Analysis of the Impact of Redispersible Polymer Powder on the Water and Frost Resistance of Cold-Recycled Mixture with Bitumen Emulsion

The subject of the research presented in the article is the assessment of the effect of redispersible polymer powder (RPP) on water and frost resistance of a cold-recycled mixture with bitumen emulsion (BE-CRM). The article presents the results of research on the influence of polymer powder EVA based on polymer (polyethylene-co-vinyl acetate) on the properties of BE-RCM. The impact analysis was determined using the assumptions of the Box-Behnken experiment plan in which three components are controlled. In this case, the variables were the content of: polymer, cement and asphalt emulsion. All ingredients were dosed with a step of 1.5% of the percentage share in the mixture composition. Polymer and Portland cement in an amount of 0.5% to 3.5%. On the other hand, the pure asphalt originating from the asphalt emulsion was 0.0%, 1.5% and 3.0%, respectively. The scope of the tests included the determination of: mixture density, void content (Vm), water absorption (nw), intermediate tensile strength (ITS), to water (TSR) as well as water and frost according to AASHTO T283.

Combined Effects of Oxidation, Moisture, and Freeze–Thaw on Asphalt Mixtures

This article demonstrates the need to laboratory condition asphalt mixtures to simulate combined environmental effects and then to test unconditioned and conditioned specimens in a manner that damage from these environmental effects can be accumulated. The current state-of-the-art for evaluating asphalt mixtures for use on projects relies on either single-mechanism laboratory conditioning such as oxidation in AASHTO R30, or test methods that cannot accumulate combined effects such as indirect tensile strength in AASHTO T283. This article evaluated hundreds of laboratory-conditioned and field-aged specimens in a hot and no-freeze climate to demonstrate a laboratory conditioning protocol that was able to simulate at least 4 years of field aging, whereas conventional single-mechanism protocols were not. Temperature and moisture conditions within asphalt mixtures were measured over time and used as part of the assessment. The conditioning protocol that showed the most promise consisted of combined exposure to oxidation, moisture, and freeze–thaw mechanisms. The specific combined-effects conditioning protocol used here was 5 days of oxidation at 85°C, 14 days of moisture while submerged in 64°C water, and one freeze–thaw cycle. Other combined-effects protocols could be more suitable for other environments or situations; the main point of this article is that inclusion of oxidation, moisture, and freeze–thaw conditioning into one protocol is promising. The environmental conditions and mechanical property test data presented here suggest the asphalt industry needs to be harsher on mixes during laboratory evaluations, and that combined environmental effects conditioning should be given implementation consideration.

Using Nanopolyacrylate and Nanocomposite as Binder Modifiers for Stone Mastic Asphalt (SMA)

This paper presents the potential benefits of using nanopolyacrylate (NP) and nanocomposite (NC) polymers as modified binders in SMA mixtures. The optimum binder content of the SMA control mix was designed using PG76 binder and Modified Lottman test (AASHTO T283) was used to determine the stripping performance. A total of six (6) SMA modified mix were prepared using NP and NC modified binder formulations at 2%, 4% and 6%. Results from tensile strength test showed that SMA-NC6 have the highest IDT (521kPa) followed by SMA-NP6 (511 kPa), SMA-Control (500 kPa), SMA-NC4 (449kPa), SMA-NC2 (403kPa) and SMA-NP2 (379kPa). The stripping test on both control and modified SMA mixtures showed that TSR values for all the mix pass the 80 percent limit which fulfils the AASTHO T283 standard requirement and are therefore least susceptible to stripping. Based on the tensile strength test results and stripping performance, it was found that the addition of NC and NP modified binder demonstrate great potential in SMA mixtures showing significantly improved cohesion as well as adhesion properties of the binder. The results from this study found that all the SMA mix are resistance to moisture damage which could sustain the load from vehicles and exposed to severe condition without large degradation of the structure.

A Comparative Study of Anti-Stripping Additives in Porous Asphalt Mixtures

Presence of water in porous asphalt mixtures detrimentally affected the bonding between binder-aggregate interface and cohesive failure within the binder-filler mastic, making them prone to stripping which contribute to the performance and durability. This paper presents the effect of anti-stripping additives in porous asphalt mixes. In this study, the Marshall specimens were prepared using quarry dust, ordinary Portland Cement (OPC) and Pavement Modifier (PMD) as filler then mixed with 60/70 penetration grade bitumen. The specimens were measured for air voids content and coefficient of permeability and subsequently tested using indirect tensile and Cantabro tests. The moisture sensitivity of porous asphalt was determined based on the ratio of dry and conditioned specimens according to AASHTO T283. The specimens prepared with PMD showed lower air voids content, hence decrease the permeability to give a higher tensile strength and lower abrasion loss compared to specimens prepared with OPC and quarry dust. Based on the results, the PMD filler has a great potential to improve resistance to moisture damage compared to mixes with OPC and specimens prepared with quarry dust fillers.

Issues Pertaining to Use of Superpave Gyratory Compactor

Agencies, industry, academia, and others are rapidly implementing the products of the asphalt research portion of the Strategic Highway Research Program, products collectively referred to as Superpave. One of the principal products has been the Superpave gyratory compactor (SGC). The results of an experimental program, conducted at the Asphalt Institute Research Center in Lexington, Kentucky, and aimed at assessing the effect of various compaction parameters on SGC test results, are outlined. Compaction results were most often different when different mold diameters were used. The length of the laboratory short-term aging period also affected test results. Compaction temperature was a critical factor when a modified binder was used. SGC affected moisture-susceptibility test results although specimens fabricated using SGC were successfully demonstrated to predict moisture damage using the AASHTO T283 protocol. The experiment also compared the compaction characteristics of several different units. This comparison demonstrated minor to moderate differences in test results when the same mix was evaluated.