以鑽心強度作為控制性低強度材料品質判斷依據之研究

Abstract

一般混凝土及控制性低強度材料(簡稱CLSM) 在施工檢驗部分，強度品質評定均以圓柱試體與鑽心試體抗壓強度試驗為主。圓柱試體抗壓強度試驗部分，一般混凝土試驗規範為CNS 1232，CLSM試驗規範為ASTM D4832，二者適用規範不同點在於加壓速率之規定不同。鑽心試體取樣部分，一般混凝土試驗規範為CNS 1238，並以CNS 1232試驗抗壓強度，惟CLSM鑽心試體取樣及抗壓強度試驗至目前為止國內外尚無明確適用規範，部分單位係比照一般混凝土鑽心試體CNS 1238之規範，並未考慮CLSM其低強度(90kgf/cm2以下)之屬性是否適用之影響，且無法出具TAF實驗室認可標誌之報告。另一般混凝土於澆置後大多未受外力擾動，亦須依規養護，而管線工程在管溝回填CLSM達初凝後(早強型約3.5小時；一般型約12小時)，為免影響交通即需鋪設瀝青混凝土並滾壓夯實，恢復通車。在滾壓夯實及車流載重之衝擊下，對CLSM初期強度發展將較一般混凝土在未受擾動及可依規養護之情形影響更大。 目前各管線單位工程契約對CLSM之鑽心試體抗壓強度折減規定不一，有些契約規定無折減，有些契約比照一般混凝土之鑽心強度折減，以設計強度之85%或75%作為品質合格與否之判斷依據。本研究實地以台灣自來水公司第三區管理處轄區新竹縣市之管線工程，以預拌混凝土場CLSM取樣之預拌實驗(對照組)及工地管溝回填CLSM取樣之現場實驗(實驗組)，採取CLSM圓柱試體及鑽心試體測試28天以上之抗壓強度，分析鑽心試體強度折減情形，由試驗數據探討CLSM施工檢驗以鑽心強度作為品質判定依據之合理性。

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.