Journal of Materials in Civil Engineering

There is a recent trend of using a higher content of reclaimed asphalt pavement (RAP) in asphalt pavement construction. When evaluating the properties of mixed RAP and virgin binder and selecting a base binder to be mixed with a high-RAP mix using a blending chart, the effect of partial blending is sometimes neglected and total blending is assumed. Such an assumption, however, has been found unreasonable. Based on an experimental gap-graded method, this paper studies blending effectiveness in RAP-binder and virgin-binder systems using both rutting and fatigue parameters and quantified the degree of blending using blending ratios. Furthermore, the blending ratios were applied to predict the properties of the blended RAP and virgin binder as well as to develop a modified blending chart for estimating the performance grade (PG) of the virgin binder when a higher RAP content was used. Results confirmed that partial blending does exist during the blending process. Blending ratios were found to be a function of RAP content, but not sensitive to the specific rutting and fatigue parameters evaluated. For higher RAP content, a modified blending chart is recommended to take partial blending into account. It was also found that the usage of a recycling agent could improve the properties and blending effectiveness of high-RAP binders in terms of both rutting and fatigue properties.

Alkali activated slag (AAS) concrete can be considered as a more environmentally friendly alternative to conventional concrete. The presence of cracks in the concrete matrix can have major impacts on its mechanical properties and permeability, and thereby on its durability. This study investigates the effect of adding polypropylene (PP) fiber to alkali activated slag concrete on its compressive, flexural, and tensile strengths and also short-term and total water absorption, water impermeability, chloride permeability, and carbonation depth. In addition, changes made by PP fiber to the microstructure of AAS concrete are studied through scanning electron microscopy (SEM). The results show that the optimal quantity of PP fiber to improve the mechanical and permeability properties of AAS concrete is 0.24% by volume. However, addition of PP fiber increases water absorption and decreases chloride penetration resistance of AAS concrete.

Developing new sustainable materials such as bioasphalt has become a research trend in recent years. In this study, bioasphalt modified with the addition of styrene-butadiene-styrene (SBS) was investigated to research whether it can replace petroleum asphalt binder of 50 penetration grade (50#) in road performance at a lower price. A series of laboratory tests were carried out to evaluate the performance of SBS-modified bioasphalt binders and mixtures, including penetration, softening point, ductility, rutting, moisture susceptibility, and low-temperature cracking. The SBS-modified bioasphalt was prepared with different of bio-oil content: 0, 5, 10, 15, and 20%. Moreover, a comprehensive evaluation was applied to all types of asphalt and a recommended selection of asphalts was provided. The research showed that the performance of SBS-modified bioasphalt could satisfy the specification requirements of 50# base binder when bio-oil concentration was less than 15%. The high-temperature stability of SBS bioasphalt mixture was worse than that of the 50# base binder mixture to some degree, but could still satisfy the specification requirements. The SBS-modified bioasphalt mixture had better thermal crack resistance and water stability than the 50# base binder mixture, and it had better adhesion at low temperatures, reaching its maximum adhesion value with an aggregate loss of 4.33% when the bio-oil content was 10%. The SBS-modified bioasphalt with 10% bio-oil (S110) is thus recommended according to the performance evaluation and cost analysis. Furthermore, from the standpoint of environmental protection and economic benefits, S110 has good development prospects.

In addition to the dynamic moduli, the damping properties of the different pavement layers are required by most algorithms used for modeling the dynamic responses of pavement caused by moving or impact loads. The importance of the damping properties in estimating the proper responses is well documented in the geotechnical engineering community. The dynamic moduli are typically estimated in the laboratory using the cyclic triaxial (resilient modulus) tests. The feasibility of estimating the damping properties with resilient modulus tests is explored in this paper. The most promising algorithm among the alternatives studied was preliminarily established from the resilient modulus tests carried out on 17 gravel bases, sandy subgrades, and clayey subgrades. The selected method was used to develop a database for further evaluation. The damping coefficient was correlated to the applied stresses, the measured strains, and the nonlinear stiffness parameters ($k_1$–$k_3$) obtained from a nonlinear constitutive model commonly used in mechanistic-empirical pavement analysis methodology.

This study developed computational models for virtually generating three-dimensional (3D) random asphalt mixture microstructure (3D RAMM) using a Voronoi diagram, and analyzed the thermal conductivity of heterogeneous microstructure. The mixture was simulated as a three-phase composite material including fine aggregate matrix (FAM), coarse aggregate, and air void. The 3D RAMM was generated considering different morphological characteristics (size distribution, sphericity, orientation) of the dispersed phases (coarse aggregate and air void) using virtual sieve analysis and an innovative shrinking algorithm. Finite-element (FE) modeling of the steady heat transfer process was used to calculate the effective thermal conductivity of an asphalt mixture. The thermal simulation results were validated with experiment data reported in the literature. The results show that the heat flux in the asphalt mixture is not uniformly distributed. The sphericity and the orientation angle of the dispersed phase have a combined effect on the effective thermal conductivity of asphalt mixture. The developed computational model provides an effective way to analyze the microstructure effect on the bulk properties of composite materials.

The main objective of this study was to evaluate calcium nitrate tetrahydrate as a healing agent and its efficiency in concrete materials. This investigation focused on improving the mechanical properties of microcapsule-containing concrete by both altering the microencapsulation procedure and modifying the concrete mix design. Results showed that both the introduction of the newly developed microcapsules and a defoamer in the mix design were key in minimizing the air content of microcapsule-containing concrete, and thus resulted in improved mechanical properties comparable to the control groups. The differences in the virgin modulus of elasticity values between the control groups and the microcapsule-containing specimens were minimal. However, microcapsule-containing specimens at the lowest concentrations were significantly less affected by damage cycles than the control specimen groups. In addition, several microcapsule-containing specimens showed significant healing potential with respect to compressive strengths and modulus of elasticity after damage, surpassing the control specimens. Based on these results, the optimum microcapsule concentration lies between 0.25 and 0.50% by weight of cement for axial compressive loads.

This study investigates the performance and microstructural development of reactive MgO and calcined dolomite-based concrete samples subjected to carbonation curing for up to 28 days. The performance of each sample is assessed via compressive strength testing, which is linked with the hydration and carbonation mechanisms studied via isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis with differential scanning calorimetry (TGA/DSC), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX). Strength gain depends on the carbonation degree and morphology of carbonate phases such as hydromagnesite and nesquehonite, whose formation is controlled by the binder composition and initial porosity of each sample. Higher contents of MgO enable early strength gain, whereas the presence of undecomposed carbonate phases in dolomite facilitates the continuation of the hydration and carbonation reactions by providing additional nucleation sites and contributing to the formation of a dense carbonate network. Continuous strength gain is achieved by the extensive formation of a carbonate network. Simultaneous use of MgO and dolomite enables 28-day strengths as high as 57 MPa, which are up to 60% higher than that of the control samples containing only MgO or dolomite.

Concrete spalling has been widely accepted as being caused by a thermomechanical process resulting from high thermal gradients, as well as a moisture-clog process attributable to the buildup of pore-water pressure. The effect of aggregate size on the influence of concrete spalling of tilt-up wall panels after exposure to a hydrocarbon fire is studied in this paper. Six reinforced high-strength concrete wall panels $\mathrm{3,360}\times \mathrm{3,880}\times 200\mathrm{mm}$ in dimension, loaded by self-weight only and consisting of 7-, 14-, and 20-mm aggregate sizes were exposed to the hydrocarbon fire curve for a period of 120 min. The specimens were approximately 70 MPa at the test date and were instrumented with in situ thermocouples to predict steam pressures based on thermal diffusivity calculations. The degree of spalling was quantified by mass loss with both solid mass and water mass being independently calculated. The concept of nominal spalling depth was introduced as a new way of quantifying the degree of spalling. The results show that aggregate size is an influencing parameter in regard to concrete spalling, with the degree of spalling ranging from 13 to 33%, respectively. Spalling is more prominent for smaller-size aggregates because of the facture-zone process.

The present study evaluates the suitability of several types of biomass bottom ashes [wood bottom ash (WBA), pine-olive pruning bottom ash (POPBA), olive stone bottom ash (OSBA), and olive pomace bottom ash (OPBA)] as an alternative source to replace ceramic raw material in the production of clay bricks. The clay and biomass bottom ash were characterized by means of X-ray diffraction (XRD) (crystallinity), X-ray fluorescence spectroscopy (XRF) (chemical composition), carbon, nitrogen, hydrogen, and sulphur (CNHS) (elemental chemical analysis), and particle-size distribution. The specimens were manufactured by mixing clay and 20 by weight (wt%) of biomass bottom ash, subsequently compacted and fired at 1,000°C. The fired samples were characterized to determine their technological properties. The results indicate that brick formulations containing biomass bottom ash decreased the bulk density of the control bricks. At the same time, they have suitable mechanical behavior. In addition, thermal properties of clay-biomass bottom ash are manifestly better than those of the clay control bricks. The heavy-metal concentration in the leaching test of the bottom ash-clay bricks establishes that the bricks do not present environmental problems.

This study presents a useful analytical method based on a statistical approach for optimizing the performance of Eco-self-consolidating cement mixture (SCCM) (mortar component). Eco-SCCM is a new class of concrete mixtures that satisfies engineering design requirements (mechanical and rheological properties) and environmental concerns. Three different phases with a total of 43 mixtures were generated using commercially available software to study the effect of using high-volume fly ash on the performance of cement mixtures. Hydrated lime was added as the third component to increase the hydration activity of fly ash. Two different curing regimes were investigated. Fresh properties were measured, and hardened properties such as compressive strength, drying shrinkage, and surface resistivity were also monitored. The results of the phases were compared to track the effect of supplemental levels of fly ash and hydrated lime. To optimize the performance of Eco-SCCM, the desirability function approach was successfully applied. Results showed that mixtures with 37% portland cement Type I/II and 63% fly ash under a moist curing regime yielded the highest performance level.

The main objectives of this research are to investigate the effect of hydrated lime (HL) treatment on the swelling behavior of a natural expansive soil, Eagle Ford clay from Texas, through centrifuge testing. So far, no studies have been performed using the centrifuge to analyze the swelling reduction in expansive soils by stabilization treatments. Also, no studies have measured the improvement of lime treatment efficiency due to variables controlled during preparation of lime-soil mixtures, such as compaction moisture content, compaction dry density, and the applied effective stress. From the analysis of the swelling versus time curves, three values were defined to examine the swelling behavior: the swelling potential (Sp), the primary swelling slope (PSS), and the secondary swelling slope (SSS). Assessment of the lime treatment efficiency, as quantified by the swelling potential reduction ratio (SPR) indicates that lime dosage requirements can be decreased by increasing the compaction moisture content and/or reducing the compaction dry density. Also the hydrated lime dosage needed to prevent swelling depends on the applied g-level (i.e., applied stress).

The dynamic modulus of an asphalt mixture plays a crucial role in pavement design and performance prediction of asphalt pavement. Among many predictive models, the semiempirical Hirsch model is one of the most popularly used dynamic modulus prediction models. However, the current Hirsch model uses several model constants that were determined based on a number of assumptions and simplifications for conventional asphalt mixtures. Considering the trend of using new types of asphalt mixtures and the potential application of the modulus properties in fundamental pavement performance analysis, those constants may not be appropriate any longer. This paper aims to modify the current Hirsch model by generalizing the model parameters based on the rule of mixtures and the theory of elasticity and viscoelasticity. Twenty-six asphalt mixtures, which contain different percentages of reclaimed asphalt pavement (RAP), sourced from China and the United States were used in this study to evaluate the predictive quality of the modified Hirsch model compared with other models. The modified Hirsch model produced the best predictive quality among three models. In addition, the modified model was suitable for predicting the dynamic modulus of high RAP mixtures. Future work was recommended to validate the proposed model using a larger database.

The hydraulic diffusivity and sorptivity of cement-based materials are commonly regarded as two important properties to characterize the durability potential of building structures, especially when they are subjected to sustained loading. This paper presents an empirical analytical approach developed to theoretically estimate the hydraulic diffusivity of concrete from easily measured sorptivity under compressive loading. On the basis of unsaturated-flow theory (UFT), a general empirical estimation model for hydraulic diffusivity $D(\theta )$ of unsaturated concrete under sustained compressive loading is developed with the water-retention curve (WRC) and saturated permeability. By introducing the Boltzmann variable, $\varphi =x{t}^{-1/2}$, the extended analytical method is applied to establish the relationship between hydraulic diffusivity and sorptivity under various compressive stress levels. An improved test apparatus was designed for real-time measuring the amount of water absorbed by hollow cylindrical concrete specimens under sustained axial loading. Compared with the traditional gravimetric method, this new apparatus can realize the combination of water movement and uniaxial loading action. By fitting the experimental results of cumulative water content versus square root of time ($i-t^{1/2}$), the quantitative relationship between sorptivity and compressive stress level was obtained, which was then used to validate the proposed theoretical estimation model. Finally, it indicates that the empirical estimation approach could be used for refined modeling and simulating of the coupling issues between loading and environment.

The asphalt paving industry has been increasing the use of recycled asphalt pavement (RAP). There is a concern about the percentage of aged asphalt binder in the RAP that can actually be blended into the virgin binder and thus become available to coat the aggregate. In this study, a laboratory procedure was proposed for quantifying the mobilization rate of the aged binder using fluorescence microscopy. A new parameter, the mean gray value (MGV), was derived from the fluorescence image and used to differentiate between the recycled and virgin binders as well as their blends. A blending chart was generated according to the MGV for the virgin-aged asphalt blends containing 0–100% RAP binder and was used as a baseline for the quantification. A linear relationship was found between the MGV and the RAP binder content. A laboratory experiment was conducted to validate the proposed method. Glass cullet was added as a special type of aggregate so that it could be retrieved after mixing and tested by fluorescence microscopy. The results showed that the mobilization rate of the RAP binder from the fluorescent method was improved with an extended mixing time and an elevated temperature.

A building material is mainly characterized by its mechanical performance, which provides proof of its quality. However, the measurement of the compressive or flexural strength of an earth-based material with plant aggregates, which is very ductile, is not fully standardized. The objective of this study is to determine the compressive and flexural strengths of a composite made of earth and 0, 3, or 6% of barley straw, hemp shiv, or corn cob. Given the manufacturing processes available, cylindrical compressed specimens were studied in compression, whereas extruded specimens were studied in flexion. Two protocols were tested for compressive strength measurements: one with direct contact between the specimen and the press and the other with reduced friction. The test with reduced friction engendered a huge decrease of the stress and a slight decrease of the strain. For both compressive and flexural strengths, the specimens made of earth alone were the most resistant, followed by composites containing straw. The influence of two different treatments applied to the straw is also discussed.

Unbonded posttension strands are used between anchorages to provide restoring forces to self-centering structures. In this research, monotonic and quasi-static cyclic tests were performed on strand-anchorage assemblies to understand their mechanical properties and prestress loss. The experimental program included 12.7-, 15.2-, 17.8-mm (0.5-, 0.6-, and 0.7-in.)–diameter, 7-wire, 1,860-MPa (270-ksi) low-relaxation strands between anchorages. Strand stress-strain relationship and wedge seating were measured. Anchorages caused stress concentration for all sizes. The stress-strain relationship given by design guidelines was revised to incorporate the degradation of mechanical properties due to anchorages. Wedge seating, which was linearly related to posttension force in the monotonic and cyclic tests, was considered in a proposed strand force-displacement relationship. A method to predict loss caused by wedge seating and inelasticity was proposed. The predictions were evaluated using results of large-scale precast concrete bridge pier tests under quasi-static and dynamic loading. The proposed force-displacement relationship predicted the elastic response better than design guidelines, but underestimated the capacity. The proposed loss method accurately predicted strand response under quasi-static loading, but overestimated the strand response under dynamic loading.

This study investigates the effect of multiwalled carbon nanotubes (MWCNTs) on the shrinkage and expansion caused by sodium sulfate attack in repair mortars; repair mortar behavior in the fresh state and the compressive strength are also measured. Three repair mortars are studied: 0.0% MWCNTs (reference), mortar from two different manufacturers. Shrinkage and sulfate attacks are evaluated according to current standards. The carbon nanotube increases the compressive strength by approximately 19.5% and decreases the fluidity. Shrinkage occurs more intensely in MWCNT-embedded mortars, although results show similar behavior between the two types of MWCNTs. The MWCNTs increase the expansion due to attack by sodium sulfate, indicating that this material may be harmful when the cementitious composite is in contact with these aggressive agents (sodium sulfate).

The use of low-calcium Class F fly ash both as a replacement material for cement and to produce geopolymers has become established practice. However, much of the fly ash produced globally is either high-calcium Class C or brown coal (BC) fly ash, whose use as a cement replacement or geopolymeric material is very limited. This study reports the results of using BC fly ash from three separate sources to assess the feasibility of geopolymer concrete manufacturing and factors affecting the compressive strength of the geopolymeric material produced. The effects of the chemical composition of the raw fly ash, alkali modulus of the activator, and mineralogical properties of the raw material are reported. The results show that the manufacture of geopolymer mortar from BC fly ash was feasible, with compressive strengths of up to 50 MPa obtained. The key factors in selecting BC fly ash and determining its geopolymer compressive strength were the combined aluminate-silicate content of raw material, reactive amorphous content, and zeta potential. The data also emphasize the need for careful consideration of the modification of the activator modulus when designing a specific geopolymer mix.

In the literature, all the micromechanical fracture models used for predicting structural steel tensile responses and fracture are based on the ductile fracture mechanism that uses the Lode angle parameter to simulate shear fracture under low-stress triaxiality. Using the phenomenological shear fracture model that uses the shear stress ratio rather than the Lode angle parameter, this technical note presents the finite element predictions of the responses of S690 steel solid and perforated coupons under tension and of the fractures of TRIP (transformation-induced plasticity) 690 steel specimens under pure shear and combined shear and tension. The calibrated phenomenological shear fracture model parameters are obtained through a phenomenological curve-fitting process that does not involve costly laboratory tests. This technical note demonstrates that the phenomenological shear fracture model can accurately predict the responses and fracture of structural steels under tension, pure shear, and combined shear and tension.