Temperature-related performance factors for chemical demolition agents

Abstract

Soundless chemical demotion agents (SCDAs) are percussion-free alternatives to blasting for rock, concrete, and masonry. They hold great potential for selective demolition of and around historic masonry. Although known to be temperature sensitive, to date their performance has not been quantified in ambient environments below 20˚C.This paper examines 6 large-scale (0.77-1.0 m 3 ) specimens in moderate, ambient temperatures (16.1-19.3˚C). Substantially slower response than that reported by manufacturers was documented. Initial cracking required 25+ hours and continued for 4-8 days. Cracks opened rapidly after Minimum Demolition Time [(MDT) -cumulative cracking around the perimeter reaching ~25 mm (1 in.)], which was at 42 hr and 70 hr, respectively in 16.8 MPa and 33.1 MPa specimens. Post-MDT, crack-width opening velocities were 0.35-0.96 mm/hr, approximately 1/3 rd to 2/3 rds of pre-MDT velocities. A 0.5°C ambient temperature drop delayed MDT by 6.5 hr amongst specimens of the same size and strength. Generally, MDT appeared to correlate with the material strength (irrespective of ambient temperature or specimen size), while TFC was more influenced by ambient temperature. Finally, SCDA reapplication proved effective for incompletely cracked specimens.