Now showing 1 - 2 of 2
  • Publication
    Expansive cements and soundless chemical demolition agents : state of technology review
    Expansive cements and soundless chemical demolition agents (SCDAs) were first introduced in the early 1970s but failed to gain widespread adoption for selective removal of rock and concrete due to their proprietary nature and a lack of usage guidelines. Nearly 40 years later, the patents have expired, and a large number of competitive products have entered the market. These factors coupled with a heightened interest in their potential environmental benefits have greatly expanded their usage. Specifically, these chemicals can be introduced into a pattern of small, drilled holes in concrete and/or rock. After a specific period (usually less than 24 hours), the in-situ material will crack sufficiently that it can be removed without the use of traditional explosives or further percussive efforts. The products generate substantially less noise and vibration than usually associated with the removal of rock and concrete. This paper provides a state-of-the-technology review of five available products. The focus is on the proposed applicability of various products under specific conditions. Special attention is paid to the viability of such agents under varying temperatures and with materials of particular strengths.
  • Publication
    Expansive fracture agent behaviour for concrete cracking
    (Institution of Civil Engineers/Thomas Telford Publishing, 2010-06) ; ; ; ; ;
    Increasing concerns regarding litigation and terrorism provide a strong dual motivation to decrease high explosives usage in the construction industry. This paper provides parameter considerations and initial guidelines for the application of expansive fracture agents, typically used for concrete and soft rock removal. This approach may be especially appropriate near environmentally and historically sensitive sites. Thirty-three unreinforced blocks (approximately a cubic meter each) of varying strengths composed of sand, cement, and flyash were tested under various temperature environments, with differing expansive agents, confinement levels, and post-cracking treatments. Cracking characteristics such as crack initiation and crack expansion were analyzed. Although the performance of expansive cement was dependent upon a highly complex set of variable interactions, higher ambient temperatures, higher agent mixture temperatures, and chemical configuration designed for colder temperatures decreased the time to first crack and hastened the extent of cracking. Conversely, higher strength material required more time to first crack, as well as an extended time to achieve a 25.4 mm wide crack. Manual interference with the normal material volume expansion slowed the cracking process but did not truncate it, while the manufacturer’s recommendation to introduce water post-cracking actually reduced and slowed the extent of cracking.
      1504Scopus© Citations 41