Anti-stripping Additives Research Articles

Experimental Evaluation of Anti-stripping Additives Mixing in Road Surface Pavement Materials

Most road surfaces in Taiwan are paved with asphalt concrete but the phenomena of rutting, cracking and stripping of the pavement are frequently occurring due to the effects of traffic flow, thermal variation and water erosion caused by rain. In this study, a series of experiments were performed to examine the effectiveness of anti-stripping fillers, which include; rock flour, rock flour with 1% lime and rock flour with 1% cement, respectively, in the mixture of asphalt concrete. The experimental mixing results showed that the case of rock flour with 1% lime has a relatively better performance in several categories including stability value, flow value, retained strength, wrapped asphalt rate in grains, resilient modulus, dynamic stability and rate of rutting deformation. The evaluated information implies that this filler can increase the asphalt concrete’s abilities to resist rutting deformation and stripping of the road surface, thus increasing the durability. The results also provide a good reference for using in road construction with similar regional characteristics to Taiwan.

New Chemical Antistripping Additives for Bituminous Mixtures

Abstract The main objective of this study was to develop new, low cost, chemical antistripping additives that have low negative effects on Hot-Mix Asphalt (HMA) properties such as stability and low temperature cracking potential. To achieve this objective, HMA specimens were prepared using limestone aggregate, asphalt with 80/100 penetration, and different types of chemical antistripping compounds. Eighteen different low cost chemical compounds were prepared and added to the HMA at different percentages. The effect of 28 different combinations of additive types and amounts on the HMA stripping was evaluated using the modified Texas Boiling Test. The results indicated that out of the 28 evaluated combinations of additive type and amount, five combinations caused a negative or no impact on stripping resistance. On the other hand, twelve additive combinations show relatively small improvements in stripping resistance. Another 11 additive combinations showed a positive effect on stripping resistance. Five of these 11 additives showed a high positive improvement in the stripping resistance (increase in coating areas was greater than 20%). However, of these five additives, four caused a high reduction in the asphalt ductility and penetration, while the fifth one (Aluminum mono-stearate) caused a small reduction in ductility and an insignificant change in penetration. This suggests that this additive is suitable for use as an antistripping agent. The effects of antistripping additives in improving stripping resistance may be explained by the formation of strong links between the metal surfactant and with both the aggregate and asphalt. The stripping resistance of metal surfactants derived from the saponification reaction between the metal hydroxide [Ca(OH)2 and Al(OH)3] and the triglyceride of stearic acid was less than those derived from pure stearic acid (by neutralizing the stearic acid with the metal hydroxides). This may be explained by the presence of glycerol in the metal surfactants derived from the saponification reaction. Since glycerol contains three hydroxyl groups, it makes strong hydrogen bonding with water and appreciable interaction with the metal surfactant due to the presence of dipole-dipole forces. Accordingly, some of the metal surfactant and its attached asphalt are leached out during the boiling test producing a lower anti stripping effect.

Relating Adhesion and Cohesion of Asphalts to the Effect of Moisture on Laboratory Performance of Asphalt Mixtures

Antistripping additives and polymer modifications are two common modifiers used to improve the fundamental properties of asphalt binders as those properties relate to the performance of asphalt mixtures. Adhesion and cohesion are two important related properties of asphalt binders that can affect asphalt mixture performance before and after water conditioning. The purpose of this study was to quantify the effects of antistripping additives and polymers on the adhesion and cohesion of binders and to relate these effects to the performance of mixtures as measured in the laboratory before and after water conditioning. The performance tests of asphalt mixtures included indirect tensile strength, uniaxial compression permanent deformation, and Hamburg wheel tracking. Asphalt mixtures were produced with different modified binders and with two aggregate types. The binders were modified with antistripping additives and polymers and by chemical treatment and oxidization methods. Granite and limestone were selected as two types of aggregate sources. The results indicate that the performance of asphalt mixtures is highly dependent on modification techniques and water conditioning. The overall performance of polymer-modified mixtures is more desirable than those of unmodified mixtures and of mixtures modified with antistripping additives. Polymers are found to improve rutting performance, adhesion, and cohesion of an asphalt binder. In contrast, the antistripping additive can improve only the adhesion without changing other properties. The results of this study also illustrate that the adhesion and cohesion of an asphalt binder are good indicators of the performance of asphalt mixtures in the laboratory when they are conditioned with water.

Relating Adhesion and Cohesion of Asphalts to the Effect of Moisture on Laboratory Performance of Asphalt Mixtures

Antistripping additives and polymer modifications are two common modifiers used to improve the fundamental properties of asphalt binders as those properties relate to the performance of asphalt mixtures. Adhesion and cohesion are two important related properties of asphalt binders that can affect asphalt mixture performance before and after water conditioning. The purpose of this study was to quantify the effects of antistripping additives and polymers on the adhesion and cohesion of binders and to relate these effects to the performance of mixtures as measured in the laboratory before and after water conditioning. The performance tests of asphalt mixtures included indirect tensile strength, uniaxial compression permanent deformation, and Hamburg wheel tracking. Asphalt mixtures were produced with different modified binders and with two aggregate types. The binders were modified with antistripping additives and polymers and by chemical treatment and oxidization methods. Granite and limestone were selected...

Classical and Contemporary Aspects of Stripping in Bituminous Mixes

ABSTRACT Stripping or removal of bitumen from an aggregate because of water penetrating into the interface causes many pavements to fail. Stripping has been existent since the advent of paving technology. It causes functional weakening of pavements leading to costly repairs. This state-of-the-art paper deals with important concepts of stripping as, bitumen chemistry and rheology, aggregate properties (chemical and mineralogical composition, surface texture, morphology, porosity, etc), traffic, water properties, construction practices (mixing, placement and in-service drainage) and nature of antistripping additives. Adhesion of bitumen onto aggregate is explained based on theories like mechanistic tenacity, molecular orientation, chemical reaction, and thermodynamic balance of interfacial forces. Stripping is elucidated using several mechanisms namely, displacement, detachment, spontaneous emulsification, bitumen film rupture, water pore pressure, hydraulic scouring, chemical disbonding, microbial activity, osmosis; and blistering and pitting. Attendant theories to the mechanisms are explained. Moisture sensitivity test methods emerged are described and discussed. The large number of tests that have evolved shows the importance of the phenomenon of stripping. Remedial measures which include use of antistripping additives, careful selection of hot mix component materials, good construction practice, and others have been proposed for use in practice.

MOISTURE SUSCEPTIBILITY OF ASPHALT MIXTURE AND EFFECTIVENESS OF ANTISTRIPPING ADDITIVE

A series of laboratory tests was conducted to evaluate the moisture susceptibility of asphalt mixtures, including moisture damage of asphalt-aggregate bond, and the influence of water immersion on the properties of asphalt mixtures. Furthermore, the effectiveness of various anti-stripping additives was investigated through a variety of tests. It was found that both the asphalt and aggregate types have dominating influences on the moisture susceptibility of asphalt mixtures; hydrated lime slurry is an effective anti-stripping additive for improving the moisture susceptibility; and the net adsorption test, Lottman test and immersed wheel tracking test are effective tools to evaluate the moisture susceptibility.

Study on preparation of asphalt antistrip additives from amines and aldehydes

Study on preparation of asphalt antistrip additives from amines and aldehydes

A Titration Method for Measuring the Amount of Liquid Amine-Based Antistrip Additive in Asphalts and Pavements

A titration method for measuring the weight percent of amine-based liquid antistrip additives in asphalts and pavements was developed. The technique involves measuring the alkalinity of the sample and relating that to the measured alkalinities of both the pure asphalt and the pure additive in order to ascertain the additive concentration. This approach proved to be at least semi-quantitative, capable of measuring additive concentrations to within about 0.2% out of total additive concentrations of around 1.0%. It is required that samples of both the pure additive and the pure asphalt be available for comparison; it will not be possible to avoid this requirement due to chemical similarities between the additives and the asphalts. It is, however, possible to measure the difference in additive concentrations between two samples of pavement with a sample of just the pure additive; a pure asphalt sample is not necessary.

Evaluation of Moisture Susceptibility of Asphalt Mixtures: Conventional and New Methods

Evaluation of a mixture’s moisture sensitivity is currently the final step in the Superpave® volumetric process. This step is accomplished by using AASHTO T-283, which tolerates a range of values in the test variables of sample air voids and degree of saturation. The tensile strength ratios determined for the mixes in this study varied with the air void level and degree of saturation. Although the levels of conditioning were within the specifications for AASHTO T-283, test results both passed and failed the 80 percent criterion, depending on the severity of conditioning. An alternative to measuring indirect tensile strength is a test that evaluates a mixture’s fundamental material properties. A relatively simple test is proposed that measures the cohesion and friction angle for asphalt mixtures. In addition, the Superpave shear tester (SST) was incorporated as a tool in evaluating moisture sensitivity. The proposed axial test determined the cohesion and angle of friction of the mix. The friction angle remained constant for the conditioned and unconditioned samples. Hence, conditioning of the samples had practically no effect on the mixture’s internal friction. The cohesion of the mix decreased when the mix was subjected to conditioning. The reduction in cohesion was greater in the case of the Fountain aggregate, which is known to be highly moisture susceptible. The shear tests to failure performed on the SST confirmed the results of the new apparatus, which provides a simple method for determining a mixture’s cohesion. The loss of cohesion due to conditioning can be used to determine a mixture’s moisture susceptibility. The three antistrip additives used in this study were hydrated lime, a liquid amine, and a liquid phosphate ester.

Use of the Hamburg Wheel-Tracking Device for Evaluating Moisture Susceptibility of Hot-Mix Asphalt

Laboratory testing of hot-mix asphalt (HMA) to evaluate moisture susceptibility has improved over the past several decades. Within the past 8 years, the Hamburg wheel-tracking device (HWTD) has gained prominence in evaluating HMA for moisture susceptibility. There are no standard test methods or specifications established for this testing device. Laboratory repeatability of the test, testing configuration, test temperature, and capability to evaluate effects of antistripping additives in HMA were evaluated in this study. The HWTD was observed to be very repeatable where six replicate tests provided consistent test results. The device yielded repeatable results for mixtures produced with different aggregates and with test specimens fabricated by different compacting devices. The conventional testing configuration was altered so that cylindrical test specimens fabricated with a Superpave gyratory compactor could be used in lieu of rectangular slabs. Results indicate that cylindrical specimens compacted with the SGC could be used for moisture evaluation in the HWTD for comparative evaluation of materials. Typically, testing with the HWTD is performed at 50°C. Six mixtures were fabricated with and without antistripping additives and tested at 40°C and 50°C. Mixtures were modified with hydrated lime and a liquid antistripping additive and all were mixed with AC-20. Test results have indicated that mixtures with hydrated lime perform best, followed by those modified with liquid antistripping additive, and worst were those without any additive at 40°C. Inconsistent trends were observed at 50°C. The HWTD properly predicted performance of the mixtures modified with antistripping additives at 40°C.

Evaluation of Stripping in Virginia’s Pavements

Virginia has struggled with stripping of asphalt mixes since the 1970s. Initially, chemical antistripping additives were used; eventually, hydrated lime was required, under certain conditions, when it proved to be effective in a limited set of field tests. The specifications were then changed to require hydrated lime or a chemical additive that could produce a tensile strength ratio (TSR) equivalent to that obtained with hydrated lime. Because of this change, it was believed that chemical additive manufacturers made improvements to produce a new generation of additives that were superior to those previously available. In 1991, a small field study was initiated in Virginia to determine the performance of the new-generation additives and hydrated lime. The pavements still showed significant stripping. A follow-up survey including 74 sites scattered throughout the state verified this finding. No significant difference in the amount of stripping was detected between the mix types or between mixes that used chemical additives and those that used hydrated lime. In the initial study, the TSR test did not indicate accurately the stripping performance of the mixes. Because of this work, the Virginia Department of Transportation is considering changing its density specification and additional research is being conducted.

The Effect of Antistrip Treatments on Asphalt-Aggregate Systems: An Environmental Scanning Electron Microscope Study

The performance of three antistrip additives—a lime-treated aggregate, an amine-treated asphalt and a styrene-butadiene rubber-treated aggregate, was studied with an environmental scanning electron microscope (ESEM). Samples were prepared with the untreated asphalt and aggregate, the treated asphalt with untreated aggregate and untreated asphalt with each treated aggregate. The same asphalt and aggregate sources were used in each test and all samples were run in duplicate. All samples were examined along the asphalt-aggregate interface in the ESEM prior to and following each freeze-thaw cycle. The samples were subjected to a total of ten freeze-thaw cycles. All three additives reduced the potential for moisture damage by maintaining asphalt-aggregate adhesion better than the control samples. Based on ESEM observation of the asphalt-aggregate interface before and after freeze-thaw cycling, the styrene-butadiene rubber-coated aggregate samples performed better than the amine-treated asphalt samples which performed better than the lime-treated aggregate samples.

Recyclability of Moisture Damaged Flexible Pavements

Stripping has damaged some of South Carolina's asphaltic concrete pavements. It is not known whether the material properties of stripped asphalt pavement will allow its use for recycling. A field and laboratory study was initiated to investigate the feasibility of reusing moisture‐damaged asphaltic concrete; to determine the effects of antistrip additives on recycled mixtures; and to evaluate the recycled mix design procedures that use cored reclaimed asphalt pavement (RAP) instead of milled RAP. A total of 144 laboratory Marshall specimens were made and tested. In addition, field cores were obtained and tested before and after recycling. The dry and wet modulus resilience (MR) and indirect tensile strength (ITS), visual strip rating (VSR), and air voids (AV) of all specimens were obtained. Marshall specimens containing moisture‐damaged asphaltic concrete mixtures produced significantly higher strength values than those using only virgin material. Antistrip agents were found to be effective in increasing ...

Thermal Degradation of Antistripping Agents and Enhanced Performance by Curing

The heat stability of antistripping (AS) additives held in hot asphalt cement is investigated by observing the changes in additive concentration and additive performance with holding time at 162.8°C. The effect of mix curing by hot storage 149°C on stripping resistance is also investigated. The diffusitivity of an additive in hot‐asphalt cement is measured to determine the rate of additive migration to the aggregate surface during curing. The concentrations of all commercial AS additives tested are observed to decrease significantly when heated in asphalt at 162.8°C, with a corresponding loss in effectiveness. It is also found that mixture curing by hot storage remarkably improved stripping resistance. This is believed to be due to improved adhesion of asphalt to the aggregate surface. Additive migration rate to the aggregate surface is shown to be higher than apparent curing rate. This implies that the enhanced stripping resistance observed with curing is not due to additive migration. Asphalt hardening occurring during mixture curing is shown to have only a second‐order effect on stripping resistance.