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In this investigation, four types of sands as alternatives to river sand, namely, crushed sand (CS), marine sand, fine recycled concrete aggregate (FRCA), and fine reclaimed asphalt pavement (FRAP), were studied for their potential for cement-concrete pavement applications. Initially, the physicochemical and morphological characteristics of these sands were understood and later linked to the hydration kinetics and the behavior of cement-mortar systems in both the fresh and hardened states. Due to their evenly graded particle size distribution, CS and FRCA exhibited higher packing densities despite having more gradient angularity, whereas the interlocking capacity of FRAP was found to be affected by the agglomerated particles. Morphology, fineness modulus, and chemical composition of the sands were observed to be the dominating parameters affecting the hydration kinetics and thus the performance of the mortar mixes. Improving these parameters, especially the grain size distribution, could help in enhancing the potential of these sands for pavement applications. [ABSTRACT FROM AUTHOR]

Pavement engineers are paying attention to the stabilization of granular layers in the modern era of sustainable construction. A well-drained pavement can extend the service life to its design life if properly designed and maintained. The water infiltrating into the pavement causes detrimental effects and reduces the service life of the pavement. The open-graded cement-stabilized macadam (OGCSM) can act as a drainage layer in sustainable pavements. Cement cannot be considered as a long-term sustainable material due to its high carbon footprint. This paper investigated the suitability of a supplementary cementitious material, ground granulated blast furnace slag (GGBFS), as a partial replacement of cement in OGCSM, a drainage layer in pavements. The strength and permeability characteristics of the mix were studied using an unconfined compressive strength (UCS) test and specially fabricated permeameters, respectively. OGCSM was optimized at 7% cement content, and cement in the OGCSM was partially substituted with GGBFS at various replacement levels. The mix was optimized at 80% replacement of cement with GGBFS, which satisfied the specified requirements for strength, permeability, and durability. The UCS, coefficient of effective permeability, and water resistance index of the optimized mix were 2.88 MPa, 60.58 m/day and 96.33%, respectively. The morphology and mineralogy characteristics of the optimized mix were determined to justify the strength gain in cementitious mixtures. The porosity of the OGCSM mix was estimated as 25.86% using computed tomography (CT) scanned images. The subsurface drainage design was carried out using drainage requirements in pavements (DRIP 2.0) software, and the quality of drainage was rated as good. [ABSTRACT FROM AUTHOR]

This paper presents research about a mixture design method of pavement concrete coblending rubber and fiber into ordinary concrete. Mechanical-based tests regarding the compressive strength, elastic modulus, splitting tensile strength, flexural strength, and four-point bending stiffness were conducted to evaluate the flexural toughness of concrete, and a slab-based three-point bending test was designed to evaluate the bending toughness improvement of the road pavement concrete slab. The results indicated that with the increase in single rubber content, the compressive strength and elastic modulus of concrete decreased continuously. The rubber concrete specimen remained relatively complete in appearance during destruction, showing the satisfied ductile failure characteristics to pavement usage with the optimal rubber content of 10%. After adding basalt fiber (BF) or polypropylene fiber (PPF), with the increase of fiber content, the bending stiffness of concrete decreased, the corresponding deflection of peak load increased continuously, and the bending deformation capacity of concrete could be significantly enhanced. Compared with the reference group, when the rubber content is 10%, and basalt fiber content is 0.5%–2%, the equivalent initial bending strength of fiber-reinforced rubber concrete is increased by 105.4%–164.4%. In general, BF is better than PPF in improving the toughness of rubber concrete, and the optimal dosage of BF is 1% of concrete volume in this test. When loaded to the limit load, the deflection of the basalt fiber–reinforced rubber concrete slab in the middle of the bottom span was about four times higher than that of the benchmark concrete slab, the bending deformation capacity and toughness of the basalt fiber–reinforced rubber cement concrete slab have been greatly improved. From the test results, the mixture design method of flexible pavement cement concrete based on rubber and fiber coblending was proposed, which contributes to the development of flexible materials for concrete pavement. [ABSTRACT FROM AUTHOR]

An investigation was carried out to analyze the flexural fatigue performance of pavement quality concrete (PQC) of M40 and M50 grades, made with conventional materials out of which river sand (RS) was replaced by copper slag (CS) by varying concentrations to the extent of 100% by volume. Experiments were conducted in the laboratory to determine the 90-day flexural strength of PQC samples (100×100×500 mm) under four-point loading. Based on respective flexural strength, repeated loads were applied for the conduct of flexural fatigue tests of PQC specimens at stress levels of 0.7, 0.8, and 0.9, each at 1 Hz frequency. In terms of fatigue life distributions, the flexural fatigue performance of several PQC mixtures has been evaluated. Three methods were used to estimate various parameters for the Weibull distribution. It is observed that the fatigue life distribution of both M40 and M50 grade PQC mixes made with CS can be modeled by a two-parameter Weibull distribution with a correlation coefficient of more than 0.95. The estimation of fatigue life of PQC mixes has also been done at different failure probabilities. The 90-day flexural strength of PQC mixes (both grades) with CS replacing RS, increased compared with conventional PQC. Further, X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) images of PQC mixes confirmed the homogeneity of the concrete. The fatigue performance was also enhanced with CS replacing RS. The goodness-of-fit test also indicated that the present model is valid at the 5% significance level for PQC (both grades) made with CS. [ABSTRACT FROM AUTHOR]

The development of new functional pavement materials and the application of sustainable concepts in road construction have led to a dramatic change in functional roads. Pouring semiflexible pavement (SFP) has superior advantages over traditional concrete and asphalt pavements in terms of road performance and convenient construction. The purpose of this research is to investigate the feasibility of SFP in terms of healing capacity, noise reduction, and electrical conductivity. First, the self-healing properties of the cement-asphalt-aggregate (C-AS-A) interface are analyzed by pull-out test, and the cracking characteristics and crack-healing capacity of SFP are investigated by semicircular bending (SCB) test and X-ray computed tomography (CT), respectively. Subsequently, the noise reduction performance of SFP, asphalt mixture, and cement concrete are compared by tire vertical drop test. Finally, different conductive SFP materials including graphite powder, carbon fiber, and steel fiber are prepared and their resistivity and road performance are analyzed. The results show that the C-AS-A interface has a significant self-healing ability; the cracks in SFP mainly occur at the C-AS-A interface (accounting for 53.12%) at −10°C. Moreover, when heated with microwave radiation, the heating-healing ratio of the SFP specimen increases by 63.33% with the addition of steel fiber. Besides, the noise reduction capability of SFP material is between that of asphalt mixture and cement concrete. By combining graphite powder and carbon fiber, the electrical conductivity and road performances of SFP are significantly improved. The results provide references for further design and development of SFP with heating healing capacity, noise reduction ability, and electrical conductivity. [ABSTRACT FROM AUTHOR]

A magnetite mortar microwave-absorbing layer that could be applied to concrete pavement was studied to improve the deicing efficiency of roads in low-temperature conditions. The magnetite cement mortar (MCM) was prepared by using magnetite as the main absorbing material. The microwave absorption ability and heating characteristics of MCM with different magnetite contents were investigated. In addition, the mechanical and durability properties of MCM were studied. Furthermore, a microwave-absorbing layer was prepared and tested for outdoor field deicing. The result showed that adding magnetite effectively improved the mechanical strength and frost resistance of MCM, which could improve its load resistance and service life. Meanwhile, the microwave absorption ability of MCM was also improved with the increase of magnetite content. At the microwave frequency of 2.45 GHz, the average heating rate of MCM with 80% magnetite content was 2.27 times than that of ordinary cement mortar. In addition, the content of magnetite was positively correlated with the heat transfer ability of MCM. Magnetite conversion of microwave energy into heat energy could quickly transfer heat to the whole mortar system. The field deicing test verified the feasibility of efficiently deicing a magnetite mortar microwave-absorbing layer in low temperature conditions. [ABSTRACT FROM AUTHOR]

Despite numerous advantages, there are a few challenges associated with the designing and fabrication of roller compacted concrete pavement (RCCP) specimens—compaction mechanisms employed in the RCCP mix proportioning, specimen fabrication, and actual pavement construction are different in principle, leading to significant disparity between the field and laboratory performance. To reconcile this discrepancy, an effort has been made to study the effect of compaction on the performance of RCCP. Initially, the effect of different compaction types, namely vibrating table, vibrating hammer, modified Proctor, and gyratory compactor (GY) on the optimum moisture content of RCCP was investigated, then the roles of moisture content and compaction type on dry density, mechanical aspects (compressive strength, indirect tensile strength, and flexural strength), rideability, and transport properties (porosity and absorption) of RCCP were elucidated. Also, alternative methods for quantifying the workability and compactability of GY compacted specimens are proposed. The findings from this study suggest employing a particular compaction mechanism both for the mix proportioning as well as specimen fabrication to avoid the under- or overestimation of RCCP performance. [ABSTRACT FROM AUTHOR]

Water has a significant impact on the dielectric constant of materials. As a multiphase composite material, the effect of water content must be taken into account when modeling the composite dielectric of cement concrete. Cement concrete traditionally has been thought of as a three-phase mixed material consisting of mortar, aggregate (limestone), and pores (air). Water was used as a constituent material of cement concrete in this paper, and its content was described in terms of water saturation. By abstracting the components of cement concrete into independent medium units and arranging them according to certain rules, the four-phase mixing model of cement concrete can be established. To investigate the effect of water, the dielectric constant of cement concrete was measured using a network analyzer at various water saturation levels. The experimental results show that water significantly can enhance the dielectric constant of cement concrete, and this effect is related to porosity: the higher the water saturation, the faster the dielectric constant increases. According to the established concrete four-phase mixed model, combined with the parallel plate capacitor theory, a composite dielectric model considering water saturation was developed which can improve the prediction accuracy under different water saturation conditions and provide a foundation for the application of ground-penetrating radar (GPR) in the quality inspection of cement concrete pavement. [ABSTRACT FROM AUTHOR]

This research documents the real-world performance of a new pavement product for use in cold regions—steel fiber-reinforced rubberized concrete (SFRRC). During the previous phase of this research, SFRRC underwent laboratory testing as proof of concept. During the current phase, precast slabs of SFRRC was installed on a public road, Abbott Road, in the Municipality of Anchorage, Alaska and monitored in the field using visual inspection, a continuous collection of strain gauge data, deflection measurements, rut depth, skid resistance, and other measures. The current location of the SFRRC is considered a high-traffic urban arterial, which makes it an effective location to study rutting, freeze-thaw resistance, falling weight deflection, skid resistance, and life-cycle cost. A comparative analysis was conducted using the same measuring techniques on hot mix asphalt (HMA) on an adjacent road section built at the same time. The results show that the SFRRC road sections have significantly better rutting resistance compared to the adjacent HMA road section, and the results of the freeze-thaw resistance and deflection field testing validate the results of the laboratory testing performed as part of an earlier phase. Furthermore, comparative life-cycle cost analyses of SFRRC and HMA justifies the use of SFRRC in roadway construction in cold regions in terms of cost effectiveness, enhanced performance, and extended life. The outcome of this research recommends the use of SFRRC for highway intersections and/or test sections on major arterials as the next phase of introducing this material for roadway construction in cold regions. The newly developed material of steel fiber-reinforced rubberized concrete (SFRRC) can be readily utilized in the construction of pavement structures where issues of short pavement life are a concern in northern climates as a result of the use of studded tires. This new material addresses the shortfalls of the use of Portland cement concrete (PCC) pavement under very low temperatures, such as micro-crack development, as a result of the freeze-thaw cycles by utilizing the added rubber in that it is readily able to expand and contract. In addition, the added steel fiber will enhance the resistance of crack development under low temperatures. Furthermore, this new material can be an alternative to Portland cement concrete pavement, where premature failures like joint cracking or raveling can occur. SFRRC is more cost-effective than traditional hot mix asphalt (HMA) pavements as it can prolong the life of the pavement and lead to less pavement maintenance costs over time. [ABSTRACT FROM AUTHOR]

Porous asphalt concrete (PAC) is an open-graded asphalt concrete with a high air void, which functions as permeable pavement with high surface frictional resistance. PAC typically requires a high amount of coarse aggregate to provide the required porous structure. An expensive high-quality polymer-modified asphalt (PMA) is commonly required to prevent draindown issues and to improve the performance of PAC. Bottom ash (BA), a high-porosity byproduct from coal-fired power plants, is used as a greener product to improve the quality of traditional asphalt cement penetration grade 60/70 (AC 60/70) for producing low-cost PAC in this research. The effect of the BA replacement ratio (0%, 10%, 15%, 20%, and 25% by total weight of fine aggregate) on the draindown, loss of particle, Marshall properties, indirect tensile strength (ITS), indirect tensile resilient modulus (IT Mr), indirect tensile fatigue life (ITFL), permanent deformation (PD), rut depth, and skid resistance of BA-AC60/70-PAC were measured and compared with PMA-PAC. The draindown and particle loss values of BA-AC60/70-PAC were found to decrease with an increase in the BA replacement ratio. The BA replacement improved the Marshall properties, strength index, ITS, IT Mr , ITFL, PD, rut depth, and skid resistance of PAC up to the highest value at the optimum BA replacement ratio of 20%. The improved ITS is associated with the improved IT Mr in a linear relationship for all BA replacement ratios. The change in ITFL was found to be linearly related to IT Mr at a specific stress level. At the same design criteria, the 20% BA replacement ratio yields the reduction of total construction cost of BA-AC60/70-PAC surface course by 33% benchmarked to the conventional PMA-PAC surface course. [ABSTRACT FROM AUTHOR]

Waste clay brick (WCB) accounts for a dominant fraction of construction and demolition waste, and it is necessary to explore the sustainable measures of it as a construction material in civil engineering. This paper evaluated the effect of WCB content on the performance of cement-stabilized recycled concrete aggregate (RCA) in pavement base/subbase applications. Based on the microscopic tests and laboratory tests of the aggregate, the compaction test, unconfined compressive strength (UCS) test, indirect tensile strength (IDT) test, resilient modulus test, freeze and thaw cycling test, and drying shrinkage test were conducted with the different WCB content cement-stabilized RCA/WCB blends. A trial pavement section was paved based on the test results, and finite element analysis (FEA) was carried out to investigate the effect of cement-stabilized RCA/WCB blends on asphalt pavement. It is concluded that the potential utilization of pozzolanic properties of WCB plays an important role in pavement applications. The moderate content of WCB fine aggregate is beneficial for the UCS, IDT, resilient modulus, freeze and thaw cycling, and drying shrinkage of cement-stabilized RCA/WCB blends, while the content of WCB coarse aggregate influences the test results to a worse degree. Besides, the performances of the trial pavement section comply with the pavement design and specifications. Furthermore, the results of FEA indicate that the maximum vertical displacement and von Mises stress increase with the reduction of the resilient modulus. This paper gives systematic research on the effect of WCB content on cement-stabilized pavement base/subbase applications, and it may improve the potential application of cement-stabilized RCA/WCB blends in pavement base/subbase. [ABSTRACT FROM AUTHOR]

Mixed mode I–II fatigue fracture of concrete is commonly encountered in practical engineering. Accurate prediction of the fatigue crack propagation process and fatigue life is essential to evaluate the safety of concrete structures. In this study, the mixed mode I–II fatigue crack propagation process of the three-point bending (TPB) beam is investigated based on the digital image correlation (DIC) method. The results indicate that the mixed mode I–II crack propagation path under fatigue loading is consistent with that under static loading, and the stress intensity factor (SIF) corresponding to the unstable failure of concrete is constant, regardless of the fatigue load level and specimen size. Based on the experimental results, a unified model for characterizing mixed mode I–II fatigue crack propagation in concrete is developed, where the equivalent SIF amplitude composed of mode-I and mode-II SIF amplitude is introduced into Paris law, and the statistical analysis is conducted to determine the probabilistic distribution of the empirical constant in Paris law. Furthermore, the feasibility of predicting the fatigue life of concrete structures is explored using the proposed model. It is concluded that the fatigue life with different reliability can be obtained when the mixed mode I–II fatigue crack propagation path is determined based on static tests. It is expected that the developed model contributes to the prediction of fatigue life and further safety assessment of concrete structures under fatigue loading. Many concrete structures are subjected to fatigue loads in service, such as concrete pavements and bridge decks suffering from cyclic vehicle loads. Under fatigue loading, the crack gradually propagates, resulting in the fatigue failure of concrete structures. Therefore, it is critical to investigate the fatigue crack propagation process of concrete such that the safety assessment of concrete structures can be conducted. In this study, a prediction model for mixed mode I–II fatigue fracture of concrete is proposed based on the well-known Paris law. When the SIFs at the crack tip are calculated based on the finite-element method, the whole fatigue crack propagation process and fatigue life of concrete structures with different reliability can be reasonably predicted using the proposed model. Furthermore, the stability analysis of fatigue crack and the reinforcement and repair of cracked concrete structures can be conducted timely according to the predicted fatigue crack propagation length and fatigue life. In general, the proposed model is of great significance to guarantee the safety of concrete structures under fatigue loading, e.g., concrete pavements and bridge decks. [ABSTRACT FROM AUTHOR]

The present study investigated the performance characteristics of concrete paver block (CPB) mixes with incorporated reclaimed asphalt pavement (RAP) aggregates under different curing regimes, namely, continuous water curing (WC), air curing (AC1 and AC2), intermittent water and air curing (WAC), water spray curing (WSC) and heat curing (HC). Seven CPB mixes were formulated by volumetrically replacing virgin coarse and fine aggregates partially and in combination with coarse RAP, fine RAP, and combined RAP fractions. For better refinement of agglomerated particles present in the RAP and to achieve a dense microstructure, the block specimens were fabricated using a design methodology that included a staged mixing approach and time-controlled compaction simultaneously with a vibratory hammer and table vibrator. Hardened CPB specimens were tested to assess mechanical (compressive, flexural, and tensile splitting strength) and durability (water absorption, porosity, and carbonation) properties of the concrete. CPBs fabricated from the considered RAP-inclusive concrete mixes manifested great potential to be used for pavement applications having medium to very heavy traffic when cured with the WC, WAC, WSC, and AC2 curing regimes. Curing regimes WAC and WSC, which involved a combination of water and air curing, were found to be the most effective for the RAP CPB mixes, resulting in superior strength properties. The presence of carbonation was detected in all the RAP CPB mixes when exposed to air curing (AC2) for a prolonged period of time. [ABSTRACT FROM AUTHOR]

Investigations into the dielectric properties of concrete form the basis for concrete quality testing and condition monitoring of internal structures when using ground penetrating radar (GPR). The formula used to describe the quantitative relationship between the dielectric properties of composite materials and the dielectric constant and volumetric ratio of each component is known as a dielectric model. In this study, a new dielectric model was deduced from circuit theory on the basis of structural abstraction to calculate the dielectric permittivities of concrete. To validate the applicability and accuracy of the proposed model, because concrete consists of matrix (cement mortar), aggregates (limestone), and air, the dielectric traits of concrete and its components were acquired using an open-ended coaxial probe. Compared with the Brown model, complex refractive index method (CRIM) model, Looyenga model, and Rayleigh model (i.e., the classical models), the results showed that among overall predictions of concrete dielectric constants, the proposed model has the greatest accuracy, because the theoretical results matched the test results more closely. This indicates that the proposed model can better interpret the dielectric properties of concrete, which lays the groundwork for future research into the application of GPR to the nondestructive testing and evaluation of concrete pavement. [ABSTRACT FROM AUTHOR]

The environmental concerns associated with the use of portland cement prompted finding an alternative. As a possible solution to this issue, fly ash–based geopolymer concrete has been developed and implemented in roller-compacted concrete pavement. The mechanical and rheological properties of roller-compacted geopolymer concrete were analyzed, accompanied by the chemical characterization through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDXS) of the optimized samples, which confirmed the formation of geopolymer. The research entailed creating a stepwise mix design to determine the aggregate proportion and particle-size distribution of mixed aggregate that can achieve high packing density, resulting in improved roller-compacted geopolymer concrete properties. The optimized mixture was developed using dry sodium hydroxide (NaOH) to produce roller-compacted concrete, and the mixture characteristics were analyzed in different weather conditions such as humidity and temperature. The compressive strength after 28 days was 58 MPa at ambient curing and 61 MPa at thermal curing conditions. Flexural strength and split tensile strength were 5.5 and 4.2 MPa, and the modulus of elasticity was 33.10 GPa. The designed concrete was tested in the field by filling patches on cement concrete and bituminous pavements and compacting them with a prototype roller developed to test the mutual adhesiveness of the concrete and roller. [ABSTRACT FROM AUTHOR]

Although roller-compacted concrete pavement (RCCP) has been considered the most popular among its counterparts, it has not been widely used due to a number of reasons. The most dominant reason is the variability in mixture proportioning methods and material selection considering its unique behavior compared to conventional concrete mixes. Therefore, the present paper focuses on the above-mentioned parameters by critically reviewing the literature over the past four decades (1984–2021). Initially, the influence of conventional and recycled waste materials on the fresh & hardened state behavior of RCCP is reviewed in detail. Subsequently, the potential applications of various mineral & chemical admixtures and the different types of synthetic and metallic fibers for performance improvement are discussed. In addition, this study has critically appraised various mixture proportioning methods ranging from conventional concrete approaches to empirical, semi-empirical, and theoretical methods for RCCP. The study concludes by noting that all considered materials (alternative aggregates, chemical & mineral admixtures, and fibers) could be used to produce high-quality RCCP; however, an optimal proportion must be prudently selected. Consequently, RCCP could be effectively proportioned by adopting solid suspension, optimal paste volume, and gyratory compaction methods. In addition, it is observed that the strength of the RCCP is related to the aggregate-cement ratio (A/C), water-cement ratio (W/C), and coarse-sand ratio (C/S); the A/C ratio shows an inverse relationship with strength, whereas a mixed behavior between W/C and strength was found. Nevertheless, RCCPs having a vebe time, A/C ratio, and C/S ratio in the ranges of 30–50 s , 5–8 , and 1–1.4 , respectively, could be used for the surface course application of pavements. [ABSTRACT FROM AUTHOR]

Top-down (TD) cracking is the main concrete pavement cracking type in seasonal frozen areas. A two-lift concrete (2LC) pavement, including a polypropylene fiber reinforced concrete (PFRC) top lift and a portland cement concrete (PCC) bottom lift, is proposed to mitigate TD cracking. This study conducted prenotched three-point bending beam tests (3PBBTs) in the laboratory and numerical models have been developed to evaluate the fracture characteristics of concrete materials, including PCC, PFRC, and 2LC, in a freeze–thaw (FT) environment. Based on the double- K fracture model, the fracture characteristics of concrete materials have been obtained. In the mesoscale, progressive damage constitutive models have been developed based on the Mori-Tanaka homogenization theory and three-dimensional (3D) Hashin failure criterion. Three-dimensional finite-element models have been developed to simulate the prenotched 3PBBTs with the progressive damage constitutive models coupled. It has been found in experiments that 2LC has better fracture resistance than PCC with and without FT treatments. Validated by experimental data, the developed FE models are capable of describing the fracture characteristics of concrete materials in the FT environment. Sensitivity analyses on factors that may influence the fracture resistance of 2LC have been conducted. This study validates that the proposed 2LCP has better TD cracking resistance than conventional PCC pavements and also suggests useful measurements enhancing the TD cracking resistance of 2LCP. [ABSTRACT FROM AUTHOR]

Repetitive loads result in increased irrecoverable strain and, consequently, fatigue cracking failure. Fatigue resistance is the prime factor controlling the service life of the concrete pavements. This research study utilized natural rubber latex (NRL) to enhance the mechanical strength and flexural fatigue resistance of normal concrete. The effect of influence factors, such as water to cement (w/c) and dry rubber to cement (r/c) ratios, on the compressive and flexural strengths and flexural fatigue behavior was studied. Normal and NRL concretes were subjected to compressive, flexural, and flexural fatigue tests. At all w/c ratios, a higher r/c ratio resulted in a lower compressive strength but higher flexural strength. The highest flexural strength was found at the optimum r/c ratios of 0.58, 1.16, and 1.73 for w/c=0.3 , 0.4, and 0.5, respectively. Concrete modified by NRL at the r/c ≤ optimum ratio had lower plastic deformation than normal concrete at the same applied flexural stress, hence, higher fatigue life (Nf). As a result, the NRL-concrete pavement at the optimum r/c ratio was found to have a thinner thickness than the normal concrete pavement for the same traffic load conditions at the same service life, which can reduce the operational cost. A cost-effective mix design method of NRL-concrete pavement with the optimized construction (operation and material) cost was also recommended. The outcomes of this research will facilitate the utilization of the NRL additive alternative to synthetic polymer for sustainable NRL-concrete pavement in Thailand and other Southeast Asian and South American countries, which are major global producers of natural rubber. [ABSTRACT FROM AUTHOR]

The alkali-silica reaction (ASR) has been recognized as a major distress in concrete for nearly a century. In the US, ASR is a major cause of the deterioration of highway concrete structures (i.e., bridges and pavements). A research study was recently undertaken in the state of Idaho to evaluate the advantages associated with implementing the miniature concrete prism test (MCPT) from current standards for various reactive aggregates. A total of 11 different aggregate materials (both coarse and fine fractions), including a nonreactive reference aggregate, were collected from various sources and tested using the 56-days MCPT as well as the commonly used accelerated mortar bar test (AMBT). In addition, selected aggregate samples were tested using the 1-year long concrete prism test (CPT) and the 6-month accelerated concrete prism test (ACPT). The results demonstrated that the 56-day MCPT method resulted in higher percent expansion compared with the 14-day AMBT and 1-year CPT methods for the fine fractions of the test aggregates. The coarse fractions of the test aggregates, on the other hand, exhibited a lower percent expansion during the 56-day MCPT compared with the 14-day AMBT. Overall, the MCPT test results were found to correlate well with the 14-day AMBT and 1-year CPT test results. In addition, the 6-month ACPT method showed similar results to the ones of the 1-year CPT method, with high correlation between both methods. Recommendations were made based on the findings from this study to facilitate the implementation of the MCPT into practice by state and local highway agencies for better assessment of the ASR potential of aggregates. [ABSTRACT FROM AUTHOR]

Magnesium phosphate cement (MPC) as a fast-setting material has been widely used in the rapid repair of cement concrete pavement. A decisive role was played in the bonding performance of the repair interface between MPC and portland cement concrete (PCC) except for the high early strength and good durability of MPC. Premising the MPC as the rapid repair material for PCC, the characterization and analysis of the interface performance are studied. The data of elastic modulus for the interfacial transition zone (ITZ) is measured by nanoindentation technology while the mechanical properties firstly. The heterogeneity and stratification in the ITZ were characterized by the combination of Raman spectroscopy and nanoindentation test. The content of each material composition was explored with scanning electron microscopy (SEM) and energy-dispersive spectrometer (EDS) experiment and X-ray diffraction (XRD) analysis. Additionally, the adhesion-like substances in the cracks, observed by SEM images in the ITZ, inferred a certain self-healing ability of the polymer-modified magnesium phosphate cement (PMPC). Finally, the elastic modulus of ITZ was simulated by DIGIMAT version 2019.1 software, indicating that the single-layer microstructure analysis is feasible for obtaining elastic modulus of the ITZ without hydration stratification, while the multilayer microstructure analysis is necessary for obtaining elastic modulus of the ITZ with the hydration stratification. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Geogrid reinforcement effectively controls the rutting of pavements under traffic loads, especially when constructed over soft subgrades. In this study, extensive large-scale model pavement experiments (LSMPEs) were performed to quantify the rut depths of flexible pavements. In all, 20 LSMPEs were performed on pavement sections overlying subgrades of different strengths with California bearing ratio (CBR) values varying from 1% to 5%. Three geogrid types were considered to study the effects of material type [polypropylene (PP) and polyester (PET)] and tensile strengths (30–60 kN/m) on the rutting behavior of flexible pavements. LSMPEs were first performed under monotonic loading to obtain the optimum depth of reinforcement within the base layer of flexible pavement. Thereafter, a series of repetitive load (haversine loading) was applied on paved sections of reinforced flexible pavements using a high-end, linear, double-acting actuator system. Rut deformations were measured at both the surface and the subgrade levels of the model pavements. The rut deformations were found to distinctly vary in accordance with the condition of the subgrade, the thickness of the pavement layers, and the type of geogrid used. The rut depth reduction (RDR) at the pavement surface was found to range from 22% to 69% for PP- and PET-geogrid reinforced base layers. Geogrid reinforcement significantly reduced the rut depths at the subgrade level (as high as 90%) compared to unreinforced sections. In addition, the model pavements were instrumented with the earth pressure cells to measure the vertical pressures transferred to the subgrade due to surface loading. The ability of geogrid reinforcement to distribute loads to wider areas was quantified in terms of the vertical stress distribution angle, αmax , at the end of the load cycles (N=100,000 cycles). The αmax maximum values for geogrid (GG1/GG2/GG3)-reinforced pavements built over weak subgrade (CBR=1%) varied from 28.4° to 32.2°, while it was 25.7° for unreinforced pavements. Likewise, αmax values for geogrid-reinforced pavements overlying a relatively fair subgrade (CBR=5%) varied from 34.5° to 43.6° against 30.4° for an unreinforced case. [ABSTRACT FROM AUTHOR]

The effective reduction of cement content in pavement concrete without compromising its fresh, mechanical, and durability properties can lead to more economical and sustainable pavement engineering. Because a reduction in cement content in concrete can be achieved by improving the particle packing of aggregates, this study attempted to improve a practical mix design procedure based on both theoretical and experimental particle packing methods. In this study, optimum aggregate blends were first identified using the Modified Toufar Model, which indicated good correlation with the experimental packing results based on a combined void content test. The Modified Box Test was then used to evaluate the fresh concrete performance and to justify the effectiveness of cement reduction. The results indicated that cement content could be reduced by up to 56 kg/m3 from the reference mix with the optimum aggregate gradation. The results from hardened concrete tests, such as compressive strength, flexural strength, and resistivity, confirmed that concrete properties were not compromised by the reduced cement content. Freeze-thaw resistance was improved with up to an 11% increase in the relative dynamic modulus at 300 freeze-thaw cycles. The optimum mixes also demonstrated reduced shrinkages, with a 12%–20% reduced strain at 180 days of free shrinkage and a delayed cracking age based on the restrained shrinkage test. Based on the laboratory test results, an improved mixture design procedure aided by the particle packing degree and the minimum excess paste-to-aggregates volume ratio is presented. [ABSTRACT FROM AUTHOR]

Due to greater durability and lower maintenance costs, concrete pavements are more competitive than asphalt pavements in areas where rigid pavements are required. To ensure the surface skid resistance of concrete pavement for driving safety, appropriate textures must be created on the concrete pavement surface. Common surface texturing treatments in Germany include exposed aggregate, grinding and grooving, and sealing methods. To investigate the influence of different surface texturing methods on the wearing resistance of concrete pavement, concrete pavement samples with six different surface textures were manufactured in this study. The advanced Aachen Polishing Machine (APM) was used to simulate the different polishing states on the extracted samples with 0, 16, 33, 100, 200, and 300 min of real-tire polishing effect. After each polishing stage, a series of surface characteristic tests was conducted to evaluate the wearing characteristics of pavement samples. The test results showed that different surface textures have different long-term polishing resistances. Of the texturing methods investigated, the exposed aggregate and sealing treatments provide the best long-term polishing resistance for plastic and hardened concrete, respectively. This research provided a comprehensive evaluation of and significant guidance on the selection of surface treatment methods for new construction of cement pavement and surface maintenance of hardened concrete pavement. [ABSTRACT FROM AUTHOR]

Shear strength and rutting characteristics play a vital role in the serviceability and performance of interlocking concrete block pavement (ICBP). The objective of the present research study is to evaluate the shear stress behavior of the interlocking paver block–bedding sand interface using the laboratory large-scale direct shear test. The research includes analyzing the influence of parameters such as interlocking paver block shape, laying angle, and gradation of bedding sand on the shear stress behavior of ICBP. Optimization of the influential parameter is analyzed by the response surface methodology using expert software. The relative movement between the blocks during the shear mechanism is assessed by the image processing technique using well-known mathematical software and is validated from the readings measured using a Vernier caliper. Numerical simulation is carried out using professional engineering software to validate the laboratory test results. Combined rutting of the interlocking paver block and bedding sand is estimated from the derived shear test results. The test results prove that the ICBP, when laid with zigzag shape over Zone II bedding sand, perpendicular to the traffic movement, exhibits better shear strength and lower rutting. [ABSTRACT FROM AUTHOR]

Foamed asphalt cold-recycled mixtures have been increasingly used in China. However, the interlayer shear performance between the foamed asphalt cold-recycled layer and its top and bottom layers is still not clear. In this study, we explored factors affecting the interlayer shear performance of foamed asphalt cold-recycled layers (FACRL). Regarding the interlayer performance between the foamed asphalt cold-recycled layer and cement-treated base (CTB), the optimal content of the prime coat asphalt was 0.8 kg/m2 , and the prime coat asphalt was recommended to be applied on the surface of the base as soon as the base was paved. Styrene-butadiene-styrene (SBS)-rubber modified asphalt with a content of 2.3 kg/m2 and aggregates with a size range of 4.74–9.5 mm was recommended for use in the seal coats. The aggregates used in the seal coat were recommended to be premixed with a 0.3% asphalt binder to improve the adhesion and to be paved with a spreading area of 65%. Regarding the interlayer performance between the foamed asphalt cold-recycled layer and top hot-mix asphalt (HMA), the interlayer shear strength and fracture energy increased and then decreased with the added tack coat asphalt. The shear strength and fracture energy of the interlayer at 50°C was only 20% and 8% of that at 25°C, respectively. The optimum usage percent of the tack coat binder is 0.4 kg/m2. [ABSTRACT FROM AUTHOR]

Effects of synthetic and neutralized vinsol resin (NVR) air-entraining admixtures (AEAs) were compared through air-content measurements of freshly mixed concrete, hardened cylinders, and cores from field and laboratory concrete, and through a modified foam drainage test. The results show that air bubbles entrained with synthetic AEAs are less likely to survive during concrete sampling procedures than those entrained with NVR-based AEAs, leading to larger discrepancies between air-content measurements using the pressure method and the air content established from pavement cores. These discrepancies in turn can prompt imposition of contractor penalties, delays in construction, and controversy with potential longer-term impacts on concrete pavement longevity. [ABSTRACT FROM AUTHOR]

This study discusses the effect of utilizing coarse reclaimed asphalt pavement (RAP) aggregates as a replacement to natural coarse aggregates (NCAs) for the production of pervious concrete pavement (PCP) mixes. Coarse RAP (RC) aggregates were utilized in proportions of 0%, 25%, 50%, 75%, and 100%, respectively. It was observed that the porosity and permeability coefficient of the PCP mixes increases considerably as the RAP replacement level increases. Meanwhile, the incorporation of RC was also found to negatively affect the mechanical properties of the PCP mixes. However, the compressive and flexural strength values were noted to be well within the prescribed limits (5–25 MPa and 1–3.2 MPa) required for a PCP mixture. On the other hand, the incorporation of RC was observed to reduce the hardened density, resistance to abrasion, and resistance against aggressive environment of chlorides and sulfates. Therefore, in order to prepare a PCP mixture such that there exists a fine balance in various properties, it is recommended that RC up to 50% may be utilized as a replacement to NCA. In view of achieving maximum sustainability, RC up to 100% may be completely utilized for the production of PCP mixes provided a binary gradation is adopted. Utilization of RAP in preparation of pervious concrete pavement mix will not only resolve the issues related to clearance of an enormous amount of RAP dumps, but would go a long way in dealing with various other environmental and ecological impacts. [ABSTRACT FROM AUTHOR]

Mechanical properties of pervious concrete (PC) are highly influenced by the applied compaction; however, the required level of compaction to achieve the desired density and strength in the field is currently unknown. In some cases, compaction is established empirically on costly test panels. In this study, the relationship between the applied compaction force and the hardened porosity (Ø) and compressive strength (fc) was investigated. Three PC mix proportions with varying paste contents were compacted in the laboratory using a lightweight deflectometer (LWD) at four different compaction levels. Porosity and 7-day fc testing were carried out on cylinders cast with each compaction level. In general, the first 15 LWD drops influenced Ø and fc significantly, while the effect of compaction beyond that level was less significant. The applied compaction force recorded by the LWD was used to obtain the required properties of a rotary roller-screed to apply an equivalent compaction force in the field. Then, regression-based models were developed to estimate the 7-day Ø and fc of PC based on the applied compaction force and the paste content. The developed models provide a practical solution to compute the required compaction force in the field to achieve the desired PC mechanical properties. [ABSTRACT FROM AUTHOR]

This paper investigates the development of compressive strength (fc′), flexural strength (fr), and static elastic modulus (Ec) in relation to the dynamic modulus (Ed) for portland concrete cement (PCC) pavement and patch mixtures. The study in this paper was motivated by the need to establish the less commonly known fr−Ed relationship in comparison with the more established fc′−Ed models. A total of 399 cylinders and 144 beams were cast and cured under laboratory (23°C) and cold (7.22°C) regimes. Experiments were conducted at concrete ages ranging from 12 h to 28 days. Cylinder specimens were subjected to fc′ , Ec , and transverse dynamic modulus (EdcT) tests. Beam specimens were subjected to fr , transverse (EdpT), and longitudinal (EdpL) dynamic modulus tests. Early opening to traffic (EOT) concrete strength criteria were accurately predicted as most fc′ and fr estimates fell within 10% of relative error when respectively using EdcT and EdpT. Overall, the normalized development of fc′−EdcT and fr−EdpT relationships reveals distinct growth trends as fr developed at a higher power factor. [ABSTRACT FROM AUTHOR]

The authors stated that for the pavement section overlying fair subgrade (5% CBR) and reinforced with same polymeric PET material (GG2 and GG3), the lower tensile strength geogrid GG2 performed better than GG3. Geogrid reinforcement of highway pavement layers has gained wide acceptance over the years as a strengthening method to offset problems associated with their inability to provide support to overlying and underlying layers, resulting in the instability of the overall pavement system from shear failure and excessive permanent deformation, or rutting, both of which often result in poor pavement rideability with a possible resultant penalty in motor vehicle repairs and accidents. As noted by Koerner ([1]) there are three types of geogrid currently available: (1) unitized polypropylene (PP), (2) coated polyester (PET) or polyvinyl alcohol (PVA) yarns, and (3) PET or PP bonded straps or rods. [Extracted from the article]

Fracture behavior is an important parameter in evaluating mechanical properties, and it is related to crack risk and propagation in concrete. Freeze-thaw damage aggravates the degradation of mechanical properties and durability of concrete in a freeze-thaw environment, which is adverse to the safety of concrete structures. Although researchers have studied compressive, tensile, and bending strengths, the fracture behavior of concrete exposed to freeze-thaw cycles is frequently neglected. Additionally, fracture behavior is more sensitive to crack development caused by freeze-thaw damage. This paper was developed to investigate the influence of freeze-thaw damage on fracture behavior of concrete. Freeze-thaw cycles, compressive strength, and fracture energy tests were carried out. The results show that the toughness and fracture behavior both decrease with increases in freeze-thaw cycles, and this decrease becomes more obvious for concrete after a large number of freeze-thaw cycles, which should be considered seriously in the design of concrete in freeze-thaw environments. Air-entrained and mineral admixture concretes have better fracture behavior than fresh concrete after suffering the same freeze-thaw cycles. In particular, there exists good linear correlation between the fracture behavior and imposed freeze-thaw damage for various concretes. [ABSTRACT FROM AUTHOR]

The water absorption properties of concretes measured by sorptivity test were investigated by using natural pozzolanic cements--CEM II/A and CEM II/B--and compared with those of ordinary portland cement (CEM I) concrete under varying water-curing periods. The mix design of concretes was made with an equal strength base at an age of 28 days under standard curing. The curing regimes include initial water curing periods of 3, 7, 14, and 28 days between continuous in-air and continuous in-water, and also 7-day delayed curing. Sorptivity and compressive strength tests were conducted at the age of 90 days. Although the difference between the sorptivities of air-cured concrete specimens for all cement types used is slight, under the water curing conditions, the differences between that of the CEM II/B concrete and those of the CEM I and CEM II/A concretes become significant. Also, considerable differences were obtained for the sorptivities of the CEM II/B concrete between the air-cured and continuous water-cured specimens when compared with those of the CEM I and CEM II/A concretes. [ABSTRACT FROM AUTHOR]

Recent studies have revealed that zyco-soil and nanosilica are among the nanomaterials that can help improve the moisturedamage resistance of asphalt mixtures. However, these also affect the properties of asphalt mixtures in different ways. For the first time, this study aims to compare their effects on some engineering properties of a typical asphalt concrete, the environmental impact, and the cost. The 60/70 penetration-grade asphalt cement was modified by adding different percentages of nanosilica (1, 3, and 5%, by the weight) and zyco-soil (0.1, 0.3, and 0.5%) content and evaluated using experiments. The results showed that nanosilica modification leads to higher resistance to permanent deformation, resilient modulus, and indirect tensile strength compared with zyco-soil modification. Beyond an optimum zyco-soil content of 0.1%, resistance to permanent deformation and resilient modulus of the mixtures decreases with increasing zyco-soil content. The results also showed that zyco-soil-modified asphalt mixtures are more resistant to moisture damage compared with the nanosilica-modified mixtures. However, the optimum zyco-soil content to achieve the highest resistance to moisture damage is different from that used to achieve stiffness and stability. For nanosilica, the optimum content to achieve the highest resistance to moisture damage and stability is the same. [ABSTRACT FROM AUTHOR]

Rutting or permanent deformation is one of the severe distresses manifested in flexible pavements caused by the various mechanisms such as densification, lateral plastic flow, and/or loss of materials under wheel path due to repeated heavy traffic loads. Various laboratory tests have been devised to determine the rutting propensity and to optimize the field performance of hot mix asphalt (HMA) mixtures as a part of the HMA mix and structural design processes. Although various approaches exist to predict the permanent deformation of HMA, this study develops a relationship of flow number (FN), dynamic modulus (DM), and uniaxial repeated-load permanent deformation (RLPD) to enable the trade-off analysis among them. Also, a novel parameter, FN index, is explored and used to determine the rutting potential of HMA mixtures. Twelve globally practiced HMA mixtures are investigated with three different performance grade binders and single limestone aggregate source. Superpave gyratory compacted specimens are subjected to performance testing (FN, DM, and RLPD) and results indicate a strong correlation of FN index with DM and exhibit better correspondence than the traditional FN (cycles) parameter. [ABSTRACT FROM AUTHOR]

This paper investigates the potential use of phase change materials (PCM) in concrete pavements to store heat, which can be used to reduce ice formation and snow accumulation on the surface of the concrete pavement. The thermal properties of the PCMs are evaluated using a low-temperature differential scanning calorimeter (LT-DSC) while a longitudinal guarded comparative calorimeter (LGCC) is used to evaluate the thermal response of cementitious mortar containing the PCM. Paraffin oil (petroleum based) and methyl laurate (vegetable based) were selected as PCMs since they have high enthalpies of fusion (~130-170 J=g) and have desirable freezing temperatures (~2-3°C) during the liquid to solid phase transformation. Two approaches were used to place the PCM in the mortar specimens: (1) placing the PCM in lightweight aggregate (LWA) in mortar and (2) placing the PCM in an embedded tube that is placed in mortar. The durability and stability of the PCMs in the cementitious system were studied by monitoring the change in enthalpy of fusion, mass loss, pulse velocity, and compressive strength. When the PCM was placed in the mortar specimen using LWA, the paraffin oil can release a considerable amount of heat during phase transformation, which can be used to melt ice and snow. However, it was observed that the methyl laurate reacts with the cementitious matrix, causing damage to the mortar. Both paraffin oil and methyl laurate showed promising performance to melt ice and snow when the PCM was placed in an embedded tube in the mortar specimen. [ABSTRACT FROM AUTHOR]

Reclaimed asphalt pavement (RAP) is widely used to construct new asphalt pavement layers, but its use is often limited in surface courses because of concerns about frictional performance, especially in areas where polish-resistant aggregates are scarce or not available. The goal of the research reported in this paper was to determine the maximum amount of RAP that can be blended with high-friction aggregates and used in surface mixes without significantly impacting frictional properties. The properties of RAP from six different sources were evaluated to determine typical RAP characteristics and used to fabricate a mixture simulating a worst-case scenario RAP with a lowfriction aggregate. That RAP mixture was used to evaluate the frictional characteristics of two types of hot-mix asphalts with various amounts and types of high-friction aggregates. Specimens were subjected to laboratory polishing to simulate the effects of traffic. Results suggest that the threshold level of RAP in surface mixes that will not have detrimental effect on their frictional properties was about 30%, even when the RAP contained a highly polishable aggregate. [ABSTRACT FROM AUTHOR]

This paper presents the results of a testing plan designed to evaluate the effects of macrosynthetic fibers on pervious concrete material properties and durability. The effects of two lengths of fibers (38 and 56 mm) were investigated at three dosage rates (1.5, 3.0, and 4.5 kg/m³) in a single mixture. The unit weight and void content of all samples were controlled to allow determination of the effects caused directly by the fibers. Samples were tested for strength and durability properties. The results indicate that fibers in general reduced permeability and the infiltration rate, while reducing surface abrasion and improving freeze-thaw durability. [ABSTRACT FROM AUTHOR]

In this research, the ability of pervious concrete pavement material to reduce pollutant concentrations and purify water was investigated. This project mainly aims to study the ability of pervious concrete pavement material to reduce pollutant concentrations such as those in diluted sulfuric acid, seawater, and motor oil. The results demonstrated that the ability of pervious concrete pavement material to reduce pollutant concentrations and purify water was effective in diluted sulfuric acid, artificial seawater, and motor oil tests. After flowing through pervious concrete pavement, a diluted sulfuric acid solution (pH value 2.0) could dramatically increase its pH value to approximately 7.0. A pervious concrete pavement system could greatly decrease the content of an artificial seawater solution (salinity 36%) to about 1%, and the oil content of motor oil combined with certain types of water could also be significantly decreased to 1%. The study demonstrates that pervious concrete pavement holds potential for environment conservation and hydrologic consideration. [ABSTRACT FROM AUTHOR]

This paper considers the effect of the thermophysical properties of concrete on temperature distributions and stresses developed in concrete pavements. The temperature distributions in concrete pavements, composed of different thermophysical properties, were calculated using a finite-difference model. These temperatures were then fed into a finite-element model as thermal loads in order to calculate tensile stresses in the concrete. It was found that the thermophysical properties of concrete can significantly influence the magnitude of tensile stresses and, subsequently, the thickness of the concrete slab. Concrete with higher thermal conductivity and diffusivity (e.g., incorporating high conductive aggregates and/or metallic fibers) will experience much more uniform temperature and, as a result, a smaller tensile stress will be developed in the concrete. Increasing the thermal conductivity of concrete from (concrete containing limestone aggregates) to (concrete containing quartzite aggregates and 1% metallic fibers) could result in a 25% reduction of the concrete slab thickness. [ABSTRACT FROM AUTHOR]

A series of spectral analyses of surface waves (SASW) tests were conducted on a cement concrete pavement by dropping steel balls of four different values of diameter () varying between 25.4 and 76.2 mm. These tests were performed (1) by using different combinations of source to nearest receiver distance () and receiver spacing (), and (2) for two different heights () of fall, namely, 0.25 and 0.50 m. The values of the maximum wavelength () and minimum wavelength () associated with the combined dispersion curve, corresponding to a particular combination of and , were noted to increase almost linearly with an increase in the magnitude of the input source energy (). A continuous increase in strength and duration of the signals was noted to occur with an increase in the magnitude of . Based on statistical analysis, two regression equations have been proposed to determine and for different values of source energy. It is concluded that the SASW technique is capable of producing nearly a unique dispersion curve irrespective of (1) diameters and heights of fall of the dropping masses used for producing the vibration, and (2) the spacing between different receivers. The results presented in this paper can be used to provide guidelines for deciding about the input source energy based on the required exploration zone of the pavement. [ABSTRACT FROM AUTHOR]

Pervious concrete pavements (PCP) are increasingly recognized and used as a best management practice to control stormwater runoff and for low-volume traffic. However, there are limited studies on the structural integrity of the PCP section on performance under vehicular loads. This study investigated the mechanical properties of field samples and the structural integrity of PCP when subjected to traffic loads using the falling weight deflectometer (FWD). The compressive strength for cored samples from the field installation was about 11.5 MPa with an average unit weight of . The deflection of the PCP sections at the load application point was about 1.7 to 4 times of the impervious concrete section, dependent on the subbase characterization. The composition of the PCP subbase materials and the compaction effort of the layers significantly affected the deflection. Back-calculation analysis showed that the loosely compacted subbase layers had lower elastic moduli and exhibited higher deflection responses, which compromised the structural integrity of the PCP systems to traffic loadings. [ABSTRACT FROM AUTHOR]

Supplementary cementitious materials (SCMs) have been used in portland cement concrete pavements (PCCP) to increase their resistance to deterioration mechanisms, such as alkali-silica reaction (ASR), freeze and thaw, and permeability. In addition, SCMs are mostly by-products that can effectively reduce material cost and improve concrete sustainability. This paper presents the results of an experimental investigation carried out to evaluate the effect of Class C fly ash, Class F fly ash, and ground granulated blast furnace slag (GGBFS) on the performance of PCCP. Laboratory testing of multiple mixes with different combinations and percentages of SCMs is presented. This testing includes slump, unit weight, air content, time of setting, compressive strength, flexural strength, alkali-silica reactivity, freeze/thaw, length change, chloride ion penetration, and wet/dry test specified by Nebraska Department of Roads (NDOR). Field applications of four candidate mixes at two separate locations are also presented. Test results from laboratory and field investigations indicated that using a combination of Class C fly ash (15-20%) and Class F fly ash (20-25%), or all three SCMs in the range of 15-20% each, improves concrete durability and overall performance. [ABSTRACT FROM AUTHOR]

The findings of an extensive literature review on the permeability of hot-mix asphalt concrete are detailed in a state-of-the-art report on the measurement and interpretation of asphalt concrete permeability data. The permeability of asphalt concrete is affected by a range of factors with various levels of importance, which are reviewed along with their impact on the coefficient of permeability. Many theoretical, empirical, semiempirical, and numerical models have been developed to predict permeability, using a range of indicators. Some of these models are reviewed and their advantages and shortcomings discussed. Recent advances in X-ray tomography studies are also summarized. The review reveals that field permeability measurements are not reported to match numerically well with laboratory measurements, though there is some correlation. The reviewed test methods for permeability all rely on an assumption of laminar flow that is unlikely in more porous mixtures. Attempts to measure connected air voids improve the chances of obtaining more meaningful correlations between permeability and air voids, regardless of the mathematical model used to link the two quantities. The lift-thickness to nominal maximum aggregate size (NMAS) ratio and/or changes in the binder content has a less significant effect on permeability than changes in the porosity and/or mix gradation. Air void gradients and distributions in compacted asphalt concrete mixtures can now be assessed with X-ray techniques: the distribution of air voids appears to be nonuniform in laboratory-prepared specimens. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio () to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying , 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 , strength is independent of cementitious content after a critical value is provided. When is constant, increasing paste content increased chloride penetrability and air permeability. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate the minimum paste volume required with an appropriate water-to-cementitious ratio () to achieve required workability, strength, and durability requirements of concrete mixtures for pavements. In this experimental program, 64 concrete mixtures with varying , 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 , strength is independent of cementitious content after a critical value is provided. When is constant, increasing paste content increased chloride penetrability and air permeability. [ABSTRACT FROM AUTHOR]

Load-transfer efficiency (LTE) of jointed concrete pavement is typically measured by the ratio of unloaded and loaded slab deflection. However, the maximum tensile stress in a slab is one of the critical mechanical responses that influences the performance of the jointed concrete pavement. Therefore, stress-based load-transfer efficiency, defined as stress reduction in the loaded slab because of the presence of an adjacent unloaded slab, is often considered an appropriate way to quantify LTE. Strain gauge data from full-scale tests collected by the Federal Aviation Administration were analyzed to compute the stress-based LTE of joints under moving loads. The effect of static aircraft gear loads and slab size on the LTE of joints was analyzed by using a two-dimensional finite-element program. FEM-calculated stress-based LTE under static aircraft loading on average was 38% lower than that measured under moving loads. LTE values were similar under various gear positions, gear configurations, and different slab sizes. [ABSTRACT FROM AUTHOR]

Nitrogen oxides (NOx) emitted from vehicle exhausts are associated with adverse health effects on the public. Self-cleaning, air-purifying concrete pavement is a rapidly emerging technology that can be constructed by using a photocatalyst such as titanium dioxide (TiO2). The main objective of this study was to evaluate the environmental effectiveness of TiO2 coating in photodegrading mixed NO2 and NO gases from the atmosphere. Results of the experimental program determined that increasing the flow rate and NO2/NOx ratio negatively affect the effectiveness of the photocatalytic process. However, within the evaluated range, the titanium content and aggregate gradation had little effect on NOx removal efficiency. The highest photodegradation rate was observed at 25% relative humidity, which balances the availability of hydroxyl radicals at the surface with NOx contact with the photocatalytic surface. [ABSTRACT FROM AUTHOR]

A very high-strength microconcrete (fc=125 MPa) containing polymeric fibers and quartzitic aggregates, but no silica fume, has been investigated both at high temperature and after cooling, in order to evaluate the thermal diffusivity and the mechanical decay as a function of the temperature, since there is still scanty information in the literature on the high-temperature behavior of this family of materials. The very high-strength concrete (VHSC) investigated turned out to be very efficient, since (1) its compressive strength exhibits a decay very close to that of normal-strength concrete, with no sizable differences between the “hot” and “residual” properties (250–750°C); (2) its specific fracture energy increases very much indeed with the temperature; and (3) its rather low thermal diffusivity guarantees good insulation properties. As an application of this material, the parking apron of an airport and its two-layered pavement subjected to a hot spot (T≤400°C) have been considered, in order to investigate whether delamination at the interface between the top VHSC layer and the bottom normal strength concrete layer and/or cracking in the bottom layer may occur. The performance of the pavement was analyzed for different values of the thickness of the top VHSC layer and also for different values of its thermal properties, and proved to be very satisfactory in terms of tensile behavior. However, the critical factor remains the initial heating rate. [ABSTRACT FROM AUTHOR]