Investigation of Retroreflective Sheeting Materials Response to Induced Strain While Mounted to Common Civil Substrates for Use as Passive Strain Sensors for Structural Health Monitoring

Abstract

Retroreflective sheeting materials (RRSM) are used for various applications in engineering, although primarily for traffic signs and roadway markings. There are several ASTM standard types of RRSM that have required values of retroreflection to ensure safe usage. Retroreflectivity (RR) is the portion of light returned to the light source measured in candelas per lux per square meter, as measured using a retroreflectometer. As load is applied to RRSM, the retroreflection changes, and many have a reasonably linear relationship to the material’s strain (ε), thus, opening the possibility for using RRSM as a passive strain sensor for structural health monitoring that is low cost, practical, and innovative. Material sensitivity (retroreflectivity divided by strain) is the most important factor when evaluating various standard RRSM types for potential use as passive strain sensors. Previous work has showed that a manufacturer, designated “B”’s standard Type VIII (designated B-TVIII) material has the highest retroreflective sensitivity to induced strain, making it the best candidate for passive sensing. Other materials are also candidates, such as manufacturer “A”’s Type XI white (A-TXIW). To continue to evaluate RRSM’s potential to be used as a sensor, an understanding of the material’s behavior while adhered to common civil substrates, such as concrete and steel, is necessary. RRSM was mounted to steel and cyclically loaded in tension to examine the RR versus microstrain (μm) relationship, assess mounting procedures and compare results to previous tension tests of the bare materials. Initial results show that the RR-μm relationship of the material tested alone in tension differs from the same relationship when it is adhered to a steel specimen. Several factors were considered, such as surface preparation, RRSM length and adhesion materials to understand why the relationship differs. Through testing, it became apparent that temperature may have an effect on the results and temperature vs RR of B-TVIII and A-TXIW were evaluated and it was determined that the retroreflectivity of the material is lower at lower temperatures.