Dallas Neville Little

Bonded Concrete Overlay (BCO) construction at the Bush International Airport (IAH) has been subjected to incidences of cracking and delamination that is speculated to be mainly climatically driven due the extremely dry and windy weather conditions prevalent throughout most of the construction period. An investigation was undertaken to determine the causes of the failure of the bond between the overlay and existing pavement as well as the mechanism associated with that. This paper reports portions of the details of the laboratory and field investigation into the distress mechanism but focuses mainly on the analytical approach used to assess the probabilities of the types of cracking and delamination observed.

The addition of calcium (Ca)-based stabilizers to sulfate-rich expansive soils is associated with the formation of ettringite, a deleterious reactant that can cause moderate-to-severe swell-related damage to overlying lightweight infrastructures. This research study was conducted to understand the effects of combining nanosilica admixtures with a traditional Ca-based stabilizer to effectively treat high-sulfate soils with an intent to suppress the ettringite formation. Engineering and microstructural studies were thus performed to gain a comprehensive understanding of the behavior of sulfate-bearing soils treated with lime in the presence of amorphous nanosilica. The engineering studies on treated and untreated soils included strength tests before and after capillary soaking, free swell strain tests, and resilient moduli studies that were performed to study and understand the macrostructural behavior of these soils at different curing periods. Supplemental studies using scanning electron microscope imaging and energy dispersive X-ray spectroscopy, thermal analyses using differential scanning calorimetry, and X-ray diffraction studies were also conducted to determine the microstructural changes that occur within these sulfate-rich soils. The results showed that additional silica phases furnished from nanosilica suppressed the precipitation of ettringite and correspondingly increased the formation of cementitious phases. This study also provided ample evidence that the application of amorphous siliceous nanomaterials positively impacts chemical treatments and reduces the precipitation of ettringite in sulfate-rich soils, thus enhancing their engineering performance.

Organic polyelectrolytes, i.e. anionic poly(sodium 4-styrenesulphonate) (PSS), cationic poly(diallyldimethylammonium chloride) (PDADMAC) and their polyelectrolyte complexes (PECs) were evaluated for stabilisation of calcareous sandy subgrade soil. This paper investigated the effects of polymer type, surface charge type of PEC, concentrations of PEC solutions and dosages of polymer solutions added to the soil on improvement of soil mechanical properties. We found that anionic polymers, for both PECs and individual polyelectrolytes, were superior to their cationic counterparts in improving soil strength. Besides, the constituent polyelectrolytes, PSS and PDADMAC, worked better than their PECs for the specific soil investigated. The strength of polymer-treated soils was also found to increase with the increase in dosages of the polymer solutions as well as curing periods. Furthermore, polymer-treated soil specimens exhibited significant toughness improvement, which was higher than cement-treated samples. Scanning electron microscopy images revealed the abundance of long palygorskite fibres covering the surfaces of larger calcite and dolomite particles and linking surrounding aggregates after adding polymers. This observation suggests the interconnection of palygorskite fibres and their linking networks between and among coarse aggregates as the likely mechanism of polymer stabilisation of the soil studied.

This study is to characterise rheological properties of sulfur-extended asphalts with/without crumb rubber at high, intermediate, and low temperatures using standard asphalt binder tests. Four dosages of sulfur (i.e. 0%, 15%, 30% and 45%) by weight of neat asphalt binder were used. The results indicated that a low level of sulfur addition, such as 15%, softened original asphalt binder. When the sulfur dosage was larger than 15%, the extra sulfur would act as fillers to stiffen asphalt binder. The addition of crumb rubber significantly increased high temperature performance grade. For sulfur-extended asphalts with/without crumb rubber, an increase in the sulfur dosage resulted in an increase of low temperature performance grade. Sulfur-extended asphalt with 15% sulfur exhibited the largest non-recovery creep compliance (Jnr) value, while the 30% and 45% exhibited the lowest values since more extra sulfur acts as fillers to stiffen asphalt binder. The addition of sulfur significantly decreased viscosity. The semi-circular bending fracture test results indicated that the mixture with the addition of 15% sulfur was softer and behaved in a more ductile manner than the others, which is consistent with the asphalt binder test results of high temperature performance grade and non-recovery creep compliance.

This study aims at employing the benchmarking strategy for assessing the state of the practice of the pavement industry in regions that have limited access to or lack the prerequisites for effective pavement practices. The research specifically seeks to propose a benchmark framework that identifies major categories and sub-categories necessary for effective evaluation of the state of practice of the pavement industry in data-scarce regions. The benchmark framework is developed and demonstrated for the case of Kingdom of Saudi Arabia (KSA), where pavement practices in KSA are benchmarked against those of select Gulf Cooperative Council (GCC) countries. For this purpose, data are collected based on a thorough review of literature and relevant industry documentation, as well as based on interviews with project stakeholders. Commonly adopted practices in North America, Europe, and Australia are used as a blueprint for identifying performance gaps and devising recommendations for improvement. Findings from this study would aid highway agencies and stakeholders in performing internal evaluation of their current state-of-practice and adapt the proposed framework to meet their local needs and constraints. Additionally, the paper provides a much-needed compilation of pavement-related data for the GCC countries—a data-scarce region.

The mechanical behavior of asphalt binder is highly sensitive to temperature. The manner in which mechanical characteristics change with temperature can also vary significantly from one asphalt to another. With such variations, grading the rutting resistance of the binder by measuring a mechanical parameter of the binder at a single temperature will not be accurate, nor will ranking by determining the temperature at which a mechanical property reduces to a certain value. For precise characterization of rutting resistance of asphalt binders, a high-temperature binder specification should take into account both the sensitivity of mechanical behavior to changes in temperature and the variations in such temperature sensitivity from one binder to another. This study conducts an experimental investigation and an analysis of existing data in the literature to examine the nature of the temperature dependence of the various material parameters used to characterize rutting resistance of binders. Particularly, the nature of the temperature dependence of the nonrecoverable creep compliance from multiple stress creep recovery (MSCR) tests is investigated. The Arrhenius relationship is found to fit the relationship between mechanical properties and temperature in the high-temperature range reasonably accurately. The activation energy corresponding to the Arrhenius equation, however, is found to vary significantly between the binders. Taking these issues into consideration, a new approach to grading the rutting resistance of asphalt binders is developed that uses the Arrhenius-like temperature dependence exhibited by asphalt binders.

Characterizing crack propagation of asphalt mixtures is helpful for optimizing mixture design and predicting cracking performance of asphalt pavements. This paper explores a new method based on the cyclic semicircular bending (SCB) test to characterize crack growth rate and evaluate fatigue cracking resistance of asphalt mixtures. For characterizing crack growth rate, the difficulty is the measurement of crack length during testing. A digital image correlation (DIC) was used to track the crack propagation during the test, which was used to establish a correlation curve with the corresponding crack mouth opening displacement (CMOD) measurements. Four sulfur-extended asphalt (SEA) mixtures with different dosages of sulfur were evaluated with the proposed cyclic SCB test. The results of the test fitted well to the Paris law function, and the Paris law coefficients of SEA mixtures were identified. They were also consistent with the test results from the monotonic SCB test and horizontal strain field of the crack tip characterized using the DIC. The cyclic SCB test showed substantially lower coefficients of variance in terms of the number of cycles to failure compared with other traditional fatigue tests such as the bending beam fatigue test and the Texas overlay test. Regarding the effects of sulfur, test results showed that a low level of sulfur addition, such as 15%, softens asphalt binder to the stage where more damage can be induced in a controlled-stress mode of loading, while extra sulfur would act as fillers to stiffen the asphalt binder when the dosage was greater, such as 30%–45%.

A model is developed herein for predicting moisture-induced crack growth during a short-term rain event, considered herein to be of duration not greater than 2 hr, in a pre-cracked asphalt concrete pavement built on an expansive base layer. The model is in two parts, the first being the prediction of moisture transport into the pavement, and this part is accompanied by an experimental component focused on measuring the diffusivity of moisture in asphalt concrete. The second part of the model deals with the prediction of the effect of moisture transport on the subsequent mechanical behaviour of the pavement, with emphasis placed on the initiation and propagation of an additional surface crack due to expansion of the base layer. Both components of the model are developed computationally via the use of an in-house one-way coupled finite element code, and a description of this algorithm is briefly reviewed herein. The model developed suggests that the pre-existing crack must extend completely through the asphalt concrete layer into the highly permeable and expansive base layer for there to be significant moisture transport during a short-term rain event. In the case wherein the initial crack extends into the base layer, the stress concentration induced due to dilatation of the base layer upon moisture absorption is predicted to cause additional cracking rapidly.