LABORATORY EXAMINATION FOR THE EFFECT OF ADDING HYDRATED LIME ON THE MOISTURE DAMAGE RESISTANCE OF ASPHALT CONCRETE MIXTURES

The main objective of this study is to investigate the effect of adding hydrated lime on the moisture damage resistance of asphalt concrete mixtures. In this study two samples of asphalt concrete mixture were prepared, the first sample represent control mixture, and the second sample contain hydrated lime with rate (0.5, 1, 1.5, 2.0, 2.5%) by the total weight of aggregate. The properties of control mixture and Lime-asphalt concrete mixture were evaluated by Marshall tests results, Indirect Tensile Strength (ITS) results, and retained Marshall Stability (RMS) test results. The results for these tests indicated improvement in mixture proprieties, increased resistance of asphalt concrete against moisture damage, and reduced effect of water on the properties of asphalt concrete. As a final result, the use of (2%) hydrated lime enhanced asphalt concrete properties and produce durable mixtures for highway construction.


Introduction
Flexible pavement or asphalt concrete is one of the most commonly types of pavement used in highway construction projects in the world. The term of asphalt concrete describes the flexible pavement layer that constructed through mixing asphalt binder with aggregate, and resting on the subbase and subgrade soil layers. Environmental stresses resulting mainly by the water (moisture damage), and temperature (temperature cracks) which influence on the pavement performance (Paul H Wright, et al, 2004). Moisture damage effects represent on the stripping action of water that entered the asphalts concrete and destroy the bonding forces between the asphalt binder film and aggregate, which lead to reduce pavement durability against distresses. The asphalt concrete materials such as asphalt properties, and aggregate characteristics & composition, in addition to environmental factors, are the main factors effecting on the moisture damage resisting (Stuart KD, 1990). To improve the resisting of asphalt concrete to moisture damage, many method where obtained, which depend on the modified asphalt concrete properties. The modification include on using anti-striping materials with asphalt mixtures to reduce the moisture damage effects. The rule of anti-striping additives is to increase physico-chemical bond between the bitumen and aggregate, and to improve wetting by lowering the surface tension of the bitumen (Majidzahed K, et al, 1968).
Hydrated lime has been used in asphalt mixtures for a long time as mineral filler and antistriping additives. The hydrated lime structure consists of large and small particles, which make hydrated lime works as filer and as anti-striping additives (Amjad, 2011). Researchers observed that when hydrated lime coats aggregate particles, it induces polar components in asphalt cement to bond to the aggregate surface. The effect also inhibits hydrophilic polar groups in asphalt from congregation on the aggregate surface (McGennis et al, 1984).
The main objective of this study is to investigate the effect of hydrated lime on the moisture damage resistance of asphalt concrete mixture depending on the flowing tests (Marshall tests), (retained Marshall stability), and (indirect tensile strength test). The lime-HMA contains hydrated lime at (0, 0.5, 1, 1.5, 2, and 2.5%) by the dry wet of aggregate and as partial replacement of filler material.

Literature Review
(Al-Suhaibani,1992) evaluated the mineral properties of hydrated lime and other local fillers available is Saudi Arabia. The mechanical properties of the mixes were studied using tests such as the resilient modulus test, the indirect tensile strength test, Hveem stability, and Marshall Criteria. The research results revealed that the amount and characteristics of the mineral fillers can have an effect on flexible pavement properties, and the using of hydrated lime showed positive effect on rutting resistance and moisture damage resisting.

Asphalt Cement
One kind of asphalt cement is used with (40-50) penetration grade brought from AL-Daurah refinery. The physical properties of asphalt cement were evaluated according ASTM standards (ASTM, 2003) and compared with Iraqi Specification known as State Commission of Roads and Bridge specifications (SCRB/R9, 2003), as shown in Table 1.

Aggregate
The aggregate used in this study (coarse and fine) were originally obtained from AL-Najaf quarries. The aggregate were sieved and recombined to meet the requirements of wearing course gradation according to SCRB specification (SCRB, 2003). The physical properties of aggregate are shown in Table 2, while Table 3 shows the aggregate gradation.

Filler
Filler materials represent mineral particles that passes sieve No .200. Filler used in this study, was ordinary Portland cement (Tasluja), at (7%) content, which represent average value of SCRB specifications (SCRB, 2003).

Hydrated Lime
The Hydrated lime used in this study was brought from Al-Noora plant in Karbala Province. Hydrated lime was used in dry state with the percentage (0, 0.5, 1, 1.5, 2, and 2.5%) by weight of total aggregate and as partial replacement of the used filler material with remain(7%) constant; Table 4 shows the properties of cement filler and hydrated lime.

Experimental Work 4.1Asphalt Concrete Mix Design
The asphalt concrete mixtures design started by mixing mixture components (aggregate, filler material, and asphalt cement), and determining the optimum asphalt content using the Marshall Mix design method in accordance with ASTM D1559 (ASTM,2003). The optimum content was found to be (4.9%) by the weight of aggregate. This value (4.9%) will be used for the asphalt concrete mixtures content hydrated lime to eliminate the effect of asphalt content on the results analysis, Table5 shows the asphalt concrete mixtures properties.

Retained Marshall Stability Test
Retained Marshall Stability (RMS) test is used to determine retained Marshall Stability for Marshall Compaction specimens after curing for 24 hours in a water bath at 60 o c.It is one of tests required by SCRB to be performed on asphalt mixes used in surface course in addition to Marshall Tests, in accordance with method ASTM D 1075. The specimens were divided into two groups; the first group (un conditioned) were immersed in water at 60 Cᵒfor 30 min, and then loaded to failure by using curved steel loading plated along with a diameter at a constant rate of compression of 51mm/min. The second group (conditioned) was placed in water bath at 60 Cᵒ for 24hr. The retained Marshall stability (RMS) was calculated according to the following equation.

Indirect Tensile Strength Test
The indirect tensile strength test was conducted in accordance with AASHTO T283, as standard test method to measure the resistance of compacted bitumen mixtures to moisture damage. A static load is increasingly applied at rate of 2.0"/min to the sample until failure. In the test, two groups of samples were used, the first one represent control samples (un conditioned) samples which were tested at 25 Cᵒ. The second one are (conditioned) samples, which they are submerged in water at 60 Cᵒ for 24hr, and then tested at 25 Cᵒ.All samples were compacted to attain 7% air voids ±0.5%.For both types of samples the indirect tensile strength is calculating according equation (2). The tensile strength ratio (TSR) (i.e., ratio of ITS of conditioned samples to the ITS of un conditioned samples) were calculated according to equation (3), and used as moisture damage resistance index for asphalt mixtures. The higher TSR is better in the moisture damage resistance.

Effect of hydrated Lime on Marshall Stability and Air Voids
The effects of hydrated lime on the Marshall Stability and air void values are shown in Figure1, and Figure2. It clear in these figures that, the Marshall stability increases with increased hydrated lime content. The maximum increase was, at hydrated lime content equals to (2.5%).
Air voids values decreased with increased hydrated lime content to the optimum content (2%), and then increased for hydrated lime content (2.5%). As the beneficial application of (2%) hydrated lime to asphalt mixtures improves mixture properties by increasing Marshall Stability, reducing air voids, which effect on the mixtures durability against environmental effects (moisture damage).

Effect of Hydrated Lime on the Retained Marshall Stability
Index of retained Marshall stability (RMS) can be used to measure the effect of water damage on the Marshall stability for the asphalt concrete mixtures exposed to moisture conditions. The results for this test are listed in Table 6, and shown in Figure 3. As shown the Marshall Stability values decrease for the mixtures which they exposed to moisture conditions. The retained Marshall Stability values were calculated for each mixtures type, and it found to be equal to (60.6%) for control mixture and increase for the mixtures contain hydrated lime. The optimum increase at(2.5%) hydrated lime, where RMS equal to (75%), which indicate that hydrated lime tends to reduce the effect of water action(stripping action), increase stiffness, and increase cohesive strength between asphalt binder and the aggregate particles.

Effect of Hydrated Lime on the Indirect Tensile Strength Ratio
The results of indirect tensile strength are listed in Table 7, the indirect tensile strength for both types of samples (un conditioned and conditions) were calculated and the TSR were determined. As shown in Figure4, the TSR value for control mixture equal to(72.3%) and this value meets the specification limit(TSR=70%, as minimum value), and for lime-HMA the TSR increase with the increase in hydrated lime content to the optimum content (2%) and then decrease. The results for this test indicate that hydrated lime had improved the moisture damage through increasing TSR.

Conclusions
Depending on the test program results the following points were concluded: 1. Using hydrated lime as additives and as a partial replacement of filler material had improved properties of asphalt concrete mixtures at different content.

2.
Marshall Stability increases with the increase of hydrated lime content, with rate equal to (40%) for (2.5%) hydrated lime content. 3. Air voids decreased with increasing hydrated lime content, especially at the optimum content (2%) hydrated lime and the rate of decrease equals to (17%), and then air voids increase. 4. According to retained Marshall stability test, hydrated lime tend to reduce the effects of water and temperature on the cohesion and stiffness of mixtures, where RMS value increase with increase hydrated lime dosage, where the maximum value equal to(75%) for(2.5%) hydrated lime content. 5. The addition of hydrated lime had improved the tensile strength for unconditioned and conditioned specimens; as a result the TSR values increase from (72%) to (81 %) which improves moisture damage resistance. 6. Finally the using of hydrated lime as partial replacement of filler material improved Marshall stability, reduce air voids, increase cohesive strength, and tensile strength, which make asphalt mixtures more stiffness and durable against environmental effects, and the optimum hydrated lime content will be (2%) as indicate from the tests results. C-131 25%, Max 30% ----------