Recently, there has been an increasing interest in the applications of recycled mixtures with a high reclaimed asphalt pavement (RAP) content. However, many government departments are hesitant about the applications of that due to being worried about the durability of its pavement, and few findings has been reported in terms of the percentage of fine reclaimed asphalt pavement (FRAP, 0~5 mm) in recycled mixtures. In this paper, 25% or more RAP by the weight of aggregates is defined as high RAP and high FRAP refers to 10% or more FRAP by the weight of aggregates. This paper examines the laboratory performances of mixtures with high RAP (30%, 40%, and 50%) and FRAP (10%, 15%, and 20%). Performance evaluations have been conducted by conventional tests, including the low-temperature bending test, fatigue test, and the moisture susceptibility test. The results show that with the increasing RAP and FARP contents, 41% (30-R-10) to 63% (50-R-15) of virgin asphalt can be saved, both the low-temperature and fatigue performance decrease, and the moisture performance firstly increases and then decreases. The results of analysis of variance (ANOVA) in terms of low-temperature and moisture performance show that RAP contents in recycled mixtures have a significant effect on the performance, while the effect of FRAP contents on the performance of recycled mixtures is insignificant.

Although it is well known that the stone mastic asphalt (SMA) pavement has good skid resistance, the skid resistance is not satisfactory and its durability is poor when the mixture design is unreasonable. In order to obtain excellent skid resistance for SMA pavement, this paper seeks to analyze the influence of mixture design parameters on the skid resistance of SMA pavement. The mixtures were designed with an orthogonal experiment. There were five factors, namely the percentage of aggregates passing the maximum size (P_NMSA), the percentage of aggregates passing the sieve size which is only one smaller than the maximum size (P_NMSA-1), the percentage of aggregates passing the control sieve size (P_CS), the percentage of aggregates passing the sieve size which is only one smaller than the control sieve size (P_CS-1), and asphalt content (AC), and each factor had four levels. The skid-resistance index (SI) obtained by the 3D measurement was used to evaluate skid resistance. The results show that the three parameters (P_NMSA, P_CS, and AC) are the key parameters to improve skid resistance. Among them, P_NMSA has the greatest impact on the skid resistance, AC is the second, and the impact of P_CS on skid resistance is the smallest. Moreover, the design parameters with best skid resistance are proposed.

Crumb rubber, as a recycled material used in asphalt mixture, has gained more attention in recent years due to environmental benefits and the advantages of its pavement, such as excellent resistance to cracking, improved durability, less road maintenance, lower road noise, etc. However, the high-temperature performance of mixture with crumb rubber does not perform well. In order to improve the performance, this paper examined the effect of additives on the laboratory performance of asphalt rubber Stone Matrix Asphalt (AR-SMA) with additives. Three groups of AR-SMA: no additives, Styrene–Butadiene–Styrene (SBS) and Granular Polymer Durable additive (GPDa) were included, with no additives as a control group. Each group was investigated at three asphalt rubber content (ARC): 6.4%, 6.9%, 7.4% with regard to high-temperature and fatigue properties. The results show that with increasing ARC, the high-temperature performance of mixture without additive decreases, and the high-temperature performance increases first and then decreases for SBS and GPDa. Moreover, the rutting resistance of AR-SMA with GPDa at 6.9% ARC performs best. Under the condition of mixtures with appropriate ARC, AR-SMA with GPDa has higher fatigue life and sensitivity to fatigue cracking than the control group. Simultaneously, the fatigue performance of AR-SMA with GPDa is not as significant as that without additive with increasing ARC. In a word, GPDa is a good choice to improve the performance of AR-SMA. However, it should be noted that optimal asphalt content of AR-SMA mixtures with GPDa is higher than that of traditional mixtures.

To describe the skid resistance attenuation of asphalt pavement during its life cycle, this paper selected a multi-variable accelerated abrasion machine to simulate the abrasion process, and British Pendulum Number was selected to evaluate the skid resistance after various abrasive cycles. During the abrasion process, three factors influencing the skid resistance were considered, including aggregate types (diorite, limestone, granite, and basalt), nominal maximum aggregate size (NMAS), and gradations (dense, gap, and open). The results show that with increasing abrasion cycles, the skid resistance of asphalt pavement firstly decreases rapidly in the first abrasion stage (0–8000 cycles), then at a relatively gentle rate in the second abrasion stage (8000–20,000 cycles), and finally at the lowest rate in the third abrasion stage (after 20,000 cycles). The skid-resistance durability and stability of pavement are ranked as basalt > granite > amphibolite > limestone. Moreover, the effect of aggregate parameters on skid resistance is in the order: angularity > PSV > WSV > CSV. The skid resistance and its stability improve as NMAS increases. The pavement skid durability is in the order: SMA > OGFC > AC. In addition, the sizes of 16 mm, 13.2 mm, 9.5 mm, 0.6 mm, 0.3 mm and 0.15 mm are the critical sieve sizes to improve the skid resistance of asphalt pavement.

After thermal braising and magnetic separation, steel slag is often ground into steel slag powder (SSP), which contains active silica (SiO₂) and can be used as a cementitious material to replace part of the cement and applied in concrete. However, there have been relatively few studies on the influence of SSP on the performance of pavement cement concrete (PCC). In this paper, SSP was used as an admixture to replace part of the cement in the cement paste, cement mortar, and PCC, to investigate the effect of SSP on the fluidity of SSP-cement slurry, the mechanical properties, and the durability of PCC. Results showed that SSP can lead to the secondary hydration reaction with Ca(OH)₂ in the cement paste and affect the hydration products, morphology, pore characteristics, and strength of the cement paste. When the SSP mixing amount was less than 20 and up to 1.3 superplasticizer was added, the fluidity of the cement slurry could be optimized. For the samples with the SSP mixing amount of less than 20, the concrete compressive strengths were greater than 50MPa, and the flexural strengths were greater than 5.0MPa. As the SSP mixing amount increased, concrete displayed a better anticarbonization performance. Finally, using 15 SSP, the best performance in terms of the concrete antipermeability (chloride ion diffusion coefficient and electric flux) and frost resistance was achieved.

Laboratory simulation is an effective method to obtain asphalt at different aging stages, like short-term aging through the Rotated Thin Film Oven Test (RTFOT) and long-term aging through a Pressure Aging Vessel (PAV). However, these methods have certain limitations: RTFOT produces small amounts of asphalt and is hard to clean, and PAV is costly. This paper presents a simple and economical way to obtain a large amount of aged asphalt with a single device called the Temperature-Cycle Aging Oven Test (TCAOT). Some key experimental parameters were investigated, including experimental conditions such as whether only thermal aging or fusion ultraviolet (UV) aging is required, the test temperature, sample quantity, sample placement, and termination criteria, etc. The rheological properties of aged asphalt from the new method were compared with traditional asphalt. The results show that the complex shear modulus after thermal aging is similar to that with UV radiation. Due to the difficulties, 125 g of asphalt is advised. For short-term aging, TCAOT at 163 °C for 120 min is like RTFOT. For long-term aging, TCAOT at 95 °C for 72 h is like PAV. With more aging, TCAOT at 95 °C for 120 h is equal to 15 years of real asphalt pavement aging. Based on TCAOT’s excellent test performance, transportation and road construction departments can consider adopting this method to improve operational efficiency and save costs to increase revenue.