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海沙為什么不可以用在建筑上？

中國擁有漫長的海岸線，具有豐富的海砂資源，海沙雖然潔凈，但是海砂不能直接被用于建筑中，主要是因為其含有兩種有害物質(zhì)：海砂中的含鹽量主要來自海水，海水中硫酸鹽含量折合SO2-4僅為Cl-的1/10左右，這樣少量的硫酸鹽對于混凝土及鋼筋無明顯有害作用，因此海砂含鹽量主要是含氯鹽的問題�；炷�土空隙中的水分，通常以飽和Ca(OH)2形式存在，其中還含有一些NaOH和KOH，pH值約為12.5。這樣的強堿性環(huán)境中，鋼筋表面形成一種鈍化薄膜，正是這種很薄的氧化膜層，使鋼筋受到保護，不致于腐蝕。氯鹽能破壞混凝土鋼筋表面的堿性保護膜，而促使鋼筋發(fā)生銹蝕�；炷�土中鋼筋不斷銹蝕的結(jié)果，不但削弱了鋼筋截面，而且由于銹蝕產(chǎn)物的膨脹作用而使混凝土保護層開裂、剝落，影響到結(jié)構(gòu)的正常使用。氯鹽對于預(yù)應(yīng)力鋼筋的危害性更大。另外，海砂中的氯鹽還可能對混凝土拌合物有促進凝結(jié)硬化的作用(含鹽量在0.2%～0.3%以上時比較明顯)；對于大體積混凝土則有初期溫升較高的問題;使用含鹽量較高的海砂的混凝土早期強度較高，但后期強度可能較低，海砂中的鹽分還可能使混凝土的干燥收縮增加。總之，氯離子是導(dǎo)致混凝土中鋼筋腐蝕的最為有害的物質(zhì)。

 

海沙中貝殼水母有機物對建筑腐蝕影響？

貝殼類主要成分為CaCO3，貝殼，水母等類雖然為惰性材料，一般不會與水泥發(fā)生化學(xué)反應(yīng)，但這些輕物質(zhì)往往呈薄片狀，表面光滑，本身強度很低，且較易沿節(jié)理錯裂，因而與水泥漿的粘結(jié)能力很差。一般來說，當(dāng)貝殼類等輕物質(zhì)含量較多時，會明顯使混凝土的和易性變差，使混凝土的抗拉、抗壓、抗折強度及抗凍性、抗磨性、抗?jié)B性等耐火性能均有所降低。因此必須對其含量加以限制。

China's long coastline provides abundant sea sand resource. Although the sea sand is clean and contains little mud, it cannot be directly used in buildings because it contains two kinds of hazardous substances: chloridion and organic matter, which influence the solidification structure of buildings and corrode the concrete. The salts in sea sand mainly come from seawater in which the SO2-4 (converted from sulfate) is only one-tenth of the Cl-. The sulfate is so little that it cannot damage the concrete or reinforcing steel bar, therefore the chloride is the main hazardous substances. Usually the moisture in the space between concrete exist in form of saturated Ca(OH)2, and a little NaOH and KOH, PH valve being 12.5. In such strong alkaline environment, a layer of passivation film will form on surface of reinforcing steel bar, and it is this thin oxide film that protect the reinforcing steel bar from being corroded. Chlorine salt will damage the alkaline protection film on the surface of concrete reinforcement, and corrode the reinforcing steel bar. The corrosion will damage the section of the concrete reinforcement, and the expansive action of the corrosion will make the concrete cover rupture and flake away, which will have an impact on the normal use of the structure. Chlorine salt do more harm to prestressed reinforcement. In addition, the chlorine salt in sea sand can also enhance setting and hardening of concrete mixture, which is obvious when the salt content is over 0.2%-0.3%; for mass concrete, it will make the temperature rise higher at preliminary stage, which makes the early strength of concrete much higher and the later strength lower. The salt in sea sand may also increase the drying shrinkage of the concrete. In brief, the chloride is the most harmful substance causing reinforcement corrosion in concrete.