超微粒水泥滲透灌漿與灌注量之研究

Abstract

本研究藉由自行設計的高速渦流攪拌機及氣壓式灌漿設備，以低壓滲透灌漿的方式，將超微粒水泥漿體灌注於兩種不同級配分佈之中、細砂的圓形砂柱試體(即渥太華砂編號250與403)，探討不同水灰比情況下之超微粒水泥漿體，達到預定改良砂柱高度所需之灌注量與其流動的情形。由試驗結果發現，不同水灰比的漿體到達預定改良砂柱高度時，所需的灌注量介於1.16倍至1.63倍的孔隙體積，且水灰比越低，所需的灌注量越少，流動越慢。除此之外，亦發現這兩種不同級配分佈之砂柱試體，灌注任一水灰比的超微粒水泥漿體，皆有相近倍數孔隙體積的灌注量；且因中砂級配分佈之圓形砂柱試體孔隙較大，其流動性較好。 為評估灌漿試體的改良成效，本研究於圓形砂柱試體灌注養護齡期7天與28天後，進行不同灌注距離試體之孔隙率試驗與抗壓強度試驗。由試驗結果顯示，灌漿改良後之試體，水灰比越低，孔隙率越小，單壓強度越高。此外，亦發現這兩種不同級配分佈之砂柱試體，灌注任一水灰比的超微粒水泥漿體時，中砂級配分佈之圓形砂柱試體的單壓強度均相對較低；原因可能是其試體有較大的顆粒與孔隙粒徑，導致其單位體積內顆粒與漿體間之膠結表面積較少和其級配比較不良。再者，以高水灰比漿體改良之試體，此現象更為明顯，原因可能是漿體水灰比越高，析離越多，穩定性越差，膠結後與中砂級配分佈之圓形砂柱試體所遺留下的孔隙較大，使單壓強度相對更低。除此之外，灌注過程中，因低水灰比漿體之壓濾失水(filtration)現象較顯著，所以距灌注點越近的第一節試體，養護齡期7天時，其單壓強度較高；然而，於養護齡期28天時，因卜作嵐效應及水化反應，導致第二節試體有較高單壓強度。而孔隙率則距灌注點越近其孔隙率越小。 本研究亦針對水灰比2情況下，探討不同爐石添加百分比(即50%與70%)對灌漿過程的影響，其試驗結果顯示，同一灌漿條件之砂柱試體，達到預定改良量高度時其所需之灌注量相近，但爐石添加百分比越高，流動性越好，灌注時間越短。

In this study, microfine cement grout with different water-to-cement (w/c) ratios was injected using a low-pressure permeation grouting technique into sand columns composed of sands having two different grain-size distributions (namely, a medium grain-size sand and a fine sand, or more specifically, Ottawa sands Nos.250 and 403) to determine grout injection amounts needed to reach a predetermined height of the sand columns and study the fluidity of grout in the columns. The grout was prepared and injected with a high speed vortex colloidal mixer and pneumatic grouting equipment designed and fabricated for the study. The experiment results show that the necessary injection amounts of grout having different w/c ratios for reaching the predetermined height were 1.16 to 1.63 times the volume of pores in the sand columns, wherein the necessary injection amounts became smaller and grout fluidity became lower as the w/c ratio decreased. It is also found that, whatever the w/c ratio, the injection amounts for the sand columns having the two grain-size distributions were similar times the volume of pores. Moreover, since the sand columns of the medium grain-size sand had larger pores, grout fluidity was higher in such columns. In order to evaluate the improvement of grouted samples, porosity and compressive strength were tested at different grouting distances within the samples on the seventh and 28th day after grouting. It is found that samples having a lower porosity and injected with a grout having a lower w/c ratio had higher compressive strength. Furthermore, regardless of the w/c ratio of the microfine cement grout, the sand columns composed of the medium grain-size sand showed relatively low compressive strength. This is probably because the particle and pore sizes in such columns were larger and therefore resulted in a relatively smaller cementing area between the particles and grout in a unit volume, and relatively poor grain-size distributions. This phenomenon became more apparent in sand columns injected with a high w/c ratio grout, probably because, as the w/c ratio of the grout rose, segregation increased and stability deteriorated, so that larger pores were left in the sand columns composed of the medium grain-size sand after cementing, which lowered the compressive strength still further. In addition, grout having a lower w/c ratio showed more significant filtration during grouting. As a result, the first sections of the samples which were closer to the injection point had higher uniaxial compressive strength on the seventh day. However, due to the pozzolanic reaction and hydration, the second sections of the samples exhibited higher uniaxial compressive strength on the 28th day. Besides, porosity lowered as the distance to the injection point decreased. This study also examined the effects of different slag contents (i.e., 50% and 70%) on grouting when the w/c ratio was 2. The experiment results show that, while the necessary injection amounts for reaching the predetermined height were similar for sand columns having the same grouting condition, grout fluidity was improved and the injection time shortened as the slag content increased.