Journal of Materials in Civil Engineering

The addition of nanomodifiers is an effective method to improve the performance of cementitious materials. However, the strengthening mechanism is still not fully understood. Molecular dynamics (MD) simulation is an effective research tool that makes it possible to understand the genome of cement-based materials and, thus, their interactions with nanomodifiers at the nanometer scale. Therefore, MD would serve as an aid to design composite materials toward improved performance, reduced material cost, and enhanced ecoefficiency. This article briefly overviews the progress in MD simulations of nanomodified cement-based materials over the past five years. It mainly includes the application of MD simulation methods in understanding the structure, properties, and microstructure evolution of C–S–H toughened by aluminum phase doping, graphene oxide, polymers, and new nanomaterials. In particular, the research on the ion curing ability and transmission properties of the toughened composite materials are reviewed. Challenges related to nanomodified concrete, as revealed by MD simulations, are also discussed.

Rock mass is a structural system composed of intact rock and joints. The properties and strength of rock mass determine the macroscopic mechanical properties of rock mass. Enhancing the self-stability of rock mass by improving the integrity of jointed rock mass and the joint strength is a popular research topic in the geotechnical field. As a new reinforcement method for joints, the microbial healing technique has attracted much attention. This study investigated a healing technique for jointed sandstone based on microbial-induced calcium carbonate mineralization, and triaxial compression tests were conducted on the jointed rock mass after healing. Bacillus cohnii (lyophilized powder) was activated in the laboratory, and calcified precipitation was induced in sandstone joints to realize healing and reinforcement of joints. Observations by X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that the mineralization products in the joints were microbial-induced calcium carbonate precipitation (MICP) and that the sandstone joints were fully cemented. Finally, triaxial compression tests were conducted on jointed rock specimens after healing to investigate their mechanical properties. The experimental results showed that the deviatoric stress of the specimens after MICP repair increased by 50% compared with that before repair. When the dip angle of the joint surface was 15°–45°, the shear failure along the structural plane was the main failure before repair; after MICP repair, the main failure was shear failure of the rock block. The strength of the rock specimen with microbial-induced calcite precipitation was analyzed theoretically using the Jaeger criterion. It was shown that the microbial-induced calcium carbonate precipitation technique not only can enhance the integrity of rock joints, but also can improve the strength of jointed rock mass remarkably. This study provides new ideas for reinforcement of jointed rock mass.

This study investigates the mechanisms of alkali-silica reaction (ASR) mitigation by supplementary cementitious materials (SCMs) under accelerated mortar bar test (AMBT) conditions. The study compares the effect of traditional SCMs (fly ash, slag, metakaolin, and silica fume) on ASR expansion, calcium silicate hydrate (C-S-H) composition, and portlandite consumption as well as on the availability of silicon and aluminum in solution. Results show that at typical SCM replacement levels for effective ASR mitigation (15% metakaolin, 25% fly ash, and 65% slag), the Si/Ca and Al/Si ratios of C-S-H are increased to comparable values, suggesting that at these dosages the SCMs contribute almost equivalent amounts of silicon and aluminum in solution. Studies of blended cement + SCM pastes show that the order of pozzolanicity is as follows: silica fume > metakaolin > fly ash > slag, which is consistent with the order of efficacy of SCMs in mitigating ASR expansion and the measured concentrations of silicon in solution. Solubility studies of the SCMs showed formation of sodium aluminum silicate hydrate (N-A-S-H) in fly ash and metakaolin and formation of calcium aluminum silicate hydrate (C-A-S-H) in slag after 28 days of exposure to AMBT conditions. This highlights the role of alkali activation of SCMs in ASR mitigation under AMBT conditions.

Cracks in cement-based materials are one of the main factors affecting the durability of structure. Recent research in the field of concrete materials showed that self-healing in cement-based systems can be achieved by triggering biogenic calcium carbonate (${\mathrm{CaCO}}_3$) precipitation. The goal of this study is to establish a comparative evaluation of the use of sepiolite, bentonite, and diatomaceous earth (DE) as an immobilization barrier of Sporosarcina pasteurii (S. pasteurii) cells to trigger self-healing in cement-based systems. For the first time in the literature, this study will provide insight into the use of natural minerals, such as bentonite and sepiolite, as protective carriers for vegetative S. pasteurii cells in cement-based materials and present a comparative evaluation of factors influencing crack healing, such as the microstructure and composition of immobilization barriers. A two-phase self-healing bioadditive was obtained by immobilizing vegetative S. pasteurii cell samples on natural porous minerals with or without the use of required nutrients. Then the samples were cracked by a three-point bending test, and the healing process was screened via stereomicroscope imaging and ultrasonic pulse velocity (UPV) testing after subjecting the cracked samples to 28 days of moist curing. Flexural cracks induced in mortar samples were filled with biogenic precipitate. Relatedly, the water absorption capacity of the samples was decreased in mortar samples containing bacterial cells, the nutrients were added in the curing solution. Fourier transform infrared spectroscopy and scanning electron microscopy analyses showed that calcite was the predominant polymorph of ${\mathrm{CaCO}}_3$ sealant in cracks.

This paper presents an investigation on the water tightness/self-healing of engineered cementitious composite (ECC) elements subjected to direct tension cracking and exposed to the coupled effect of sustained loading and pressurized water. A setup was presented to simulate a wall segment of liquid containing structures subjected to direct tensile forces. The experimental program included ECC panels with different supplementary cementitious materials (SCMs), comprising fly ash Class-F, fly ash Class-C, and granulated blast furnace slag. Each panel was subjected to direct tensile load to induce full depth cracks and then a leakage test was carried out under sustained load and various water pressures. To consider the effect of ECC composition on the cracking/self-healing behavior of panels exposed to loading and pressurized water, the leakage rate was continuously studied until complete sealing. Additionally, a detailed microstructural analysis was completed on full depth drilled cores, in which the samples were taken from three layers of the healed cracks to investigate the influence of pressurized water on the self-healing products. The results of this study confirmed the high effect of water pressure and SCM type on the self-sealing capability of ECC, especially after the first 30 h of leakage. The fly ash-ECC panel was shown with lower crack opening and leakage rates, which also resulted in greater cracking/self-healing behavior under coupled sustained loading and high-water pressure. Different concentrations of ${\mathrm{CaCO}}_3$ and C-S-H/CH products were found in each crack mouth and elevation, indicating that self-healing under pressurized water likely developed from the core and bottom areas to the top layer of crack lines.

Ultrahigh-performance concrete (UHPC) is a smart material used in engineering structures that are subjected to high flexural, shear, impact, and dynamic loadings to ensure safety against explosions and other accidental loads. However, in order for UHPC to be used in structural members in nuclear power plants, it needs to provide radiation shielding due to its high density in addition to being structurally sound. In this study, an attempt was made to develop high-density ultrahigh-performance concrete (HDUHPC) using hematite powder as a partial replacement for sand. The effect of hematite powder content on the microstructure, density, and mechanical properties of HDUHPC was studied using six mixtures that incorporated 0%–50% hematite powder by volume (partially replacing the sand). The test results indicated that as the dry density of the HDUHPC increased with increasing hematite powder content, the mechanical properties of the HDUHPC were uncompromised; in fact, the mechanical properties improved slightly due to densification of the microstructure of the HDUHPC with the inclusion of very fine particles of hematite powder. In addition, the effect of varying dosages of steel fibers on the mechanical properties of the HDUHPC was examined by considering three different dosages of steel fibers (2%, 4% and 6% by weight) in the concrete mixture. The results showed significant improvements in the mechanical properties at higher fiber contents. Correlations between fiber content and different mechanical properties of the HDUHPC mixtures were obtained with high degrees of fitting.

This work analyzed the technical viability of the use of granite rock fines (GRF) for the manufacture of portland cement. The simultaneous influence of the contents of MgO, ${\mathrm{SO}}_3$, and alkalis (${\mathrm{Na}}_2\mathrm{O}$ and ${\mathrm{K}}_2\mathrm{O}$) present in the GRF in the formation of the mineralogical phases of the portland clinker was evaluated. Laboratory clinkers with replacement of clay by GRF at contents of 50% and 100% were characterized by X-ray diffraction and used to produce portland cement. Then, the physical–mechanical properties of this cement were evaluated. The addition of GRF replacing 25% and 50% clay increased the content of alite (${\mathrm{C}}_3\mathrm{S}$) in the clinkers and stabilized the ${\mathrm{C}}_3\mathrm{S}{\mathrm{M}}_3$ and ${\mathrm{C}}_3\mathrm{A}$ orthorhombic polymorphs due to the presence of MgO and ${\mathrm{Na}}_2\mathrm{O}$ in their composition. Cements made with replacement contents of 50% and 100% of clay by GRF showed higher compressive strength than reference cement.

This paper introduces the in-situ formation of biomodified polyurethane in bitumen as a novel strategy to enhance the healing capacity and aging resistance of bitumen. Bitumen is a substance that is known to have the capacity for healing. Self-healing bituminous composites can recover their properties. An increase in bitumen’s healing capacity can be facilitated using various modifiers. This study examined the merits of using a biobased polyurethane to both improve the healing capacity of bitumen and to enhance its resistance to aging through in-situ polymerization of polyurethane. The effect of aging on healing capacity was examined by studying specimens before and after aging in the laboratory. To do so, thermomechanical analysis and spectroscopy were used to characterize bitumen containing a biobased polyurethane from castor oil. It was found that the biobased polyurethane was quite compatible with bitumen, and the presence of polyurethane improved the overall thermomechanical properties of the bitumen. To evaluate the extent of healing, a time-sweep rheometry test was used to create samples with specific initial damage degrees. The degree of damage was selected to be a 30%, 45%, or 60% reduction in complex modulus. A healing index was calculated for each of the three damage levels after a $60\text{-}\min$ rest period. The study results showed that the introduction of biobased polyurethane not only improved the healing index, it also mitigated the negative effects of aging on bitumen’s healing capacity. Compared to samples of unmodified bitumen, the average healing index of samples containing biomodified polyurethane was 1.3 times higher at 16% in the unaged state and 3.5 times higher at 7% in the aged state. In addition, the samples containing biomodified polyurethane showed better resistance to aging as evidenced by average 72% and 50% lower increases, respectively, in carbonyl and sulfoxide (known products of aging in bitumen) when exposed to the same aging protocol.

Electrically conductive asphalt mixtures (ECAM) were fabricated by adding two conductive materials (steel wool and graphite) in this paper. Effects of steel wool and graphite on the electrical conductivity and pavement properties of ECAM were studied. Results showed that steel wool can greatly reduce the electrical resistivity of asphalt mixtures. Meanwhile, ECAM with steel wool has an excellent low-temperature cracking resistance and a good moisture susceptibility and rutting resistance compared with the plain asphalt mixture. However, the aggregation problem of steel wool cannot be avoided at its high content. As a result, there is an upper limit of the content of steel wool. Graphite can not only effectively decrease the electrical resistivity of asphalt mixture but also has a good rutting resistance, and it can be easily dispersed in the mixture. To fabricate a uniform ECAM with better electrical conductivity and pavement properties, the hybrid addition of steel wool and graphite is employed. This method can reduce the steel wool content, thus solving the dispersion problem and further improving the electrical conductivity and pavement properties of asphalt mixture. Therefore, the hybrid addition method is more suitable for fabricating conductive asphalt mixtures.

This study presents an investigation into the fatigue performance of warm mix asphalt (WMA) and the effect of mixing temperature on fatigue cracking of WMA tested in a dynamic shear rheometer (DSR). WMA (organic and chemical technologies) was manufactured at 125°C (for modified soft binder, $100/150$) and 135°C and 145°C (for modified hard binder, 40–60), while the control hot mix asphalt (HMA) was mixed at 145°C for modified soft binder and 155°C for modified hard binder. Despite the fact that WMA modified with hard binder was successfully manufactured at a temperature 20°C lower than the traditional HMA and the aggregate was completely coated, its fatigue life was lower than the traditional HMA. However, when WMA modified with hard binder was manufactured at a temperature only 10°C lower than the traditional HMA, its fatigue resistance significantly increased. In addition, successful reduction in the production temperature of up to 20°C was achieved for WMA modified with soft binder. In other words, the WMA production temperature should be identified based on the grade of the bitumen in order to produce an asphalt mixture that has a better performance than the traditional HMA. After taking the production temperatures into account, in all scenarios, Rediset WMX increased the fatigue life by approximately 32%, while Rediset LQ doubled the fatigue life of the asphalt mixture and Sasobit increased the fatigue life by approximately 90%. Furthermore, an artificial neural network (ANN) was used to model and predict the fatigue performance of WMA.

Flash flood occurrence on roads due to heavy rainfalls is reported frequently. Ponded or accumulated water on roads is a nuisance to traffic users if not properly conveyed. This paper introduces a pervious concrete pavement curb technology to address such problem. This technology is able to infiltrate ponding water into pervious curbs placed along the road. The pervious concrete mix design was adapted from the established literature. The main intention of the paper was to understand the hydraulic capacity of the pervious curb under varying lateral flows. Experimental testing was carried in the laboratory using a fabricated roadway flume. A testing tool to measure the lateral infiltration capacity was introduced. The capacity of the pervious curb was compared with the performance of roadways designed with grate inlets. The results showed that placing a pervious curb next to an existing grate inlet enhanced the performance better than using the curb alone. The pervious concrete pavement curb technology is believed to provide cheaper solutions to managing floods during rainfall events.

Paper mill sludge ash (PMSA), sewage sludge ash (SSA), and desulfurization gypsum (DG) were mixed and calcined by microwave radiation to acquire a product with higher hydration activity. The resulting mixture was used as a supplementary cementitious material to prepare backfill materials for mining. The influence of the mixing ratio of raw materials, microwave parameters, and sample size on the properties and microstructure of the microwave-sintered sludge ash (MSSA) and MSSA-cement pastes was determined. Both the MSSA and the prepared pastes were characterized using X-ray diffraction (XRD), Fourier infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDAX). Results indicated that the minerals in the MSSA were rankinite, mayenite, and belite, which all exhibited relatively high hydration activity and significantly improved the degree of hydration of the MSSA–cement system. As the microwave power and irradiation time increased, the water demand of the MSSA–cement pastes decreased, the setting time decreased, and the compressive strength increased. The MSSA prepared with a small length-to-diameter ratio produced more crystals and gels compared with that prepared with a larger length-to-diameter ratio. The gels mutually fused to form a dense structure, and this further enhanced the strength of the MSSA–cement pastes.

Experiences of highway agencies show that the costs of repairing rutting distresses are high. The common solution to overcome this issue is using a modified asphalt binder. The modifier enhances the asphalt binder’s rheological and physical properties but increases the production temperatures of asphalt pavement. Nevertheless, warm mix asphalt (WMA) production at temperatures lower than hot mix asphalt (HMA) could lead to lower aging of asphalt binders. In this study, the physical and rheological properties of modified asphalt binders with different contents of Gilsonite and their combination with Sasobit as a WMA agent were investigated. Accordingly, 5%, 9%, and 13% Gilsonite, as well as 3% Sasobit in combination with Gilsonite, were used to modify asphalt binders. Dynamic shear rheometer (DSR), rotational viscosity (RV), surface free energy (SFE), Fourier-transform infrared spectroscopy (FTIR), and some conventional tests (i.e., penetration grade, softening point, and storage stability) were conducted to evaluate the properties of the binders. The results of chemical analysis tests (i.e., SFE and FTIR) indicated that using Gilsonite and Sasobit as composite modifiers could further improve the thermomechanical properties. The DSR test results also showed that the Gilsonite and its combination with Sasobit improve the high-temperature performance of asphalt binders and, consequently, increase the rutting resistance. However, Gilsonite could raise the asphalt binder elasticity and showed better results when Sasobit was incorporated. In general, Gilsonite increased the asphalt binder stiffness, and consequently, it could reduce the workability and compactability of mixtures. Therefore, the use of Sasobit as a complement for Gilsonite reduces the viscosity of the asphalt binder and enhances the mixture workability. This could pave the way to use Gilsonite in WMA, resulting in more durable and sustainable asphalt mixtures.

Maintenance and the deicing of pavement are of significance for pavement service life and safety. This study designed asphalt cement (AC)-5 and stone matrix asphalt (SMA)-5 asphalt mixtures with steel fiber and steel slag, which are the materials of a functional ultrathin friction course. It is expected to be used for the maintenance and induction heating on asphalt pavement. Mechanical performance, such as skid resistance, interface shear resistance, semicircular bending (SCB), and corresponding fatigue tests, were investigated. In addition, the induction heating efficiency conducted at different distances was tested as well. The results show that SMA-5 showed better skid resistance than AC-5. Steel fiber raised the interface shear strength of AC-5 but reduced that of SMA-5. Fracture displacements of SMA-5 at the interface were lower than that of AC-5. Steel fiber-enhanced cracking resistance of SMA-5, while steel slag showed a negative effect. Fatigue properties of basalt-based SMA-5 showed a rising trend along with the increasing steel fiber. The distance between the mixture and magnetic coil showed a negative effect on induction heating efficiency.

The maximum interface sheer stress and crack density can be used as criteria for the interfacial bonding property and fracture performance, respectively. In this paper, interface stress and crack density as a function of applied strain of Zn–Zn-Al multilayer coating/304 stainless steel substrate system with different coating thicknesses were studied using uniaxial tensile tests. For comparison, Zn and Zn-Al monolayer coatings also were prepared. The saturated crack density of the Zn–Zn-Al coating was the largest, and that of the Zn-Al coating was the smallest. Furthermore, the maximum interfacial shear stress of the Zn–Zn-Al coating substrate system with 0.24-mm coating thickness was the largest. Finite-element simulation was used to analyze the development of interfacial cracks of the multilayer coating–substrate system during three-point bending. The simulation results showed that the interfacial crack was dominated by shear stress in the Zn–Zn-Al multilayer coating–substrate system with a total coating thickness of 0.32 mm, which proves the accuracy of the experiment.

The initiation and development of microcracks (with width generally less than 100–150 μm) introduced by heating or fire plays a critical role in the stability and durability of concrete structures, especially for large dams, nuclear power plant containments, or structures under fatigue loading. However, the concealment of microcracks and the nonlinearity of concrete materials make it difficult to evaluate appropriately the extent of microcracks and the effect on the compressive strength of concrete after thermal damage. This paper used broadband frequency excitation instead of traditional dual-frequency excitation to excite thermally damaged concrete, and the microdamage state was reflected in the generated ultrasonic modulated signal. The variation characteristics of modulated signals was described using the concept of a damage index (DI) based on the sideband peak count (SPC). The results showed that the peak value of DI based on broadband frequency coupling of the nonlinear ultrasonic modulation method is more stable and accurate than the resonance method. The development state of microcracks under the influence of different parameters (water-to-cement ratio, fine-to-coarse aggregate ratio, and heating temperature) was measured sensitively using the peak value of DI. The established statistical relationship of the peak value of DI provides a method and reference for the evaluation of the state of microcracks and the loss of compressive strength in actual structures.

Self-compacting rubberized concrete (SCRC) is an excellent environment-friendly material that can be applied well in road and bridge engineering. In this study, the tensile and compressive creep performance of SCRC at early age were investigated by using the universal testing machine (UTM) and temperature stress testing machine (TSTM). In particular, the tensile creep at different ages, stress levels, and temperatures corresponding to different stages in the cracking process were analyzed. The results indicate that both the tensile and compressive creep deformation of SCRC increase obviously with the increasing rubber content at different temperatures, loading age, and stress level. Creep increase at early age is more significant in SCRC. The compressive and tensile creep coefficient of SCRC also increase with the increase of rubber content. Finally, the compressive and tensile creep of SCRC can be simulated well by the double power law (DPL) model. Therefore, the creep increase is also the reason for cracking risk reduction of SCRC.

This study elucidates the important role of styrene-butadiene-styrene (SBS) concentration and storage temperature on the extent of property deterioration in SBS-MBs and their corresponding mixes. SBS-MBs with varying SBS content (3%, 4.5%, and 7% by weight) were first stored in closed metal containers at 150°C and 180°C. It was observed that the properties of the SBS-MBs remained stable at 150°C, but erosion was evident when stored at 180°C due to SBS degradation. The conventional, rheological, and morphological analysis demonstrated that the magnitude of property erosion at 180°C strongly depended on the concentration of the SBS polymer. SBS-MB with 4.5% by weight SBS polymer exhibited the maximum deterioration in the properties, while binder with 3% and 7% by weight SBS content showed subdued property erosion at 180°C. Asphalt mixes were prepared using the fresh and stored SBS-MBs with varying SBS content. Results showed a substantial drop in mixes Marshall stability, indirect tensile strength, fatigue, and rut resistance properties after using 4.5% by weight SBS-MBs that were stored at 180°C for 7 days. The consequential outcome of such property deterioration of asphalt mixes may impede pavement stability and service life. Meanwhile, only $\approx 10\%$ property reduction took place in asphalt mixes that were prepared using 3% and 7% by weight SBS-MBs stored at 180°C. The findings from the study are practically significant while using SBS-MBs for pavement construction. Results also illustrate that the trend in deterioration is similar for SBS-MBs irrespective of grade and source of the base binder.

The use of reclaimed asphalt pavement (RAP) in hot asphalt mixtures has been investigated widely, mainly to increase the amount of RAP incorporated into new asphalt mixtures as secondary material. A key point to successfully increase the amount of RAP in mixtures is a comprehensive understanding of the blending between different bitumens, such as old and fresh bitumen. This paper introduces a mechanical model to simulate the diffusion phenomenon between two different bitumens on the basis of their rheological properties. A double-layer dynamic shear rheometer (DSR) specimen with a 25 mm diameter and 0.5 mm total thickness in plate–plate configuration was prepared by superposing two 0.25-mm-thick layers, each composed of a different bitumen. The evolution over time of the equivalent shear complex modulus of the whole double-layer specimen was investigated by performing a series of frequency sweeps at 50°C every $30\min$. The time-dependent evolution of the equivalent modulus was modeled by considering an intermediate layer, composed of fully blended bitumen, at the interface between the two layers of the two base bitumens. The thickness of the intermediate layer increased as a function of time, due to diffusion. The validity of the model was confirmed by a frequency-independent thickness of the intermediate layer. Extrapolating the results, the model gives an indication of the blending of the two bitumens in the long-term, and the findings may suggest an interaction between different bitumens in asphalt mixtures containing RAP. The results are promising for the development of a more-refined mechanical model.

This paper presents a validation of a new protocol for the characterization of drying shrinkage of cement paste. The method consists of using environmental scanning electronic microscope (ESEM) or climatic chamber (CC) assisted by digital image correlation (DIC) to study the drying shrinkage of cement-based materials. The final motivation is to study the influence of the drying rate on cement-based materials’ delayed strain at the microscopic scale. Hence, the impact of specimen shape, size, and the imposed relative humidity history on the drying shrinkage is studied. Results show that for a given material, the amplitude of drying shrinkage is independent of the rate of drying and the specimen shape. Advantage was taken of the two techniques proposed in this paper to perform drying length change measurement both in ESEM and CC.

The integrality and connectivity of detected cracks are critical to quantitatively analyzing the fracture patterns of cementitious materials using X-ray computed tomography (XCT). Owing to noise, uneven gray values, pores, and other additions with gray values similar to those of the cracks in the raw images, image segmentation results of microcracks always have poor continuity and integrality. In this paper, a sophisticated image processing method is proposed to detect integral microcracks in XCT images accurately, and a reconnecting algorithm is proposed to enhance the continuity and integrality of microcracks in the concrete fracture XCT image. The analysis of XCT images of fractured rubber concrete samples verified that the method could visualize and quantitatively analyze the fracture pattern, demonstrating the method’s robustness.

To improve the performance of epoxy grouting materials and achieve better repair of microcracks in cast-in-place concrete bridge deck pavements, polydimethylsiloxane (PDMS) and diluent were used to modify epoxy resin. The mechanical properties of silicon-modified epoxy grouting materials produced using different preparation processes were analyzed, and the best preparation process was optimized. The working performance of silicon-modified epoxy grouting material was determined, and the environmental adaptability before and after composite modification was explored. The results showed that the suitable reaction temperature, time, and PDMS content are 100°C, 3 min, and 8%, respectively. The higher the temperature, the better was the groutability and the shorter was the curing time. Therefore, the construction temperature should be at least 35°C. The impact resistance and strength of the grouting materials were improved significantly after the addition of PDMS. In addition, the strength essentially was formed after 5 days. This indicates that the curing age is 5 days. Silicon-based modified epoxy grouting materials have good environmental adaptability. After thermal shock, 30-day temperature variation treatment, and 30 freeze–thaw cycles, the flexibility and bonding properties of the materials were excellent, and were much higher than those of the unmodified materials. Although the tensile strength was slightly lower than that of the unmodified materials, it still remained at about 60 MPa.

The bond between bitumen and aggregate is important in ensuring suitable performance of flexible pavements in different environmental conditions. The bonding properties of bitumen–aggregate samples can be affected by different factors (i.e., aggregate types, bitumen types, temperature variations, aging phenomenon, and moisture conditioning). This study illustrated the effects of different factors on the bonding properties of bitumen–aggregate samples and aimed to identify the significant factors. The experimental variables in this study were aggregates (limestone and granite), bitumen (traditional black bitumen, clear binder), aging duration, curing conditioning, and curing times. Bitumen bond strength (BBS) tests and rolling bottle tests (RBTs) were performed to determine the pull-off tensile strength (POTS) and stripping degree of bitumen–aggregate samples, respectively. BBS test results illustrated that aging initially improved the bond strength of the samples, but further increases in aging duration attenuated bond strength because of bitumen embrittlement. In general, temperature changes showed an inverse relation to the bond strength of the samples. Failure type changed from cohesive to mix failure or adhesive failure at low temperatures. BBS results also showed that bonding between bitumen and aggregate was dominated by bitumen type when cohesive failure was observed, and in cases of adhesive failure or cohesive-adhesive failure, aggregate types had a significant effect on bonding properties. Cohesive-adhesive failure or adhesive failure was observed at low temperatures and in wet conditioning. RBT results showed that a bitumen–granite mixture showed high moisture susceptibility. Statistical analysis suggested that all variables of this study except aggregate types were statistically significant and affected bond strength in dry conditioning. In wet conditioning, all the variables were significant, and curing time was the most influential variable. Partial eta squared values were highest for bitumen type, indicating the importance of this factor for bitumen–aggregate bond strength.

To simulate the influence of the corrosion environment caused by snow-melting agent on pavement, an asphalt mixture was treated by dry-wet cycle in a NaCl solution with various concentrations. The rutting test, bending test, freeze-thaw splitting test, immersion Hamburg wheel-track test, industrial computed tomography (ICT) test, and scanning electron microscope (SEM) test were conducted to evaluate the adverse effect of snow-melting agent on road performance, durability, and the microstructural characteristics of SMA13, AC13, and SUP13 asphalt mixtures. The damage mechanism of performance for asphalt mixtures in a corrosion environment was also discussed. The results show that the road performance and durability of SMA13, SUP13, and AC13 asphalt mixtures decrease by various extents after being treated by the method of dry-wet cycle in chloride salt solution. Among the three kinds of asphalt mixture, SMA13 shows the best resistance to the corrosion of NaCl solution, followed by SUP13 and AC13. After being treated in salt solution, the void parameters such as total void volume, average void volume, equivalent void diameter, and air void of a Marshall specimen grow fast first and then tend to stabilize. The crystallization expansion of NaCl crystals results in structural damage inside the mixture, and then the strength of the asphalt mixture greatly declines, leading to the deterioration of road performance and durability in a salt corrosion environment. SMA13 asphalt mixture is recommended for pavement surface layers where the snow-melting agent is often used.

This paper reports moisture damage analyses of recycled asphalt pavement (RAP) aggregate–enriched bituminous concrete (BC). This investigation determines the effective RAP aggregate percentage for producing a moisture-resistive 19-mm nominal-sized aggregate–enriched BC mix. To execute such a study, virgin aggregate (VA) has been replaced by 0%, 10%, 20%, 30%, 40%, 50%, 60%, 75%, and 100% RAP aggregate a on random selection basis at laboratory scale to explore the effect of each sample in BC mix. After calculating the optimum bitumen contents (OBCs) for the aforementioned BC mixes via the Marshall mix design, a moisture damage analysis was conducted using a modified Marshall immersion test. Experimental results show that 50% RAP aggregate–enriched BC mix may be used in low-volume roads in colder regions containing 0.07% less OBC than conventional BC mix. That mix may have 83.71% moisture damage resistive potency up to a 7-day immersion period. This improvement is due to the presence of a sufficient amount of carbonyl compound in the binder. Quantifying such compounds in the bitumen has been done by Fourier transform infrared analysis of the bitumen, as reported in the literature (Karmakar et al. 2018; Karmakar and Roy 2021). The moisture resistive potency of the 50% RAP aggregate–enriched BC mixes has also been confirmed by the indirect tensile strength (ITS) test, energy loss ratio test, and boiling water test. The results of those tests revealed that the presence of carbonyl compound in the binder of 50% RAP–enriched BC mix elevates the mix’s flexural resistance against moisture damage for a 4-day immersion period due to having 1.15% more coating ability than a virgin binder.

In this study, basalt fiber-reinforced and polymer-modified magnesium phosphate cement (BFPMPC) mortar, a novel rapid repair material, is proposed for portland cement concrete pavements (PCCP). A practical mixture design was selected from the orthogonal experiments. The properties of this mixture under different environments were studied. Considering the horizontal load of vehicles, the bonding mechanism between magnesium phosphate cement (MPC) mortar and PCCP was studied through shear strength tests. The experimental results show that the BFPMPC mortar proposed has not only reliable compressive and flexural strengths but also good water resistance in the interfacial transition zone (ITZ) and good bonding performance with the old cement concrete. Additionally, the ITZ between the BFPMPC mortar and old concrete has good freeze-thaw resistance. Then, the salt freeze-thaw cycles were found more destructive to the repair interface than freeze-thaw cycles. The addition of the styrene-butadiene copolymer (SBC) emulsion in BFPMPC mortar was formed without new hydration components, which was observed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The ability to enhance the bonding strength with the addition of SBC was found by scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). In summary, the BFPMPC mortar can be used as a rapid repair material for PCCP in seasonally frozen areas.

As an important ecofriendly material in pavement engineering, bioasphalt has received more and more attention recently. However, the negative high-temperature behavior of bioasphalt limits its extensive application. With the purpose of enhancing the bioasphalt high-temperature behavior, polyphosphoric acid (PPA) was used to modify bioasphalt. The PPA/bio-oil composite–modified asphalt’s high-temperature behavior was investigated by the dynamic shear rheometer (DSR) test. The low-temperature behavior was evaluated by using the bending beam rheometer (BBR) test. Finally, the modification mechanism of modified asphalt was analyzed by carrying out a Fourier-transform infrared reflection (FTIR) test. The results indicated that compared with the neat asphalt, the rutting index of PPA/bio-oil composite–modified asphalt was significantly improved. Also, it had excellent low-temperature crack resistance. As the bio-oil and PPA contents in respect to the weight of neat asphalt were 15% and 5%, respectively, PPA/bio-oil composite–modified asphalt performance was optimal. Shear time and shear rate did not have a remarkable effect on PPA/bio-oil composite–modified asphalt performance. Moreover, bio-oil did not affect the chemical structure of the neat asphalt. But, PPA generated new chemical functional groups with neat asphalt and produced chemical modification. This research makes pavement engineering greener, more economical, and environmentally friendly.

This study was designed to evaluate the performance and microstructure of eco-cements containing rice husk ash (RHA), ground granulated blast furnace slag (GGBFS), and circulating fluidized bed combustion (CFBC) fly ash (CFA). Eco-cement samples with a water to ($\mathrm{GGBFS}+\mathrm{RHA}+\mathrm{CFA}$) mass ratio of 0.40 were prepared with four $\mathrm{RHA}/(\mathrm{GGBFS}+\mathrm{RHA})$ mass percentages of 0%, 15%, 30%, and 45% and three $\mathrm{CFA}/(\mathrm{GGBFS}+\mathrm{RHA})$ mass percentages of 10%, 20%, and 30%. The compressive strength performance and overall quality [tested using ultrasonic pulse velocity (UPV)] of the eco-cements were found to be significantly and differently affected by the percentages of RHA, GGBFS, and CFA used. Although CFA was found to reduce compressive strength and UPV at early ages of curing, CFA enhanced these values at later ages and promoted the development of the eco-cements due to the increased formation of hydration products [ettringite (AFt), C─ S─ H, and C─ A─ S─ H], as identified using energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier-transform infrared (FTIR) analyses. The incorporation of more RHA was found to reduce the compressive strength and UPV values of the eco-cements. The compressive strength values of the eco-cements at 28 and 91 days were in the ranges of 20.4–39.1 and $24.1–45.3\mathrm{MPa}$, respectively, whereas the UPV values of all eco-cements at 28 and 91 days were in the ranges of 2,897–3,368 and $\mathrm{3,062}–\mathrm{3,462}\mathrm{m}/\mathrm{s}$, respectively. The RHA-free eco-cement activated by 20% CFA had the highest compressive strength and UPV values at all curing ages. The substitution of GGBFS with 15%–45% RHA can be used to produce eco-cements used in mortar/concrete with various requirements such as low to medium strength and low cost.

Although several studies have been conducted regarding the use of lime sludge (LS) in engineering and agricultural applications, its use for stabilizing subgrade soils has not been fully investigated. In this study, an effort was made to evaluate the suitability of using LS alone or in combination with traditional stabilizers [fly ash and portland cement (PC)] to stabilize a frost-susceptible loess soil (LOE). A series of unconfined compression (UC), pH, and freeze-thaw (F-T) tests, as well as scanning electron microscopy (SEM), were performed for the evaluation. Test results indicated that using LS alone effectively improved the unconfined compressive strength (UCS) of the soil. In addition, using LS in combination with fly ash yielded further improvements in the UCS of the soil compared with using only fly ash for stabilization. Alternatively, using LS in combination with PC improved the UCS of the soil to a lesser extent than using PC alone for stabilization. In all the cases, the presence of LS in the soil matrix reduced the F-T durability.

In recent years, the construction sector has generated large amounts of construction and demolition waste (CDW). In Europe, more than 50% of this waste is ceramic waste (CW). Therefore, and in accordance with the Circular Economy Action Plan, the building sector should reintroduce a certain amount of CDW into the life cycle of buildings. Many studies have sought to incorporate CDW in gypsum plaster and cement mortars for construction. However, few studies have analyzed the feasibility of replacing raw materials such as gypsum, cement, or sand with CW. A three-phase experimental plan was designed to introduce various types of CW—from new construction and from rehabilitation works—in a gypsum matrix. The viability of the new mortar and its capacity to improve the mechanical and physical properties of gypsum without additions were analyzed. In the first phase of the experimental plan, CW was added in different percentages and granulometries into the gypsum matrix to make different mortars samples, and mechanical tests were conducted. The plaster mortar with the best results for use as coating was selected. The following tests, considering the final application of the mortar, were carried out: setting time, water capillarity absorption, and adherence. A chemical and mineralogical characterization was performed on the CW. The results showed that it is feasible to replace part of the raw gypsum material with recycled ceramic material. The superficial hardness, water absorption, adhesion, and mechanical resistances of the gypsum mortars containing CW were improved compared with those of gypsums without additions.

Porous asphalt pavement has been used for multiple purposes, but its large porosity makes it easy to age by long-term weathering conditions; this causes its premature failure through raveling, fatigue, and so forth. This study explored the fatigue performance of aged porous asphalt mixtures produced with epoxy asphalt binders. Gradations of three porous asphalt mixtures were first designed in the laboratory: (1) a porous asphalt mixture 13 with an epoxy asphalt binder (EPA-13); (2) a porous asphalt mixture 13 with a high-viscosity asphalt binder (HPA-13) as a control; and (3) a dense-graded asphalt mixture 13 with a high-viscosity asphalt binder (HDA-13) as another control. Then, fatigue tests were conducted under different strain levels on porous asphalt mixture samples before and after aging. In addition, the effect of loading sequence on fatigue was examined for samples under two-stage continuous loading conditions. The results showed the following three things. First, the use of epoxy asphalt binder can tremendously improve the fatigue resistance of porous mixtures. the fatigue life of EPA-13 was 2.0 to 4.5 times greater than that of HPA-13, depending on the strain level. Second, after long-term aging, the fatigue life of the EPA-13 subjected long-term aging decreased by 82.3%. The retention rate of the initial modulus was about 50%. The fatigue life of the weathered EPA-13 was still much better than that of the weathered HPA-13. Third, loading sequence had a remarkable influence on the damage accumulation of all mixtures discussed.

Pyrolysis is being employed as a viable option for the disposal of different industrial and agricultural wastes, including end-of-life vehicle tires. Tire pyrolytic char (TPC), a solid fine carbonaceous material obtained as a by-product during the pyrolysis of waste tires, is gaining interest among pavement researchers for its use in asphalt binder modification. Good storage stability is essential to ensure that a modified binder retains the desired properties after its fabrication. Cross-linking agents are frequently used to enhance the storage stability of modified binders. This study characterized the storage stability performance of TPC-modified binders with and without the incorporation of cross-linking agents. Bituminous binders modified with TPC were analyzed for storage stability at multiple dosages of two widely used cross-linking agents: polyphosphoric acid (PPA) (0.5%, 1.0%, and 1.5%) and sulfur (0.15%, 0.3%, and 0.45%). In addition to softening point difference (SPD), separation indices (SIs) derived from frequency sweep, temperature sweep, and multiple stress creep and recovery (MSCR) tests were employed to characterize the storage stability. Compatibility evaluation was also done through Cole-Cole plots. Fourier transform infrared spectroscopy (FTIR) was used to study the storage stability through the changes in binder spectra. Remixing of the TPC-modified binders was also performed to assess the retrieval of homogeneity in a segregated TPC-modified binder. All the SIs were measured and compared for binder specimens before and after remixing. Binders were ranked based on the SIs, followed by sensitivity and correlation analyses of the SIs. TPC-modified binder showed a good storage stability performance with sulfur (at 0.3% optimum dosage) and PPA (at 1% optimum dosage). Remixing resulted in further enhancement in the storage stability performance of TPC-modified binders. The results of the study are quite useful considering the practical usage of TPC for a storage-stable modification of asphalt binder.

To explore the macroproperties of biorecycled asphalt and the correlation between its components and macroproperties, the cooking-aged waste soybean oil was used as the base oil, along with mixing additives, to prepare the biorejuvenator, and a total of six biorejuvenators with different component ratios were first developed. Then, using these rejuvenators, six biorecycled asphalts were prepared and their chemical components and viscosity and a series of pavement properties were measured and evaluated. Finally, using the gray correlation theory, gray correlation analysis between macroproperties and four components was conducted for recycled asphalts. Results show that the addition of biorejuvenator can adjust the component distribution in the aged asphalt, and the components in the aged asphalt can be gradually restored to the original level, thus achieving the regeneration of aged asphalt. Biorejuvenator can restore the penetration, softening point, ductility, and viscosity of aged asphalt to the same level as original asphalt. Further, the biorejuvenator with appropriate composition can restore the rheological parameters such as $G^{*}$, $\delta$, $J_{nr}$, $N_f$, $S$, and $m$ of aged asphalt to the level consistent with that of original asphalt. And it can significantly improve the low-temperature and fatigue properties of aged asphalt, while ensuring that the high-temperature performance of regenerated asphalt meets the specification requirements. Overall, the regeneration effects of R5 [base oil: dibutyl phthalate (DBP): antiaging agent: $\mathrm{stabilizer}=88:10:1:1$] and R6 (base oil: DBP: antiaging agent: $\mathrm{stabilizer}=90:8:1:1$) are optimal, which can guarantee that the pavement performance of recycled asphalt basically meets the requirements of original asphalt. The gray correlation analysis shows that the change of the four components of biorecycled asphalt will significantly affect its viscosity, high- and low-temperature performance, and fatigue behavior. The seven indexes of $\delta$, softening point, penetration, $m$, viscosity, $S$, and $N_{f2.5}$ demonstrate a higher gray correlation with the four components of asphalt (all exceed 0.6), followed by ductility, $J_{nr0.1}$, and $J_{nr3.2}$. However, $G^{*}$ correlates poorly with the four components of asphalt, whose gray correlation degree is not more than 0.4.

This study aimed to evaluate the effect of laboratory aging levels on chemical and rheological properties of asphalt binder as well as fracture performance of asphalt mixture. Compacted asphalt mixtures were laboratory aged at 85°C for 0, 2, 5, 7, and 10 days and then subjected to the semicircular bending (SCB) test. Asphalt binders were extracted from the aged samples for further chemical and rheological characterization. Chemical characterization included Fourier transform spectroscopy (FTIR) and gel permeation chromatography (GPC). Rheological tests included bending beam rheometer (BBR) and linear amplitude sweep (LAS) tests. Asphalt binder rheological characterization showed that the cracking resistance of asphalt binders decreased with an increase of aging level. Statistical analysis of SCB test results indicated that there is no significant drop in the critical strain energy release rate, $J_c$, between 2- and 5-day aging, but 10-day aging resulted in a significant decrease in $J_c$. It was observed that the aging susceptibility of asphalt mixtures in terms of SCB results was consistent with FTIR and LAS test results.

Soil-rubber mixtures are potential construction materials for use in civil engineering applications such as the thermal insulation layer for buried pipelines in the permafrost zone and underground energy storage systems. Currently, however, the thermal conductivity of soil-rubber mixtures in various stress, saturation, and void ratio conditions is not fully understood. In this study, a stress-controlled apparatus based on the thermal needle probe technique was developed. It was employed to study the influence of the aforementioned factors on the thermal conductivity of sand-rubber mixtures. Thirty-four tests were completed with a wide range of net stresses ($0–600\mathrm{kPa}$), initial degrees of saturation (0%–100%), void ratios (0.45–0.95), and rubber contents (0%, 10%, and 20%). Three replicates were used in each condition. The results showed that the thermal conductivity was strongly dependent not only on void ratio, rubber content, and degree of saturation but also on net stress. For instance, the thermal conductivity of a dry sand-rubber mixture increased by 30% when the stress increased from 0 to 600 kPa. This increase in thermal conductivity can mainly be attributed to an increase in interparticle contact area, accounting for about 25% of the 30% increase; the reduction in void ratio played a minor role. A semiempirical equation was proposed to calculate the thermal conductivity of sand-rubber mixtures at different stress levels.

The high viscosity and poor storage stability of crumb rubber–modified asphalt (CRMA) can be partially addressed by the appropriate degree of degradation of the crumb rubber modifier. However, the low-temperature and fatigue characteristics of degraded crumb rubber–modified bitumen (DCRMB) in different aging states are not well understood. In this study, two types of DCRMB—namely, terminal blend rubberized asphalt (TBRA) and terminal blend hybrid asphalt (TBHA)—were prepared with sulfur, styrene-butadiene-styrene (SBS) polymer, and crumb rubber (CR). All DCRMB binders were short-term aged with a rolling thin film oven test (RTFOT) and long-term aged with a pressure aging vessel (PAV). Afterward, a bending beam rheometer (BBR) test and a linear amplitude sweep (LAS) test were conducted to characterize the low-temperature and fatigue properties of DCRMB binders at different aging degrees, respectively. Based on the rheological test results, several conclusions can be drawn. First, the BBR results indicated that the increase in CR content led to a slight increase in creep rate and a significant decrease in stiffness. Especially in PAV aging, the low-temperature properties of DCRMB were much better than those of neat asphalt. Meanwhile, DCRMB demonstrated an advantage over neat asphalt in integrity and fatigue resistance before and after aging. Finally, based on correlation analysis, the LAS test is recommended for evaluating the fatigue properties of DCRMB before and after aging.

Cracking is one of the most common distresses in asphalt pavement. Because asphalt concrete is relatively weak in tension, synthetic fibers have shown to increase its tensile strength and, therefore, reduce the chance of cracking. An approach was used in this study with the aim of evaluating the interaction between fibers and asphalt mastic and the fiber distribution in asphalt concrete. Three types of aramid fibers and two types of nylon fibers were used. A pullout test was used to determine the typical shear bond strength between fibers and the asphalt mastic. The bond strength obtained from the pullout test was then used to calculate the minimum fiber embedded length on each side of the crack in order for the fiber to reach its full capacity before being pulled out. Of course, increasing fiber length increases the chance of bridging cracks considering the random distribution of fibers in fiber-reinforced asphalt concrete (FRAC) and the random orientation of fibers relative to cracks. On the other hand, increasing fiber length may result in uneven distribution of fibers in the FRAC. Fiber extraction and recovery tests were then used to determine the dispersion of aramid fibers in the FRAC with different fiber lengths. The study showed that aramid fibers in the order of 20 mm would provide a good bond with the asphalt mastic and result in reasonable dispersion in the FRAC. The uniaxial fatigue test and flow number test were also performed on FRAC with different aramid fiber lengths. The 19-mm fibers also showed better performance test results than the 10- and 38-mm fibers. A similar length is recommended for the Nylon 1 fibers based on the bond properties only. Longer Nylon 2 fibers are recommended, but caution needs to be taken to avoid uneven fiber dispersion in the FRAC.

The use of geosynthetic-reinforced soil (GRS) structures instead of pile foundation in bridge abutment walls leads to reduction in costs and bridge bump. This study evaluates the effect of geocell as reinforcement on the bearing capacity of the backfill soil, the footing settlement, and the horizontal displacement of the wall facing of the GRS abutment wall. For this purpose, through physical modeling of the abutment wall and strip footing on backfill soil, a series of tests was carried out with changes in the value of the parameters such as the diameter of an equivalent circular area of the geocell pocket opening, the number of geocell layers, and the distance of backfill soil surface to the first layer of geocell. The output of the experiments showed that the increase in the diameter of an equivalent circular area of the geocell pocket opening results in greater horizontal displacement of the wall facing and reduction in bearing capacity of GRS abutment wall. Also, the best performance of the geocell-reinforced soil wall can be seen when the distance of the backfill soil surface to the first layer of geocell was 0.1 times the footing width. Increase in the numbers of geocell layers leads to increase in the bearing capacity of footing and the optimal number of geocell layers as reinforcement depended on the amount of pressure applied to the abutment wall. The results show that the optimum number of geocell layers as reinforcement for the footing pressures of 156, 188, and 205 kPa were four, five, and six, respectively. Also, the results showed that the abutment wall facing was deformed in the form of bulging and the rotation outward.

This paper presents a methodology to construct a water pond in sand using bioslurry layer via the microbially induced carbonate precipitation (MICP) process. Bioslurry is calcium carbonate crystals containing high-urease active bacteria cells, allowing further microbially induced calcium carbonate precipitation when introducing cementation solutions (urea and calcium ions). With the effect of a top sand layer, the daily seepage rate of the water pond was dramatically reduced to $3\mathrm{mm}/\mathrm{day}$ through four rounds of treatments with $1.6\mathrm{M}$ of cementation solution. In this way, a bioslurry-based waterproofing layer was formed for the construction of a water pond. Due to the bonding strength gained from calcium carbonate crystal precipitation, the flexural strength of bioslurry layer was in the range of 3.6–4.2 MPa. This is sufficient to support the hydrostatic pressure and avoid bending for water pond. With the low seepage rate and high flexural strength, the proposed bioslurry layer is a promising method for the construction of a fishpond in sand; other potential applications include stabilization of sand dunes and concrete healing.

In this investigation, polyethylene terephthalate (PET) fibers obtained from the plastic bottles were used in engineered cementitious and geopolymer composites (ECC and EGC). These composites were compared with polyvinyl alcohol (PVA) and polypropylene (PP)–reinforced ECC and EGC. A total of eight mixtures (four for ECC and four for EGC) were prepared with 0% to 2% volume fraction of fibers. In each ECC and EGC series, one mixture was a control (without fibers) and a 2% volume fraction of PET, PVA, and PP fibers were added in the remaining three mixtures. The specimens prepared using these mixes were tested to failure under bending, compression, and direct tension to observe the multiple cracking and pseudo-strain-hardening (PSH) response associated with ECC. The flexural load–deflection response of fiber-reinforced ECC and EGC was observed and compared with the control mix without fibers. Besides mechanical properties, the field emission scanning electron microscopic (FESEM) images were also envisaged to observe the microstructure of the composites. It was found that the behavior of PET fiber–reinforced ECC and EGC in terms of mechanical properties was better among all combinations. PET fiber–reinforced ECC and EGC were also found competitive to PVA fiber–reinforced ECC and EGC in terms of strength and multiple cracking PSH response.

The adjusted porosity/cement index $\eta /(C_{iv}{)}^a$ showed to be an interesting empirical rational dosage methodology for soil-cement purposes as it inputs into a single parameter the role of the compactness and the amount of cement on the strength of such materials. Ergo, by establishing a specific $\eta /(C_{iv}{)}^a$, the same unconfined compressive strength result could be obtained through several combinations of cement contents and porosity values. Still, such an assertion has not yet been verified for a broad range of distinct dosages within specific $\eta /(C_{iv}{)}^a$ values. The present research intends to address this gap by conducting unconfined compressive strength tests on distinct mix designs established within seven specifics $\eta /(C_{iv}{)}^{0.28}$ values (i.e., 45, 40, 30, 35, 25, 22.5, and 20). At least three distinct dosages were assembled within each adopted porosity/cement index value for compacted clayey sand-cement mixtures. The results within each $\eta /(C_{iv}{)}^{0.28}$ were evaluated by means of Tukey´s multiple comparison test in order to assess the statistical equivalence of the attained strength results for each mixture design setting (dosage). In general, statistical differences were encountered among some dosages within each $\eta /(C_{iv}{)}^{0.28}$ index. Nonetheless, all of the strength results could be successfully correlated to this index with a great coefficient of determination ($R^2=0.97$).

Carbon-filler composite artificial timber was processed and characterized. With a small amount of epoxy binder, the flexural strength was $\sim 18\mathrm{MPa}$. The binder dispersion was achieved through compaction self-assembly, aided by a diluent. The optimum filler material was amorphous graphite; the optimum binder content was $\sim 4\%$ by weight. This study may pave the road to the development of carbon-based green construction materials.