高流動性海砂混凝土可行性研究

Abstract

海砂因受海水沖洗，紋理較平滑，顆粒較趨圓形，利用其粒形上優點，來探討海砂使用在 一般強度下(中低強度)高流動化混凝土之可行性及工程性質，並與河砂作相互比較。本研 究並適當添加飛灰及G Type強塑劑等，使其坍度在23∼25公分，流度在50公分以上且無骨 材析離及泌水，研究中採用觀音的海砂和西螺的河砂，配比設計採四種水灰比，飛灰取代 水泥重量0％及20％強塑劑劑量為0％，1.5％，並借由不同的拌合置料程序，S/A為變數來 配出不同配比，及拌合方式，量測新拌混凝土性質、抗壓強度、抗拉強度、乾縮性質等。 經由試驗結果顯示，水灰比大於0.45之一般性混凝土，因海砂粒形趨圓，細度模數(FM)約 1.43者，粒形的正面效應大於細度模數偏小的負面效應，有利於流動性增加，工作度提升 ，在相同水灰比及水泥用量下，純水泥組海砂大於河砂(FM=2.3)混凝土之坍流度值。但海 砂混凝土添加飛灰及SP後,在中低水膠比時不利於海砂混凝土流動性。研究中發現以下情 形：(1)以飛灰取代水泥量使得整體細度提升,會與顆粒細小海砂互相爭奪水份，使拌合水 量大幅增加。(2)在拌合水量增多情形下,SP與水混合後濃度降低,其釋水效果不佳。(3)拌 合程序不同會影響坍流度值。以上皆為影響到流動性因素，經試驗尋得之改良方法：(1) 在飛灰取代水泥量下，以試拌方式尋求最佳組合之S/A值，降低整體細度提供足夠水份潤 滑拌合料。(2) SP不與拌合水混合，採單獨加入提高釋水效果。(3)經試驗結果：海砂混 凝土添加飛灰及SP最佳拌合程序為：粗骨材→(水泥＋飛灰)→細骨材→拌合水→強塑劑。 經由以上改善結果：在水灰比=0.45時(1)可節省水泥用量(2)拌合水量減少34% ~30%(3) 9 0天已超越同水灰比之純水泥組抗壓強度。(4)流動性增加，提高工作度，達與純水泥組結 果相同。另飛灰取代水泥量20％，強塑劑量1.5％在相同水膠比使工作度變差，其乾縮及 重量損失率也較同坍度之一般純水泥組大。 Because of the pounding of the waves, sea sand grains tend to be relatively ro unded and smooth in shape. This project has attempted to take advantage of thi s grain shape and performed an investigation of the feasibility and engineerin g characteristics of using sea sand in ordinary strength (low to medium streng th) high-mobility concrete, and also made a comparison with the use of river s and. This study added fly ash and G type strengthener in order to obtain a col lapse strength of 23-25cm, a mobility greate Experimental results show that for ordinary concrete with a water/ash ratio greater than 0.45, the round ed grains of the sea sand exert a positive effect greater than the negative ef fect of their somewhat small fineness modulus of more than 1.43. Thus sea sand can serve to increase mobility and workability. With identical water/ash rati os and amounts of cement, the collapse/mobility values of the pure cement grou p were higher for sea sand than for river sand (FM=2.3). However, after fly as h and SP were added to sea sand concrete, moderate to low water/plasticizer ra tios did not enhance the concrete's mobility. The following discoveries were m ade: (1) Use of fly ash to replace cement increased the overall fineness of th e concrete; because the fly ash competed with the fine sea sand grains for wat er, the amount of water used in mixing greatly increased. (2) When a greater a mount of mixing water was used, and the thickness decreased after SP and water were added, the results of dilution water were poor. (3) Different types of m ixing procedures affected the collapse/mobility value. These are all factors that influence mobility. The following improvement methods were found through experiment: (1) When fly ash replaced cement, experimental mixing methods were used to determine the optimum S/A value that would reduce the overall finenes s value and provide sufficient water for complete mixing. (2) SP was not added to mixing water, but instead added alone to that influence mobility. The following improvement methods were found through experiment: (1) When fly ash replaced cement, experimental mixing methods were used to determine the optimum S/A value that would reduce the overall finenes s value and provide sufficient water for complete mixing. (2) SP was not added to mixing water, but instead added alone to increase the dilution water effec t. (3) Experimental results show that the optimum mixing method for adding SP and fly ash to sea sand concrete is: coarse framework material (fly ash + ceme nt) --- fine framework material --- mixing water --- strengthener. The results of these improvement methods were: when a water/ash ratio of 0.45 is used (1) the cement could be saved; (2) mixing water can be reduced by 34%-30%; (3) co mpression strength exceeded that of pure cement with the same water/ash ratio after 90 days.