Pavement concrete joints are the weakest locations in concrete pavement systems. They are man-made cracks to accommodate concrete slab expansion and contraction due to temperature fluctuations. Sealant is usually used in pavement joints to prevent roadway debris, deicing chemicals, and moisture from entering the joint. When sealant fails, the pavement deteriorates rapidly; and when joint sealant performs adequately, the pavement preserves its intended performance. In the field, joint sealant undergoes two types of mechanical loading simultaneously. The sealant is experiencing tension or compression as slabs contract (low temperature) or expand (high temperature), respectively. Sealants also experience shear as heavy trucks travel over the joint and deflect the ends of the pavement slabs. In addition, sealants may also be exposed to a variety of environmental conditions, such as moisture, ultraviolet light, and jet fuel, which in some cases could be detrimental to their performance. In this study, the effects of vehicular and environmental loading on joint sealant performance were evaluated. To simulate the sealed joint performance, specimens were constructed by sandwiching a sealant between two 50.8 mm Portland cement concrete (PCC) cubes. Prior to mechanical loading, specimens were subjected to partial immersion in distilled water, partial immersion in jet fuel, and/or exposure to UV-A light. The specimens were then subjected to static horizontal tension, simulating slab contraction, and cyclic deflection-controlled shear, simulating heavy trucks travelling over the joint. The cycle consists of one 0.2 second period of sinusoidal loading (total 6.4 mm deflection) followed by a 0.4 second relaxation. The mechanical loading was applied using a special fixture developed at Virginia Tech, which is connected to a closed-loop servo-hydraulic loading machine. Two types of sealants (preformed neoprene and field-molded silicone with a primer) were tested using PCC mixes with two different aggregate types. In, addition, two different joint widths were evaluated for each sealant type. From the results of the cyclic testing and environmental conditioning, it was shown that the use of a primer greatly enhances the performance of the silicone sealant used with concrete containing limestone aggregate. In addition, severe swelling occurs when silicone sealant is exposed to jet fuel, and the failure of the field-molded silicone initiated at the bottom of the sealant and propagated upward. The preformed neoprene sealants proved very durable despite any combination of environmental conditioning, provided that the sealant remained in compression.