Journal of Materials in Civil Engineering

Warm asphalt has been gaining popularity in recent years around the world due to many reasons, including its energy saving and environmental benefits. Some of the warm-mix additives lower the viscosity of the binder at low temperature, whereas many of those available on the market do not alter the viscosity of the binder but are effective only when mixed with bitumen in the presence of aggregate. Recently there has been considerable interest in the use of zero shear viscosity as a specification criterion for asphalt binders. In this paper, the zero shear viscosity of bitumen-filler mastics modified with two different warm-mix additives (Evotherm and Sasobit) at their four different doses are measured by using a dynamic shear rheometer (DSR) at 40 and 60°C on the basis of the Cross model of calculation. Temperature sweep tests were also conducted to find the failure temperature and the rutting parameter $G^{*}/\sin \delta$ at 60°C. From the test results it was observed that the addition of Sasobit increased the ZSV of both binders and of bitumen-filler mastics at the dosage of 3% by weight of asphalt binder and Evotherm additive showed the best results at the dose of 0.5% by weight of asphalt binder.

Due to an increasing rate of traffic volume and truckloads in recent years, asphalt binders are often modified with synthetic polymers to increase stiffness and sustain excessive heat during hot summer days. However, the cost of polymer-modified binders (PMBs) is significantly higher than unmodified binders. Nanoclays, on the other hand, are relatively inexpensive and naturally abundant, and have favorable intrinsic properties, such as nanoscopic size and high surface area. To this end, the research reported in this paper investigated moisture resistance properties of a commonly used Performance Grade (PG) 64-22 binder modified with different dosages of two selected nanoclays [(1) Cloisite 15 A, and (2) Cloisite 11B]. The state of dispersion of the nanoclay in the binder was examined using a scanning electron microscope and small-angle x-ray diffraction. The morphological analyses of scanning electron microscope scans and inter-gallery distances ($d$-spacing values) of small-angle x-ray diffraction data of the two selected nanoclays are effective in evaluating the state of exfoliated microstructure of nanoclays in asphalt binders. In particular, the small-angle x-ray diffraction data of two of the tested samples [(1) 4% of Cloisite 11B, and (2) 6% of Cloisite 11B] showed fully exfoliated microstructure. Moisture resistance of nanoclay-modified binders was evaluated through the surface free energy (SFE) technique. The adhesive energies and compatibility ratios (CRs) of nanoclay-modified binder and selected aggregate (four acidic and four basic) systems were also evaluated. The total SFE increases when the asphalt binder is modified by nanoclays. When the asphalt binder is modified with nanoclays, the wetting ability decreases. A 4% Cloisite 15 A and a 6% Cloisite 11B (by the weight of the binder) showed the highest adhesive energy in maintaining good wetting ability, with different acidic and basic aggregates. The work-of-adhesion values under dry and wet conditions of nanoclay-modified binders were highly dependent on the nature (acidic or basic) of aggregate. The CR, an indicator of moisture resistance or bond strength in wet conditions, of the nanoclay-modified asphalt binder decreased for all aggregates except for granite, which showed a slight increase of the CR values. Thus, unless modified with an antistripping agent or other additives, nanoclay modified binders are expected to have poorer moisture resistance than the base binder. While maintaining a dosage level of 4% (by weight) nanoclay, Cloisite 15 A, consisting of smaller particle size than Cloisite 11B, is more compatible with different aggregates than Cloisite 11B. At a lower dosage level (2% by weight), Cloisite 11B is more compatible than Cloisite 15 A. Furthermore, the nanoclay technology is expected to be a cost saving approach, which can reduce the cost per metric ton of asphalt binder from 22–33% compared to the polymer-modified binders. Findings of this paper are expected to assist pavement professionals in evaluating moisture resistance of nanoclay-modified asphalt binders through a fundamental science approach.

The authors studied the solid-phase composition and morphology, pore structure, damage, and deterioration of microstructure, and nano-mechanical properties of cementitious materials in accelerated carbonation reaction. The solid-phase composition and morphology were investigated by X-ray diffraction (XRD), thermal gravimetric and differential scanning calorimetry (TG-DSC), and environmental scanning electron microscopy (ESEM). The characteristic of pore structure was obtained by mercury intrusion porosimetry (MIP) tests. Furthermore, the damage deterioration of microstructure was detected by X-ray computed tomography (XCT). Finally, the nano-mechanical properties were investigated by nanoindentation. These microstructure parameters have paved more precise way for the carbonation model.

This paper summarizes a methodology for using moisture content (MC) together with soil index properties to study and predict the progression of longitudinal shrinkage cracking (LSC) along low-volume roads through finite-element analysis. Extensive laboratory tests were performed on soil samples retrieved from six representative clayey sites in Texas, including five high plasticity index (PI greater than 25) sites and one low-PI site. Field measurements of moisture content, suction, and crack development were carried out at five representative farm-to-market roads constructed over the high-PI clayey materials in southern and eastern regions of Texas for verification. Compared to the prevailing suction-based approach, the MC-based approach offers more flexibility in terms of incorporating different drying/wetting paths into numerical modeling by laboratory-based material constitutive models. The estimated critical moisture content thresholds and locations of LSC showed good agreement with the field measurements. It was found that the most crucial steps in improving the overall performance of low-volume roads built over expansive soils are to enhance subgrade mechanical properties and to minimize subgrade moisture fluctuations, as opposed to an overly conservative pavement structure.

This paper focuses on the biotechnology of concrete. Oil palm shells (OPSs) are a main solid pollutant of the environment and can be used as a replacement for the conventional aggregate in lightweight concrete. An experimental investigation on the impact resistance of OPS lightweight concrete with a geo-grid was performed. A mix design was determined through various trial mixes to ensure the OPS lightweight concrete could achieve the required structural performance. A self-fabricated drop-weight impact test rig was used to simulate a low-velocity projectile impact on the slab specimens. Three parameters were tested for impact resistance on specimens with and without geo-grid reinforcement, as follows: (1) OPS content, (2) geo-grid types, and (3) geo-grid layers. Inclusion of OPS reduces the impact resistance of concrete and a geo-grid layer improves the impact resistance, but the effect is more pronounced for ultimate crack resistance than the first crack resistance. A comparison between geo-grid types indicated that Geo-Grid 80/80 has an overall better performance in lightweight concrete for impact resistance.

Thermal cracking performance assessment of flexible pavements is paramount to improve the quality of the roads in cold-climate regions. In this paper, a reduced testing framework for analysis of hot-mix asphalt (HMA) concrete is proposed to replace the indirect tensile (IDT) creep compliance and strength testing by dynamic modulus and fatigue tests performed on an asphalt mixture performance tester (AMPT) device. The theoretical aspects of the methodology are shown as well as its validation with laboratory results. Mixtures containing various percentages of reclaimed material (RAP) were investigated to assess the adequacy of the proposed method to this type of material. Results showed that the proposed framework can be successfully used to predict the low-temperature creep compliance and IDT strength, which are the two key elements in thermal cracking performance analysis of flexible pavements.

In this paper the properties of self-consolidating concrete (SCC) used for repair applications and prepared with two commercially available ternary blended cements and chemical admixtures such as a high-range water reducer (HRWR) and a viscosity modifying admixture (VMA) were investigated under restrained shrinkage. The examined properties include compressive strength, indirect tensile strength, static elastic modulus, free shrinkage, and restrained shrinkage. From the results, it became clear that the resistance of SCC to shrinkage crack was quite different depending on the nature of HRWR and the binder type in use. The cracking age increases in mixtures proportioned with polycarboxylate (PC)-based HRWR compared with polynaphthalene (PNS)-based HRWR. The SCC mixtures based on blended ternary cement containing Class F fly ash show shorter cracking age than the corresponding SCCs proportioned with ternary blended cement containing slag. Finally, it was found that the potential of shrinkage cracking of SCC is not influenced only by the amount of shrinkage but also by the shrinkage rate and tensile creep.

Due to the role of ${\mathrm{Cl}}^{-}$ ions in inducing the corrosion of steel rebar in reinforced concrete, it is of interest to use chloride-free accelerators in concrete construction. $\mathrm{Ca}{({\mathrm{NO}}_3)}_2$ (CN) is a ${\mathrm{Cl}}^{-}$ free admixture, which accelerates set and is thought to inhibit steel corrosion. This study carefully compares the influences of both $\mathrm{Ca}{({\mathrm{NO}}_3)}_2$ and ${\mathrm{CaCl}}_2$ (CC) additions on reaction and property evolutions across a range of cementing materials including ordinary portland cements (OPCs) and blended OPCs, i.e., those containing Class F fly ash, slag, or fine limestone. The results indicate that CN acts as a set accelerator, though in relation to its dosage a slight drop in early age (i.e., 1 day) strength is noted. However, this effect is transient, with similar strengths being recorded across all dosage levels by 28 days. While CC is noted to be a superior (i.e., setting and hardening) accelerator, both additives show similar performances by 28 days. The results from a phase boundary nucleation and growth (BNG) model indicate that differences in admixture performance are a function of the differing abilities of these admixtures (and specifically, their anions) to accelerate chemical reactions. Based on observed behaviors, recommendations are made for dosing both admixtures as a function of the binder chemistry. While the benefits of these additives vary as a function of the OPC chemistry, the results indicate that CN, on account of its ${\mathrm{Cl}}^{-}$ free composition, is a very promising accelerator for use in concrete construction.

This paper presents the results of an extensive test program on the residual mechanical properties of engineered cementitious composites (ECC) exposed to elevated temperatures up to 800°C. ECC cube specimens were heated to four different target temperatures (200, 400, 600, and 800°C) in an electric furnace then kept at constant temperature for three time durations (0.5, 1, and 2 h). Two cooling schemes, quenching in water and cooling in air, were used to cool the specimens. The residual mechanical properties of the ECC specimens were then evaluated. The residual strength and stiffness generally decreased with the increasing temperature and heating duration, except for the 200°C temperature exposure. Compared to the compressive strength, the stiffness was affected much more significantly by the cooling scheme. For the specimens subjected to 800°C for 2 h of exposure, quenching in water facilitated the strength and stiffness recovery. The microstructural characterizations, which were performed both before and after the elevated temperature exposure using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP), effectively explained the observed postexposure mechanical properties of the ECC specimens.

Increased usage of reclaimed asphalt pavement (RAP) and reclaimed asphalt roofing shingles (RAS) in hot mix asphalt (HMA) has increased the need for recycling agents intended to return the age-hardened RAP/RAS binder (asphalt) to its original state. However, a decreasing supply of liquid asphalt and concerns over adverse health effects when using petroleum-based recycling agents have created the opportunity for bio-based solutions to these issues. The guayule plant is a woody perennial shrub that is native to areas of the southwestern U.S. and is a well-documented source of resin and high-quality rubber. The study objective was to determine the viability of using guayule-based materials as recycling agents in HMAs with high contents of RAP and/or RAS. Of the many guayule-based materials investigated, an acetone-extractable, residual resin in the rubber was shown to be effective in meeting the study objective.

This paper examines the self-cementing phenomenon of the road construction material known as recycled concrete aggregate (RCA). Two RCA types were selected as study materials: (1) high-grade RCA (HRCA), a quality RCA manufactured from relatively high-strength concrete structures; and (2) road base RCA (RBRCA), a high-grade RCA blend combined with brick and general clean rubble (road base material). Laboratory tests were performed to obtain the unconfined compressive strength, indirect tension dynamic modulus, and resilient modulus of the test samples to examine their hardening characteristics when subjected to varying curing periods. These tests were performed in conjunction with microstructure analyses from X-ray diffractometry (XRD) and scanning electron microscope (SEM) techniques. The HRCA samples, which were prepared and subjected to varying curing conditions, transformed from an initially unbound material into a bound (fully stabilized) material. The results of XRD and SEM analyses clearly demonstrate that secondary hydration occurred. The RBRCA samples were able to maintain their unbound granular properties, with nonsignificant self-cementing, thus supporting the hypothesis that the mixing of nonactive materials such as bricks and clean rubble into RCA will lessen the tendency of RCA toward self-cementing.

Nondestructive testing (NDT) methods for identifying stress levels in materials mostly rely on the theory of acoustoelasticity. However, the sensitivity and the accuracy of acoustoelasticity are affected by several factors such as the (1) type, (2) propagation, and (3) polarization directions of the used signals. This paper presents the results of an experimental investigation of longitudinal waves propagating perpendicular to the applied uniaxial tensile stresses in structural steel specimens. The changes in four ultrasonic signal characteristics were investigated with increasing stress levels ranging from below to above the yield stress of steel. The considered signal characteristics were the peak amplitudes and signal energy in the time domain, and the fast Fourier transform (FFT) and chirp-Z transform (CZT) in the frequency domain. Even though the acoustoelastic effect on the type ultrasonic signal used is very small, clear distinctions between prior to and postyielding are observed for all investigated parameters. The results are presented with a detailed statistical and receiver operating characteristics (ROCs) analyses. The results show that identifying damage to steel structures due to local yielding is possible using the simple ultrasonic signal classification.

This study aims to examine the use of concrete sludge from water treatment installations of ready-mixed concrete plants as an alternative raw material for portland clinker kilns, and to enumerate possible limitations. By its extensive and representative collection of concrete sludge samples data, it may also be used for other investigations. The chemical variations of this sludge were evaluated by gathering 87 sludge samples over a period of two years. Furthermore, a treatment phase was proposed. Numerical simulations were conducted based on the chemistry of a representative concrete sludge sample, before and after a specific treatment phase, together with classic raw materials of three reference clinker factories to investigate the influence of the sludge on the clinker meal composition. Based on these simulations, experimental clinkers were produced, which were fully analyzed and evaluated for possible mineralogical influences. Based on the findings of this investigation, it was concluded that sludge out of concrete plants could not be classified as a feasible alternative raw material. Nevertheless, this paper has unveiled some attention points for the use of recycled materials or by-products as alternative raw materials for portland clinker production.

An important aspect of sustainable construction is the recycling or reuse of the construction and demolition (C&D) waste to maintain a friendly green environment. The wide range of building materials and its compositions inhibit the efficient waste management and complete recycling after demolishing. To contribute in this field and promote the use of local waste as 100% alternative coarse aggregate in construction industry, an experimental program was carried out using samples of main Iraqi building C&D waste. The types of aggregate used represent the three main constituents within recycled aggregates: unbound stone, crushed concrete, and crushed brick. Tests for mechanical properties of different types of recycled aggregate included crushing value and abrasion resistance. Using multilinear correlation analysis, the influences of these aggregate characteristics and other parameters on the properties of recycled aggregate concrete were evaluated. The results showed that the performance of the concrete containing each type of RA was largely influenced by the aggregate nature and quality, in addition to attached mortar content.

The tensile fracture characteristics of compacted soils are very important for the stability of earth structures. In this work, a horizontal displacement-controlled, uniaxial, direct-tension test apparatus was developed to capture the complete tensile stress-deformation response of cohesive soils. A series of uniaxial tensile tests were performed on two compacted soils, and the cracking process was observed. The tensile stress-deformation curves showed a clear postpeak softening behavior along with the development of tensile cracks. The influences of water content and dry density on the tensile strength and softening behavior of compacted soils were analyzed. On the basis of the fracture process zone concept, a method was proposed to extract the tensile stress-strain curve for the fracture process zone from the test data and a constitutive model was established to describe the complete stress-strain relationship of compacted soils under uniaxial tension. The model fits the experimental results well.

Particle morphology plays a significant role in influencing engineering behavior of granular materials. Surface texture, roundness, and sphericity represent distinct multiscale measures needed to fully describe particle morphology. Most studies reported in the literature rely on two-dimensional (2D) projected images of particles with a few three-dimensional (3D) images that mostly focused on relatively large-size aggregate samples. In this paper, 3D synchrotron microcomputed tomography (SMT) was used to acquire high-resolution images of glass beads, F-35 Ottawa sand, #1 dry glass sand, GS#40 Columbia sand, Toyoura sand, and Hostun RF sand. New roundness and sphericity indexes are proposed and calculated for the samples based on 3D measurements of surface area, volume, and three orthogonal diameters of particles. In addition, the surface texture of particles were measured using optical interferometry technique. The measurements reported in this paper can serve as a good source for other researchers working on sands to build on these intrinsic particle properties to link engineering behavior of sands to their morphology.

This paper is aimed to improve the mechanical properties (namely compressive and tensile strengths) of a recently developed fly ash-based engineered geopolymer composite (EGC) with relatively low-concentration activator combinations. In this regard, four different activator combinations (including two Na-based solutions and one K-based activator solution, and one lime-based activator combination in the form of powder) were used to develop the fly ash-based EGCs exhibiting strain hardening behavior under uniaxial tension. Randomly oriented short polyvinyl alcohol (PVA) fibers (2% v/v) were used to reinforce the relatively brittle low-calcium (Class F) fly ash-based geopolymer matrix. The matrix and composite properties of the developed fly ash-based EGCs [including workability of the fresh matrix, density, compressive strength, matrix fracture properties (comprising elastic modulus, fracture toughness, and composite crack tip toughness), and uniaxial tensile behavior] were evaluated. A counterpart conventional engineered cementitious composite (ECC) with a water-to-cement ratio corresponding to the activator solution to fly ash ratio of the EGCs was also made for comparison. Experimental results revealed that in fly ash-based EGCs, the use of Na-based activator combination composed of 8.0 M NaOH solution (28.6% w/w) and ${\mathrm{Na}}_2{\mathrm{SiO}}_3$ solution (71.4% w/w) with a ${\mathrm{SiO}}_2/{\mathrm{Na}}_2\mathrm{O}$ ratio of 2.0 is highly beneficial in terms of lower cost, higher compressive strength, higher matrix fracture properties, and superior uniaxial tensile behavior compared to the other three activator combinations.

This paper constitutes a special importance for developing countries where an affordable trowel-based strengthening system is needed. This paper also provides an affordable strengthening solution when it is not possible to entirely remove the effect of live load on the strengthened element. A series of 13 ferrocement strengthened beams of 2,400 mm in length and a rectangular cross section of $120\times 200\mathrm{mm}$ were tested. The beams were cast and preloaded to different load fractions (45 and 60%) of its ultimate capacity; then the load was partially released (by 15% of the ultimate load) and maintained, while the beams were then strengthened and reloaded until failure. The load released simulates the removed live load while strengthening an actual beam. The research reported in this paper features designing and manufacturing a special loading frame to apply, release, and reapply the loads on the tested beams. The frame allows implementing the strengthening process while maintaining the strengthened beams partially loaded. The use of flat and U-shaped ferrocement layers of three different volume fractions (VFs) of mesh reinforcement have been assessed. The overall response of the specimens was investigated in terms of the load carrying capacity, crack patterns, and propagation and modes of failure, and the deformational characteristics that include deflection, ductility, and energy absorption characteristics. The results indicated that the ferrocement strengthening system is effective in enhancing both strength and ductility of the RC beams.

The influence of recycled coarse aggregates (RCAs) on the fresh, hardened, and freeze-thaw durability properties of recycled aggregate concrete (RAC) is investigated in the research reported in this paper. Four different mixes were considered with natural aggregate and three different replacement levels of RCA [i.e., (1) 30%, (2) 40%, and (3) 50%]. The fresh and hardened properties of RAC were investigated according to national standards where the target strength was 35 MPa in 56 days. The compressive strengths of different concrete mixes were determined after 3, 7, 28, 56, and 120 days of moist curing. The results are also presented in terms of stress-strain curves, modulus of elasticity, and Poisson’s ratio. Freeze-thaw durability performance of RAC was studied in accordance with a national standard. This paper shows that the performance of RAC slightly decreases with increasing RCA replacement levels; however, their overall performance is comparable to natural aggregate concrete (NAC). This paper indicates that the use of RCA in new concrete production can lead to a greener environment and pave the way for sustainable construction.

The objective of the present study was to investigate the engineering characteristics of polyester-reinforced cement-stabilized macadam (PETCSM). Shrinkage and mechanical tests were performed to analyze the water loss rate, shrinkage coefficient, compressive strength, cleavage strength, and compression rebound modulus of PETCSM as functions of the age and fiber content of the material. An optimum fiber content of PET was proposed. The effects of PET were compared with those of polypropylene (PP) fibers. As the fiber content increased, the water loss rate of PETCSM decreased and then increased, with the minimum water loss occurring at a fiber content of 0.7‰. The shrinkage coefficient of the PETCSM gradually decreased as the fiber content increased, with the critical point of zero shrinkage appearing when the fiber content reached 0.7‰. The PET fibers had a greater effect on enhancing the mechanical performance of the CSM than did the PP fibers. The strength of the PETCSM was primarily affected by the maturity of the hydration reaction, by active enhancement effects, and by the passive blocking effects of the fibers. The strength was also affected by the fiber age and fiber content. The cleavage strength was more sensitive to the fiber content than was the compressive strength. The addition of PET altered the elastoplastic behavior of the PETCSM and significantly decreased shrinkage in the CSM. The optimum fiber content in the PETCSM is 0.7‰. The PETCSM has better engineering properties than CSM without fiber. This paper may provide a solid theoretical foundation for the widespread use of PETCSM in engineering applications.

In this paper, various Atomic Force Microscopy (AFM) techniques are utilized to study the effects of different warm mix asphalt (WMA) additives on the nanostructure and microstructure as well as the adhesive and cohesive properties of an asphalt binder. To achieve this objective, a control asphalt binder was modified with three different types of WMA additives, which included: Advera (a synthetic zeolite), Evotherm, and Sasobit (a commercial wax). The AFM tapping-mode imaging technique was used to examine the nanostructure and microstructure of the different asphalt material considered. In addition, AFM force spectroscopy experiments were conducted using chemically functionalized AFM tips to measure the nanoscale level adhesive and cohesive forces for the control and WMA asphalt binders before and after moisture conditioning. The results of the AFM imaging showed that while the Sasobit additive has reduced the width of the so-called “bee-like” structures within the asphalt binder, the other WMA additives did not have any significant effect on these structures. In addition, the results of the force spectroscopy experiments indicated that the inclusion of the WMA additives significantly increased the adhesive forces of the asphalt binder prior to moisture conditioning. However, all WMA additives except the Sasobit did not have any significant effect on the adhesive forces after moisture conditioning. Finally, Sasobit and Advera were found to reduce the nanoscale cohesive forces within the considered asphalt binders upon moisture conditioning, indicating that these might adversely affect the cohesive bonds within the asphalt binder.

Using hard and polymer-modified binders in stone mastic asphalt mixtures reduces workability considerably. In this study, Sasobit (Sasolwax, Worthdamm, Hamburg) is used in bitumen to increase the workability and efficiency of styrene-butadiene-styrene (SBS)–modified binders. The properties of SBS-modified and Sasobit-modified binders and mixtures were evaluated for their rheological and mechanical performances using different experimental techniques such as rheological bitumen tests—i.e., dynamic shear rheometer (DSR), bending beam rheometer (BBR), and hot-mixture performance tests; i.e., dynamic creep, fatigue, and toughness index tests. Sasobit improves the effectiveness of SBS modification, especially at medium to high temperatures, although it is not as flexible as SBS at low temperatures. In some cases, SBS modification is more effective than Sasobit modification when used alone. However, a better performance is achieved when 3% SBS plus 3% Sasobit is used when the two modifiers are mixed in the same binder, especially in terms of fatigue performance.

Repeated loading test has been widely used to simulate the true stress state of pavement materials under traffic loading with more accuracy. In this paper, a half-sinusoidal load with 0.1-s loading duration and 0.9-s rest period was selected to simulate the dynamic traffic loading. A generalized Kelvin viscoelastic model of asphalt mixtures based on linear-superposition principle under repeated load is developed. The Prony-series coefficients of the generalized Kelvin model are obtained by the static creep tests of AC-13C and AC-20C unmodified and modified asphalt mixtures. Then, the strain of AC-13C and AC-20C asphalt mixtures under repeated load could be predicted by the proposed viscoelastic model. Comparing the predicted strain obtained by retardation-time spectrum having and not having fixed time with the measured strain, it is believed that the retardation-time spectrum covering both the loading and unloading time processes should be selected in predicting strain of asphalt mixtures under repeated load. The proposed generalized Kelvin viscoelastic model under repeated load allows for prediction of permanent deformation of asphalt mixtures as well as rutting in asphalt pavement.

In this study, glass fiber silica aerogel composites were fabricated and used to protect steel frames against fire. Glass-fiber-coated silica aerogel was synthesized by immersing glass fibers into silica sol. Following gel formation, surface modifications were carried out. Samples were dried carefully at relatively high temperatures and ambient pressure. The samples were then prepared at two different solution pH values and four different aging times. Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques have been employed to find the specific surface areas and pore diameters of the silica aerogel, formed as a coating on the glass fibers. Fourier transform infrared spectroscopy (FTIR) was used to investigate the chemical reactions. The coverage of fibers by the aerogel was also verified by scanning electron microscopy (SEM). To examine the composites’ fire resistance, a laboratory turbotorch and infrared thermometer have been used. Fire was applied directly to the composite surface while the temperature was read on the other side. The relationship between the fire resistivity of the composites and physical characteristics of the aerogel such, as porosity and specific surface area, is discussed.

Long-term draindown is the term adopted in this study to describe the downward flow of binder in a porous asphalt mixture due to the force of gravity at high temperatures experienced during service, especially in warmer climates. The concept of long-term draindown has been qualitatively noted in field observations of porous asphalt mixtures, including open graded friction courses (OGFC). This research quantified the long-term draindown of three different OGFC mixtures by measuring the permeability of the mixes throughout an 84-day conditioning period at 60°C. The results showed that the permeability of all three mixtures decreased over the first 56 days and then leveled off or increased for the remaining 28 days. To verify that the permeability reduction was due to binder draindown, the distribution of binder content of randomly selected specimens was measured. The results from this study indicated that cellulose fibers did not have any influence on the long-term draindown of the mixtures evaluated as the other mixtures [one made with ground tire rubber modified binder and the other with Evotherm 3G (MWV Specialty Chemicals, North Charleston, South Carolina)] exhibited slightly lower rates of permeability loss despite not containing fibers.

As the usage of warm mix asphalt (WMA) has gained popularity in recent years, the need has arisen for more characterization techniques and performance prediction through accelerated laboratory testing. This paper presents an experimental study on the shear modulus and damping ratio of asphalt specimens prepared using three WMA technologies: Evotherm, Sasobit, and water foaming, as well as conventional hot mix asphalt (HMA) technology through resonant column (RC) testing. To enable RC testing of asphalt concrete specimens, minor modifications to a traditional RC apparatus were made, which included rigidly attaching additional mass to the driving system to lower the resonant frequency and using epoxy to fix asphalt concrete specimens to the loading plates of the apparatus. The effect of temperature and WMA technology on the dynamic properties was investigated. It is concluded that for the range of temperature tested, specimens prepared using Sasobit technology exhibited the highest shear modulus. Evotherm did not alter the shear modulus of asphalt concrete in a significant manner; while specimens prepared using water foaming technology exhibited slightly softer behavior as compared to those prepared using the conventional HMA technology. It was observed that damping ratio was not significantly altered as a result of using WMA technologies. The four technologies investigated in this study have different temperature sensitivities at different temperature ranges. Hence, it is suggested that shear modulus at a given temperature and its temperature sensitivity at different temperature ranges must be taken into account for evaluating different WMA technologies.

The objective of this study was to determine the tensile behavior for dam concrete under simulated earthquake loading conditions (loading frequency 5 Hz). Four-point loading tests were conducted on large beam specimens ($\mathrm{1,700}\times 450\times 450\mathrm{mm}$). This paper describes the behavior of dam concrete subjected to dynamic elevated-amplitude cyclic loading with different initial static load levels. Stress-strain measurements were made on the concrete specimens. The test results show that dynamic increase factor of dam concrete increases with increasing initial static stress levels. The results of this study should be useful in determining the earthquake resistance of dam structures.