Special Issue on Materials Innovations for Sustainable Infrastructure

DOI: 10.1061/(ASCE)MT.1943-5533.0000840Nowadays, the concept of sustainability has gained widespreadacceptanceandawarenessinthetransportationinfrastructureindus-try (Huang and Liu 2011; Mehta 2009). Numerous innovations inpaving materials and construction techniques have been adopted tomeet the challenge of sustainable development (Huang et al. 2012;Miller and Bahia 2009; Aitcin 2007; Van Dam et al. 2011).This special issue contains 16 technical papers in this area, whichcan be divided into the following four categories: (1) recycledmaterials, (2) sustainable materials accommodating climaticchange, (3) pavements for longer service life, and (4) low-energy-consumption materials.Recycled MaterialsRecycling of solid waste materials into paving materials reducesnot only environmental issues associated with waste disposal butalso the demand for virgin asphalt cement or Portland cementbinder, and coarse and fine aggregates, leading to potential costsavings. This is especially important when faced with the ever-growing world population and increasingly dwindling naturalresources. Recycled asphalt pavement (RAP), recycled asphaltshingles (RAS), crumb rubber, and steel slag have been widelyaccepted by state highway agencies and recycled into asphalt pave-ments (Schroeder 1994; Shelburne and DeGroot 1998; Huanget al. 2002, 2005a, 2007, 2010a, b, 2011; Xiao et al. 2007, 2009;Shu et al. 2008, 2012; Zhao et al. 2012, 2013). In addition to thefour types of supplementary cementitious materials (SCMs)—flyash,slag,silicafume,andnaturalpozzolans—manyothermaterialssuch as recycled concrete aggregate (RCA), cement kiln dust(CKD), foundry sand, waste glass, bottom ash, crumb rubber,plastics, ceramics, and even RAP have been recycled into Portlandcement concrete (PCC) materials (Ansari et al. 2000; Naik 2002;Huang et al. 2004, 2005b, 2006b, 2009b, 2013; Li et al.2004a, b). Like SCMs contributing to the properties of hardenedPCC through hydraulic and/or pozzolanic reactions, RAP andRAS can also improve the binding properties of asphalt pavingmaterials through the aged asphalt binder in them, which makesthem more technically and economically beneficial.Thisspecialissuepresentssixtechnicalpapersregardingtheuseof recycled materials such as RAP, RCA, waste phosphorous slag,sludge, low-quality fly ash, and waste ceramic aggregate. Lin et al.investigated the effects of rejuvenator sealer material on aged as-phalt binder through laboratory testing. Their test results show thatrejuvenator can serve as a softening agent, reducing viscosity andcomplex modulus of aged asphalt binder. Chemical analysis indi-cates that addition of rejuvenator can slightly change the fractionsof aged asphalt binder and thus balance its asphaltene-malteneratio. Because rejuvenator is not very common in the recyclingof RAP in asphalt mixtures, this study may shed new light on com-bining rejuvenator with RAP and serve as a booster to incorporatemore RAP in asphalt paving materials.Self-healing is an intrinsic property of asphalt binder and maypotentially be beneficial in improving the properties of recycledasphalt mixtures. Qiu et al. developed three new test methods tosimulatetheself-healingprocessofasphaltbinder,mastic,andmix-ture in the laboratory and investigate the self-heading mechanism.Intheirstudy,theself-healingprocesswastobehypothesizedtothereverse process of cracking, consisting of two phases—crackclosure and strength gain. They also found that the self-healingcapability of asphalt materials is significantly affected by twofactors—temperature and healing time.Qian et al. and Feng et al. both used waste industrial by-productin asphalt mixtures. Qian et al. incorporated phosphorus slag asmineral filler in hot-mix asphalt (HMA) and used multiple charac-terization techniques to assess the feasibility of recycling thisindustrial waste into HMA mixtures. Their test results indicate thatphosphorus slag filler significantly increases the resistance ofHMAs to rutting and moisture damage. Feng et al. attempted torecycle ceramic waste aggregate (CWA) into wearing layer of as-phalt pavement. Their concern is on the thermal effect and the mix-ture performance attributed to adding CWA. Their finite elementmethod (FEM) simulation results show that CWA can reducethe thermal conductivity of asphalt mixtures and subsequently re-duce the temperature gradient of pavement. Basing on the perfor-mance test results, they recommended that less than 40% CWA beadded into asphalt mixtures to replace natural coarse aggregates.Qiao and Chen introduced an innovative chemical admixturecalled mesoporous inorganic polymer (MIP) to improve themechanical properties and early-age shrinkage resistance of re-cycled aggregate concrete (RAC). The properties of RAC are usu-ally compromised because of the addition of RCA, such asincreased shrinkage and creep, reduced strength and modulus,and poor durability. To overcome these inferior properties, a prom-ising chemical admixture, an atomic polymer technology (APT) inthe form of MIP, was added and successfully enhanced themechanical and early-age shrinkage performance of RAC. Com-bined with this technology, more RAC can potentially be madeto promote sustainability in the PCC industry.Yang et al. used river sludge, low-quality fly ash, and glasspowder to produce high-strength ceramsite. They looked into dif-ferent recipes and different fabrication conditions and successfullyproducedhigh-strengthceramsitethatmeetsChinastandards.Their