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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]

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 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]

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]

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]

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]

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]

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]

Creep compliance (or relaxation modulus), which is a fundamental property that determines the strain (or stress) development in flexible pavements or damage evolution in asphalt mixtures, can be determined from either a creep compliance test using static loading or a complex modulus test using cyclic loading. Since the nature of each test is different, creep compliance determined from the complex modulus test was significantly different compared with that determined from the creep compliance test. From this rigorous experimental and analytical study, it was concluded that the creep compliance or complex modulus test alone is not capable of providing complete information over the typical time or frequency range used in single-temperature tests. In general, the complex modulus test provides accurate creep compliance at short loading time, while the creep compliance test provides accurate creep compliance at longer loading time. An approach to determine accurate creep compliance from the combination of creep and complex modulus tests at a single temperature was developed. The method provided accurate creep compliance values that corresponded to short-term and long-term experimental data. [ABSTRACT FROM AUTHOR]