Journal of Materials in Civil Engineering

Concrete highways and airfield pavements are subjected to a large number of traffic loads, which may cause failure of the pavement due to fatigue. In the present work, an experimental study has been carried out on plain concrete beam specimens to investigate the crack propagation and incremental damage characteristics of concrete under cyclic loading. A compliance test was conducted on beam specimens with different notch depths, and a relationship between notch depth and compliance was established. The fracture toughness of concrete was also estimated in a beam bending test. Fatigue tests were conducted on different sets of beam specimens under different load levels. Vertical displacement and crack mouth opening displacement were measured at each load cycle. The variation of stress intensity factor with load repetitions was observed using the crack lengths estimated from the compliance values corresponding to different load repetitions. The ratio of stress intensity factor to critical stress intensity factor (at failure), termed as toughness ratio in this work, has been found to influence the fatigue life. The fatigue life, as expected, also depended on stress ratio. A fracture mechanics–based damage prediction model was proposed for estimating the progressive damage at any intermediate load cycle. The damage prediction model was validated using the experimental results available in literature. Predicting fatigue damage at intermediate stages and due to variable sequence of loading is convenient for the design and evaluation of concrete pavements. Although the effects of frequency (in the ranges applicable for highway pavements) on the fatigue performance may not be significant, the applicability of the present model may be limited by the specific specimen size and loading waveform considered in this study.

Pastes and mortars of alkali-activated palm oil fuel ash (POFA) are synthesized with three types of alkaline solutions and are characterized for molecular functional groups by Fourier transform infrared (FTIR) spectroscopy, microstructure observation, and chemical composition by scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and mechanical strength using a universal mechanical tester. The alkali activators chosen for this investigation are 12 M sodium hydroxide (NaOH), 3 M sodium silicate (${\mathrm{Na}}_2{\mathrm{SiO}}_3$), and a combination of both activators (${\mathrm{Na}}_2{\mathrm{SiO}}_3$ and NaOH) by mass ratio of $3:1$. POFA with ${\mathrm{Na}}_2{\mathrm{SiO}}_3$ solution yields the highest compressive strength in comparison to the other activators. The main gel binder dominantly composed of silica with varying calcium/silica ($\mathrm{Ca}/\mathrm{Si}$) ratios is analyzed by analytical techniques through FTIR and SEM-EDX.

Composite materials are widely used in retrofitting bridge and building construction in order to improve the load-carrying capacity of understrength or deficient structural members. This paper presents experimental research conducted on full-scale one-way RC slabs strengthened using three different composites. The flexure performance of a new innovative composite, fiber-reinforced cementitious matrix (FRCM), is evaluated and compared with that of conventional fiber-reinforced polymers for some specimens under laboratory condition and for other specimens exposed to environmental conditioning before testing. The test results illustrate the impact of the composite materials on enhancing the flexural strength of RC slabs and their durability performance.

Traffic loads and environmental (climate) conditions are among the most important variables governing the long-term performance of asphalt pavement developed by pavement designers. Several studies done at Carleton University indicate that construction methods can also affect the long-term performance of asphalt pavement by creating hairline surface cracks that allow water to penetrate the asphalt layer. This reduces the tensile strength of the asphalt layer and destroys the bonds in the asphalt between pavement layers. This paper presents the results and major findings of an experimental investigation performed on large-scale asphalt slabs that were extracted from newly laid pavement from an actual highway project. The laboratory work included testing the slabs under direct tensile stress and subjecting them to temperatures ranging from room temperature ($+20°\mathrm{C}$) to $-20°\mathrm{C}$. The testing included one hundred nineteen $300\times 100\mathrm{mm}$ asphalt samples, with thicknesses of 50 mm for single layer and 100 mm for double layer. The research also included evaluating the bonds between asphalt layers built in the field for what the authors believe is the first time. The results showed that construction-induced cracks affect the tensile strength of new asphalt roads and can weaken the bond between the upper and lower layers when overlays are constructed. Statistical analysis confirmed that the differences observed in the results are significant.

Chemical admixtures are often added to concentrated cementitious suspensions in an effort to adjust their (1) rheology, i.e., yield stress and viscosity; (2) time of set, i.e., when plasticity is lost; and (3) hardening rate. Although the first adjustment is affected by dosage of dispersants, the subsequent two adjustments are made by dosing chemical additives that alter the binder’s reaction rate. To ensure desirable field performance, e.g., at subambient temperatures, dispersants and reaction rate enhancers may be dosed simultaneously. In such cases, it is critical to ensure that the dosed additives are compatible with each other. To assess such admixture compatibility and synergy, an original rheology-based method is developed. The method involves assessing the yield stress and plastic viscosity of cementitious suspensions with and without admixtures over a wide strain rate range (${10}^{-4}\le \dot{\gamma }\le {10}^2$). Three fluidity parameters are examined, including (1) plasticity retention; (2) placement limit, i.e., time at which pumpability/pourability is lost; and (3) the rate of hardening following loss of plasticity. To provide a basis of comparison, each of these parameters is assessed relative to neat cement suspensions, across a range of liquid-to-solid ratios (by mass). The method is demonstrated for cementitious suspensions dosed with polycarboxylate ether (PCE) dispersants and calcium nitrate (CN), a set accelerator. The results highlight a means to identify dispersant/set accelerator combinations (or more generally, chemical admixture combinations) that yield optimal synergistic benefits.

In order to improve the rather insufficient knowledge about the hydromechanical behavior of soil–rockfill mixtures (SRMs) applied in embankment dams, a testing program was undertaken in which several mixtures with different coarse fractions (CFs) were tested (30, 40, 50, and 70%). SRMs are an environmentally-friendly material that takes advantage of the material excavated for spillways, cut-off trenches, outlet works, and other structures that can be reused. This study presents, for the first time, a systematic experimental program for this type of natural material, involving isotropic and $K_0$ compression tests, undrained triaxial tests, and permeability tests for different CFs. It aims to improve the knowledge about the behavior of this material. All tests performed revealed that SRMs present the same mechanical behavior irrespective of the CF of the mixture. Also, it may be concluded that it is beneficial to add soil to rockfill to constitute an SRM because this results in a stiffer material.

The generation of huge quantities of waste materials from industries like iron, steel, thermal power plants, etc., is resulting in shortage of disposal areas and causing serious environmental pollution. In this paper, a comparative study of important engineering properties, namely unconfined compressive strength, triaxial shear strength, elastic modulus, resilient modulus, and permanent strain characteristics, of some industrial waste mixtures has been carried out for their use in the subbase layer of flexible road pavements. These materials, namely a Black Cotton soil–dolime (BCD) mixture, fly ash–dolime (FD) mixture, copper slag–fly ash (CF) mixture, and granulated blast-furnace slag–fly ash (GBF) mixture, were chosen based on the proximity of various industries that generate these materials as waste products. The behavior of these materials is also compared with that of conventional granular subbase (GSB) material. The values of deviator stress at failure of these mixtures were found to be greater than that of the granular subbase. Although BCD and FD mixtures exhibited higher elastic modulus and resilient modulus compared with GSB, the corresponding values were lower for CF and GBF mixtures. The prediction of resilient modulus was compared for different stress-dependent models, and the model constants of these mixtures for the best-fit three-parameter model are presented.

A comparative life-cycle assessment (LCA) is undertaken to evaluate the environmental impacts of fired-clay bricks incorporating biosolids from Melbourne Water’s Victorian Eastern Treatment Plant (ETP) and Western Treatment Plant (WTP). The scope of this comparative LCA study ranges from cradle to gate and involves brick soil and biosolids extraction, transportation, crushing and proportioning, grinding and screening, shaping, drying, firing, and packaging. The energy used during the firing process of the biosolids-amended bricks, concentrate of gas emission, and emission factors is quantified experimentally at the laboratory scale. The potential environmental impacts are analyzed and compared by means of the ReCiPe midpoint LCA method using SimaPro 8.0.5.13. The results of the life-cycle impact assessment (LCIA) show that the incorporation of biosolids into bricks is environmentally favorable and is a promising alternative approach with respect to most of the environmental impacts except water depletion, which is mainly due to the higher water demand of biosolids-amended bricks during the shaping process. In addition, bricks incorporating ETP biosolids show a relatively higher potential for ozone depletion and acidification because of the higher fuel usage for ETP biosolids transportation compared with that of brick soil and WTP biosolids. A sensitivity analysis is carried out to address the impact of the assumptions and variables used in the LCA model on the final comparative LCIA results. A comparative uncertainty analysis is conducted to assess the effect of uncertainty in the inventory data on the results of the LCIA indicators. The methods used in this study and discussed in this paper can be used for the LCA of different construction materials.

Use of recycled materials such as recycled asphalt pavement (RAP) and recycled asphalt shingle (RAS) in hot-mix asphalt (HMA) is common now due to their economy and sustainability. However, the effects of RAP and RAS on mixture performance are not fully known. In this research, three recycled Superpave mixture with 9.5 and 19 mm nominal maximum aggregate size (NMAS) were studied as control mixtures. Binder grades in mixtures containing higher percentages of recycled materials (RAP and RAS) were established using a blending chart. Nine laboratory-designed mixtures with different virgin binder contents were evaluated for potential early fatigue cracking using the dynamic modulus and simplified viscoelastic continuum damage direct tension fatigue tests. Moisture susceptibility of the mixtures was evaluated using the Hamburg wheel tracking and modified Lottman tests. Decreased virgin binder content resulted in inferior moisture and rutting performance for 9.5-mm mixtures. Similar fatigue performance was predicted for the mixtures made with the same source of materials regardless of NMAS. In general, mixtures with virgin binder content of 65% of total effective asphalt content and higher showed better performance properties.

Calcium leaching is an important durability issue of cement asphalt (CA) mortar used in high-speed rails. Calcium leaching affects CA mortar’s mechanical properties, which are critical for its structural performance. In this paper, the calcium leaching of CA paste and its effects on the dynamic mechanical properties of CA paste are studied. CA pastes were immersed in $6\mathrm{mol}/\mathrm{L}$ ammonium nitrate solution for different ages. The concentrations of the calcium and silicon ions in the leaching solution were monitored by inductively coupled plasma-atomic emission spectrometry (ICP-AES). Changes in porosity, bulk density, and contents of calcium hydroxide and calcium silicate hydrate (C-S-H) in leached specimens with time were measured. The dynamic mechanical properties of CA paste were measured by dynamic mechanical thermal analysis (DMTA). Results showed that the calcium leaching of CA paste by $6\mathrm{mol}/\mathrm{L}$ ammonium nitrate solution was mostly completed within 7 days. Thermal gravity analysis (TGA) results showed that the calcium leaching, which caused significant mass loss and porosity gain, was mainly contributed by the decomposition of calcium hydroxide (CH) and partly by C-S-H gel. The addition of asphalt only changed the volume fraction of cement hydrates in the CA paste, but did not improve the leaching resistance of cement hydrates. The calcium leaching negatively affected the storage modulus, but positively affected the loss factor of CA pastes.

The hot-mix asphalt (HMA) dynamic modulus ($E^{*}$) is a fundamental mechanistic property that defines the strain response of asphalt concrete mixtures as a function of loading rate and temperature. It is one of the HMA primary material inputs for common software for the mechanistic-empirical design of pavements. Laboratory testing of dynamic modulus requires expensive advanced testing equipment that is not readily available in the majority of laboratories in Middle Eastern countries, yet some of these countries are looking for implementing new pavement design methods such as those given in current standards. Thus, many research studies have been dedicated to develop predictive models for $E^{*}$. This paper aims to apply artificial neural networks (ANNs) for $E^{*}$ predictions based on the inputs of the models most widely used today, namely: Witczak NCHRP 1-37A, Witczak NCHRP 1-40D and Hirsch $E^{*}$ predictive models. A total of 25 mixes from the Kingdom of Saudi Arabia (KSA), and 25 mixes from Idaho state were combined together in one database containing $\mathrm{3,720}{E}^{*}$ measurements. The database also contains the volumetric properties and aggregate gradations for all mixes as well as the binder complex shear modulus ($G_b^{*}$), phase angle ($\delta$), and Brookfield viscosity ($\eta$). A global sensitivity analysis (GSA) was applied to investigate the most significant parameters that affect $E^{*}$ predictions. The GSA procedures based on the Fourier amplitude sensitivity test (FAST) and Sobol sequence approaches were implemented in commercially available software to evaluate the sensitivity of the three regression models to their input parameters. The ANN models, using the same input variables of the three predictive models, generally yielded more accurate $E^{*}$ predictions. Moreover, the GSA showed that aggregate, binder, and mixture representative parameters have convergent effects on $E^{*}$ predictions using one model applied, whereas binder representative parameters have the dominant effect on $E^{*}$ predictions using both of the other two models.

The identification of significant input variables to the output provides very useful information for mix design for soil-fly ash geopolymer in order to obtain the optimum compressive strength. The importance of input variables to the output of soil-fly ash geopolymer is quantified by Garson’s algorithm and connection weights approach in an artificial neural networks (ANN) model, whereas model analysis and fitness method are used in a genetic programming (GP) model. The former approaches in the ANN model use the connection weights among the input, hidden, and output layers to evaluate the importance of the input variables. The latter methods in the GP model assess the frequency of variables used in the model and the value of fitness for the evaluation. The assessment results identify the percentages of fly ash, water, and soil as important input variables to the output. The percentage of hydroxide and the ratios of silicate to hydroxide and alkali activator to ash are ranked as less important input variables. The positive or negative relationships between these input variables and the output demonstrate a very significant influence on the strength development of soil-fly ash geopolymer, showing a positive or negative effect on the compressive strength.

This study used the Taguchi method to determine optimum conditions for Gilsonite and glass fibers as modifier materials in hot mix asphalt (HMA) by conducting the mixed Mode I/III fracture test. These modifier materials were used under different experimental parameters. The parameters and their levels were angle of fracture ($\alpha =30°$ and 45°), nominal maximum aggregate size (9.5, 12.5, and 19 mm), air void content (4, 7, and 10%), Gilsonite content (6, 12, and 18%, as percentage of binder weight), glass fiber content (0.1, 0.2, and 0.3%, as percentage of aggregate weight), glass fiber length (3, 8, and 12 mm), and experimental temperature ($\Theta =0$, $-15$, and $-30°\mathrm{C}$). The optimum conditions for experimental parameters were fracture angle ($\alpha =45°$), air void content (4%), nominal maximum aggregate size (9.5 mm), Gilsonite content (6%), glass fiber weight (0.3%), glass fiber length (12 mm), and experimental temperature ($\Theta =-15°\mathrm{C}$).

In this study, the effect of flexural loading on the chloride-induced corrosion behavior of steels in large-sized concrete was characterized using various electrochemical methods and X-ray computed tomography (X-CT). Electrochemical measurements revealed that steels embedded in loaded concrete exhibited higher corrosion rate than those in unloaded concrete after 15 days of accelerated corrosion. However, after accelerated corrosion for 60 days, similar corrosion behavior was identified for steels in both loaded concrete and unloaded concrete. It was found that the penetration and the distribution of corrosion products in concrete were significantly affected by the sustained flexural loading after the occurrence of load-induced transverse cracks.

Corroded reinforced concrete (RC) members are repaired using ultrahigh toughness cementitious composite (UHTCC), and the bonding between corroded rebar and UHTCC has a significant effect on the mechanical properties of repaired members. In the present paper, the bond behaviors of UHTCC and corroded reinforcement obtained in a concrete environment were investigated via central pullout tests. Parameters including the corrosion ratio and the ratio of the cover thickness to the rebar diameter ($c/d$) were varied. The experimental results revealed that, compared with concrete specimens, UHTCC specimens exhibited a higher nominalized bond strength and full bond-slip response with a slip plateau near the peak bond stress. The dependence of the bond strength on the corrosion ratio was correlated with $c/d$. Furthermore, at the considered corrosion levels, the residual bond strength and the bond toughness of the corroded rebar were higher than that of the noncorroded rebar. A bond-slip constitutive model derived from the existing models was proposed, and the predicted curves provided a reasonable description of the bond characteristics.

This study explored the effect of amorphous nanoaluminosilicate, with controlled silicon to aluminum ratio, on the hydration of portland cement. The effect of these nanomaterials on the early hydration reaction of cement was evaluated using isothermal calorimetry. The xerogel samples of the nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR) before and after exposure to simulated cement paste pore solution. The performance of these nanoaluminosilicates was compared against nanosilica and nanoboehmite. The results show that the nanoaluminosilicates affected principally the hydration of the calcium aluminate phase by removing sulfate from the pore solution. The same effect was reported in cement paste samples containing 10 times more concentration of metakaolin. The effect was found to be strongly dependent on the particle size, which was ultimately affected by the silicon to aluminum ratio of the original nanoparticle. Beside sulfate, it was found that the nanoparticles also incorporate alkalis, calcium, and chloride from the pore solution to form calcium aluminosilicate hydrate and hydrated calcium aluminates (AFm) phases.

Nickel slag autoclaved aerated concrete (NS-AAC) was fabricated through a hydrothermal synthesis method by using a novel solid waste, mechanically activated magnesium-rich NS, as the main raw material. The influence of the calcium:silicon ($\mathrm{C}:\mathrm{S}$) ratio on the macroscopic and microscopic performance of NS-AAC was investigated. NS-AAC was analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Results showed that a formulation with 0.65 of $\mathrm{C}:\mathrm{S}$ exhibited exceptional compressive and flexural strength, which were 3.5 and 2.1 MPa, respectively. The hydrothermal production of NS-AAC, transformed from C-S-H and Ettringite (AFt) to interfingered and overlapped tobermorite and anhydrite, resulted in exceptional mechanical properties. This work proposes a novel approach for the utilization of NS.

In this study, the effect of combined nanosilica (nS) and microsilica (mS) on sulfate resistance of portland cement mortars was compared with cement-only control mortars and mixtures with equivalent contents of only one form of silica. Silica-contained mortars had 6% cement replacement of either nS, mS, or 3% of each. An additional mixture with 3% mS was also tested. The series of mortars were prepared with both a moderate ${\mathrm{C}}_3\mathrm{A}$ (7.2%) and a low ${\mathrm{C}}_3\mathrm{A}$ (4.1%) cement to evaluate the effectiveness of each silica replacement paired with a chemically sulfate and nonsulfate-resistant cement. The mortars in this study were subjected to a 1.5-year period of full-submersion sulfate attack in a 5% sodium sulfate (${\mathrm{Na}}_2{\mathrm{SO}}_4$) solution. The mortars tested were measured for expansion and compressive strength. Additional testing for absorption, rapid sulfate penetration, and mercury porosimetry of select mortar mixtures, paired with laser diffraction particle analysis of sample silica particles suspended in water, supplemented the interpretation and explanation of the results. The expansion measurements indicated that mS replacement mortars outperform both nS-only and $\mathrm{nS}+\mathrm{mS}$ combination replacement mixtures. A negative effect of the dry nS powder replacement attributed to agglomeration of its fine-sized silica particles during mixing negated the expected superior pozzolanic activity of the nanomaterial. In light of the results, most of the beneficial contribution from the cement replacement with the combination mixtures could be attributed to the mS proportion given that the combination mixtures’ expansion performance was comparable to that of the 3% mS-only mortars.

The present study examines the behavior of particulate rubber–sand mixtures (PRSM) due to the replacement of sand with fly ash. Particulate rubber (PR) of different gravimetric proportions (0, 10, 30, 50, and 100%) is mixed with sand and fly ash for the present study. Vibratory table technique, Proctor compaction technique, and minicompaction technique are adopted to determine a suitable method for finding the maximum dry unit weight of the mixtures. It is found that the Proctor compaction technique is suitable for PRSM and minicompaction technique is suitable for particulate rubber–fly ash mixtures (PRFM). Direct shear tests are carried out on the samples prepared at a relative density subjected to three different effective normal pressures. The tests results show that PRFM possesses higher shear strength, lesser compressibility, and higher shear stiffness than PRSM when PR content is more than 10% in the mixtures. Microstructure study shows that the higher strength of PRFM is attributed to the more interparticle contacts between PR and fly ash.

Historically, the use of internal curing began with a low water-to-cement ratio ($\mathrm{w}/\mathrm{c}$) and high-strength concrete. More recently, the benefits of reduced autogenous shrinkage and improved hydration have been recognized over a wider range of mixtures. In North America, the internally cured mixtures are typically made using prewetted fine lightweight aggregates (FLWA). The volume of FLWA used in an internally cured concrete is usually determined on the principle that the FLWA provides a volume of internal curing water that is equivalent to the volume of chemical shrinkage. This study examines whether it is possible to reduce the volume of the FLWA while still achieving the benefits of internal curing with respect to the reduced autogenous shrinkage and increased relative humidity. An alternative mixture methodology is presented that utilizes the pore-size distribution of the cementitious paste to calculate the amount of internal curing water needed to maintain a specific relative humidity (that is, to provide water sufficient to keep pores of a certain size filled) in the mixture. The proposed approach can be used to calculate the volume of water required to fill the pores of a specific size that empty, so that the effects of self-desiccation are minimized to an acceptable level. This approach maintains a high relative humidity to reduce the autogenous shrinkage and increase the early-age hydration. Although many applications such as bridge decks are still designed with the more conventional design approach, it is hypothesized that this assumption generally overestimates the amount of water needed to effectively reduce the autogenous shrinkage of a concrete mixture. Other applications where larger volumes of materials are involved, such as pavements, may benefit from a design approach that optimizes the volumes of FLWA, due to the reduction in the raw materials required, which has benefits from the perspectives of both the cost and the staging.

The Hamburg wheel tracking device (HWTD) test is widely used; however, limited research has been performed to fully understand the damage evolution of the asphalt mixture in the wet HWTD test. In this study, intuitive image analysis and air voids (AV) content analysis based on computed tomography (CT)-scanned samples confirmed and further supplemented the failure pattern of the HWTD testing specimens in three stages. The results indicate that the change in the calculated AV content and 3D reconstructed AV images from the CT analysis correlated well with the responses of the HWTD testing samples at different stages. Additionally, the decrease in closed voids in the sample can be used as an indicator of both the integrity of the specimen and the degree of damage in the HWTD test. Further, it was found that the optimum binder content determined by the wet HWTD test can reflect both the rutting resistance and moisture sensitivity of the HMA. The HWTD test is recommended as a pass/failure criterion during the design process of asphalt pavement.

The rheological properties of concrete mixtures are presently important when new technologies for transporting, handling, placing, and compacting concrete are used in new concrete construction technologies. A new methodology and equipment, the remolding type viscometer, was developed for testing the rheological properties of concrete mixtures. During the vibration, the flowing time of the concrete mixture from an inner cylinder to a cylindrical vessel with different pressure is measured and the rheological characteristics, the yield stresses and viscosity, are calculated according to the developed equations. By using this equipment the rheological behaviors of concrete mixtures (thixotropy and dilatancy) can be analyzed. This testing methodology can be used to optimize the proportions of different concrete mixtures addressing factors such as aggregate granulometry, admixtures dosage optimization, and other considerations. Experiments were conducted with vibrated concrete mixtures having sand content from 50 to 75% in the aggregate mixture. The yield stresses, viscosity, and dilatancy of concrete mixtures were calculated according to the abovementioned testing methodology. The tests revealed that the rheological curves of the concrete mixture are not linear as in Bingham’s model but have a curved shape. Increasing the sand content in the aggregate from 50 to 65% increases the yield stress of concrete mixture approximately 1.5 times and afterward remains constant. The lowest viscosity and highest workability is obtained with the sand content in the aggregate ranging between 50 and 65%. The lowest values of dilatancy index were obtained with the sand content in the aggregate ranging within 50–65%.

This study was conducted to investigate the potential of using treated wastewater in the compaction of base course layers in pavement structures. Three different types of base course material and two sources of treated wastewater in addition to tap water were considered. Chemical analysis tests were conducted on the treated wastewater (TWW) to evaluate the suitability of their use in construction. Modified Proctor compaction and California bearing ratio tests were conducted on the prepared road base samples. In addition, pavement analyses were performed using the Mechanistic-Empirical Pavement Design Guide (MEPDG) to evaluate the effects of using TWW on the pavement performance. The economic and environmental impact of using TWW in pavement construction was also evaluated. The results of this study indicated that TWW can be a suitable replacement for fresh water in base course layers in pavement construction. The cost and environmental impact analyses showed that using TWW in base layers can result in up to 68% reduction in water cost and can have a clear positive impact on the environment.

High-fluidity gypsum-based materials have been widely used in grouting materials, self-leveling floors, wall materials, and three-dimensional (3D) printing materials. High fluidity means excellent workability without any segregation and bleeding, and generally, this can be obtained with addition of both polycarboxylate superplasticizer (PCE) and hydroxypropylmethyl cellulose (HPMC). However, the interaction between these two additives in gypsum paste has not been completely understood until now. In order to obtain a deeper insight into this interaction, this paper investigates the rheological performance of the gypsum pastes in the presence of these two materials with different orders of addition and discusses the adsorption behavior of these organic materials and the hydration process of the gypsum at very early age. Dispersion models are proposed to explain the mechanisms behind the interaction. The results show that both HPMC and PCE can adsorb onto the surface of gypsum particles. HPMC can hinder the adsorption of PCE due to competitively adsorbing behavior, resulting in a negative effect on dispersion of PCE. Preferential addition of PCE can effectively reduce this negative effect, whereas the preferential addition of HPMC has a positive effect on enhancing the viscosity of gypsum slurry. These results can provide useful guidance for the preparation of high-fluidity gypsum paste in practical engineering.

This paper investigates the influence of different types of steel fibers on the engineering properties of ambient cured alkali-activated slag–fly ash concrete. The engineering properties investigated include workability, compressive strength, splitting tensile strength, flexural strength, direct tensile strength, and stress–strain response under axial compression. Three types of steel fibers, i.e., straight micro steel fiber, deformed macro steel fiber and hybrid steel fiber, were added to the alkali-activated slag–fly ash mixes. It was found that the workability of the alkali-activated slag–fly ash concrete mixes decreased with the increase in the volume fraction of steel fibers. It was also found that the compressive strength, splitting tensile strength, flexural strength, and direct tensile strength of alkali-activated slag–fly ash concrete mixes increased with the addition of steel fibers. The stress–strain response of alkali-activated slag–fly ash concrete mixes changed from brittle to ductile by the addition of steel fibers. Significant improvements in the mechanical properties of alkali-activated slag–fly ash concrete were observed for the addition of 2% by volume of all three types of steel fiber. The addition of hybrid steel fiber (1% straight micro steel fiber plus 1% deformed macro steel fibers) showed the highest improvement in the mechanical properties of ambient cured alkali-activated slag–fly ash concrete.

This paper focuses on the production of high-strength geopolymer binder by alkali activation of binary mix of fly ash and calcium aluminate cement (CAC). The fly ash was partially replaced with CAC (8, 16, and 24%) to increase the reactive phases of source materials, and the resulting blends were activated by aqueous solution of NaOH and sodium silicate with different ${\mathrm{Na}}_2\mathrm{O}$ contents and ${\mathrm{SiO}}_2/{\mathrm{Na}}_2\mathrm{O}$ ratios and were cured hydrothermally at 95°C for 20 h. The compressive strength of the geopolymer mortar increased up to 59 MPa by optimizing the process parameters. The optimized geopolymer specimens were then immersed in HCl and ${\mathrm{H}}_2{\mathrm{SO}}_4$ solutions ($\mathrm{pH}=1$) for 6 months to monitor changes in the physical and mechanical properties of the mortars. These experiments were repeated with Portland cement and high alumina cement mortars as control specimens. Microstructural and characterization tools were also employed to examine the compositional and microstructural changes of the geopolymer paste. The findings showed the superior performance of geopolymer mortar against both acidic solutions compared to the control mortars due to the more stable cross-linked aluminosilicate structure formed in the geopolymer samples. XRD studies also revealed that gypsum is the dominant product in the geopolymer sample exposed to sulfuric acid as a result of reaction between calcium compounds and sulfate ions.

The influence of sugarcane-bagasse ash (SCBA) and rice-husk ash (RHA) as cement replacement materials on the mechanical and durability properties of mortars was investigated in this study. Portland cement was replaced by RHA and SCBA at a rate of 10–30% and 10–25% by weight of cementitious materials, respectively. Also, ternary mixtures were prepared by the incorporation of both additives. Replacement dosages were selected based on the former research studies to cast the mortar. Additionally, a control mixture, containing only cement, was prepared to clarify the effectiveness of replacement materials. Compressive strength tests were conducted to evaluate the mechanical performances of the specimens. In addition, the transport tests (water absorption and capillary absorption), electrical resistivity, rapid chloride migration test (RCMT), and acid resistance of mortars were evaluated in order to investigate the effect of SCBA and RHA on the durability properties of mortar. Results showed that RHA was more effective at enhancing the mechanical properties of mortars than SCBA. However, according to the durability tests’ results, both SCBA and RHA were found to be effective since ternary mixtures were more durable when compared to the control mixture.

Insulated concrete elements used in building facades, e.g., sandwich panels, are frequently exposed to sun radiation, which causes high temperatures on the outside. Although the inner and outer cladding are supposed to be independent, a high temperature difference between the outside and the inside of the elements causes thermal bending, which can lead to cracking. These cracks may have an impact on the durability of the outer cladding and are not wanted from an esthetic point of view. A possible solution for this problem is the embedment of encapsulated polyurethane in the concrete matrix in order to repair cracks autonomously. However, healing agents with suitable properties are needed to heal cracks at these conditions. In this research, newly developed polyurethane resins with relatively high viscosity were tested for their healing efficiency at high temperatures. The mechanical properties of the polyurethanes such as bond strength and elasticity were determined. Second, the healing agents were encapsulated and evaluated for their efficiency to heal cracks by capillary absorption tests, strength regain evaluation, and X-ray computed tomography. The new polyurethanes were much more elastic than the commercially available ones and thus more able to withstand opening and closing of cracks due to temperature changes. The water ingress in specimens with healed cracks was found to decrease with increasing viscosity of the polyurethanes. At a temperature of 50°C, the polyurethanes were able to heal cracks so that the water absorption of cracked mortar was reduced to a value that was comparable to the water absorption of uncracked mortar. Also, a strength regain of 100% or more was obtained. Therefore, using self-healing concrete in building facades may have a positive effect on the durability and service life of the construction elements.

The purpose of this paper is to investigate the electrochemical and semiconducting properties of passive films on steel surfaces in alkali-activated slag extraction solution (NSAS) using potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), and Mott-Schottky (M-S) analysis. The diffusivity of point defects ($D_0$) in the passive film on steel surfaces in NSAS, based on the point defect model (PDM) theory, was calculated for the first time. Passive film on steel surfaces in an ordinary portland cement extraction solution (OPCS) was also studied for comparative purposes. The results show that steels in NSAS and OPCS all show typical passive system features. Passive film on steel surfaces in NSAS was thicker than that in OPCS at the same film formation potential. All the passive films in this paper were n-type semiconductors, and the donor density of the passive film in NSAS was on the order of ${10}^{19}–{10}^{20}{\mathrm{cm}}^{-3}$, and that of passive films in OPCS was on the order of ${10}^{20}{\mathrm{cm}}^{-3}$. The $D_0$ of steel in NSAS was lower than that in OPCS. The EIS analysis, M-S analysis, and calculation of $D_0$ all supported the same conclusion: passive film on steel surfaces in NSAS was more protective than that in OPCS.

In this paper, the combined effect of adding polyphosphoric acid (PPA) and distillate aromatic extracts (DAE) oil on rheological and mechanical characteristics of neat asphalt binder at high and low temperature is investigated. PPA was added to neat asphalt binder with three different contents of 0.5, 1, and 2% by weight of asphalt, and DAE was added to neat and PPA-modified asphalt binders to the extent of 10%. In total, one neat and seven modified asphalt samples were investigated in this research by implementing dynamic shear rheometer and bending beam rheometer for evaluating high and low temperature respectively. Using superpave protocol criteria, high and low service temperature of all specimens are determined. In addition, an extension of the simple fractional viscoelastic model is developed as a generalized fractional viscoelastic model to determine and describe low temperature parameters of all samples including damping ratio and dissipated energy ratio. Results show that using 1% of PPA in conjunction with 10% of DAE can balance high and low temperature appropriately to obtain a modified asphalt binder of PG70-28 from a neat asphalt binder of PG64-22. Also, implementing the generalized fractional viscoelastic model successfully resolved shortcomings of simple fractional element, especially for capturing variation of damping ratio and phase angle versus frequency.

Wood-composite I-joists are commonly used in residential and light commercial construction. I-joists are intended for use in dry-service environments, but rare situations exist in which I-joists may be subjected to environments that promote elevated moisture content levels. For example, flooding, poor construction practices or disaster situations leading to unprotected exposure, or abnormally long construction delays may arise. In these extreme situations it becomes necessary to characterize I-joist performance to determine if replacement is needed. This research subjects wood-composite I-joists (302 mm deep by 1.32 m long) to two extreme environments intended to assess moisture durability: laboratory-accelerated weathering and unprotected outdoor exposure. Joists are tested in short-span bending to assess shear capacity after conditioning back to the dry state. Shear capacity decreases as a result of exposure to high moisture conditions. All outdoor exposure intervals lead to greater losses in shear capacity than do any of the laboratory-accelerated weathering periods evaluated. In addition, the failure mode of I-joists changes with exposure type and duration.

Peat deposits cover large areas in Northern Canada. Peat in the study area in Northern Manitoba has an average thickness of 4 m, with the upper half classified as fibrous and the lower half as amorphous with strong to complete decomposition. Design, construction, and maintenance procedures for new road embankments on seasonally frozen peat deposits require mechanical, hydraulic, and thermal properties of the foundation. Laboratory tests were conducted on samples obtained from a test section along a newly constructed road. Hydraulic conductivity tests were conducted at different vertical stresses to determine permeability. Thermal conductivities were determined at frozen and unfrozen states. Conventional incremental-loading (IL) odometer tests were performed to determine the compressibility and secondary compression indices of the peat layers. Constant-rate-of-strain (CRS) tests were also done to supplement the results obtained from the conventional method. Isotropically consolidated undrained (CIU) triaxial tests were carried out, and a new method of evaluating the shear strength of peat was implemented. Numerical modeling that used the measured mechanical, hydraulic, and thermal properties simulated reasonably well the performance of road embankments constructed on seasonally frozen peat. With these properties, construction and long-term performance of highway embankments and future infrastructure development on peat foundations can be reasonably predicted, leading to effective construction and maintenance procedures.

The laboratory aging tests for binders were developed based on Strategic Highway Research Program (SHRP) tests in the 1990s (i.e., performance grading); the applicability of performance grade (PG) to recently developed tests, such as multiple stress creep recovery (MSCR), is not clear. In addition, the ability of laboratory aging to represent field pavement aging, especially when polymer-modified asphalt (PMA) and warm-mix asphalt (WMA) binders are used, has been a concern to paving practice. This paper investigates quantitatively the level of laboratory aging compared to the field aging for both the control hot-mix asphalt (HMA) binders and WMA and PMA binders. The study focuses on a number of binder parameters, as well as evaluating whether the current laboratory aging conditions (loose-mix oven aging) will provide correlation to field short-term aging. HMA and WMA binders from four field projects that covered different climatic zones, pavement structures, and materials were selected. Binder properties including high-temperature PG, MSCR nonrecoverable creep compliance, low-temperature binder PG, and fracture energy were used for analysis. The results show that the laboratory rolling thin-film oven (RTFO) aging method is not sufficient to simulate field short-term aging conditions for most cases except for the low-temperature PG test. The aging of asphalt binder is parameter sensitive; depending on the parameters used, the comparison results between laboratory aging and field aging could be different. The effect of aging on PMA binder, especially when mixed with Sasobit additive, differs from non-polymer-modified binders. Limited results from non-polymer-modified binder mixes suggested that loose-mix oven aging at 85°C for 2, 5, and 7 days appears to provide a reasonable simulation of field pavement aging right after compaction (0 years), 1.8 years, and 3 years.

In recent years, concerns about the depletion of nonrenewable resources, infrastructure sustainability, and environmental impact in pavement engineering have led to substituting petroleum-based paving materials with their biobased counterparts. Research efforts have been attempted to produce asphalt from renewable bioresources. As a special modifier for asphalt, petroleum-based epoxy resin has been used in a few asphalt paving projects that require superior performance of asphalt mixtures. This paper presents an attempt to develop a biobased epoxy modifier for asphalt using an epoxidized soybean oil (ESO) and a biobased curing agent, maleic anhydride (MA). The proper proportions of ESO, MA, and a base asphalt were determined to achieve a homogenous biobased epoxy asphalt binder (BEAB) with the desired properties evaluated by a rotational viscosity test, a penetration test, and a dynamic shear rheometer test. Pavement performance–related properties of asphalt mixtures using such a BEAB were also preliminarily evaluated using a Marshall stability test. At an optimum ratio of $0.45:1:8$ for $\mathrm{MA}:\mathrm{ESO}:\text{asphalt}$, the BEAB showed higher Marshall stability than a mixture containing the base asphalt. Further research, however, is still needed to evaluate the asphalt mixtures with more pavement performance–based tests and to refine the BEAB formula.