Journal of Materials in Civil Engineering

Investigators over the past 16 years have considered the nature of surface structuring, referred to as bee structures, in bituminous asphalt, commonly identified by atomic force microscopy. Recently it has been suggested that the interaction between nonpolar molecules present in asphalt, including $n$-paraffin waxes, are responsible for these surface microstructures. Several research groups now tend to agree that the interactions between crystallizing $n$-paraffin waxes and the remaining nonwax asphalt molecules are responsible for much of the structuring, including bee-structures. To date, a plausible mechanism to explain the physicochemical manifestation of this type of surface structuring in asphalts has yet to be offered. In this paper a theory is presented that explains the physicochemical nature of surface structuring in asphalts and asphalt fractions based on investigations of simpler material systems reported in the literature pertaining to paraffin and polymer crystallization. Experimental results obtained over the past several years by the writers are presented in support of the theory presented.

Two organic rectorites (ORECs) were prepared by using cetyltrimethyl ammonium bromide (CTAB) and octadecyl dimethyl benzyl ammonium chloride (ODBA) as organic modifiers to modify the rectorites. Rectorite and OREC modified bitumens were prepared by melt blending. Microstructures of the modified bitumens were characterized by X-ray diffraction (XRD). The effect of rectorite (REC) and its organic modification on the physical and aging properties of bitumen was investigated. X-ray diffraction results show that REC and ODBA-REC modified bitumens form the intercalated nanostructure, whereas CTAB-REC modified bitumen forms an exfoliated nanostructure. Compared with RECs, ORECs show the better compatibility with the bitumen as well as the higher improvement in softening point, viscosity, and aging resistance of the bitumen. The CTAB-REC modified bitumen shows lower viscosity aging index values and softening point increment in comparison with the ODBA-REC modified bitumen, indicating its good aging resistance.

This paper focuses on the three-dimensional (3D) linear viscoelastic (LVE) behavior of bituminous mixtures and the damage occurring after a great number of cyclic loadings. Two complex modulus tests were carried out before and after a fatigue test. The complex modulus $E^{*}$ and complex Poisson’s ratio ${\nu }^{*}$ were measured for large ranges of temperatures (from $-25$ to 30°C) and frequencies (from 0.03 to 10Hz). First, it is shown that the time temperature superposition principle (TTSP) is verified and applicable in the 3D case. Then, the change of the complex modulus created by fatigue test was analyzed. Lastly, a model with a continuum spectrum called two springs, two parabolic elements, one dashpot (2S2P1D), developed at the Ecole Nationale des Travaux Publics de l’Etat (ENTPE), was used to simulate the 3D linear viscoelastic behavior of the tested bituminous mixture before and after fatigue damage.

Styrene-butadiene-styrene (SBS) modified asphalt has been used in many road projects for its good performance at high and low temperatures. However, there was no final conclusion whether SBS could change the chemical structure of asphalt binders. The objective of this study was to analyze the impact of SBS on the molecular agglomeration behavior of asphalt binders by means of molecular simulation techniques. Two types of modifiers (SBS, MAH-g-SBS) were added into two asphalt models. Results of simulation show that three types of SBS all have impact on the molecular agglomeration behavior of asphalt binders. The impact of modifiers is largely dependent on the molecular structure of asphaltenes. The molecular agglomeration of asphalt with longer asphaltene alkane side branches is more regular. The agglomeration structure of asphalt molecules is more susceptible to SBS when the asphaltene alkane side branches are longer. The difference of influence on asphalt binders among two types of SBS is small.

This paper presents a laboratory investigation aimed at establishing a protocol for the production of homogeneous asphalt mixtures test specimens, incorporating reclaimed asphalt by using a gyratory compactor with coring and trimming works. Stone mastic asphalt specimens were compacted at the previously identified target densities with the final aim of obtaining specimens with a fixed and homogeneous air void distribution. A microstructural study was conducted to characterize the homogeneity in the air void distribution using X-ray computed tomography (CT) combined with image analysis techniques. The study concluded that the gyratory compactor is suitable for producing homogeneous test specimens for the specified mixtures and a set of detailed procedures has been proposed for the production of the compacted specimens and to perform the microstructural study.

Hydrated lime and liquid antistrip agents have long been used as an asphalt additive to improve resistance to moisture damage. Previous studies have shown that the addition of hydrated lime to asphalt binders reduced the aging propensity of asphalt by adsorbing naturally occurring oxidation catalysts or promoters from the asphalt binders. This study was conducted to evaluate the impact of lime and liquid antistrip on the long-term aging of five asphalt binders. The first part of the study evaluated the intermediate- and low-temperature rheological properties of these asphalt binders with no additive, blended with hydrated lime, and blended with liquid antistrip. The rheological properties of the binders were evaluated at the original and long-term aged stages. The second part of this effort evaluated the aging characteristics (e.g., $G^{*}\sin \delta \mathrm{\Delta }$, creep stiffness, and m-value) of the binders with and without the antistrip additives. The work in this study was designed to determine how the rheological properties of antistrip-treated asphalts vary with aging time when compared with untreated asphalts aged at temperatures in the pavement temperature range. An apparent question begging an answer is whether antistrip-treated asphalt ages to the same viscosity as an untreated asphalt when other rheological properties are similar. The test results indicated that hydrated lime stiffens the binders but it does not negatively impact their long-term aging characteristics. Therefore, lime-treated binders are expected to be stiffer than untreated and liquid-treated binders in their early life which increases their resistance to rutting but not too brittle in their later life to negatively impact their resistance to fatigue and thermal cracking.

To evaluate the properties of asphalt accurately, a new index, dynamic viscoelastic index ($Dvi$), is proposed on the basis of rheological mechanics. To verify this new index, six kinds of asphalt are evaluated with $Dvi$, and six kinds of asphalt mixtures are tested at high and low temperature with asphalt pavement analyzer and indirect tensile test, respectively. It is found $Dvi$ and temperature shows a good relationship and can be fitted with quadratic function. Also, the slope of the curve changed at around 50°C, and the curve can be fitted with linear model respectively. It is recommended that $Dvi$ be used as the index of high-temperature and low-temperature performance of asphalt since there is a good relationship between $Dvi$ and performance of asphalt mixture.

Application of rejuvenation products on porous asphalt pavements as a preventive maintenance technology has been investigated recently by the Dutch Ministry of Transportation. Traditionally, the main contribution of rejuvenators to porous asphalt pavements is considered as restoring its flexibility. Whether this really is the case is investigated in the research reported in this paper. For this purpose, identification of rejuvenators is done using optical microscopy and nanoindentation technology. Visual inspection from optical microscopy shows that all applied rejuvenation products, except for bitumen emulsion BE-1, provide an additional bituminous binder film to the mortar and also fill microcracks. The decrease of indentation modulus of the mortar shows that BE-1 and BE-2 can penetrate into the mortar and improve its flexibility.

Through contact angle test, the contact angles of mineral powder and asphalt were obtained; Using contact angle measurements, the surface energy parameters of the mineral powder and asphalt were calculated; Work of adhesion of the asphalt mortar with different mineral powder diameters and different mineral powder–bitumen ratios and was calculated according to surface and interface theory. The high temperature performance parameters of asphalt mortar were tested by means of the softening point and dynamic-shear-rheometer (DSR) test. The analysis results indicate that variations of the contact angles of asphalt with the changes of asphalt type is much less than that of the contact angle of mineral powder with the changes in the filler diameter. The contact angle of mineral powder increases when the diameter of mineral powder decreases and the surface tension increases. Using the same mineral powder bitumen ratio mortar, the work of adhesion decreases with decreasing filler diameter, but the specific work of adhesion increases when the diameter of the mineral powder decreases. At the same filler-bitumen ratio, the softening point and rutting factor ($G^{*}/\sin \delta$) of asphalt mortar increase as the diameter of the mineral powder decreases.

The durability and sustainability of concrete structures is a prime socioeconomic concern of contemporary society. The lifecycle of these structures is typically determined by the rate of moisture ingress, in which dissolved and unwanted substances are transported into the structure. Therefore finding a sufficient means to measure these rates is of utmost importance. A sorptivity testing scheme as outlined by a commonly used standard can be a useful means of measuring how quickly liquid can be transported unidirectionally through concrete samples in the laboratory. Currently the standard prescribes that disc specimens 100 mm in diameter and 50-mm thick be sealed in such a manner to ensure unidirectional flow through one, unsealed face of the sample, while all other surfaces are appropriately sealed. However the standard does not specify how this seal is to be achieved. Furthermore, differing methods have yielded a likewise array of varied results, which may not be representative of the true sorptivity. The objective of this paper is to propose a simple but effective means of sealing the specimens that will yield more consistent results, which are more representative of the actual absorption properties of the concrete. This was accomplished by studying the performance of electrical insulation tape and cellophane (as suggested in the standard) against paraffin wax using three different mixture designs, as follows: (1) involving normal strength concrete without air entrainment, (2) a normal strength concrete mixture with air entrapment, and (3) self-consolidating concrete without air entrapment. The prepared specimens were subjected to various freeze-thaw cycling periods, conditioned, and then tested for sorptivity. Batches of samples were exposed to freeze-thaw cycling periods of 0, 50, 100, 150, 200, and 300 cycles. Within each group of samples, half of the specimens were sealed with electrical tape and cellophane, and the other half were sealed with paraffin wax in order to conduct sorptivity testing. Specimens coated in wax typically exhibited lower absorption values than those wrapped in tape. Furthermore, the tape would not adhere perfectly with the concrete at the edge formed by the cylindrical wall and the exposed surface, resulting in increased sorptivity values. Statistical analysis was done on the rates of early-age (0–6 h) and late-age (1–8 days) sorptivity by using the F-test to examine variability (with an 80% confidence interval) and the student-$t$ test was used to evaluate the significance of differences in sample means. Generally, sorptivity rates were higher for taped samples than those for waxed samples. These results further reinforced visual observations. The waxed samples yielded more reliable results primarily because they did not absorb moisture artificially along the sides in the manner as observed in the taped specimens. Moreover, the paraffin wax sealant method also resulted in less variability within test results. Therefore it was believed that the wax facilitated more representative results of the true sorptivity. It was suggested that the procedures of the common standard discussed in this paper should be refined such that the sealing of test specimens should be done with the use of paraffin wax, or some other similar substance, such as silicone, which is impermeable and readily available commercially.

As an approach to mitigate the harmful effects of urban heat islands (UHI), the use of glass cullet in the production of asphalt roof shingles has the potential to be employed as a cool roof strategy. The objective of this study was to test the hypothesis that the use of recycled glass cullet increases the solar reflectance index (SRI) without affecting the performance of asphalt roof shingles. In order to evaluate the feasibility of using recycled glass cullet in this new application, the engineering properties of glass cullet were measured and compared to conventional aggregates used in the production of asphalt roof shingles. Laboratory shingle specimens were then prepared in order to measure solar reflectance properties and strength characteristics of conventional and recycled glass roof shingles. Results show that while the use of recycled glass cullet as a replacement to standard ceramic coated black roofing granules on the top surface of asphalt shingles increased the SRI, the addition of white pigment powder (anatase ultrafine titanium dioxide [${\mathrm{TiO}}_2$] particles passing mesh #320) to the surface granules greatly improves the reflectance properties of the roof to a level that meets the cool roof threshold.

This investigation is focused on the physical and mechanical properties, as well as the microstructure of autoclaved aerated concrete (AAC) incorporating both rice-husk ash (RHA) and aluminum (Al)–containing waste (AW) as a partial aggregate and expansive agent replacement. Normally, these wastes are disposed of in landfill and have low reactions at room temperature. Thus, the use of these wastes in AAC could reduce waste in the environment as well as reduce autoclaving time or temperature. The fineness of ground AW, analyzed by laser particle-size distribution, were classified as high (AWH), medium (AWM), and low (AWL), with the mean particle sizes of 9.71, 29.91, and 51.11 μm, respectively. The AW was used to substitute metallic aluminum powder at levels of 5, 10, 15, and 20% by weight. Samples with AW substitution gave lower unit weights and compressive strengths than the reference sample, except at 5% of AAC containing medium and low fineness. Scanning electron microscopy (SEM) micrographs reveal that at a higher replacement level and higher fineness of AW, fibrous calcium silicate hydrate (CSH) was formed instead of tobermorite, at 4-h autoclave curing.

Epoxy resin concrete can be used as one kind of repairing material for pavement. In this study, Bisphenol A epoxy resin (E51) and four different types of curing agents were selected. By comparing the mechanical strength of different epoxy gel systems under microwave curing conditions, a polyamide (V-125) curing agent was confirmed for its good comprehensive mechanical properties. The addition of diluents decreases the viscosity of the gel system, which is beneficial to construction. The compressive and tensile strength decrease, but the impact strength increases with increasing dosage of diluent. Ten percent diluents was recommended through comprehensive consideration. The compressive strength, tensile strength, and impact strength of E51/V-125 with 10% diluent under microwave curing conditions are slightly higher than that under thermal curing conditions. A self-made microwave radiation device was applied for curing the large size epoxy concrete specimens. The index of Marshall stability, air voids, and flow value of epoxy resin concrete were put forward. The gradation middle value of dense-graded asphalt concrete (AC-13) and 5.0% gel-stone ratio were determined using the Marshall method. The high and low temperature, and water-resistant, oil-resistant, and anti-skid properties of the microwave curing concrete were evaluated, and the results shows it has good pavement performance.

Evaporative cooling is a traditional strategy to improve summer comfort, which has gained renewed relevance in the context of the transition to a greener economy. Here, the potential for evaporative cooling of common porous building materials, like natural stone and ceramic brick, is evaluated. The work has relevance also to the protection of built heritage because evaporation underlies the problems of dampness and salt crystallization, which are so harmful and frequent in this heritage. It was observed that the drying rate of the materials is, in some cases, higher than the evaporation rate of a free water surface. Surface area measurements by a three-dimensional optical technique suggested, as probable cause of this behavior, that surface irregularity gives rise to a large effective surface of evaporation in the material. Surface temperature measurements by infrared were performed afterward during evaporation experiments outside during a hot summer day in Lisbon. Their results indicate that ordinary building materials can be very efficient evaporative media and, thus, may help in achieving higher energy efficiency while maintaining a simultaneous constructive or architectural function.

In the research reported in this paper, an in-situ observation on the hydration of cement pastes with various water-to-cement ($\mathrm{w}/\mathrm{c}$) ratios was implemented by Raman spectroscopy (RS). The RS was applied to study the paste continuously after cement mixing with water until the final setting was complete. Hydration products, including calcium hydroxide (CH), calcium-silicate-hydrate (C-S-H) gel, and ettringite were detected. The CH and C-S-H gel were present consistently with slight intensity changes in the RS patterns after their first detections. In all the pastes studied, the intensity of ettringite remained constant first, followed by a rapid increasing period; thereafter it began to decrease. Within the measuring duration a new peak assigned to monosulfate was detected in the pastes with $\mathrm{w}/\mathrm{c}$ ratios of 0.35 and 0.40. These Raman detections were also analyzed together with the setting time and heat evolution to elucidate the early hydration mechanism.

Cementitious materials, ceramic aggregates, and fiber are used as basic materials; ceramics cement–based porous material (CCPM) and basalt fiber-reinforced ceramics cement–based porous material (BFRCCPM) are prepared on the basis of Closest Packing Theory. After the tests, the internal relation between the average change rate of incident energy and the physical essence of the ensemble damage modes is discussed, and the change law of energy is probed. BFRCCPM’s compression energy properties during the dynamic deformation damage process are analyzed, and based on that, the effect of basalt fiber on the dynamic damage characteristics are studied. Results show that the damage level and energy absorption of CCPM and BFRCCPM get more serious or increase with the average change rate of incident energy; the damage level of BFRCCPM is obviously lower than that of CCPM. Moreover, BFRCCPM possesses better energy absorbing properties than CCPM. This advantage is more obvious when the average change rate of incident energy is very high; the impact-damage resistance of CCPM and BFRCCPM increases with impact strength. The impact-damage resistance of BFRCCPM is stronger than that of CCPM. Thus it can be seen that basalt fiber can prevent microdamages from developing and evolving, which can enhance the impact-damage resistance of CCPM.

${}^{29}\mathrm{Si}$ and ${}^{27}\mathrm{Al}$ magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy techniques were employed towards evaluation of hydrated cement paste and concrete subjected to accelerated sulfate attack. Quantitative analyses of the ${}^{29}\mathrm{Si}$ NMR spectra of specimens subjected to different periods of sulfate attack indicated that the chain length $CL$ of ${\mathrm{SiO}}_4/{\mathrm{AlO}}_4$ tetrahedra was lowered by sulfate attack. ${}^{27}\mathrm{Al}$ NMR spectra indicated that sulfate attack produced a significant rise in the intensity of ettringite and a sharp drop in the concentration of monosulfate hydrate, which are some primary indications of sulfate attack on concrete. Fourier-transform infrared (FTIR) spectroscopy method was employed in order to verify the result of NMR spectroscopy.

This paper reports nonlinear stress-strain characteristics and failure mechanisms of fly ash brick masonry and its constituents (fly ash brick units and mortar) obtained under compression and shear. Based on the experimental results, simple relations were proposed to evaluate the modulus of elasticity of fly ash brick masonry prisms in terms of the compressive strength of masonry prisms. Shear strength and shear modulus of masonry were evaluated by testing two different sizes of masonry wallettes, and a parametric study was carried out to evaluate the effect of the compressive strength of brick units, mortar cubes, and masonry prisms on the shear strength of masonry wallettes. The compressive strength of masonry prisms and fly ash brick units was found to be less than that of the mortar cubes. Fly ash bricks exhibited a very weak and soft nature in comparison with that of burnt clay bricks.

This paper reports test results on the corrosion durability of reinforcing steel in three series of precracked beams of ordinary mortar; a high-performance fiber-reinforced cementitious composite (HPFRCC) containing polyethylene (PE) fibers, referred as mono HPFRCC; and hybrid combinations of steel cord (SC) and PE fibers, referred as hybrid HPFRCC. In each series three precracked beams with a maximum crack width of 0.1–0.5 mm were tested. All beams were subjected to an accelerated corrosion regime consisting of applying constant 3-V DC potential across rebar (anode) and cathode and cyclic wetting and drying cycles. The durability performance of the specimens was examined through regular monitoring of corrosion current—hence, the calculated steel loss, the corrosion-induced damage measured by the longitudinal crack width and through visual inspection. At the end of the corrosion tests, the reinforcing bars in all specimens were exposed to observe the corrosion depth, corroded area, actual amount of steel loss, and residual tensile strength. Results showed that the hybrid HPFRCC specimens exhibited better performance than did the mortar and mono HPFRCC specimens. Relationships of maximum crack width with actual steel loss, maximum corrosion depth, and residual tensile strength were observed in mono and hybrid HPFRCC beams. However, no correlation between maximum crack width and corroded area was observed in all series. The relationship of maximum corrosion depth and actual amount of corrosion in the hybrid and mono HPFRCC series was also observed in this study.

Magnetorheological (MR) fluids are a new type of smart material whose performance can be evaluated by considering three important factors: stability, viscosity, and shear yield stress of the fluids. In this study, to produce fine, antisettling, and well-dispersed MR fluids, appropriate components and preparation techniques were adopted and a surface treatment method was developed involving different surfactants. Property tests of the MR fluids were conducted, and the results demonstrated that the proposed preparation method decelerated the sedimentation of MR fluids, that the viscosity of the MR fluids varied with temperature and shear rate, and that liquid paraffin can reduce the viscosity of the MR fluids more gradually than oleic acid. In addition, variations in shear yield stress with magnetic induction intensity and volume fraction were determined. To accurately describe the shear yield stress of the MR fluids, a limited chain model that considers the spatial distribution of carbonyl iron (CI) particles, model size, and magnetic saturation phenomenon was proposed. A comparison between the theoretical and experimental values obtained in this study indicates that a seventh-order limited chain model can effectively calculate the shear stress of MR fluids.

The combined attack of (1) mechanical fatigue load, and (2) freeze-thaw, can lead to premature deterioration of concrete materials in cold climate regions. The interactive effect of these two loads on the damage of concrete was studied numerically and experimentally. First, experiments were conducted for proof-of-concept of the numerical analysis. A numerical model was then constructed from the view that fatigue damage induces preferentially permeable concrete locally, which can lead to degraded stiffness by freeze-thaw effect and thus more fatigue damage. The numerical results demonstrated that the crack length decreased with the degree of freeze-thaw damage but the crack width, in contrast, increased. The experimental results agreed generally with the numerical results for more saturated conditions considering that the potential transport events of moisture and the heterogeneous microstructure should be included. The research reported in this paper sheds light on how mechanical load and environmental factors interact with each other in this complicated system to result in the ultimate failure of cement-based materials.

An empirical model based on constant flux is presented for chloride transport through concrete in atmospherical exposure conditions. A continuous supply of chlorides is assumed as a constant mass flux at the exposed concrete surface. The model is applied to experimental chloride profiles obtained from a real marine structure, and results are compared with the classical error-function model. The proposed model shows some advantages. It yields a better predictive capacity than the classical error-function model. The previously observed chloride surface concentration increases are compatible with the proposed model. Nevertheless, the predictive capacity of the model can fail if the concrete microstructure changes with time. The model seems to be appropriate for well-maturated concretes exposed to a marine environment in atmospherical conditions.

Seven full-scale concrete beam specimens are tested under gradually increasing monotonic loading to investigate their overall flexural response due to the addition of both metallic and nonmetallic fibers to the concrete. Steel and polypropylene fibers of 0.5% and 1.0% volume fraction are used in the fiber-reinforced concrete (FRC) beam specimens. No improvement is noticed in the compressive and splitting tensile strengths of concrete due to the addition of polypropylene fibers only. However, an improvement of 25–100% in the concrete splitting tensile strength is noticed when either steel or combined fibers are added to the concrete. Although an increase in fiber content in the combined FRC improves various mechanical properties, its influence on the peak load-resisting capacity of the full-scale beam specimens is rather limited. An increase of both steel and polypropylene fibers in excess of 0.5% volume fraction does not improve the ultimate flexural resistance of beams due to the uneven distribution of similar sizes of fibers in the presence of reinforcing steel bars. However, displacement ductility of the beam specimens is improved by 120% as compared with the RC specimen, when only polypropylene fibers of 1% volume fraction are added to the concrete. A better postpeak residual strength response is noticed in case of all FRC beam specimens due to multiple cracking associated with the fiber-bridging action.

An investigation into the potential for sequential dissolution of asphalt fractions in a staged extraction scenario was conducted for common asphalt solvents. Asphalt cement subjected to six sequential washes in trichloroethylene (TCE), tetrahydrofuran (THF), toluene, or decahydronaphthalene (decalin) were evaluated using Fourier-transform infrared spectroscopy (FTIR) and fractionated for asphaltene content. The results from the FTIR were evaluated statistically using a one-way ANOVA test and the solvents induced no difference in mean carbonyl index. However, the fractionation of the asphalt cement after staged extraction showed that decalin and THF sequentially dissolved the asphalt cement while toluene remained suspect. Trichloroethylene does not appear to sequentially dissolve the asphalt cement fractions. The findings are in agreement with solubility calculations based on Hansen solubility parameters.

Reinforced concrete structures inevitably experience variable mechanical loads and continuous degradation from aggressive environments such as deicing salts. In this study, several electrochemical measurements were performed on steel immersed in simulated concrete pore solution (with and without chloride ions) under different types and levels of mechanical loadings. Results indicate that steel specimens immersed in chloride-free pore solution under tensile loadings passivate more rapidly compared with those under compressive loadings. However, the situation in chloride-contaminated solution is different, and steel under tensile stress exhibits more corrosion than steel under compressive stress or under no load.

The main objective of this study was to develop predictive models to estimate the viscoelastic phase angle ($\varphi$) of different asphalt mixtures using robust mathematical functions and operators in the form of a powerful beta distribution format. A total of 163 conventional dense-graded asphalt concrete (DGAC), 13 asphalt-rubber asphalt concrete (ARAC) gap graded, and 7 asphalt-rubber friction course (ARFC) open-graded mixes were available, amounting to a total of 5,490 data points. The asphalt materials parameters were used to develop $\varphi$ predictive equations for DGAC, ARAC, and ARFC mixes separately using principal component analyses techniques and mathematical regression. In addition, $\varphi$ master curves were developed for each mix type using the predicted $\varphi$. The statistical goodness of fit measured for all of the predictive models, DGAC, ARAC, and ARFC, were very good to excellent with $R_{\mathrm{adj}}^2$ between 0.80 and 0.85, and $S_e/S_y$ less than 0.35. The performance and accuracy of the $\varphi$ predictive models was assessed by comparing the predicted and the actual $\varphi$ measured on similar mixtures obtained from past studies. The $\varphi$ model predictions had very good to excellent correlations with the measured values indicated by very high $R^2\ge 90\%$. Overall, the models and the relationships showed low bias and high precision indicating that the newly developed $\varphi$ models are an excellent means of acquiring the $\varphi$ for the three different asphalt mixes in the absence of testing capabilities. Furthermore, it is envisioned that $\varphi$ can be incorporated in futuristic sustainable flexible pavement designs and practices, complementing stiffness parameters such as moduli and contributing to a comprehensive understanding of the intricate viscoelastic characteristics of the asphalt mixes.

The effect of different proportions and different reactivities of MgO on the drying shrinkage and compressive strength of alkali-activated slag pastes (AAS) has been investigated. The slag was activated by 6% by weight sodium hydroxide and liquid sodium silicate at a ratio of $3:3\%$ by weight. The MgO of different reactivities were produced from calcination of hydromagnesite at different temperatures (550, 1,000, and 1,250°C). The results showed that the reactivity of magnesium oxide decreases with the calcination temperature. Also, the drying shrinkage of AAS was reduced by the replacement of slag with different reactivities of MgO. The ${\mathrm{MgO}}_{550}$ accelerated the hydration of AAS at early ages. The replacement of slag with 5% ${\mathrm{MgO}}_{550}$ increased one-day compressive strength by $\sim 26\%$, but ${\mathrm{MgO}}_{1250}$ had little effect. A significant increase in strength was observed after 7 days with the replacement of slag with 5% ${\mathrm{MgO}}_{1250}$. The MgO reacts with slag to form hydrotalcite-like phases (Ht) as detected by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric and derivative thermogravimetric analysis.