Journal of Materials in Civil Engineering

Because global landfills are filling at a fast rate with waste that can potentially be recycled, it is now time for the development and implementation of sustainable materials in construction. This article investigates the properties of a new generation concrete containing fiber reinforced polymer (FRP), fiber scrap aggregate (FSA), and recycled concrete aggregate (RCA). Although previous research has been undertaken for the use of RCA in concrete, the use of FSA is a new research area and has been found in this study to have exciting potential. Through different replacements of these aggregates in the concrete, both individually and in combination, conclusive test results were produced. The results indicate that both the fresh and hardened RCA concrete properties were similar to those of the control concrete containing only natural aggregate. In the case of fresh properties, the RCA concrete experienced slightly lower slump than the control concrete. The FSA concrete had a lower compressive strength than the control concrete; however, it produced sufficient strength for nonstructural applications. The results determined for FSA and RCA concrete were better than expected and illustrate the potential for concretes be used for nonstructural and structural applications. The results found for the combination batches indicate that both their fresh and hardened properties produce values between the individual RCA and FSA concrete batches that were mixed and tested. The conclusions drawn from this research will hopefully encourage further development of new sustainable materials in the construction industry.

Fine tuning of concrete recycling processes requires a comprehensive understanding of the overlapping interactions and effects of the various influencing parameters. The most important parameters associated with recycled concrete aggregate (RCA) production that may affect quality and yield include such properties of the parent concrete as the composition, strength and aggregate grading, type of crushers used, number of crushing stages, the size of the RCA particles, and the size reduction sequence. The effects of such parameters overlap and interact with one another and render it impossible for firm conclusions to be drawn on the effects of one parameter in isolation as evidenced by results reported in available literature. The present paper reports on the findings of an experimental study on the concomitant effects of the strength of the parent concrete, size of the natural aggregates used in the parent concrete, and the number of crushing stages on the properties of coarse recycled concrete aggregates, including mortar content, water absorption, bulk density, Los Angeles abrasion loss, and compressive strength of the recycled aggregate concrete. The study is confined only to granitic coarse aggregates, as this is the only type used in Singapore for ordinary concrete.

Knowledge of microscopic geomorphic structures is critical to understanding transport processes in porous building materials. X-ray scans were obtained of a variety of commonly used porous building materials to both qualitatively and quantitatively evaluate their pore structures. The specimens included natural materials (two sandstones and a limestone) and engineered materials (three types of concretes and a brick). Scanned images were processed to reconstruct the geomorphic structures of these materials. Random walk analyses were performed on the reconstructed pore structures to estimate macroscopic transport properties (including tortuosity, specific surface, and permeability). The effective porosity and permeability of these materials were also experimentally determined and compared to computed values. Calibration of the threshold pixel value used in the postprocessing of X-ray images against measured effective porosity appears to be a more appropriate method of selecting this value than the typical approach, which employs selection based solely on observed histograms. The resulting permeabilities computed by using a calibrated threshold pixel value compare better with the measured permeabilities. This study also demonstrates that the relatively homogeneous and heterogeneous pore structures associated with the natural and engineered building materials under investigation can be captured by X-ray tomography.

The master curve of an asphalt binder provides a relationship between the binder stiffness and reduced frequency over a range of temperatures and frequencies. Accordingly, the master curve makes it possible to predict viscoelastic properties over a wide frequency range and also to predict viscoelastic properties at any temperature. To construct a master curve, the stiffness of an asphalt binder at multiple temperatures and frequencies is measured. The data are then fitted into a viscoelastic model applied to asphalt binders. Recently, a methodology has been developed that utilizes the measured dynamic modulus of a hot-mix asphalt (HMA) mixture and the master curves for the as-recovered binders to determine the degree of blending between aged and virgin binders in asphalt mixtures that incorporates recycled materials. This study presents the methodology for constructing asphalt binder master curves in a step-by-step format. The study also describes in a step-by-step format the methodology for evaluating the degree of blending between aged and virgin binder. Furthermore, to clarify the method and elaborate on the analysis of experimental results, plant-produced mixtures containing different percentages of recycled asphalt pavement (RAP) were obtained and tested. The test results were used to develop the master curves and examine the degree of blending by the aid of the methodology explained in the paper.

The application of ultrahigh performance concrete (UHPC) as an alternative to conventional concrete has grown rapidly in recent years. However, to date, little is known about the confinement behavior of UHPC, knowledge that is necessary to develop design guidelines for UHPC columns. In a previous study, the authors investigated the stress-strain behavior of a series of UHPC-filled fiber-reinforced polymer (FRP) tubes with different fiber types and thicknesses under uniaxial compression. The FRP confinement was shown to significantly enhance both the ultimate strength and strain of UHPC. It was also shown that the existing confinement models are incapable of predicting the behavior of FRP-confined UHPC. Therefore, in this study, two commonly used FRP confinement models are recalibrated based on test results of FRP-confined UHPC. A model was further modified based on the stress-strain model of unconfined UHPC to better capture the linear response of UHPC before the activation of FRP confinement. A comparison of the three models showed that a recalibrated model provides the most accurate prediction of the stress-strain behavior of FRP-confined UHPC in terms of the stress-strain curve and ultimate strength and strain.

This paper investigates the feasibility of developing ultrastrength high-performance flowable concretes made with a high content of supplementary cementitious materials (SCMs). A total of 25 concrete mixtures were prepared and tested. Mixtures were divided into three different groups with water-to-cementitious materials ratios ($\mathrm{w}/\mathrm{cm}$) of 0.3, 0.33, and 0.37, respectively. All mixtures were prepared to achieve a target slump flow equal to or higher than 500 mm (24 in.). The control mixture for each group was prepared with 100% portland cement whereas all other mixtures were designed to have up to 70% of portland cement replaced by a combination of SCMs such as class C or class F fly-ash, granulated blast furnace slag, and silica fume. The properties of fresh concrete investigated in this study include flowability, deformability, filling capacity, air content, and resistance to segregation. In addition, the compressive strength at 1, 7, 28, and 90 days, the unrestrained shrinkage up to 90 days, and the concrete permeability were also investigated. A critical analysis for the properties of fresh and hardened concrete shows that ultrastrength high-performance flowable concrete can be developed with low $\mathrm{w}/\mathrm{cm}$ and up to 70% of cement replaced by supplementary cementitious materials. Properties of such concrete are superior to those of the control mixture made with 100% portland cement.

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio ($\mathrm{w}/\mathrm{cm}$) to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying $\mathrm{w}/\mathrm{cm}$, cementitious content, and binder type were prepared and tested. The fine aggregate-to-total aggregate ratio was held constant for all the mixtures. Fresh and hardened concrete properties of the mixtures were determined at various ages. Test results have shown that approximately 1.5 times more paste by volume is required than voids between the aggregates to achieve a minimum performance in concrete for pavements. For a given $\mathrm{w}/\mathrm{cm}$, strength is independent of cementitious content after a critical value is provided. When $\mathrm{w}/\mathrm{cm}$ is constant, increasing paste content increased chloride penetrability and air permeability.

This investigation reports the viscoelastic solid to fluid transition of asphalt as the temperature is varied. Air blown, blended asphalt and pitch obtained from Arab mix crude were tested under unaged, short-term aged, and long-term aged conditions. All the materials were subjected to two experimental protocols in the 20–50°C temperature region. In the first experimental protocol, the material was subjected to frequency sweep in small amplitude oscillatory shear and in the second protocol the material was subjected to large deformation stress relaxation. From the analysis of the experimental results, it was seen that asphalt exhibited a viscoelastic solid regime, a viscoelastic fluid regime, and a transition regime in the temperature range tested. In the small amplitude oscillatory shear, the transition regime was captured using a frequency-dependent storage modulus ($G^{\prime }$)—loss modulus ($G^{″}$) crossover. In the stress relaxation experiments, the material exhibited three distinct slopes and the transition temperatures were identical with what was seen for frequency sweep experiments. The transition regime for blended and air blown asphalt varied from 15–35°C and the transition temperatures shifted to higher values as the material aged. The variation of damping energy and the failure of time temperature superposition principle also confirmed the transition from viscoelastic solid to viscoelastic fluid behavior in such temperature regions.

This paper reports the properties of concrete containing recycled coarse aggregate (RCA) sources from local construction and demolition (C&D) wastes and fly ash (FA) sourced from Western Australia (WA). The RCA is used as 25, 50, 75, and 100% (by weight) replacement of natural coarse aggregate (NCA). In addition, the effect of 40% (by weight) class F fly ash as partial replacement of cement on the properties of recycled aggregate concrete is also evaluated. The properties of concrete evaluated are the compressive strength, indirect tensile strength, flexural strength, and water absorption. All properties are measured at 7, 28, 56, and 91 days. The results show that better compressive, tensile, and flexural strength of concrete containing 25% RCA as partial replacement of NCA can be obtained in recycled aggregate concrete. However, in the case of recycled aggregate concretes containing 40% fly ash, the compressive strength at later ages, such as at 56 and 91 days is increased but the indirect tensile and flexural strengths are decreased at all ages. It is observed that the water absorption is decreased as RCA content increased. It is also observed that the water absorption is decreased significantly in recycled aggregate concretes containing 40% fly ash at all ages.

The main objective of the present study is to quantify the influence of important factors such as fly ash content, dolime content, and curing period on the shear strength and stiffness characteristics of copper slag–fly ash–dolime (CFD) mix for its effective utilization in the base course of flexible pavements. Unconfined compression tests are conducted on specimens with different fly ash (10–40%) and dolime (0–20%) contents cured up to 28 days. A mix of 20% fly ash and 80% copper slag stabilized with 15% dolime was found to be the optimum for use in the base course of flexible pavements. Next, durability tests and unconsolidated undrained triaxial tests are performed on the optimum mix. The strength achieved after 28 days of curing period for the optimum mix was found to be least susceptible to the effect of alternate wet and dry cycles. Empirical relationships are developed to estimate important design parameters such as deviator stress at failure, elastic modulus, and cohesion of the stabilized mix, which can be used to determine dolime and fly ash contents to achieve a target strength within a given curing period. Finite-element analyses of a five-layer flexible pavement system are carried out; and the equivalent thickness, service life ratio, and cost-effectiveness of CFD mix in relation to the conventional water-bound macadam (WBM) layer are evaluated.

Given the schedule pressure of lime-stabilized soil construction, many agencies specify the use of elevated temperature (e.g., 41°C), shorter duration (e.g., 5–7 days) accelerated specimen curing for unconfined compressive strength ($q_u$) testing and acceptance as a proxy for $q_u$ of specimens normally cured under 28-day 23°C conditions. Moreover, lime and highway transportation industry associations prescribe a unique accelerated curing regime for all lime-stabilized soils (7-day, 41°C). This paper presents the results from a laboratory investigation of stress-strain-strength development of four lime-stabilized soils under 2–8 day 41°C accelerated curing and the 0–28 day 23°C normal curing regime. Specimens cured at 41°C reached $q_u$ values equivalent to 28-day 23°C $q_u$ after 1.8–5.9 days. Accordingly, 7-day 41°C curing overestimates 28-day normal cure $q_u$ by 13–260%. When combined with a detailed analysis of data available in the literature, the results illustrate that the prescription of a unique equivalent accelerated curing regime is oversimplified and can lead to significant overestimation of design $q_u$.

Reclaimed asphalt pavement (RAP) and warm mix asphalt (WMA) have become the primary methods for enhancing sustainability in the asphalt industry in recent years. To further enhance sustainability benefits, asphalt producers have begun using RAP and WMA in combination. Research to date has focused on evaluating WMA-RAP mixtures in terms of moisture sensitivity and permanent deformation characteristics as measured in laboratory performance tests. In the present paper, the authors investigate a set of WMA mixtures that encompass a variety of variables, including four WMA additives (Evotherm 3G, Rediset LQ, Sasobit, and Advera) and three RAP contents (0, 15, and 45%). A common belief among practitioners is that the reduced aging in the asphalt binder associated with lower production temperatures in WMA mixtures leaves additional headroom for the incorporation of higher amounts of RAP, which is generally a stiffer, more brittle material. To fully characterize the performance of WMA-RAP mixtures, the authors evaluated the low-temperature, cracking behavior of these mixtures in conjunction with moisture and rutting resistance characterization. They achieved the low temperature testing of WMA-RAP mixtures through the disk-shaped compact tension [DC(T)], indirect tension (IDT) creep compliance, and acoustic emission (AE) tests. Test results showed that chemical additives improved moisture susceptibility according to the AASHTO T 283 standard test and fracture and bulk stress relaxation characteristics using the DC(T) and IDT tests, respectively. The organic Fischer-Tropsch wax-modified WMA mixtures performed the best among the WMA mixtures in terms of rutting resistance. The introduction of RAP led to the increased resistance to permanent deformation and moisture damage. Conversely, RAP reduced thermal cracking resistance according to the low-temperature performance tests in both HMA and WMA. The authors observed the same trend in AE test results as WMA-RAP mixtures exhibited warmer embrittlement temperatures as compared with control mixtures and are therefore expected to be more prone to thermal cracking. On the basis of these findings, thermal cracking resistance remains an issue to be considered in WMA mixtures containing RAP. Additionally, performance testing has shown to be a valuable tool for the evaluation of RAP and WMA mix designs to avoid performance issues in the field.

Remediation methods and strength predictions were evaluated for wood I-joists with single, circular holes in the webs, leaving utilities in place. A full-scale bending test using four equally spaced point loads was applied to three depths of joists with varying flange widths and span lengths of 4.88 and 2.44 m. Failure modes for long-span joists without holes were in the flanges in tension, compression, or lateral buckling, but once a hole was introduced, the majority failed in shear. The curved beam approach and manufacturers software were used to predict strength. Seven remediation techniques were investigated initially, and remediation effectiveness was evaluated on the basis of strength, stiffness, and ease of installation/cost. The oriented strand board (OSB) collar remediation worked very well and returned 8 of 12 series of joists to a strength statistically equivalent to the “no hole” condition. The OSB collar was not quite as effective in returning stiffness to the joists but was easier to install and less expensive than a laminated strand lumber patch.

The objective of this study is to investigate the effectiveness of an alternative technique for strengthening masonry columns, based on the use of steel cords. Although fiber-reinforced polymer (FRP) strips or jackets are successfully used as strengthening elements for this kind of application, such a strengthening method represents a new opportunity to restore ambit, with considerable development in unreinforced masonry wrapping. Thus, to assess the potential of steel cord wrapping, this paper presents the results of an experimental program consisting of 48 solid-brick specimens subjected to uniaxial compression load. Different cross-section geometry (octagonal, square, and rectangular) and different amounts and different schemes for confining reinforcement were investigated. The primary experimental outcomes are presented and discussed in the paper considering the mechanical behavior of specimens and the axial stress–axial strain relationships. Test results have shown that the investigated confining systems are able to provide significant gains, both in the compressive strength and in the deformation capacity of masonry columns.

Results of an extensive series of repeated load triaxial tests performed on three major recycled construction and demolition (C&D) materials at various moisture contents and stress levels were analysed to ascertain their performance in pavement subbases. The development of the resulting permanent deformation that accumulates with the repeated loading and the determination of resilient modulus by two phases of the test are described. The experimental study shows that the C&D materials perform satisfactorily at a moisture content of about 70% of their optimum moisture contents. Furthermore, the C&D materials also satisfy the two-parameter and three-parameter models. The results of this study indicate that, at a density ratio of 98% compared to maximum dry density obtained in the modified proctor test and with moisture contents in the range of 65–90% of the optimum moisture content, most of the recycled C&D materials produce comparatively smaller permanent strain and greater resilient modulus than natural commonly used granular subbase materials in pavement subbase applications.

Carbonation of concrete under various humidity conditions was examined in this study. Cylindrical specimens were subjected to accelerated carbonation using 50% carbon dioxide by volume at 25°C. Two relative humidities (RHs) (70 and 90% RH) and two humidity cycles (70–90% and 50–90% RH) were applied during the process. The results showed that carbonation of concrete was affected by the ambient humidity, humidity cycles, and surface geometry. The extent of carbonation was quantified using the coefficient of carbonation, which is the ratio of the carbonation depth to the square root of time. The maximum coefficient of carbonation occurred at 70% RH, and humidity cycles induced coefficients of carbonation between those induced at 70 and 90% RH. Specimens with curved surfaces had higher coefficients of carbonation than specimens with plane surfaces. The carbonation coefficients measured in the accelerated tests were also related to the carbonation of on-site concrete, which indicates that taking humidity cycling into account results in better prediction of accelerated carbonation than assuming a single humidity.

When hot mix asphalt (HMA) overlays are placed on distressed flexible or rigid pavement, it is only a matter of time before cracks in existing pavement reflect to the new overlay surface. Asphalt rubber membrane interlayer (ARMI) is one type of interlayer system that has been suggested to mitigate reflective cracking in HMA overlay. However, in terms of reflective cracking performance, mixed results were reported. Also, the ARMI layer has the potential to contribute to instability rutting. In this study, composite specimen interface cracking (CSIC) tests were performed on composite specimens constructed with and without the ARMI layer to evaluate its effects on HMA overlay reflective cracking performance. HMA fracture mechanics was employed to characterize the mechanism of ARMI layer effects on HMA overlay reflective cracking resistance. Results indicate that ARMI not only cannot delay reflective cracking, but it also reduces reflective cracking resistance to some extent.

The effects of portland cement (PC) replacement with magnesia (reactive magnesium-oxide) on properties of PC-based pastes, mortars, and concretes were investigated. The research included determination of mechanical properties and frost durability in addition to studies of the microstructure and microchemistry. The mortar and paste mixtures contained from 10–80 weight percent (wt%) replacement of PC by magnesia and had water to cementitious-binder ratios from 0.4–0.7, whereas concretes contained from 5–10 wt% magnesia and had a water to cementitious-binder ratio of 0.53. Replacement of PC by magnesia had adverse effects on the mechanical properties and frost durability. The magnesia reduced microcracking of the binder matrix in comparison with pastes containing only PC. The primary hydration product of magnesia was brucite in addition to regular hydration phases of PC. The amount of formed portlandite was increased. Magnesia caused densification of the microstructure but also increased the capillary porosity, resulting in lower frost-durability.

The authors investigated the ability of different high-performance concrete (HPC) composites to restrain an alkali-silica reaction (ASR) in the presence of reactive aggregates. They evaluated the effectiveness of different binary and ternary blended cementitious systems comprising optimized contents of pulverized fly ash (PFA) and silica fume (SF) in suppressing ASR expansion. They assessed different mortar mixtures made of different contents of PFA (up to 40%) and SF (up to 15%) with water-to-binder (W/B) ratios of 0.27 for ASR expansion according to standard procedures for accelerated mortar bar test. The results showed a given pessimal combination among the ternary mixtures in which there was an obvious synergistic interaction where ASR expansion was at its minimum level.

The establishment of a cement concrete dielectric constant model is the basic and key technique for applying the electromagnetic wave technology to concrete structure quality testing and internal damage detection. Based on the characteristics of the cement concrete, a new dielectric constant model is developed in theory after the linear model, the root-mean square model, and Rayleigh model are analyzed comprehensively. Dielectric constants of cement concrete are measured using hardware to evaluate components and circuits for frequency ranges. The theoretical analyses and experimental studies show the proposed model precision is highest and most suitable to interpret cement concrete dielectric properties when compared with the other three models.

A new product, steel-reinforced high-density polyethylene (SRHDPE) pipe, with high-strength steel reinforcing ribs wound helically and covered by corrosion-resistant high-density polyethylene (HDPE) resin inside and outside has obvious advantages. To investigate the behavior and performance of such a new pipe, three parallel plate tests were conducted in air. The deflection profiles of the pipes and the strains on both steel and polyethylene plastic were measured. No cracking was observed on the plastic during the experiment. The photogrammetry technology was effective in measuring the deflection profiles of the pipes during loading. The light detection and ranging (LiDAR) technology could obtain three-dimensional images of the pipes but was suitable for stationary targets. Strain gauge data indicated the occurrence of out of plane buckling of the steel ribs at failure and the strain incompatibility between the steel ribs and the plastic cover during loading.

The behavior of soil-geosynthetics interfaces depends on the different properties of soil, including particle size, particle shape, density, gravimetric water content, degree of saturation, and properties of geosynthetics that include structure, texture, and other elements. This paper pertains to the study of the influence of the particle shape of sand on the behavior of the sand-geotextile interface. Experiments were conducted using a conventional-sized direct shear box modified for interface testing. In the present study, two different natural sands (one with angular particles and the other with rounded particles) and two different geotextiles were used. The results showed that particle shape significantly influences the interface behavior, especially the postpeak behavior.

The phase separation between polymer additives and virgin asphalt binders during hot storage is an important issue in the asphalt industry. Traditionally, it has been customary to evaluate the degree of phase separations in polymerized asphalts by laboratory testing, such as the cigar tube test (CTB). However, the test circumstances, temperature, and storage time vary depending on different standards used in many countries. Based on a comprehensive literature review, the range of temperatures and oven storage times were selected to be 140–180°C and 2–7 days, respectively. The phase separation of 11 storage stability conditions selected from 12 different places using crumb rubber modified asphalts (CRMAs) were compared and evaluated in this study. The CRMAs produced in the laboratory were made with PG 64-22 virgin binder and ambient crumb rubber with various concentrations (10, 15, and 20% by weight of virgin binder). The CTB was used as the storage stability test method, and percent separation was obtained from the $G^{*}/\sin \delta$ relationship between the top and bottom portion of the tube. The storage stability tests indicated that the viscosity of the CRMAs had a significant influence in the phase separation of the binders; the higher the viscosity of the binder, the less the degree of the separation.

This paper presents a study in which a universal-type test machine was configured to apply torsion load-to-failure to estimate the orthotropic shear strengths of full-size laminated veneer lumber (LVL). The objective of the study is to provide insight and detail to a lesser known torsion test setup, while at the same time estimating the torsional shear strength of 1.9E eastern species LVL, hitherto unknown. It was found that at large angles of twist of approximately 23° or more, the test apparatus experienced slippage at the bearings and had the potential to become unstable due to high lateral forces. This was not an obstacle for calculating the shear strength of LVL in this study, as it is a relatively noncompliant material, but likely would be an issue for more compliant materials. The mean in-plane and through-thickness plane shear strengths of 1.9E eastern species LVL were estimated to be in the range of 7.2–11.2 MPa and 5.9–7.3 MPa, respectively.

Polyurea is a polymeric material that can be used to provide environmental protection and structural enhancement. In this study, a low modulus polyurea coating, having high elongation, high energy absorption capacities, and a fast gel time, was sprayed under field conditions onto the surfaces of high-performance cementitious composites (${\mathrm{HPC}}^2$). Flexure tests were conducted to measure toughness so that predictions could be made regarding the impact performance of two uncoated and coated matrices, one containing polyvinyl butyral (PVB) as the only aggregate, the other with polyvinyl alcohol (PVA) fibers added for reinforcement. Results from the flexure tests showed that encapsulation by plain polyurea increased the flexural strength of specimens by at least 60%. Results from drop-weight tests showed that the PVA fibers helped to improve impact resistance. A visible reduction in damage was seen when polyurea was applied to one surface, more so by coating the tension side opposite the striker. Coating both surfaces further increased impact resistance.

The feasibility of steel slag powder as a combined admixture with ground granulated blast-furnace slag (GGBFS) in cement based materials was explored. The effects of steel slag powder on the normal consistency water requirement, setting times, compressive strength, and hydration products of cement paste/mortar were studied. The results showed that the preferred additional content of steel slag powder in a combined admixture was less than 20%. Steel slag powder decreased the normal consistency water requirement and retarded the setting time of cement paste. With curing ages increasing, the compressive strength of mortars with the combined admixture increased rapidly, even higher than that of the blank sample. Hydration products primarily included C-S-H gel, C-S-Al-H gel, and $\mathrm{Ca}(\mathrm{OH}{)}_2$. Mixing these two powders of GGBFS and steel slag powder had a positive effect regarding the hydration of steel slag powder. Additionally, this research contributes to our understanding of how to sustainably manage industrial wastes and has the potential to provide several important environmental and economic benefits.