Application of the pneumatic pin penetration test to estimation of compressive strength of shotcrete in Korea

Shotcrete plays a key role in reactions with ground deformation as a primary support and shows time-dependent behaviors after installation. Therefore, it is very important to estimate compressive strength rapidly as well as accurately for quality control of shotcrete. The specification for shotcrete is mainly based on its compressive strength in most countries, although flexural strength and toughness properties are also important components to be considered in the quality control of Steel Fiber Reinforced Shotcrete (SFRS). Therefore, compressive strength is considered to be the most important and fundamental factor among a number of mechanical properties of shotcrete in the quality control. However, it needs much time and sometimes many cares to obtain shotcrete specimens cored from tunnel wall. In addition, the effects of ground conditions, high-pressure during spraying and accelerator dosage cannot be considered in moulded specimens. From these backgrounds, a test method to measure compressive strength rapidly as well as effectively has been demanded in fields. In this study, the pneumatic pin penetration test was applied to estimate compressive strength of shotcrete more rapidly, accurately and safely. The test have many advantages over conventional methods which are to replace explosives with compressed air, and cover a wide range from low strength of below 10 MPa up to 30 MPa. It was intended to verify its applicability through field tests in a tunnel as well as laboratory tests with mortar specimens. In laboratory tests, mortar specimens were prepared under homogeneous conditions. As results, the variation of penetration depths for a specimen took place with maximum errors below plus or minus 5 mm, showing excellent repeatability. At early ages of installation of shotcrete, estimated and actual uniaxial compressive strengths were in good agreement each other. However, as shotcrete hardened, the average strength estimated from the pneumatic pin penetration tests became higher than those from mortar specimens. In field tests, shotcrete cores were bored from tunnel sidewall at different ages in order to compare the estimated strengths from the pin penetration tests with the actual core strengths. The results from the field tests showed the same tendency as those from laboratory tests. The probable reason for the discrepancy between the estimated and actual compressive strengths at later ages may be due to a size effect, hardness of shotcrete surface, aggregates and the relationships derived from pull-out tests for the estimation of early-age strength. To apply the pneumatic pin penetration test to the estimation of compressive strength at later ages, further studies to consider such effects might be necessary. Since results of Schmidt hammer tests were not significantly different at different ages, it was concluded that the Schmidt hammer test might be difficult to be applied to the estimation of shotcrete strength. (A) "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • Authors:
    • BAE, GYU-JIN
    • Lee, Seok-Won
    • CHANG, SOO-HO
    • PARK, HAE-GEUN
    • LEE, MYEONG-SUB
    • KIM, JAE-KWON
  • Publication Date: 2004-7

Language

  • English

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Filing Info

  • Accession Number: 01011601
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:20PM