Journal of Materials in Civil Engineering

Cement kiln dust (CKD), a waste by-product, is a major problem at many cement manufacturing plants because of high alkalinity, metals, and sulfates. CKD possesses the same cementitious characteristics as those of cement, but the use of high-alkaline cement kiln dust reduces the quality of the cement and the strength of the concrete. In this study, the CKD used contained high alkali ($\mathrm{1,467}\mathrm{mg}/\mathrm{L}$) and hardness ($467\mathrm{mg}/\mathrm{L}$) content in leachate, which on treatment with bacterium Bacillus halodurans strain KG1 showed a decrease of 67.3% alkalinity, 85.6% hardness, 46% ${\mathrm{K}}_2\mathrm{O}$, and 27% ${\mathrm{SO}}_3$ in powdered CKD after 20 days of treatment at $35\pm 2°\mathrm{C}$. This study investigates the effect of bacterial-treated CKD as a partial replacement (10, 20, and 30%) for portland cement on compressive and splitting tensile strength, water absorption and porosity, ultrasonic pulse velocity, and chloride permeability of concrete at the age of 28 and 91 days. Utilization of 10% bacterial-treated CKD in concrete resulted in 26.6 and 25.6% increases in compressive and splitting tensile strength at 91 days of curing compared with the control (CC) treatment. Reduction in both water absorption (64%) and porosity (53%) was observed. Similary, the reduction in chloride permeability was 22%. SEM and XRD analysis revealed increased formation of calcium silicate hydrate (CSH) gel that resulted in dense structure and low permeability.

Benchtop experiments demonstrate the promise of hydrogel-assisted enzyme-induced carbonate precipitation (EICP) as a means of enhancing EICP for soil stabilization. Enzyme-induced carbonate precipitation uses hydrolysis of urea (ureolysis) catalyzed by the urease enzyme to precipitate ${\mathrm{CaCO}}_3$ in the presence of urea and calcium in a water-based solution. Xanthan and guar gum biopolymers and an inert polyol-cellulose hydrogel were used to assess the ability of a hydrogel to enhance EICP by retaining reaction product around the soil particles. The experiments were conducted in sand-filled paper cups and soilless glass beakers at 1.66 and 0.33 M of initial calcium chloride (${\mathrm{CaCl}}_2$) concentrations using high-activity and low-activity plant urease. Ureolysis and ${\mathrm{CaCO}}_3$ precipitation occurred in all hydrogel-assisted EICP tests, suggesting that the hydrogels used in this study do not interfere with EICP. Furthermore, hydrogel-assisted EICP appeared to retain moisture for extended periods of time and reduce penetration of the EICP solution into the soil, extending reaction time, increasing precipitation efficiency, and enhancing the formation of a crust. Gas bubble formation in the hydrogel solutions suggests that ammonia (${\mathrm{NH}}_3$) and/or carbon dioxide (${\mathrm{CO}}_2$) off-gassing may be reduced, which may also increase precipitation efficiency. Guar and xanthan gums were found to have the greatest water retention ability and to significantly reduce water evaporation.

This paper presents a nanomechanical test-analysis method to measure the elastic modulus and hardness of constituent phases of bituminous paving mixtures. Quasi-static nanoindentation tests were conducted on small-volume specimens using a Berkovich nanoindenter tip. The elastic modulus and hardness were analyzed from the responses of the material measured during the unloading segment of the nanoindentation tests using a contact mechanics–based analytical model. The correlation of the scanning probe images and nanoindentation results reveal that the aggregates and matrix have the highest and the lowest stiffness-hardness in the mixture as expected, and a gradual change in the elastic modulus and hardness occurs across the aggregate-matrix interphase with an approximate 30–60 μm width. This study clearly demonstrates that a nanoindentation approach can be effectively used to characterize the fundamental properties of different phases and critical locations in heterogeneous mixtures using readily available small-volume specimens. The possibility of obtaining more accurate and statistically reliable material properties can improve the accuracy of materials characterization and performance prediction modeling of mixtures and structures.

Asphalt-treated permeable base (ATPB) mixtures have been widely applied for drainage layers in pavements to avoid moisture-induced problems in the United States. However, with frequent exposure to water, the ATPB drainage layer itself is at high risk of moisture damage. In this study, the dynamic modulus and phase angle are used as the indicators to evaluate the potential moisture-induced deterioration of typical ATPB materials adopted in Virginia and Oklahoma. The modified dynamic modulus test appropriate for testing drainage layer materials with moisture deterioration were determined and adopted. Comparisons between the dynamic modulus of the conditioned and unconditioned specimens primarily show that the moisture-induced dynamic modulus reduction tend to be larger as the voids in total mixture (VTM) increases, and the drainage layer materials may become more sensitive to VTM but less sensitive to temperature after being conditioned in moist environment. The investigation of phase angle ratio and storage modulus ratio further reveals that moisture conditioning also influences the viscoelastic characteristics of the ATPB materials especially at larger VTMs. In addition, corresponding field performance is also evaluated and found to be consistent with the laboratory-determined moisture resistance for the ATPB-VA mixture by far.

In the present study, new empirical models are derived to predict the compressive strength of preformed foam cellular concrete using volumetric and weighted approaches. The proposed models are generated by utilizing a robust predictive tool known as genetic programming. A comprehensive database is collected from the literature to cover a wide range of mixture components (such as sand and pozzolans) and mix proportions. The models link the compressive strength to binder, water, and foam volume. Validation of the best model is carried out by using a portion of the data set that is not employed in the calibration process. A comparative study is conducted to evaluate the performance of the proposed model versus other models presented in the literature. Sensitivity and parametric analyses were conducted. The final model has a simple formulation and provides better prediction performance than the other models in the literature.

Recently, strain hardening cementitious composite (SHCC) material has been used for the shear strengthening and the structural rehabilitation of reinforced concrete structures. However, the shear behavior of this material has not been yet fully understood due to lack of an appropriate and accurate direct shear test method. This paper aims to investigate the shear properties of the SHCC material. For this purpose, Iosipescu shear test was selected, where loads are applied in antisymmetric four-point bending, assuring a pure shear section at the center of the specimen. A special geometry for the specimen was adopted in order to assure a uniform shear stress distribution in the pure shear section. This experimental test can characterize the shear behavior of SHCC material. The experimental test was simulated by the finite element method (FEM)-based computer program, FEMIX. To predict the average shear stress–sliding response, the shear crack softening diagram, available in the multidirectional fixed smeared crack model, was used. After demonstration of the good predictive performance of the numerical model, a parametric study was carried out to evaluate the influence of shear retention factor, fracture energy of mode II, and crack shear strength on the average shear stress–sliding response of the SHCC. The advantage of SHCC instead of conventional mortar was also studied.

The performance and economy of infrastructure system is dependent on the specifications used to construct it. Good specifications contain requirements that correlate with improved performance and/or economy. There are several standards and specifications for mixing field concrete. These documents provide requirements for the mixing process. However, limited research has been performed on how mixing time and number of drum revolutions affect concrete characteristics. With advanced technologies that can delay the set and improve the workability, the current documents may not be applicable. This paper presents an assessment of pastes and mortars mixed for different times and varying number of mixer revolutions. Early-age characteristics include the assessment of time-variant ion concentration in solution, flowability, setting time, and chemical shrinkage. Results indicate that these early-age characteristics of pastes and mortars mixed in the laboratory are influenced by the mixing time and number of mixer revolutions. The rate of dissolution ($R_d$) of ions in solution and temperature are the material parameters directly affected by the mixing processes and these parameters can alter the rates of hydration reactions, resulting in changes of the early-age characteristics of cement systems.

This paper presents an examination of the fatigue characteristics of cement-treated base (CTB), a cement-stabilized material for use in road pavement construction based on CTB beam test specimens prepared and tested under laboratory conditions. The beam fatigue protocol for asphalt concrete, following the Austroads standard test method of AG:PT/T233, were adapted to examine the fatigue characteristics of the CTB test specimens. Standard road base (Granite/Diorite) from the local quarry in Western Australia was employed as the parent material of CTB. The beam-fatigue tests were conducted under the strain-controlled (constant strain) and stress-controlled (constant stress) testing conditions with varying cement contents (3–10%) of CTB test specimens. Two different loading waveforms of sinusoidal and haversine load curves were also investigated. The results show that for the strain-controlled testing condition, the fatigue characteristics of the CTB test specimens were not affected by the difference in both loading waveforms. Furthermore, the fatigue characteristics of the CTB test specimens were significantly influenced by the levels of the applied strains. Under the strain-controlled testing condition, the test results also indicated the existence of fatigue endurance limit, which occurred based on the test condition of the applied strain level of 150 microstrains or less subjected to 5% cement specimens. This fatigue endurance limit increased with respect to higher cement content and initial cyclic flexural stiffness. For the stress-controlled testing condition, this study found that the conclusion cannot be made that a relationship exists between applied stress level and fatigue characteristic of the CTB test specimens. This is because half of the test specimens in this study were damaged in the early stages of loading cycles with small increases in applied stress levels. Considering all the test results, the strain-controlled testing was preferable, based on the test conditions and environment used in this study. This study confirms that the use of the adapted beam-fatigue test protocol of asphalt concrete is suitable to determine the CTB fatigue characteristics, which are difficult to obtain with no standard test protocol. This would lead to more effective use of this material in road pavement design and construction.

Long-term pavement performance (LTPP) projects with hot mix asphalt were evaluated using three proposed indicators for low temperature cracking resistance. The primary objectives were to compare ways to combine stiffness and relaxation properties to correlate with cracking, assess data collection schemes in the LTPP relating to the analysis methods, and provide agencies with information to develop approaches for cataloging binders and performance. The Superpave low-temperature specification was compared with the recently developed Glover-Rowe parameter to relate laboratory-measured properties to field cracking. Complex modulus and phase-angle master curves were constructed to plot binder properties in Black Space. Results show the Superpave specification and Glover-Rowe parameter were able to capture one significantly cracked section which had test data obtained within a reasonable amount of time from field measurement. However, the available LTPP data was not ideal for Glover-Rowe analysis, where frequency sweeps at several temperatures are desired. The information presented is particularly relevant as tighter budgets delay maintenance and rehabilitation, exposing pavements to extensive aging.

Only a small amount of published literature has presented any agreement on how aggregate properties affect the workability of concrete, and some of these historic aggregate design methods may give conflicting recommendations. This research aims to provide insight by comparing several historic aggregate concepts to the workability performance of low flow concrete for slip-formed applications. The workability performance of each mixture was measured using the slump test and the box test. By leaving the paste volume constant and systematically changing aggregate concepts such as gradations and proportioning techniques, it allowed for a quantitative comparison between these different aggregate concepts and techniques. The results show the individual percent retained (IPR) chart was the most useful to predict influences of aggregate gradation. Other aggregate gradation and proportioning concepts such as the coarseness-factor chart, the Power 45 chart, specific surface area, and some popular packing methods were not able to accurately predict workability performance for slip-formed applications. The shape and texture of aggregate was also shown to be important for workability of these mixtures.

Fatigue cracking is the main form of structural damage in hot mix asphalt (HMA) at moderate temperatures. The one of ways to reduce this type of distress is use of nanomaterials as additives in asphalt mixtures. In this study, the effects of using $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ as an asphalt binder modifier on the fatigue life of asphalt mixtures are assessed by surface free energy (SFE) method and indirect tensile fatigue (ITF) test. The HMA mixtures containing 0, 3, and 6% of $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ are plant prepared with two sources of aggregate (granite and limestone), and one type of asphalt binder with 85/100-penetration grade. The results showed that fatigue lives of mixtures containing $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ were higher than the control mixtures. This is attributed to the fact that adding $\mathrm{nano}\text{-}{\mathrm{TiO}}_2$ leads to decrease of the acid component of SFE and increase of the basic component in SFE of the asphalt binder that enhances the adhesion between asphalt binder and aggregate. Furthermore, the asphalt mixtures made with the modified asphalt binder showed greater fatigue life than the control mixtures because of improved cohesion energy and higher resistance to fatigue cracking in asphalt film.

In the present study, six concrete mixtures were prepared to examine the effect of the types of binder and concrete on the fatigue performance of concrete under compression. The selected binder types include ordinary portland cement (OPC); high-volume supplementary cementitious material (SCM) composed of 30% OPC, 20% fly ash (FA), and 50% ground granulated blast-furnace slag (GGBS); and alkali-activated (AA) binder composed of 50% FA and 50% GGBS activated by the combination of ${\mathrm{Na}}_2{\mathrm{SiO}}_3$ and $\mathrm{Ca}{(\mathrm{OH})}_2$. Using the prepared binders, normal-weight concrete (NWC) and lightweight concrete (LWC) with a unit weight of $\mathrm{1,700}\mathrm{kg}/{\mathrm{m}}^3$ were produced. For cyclic loading of concrete samples, the constant maximum stress level varied among 75, 80, and 90% of the static uniaxial compressive strength of concrete, whereas the constant minimum stress level was fixed at 10% of the static strength. On the basis of a regression analysis conducted using test results, the fatigue life and fatigue stress-strain curve for concrete were formulated to evaluate the incremental strain with the number of cyclic loading. Test results clearly showed that the fatigue life of LWC tended to be slightly lower than that of the companion NWC, whereas the incremental fatigue strain in LWC was higher than that in NWC. These observations were more pronounced for concrete mixtures using high-volume SCM or AA binders than for OPC concrete. The proposed fatigue stress-strain model provides good mathematical simplicity and accuracy in predicting full fatigue stress-strain curves for concrete and/or a single piece curve at a certain number of cycles, without the need for a tedious step-by-step calculation procedure.

The evolution of asphalt microstructures under thermal loading has always been a critical issue for pavement engineers. Previous researches show that phase separation will greatly affect the mechanical performance of asphalt at microscale. To analyze this important phenomenon, the conserved phase-field model is coupled with the Navier–Stokes equation to simulate the phase kinetics in this paper. The asphalt is chemically simplified to a quaternary system consisting of four chemical components: asphaltene, resin, oil, and wax. The coupled Navier–Stokes phase-field system is solved in a unified finite element framework in COMSOL software. It is observed that phase separation has a significant influence on the thermal stress distribution. Moreover, stress concentration is observed at the interfaces between different phases, which may result in microcracks. This conclusion is validated by atomic-force microscopy (AFM) experiment results.

Basalt fiber bundle (yarn) and basalt fiber–reinforced polymer (BFRP) samples are tested under four different strain rates (40, 80, 120, and $160{\mathrm{s}}^{-1}$) and four distinct temperatures (25, 50, 75, and 100°C) using a drop-weight impact system in this study. Experimental results show that the mechanical properties of the samples tested in this study are sensitive to strain rate and temperature. For the basalt yarn specimens, Young’s modulus increases with increasing strain rate but decreases with increasing temperature; tensile strength increases with increasing strain rate, but decreases first and then increases again when the temperature increases; the maximum strain and toughness generally increase with increasing temperature. For the BFRP specimens, Young’s modulus shows a relatively modest increase compared with the yarn with increasing strain rate but decreases with elevated temperature; the tensile strength firstly increases and then decreases with increasing strain rate, and decreases with elevated temperature. Toughness increases with increasing strain rate but decreases with elevated temperature. Finally, Weibull statistics were employed to quantify the variability of strength at different strain rates and temperatures and to obtain Weibull parameters for future numerical analysis and engineering applications.

The present work aims to evaluate the feasibility of iron ore tailings from tailing dams as an alternative material for road infrastructure. The iron ore tailings were characterized according to their chemical, mineralogical, environmental, and physical properties. Subsequently, the tailings were chemically stabilized using cement, lime, or steelmaking slag as binder. The tailing-cement, tailing-lime, and tailing-slag mixtures studied consisted of 1, 2, 5, and 10% binder content, each. The characterization methodology included chemical and mineralogical analysis through X-ray fluorescence and diffraction; environmental analysis with leaching and dissolution tests; evaluation of compaction curves; California bearing ratio (CBR) tests and expansion assessment; compressive strength, with curing in moisture chamber or at open air; water absorption; and evaluation of durability of the mixtures. Overall, the results indicate that the iron ore tailings are a feasible solution for use as layers for road paving, once chemically stabilized. The cement is the most efficient stabilizer among the studied binders. The slag-tailing sample did not endure the durability cycles; thus, further research is required to ensure its technical feasibility.

This paper presents the corrosion degree effect on yield and ultimate strengths (nominal and effective) of protruding reinforcing steel that remained buried for 60 years; thus, the natural corrosion process during this period was analyzed. Tensile tests were performed on specimens taken from this protruding reinforcing steel. A characterization of the local soil where the reinforcement remained buried as an aggressive medium was performed, and micrographs were obtained in order to observe the presence of pits. The results were in agreement with studies of accelerated corrosion in a laboratory. As the corrosion degree increases, the greater is the difference between the nominal and effective strengths. Specimens with a corrosion degree of about 25% had an effective strength similar to specimens with lower corrosion degrees. Thus, care must be taken in interpreting the effective strengths for predicting the capabilities of structural elements degraded by corrosion.

Rheological characteristics are one of most important properties needed to be considered in the design and construction for the long-term stability and serviceability of underground structures in the rock mass. To date, although extensive studies on the rheological properties of rocks are available in the literature, most of the existing studies reported the strain-time data for the axial deformation through the compression rheological method and did not mention the lateral deformation, and mainly focused on the soft rocks at shallow depth. Thus, very limited attention has been paid to the rheological properties of deep and hard rock, neglecting the effects of structural anisotropy on the rheological properties. This paper presents a comprehensive, in-depth study of the rheological behaviors of super-deep hard rock, considering the effects of structural anisotropy by using the uniaxial and biaxial creep tests. The results revealed that significant creep behavior can be observed in the hard rock specimens under high stress in the in situ conditions, and the strain-time behavior of hard rock exhibited brittle failure. The strain-time curves of hard rock exhibited two obvious phases of instantaneous creep and steady-state creep, without the phase of accelerated creep. Moreover, it was observed that the rheological behaviors, including the instantaneous modulus, transient creep duration, axial and lateral creep deformations, steady-state creep rate, volumetric strain, and contraction ratio are strongly affected by the structural anisotropy. Based on the experimental data, empirical models of the parameters governing creep behavior have been established.

This paper presents the results of an experimental study of the effects of clay mixtures on the mechanical properties of mixed clays with controlled levels of plasticity, prior to the firing of porous ceramic water filters for water filtration. Two clays with well-characterized initial compositions (Iro and Ewuya clays) are mixed with varying proportions to control their plasticity. The mechanical properties of the mixed and fired clays are then studied using a combination of experiments and theoretical models. These include the flexural strength, fracture toughness, Young’s modulus, and thermal shock resistance of fired clay mixtures. The results show that clay mixtures with 45–60 vol.% of Iro clay and 40–55 vol.% Ewuya clay can be used to produce clay composite filters with robust mechanical properties. The thermal shock resistance of a mixed clay filter (containing 50% Iro clay and 50% Ewuya clay) is also explained using a combination of elastic and viscoelastic crack-bridging models. The regimes for effective viscoelastic crack bridging are identified by comparing the relaxation times to the thermal shock durations. The implications of the results are then discussed for the mixing of locally available clays into robust micro- and nanoporous materials for applications in clay ceramic water filters.

There is a growing need to use the waste materials in the construction of transportation routes because of lack of good quality aggregates on one hand and concerns regarding disposal of huge quantity of waste materials on the other. In this study, engineering properties of steel slag-fly ash-dolime (SFD) mixes were investigated for their effective utilization as base course material in flexible pavements. The effects of fly ash and dolime percentages and the curing age on the resilient modulus and permanent strain of SFD mixes were investigated. The performance of various stress-dependent models for the prediction of resilient modulus was compared, and the model constants of SFD mixes for a three parameter model were presented. A mix of 75% steel slag, 25% fly ash, and 15% dolime was obtained as the optimum mix. The optimum SFD mix with a 28 day curing period exhibited 60% higher resilient modulus and 83% lower permanent strain than the conventional Wet Mix Macadam (WMM). Volumetric swelling of the optimum mix was found to be within the acceptable limits. Observed test results were explained through a microlevel study using X-ray diffraction (XRD) and scanning electron microscope (SEM) tests. Finite element analyses were performed for a flexible pavement system with five layers, and the service life of the pavement with SFD mix as the base material was found to be approximately fifty percent higher compared to that of the pavement with WMM base layer.

The use of self-consolidating concrete (SCC) gained wide acceptance in the construction industry. The main objective of this paper is to classify the performance of freshly mixed SCC including stability, formwork pressure, and multilayer casting according to its thixotropic level ($A_{\text{Thix}}$); this would facilitate prediction of casting and precasting results at the construction site. Test results showed that low thixotropic mixtures having $A_{\text{Thix}}$ less than $0.2\mathrm{Pa}/\mathrm{s}$ are not recommended for construction works given the reduced stability associated with high bleeding and sedimentation rates. In contrast, high thixotropic mixtures with $A_{\text{Thix}}$ larger than $0.75\mathrm{Pa}/\mathrm{s}$ are very stable, and particularly adapted for casting vertical elements given the reduced formwork pressure. Yet those later mixtures are very sensitive to delays or stoppages between successive concrete lifts, resulting in reduced interfacial bond strengths. The moderate thixotropic mixtures having $A_{\text{Thix}}$ between 0.2 and $0.75\mathrm{Pa}/\mathrm{s}$ showed adequate performance regarding multilayer casting in horizontal elements.

Cold-mix asphalt (CMA) is routinely used for temporary or emergency pothole repair to prevent further deterioration of the asphalt pavement until resurfacing can be performed. One of the difficulties encountered with CMA is that the majority of laboratory evaluations and tests were originally designed for hot-mix asphalt. There exists an incomplete understanding between viscosity gain of cold-mix binder (CMB) and strength development of CMA. The objective was to develop effective test procedures to assess the engineering properties and performance of the CMA. Results showed that the accelerated curing process with 110°C for 24 h has the potential for predicting the engineering properties of the CMAs at mature state. The stability and rutting resistance of the CMAs with high CMB viscosity appear to be comparable with those of hot-mix asphalt. The CMB viscosity of $13\mathrm{Pa}·\mathrm{s}$ (130 poise) was suggested to specify the engineering properties and performance of the CMAs. In addition, simplified wheel track testing could be useful to simulate the detrimental influence of moisture on the performance of the CMAs in the field pothole. In this study, as the workability was within the specification range, a dense-graded mix with a fast curing rate at full compaction was desired for use as a good asphalt patching material.

The purpose of this paper is to investigate the diffusivity of the interfacial transition zone (ITZ) experimentally using cementitious composite materials made of rod-shaped aggregates and cement mortar. Two types of tests were conducted: the porosity distribution of the ITZ at different distances from aggregate surface was measured by backscattered electron images, and the water vapor diffusivity of the composites was measured by the penetration rate of water vapor through thin slides of specimens. The surface roughness of rod-shaped aggregates was considered as a testing parameter. The diffusivity of ITZ was calculated based on the measured diffusivities of the composite and it was also modeled according to the measured porosity distribution within the ITZ. The results showed that the porosity of ITZ decreases with increasing distance from the aggregate surface, a rougher aggregate surface decreases the porosity of ITZ in the first 10 μm from the aggregate surface, and the ratio of averaged water vapor diffusivity of ITZ to the diffusivity of bulk cement paste is approximately 60, which agreed with the test results quite well.

Two earthquakes occurred on October 23 and November 9, 2011, in Van, Turkey, with magnitudes ($M_w$) of 7.2 and 5.6, respectively. The types of the damage and collapse that occurred in both earthquakes necessitate a detailed examination of the load-bearing elements, which essentially comprise the components of RC buildings, in terms of their material quality. For this purpose, the compressive strengths, X-ray diffraction (XRD), and scanning electron microscopy with X-ray microanalysis (SEM/EDS) were performed on concrete samples collected from the collapsed buildings, with a view to understand the role of the materials in the devastation caused by the earthquakes. Visual observations and the results of the tests showed that there were not only construction and manufacturing failures, but also the strength of the concrete was a crucial factor that contributed to the damage and collapse of the buildings. In addition to these conclusions, results obtained from XRD and SEM-EDS showed that compressive strength increased with the size of calcium-silicate-hydrate (C-S-H) peaks, but much less significantly with the Ca-Si (C/S) ratio.

This paper presents the results of an extensive experimental program undertaken to optimize compressive strength, ultrasonic pulse velocity (UPV), and abrasion wear of heated high-performance concrete using Taguhi method and the utility concept. The design of experiments (DOEs) was first carried out by Taguchi method using a standard L $25(3^5)$ orthogonal array of three factors with five materials parameters levels. The factors considered in this context of HPC were: fiber volume fracture, age time, and postheat temperature. The prism specimens $60\times 60\times 300\mathrm{mm}$ with various volume fractions were casted, left for different age times (7, 28, and 56 day), then heated up to 200, 400, and 800°C for a time of 3 h; they were subsequently tested in the cooled conditions. Based on the experimental results, the materials parameter responses were analyzed and the level of importance of the input parameters on the measurement values was determined using ANOVA method. The results show that the mix parameters change their influence on the residual properties of high-performance concrete (HPC) with the change in temperature of exposure.

Different polycarboxylate (PC) superplasticizers have been successfully synthesized by varying side-chain density as well as sequence structure through free radical polymerization and reversible addition-fragmentation chain transfer polymerization (RAFT), respectively. Characteristic connections between molecular structure and early age properties of cement paste have been systematically evaluated by various methods, such as adsorption, flowability, calorimetric measurements, amount of hydration product, and dissolution of cement grains. The results show that block PC adsorbs faster with a larger adsorption amount onto cement particle surfaces than random PC, thereby having a better initial flowability and faster loss of workability. Moreover, the dormant period of cement paste with block PC could be effectively shortened by 3 h with block PC as well as the onset of the acceleratory period could be promoted. The results from X-ray diffraction (XRD)-Rietveld refinement show that block PC promotes both ${\mathrm{C}}_3\mathrm{A}$ and ${\mathrm{C}}_3\mathrm{S}$ reaction than that of random PC. In addition, a larger number of clusters of C-S-H is formed on the cement particle surfaces at the very early age with block PC and then C-S-H clusters developed a continuous structure with prolonged time, which may increase the early strength of cement paste. Furthermore, the dissolution rate of cement minerals is drastically faster with block PC compared with random PC. All these findings are helpful not only for understanding the relationship of the molecular structure of PC and the early age properties of cement paste, but also further designing the optimum molecular structure of PC to meet the requirement of continuous materials with early strength.

Ultrahigh-performance concrete (UHPC) offers a superior alternative to normal-strength concrete (NSC) due to its significantly higher compressive and tensile strengths, improved ductility, and enhanced durability. This paper presents an experimental study of the stress-strain behavior of UHPC confined by conventional transverse steel reinforcement. Test results are compared with two confinement models, as well as a large amount of available data on steel-confined NSC and high-strength concrete (HSC), and limited data available for UHPC confined by fiber-reinforced polymers (FRP). The study shows a potential threshold of confinement ratio beyond which the confinement effectiveness of UHPC exceeds that of HSC and nears that of NSC. This may have implications on the minimum level of confinement reinforcement for UHPC. For the most part, steel reinforcement is more effective than FRP as the confining device for UHPC, except for the very high end of confinement ratios, where FRP may become more effective. For the same confinement ratio, steel-confined UHPC has a larger ultimate strain than FRP-confined UHPC. Of the two types of FRP, glass leads to a higher ultimate strain than carbon, primarily due to its lower elastic modulus, and hence higher deformability. Additional research on larger-scale columns can help develop requirements for confinement reinforcement of UHPC.

Based on loading and failure analyses, a brittle-ductile transition index $I_T$ is derived for ball indentation, ball impingement, and liquid drop impact: $I_T=K_{Ic}^n/{\sigma }_C^{2n/3}$. Materials with low index numbers respond brittle (elastic), whereas materials with high index numbers respond ductile (plastic). For $n=2$, the index has a linear relationship to a critical indenter (particle, drop) radius, which determines whether materials respond elastically or plastically. The index is inversely related to the ratio between critical plastic load and critical elastic load. The numbers for n depend on the loading situation: ball indentation, $n=6/3$; ball impingement, $n=5/3$; liquid drop impact, $n=2/3$. Experimental results are analyzed to verify the index. Additional transition situations are analyzed and linked to the transition index.

Because of a lack of existing studies of fatigue testing of interlaminar anticracking materials, this study analyzes the principle of generating reflective cracks using three types of composite specimens: a direct overlay asphalt mixture layer, a repaving-impregnated nonwoven geotextile layer, and a repaving anticracking material layer. The study proposes a method for laboratory fatigue testing and observing reflective cracks. The specimens were used in a bending fatigue test with a centric load and a shear fatigue test with an eccentric load. The test results were analyzed by regression analyses that showed that the anticracking material layer had much better crack resistance than the direct overlay asphalt mixture layer and the repaving-impregnated nonwoven geotextiles layer, because the anticracking material layer could absorb most of bending and shear stresses near the cracks to efficiently delay the generation and expansion of reflective cracks. This study can be used as a reference to make a reasonable selection of an interlaminar anticracking material for rigid-flexible composite pavements.