Journal of Materials in Civil Engineering

In quantifying the morphological features of aggregate, X-ray computed tomography (CT) is one of the most popularly used approaches for capturing aggregate images that is considered accurate and reliable. In this study, however, a three-dimensional (3D) optical scanner was also employed to characterize aggregate morphology in addition to X-ray CT. The major objective is to validate the accuracy of the optical scanner–based image analysis method through a comparative study of the optical scanning and X-ray CT results. Four types of aggregate particles were selected, and their aggregate images were obtained through those two methods. Second, the scanned aggregate images were saved in STereoLithography (STL) files and analyzed. Then the differences in the morphological features of aggregate obtained from these two methods were quantified and evaluated. Through this study, it was found that even though there were relatively large differences in special aggregate particles (flat or elongated aggregates), the 3D optical scanner was comparable with the X-ray CT in the overall quality of the morphological characteristics of aggregate. Furthermore, differences between the two scanning technologies are dependent on particle shape and surface features. Aggregate particles with sharp angles or rich surface features may induce larger differences.

Ultrahigh-toughness cementitious composite (UHTCC) is a new type of cementitious material that is suitable for durability repair of deteriorated concrete structures. One of the key issues in this repair technology is the behavior of interfacial bonds. In this study, the bond properties between the UHTCC and the old concrete were evaluated by conducting four-point bending tests. The UHTCC was prepared using two methods: cast-in-situ and prefabrication. The test parameters include the roughness of the concrete substrate, roughness of the prefabricated UHTCC, strength of the old concrete, primer, and bonding agent. Two-way analysis of variance was used to analyze the effect of these test parameters on the bond strength. Moreover, two regression formulae were proposed to predict the flexural bond strength of the composite beams. The results showed that the flexural bond strength of the repair system tended to increase with the increase in the roughness values of the concrete substrate and prefabricated UHTCC and strength of the old concrete. However, a very high roughness could damage the interfacial zone; hence, the roughness should be controlled in a particular range. The results also revealed that suitable primers and bonding agents, e.g., polymer-modified material and fly ash–silica fume-modified material, could improve the bond strength of the interface. Moreover, double-layer bonding configurations were found to exist in the prefabricated repair system. The flexural bond strength depends on the weaker bonding plane, and the interface control needs to be considered during the design and construction. In particular, two-way analysis of variance was proven a reliable tool in evaluating the experimental results. The predicted flexural bond strength was in good agreement with the experimental value.

Waste plastic is harmful and affects the environmental cycle. This paper proposes the use of fiber extracted from refrigerator door panels (FERD) and waste plastic in bituminous mixes for road construction. The effect of modification of bituminous mixes like stone matrix asphalt (SMA) and asphalt concrete (AC) with FERD and processed waste plastic in granular form was studied. The FERD was used to modify the SMA and AC, whereas waste plastic was used to modify AC. Different mixes of SMA and AC were prepared with and without filler material. Furthermore, the study was done with varying lengths of fibers (2, 4, 6, and 8 mm), which were added to the SMA and AC mixtures. Asphalt concrete mixtures with 0, 4, 6, 8, 10, and 12% waste plastic by weight of bitumen were prepared. The effect of the preceding on drain down, Marshall stability, and indirect tensile strength was promising.

Steel furnace slag (SFS) and coal wash (CW) are two common by-products from the coal-mining and steel industries in Australia. Rubber crumbs (RC) is a material derived from waste tires contributing to environmental problems in most developed countries. Reusing and recycling these waste materials is not only economically beneficial and environmentally sustainable, but it also helps to address geotechnical problems such as track degradation. In this study, SFS, CW, and RC are blended to explore the feasibility of obtaining an energy-absorbing capping layer with properties similar or superior to conventional subballast. Comprehensive laboratory investigations have been carried out to study the geotechnical properties of $\mathrm{SFS}+\mathrm{CW}+\mathrm{RC}$ mixtures, from which seven parameters (including gradation, permeability, peak friction angle, breakage index, swell pressure, strain energy density, and axial strain under cyclic loading) were used to evaluate the properties of these mixtures used as subballast. It was found that a mixture with $\mathrm{SFS}:\mathrm{CW}=7:3$ and 10% RC (63% SFS, 27% CW, and 10% RC) is the best mixture for subballast.

The demand for stable and high-quality granular materials for the construction of flexible granular pavements is constantly increasing due to population growth and the ever-expanding urbanization of the planet. Thus, the function of material stabilization to improve the quality and enable the use of available low-quality granular materials is becoming increasingly important. Traditionally, cement-based additives have been used for such stabilization. However, alternate additives such as polymers have recently been shown to also enhance strength and stiffness characteristics. Furthermore, as an added benefit, the use of polymer-based additives results in a far lower carbon footprint than cement-based additives. In the study reported herein, an extensive laboratory investigation was carried out to evaluate the use of polymeric stabilization to improve engineering properties of pavement materials. The engineering properties of three types of soils were evaluated after being treated with a polyacrylamide (PAM). Strength and stiffness properties were determined by conducting unconfined compressive strength (UCS) and repeated load triaxial (RLT) tests. The experimental program showed that the addition of PAM consistently enhanced the strength properties of all tested soils. The PAM-treated samples also showed improvements in the resilient moduli when compared to samples treated with traditional additives of lime and cement. Furthermore, multiple regression models were developed and the resulting three-parameter model revealed an excellent fit to actual resilient moduli. Finally, resilient modulus values were used to analyze the structural coefficient of a granular subbase layer and the results confirmed the improvements in structural capacity of all treated samples.

In this paper, the impact of curing parameters such as precuring time, curing time, and temperature on compressive strength of mortar with phosphorous-slag cement activated with two different compound activators including $\mathrm{NaOH}+{\mathrm{Na}}_2{\mathrm{CO}}_3$ and ${\mathrm{Na}}_2{\mathrm{CO}}_3+\mathrm{Ca}(\mathrm{OH}{)}_2$, as well as the microstructure morphology of the hardened mortars, are studied. Furthermore, variance analysis is used to evaluate the effectiveness of each curing parameter. The results show that application of such a combined low-temperature and high-temperature curing regime can effectively improve the quality of the transition zone (porosity and bonding of the cement matrix to aggregate), in addition to the development of more polymeric structures (silicates of $Q^3$-structures) in hydration products. These improvements together result in a threefold increase in the compressive strength compared with environmental curing conditions.

The present research work was undertaken to evaluate the rutting performance of carbon nanotube (CNT)–modified asphalt binders. Additionally, intermediate-temperature performance, aging resistivity potential, and high-temperature storage stability were also evaluated. Reported literature on rutting performance of CNT-modified asphalt binders is mainly based on the Superpave rutting parameter ($G^{*}/\sin \delta$), which does not account for the recovery aspect of binder. The paper first highlights the importance of the elastic response of CNT-modified asphalt binders for better understanding about its rutting performance. Further, different approaches such as the evaluation of zero shear viscosity (ZSV), creep test, and multiple stress creep recovery (MSCR) were utilized to reach appropriate conclusions. A recently developed approach, linear amplitude sweep (LAS), was used for evaluating intermediate-temperature performance. The CNT was varied as 0, 0.4, 0.75, 1.5, and 2.25% by the weight of control binder. The $G^{*}/\sin \delta$ value was found to increase until 1.5% CNT content; however, the addition of 2.25% CNT resulted in decreased $G^{*}/\sin \delta$, indicating reduced rutting performance at higher CNT content. Contrary to the $G^{*}/\sin \delta$ trend, significant improvement in recovery value was observed for all CNT percentages. Further, based on detailed analysis carried out for different rheological parameters such as ZSV value (evaluated using the steady shear approach), deformation resistivity potential from creep test, recovery (R), and nonrecoverable creep compliance ($J_{nr}$) from the MSCR test, CNT addition to the control binder showed significant improvement in rutting resistivity potential for all CNT percentages. Although ZSV value significantly improved with the addition of CNT, the increase in CNT content showed an early transition from Newtonian to non-Newtonian behavior. Further, analysis for stress sensitivity was carried based on the R and $J_{nr}$ values obtained from the MSCR test, which showed an increase in stress sensitivity with the addition of CNT to the control binder. The need for improvement in the current protocol used for evaluating stress sensitivity of asphalt binder (based on the MSCR test) has also been discussed. Improvement in intermediate-temperature performance evaluated through LAS test was also observed. Also, CNT addition to asphalt binder was found to be stable under high-temperature storage conditions. Overall, improvement in high- and intermediate-temperature performance can be expected with the addition of CNT to the control binder.

In this paper, the compressive stress-strain behavior of recycled aggregate concrete with different replacement levels of conventional fine aggregate by recycled particles obtained from used refractory bricks (0, 25, 50, 75, and 100% replacement level by volume) is investigated in two groups, one containing ordinary portland cement and the other containing calcium aluminate cement, after exposure to elevated temperatures (110, 200, 400, 600, 800, and 1,000°C). For this purpose, the parameters that affect the compressive behavior of recycled refractory brick aggregate concrete (RRBC), including compressive strength, strain at peak stress, modulus of elasticity, and toughness, as well as the shape of the stress-strain curve following exposure to elevated temperatures were evaluated and compared to those predicted by international codes. Finally, a stress-strain model to predict the compressive behavior of RRBC at elevated temperatures was proposed. The results indicate that a significant degradation occurs for most of the mechanical properties of the ordinary cement-containing concrete at 400°C and for the aluminate cement-containing concrete at 110°C. Furthermore, higher contents of refractory brick fine aggregate improve the concrete compressive behavior at higher temperatures.

Concrete is a composite material composed mainly of water, sand, aggregate, and cement. The characteristics of high attenuation of concrete for ultrasound degrade the performance of ultrasonic testing (UT), especially when the size of the target is much smaller than the aggregate. Thanks to recent improvements in electronic devices and computing technology, the total focusing method (TFM) and the phased array (PA) technique have been applied to facilitate UT for concrete. However, the question of which approach is better for the UT of concrete has not yet been addressed. Thus in this preliminary study, a synthetic PA image, which is similar to an image acquired by the PA system, and a synthetic TFM image, which is similar to an image acquired by the TFM system, were made for the UT of concrete. The qualities of these images were compared with those produced by the traditional B-scan and the synthetic aperture focusing technique (SAFT). Excluding the expense, difficulty, complexity, and efficiency of these techniques, the results of this study show modern (TFM and PA) techniques are always better than traditional (B-scan and SAFT) methods based on 100 kHz ultrasonic experiments with a low signal-to-noise ratio (SNR) condition. The SAFT method can only slightly improve the quality of the B-scan image. In addition, a moderate distance between the source and receiver is suggested for detecting shallow and small targets in concrete in order to avoid near-source backward scattering. However, the PA technique has superior performance in detecting a small target at a specific depth in concrete. On the other hand, while detecting a large target in concrete, the TFM shows better performance than the PA technique. Study results indicate both the PA and the TFM have their own merits and demerits. The PA shows good performance in the status of a low SNR environment, and the TFM works better in a high SNR situation. In conclusion, to detect a small target at a specific depth in concrete, the PA technique is recommended. Otherwise, to detect a large target in concrete, the TFM is a better choice.

The in-plane stiffness of timber diaphragms commonly found in vintage unreinforced masonry (URM) buildings is largely determined by the rigidity of the fastener connections. Currently in the literature, however, there is limited experimental data on the behavior of floorboard-to-joist connections, and consequently the aim of the present study was to supplement that knowledge. The existing data provided the paramount input parameters for the finite element modeling of timber diaphragms, in order to model and validate the results obtained from the experimental testing of full-scale timber diaphragms. The floorboard-to-joist connections were extracted from two vintage URM buildings and were tested using three different test setups to address various realistic loading configurations. In addition, the floorboard-to-joist connections were improved using new nails or new screws. Specimens comprising plywood or fire-rated gypsum-board panels connected to the salvaged floorboards or joists were also tested as a method for improving the overall diaphragm lateral behavior. The experimental study of timber diaphragm fastener connections consisted of 43 samples, of which the results are presented here.

The ability of Deurex natural sugar cane wax to reduce the blending and compaction temperatures of warm-mix asphalt renders it a promising technology in pavement construction to reduce ${\mathrm{CO}}_2$ emissions and save energy. This new warm-mix additive might revolutionize pavement construction and warm-mix asphalt production by introducing a new class of mixtures with excellent environmental performance. The goal of this study was to evaluate the feasibilities and benefits of the incorporation of Deurex into asphalt binders. Deurex was blended into asphalt at contents of 1, 3, 5, and 7%, and the following tests were performed: physical properties, performance grade, multiple stress creep recovery, frequency sweep, separation, differential scanning calorimetry (DSC), and Fourier transform infrared rheometer (FTIR). The test results showed that the increase in Deurex significantly reduces the viscosity of asphalt binders, implying that a decrease in the blending and compaction temperatures of asphalt mixtures can be achieved during pavement construction. In addition, the tests showed that the addition of Deurex increases complex modulus ($G^{*}$), rutting factor ($G^{*}/\sin \delta$), average percentage recovery, and phase angle, and reduces nonrecoverable creep compliance and phase angle. It is suggested that Deurex-modified binders are less subject to permanent deformation at high temperature. Moreover, DSC analyses showed that Deurex has little effect on asphalt thermal properties. Further, FTIR analyses showed that chemical reactions might happen during the mixing of Deurex and asphalt. Overall, the good performance of Deurex-modified asphalt showed its potential as a new additive in warm-mix asphalt manufacture.

Precise evaluation of the condition of RC bridge decks, particularly for corrosion-induced delaminations, is decisive for ensuring bridge performance and safety. Although infrared thermography (IRT) and ground penetrating radar (GPR) have considerably aided this task, cogent procedures for deciphering their data have yet to be developed. Postprocessing of IRT and GPR data still relies on user interpretation to construe quantitative appraisal of subsurface anomalies, where predefined threshold values are arbitrarily selected. Such a subjective analysis can produce inconsistent results. The present study proposes a robust procedure for analysing IRT and GPR test data and uniting their results. A mosaicked thermogram of the entire bridge deck from thermal images was created using custom-developed codes, whereas the numerical amplitude method was used to analyze GPR data. To identify objective thresholds, the k-means clustering function was used. Accordingly, condition maps of bridge decks delineating different severity levels of delamination and potential active corrosion could be generated. The analyzed IRT and GPR data were then integrated to develop an overall bridge-deck condition map. The proposed procedure was instigated to analyze thermal and radar data acquired from two full-scale RC bridge decks. It is shown that rationally integrating IRT and GPR results offers a superior tool for detecting subsurface anomalies in bridge decks. Thus, it could enhance bridge-deck inspection programs, allowing stakeholders to optimize budgets and prioritize maintenance, repair, and rehabilitation efforts.

This investigation introduces the formulation of a new closed-form representation of the evolution of the relative compressive strength of a class of ultrahigh-performance concrete (UHPC) materials hydrated under saturated and adiabatic conditions. The Laplace transformation of the governing differential equation for the maturity leads to an accurate estimation of the sample equivalent age at the reference temperature. The maturity allows the estimation of the relative strength attained by means of a simple, previously experimentally verified, linear hyperbolic model expressed in the frame of the reference temperature. The evolution of the relative strength at the reference temperature provides a universal frame for the description of that evolution in samples hydrating under saturated and adiabatic conditions but starting at different temperatures. All required model parameters are identified through virtual tests. Parametric studies on the relative compressive strength evolution and their comparison with other semiempirical models in the literature revealed that the saturated and adiabatic hydration of low water-to-binder ratio silica-fume UHPC follows a proper version of the law of mass action in chemistry.

To understand the long-term performance degradation of asphalt, ultraviolet (UV) photo-oxidation has been used to accelerate the aging process. Three types of asphalt binders extracted from reclaimed asphalt pavements (RAPs) and one extracted from fresh hot-mix asphalt (HMA) were aged under continuous UV exposure and UV/moisture/condensation exposure. After accelerated aging tests, the weight percentage of oxygen (WPO) in all samples were measured by using energy-dispersive X-ray (EDX) spectroscopy. The testing results indicate that the aging rates of the asphalt binder under both UV and UV/moisture/condensation are fast at the beginning and stabilize after a certain period. Experimental results were also modeled by two classic asphalt aging models, namely, the fast rate–constant rate (FRCR) and nonlinear differential dynamic (NDD) models. Although the NDD model exhibits acceptable agreement with the experimental results from both the UV aging and UV/moisture/condensation aging samples, the FRCR model fits the UV/moisture/condensation aging better and thus is recommended for future UV/moisture/condensation aging performance prediction. Additionally, although exposed under UV for the same time, the WPO in samples after UV/moisture/condensation aging were lower than those in samples after continuous UV aging. This indicates that condensation and moisture reduce the UV-induced photo-oxidative aging rate.

Standard specifications for ready-mixed concrete (RMC) specify a limit of mixing time and revolution count of a RMC truck. More than half of today’s RMC contains a blended cement and chemical admixture. For this reason, the current specification may be outdated. This paper aims to gain technical knowledge on a behavior of mixing time and revolution count of the blended cement system containing rice husk ash (RHA) and chemical admixture. This paper assesses the effects of mixing time and revolution count on ion concentration, flowability, setting time, chemical shrinkage, porosity, compressive strength, and chloride diffusivity of pastes and mortars containing several types of RHA. The RHA types evaluated include as-received RHA (AR-RHA), chemically transformed (alkali-treated) RHA, and AR-RHA with retarder. Results indicate that although the mixing conditions influence the characteristics of the blended cement system, RHA type has a greater effect on these characteristics. Controlling the performance of RMC can be achieved by selecting the proper RHA type to add into the mixture.

Understanding capillary water absorption in concrete is of major significance for the durability assessment of concrete structures, particularly when cracks are present. The paper develops a three-dimensional (3D) finite-element (FE) model to simulate water absorption in concrete samples with discrete crack networks. In this model, the uncracked domain is discretized into solid elements whereas discrete cracks are modeled by zero-thickness crack elements, with the unsaturated flow theory applied to describe the water penetration process. The proposed model is validated by comparing with experimental data from the literature. Concrete samples containing randomly generated 3D crack networks are employed for investigating water uptake, and the effects of crack configurations (i.e., crack density, length, and width) on the sorptivity are evaluated numerically. The proposed model is shown to be capable of simulating the capillary flow within unsaturated cracked concrete, indicating that the discrete cracks play a significant role in accelerating the absorption rate of water.