A Study on the Controlled Low-Strength Material Quality Determination based on Drilled Cores intensity

• Main Authors: Chiu, Tsung-Jen, 丘宗仁
• Other Authors: Dzeng, Ren-Jye
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/31113243011326672604

碩士 === 國立交通大學 === 工學院工程技術與管理學程 === 99 === In construction inspection, the strength quality of general concrete and controlled low-strength material (CLSM) is mainly evaluated based on the compressive strength of cylindrical specimens and drilled core specimens. For testing the compressive strength of cylindrical specimens, CNS 1232 is the specification for general concrete, and ASTM D4832 for CLSM. These two specifications are different because of varied compressive rates. For drilled core sampling, CN1238 is the specification for general concrete, while CNS1232 is applied for testing the compressive strength. Unfortunately, there is no suitable specification for either CLSM drilled core specimen sampling or CLSM compressive test, domestically as well as internationally. Some divisions adopt CNS1238, a specification for general concrete’s drilled core specimens, for CLSM's drilled core specimens, but due to the low-strength attribute of CLSM (under 90kgf/cm2), it is not clear whether CNS1238 is suitable or not. Furthermore, no report with an approval mark from the TAF research office can be provided. For most general concrete after pouring, it is undisturbed by external forces and has to be maintained according to regulations. Bur for CLSM on the other hand, after the initial setting of CLSM in trench backfill of pipeline projects (an early strength type would take 3.5 hours; a general type would take 12 hours), asphalt concrete has to be paved, rolled, and compacted to avoid disturbing the traffic. In contrast to the fact that general concrete is undisturbed and can be maintained by following regulations, those impacts from rolling and compacting as well as traffic loads on CLSM could significantly affect the initial strength development of CLSM. Presently, reduction regulation on the compressive strength of drilled core specimens of CLSM specified in the construction contract of different pipeline divisions is inconsistent. Some contracts allow no reduction while others reduce the required strength to 85% or 75% of the drilled core strength of general concrete and treat this value as a reference value for quality. This on-site study took place at pipeline projects in Hsinghsu City and County, which is under the jurisdiction of Taiwan Water Corporation Third Branch. Treated as the control group, CLSM specimens from pre-mixed concrete fields were used for a pre-mixed experiment. CLSM specimens from trench backfill construction sites, i.e., the experimental group, were used for an on-site experiment. CLSM Cylindrical specimens as well as drilled core specimens were obtained, and they were tested for over 28-day compressive strength in order to analyze the degree of strength reduction of drilled core specimens. The authors discussed the appropriateness of using drilled core strength as a quality determinant in CSLM construction inspection based on the acquired data.