碎砂取代海砂細骨材可行性研究

Abstract

海砂先天上顆粒太細、粒形圓，而碎砂顆粒較大、粒徑不圓，均是不良級配。其拌製出的 混凝土前者黏稠度較大，後者則凝聚性不佳，二者工作性皆屬不良，用水量及水泥用量相 對增加，因此較不經濟，故加以混合使用。為探討以碎砂取代部分海砂細骨材使用的可行 性，本研究以大安溪下游碎砂及觀音海砂為研究對象，探討對不同取代量下的混凝土之工 程性質。研究採五種不同的取代量，配比設計採一種坍度及四種水灰比的條件，比較不同 取代量下的混凝土之工程性質，其中包括工作度、抗壓強度、抗彎強度、劈裂強度、透水 性、泌水性、耐久性、凝結、乾縮等。研究結果顯示除了取代量高至80%以上外，以碎砂 取代海砂，不但可以提高海砂細度模數改善工作性及提升強度，並可減少用水量。隨著取 代量的增加則抗壓強度隨著增加，在取代量40%抗壓強度達最大值。劈裂強度、抗彎強度 、水密性及泌水量之變化則類似抗壓強度之變化，隨取代量的增加在取代量60%時，耐久 性最佳及凝結時間最長。與河砂海砂混合的混凝土比較，河砂的添加不似碎砂的添加可以 有效提升海砂混凝土的強度。另外與碎砂取代河砂混合的混凝土比較，碎砂取代河砂20% 雖然有助於強度的提升，但仍比碎砂取代海砂20%及40%強度為低，且單位水泥用量也較多 。所以碎砂取代海砂具有工程及經濟上效益。 Because of the too small particles and globular shape of offshore sand and big ger particles and unglobular of crushed sand, so they are not good gradings. T he consistency of concrete made from offshore sand is larger than crushed sand , and the cohensive of concrete made from crushed sand is not good . Both of t heir workability are not good . It is not economic because that water and ceme nt requirements increase, so we combine both of them to use.In order to explor e the usability of substituting crushed sand for part of offshore sand as fine aggregate, the research takes the crushed sand of downstream of Da-An river a nd the offshore sand of kwan-In as main research materials to explore the engi neering property of different substitutions of concrete. The research takes fi ve different substitutions and the proportion design takes one slump and four water-cement ratios to compare the engineering properties of concrete in diffe rent substitutions, includThe result of the research indicates that besides th e replacement above 80%, replacement of offshore sand by crushed sand will not only raise the fineness modulus. of offshore sand, workability and strength, but also reduce the water requirements. With the replacement increasing, the c ompressive strength raises. When 40% replacement, the compressive strength rea ches the max. value. The changes of split strength, flexural strength, water t ightness and bleeds are similar to the change of compressive strength.