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Moisture damage of asphalt mixtures is a major distress affecting the durability of asphalt pavements. The loaded wheel tracking (LWT) test is gaining popularity in determining moisture damage because of its ability to relate laboratory performance to field performance. However, the accuracy of LWT’s “pass/fail” criteria for screening mixtures is limited. The objective of this study was to evaluate the capability of the LWT test to identify moisture susceptibility of asphalt mixtures with different moisture conditioning protocols. Seven 12.5 mm asphalt mixtures with two asphalt binder types (unmodified PG 67-22 and modified PG 70-22), and three aggregate types (limestone, crushed gravel, and a semi-crushed gravel) were utilized. Asphalt binder and mixture samples were subjected to five conditioning levels, namely, a control; single freeze–thaw-; triple freeze–thaw-; MiST 3500 cycles; and MiST 7000 cycles. Frequency sweep at multiple temperatures and frequencies, and multiple stress creep recovery tests were performed to evaluate asphalt binders. LWT test was used to evaluate the asphalt mixture samples. Freeze–thaw and MiST conditioning resulted in an increase in stiffness in the asphalt binders as compared with the control. Further, freeze–thaw and MiST conditioning resulted in an increase in rut depth compared with the control asphalt mixture. The conditioning protocols evaluated were effective in exposing moisture-sensitive mixtures, which initially showed compliance with Louisiana asphalt mixture design specifications.

This paper evaluates the mechanical properties of rubberized asphalt binder and mix containing 5% and 10% rubber. This rubberized asphalt binder was manufactured in a field-blend process using devulcanized rubber particles, finer than 250 microns, derived from waste tires. Comparison between the rubberized binder and the base binder test results showed that the rubberized binders had higher complex moduli and lower phase angles at the grade temperature. They also had a higher percentage recovery in the multiple stress creep recovery test, and a significant creep stiffness reduction in the bending beam rheometer test. Given the low rubber content and small rubber particle size, this rubberized binder can be used in dense-graded mixes, whereas asphalt rubber binders, with larger rubber particles and higher rubber content (>15%), must be used in gap- or open-graded mixes. This rubberized dense-graded mix met the volumetric design criteria at the same binder content as the control mix prepared with the unmodified base binder. Laboratory tests on the mix included repeated load triaxial, Hamburg wheel track, flexural dynamic modulus, and beam fatigue. The rubberized mixes had slightly lower stiffnesses than the control mix, but better resistance to moisture damage, rutting, and fatigue cracking. A strong linear correlation was found between the carbonyl area index and the rheological properties of the long-term aged binder and fatigue life of the mixes. Based on these findings, these rubber-modified binders can be considered for use in dense-graded mixes to improve overall performance and make use of waste tires.

Open graded asphalt friction courses (OGAFCs) are specialty asphalt mixtures used to improve skid resistance and surface drainage. OGAFCs have additional benefits of reduced splash and spray, and lower tire–pavement interaction noise. Prolonged exposure to rainwater and load transfer through stone-on-stone contact in OGAFCs demands aggregates that are strong and hydrophobic. Rainwater acidity is expected to affect the aggregate–asphalt bond and thus moisture damage performance of OGAFC. This paper investigates the effect of rainwater acidity on moisture sensitivity of OGAFC mixtures with different aggregate types (natural aggregate, basic oxygen furnace (BOF) steel slag, and combinations of both) and modified binder types. For the first time, the present research reports the moisture damage potential of BOF OGAFC mixtures under different moisture conditioning environments created by varying the pH of contact water. With different combinations of BOF slag and natural aggregates (100:0, 25:75, 50:50, 75:25, and 0:100), and binders (polymer and crumb rubber modified), OGAFC mixtures were characterized for moisture damage through tensile strength ratio, wet Cantabro abrasion loss, and modified boiling water tests. Functional aspects of OGAFC mixtures subjected to moisture conditioning under different pH environments were also evaluated through permeability testing. Results showed that an acidic environment exacerbated the moisture damage, however, OGAFC mixtures containing BOF slag showed better performance than the control mixture (with natural aggregates only). Inclusion of BOF slag in OGAFC mixtures enhanced resistance to moisture damage under both pH environments. OGAFC mixes with 100% BOF slag content performed the best considering all moisture damage tests under both conditioning environments.

Crack sealing prevents the ingress of water in the pavement structure, thus preventing the weakening of the pavement and delaying its deterioration. Earlier studies indicate that sealing pavements in areas with a high ground water table (GWT) may prevent moisture from escaping upwards through cracks in asphalt pavements, therefore, accelerating stripping. The objective of this study was to provide guidelines for using crack sealing to minimize moisture entrapment under cracks, thus reducing stripping on low volume roadways. To achieve this, a calibrated Finite Element (FE) model was used to model a field experiment consisting of cracked and crack-sealed asphalt pavement sections. Sensitivity analysis was then conducted to compare crack-sealed and unsealed sections under different GWT levels, air relative humidity, air temperatures, rain intensities, and asphalt hydraulic conductivities. Results indicate that crack sealing could be applied under common rain intensities in Louisiana and any GWT depth without potential for stripping because of moisture entrapment if the hydraulic conductivity of the original pavement does not exceed 2 × 10–6 m/s. Yet, crack sealing should be applied after a dry period to ensure that the existing moisture in the original pavement is minimal. A non-linear regression model was developed for use in the Southern United States to help determine whether crack sealing should be used to avoid moisture damage in a cracked pavement at a given site based on the GWT and air relative humidity without the need for FE simulations. This can be a useful tool when planning maintenance activities.

One of the major causes of premature failure in asphalt pavements is moisture damage. Asphalt mixtures designed without considering climate impacts may suffer from durability problems caused by movement of water inside the asphalt mixture. Rolling traffic over wet pavement builds up pore pressure in the mixture, which will consequently accelerate deterioration. The objective of the study was to assess the moisture damage to asphalt concrete mixtures by means of complex modulus testing of dry and moisture-conditioned asphalt specimens with various mixture compositions. The asphalt mixtures were conditioned with the Moisture Induced Sensitivity Tester (MIST), which aims to replicate pore pressure in field conditions. The results showed a decline in stiffness modulus and a reduction in elastic properties after MIST conditioning. In addition, the results indicated that binder content and air void content had a significant influence on the reduction in stiffness. To capture the relationship between air void content, binder content, and the reduction in stiffness, a relationship was developed and validated with measurements on cores extracted in the field.

Asphalt mixes often have many ingredients that can interact with each other. When put into service, where there are multiple environmental effects, there are many interactions that need mixture testing. This paper’s objective was to evaluate laboratory conditioning protocols coupled with subsequent property measurements for their ability to detect damage of asphalt mixtures in the southeastern U.S. climate (or similar climates). The investigation’s focus is the property measurements themselves, and in particular how a given test can simultaneously assess multiple types of damage (i.e. oxidation, moisture damage, and freeze-thaw damage). While in service, mixtures can be damaged in multiple manners so laboratory conditioning protocols that expose specimens to multiple types of damage are needed as are test(s) that can detect these damages in a manner that can help assess performance during service. Four plant produced mixtures with all virgin ingredients were evaluated at intermediate temperatures with mixture and binder tests. The mixtures were well suited for such a comparison because they consisted of all virgin binder. Indirect tensile (IDT) strength did not relate to Cantabro Mass Loss (CML) or binder test results, which was concerning. Even more concerning was IDT’s inability to respond to laboratory conditioning protocols that considered multiple environmental effects (i.e., oxidation, moisture, and freeze-thaw). CML results related to binder properties and were able to reasonably detect multiple types of environmental effects. As such, Cantabro testing is recommended over tensile strength for intermediate temperature mixture property assessments related to non-load associated environmental effects.

The Hamburg wheel-tracking test (HWTT) has shown promise to predict permanent deformation resistance and moisture damage potential of asphalt mixtures. Several state agencies have implemented the test as a mixture evaluation and design tool. One aspect of the test that remains a topic of research is the testing temperature. Many studies and specifications use 50°C for all testing, but some use a test temperature that depends on the base asphalt used in the mixture. Concern exists about the use of 50°C as the sole test temperature in cooler weather regions, such as Wisconsin, because the asphalts used in such regions tend to be relatively soft (high temperature grades of PG 58 and below). This paper presents findings in support of an effort to apply the HWTT to mixtures in cold climates with the use of three test temperatures and several mixture design variables. The paper presents the effects of the mixture design traffic level, the PG of the binder, and the binder modification level on the deformation resistance, creep slope, stripping slope, and stripping inflection point (SIP). The HWTT was found to be sensitive to the factors evaluated in this study. On the basis of statistical analysis of the test data, logical trends were observed. The testing temperature was found to affect not only the response variables but also the level of significance of controlled factors. The effectiveness of the SIP to characterize the moisture sensitivity of mixtures requires more research to validate the effect of moisture damage on HWTT results.

With the growing awareness of sustainable construction practices and because warm-mix asphalt (WMA) is environmentally friendly, WMA is gaining popularity for pavement construction in the United States. Currently, it is generally believed that rutting and moisture damage are two major concerns for WMA pavements, but because WMA requires less aging, its cracking resistance is expected to be improved. One of the primary cracking distresses of concern is transverse cracking, which could be thermal cracking in asphalt pavement or reflective cracking in asphalt overlay caused by underlying thermal cracking. Thus, transverse cracking is another primary distress. This study investigated the long-term field transverse cracking of 28 pavement projects, including WMA pavements and corresponding hot-mix asphalt (HMA) control pavements across the United States, covering different climate zones, WMA technologies, service years, pavement structures, and traffic volume levels. Two distress surveys were conducted at an interval of 2 years, and the material properties of the asphalt mixtures and binders were determined with field cores and extracted binders. The long-term field performance of the WMA and HMA pavements were compared for transverse cracking. The study found that HMA and WMA pavements exhibited comparable transverse cracking. Fracture work density obtained from indirect tensile testing at 14°F was found to be the significant determinant for transverse cracking. Significant mix design parameters were identified that can affect the resistance of mixtures to transverse cracking and that can be employed to guide the development of a well-performing mix design.

Because of the difficulties associated with the generation of finite element meshes based on X-ray computed tomography scans and with the extraordinary computational demands in performing three-dimensional (3-D) finite element analyses, past modeling efforts have focused primarily on two-dimensional representations of asphalt mixtures and have placed no emphasis on the inclusion of the air voids network in the body of an asphalt concrete specimen. A 3-D micromechanical moisture damage model has been developed and implemented in the finite element system CAPA-3D capable of addressing individually the three main phases of asphalt concrete: aggregate, mastic, and air voids. The 3-D finite element meshes of different types of asphalt mixtures were generated on the basis of X-ray scans. By means of CAPA-3D, the significance of the air voids structure in the development of moisture damage in asphalt concrete specimens was demonstrated. Availability of the model enables evaluation and ranking of the contribution of the characteristics of the individual mixture components to the overall mixture moisture resistance.

Moisture damage-related distress is a primary concern limiting the application of cold-mix asphalt (CMA) as an alternative to hot-mix asphalt in the field. Thus, a simple and effective method is needed in the materials selection process to identify moisture susceptible materials. This study presents a modification to the boiling test procedure specified in ASTM D3625 based on the concept that a mix designer can limit moisture damage by controlling coating quality. The test was modified to present CMA-specific sample preparation guidelines and to remove subjectivity from the test by quantifying coating according to image analysis. Coating quality was evaluated with the coating loss ratio, defined as an index to compare coating before and after the boiling of cured loose mixtures. The relationship between coating quality and moisture resistance was verified with two separate tests: the AASHTO TP-91 binder bond strength test and the AASHTO T-283 tensile strength ratio test. The binder bond strength test prov...

The Hamburg wheel tracking test (HWTT) has been widely used as a standard laboratory test to evaluate the moisture susceptibility and rutting resistance of asphalt mixtures. The stripping infection point and the rut depth at a certain number of load cycles are two common parameters obtained from the test. Although these parameters have been widely adopted by several transportation agencies, the accuracy and variability in characterizing mixture properties of these parameters have been questioned. In this study, a novel method to analyze the HWTT results is introduced and three new parameters are proposed to measure the moisture susceptibility and rutting resistance of asphalt mixtures. The new parameters are compared against the current ones to assess their capability to discriminate between three types of asphalt mixtures with different performance results in the HWTT. Significant advantages in characterizing mixture resistance to stripping and rutting are demonstrated by the new parameters. In addition, the effect of antistripping additives and recycled materials on mixture performance in the HWTT is evaluated with mixtures from a field project in Texas. Test results for the new parameters show that the addition of antistripping additives improves the susceptibility of asphalt mixtures to moisture. Specifically, the use of lime is more beneficial for improving mixture performance than a liquid antistripping agent. Conversely, the addition of recycled materials provides mixtures with increased moisture susceptibility but improved rutting resistance.

Long-term moisture exposure has been shown to affect the mechanical performance of polymeric composite structures. This reduction in mechanical performance must be considered during product design in order to ensure long-term structure survival. In order to determine the long-term moisture effects on composite components, representative parts are commonly tested after having been exposed to an accelerated moisture conditioning environment. Accelerated moisture conditions are established in order to rapidly drive moisture into test specimens simulating worst-case long-term exposure scenarios. Currently, accepted methodologies for analyzing the time required to condition specimens are limited, allowing only simple geometry and an assumption that diffusivity rates are independent of the flow path or direction. Therefore, a more advanced finite element method is desired. In this study, a three-dimensional model is developed and implemented in commercial finite element code. The parametric study has been conducted for three-dimensional shapes, moisture diffusion pathways, and varying moisture and temperature conditions. Finite element results are validated with a one-dimensional analytical model and experimental results. A user-subroutine was implemented in commercial finite element code to calculate the moisture content. The ultimate goal for this research is to determine the exposure time for accelerated conditioning that produces the most accurate moisture distribution with the part and minimize over-conditioning of the laminate.

The incorporation of reclaimed asphalt pavement (RAP) into asphalt mixtures exposes some challenges from the design perspective because of the aged asphalt binder in RAP. Steps are being taken to offset the addition of stiff materials, often with the use of rejuvenating additives. This paper summarizes the laboratory evaluation of one of the available bio-rejuvenating agents called BituTech RAP. High RAP content mixtures used in Manitoba, Canada, were evaluated to study the impact of BituTech RAP on the viscoelastic properties of asphalt mixtures to overcome any possible moisture damage or thermal cracking problems that might arise in such a wet–freeze environment. The laboratory experiment consisted of the production and test of mixtures that contained 15% and 50% RAP, with and without BituTech RAP. The 2S2P1D analogical model was used to generate the complex modulus (E*) of the various evaluated mixtures and to assess the influence of BituTech RAP on the storage and loss moduli. The addition of BituTech RAP improved the moisture resistance of the mixtures that contained RAP, as observed after three freeze–thaw cycles. The addition of BituTech RAP restored the thermal cracking properties of the mixtures revealed by the thermal stress restrained specimen test. The use of BituTech RAP could result in cost savings without the need to use a softer binder, as long as the high-temperature properties of the mixtures were not jeopardized.

Loose aggregate raveling from a runway surface creates a risk for foreign object damage to aircraft. To reduce the probability of surface raveling and cracking, engineers often use polymer-modified asphalt (PMA), which has been widely shown to reduce pavement surface damage. Unfortunately, every paving paradigm has exceptions, including performance expectations for PMA. When two high-quality PMA pavement sections exhibited raveling before any damage was noted in the conventional PG 64-22 mix, a forensic analysis was begun. Numerous binder and mixture properties were evaluated, with particular emphasis on moisture damage and accelerated aging coefficients that might indicate binder hardening or embrittlement. The initial (2004) forensic analysis of these 5-year-old pavements eliminated moisture damage as the cause and focused primarily on binder aging. Although significant increases in binder and mixture moduli were noted near the surface as the pavement aged, no definitive failure criteria could be directly tied to the initiation of raveling or surface cracking. This older forensic study is revisited to evaluate the recently proposed Glover–Rowe parameter as a predictor of age-induced surface damage. This damage index, which is easily measured in a dynamic shear rheometer at intermediate temperatures, has been proposed as a materials indicator for timing pavement preservation strategies. For this limited field study, the Glover–Rowe parameter correctly predicted the unexpected onset of raveling for the two PMA sections, as well as the good performance of the conventional section, but other common aging or cracking parameters failed to rank the materials correctly. Further field validation of this parameter is recommended.

Since the late 1970s there has been much research performed to understand better the stripping phenomenon in asphalt mixtures. As a result, there have been changes in both materials and technology over the past 30 years to improve the resistance to moisture damage and the ability to test for performance under adverse moisture conditions. Because of the changes in materials and technologies related to the development and improvement of antistrip agents, this research study was conducted to evaluate the effectiveness of current antistrip agents used in hot-mix asphalt pavements. The objectives of this project were to construct a field test section that used three different antistrip agents in a conventional Superpave® surface mixture and conduct a series of laboratory performance test comparisons using different aging periods to make long-term comparisons of the effectiveness of hydrated lime, liquid additive, and warm-mix asphalt antistrip additives. Multiple freeze–thaw cycles of zero, one, five, and 10 cycles were used for a portion of the research study. The results showed that hydrated lime had the highest tensile strength and highest tensile strength ratio (TSR) values and was the only additive treatment to meet the minimum of 80% TSR for all freeze–thaw cycle combinations. Both five and 10 freeze–thaw cycles were significantly more discriminating for moisture susceptibility than one freeze–thaw cycle alone. Warm-mix asphalt treated mixtures produced low initial tensile strengths, but the strength of these mixtures improved with time.

This paper presents the results of tests of warm-mix asphalt (WMA) mixtures designed for airfield pavements. The study was conducted in two phases. The first phase included laboratory tests on 11 WMA technologies. The tests in Phase 2 were performed on three WMA mixtures and one hot-mix asphalt (HMA) mixture produced in an asphalt plant. The evaluation included performance tests to assess WMA susceptibility to permanent deformation and moisture damage compared with that of HMA produced with the same aggregate blend. Test results indicated that WMA potentially was a viable product for surface mixtures on airfield pavements. Although WMA exhibited poorer performance than HMA in moisture damage tests on laboratory-produced specimens, the plant-produced mix indicated little difference compared with HMA. Rutting potential for WMA was somewhat greater than for HMA for mixtures produced both in the laboratory and in an asphalt plant according to asphalt pavement analyzer and Hamburg wheel tracking tests. Differences in performance of WMA mixtures were not attributed to a specific WMA technology category. Variations in performance test results between laboratory-produced specimens and plant-produced specimens were noted and indicated a need to require performance testing as part of a comprehensive quality assurance plan.

Despite the detrimental effects of moisture damage in asphalt pavements, few macroscale models are capable of modeling this important phenomenon. Existing models have limitations in accounting for the irreversibility and time dependency of moisture-induced damage. This study presents a moisture damage model based on continuum damage mechanics. Adhesive and cohesive moisture damage phenomena are modeled independently; this procedure allows for the introduction of fundamental mechanical properties for each process and for modeling the transition between adhesive and cohesive damage. Two- and three-dimensional simulations are performed, and the results of the simulations are presented to demonstrate the applicability and utility of these micromechanical computational models. It is shown that the proposed moisture damage model can simulate the effect of moisture damage on the mechanical response of asphalt concrete subjected to different loading conditions. The model also provides useful insight into the effect of mixture design and material properties on resistance to moisture damage.

This study evaluated the resistance of field-produced warm-mix asphalt (WMA) mixtures obtained from field sections in Manitoba, Canada, to moisture damage, reflective cracking, and permanent deformation. The project, constructed in the summer of 2010, included a side-by-side hot-mix asphalt (HMA) control section and three WMA sections in which the Advera, Evotherm 3G, and Sasobit technologies were used. The mixtures' susceptibility to moisture damage was evaluated by their unconditioned and moisture-conditioned indirect tensile strength (ITS) and dynamic modulus (|E*|) at multiple freeze–thaw cycles. All mixtures met the minimum unconditioned ITS criterion of 65 psi at 77°F and the minimum indirect tensile strength ratio of 80% after one freeze–thaw cycle. Although comparable tensile strength and |E*| ratios were observed for the mixtures after one freeze–thaw cycle, the WMA–Sasobit mixture exhibited lower resistance to moisture damage when assessed after three freeze–thaw cycles. Except for the WMA–Sasobit mixture, the WMA mixtures showed similar or higher resistance to reflective cracking when measured by means of the Texas A&M Transportation Institute overlay tester. All WMA mixtures exhibited similar resistance to permanent deformation in the flow number test at the LTPPBind 50% reliability temperature (118°F) as compared with the HMA control section. However, none of the mixtures (including the HMA) met the proposed flow number criterion for WMA. When the mixtures were tested in the flow number test at the effective pavement temperature (92°F), a different ranking for their resistance to rutting was detected. Continuous field monitoring for performance of the various sections will help in assessing any proposed criterion as well as the effectiveness of WMA mixtures in cold weather areas such as Manitoba.

The compaction of asphalt mixtures has a significant influence on their performance. Insufficient compaction leads to several distresses, such as premature permanent deformation, excessive aging, and moisture damage, even if all desirable mixture design characteristics are met. Currently, no acceptable method relates asphalt pavement density to the compaction pattern. The compaction pattern required to achieve the desired density is established on the basis of experience and trial and error, a process that is time-consuming and expensive. This study involved comprehensive experimental evaluation of several test sections that were constructed with different asphalt mixtures by various compaction methods. Results of these experiments were used to determine the effects of compaction temperature, compaction method, mixture design, and base type on the compactability of asphalt mixtures. In addition, the paper presents a systematic method to determine the compaction pattern required to achieve the desired density of asphalt pavements. This method lends itself to integration in an automated system that can be used by roller operators to estimate density during construction.

This study extensively evaluated the resistance to moisture damage and thermal cracking of hot-mix asphalt (HMA) mixtures with high recycled asphalt pavement (RAP) content (up to 50%) from field sections on provincial Highway 8 between Gimli and Hnausa in Manitoba, Canada. A comparison between the properties and performance of the field-produced and laboratory-produced mixtures was also conducted and was included in this study. HMA mixtures with 50% RAP resulted in acceptable resistance to moisture damage and thermal cracking. The use of multiple freeze–thaw cycles provided a better characterization of the mixtures' resistance to moisture damage. Acceptable correlations were observed between the estimated critical temperatures from the blending chart and the measured ones from the recovered asphalt binders. Overall, laboratory-produced mixtures could be used to evaluate the relative resistance of the field-produced mixtures to moisture damage and thermal cracking.

Understanding moisture damage mechanisms in asphalt pavements and evaluating the right combination of materials that are resistant to moisture damage are important. Moisture damage is the loss of strength or stiffness in asphalt mixtures caused by a combination of mechanical loading and moisture. Many test methods have been developed to evaluate loss of adhesion and cohesion in binders. However, a simple procedure to address moisture damage in the asphalt–aggregate interface is not available. The feasibility of the newly developed bitumen bond strength (BBS) test for moisture damage characterization was investigated. An experimental matrix that included various binders, modifications, and aggregates to account for the chemical and physical conditions in the aggregate–asphalt interface was completed. A statistical analysis was performed to verify reproducibility of the BBS test. The results indicated that the bond strength of asphalt–aggregate systems was highly dependent on modification and moisture exposure time. Polymers were found to improve the adhesion between asphalt and aggregate as well as the cohesion within the binder. Results from this study indicated that the BBS test was repeatable and reproducible. To further validate the effectiveness of the BBS test, a comparison of the BBS test results and the modified dynamic shear rheometer strain sweep test was conducted. The comparison showed that the BBS test could rank materials similarly to a more sophisticated and time-consuming test.

An ongoing research effort seeks to develop alternative asphalt surface mixes that will be quiet and durable without sacrificing safety. The effects of several common combinations of binder type and additive on noise reduction and durability of an open-graded asphalt mix with small aggregate size were investigated. Five binder types and two additives were selected for a 4.75-mm nominal maximum aggregate size gradation. A series of laboratory tests was conducted to evaluate their performance-related pavement surface properties. Results showed that the use of polymer-modified or rubberized binders instead of unmodified binder in the 4.75-mm open-graded mixture reduced permeability but increased acoustic absorption, with the mixture containing asphalt rubber binder showing the most acoustic absorption improvement. The use of asphalt rubber could also increase the mixture resistance to moisture damage, premature failure, raveling, and rutting. There were preliminary indications of friction improvement by replacement of conventional binder with asphalt rubber binder in the small-size-aggregate, open-graded asphalt mix.

Significant amounts of money are spent annually on the rehabilitation of damaged pavements and approach slabs near bridge ends. Investigation of such failures often reveals that saturated base and subgrade materials or the loss of soil material from underneath the approach slab, pavement, or rip-rap slabs have contributed to failure. This paper reports findings from a research study entitled Water Intrusion in Base–Subgrade Materials at Bridge Ends. The objectives of this research project were to identify potential sources of water intrusion at bridge ends and develop maintenance strategies that can be economically implemented in the field to minimize future occurrences of the problem. The study focused on existing, in-service bridges and remedial strategies that have been successfully implemented. A survey questionnaire was developed and sent to all 25 Texas Department of Transportation administrative districts to collect information about the major factors contributing to water intrusion and bridge-end settlement problems. Field evaluations of selected bridges in four Texas DOT districts were conducted, and one bridge site was selected for detailed field study. On the basis of the information collected, the researchers developed a site assessment protocol to evaluate the potential of a particular site to incur water intrusion and methods to develop optimum repair strategies. The paper reports on the commonly observed sources of water intrusion at the bridge sites investigated. It also lists the preventive maintenance steps that must be taken to ensure that bridge approach pavements have adequate service lives.

The Superpave® mix design method has been used by the Colorado Department of Transportation since 1995. Initially, the number of design gyrations used was as recommended by SHRP research. However, the asphalt contents of these preliminary paving mixtures were lower than what had been historically successful for similar dense graded mixtures under similar conditions. This lower asphalt content began leading to premature moisture damage failures. Therefore, a study was initiated to determine how the pavements constructed according to the original Superpave compaction criteria densified under traffic. An experiment was designed to evaluate the in situ voids in 22 full-scale pavements over a 6-year period. Projects were selected on the basis of variation in traffic, environment, temperature, and elevation. Results of this research indicate that the original number of design gyrations recommended by SHRP for field-mixed–laboratory-compacted materials results in pavements that did not compact sufficiently under traffic, resulting in higher air voids than desired after 3 years service. An adjustment to the original SHRP design gyration levels was done in a subsequent study based on NCHRP research. The result of this revision has been a decrease in voids levels after 3 years of service with a corresponding improvement in performance. Further fine-tuning is needed and will be implemented in the future.

Conventional methods to quantify the moisture sensitivity of asphalt mixtures are based on the comparison of mechanical properties of the mix before and after a moisture-conditioning process. Although this approach consolidates the effect of material and mixture properties on moisture sensitivity, it does not identify the causes responsible for the poor or good performance of the mixture. In this study, surface free energy of asphalt binders and aggregates was used to derive energy parameters that quantify the moisture sensitivity of various combinations of materials. The moisture sensitivity of 12 asphalt mixtures carefully designed to represent a wide range of asphalt-aggregate interactions was measured in the laboratory under controlled conditions. Test results indicate that the moisture sensitivity of these mixtures correlates well with the energy parameters, which are based on the surface energy properties of the constituent materials. Incorporating the specific surface area of the aggregate into the energy parameters improved this correlation. The proposed energy parameters have the potential to serve as an effective tool by which to select material combinations that result in asphalt mixtures that are more resistant to moisture-induced damage.

Warm-mix asphalt (WMA) mixes produced by an emulsion process were evaluated under accelerated loading in three total sections of the National Center for Asphalt Technology Test Track and used as the surface mix for two of the sections. Evotherm was incorporated into the same mixes used previously on the track. In-place densities of the WMA surface layers were equal to or better than the hot-mix asphalt (HMA) surface layers, even when compaction temperatures were reduced by 8°C to 42°C (15°F to 75°F). Laboratory rutting-susceptibility tests conducted in the asphalt pavement analyzer indicated similar performance for the WMA and HMA surface mixes with the PG 67-22 base asphalt. However, laboratory tests indicated an increased potential for moisture damage with the WMA mixes. The two WMA sections and the HMA section showed excellent rutting performance in the field after the application of 515,333 equivalent single-axle loads in a 43-day period. One of the WMA sections was also evaluated for quick turnover to traffic and showed good performance.

The presence of pore water in mixtures can cause premature failure of hot-mix asphalt pavements. The processes typically associated with moisture damage are complex and occur over a long period of time in the field. Short of being able to simulate each of the possible mechanisms of moisture damage directly, the ideal laboratory-based conditioning system should accelerate the penetration of moisture through the asphalt film and at the same time minimize complicating effects. This paper presents the results of an experiment conducted to determine whether it was possible to use cyclic pore pressures to induce enough damage to distinguish between mixtures known to be highly resistant from mixtures known to be susceptible to moisture damage. Experimental constraints included requirements that conditioning be accomplished within a reasonable length of time and that typical laboratory equipment be used. Evaluation of the resulting effects of moisture damage included the use of the Superpave® indirect tension test and the energy ratio parameter. Findings show that cyclic pore pressures can be used to accelerate moisture damage enough to distinguish between mixtures known to be strippers and those known to be highly resistant to moisture damage. The use of cyclic pore pressures to accelerate moisture damage in mixtures may minimize the introduction of other confounding damage effects on the mixtures.

Questionnaires collected from occupants and visual inspections have been used to assess exposure related to moisture damage in buildings. Aims of this study were to find out if observations of moisture damage made by occupants were different from observations made by an independent inspector, and if inspectors’ observations were independent of the observing inspector. Interviewer-administered questionnaires were collected from occupants of 363 residences; subsequently, the buildings were inspected by a civil engineer. A second examination was done in 15 buildings by another engineer with similar training and work experience. The questionnaire collected from the occupants included the same items as the inspectors’ checklists related to occurrence of moisture damage, visible mould growth and odours. The inspectors collected additional data including moisture and temperature measurements and estimated size of damage. The inspector observed more damage sites than the occupants, and the overall agreement between the inspector and the occupants was poor (average 0.23). On the other hand, the agreement between the 2 inspectors was higher (average 0.41). Overall, the results suggest that studies related to moisture damage in buildings should preferably include standardised inspections by trained staff.

Indoor air problems present a considerable challenge for workplace personnel. Here, we report the follow-up results of employees in a healthcare centre in Southern Finland. In this building there was moisture damage, including moulds and other microbial growth, as well as associated indoor air problems, such as sporadic high ammonia concentrations, and there was suspicion of mites. The indoor air quality was determined through mould and volatile organic compound measurements. Symptoms were recorded on the MM-40-FIN questionnaire. Two employees were also examined at the Clinic for Indoor Air Health Problems, Helsinki University Central Hospital. Employees’ complaints about dustiness and stuffiness remained mostly unchanged during the 6 follow-up years. After several renovations of the building, the eye complaints diminished to about half. Two case reports showed disappearance of symptoms when their exposure ceased. However, the complexity of indoor air problems makes it difficult to improve the indoor climate and relieve symptoms with simple renovations. Sensitive or allergic individuals may more readily react than others to these moistureassociated problems.

Effective source control is the key issue in all matters concerning hygiene and hospitals are by no means an exception. Besides taking steps to provide good isolation, this means that local ventilation exhausts and isolating enclosures should be used if there are obvious or even probable sources. Quick repair of moisture damage from whatever source is important. The control of microbes dispersed by the personnel in a hospital is also controlled most effectively by wearing special protective clothing and restricting it to the environment where it is needed. Even though it is generally admitted by the medical professionals that prevention is highly cost-effective, this is, nevertheless, commonly forgotten in hospitals.

The pavement community has recognized that moisture damage of hot-mix asphalt (HMA) has been a serious problem since the early 1960s. Numerous additives have been evaluated with the objective of reducing the potential of moisture damage in HMA mixtures; lime has been one of the most common ones. The Nevada Department of Transportation has been using lime in HMA mixtures since the mid-1980s. The objective of this research was to quantify the improvements in pavement performance that have been realized through the addition of lime to HMA mixtures. The program evaluated field samples and pavement performance data from untreated and lime-treated pavements. The properties of untreated and lime-treated mixtures from field projects in the southern and northwestern parts of Nevada indicate that lime treatment of Nevada's aggregates significantly improves the moisture resistance of HMA mixtures. The study showed that lime-treated HMA mixtures become significantly more resistant to multiple freeze–thaw cycles than do the untreated mixtures. Long-term pavement performance data indicate that under similar environmental and traffic conditions, the lime-treated mixtures provide better-performing pavements with fewer requirements for maintenance and rehabilitation activities. The analysis of the impact of lime on pavement life indicates that lime treatment extends the performance life of HMA pavements by an average of 3 years. This extension represents an average increase of 38% in the expected pavement life.

A micromechanical model was established based on the fluid dynamics theory. This model could be used to calculate several kinds of data when the asphalt pavement under the influence of traffic loading is in water-saturated condition. The results showed that the maximum pressure inside the effective pore was located at the junction between exit slits and the pore wall. There was a positive correlation between the pressure and the vehicle speed. Therefore, the repeated traffic loading could cause emulsification, shift and even peeling of the asphalt membrane. Moreover, the bigger size of the exit slit is, the higher velocity of the fluid has. The high velocity flow keeps scouring both the exit slit and the lower boundary of pore wall. It will cause a bigger slit. Pressure distribution inside the effective pore is related to the number of the exit slit which connect with the pore. More exit slits means bigger pressure inside the effective pore. In addition, if asphalt membranes at exit slits have micro-cracking, the cumulative damage could appear easily and asphalt membranes could be peeled easily. Finally, a test was conducted so as to obtain the bonding strength and adhesion strength between asphalt and aggregate. Then, we can get accurate damage form and position during the scour process by comparing the numerical simulation results with experiment results.

The Florida Department of Transportation (FDOT) initiated monitoring of its first Superpave section on I-75 in Columbia County for stripping potential using AASHTO T 283, which specifies that all conditioned test samples be saturated to between 55 and 80 percent based on 7 ± 1 percent air voids. A fairly large saturation range is allowed because it was thought that mixtures may have different percentages of permeable air voids. However, the potential interaction between air void content and the level of saturation has not been fully investigated. It is also not clear whether test results from samples saturated to 55 percent are comparable with those of the same mixture saturated to 80 percent for a similar air void content. Therefore, although FDOT adopted AASHTO T 283, it also initiated a parallel study on the effects of different degrees of saturation on moisture damage. Findings are reported of both the ongoing monitoring of the I-75 project for potential stripping and the investigation of the effects of different levels of saturation on moisture susceptibility test results as determined using AASHTO T 283.

The performance of three antistrip additives—a lime-treated aggregate, an amine-treated asphalt and a styrene-butadiene rubber-treated aggregate, was studied with an environmental scanning electron microscope (ESEM). Samples were prepared with the untreated asphalt and aggregate, the treated asphalt with untreated aggregate and untreated asphalt with each treated aggregate. The same asphalt and aggregate sources were used in each test and all samples were run in duplicate. All samples were examined along the asphalt-aggregate interface in the ESEM prior to and following each freeze-thaw cycle. The samples were subjected to a total of ten freeze-thaw cycles. All three additives reduced the potential for moisture damage by maintaining asphalt-aggregate adhesion better than the control samples. Based on ESEM observation of the asphalt-aggregate interface before and after freeze-thaw cycling, the styrene-butadiene rubber-coated aggregate samples performed better than the amine-treated asphalt samples which performed better than the lime-treated aggregate samples.

This paper presents the results of work performed to enhance understanding of water penetration and moisture characteristics of barrier Exterior Insulation Finish Systems (EIFS) clad walls. The investigation was prompted by recent failures of barrier EIFS clad walls on houses in the Wilmington, North Caro lina area. The objective was to determine the cause of the problem and gain a better understanding of water penetration and moisture transport in these systems. The study included a field investigation, laboratory experiments, and computer simulation. The experimental results indicate that barrier EIFS clad walls are prone to leak in areas around penetrations and allow water to enter into the wall cavity. A drainage cavity wall was also tested, and observed to perform well, managing water around penetrations and preventing leakage into the wall cavity. The computer simulation indicates that barrier EIFS clad walls in Wilmington have low moisture tolerance due to slow drying rates. In conclusion, barrier EIFS clad walls do not provide effective management of rain penetration. As such, in-service performance is unpredictable and unreliable. In con trast to barrier EIFS clad walls, walls using a drained cavity approach were shown to provide good control of rain penetration.

To control rain ingress, the Exterior Insulation and Finish Systems (EIFS) can be constructed with one of two design principles • a drain screen (rain screen, pressure equalized rain screen-PER) approach • a face sealed (barrier) approach While the barrier approach has an inherently higher risk for moisture damage, it offers econormc advantages and may be successfully used under a multitude of cli matic and service conditions. Its performance evaluation is carried out in three steps: 1. Examine whether this system can be used for a specific set of climatic and use con ditions 2. Formulate necessary measures for material and field quality control in the design specifications 3. Examine the system for integrity under cycling environmental conditions and long-term performance Step 1 of this evaluation is based on the moisture control strategy of the whole wall assembly. Step 2 requires the addition of several small-scale material tests, and Step 3 involves full-scale system testing. The full scale testing is necessary to incor porate several parameters that act on the system simultaneously (thermal stress, thermal and moisture originated expansion and contraction, structural movements, material changes caused by weathering and aging, presence of moisture, etc.). The in teraction among these factors may provide conditions with severity significantly in excess of those achieved when these parameters are tested separately. This discussion paper consists of three parts: Part 1: Deals with the assessment of constituent materials of the EIFS with a view to ensuring (characterizing) hygrothermal performance of the system (by testing and characterization of the constituent materials, one may limit the range of variation in the hygrothermal performance of the whole system). Part 2: Postulates a new test for evaluation of EIFS integrity under simulated expo sure to climatic cycling. Part 3: Recommends EIFS design solutions and construction details for both new and retrofit construction. These details are discussed in the context of specific environmental/climatic conditions. This will be published in a later issue of JTIBE. Testing EIFS cladding systems for integrity under simulated exposure to climatic cycling involves preconditioning under simultaneous exposure to a water vapor gra dient and temperature gradient followed by exposure to severe conditions of one- sided, uni-directional climatic cycling. The testing and characterization of the con stituent materials (Step 1) coupled with the full-scale test for EIFS integrity under exposure to climatic cycling (Step 2) will increase the reliability of the EIFS systems in North America. Part 3 fills the gap between the current understanding of moisture control princi ples and construction practices. Many small changes in materials and technology create a compound effect that increases the frequency of inadequate field perform ance. Though most inherent EIFS flaws may be minor, those, when coupled with a number of failures of wall systems involving EIFS, caused an adverse attitude toward EIFS, perhaps more prevalent in some regions of North America. This paper pro vides a fundamental framework to cement many of the previously postulated correc tive measures into a coherent package aiming at the improvement of the EIFS reli ability in North America.

A 5-year study of newly constructed pavements showed that a reduction in in situ air voids occurred both within and between wheelpaths for highways with an average daily traffic (ADT) load of less than 10,000 vehicles. Regardless of the level of voids immediately after construction, mixtures in the upper 65 mm (2.5 in.) within the wheelpath indicated a reduction in voids by 3 to 5 percent (e.g., from 10 to 6 percent voids), and by between 2 to 4 percent between the wheelpaths. Because only limited densification occurred below this depth for lower–traffic-volume facilities, reducing the mix design level of air voids from 4 percent to 2 percent for the lower lifts was suggested so that lower initial voids could be obtained during construction. An evaluation of older pavements indicated that moisture damage to the lower pavement layers was typical; thus, a change in mix design procedures might also help improve durability by increasing the film thickness. Pavements with high traffic volumes (>50,000 ADT) consistently indicated an increase in voids over time in the upper lift [40 mm (1.5 in.)], little change in the middle 65 mm (2.5 in.), and a decrease in the bottom 65 mm (2.5 in.). The hypothesis suggested to explain these findings was that a loss of material in the upper lifts was occurring, most probably due to moisture damage as the upper, more permeable wear course, commonly used in Minnesota, allowed water trapping at the wear and binder course (i.e., less permeable) interface. A further investigation of in situ void changes on an interstate indicated that for a pavement constructed with the same fine gradation in all lifts, traffic compacted the mixtures in a manner similar to that in low-volume roads. When the initial in situ voids increased from around 7 percent to nearly 10 percent, the influence of traffic on the densification was substantially increased.