy properties over ligament length for crack propagation process accompanied by fracture process zone (FPZ) advancement. Local fracture energy as well as its average value along the crack path is investigated by considering the influence of specimen boundaries on the development of FPZ. To address the specimen boundary affected region over which local fracture energy generally spreads in a non-uniform manner, two concepts are introduced: Back boundary affected length and overall boundary affected length. Tests were conducted on wedge splitting concrete specimens to identify the variation of fracture energy dissipation when FPZ evolves toward the specimen back surface. Results included here reveal that the back boundary affected length is decreasing approximately in a linear way along with crack evolution. The overall boundary affected length, however, proves to be increasing at early stages of crack growth and then decreasing in a way similar to the back boundary affected length. Local fracture energy over crack extension decreases before FPZ gains its full development. For the case of a full-developed FPZ, it can be described by two different forms: one is in the form of a horizontal line, the other part shows to be decreasing but with a constant average value. The average value of local fracture energy, however, is predicted to increase along with the evolution of FPZ.

Moisture damage in asphalt concrete pavements is a major cause for high maintenance costs of state and federal highways. Moisture damage in asphalt concrete is largely due to loss of adhesion between bitumen and aggregate, and loss of cohesive strength in the mastic (bitumen and mineral filler). Surface energy components of bitumen and aggregate are used to calculate their interfacial bond strength and effectively quantify moisture susceptibility of asphalt concrete mixes. This technology has several advantages over conventional mechanical tests currently being used to identify moisture susceptible mixes. However, accurate surface energy characterization of bitumen and aggregate is the key element to calculate interfacial bond strengths. This paper presents development of a sorption based method to measure specific surface area and surface energy components of aggregate. Measured surface energy components and precision statements are presented for five aggregates. The paper also illustrates application of bond strengths calculated from surface energy components of aggregate and bitumen in the selection process of compatible pairs of aggregate and bitumen to produce a durable mix.

The lamellate structure of clay and the extrusion forming process cause terra cotta ceramic’s anisotropic elastic behavior at low strain and may induce gradients of macroscopic mechanical properties. Among other techniques, strain measurements obtained through digital image correlations were used to locally characterize transverse isotropic elastic behavior. Kinematic field measurements on small specimens were also compared with fields derived from three-dimensional finite element computations in order to check the consistency of the local characterization procedure.

Mechanical characteristics of self-consolidating concretes subjected to elevated temperatures up to $700°\mathrm{C}$ were experimentally investigated in this paper. Eight different concretes [four self-consolidating concretes (SCC) and four conventional concretes (CC)] of different strength categories were produced. At the age of 120 days, specimens were placed in an electrical furnace and the heating was applied at a rate of $5°\mathrm{C}∕\min$ until the desired temperature was reached. A maximum temperature of 100, 300, 500, and $700°\mathrm{C}$ was maintained for $1\mathrm{h}$ . Specimens were then allowed to cool in the furnace and tested for compressive strength, splitting tensile strength, and ultrasonic pulse velocity. Similar tests were also performed at room temperature $(20°\mathrm{C})$ for the reference specimens. Residual strength of both SCC and CC was reduced almost similar up to the maximum temperature tested. Explosive spalling occurred in both SCC and CC of the highest strength category at temperatures greater than $380°\mathrm{C}$ . The residual compressive strength of SCC mixtures was higher than the one of CC mixtures for the same strength class. The tentative spalling behavior of SCC and CC was the same and depended only on the strength category.

This paper evaluates the relationship between the air void distribution in asphalt mixes and their moisture susceptibility. Asphalt mix specimens were prepared to have different air void distributions through using two different gradations, using two different compaction angles in the Superpave gyratory compactor, and trimming the specimens at different locations. An x-ray computed tomography system was used to capture the internal structure of the specimens, and image analysis techniques were used to quantify the air void distribution and connectivity. Specimens in unconditioned (dry) and moisture-conditioned (wet) states were subjected to dynamic loading, and damage was evaluated using a crack growth index based on fracture theory. The parameters required for the crack growth index were obtained from mechanical and surface energy tests. The analysis results clearly demonstrate the influence of air void distribution on moisture susceptibility. Consequently, the analysis method presented in this paper can be used to evaluate alternative mix designs and internal structures, even when the same materials are used, in order to optimize the resistance to moisture damage.

The effect of combined water immersion and sustained bending on the degradation response of E-glass/vinylester composites is characterized through mechanical testing (tension and short-beam-shear) and moisture uptake. It is seen that moisture uptake and coefficient of diffusion increase with levels of sustained strain and that uptake characteristics can be predicted with a reasonable level of accuracy using a model incorporating the free volume approach. Both tensile strength and short-beam-shear strength decrease with increasing periods of immersion and level of sustained strain. A transition in degradative response can be identified in terms of level of sustained strain. Comparisons of response with ACI-440 guidelines indicate that the use of stress limitations is essential in specifying design allowables since the use of ACI thresholds involving environmental exposure factors alone may be unconservative for long periods of service. It is emphasized that synergistic effects of sustained bending and water immersion are accelerative and that further research is needed on ascertaining the safe level of sustained loading for use in civil infrastructure.

The results of early age reflection and transmission properties of young mortar samples with different water-to-cement ratios $(w∕c)$ changing between 0.40 and 0.60 with a 0.05 of increment are presented. Hourly nondestructive and noncontact measurements are conducted during 20–30 and $44–54\text{hours}$ at $X$ band $(8–12\mathrm{GHz})$ by free-space method. Two measurement systems are used for comparison and validation of measurements. One is a simple and relatively inexpensive (direct current volt meter and T-meter combination) and the other is expensive and complex in operation (Agilent Technologies power meter). A new approach (relative slope approach for reflection properties) is introduced to predict the history of the hydration process of young mortar samples. It is shown that the difference between the relative slopes of reflection properties of mortar samples with 0.40 and 0.45 $w∕c$ ratios is greater than that of other mortar samples whose $w∕c$ ratio difference is 0.05. This result shows that a mortar with a lower $w∕c$ ratio will gain hydration (and strength) quicker than the one with a higher $w∕c$ ratio (a nonlinear relationship between the degree of hydration and $w∕c$ ratios at early ages of curing). It is shown that a lower amplitude of transmission coefficient corresponds to the young mortar sample with a higher $w∕c$ ratio at early ages of curing. This is the opposite case for hardened cement samples. Therefore, early age transmission properties can be used to monitor the porosity level inside cement samples and this monitoring can be very useful for the quality enhancement of these samples. It is observed that the measurement results of both systems are almost the same (maximum 4% difference), and simple and relatively inexpensive system can be adapted for the detection of hydration, evaporation process, and porosity level detection inside cement samples at construction site.

A one-dimensional mathematical model was developed, based on the fundamental energy balance, to calculate the pavement near-surface temperatures using hourly measured solar radiation, air temperature, dew-point temperature, and wind velocity data. An analysis was conducted to predict the diurnal temperature effects of pavement thermophysical properties with the aim of seeking an optimum composition of paving materials for future infrastructure projects. Appropriate paving materials not only ensure stability and safety for road users, but also the ability to mitigate heat absorption and high surface temperatures contributing to the Urban Heat Island Effect and human comfort. This paper evaluated the effects and sensitivities of the thermophysical properties on the pavement surface temperatures. The results indicated that both albedo and emissivity have the highest positive effects on pavement maximum and minimum temperatures, respectively, while increasing the thermal conductivity, diffusivity, and volumetric heat capacity help in mitigating the maximum but not the minimum pavement near-surface temperature.

An investigation involving mechanical testing and microstructural characterization was undertaken to examine the influence of moisture state at the time of testing on the performance (i.e., strength, toughness, and failure mode) of pulp fiber-cement composites. Samples, prepared with fiber volume fractions of 0, 1.2, and 2.0%, were tested in oven dry, air dry, and wet states. Both compressive and flexural strength were found to be greatest in the oven dry state, presumably due to increased fiber and matrix strength as well as increased fiber/cement bonding which occurs with the controlled removal of water. Flexural toughness, however, was decreased for oven dry samples, and greater fiber fracture (as opposed to the more ductile failure mode of fiber pull-out) was observed in the oven dry samples. It is proposed that this results from differential shrinkage in the fibers’ S1 and S2 layers and increased fiber/cement bonding with drying.

In order to represent the behavior of asphalt concrete mixtures during fatigue tests, a phenomenological model based on the continuous damage theory has been developed. From this model, a method for estimation of fatigue curves was formulated. From a practical point of view, this method could allow us to estimate classic fatigue curves testing a smaller number of specimens. The formulated method was applied to three mixtures, and results were compared with ones from the standard procedure for determining fatigue curves.

In prestressed concrete elements, the stress relaxation losses in steel tendons are of paramount importance to structural design. In this work, experimental and numerical results show a clear relationship between stress relaxation and the presence of residual stresses in steel wires for prestressing concrete. Stress relaxation tests were performed at different initial loads, from 50 to 98% of the rupture load, with three types of wire differing only in their distribution of residual stresses. Cold-drawn wires having the same mechanical properties required by standards (ASTM E421, ISO15630/3) but with different residual stresses will exhibit different stress relaxation losses; such losses increase with increasing surface tensile residual stresses (as a consequence of cold drawing) or increasing inner residual tensile stresses (as a consequence of mechanical postdrawing treatments). Actual expressions for prediction of stress relaxation losses do not take into account residual stresses. Better performance of the wires can be achieved by changing the profile of residual stresses according to the requirements of the structures. This note shows how to deal with this challenge.