The responses of rat neocortical neurons in vitro to iontophoretically applied N-methyI-D-aspartatc (NMDA) were investigated by means of intracellular recording in the presence and absence ofextracellular magnesium ions (Mg~'+). At Mg ~' + -concentrations of 1.3 mM the neurons responded with a depolarization accompanied by an increase in membrane resistance. Upon removal of Mg 2+ the NMDA-induced depolarization was markedly potentiated. However, even in neurons recorded from slices which were incubated in a Mg e'-free solution for 3 7 h, the NMDA response was still associated with a resistance increase, suggesting that the voltage-dependence of the NMDA-activated conductance is not exclusively determined by Mg ~ +.The depolarizing action of the excitatory amino acid N-methyl-D-aspartate (NMDA) on neurons of the mammalian central nervous system (CNS), including neocortical neurons, is associated with an apparent membrane resistance increase [1 6, 9, 10, 13, 14]. This conductance decrease was explained by the voltage-dependent activation of a cation (Na +, Ca2+)-selective channel [7,9] coupled to the NMDAreceptor. Because upon removal of extracellular magnesium ions (Mg 2+) the NMDA-activated conductance (gNMDA) became independent of the membrane potential, it was suggested that the voltage dependence of gNMDA is produced by Mg 2+, which, at physiological concentrations, reduces or blocks gNMDA at membrane potentials larger than -40 to -50 mV [9][10][11]. In contrast, it has been proposed that NMDA either activates a voltage-dependent Ca-conductance (ref. 2, but see ref. 4) or a TTX-resistant, voltage-dependent Na-conductance [3,8]. Previous intracellular investigations of the actions of NMDA on rat neocortical neurons in vitro suggested

Asphalt mixes often have many ingredients that can interact with each other. When put into service, where there are multiple environmental effects, there are many interactions that need mixture testing. This paper’s objective was to evaluate laboratory conditioning protocols coupled with subsequent property measurements for their ability to detect damage of asphalt mixtures in the southeastern U.S. climate (or similar climates). The investigation’s focus is the property measurements themselves, and in particular how a given test can simultaneously assess multiple types of damage (i.e. oxidation, moisture damage, and freeze-thaw damage). While in service, mixtures can be damaged in multiple manners so laboratory conditioning protocols that expose specimens to multiple types of damage are needed as are test(s) that can detect these damages in a manner that can help assess performance during service. Four plant produced mixtures with all virgin ingredients were evaluated at intermediate temperatures with mixture and binder tests. The mixtures were well suited for such a comparison because they consisted of all virgin binder. Indirect tensile (IDT) strength did not relate to Cantabro Mass Loss (CML) or binder test results, which was concerning. Even more concerning was IDT’s inability to respond to laboratory conditioning protocols that considered multiple environmental effects (i.e., oxidation, moisture, and freeze-thaw). CML results related to binder properties and were able to reasonably detect multiple types of environmental effects. As such, Cantabro testing is recommended over tensile strength for intermediate temperature mixture property assessments related to non-load associated environmental effects.

In recent years, warm technologies have made enormous changes to the flexible pavement industry in a variety of ways. Warm-mix asphalt is the most recognizable warm technology product, although other advantages are associated with better compaction over a wide range of temperatures and have made long-haul distances appealing for some applications. This paper focuses on using warm-mix technology at traditional hot-mix production temperatures for the purpose of facilitating long haul distances. The primary objective of this study was to investigate how binder-related properties change with haul time when material was mixed at hot-mix temperatures. A secondary objective was to determine if any behavioral differences were present between asphalt binders with no additive, foamed asphalt binders, and asphalt binders with a chemical additive. Plant-mixed asphalt was used for the investigation. The overall conclusion of the research was that haul times of 1 to 8 h produced no major differences in aging for a given binder type or between binder types. Subtle differences were observed between binder types in some instances (e.g., low-temperature properties were slightly better for mixes using warm-mix technologies).

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.

One of the most subjective decisions made during chip seal construction concerns when to allow brooms and traffic on the newly placed surface. If traffic is allowed too early, damage to the surface and to vehicles may occur. If the chip seal is opened too late, traffic is disrupted and motorists are inconvenienced. The curing of asphalt emulsions in the field is related to many factors, all affecting how fast the asphalt emulsion cures. Three laboratory test methods that measure adhesive strength gain as a function of moisture loss are presented. Two of the methods were sweep tests, one performed according to ASTM D7000 and the other according to a modified method. The third test used frosted marbles to measure adhesive strength gain. Results of all tests were similar and indicated that strength in emulsion residues increased as the total moisture in the system was reduced. This finding is important because the moisture content is independent of the mechanism reducing it. Therefore, prediction of strength gain should be possible by measurement of the moisture loss of a given chip seal system. The time required to obtain that strength gain varies in seals because of differences in emulsion, aggregate, interaction factors, weather, ambient temperature, and other environmental factors. Test results indicated that as moisture loss approached 75% to 90%, strength gain was significantly enhanced.