Journal of Materials in Civil Engineering

High-density polyethylene (HDPE) pipes are subjected to tensile stresses and strains in the axial direction during and after a pulled-in-place installation by horizontal directional drilling or pipe bursting. During these types of installation techniques, creep and stress relaxation are prevalent conditions acting on the pipe. Results from stress relaxation and creep experiments conducted on both whole HDPE pipe samples and coupons trimmed from a pipe’s wall are reported. Stress relaxation experiments were performed at axial strain levels of 3, 1, and 0.5%, and creep experiments were performed at stress levels of 8 and 4 MPa. The merit of testing whole pipe samples as opposed to simply testing coupons trimmed from the pipe wall is investigated by comparing the responses of the pipe samples and coupons. For the particular conditions tested, it was shown that coupons trimmed from the barrel of a pipe responded differently than the whole pipe barrel. In fact, the coupons appeared to exhibit a higher modulus than the whole pipe samples. However, the benefit of testing whole pipe samples is overshadowed by the relative ease with which experiments on coupons can be conducted.

Maxwell models have been parameterized on the basis of rheological data from the literature for bitumens used in pavements to relate differences in rheology to underlying differences in mechanical relaxation times. The data employed were previously measured for bitumens without aging, with rolling thin-film oven (RTFO) aging, and with subsequent pressure aging vessel (PAV) aging. Bitumens in different data sets included different types of bitumen modification. Full time-temperature superposition was applied, with horizontal shift factors $a_T$ based on achieving superposition of phase angle tangent ($\tan \delta$) and vertical shift factors $b_T$ determined based on overlap of storage and loss moduli. The results determined for the horizontal shift factor followed the Williams-Landel-Ferry equation with parameters that differed for each bitumen. Dynamic modulus data were represented by using a series of discrete Maxwell models. Fand suggested a continuous yet asymmetric distribution of relaxation times on a logarithmic time axis. PAV-aged bitumens showed increased modulus contributions at longer relaxation times than RTFO-aged bitumens.

The research presented in this paper is related to the durability of cement renders on façades, based on fieldwork data relative to the condition and extent of degradation of 100 façades of residential buildings in Portugal. Deterioration paths are obtained for staining, cracking, and detachment that show the loss of performance of the façade over time until a critical minimum acceptance level is reached, which is considered an estimated durability limit. These degradation patterns are analyzed individually to confirm whether any of three types of defects can effectively be considered limit states for the durability of cement renders on façades. The combined effect of all the defects that occur is also modeled as a single degradation path, and the expected service life is quantified. The results confirm that detachment constitutes a limit state of cement-rendered façades because it directly affects the physical durability of renders. Staining and cracking alone do not generally tend to signal the end of the physical durability threshold of renders, regardless of their impact on the performance and visual quality of the façade. However, when all degradation mechanisms are considered simultaneously, the estimated durability intervals correspond to a 50% additional decrease of the physical durability limit of renders. These results are in line with the general perception of damage to the façade, on which the decision to repair is based. The conclusions suggest that actual service life should be used (as reference service life), as opposed to durability data obtained through limit state conditions.

Magnesium potassium phosphate cement (MKPC) is usually produced by using dead burned MgO and potassium dihydrogen phosphate. A new MKPC was prepared by using combination of potassium dihydrogen phosphate (${\mathrm{KH}}_2{\mathrm{PO}}_4$) and disodium hydrogen phosphate (${\mathrm{Na}}_2{\mathrm{HPO}}_4·12{\mathrm{H}}_2\mathrm{O}$) in certain ratios instead of potassium dihydrogen phosphate alone. To investigate the effect of disodium hydrogen phosphate on hydration and hardening of MKPC, pH value, hydration temperature, setting times, and strength development were measured. The results indicated that disodium hydrogen phosphate increased the pH value of MKPC paste, resulted in endothermic reactions, and cooled MKPC paste. Thus, it retarded early hydration, improved the fluidity, and increased setting times of MKPC paste. Although the early compressive strength of hardened MKPC made with a combination of the two phosphates was slightly lower than that of hardened MKPC prepared with single potassium dihydrogen phosphate, its strength development is sustaining and was higher than that of hardened MKPC with single potassium dihydrogen phosphate at 60 days because of better crystallization and more stable hydration products.

In this paper, two types of acrylics, polyacrylate (PA), a copolymer of methyl methacrylate, acrylic acid, and others, and polyurethane-modified PA (PU/PA), are investigated in their interactions with inorganic phases in polymer-modified cement-based mixtures and in their mechanisms in improving both mechanical properties and durability of cement-based materials. In these investigations, the total organic carbon content (TOC) method is used to study the adsorption of polymer particles in mixtures. An aqueous tube test, x-ray diffraction (XRD), thermal gravity analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) are employed to study the possible chemical reactions between the latexes and cement hydrates. Scanning electron microscopy (SEM) and energy-dispersive x-ray analysis (EDX) are used to observe the film formation and the final morphology of PA- and PU/PA-modified mortars. PU/PA latex is found to be relatively stable, and the behaviors of PU/PA-modified mixtures can be explained by Ohama’s model. On the other hand, molecules of PA latex are very active in cement-based mixtures. Moreover, the normal assumption that polymer particles are uniformly dispersed in aqueous phase is invalid in PA-modified mixtures. Chemical reactions occur between PA latex and cement hydrates, especially calcium hydroxide. In the final comatrix of PA-modified mortar, no PA film with high purity can be distinguished by SEM/EDX. Based on the findings, a new model with a four-step procedure is proposed to explain the behaviors and properties of PA latex-modified cement-based materials.

During the last two decades, several test methods and performance-based test specifications have been developed to select asphalt binders for use under different traffic and environmental conditions. The test equipment and methods are continually being improved to enhance the reliability with which materials can be selected for optimal performance. One of the procedures to assess rutting susceptibility of asphalt binders is the multiple-stress creep recovery (MSCR) test. Although the MSCR is a promising test method, test variables such as stress level, test geometry, and the number of cycles (total time) need to be carefully evaluated. This paper presents findings from a laboratory investigation of some of these variables. The dynamic shear rheometer (DSR) was used to evaluate the mechanical response of the asphalt binder by varying the stress level, test geometry, and temperature. The results were analyzed on the basis of recoverable and permanent strain to estimate the effect of changing geometry and increasing stress level. Results show that the test geometry used with the DSR (parallel plate versus cone and plate) has a significant effect on the measured properties, particularly at high stress levels or longer durations of loading. Standard parallel plates with a 1 mm gap may allow the binder to flow because of instability and lead to change in the specimen geometry during a repeated loading test. This tertiary-like behavior, which primarily happens at higher number of cycles (more than 10) might be mistaken for tertiary flow and can be misleading. Although decreasing the gap to 275 micrometers will increase the confining stress and alleviate the problem to some extent, using a cone and plate instead of a parallel plate is highly beneficial to reflect the true material behavior. The findings point out the importance of considering specimen geometry type and size effect while interpreting test results. With cone and plate geometry, the results also demonstrate that tertiary flow is an important part of binder behavior at high stress levels and extensive loading times. These considerations are particularly important when correlations between binder and mixture permanent deformation, as measured in the new flow number test, are under investigation.

An inspection and diagnosis support system is proposed for natural stone cladding (NSC) on walls and pavements in order to systemize inspections and make them more objective. The inclusion of this system in a maintenance plan aims at preventing degradation of this type of cladding and its substrate. The system is based initially on the identification and classification of defects and probable causes associated with NSC. These data are used to compile correlation matrices of defects/probable causes and defects/defects and create defect forms with relevant data on each defect. The appropriate diagnosis and repair methods are then identified and classified, and correlation matrices of defects and diagnosis methods and defects and repair methods are assembled. An individual form with relevant data is created for each diagnosis and repair method. The system proposed was validated through 128 inspections of NSC, which were afterwards subjected to statistical posttreatment and analysis.

This paper presents the findings of a laboratory investigation of the characterization of recycled crushed brick and an assessment of its performance as a pavement subbase material. The properties of the recycled crushed brick were compared with the local state road authority specifications in Australia to assess its performance as a pavement subbase material. The experimental program was extensive and included tests such as particle size distribution, modified Proctor compaction, particle density, water absorption, California bearing ratio, Los Angeles abrasion loss, pH, organic content, static triaxial, and repeated load triaxial tests. California bearing ratio values were found to satisfy the local state road authority requirements for a lower subbase material. The Los Angeles abrasion loss value obtained was just above the maximum limits specified for pavement subbase materials. The repeat load triaxial testing established that crushed brick would perform satisfactorily at a 65% moisture ratio level. At higher moisture ratio levels, shear strength of the crushed brick was found to be reduced beyond the acceptable limits. The results of the repeat load triaxial testing indicate that only recycled crushed brick with a moisture ratio of around 65% is a viable material for usage in pavement subbase applications. The geotechnical testing results indicate that crushed brick may have to be blended with other durable recycled aggregates to improve its durability and to enhance its performance in pavement subbase applications.

This paper presents the results of our study to investigate the influence of natural wax in asphalt binders, warm-mix asphalt (WMA) additives, and reduced short-term aging on viscosity, stiffness, susceptibility to permanent deformation, fracture resistance, and thermal cracking resistance of asphalt binders. We used two controls to differentiate between the influence of WMA additive and that of reduced aging on the rheology of asphalt binders. The asphalt binder used in a WMA undergoes reduced short-term aging and consequently has relatively reduced stiffness compared with the binder in a similar hot-mix asphalt (HMA). Results indicate that certain WMA additives compensate, whereas others aggravate the initial reduced stiffness of asphalt binders used in WMA. Short-term aged binders with high natural wax content demonstrated strong interactions with some of the WMA additives and increased susceptibility to permanent deformation. In most cases, pressure aging vessel (PAV) residues of binders with WMA additives had similar or lower fracture resistance compared with PAV residues of binders that were subjected to conventional short-term aging. Results from this study suggest that strategies—such as the use of recycled asphalt—to compensate for the initially reduced stiffness of binders in WMA mixtures must be carefully selected for each asphalt binder–WMA additive pair to avoid an adverse impact on the fatigue cracking performance of the mix.

This research evaluates the average crack spacing of overlay-strengthened RC beams. Current equations in different structural codes for predicting the average crack spacing of RC beams with multilayered reinforcing bars have proved inapplicable to overlay-strengthened RC beams, although both types of beams are reinforced with multiple layers. We have developed a simple, practical analytical model that can predict the average crack spacing of this type of beam. We analyzed an overlay-strengthened beam element using equilibrium and compatibility equations to formulate the average stresses of concrete, overlay, and tension reinforcement. Then we made a series of comparisons among various types of beam elements, using the experimental investigations to verify the model’s validity and reliability. The proposed model performs satisfactorily against measured responses from the experimental database.

Asphalt mixtures have been demonstrated to be anisotropic materials in both laboratory and field tests. The anisotropy of asphalt mixtures consists of inherent anisotropy and stress-induced anisotropy. In previous work, the inherent anisotropy of asphalt mixtures was quantified by using only the inclination angles of the coarse aggregate particles in the asphalt mixtures. However, the inclination of fine aggregates also has a contribution to the inherent anisotropy. Moreover, the contribution to the inherent anisotropy of each aggregate may not be the same as in the previous work but will depend on the size, orientation, and sphericity of the aggregate particle. This paper quantifies the internal microstructure of the aggregates in asphalt mixtures by using an aggregate-related geometric parameter, the vector magnitude. The original formulation of the vector magnitude, which addresses only the orientation of coarse aggregates, is modified to account for not only the coarse aggregate orientation, but also the size, orientation, and sphericity of coarse and fine aggregates. This formulation is applied to cylindrical lab-mixed lab-compacted asphalt mixture specimens varying in asphalt binder type, air void content, and aging period. The vertical modulus and the horizontal modulus are also measured by using nondestructive tests. A relationship between the modified vector magnitude and the modulus ratio of the vertical modulus to the horizontal modulus is developed to quantify the influence of the inherent microstructure of the aggregates on the anisotropy of the mixtures. The modulus ratio is found to depend solely on the aggregate characteristics including the inclination angle, size, and sphericity, and it is independent of the asphalt binder type, air void content, and aging period. The inclination angle, itself, proves to be insufficient to quantify the inherent anisotropy of the asphalt mixtures.

This paper presents a study on the effects of two laboratory compaction methods, namely, vibrating compaction and modified Proctor compaction on the stress-strain characteristics and shear strength of graded crushed stone. The results of the triaxial shear test show that samples made by vibrating compaction possess higher peak strength, higher initial modulus of elasticity, and lower failure strain than samples made by the modified proctor compaction. Specifically, the cohesion, friction angle, and shear strength of the samples made by the vibrating compaction increase by 38%, 2 degrees, and 10%, respectively, over the samples made by the modified Proctor compaction. In summary, the vibrating compaction method generally performs better than the modified Proctor compaction method, owing to a better distribution of particle orientation. Therefore, it is recommended that, in practice, the vibrating roller should be applied for the construction of graded crushed stone.