tional hot-mix asphalt (HMA). Typically, the mixing temperaturesof WMA range from 100C to 140C (212F to 280F) comparedwith the mixing temperatures of 150C to 180C (300F to 350F)for conventional HMA (13). Thus, warm asphalt has been gainingincreasing popularity in recent years. Rising energy prices, globalwarming, and more stringent environmental regulations have gen-erated an interest in WMA technologies as a means of decreasingthe energy consumption and emissions associated with conventionalHMA production (17 ).
Moisture damage is usually not limited to one mechanism but israther the result of a combination of many processes. From a chemicalstandpoint, the literature is clear that although neither asphalt noraggregate has a net charge, components of both have nonuniformcharge distributions, and both behave as if they have charges thatattract the opposite charge of the other material (810). The foamingprocess caused by WMA additive makes the charge redistribution morecomplex and thus may affect the mixtures moisture susceptibility.Especially at the mixing temperature of 100C to 140C (212F to280F), the aggregate may not be completely dried during the mixingprocess. Even though some of states in the United States and othercountries have specifications that require a completely dry aggregatein WMA mixtures (11), not many research projects are conductedto determine the effects of the moist aggregates with WMA additives,which may result in moisture damage and further lead to the failureof the pavement.
The objective of this study was to gain a more fundamental under-standing of the influence of WMA additive and moisture content ofaggregate on the anti-stripping resistance of the mixture of threeaggregate sources by means of conventional moisture susceptibilitytesting procedures, such as indirect tensile strength (ITS), tensilestrength ratio (TSR), deformation, and toughness analysis.
EXPERIMENTAL PROGRAM AND PROCEDURES
The experimental design detailed in this study included two WMAadditives (Asphamin and Sasobit), two moisture percentages (0%, and0.5% by weight of dry aggregate), and three hydrated lime contents(0%, 1%, and 2% by weight of dry aggregate). Three aggregate sources(A, B, and C) were used for preparing samples, and one binder grade(PG 64-22) was used for this project. The engineering properties ofaggregate sources are shown in Table 1. Aggregate sources A and C(granite) are composed predominantly of quartz and potassiumfeldspar, while aggregate source B (schist) is a metamorphic rock.
Laboratory Investigation of MoistureDamage in Warm-Mix Asphalt ContainingMoist Aggregate
Feipeng Xiao, Jayson Jordan, and Serji N. Amirkhanian
In recent years, rising energy prices, global warming, and more stringentenvironmental regulations have generated interest in warm-mix asphalt(WMA) technologies as a means to decrease energy consumption andemissions associated with conventional hot-mix asphalt. In this study, alaboratory investigation was conducted of moisture damage in WMAmixtures containing moist aggregates. Indirect tensile strength (ITS),tensile strength ratio, deformation, and toughness tests were performedto determine the mixtures moisture susceptibilities. The experimentaldesign included two percentages of moisture content (0% and 0.5% byweight of the dry mass of the aggregate), two WMA additives (Asphaminand Sasobit), and three aggregate sources. In this study 15 mix designswere performed, and 180 specimens were tested. Test results indicatedthat, as expected, dry ITS values were affected by aggregate moistureand hydrated lime contents, whereas a WMA additive did not signifi-cantly alter the dry ITS and toughness values. Statistical analysis showedno significant differences in the wet ITS values of WMA mixture of threetypes of mixtures (control, Asphamin, and Sasobit) under identicalconditions (same moisture and lime contents). Statistical analysis alsoshowed that wet ITS values, generally, were statistically different formixtures made with various aggregate sources. The deformation resis-tance values of mixtures containing moisture were lower than those ofmixtures made with dry aggregate. However, the results indicated thatthe addition of hydrated lime increased the deformation resistance of allmixtures.
Moisture damage, caused by a loss of bond between the asphalt binderor the mastic and the aggregate under traffic loading, can result in adecrease of strength and durability in the asphalt mixture and ultimatelyaffect its long-term performance. Moisture damage, in general, inflexible pavements occurs because of the separation and removal ofasphalt binder from the aggregate surface in the presence of water,which leads to stripping in the asphalt pavement and potentially causespremature failure.
In recent years, the asphalt industry has investigated warm asphalttechnology as a means of reducing the mixing and compaction tem-peratures of asphalt mixes and thereby saving energy and reducingemission. Warm-mix asphalt (WMA) is an asphalt mixture that ismixed and compacted at temperatures lower than those for conven-
Department of Civil Engineering, Clemson University, Clemson, SC 29634-0911.Corresponding author: F. Xiao, firstname.lastname@example.org.
Transportation Research Record: Journal of the Transportation Research Board,No. 2126, Transportation Research Board of the National Academies, Washington,D.C., 2009, pp. 115124.DOI: 10.3141/2126-14