文献翻译
Bridge Maintenance Techniques
Essential maintenance generally involves strengthening or replacement of bridge elements . Strengthening techniques include welding , plate bonding and external post-tensioning which increase the stiffness of bridge decks . Replacement of elements has been used for deck slabs and beams, piers and columns. The primary purpose of essential maintenance is to increase the load carrying capacity and the reason for the inadequate capacity is secondary . If the reason is simply increased loading the maintenance can be limited to increasing the capacity , but if the reason is deterioration then maintenance must also include repairs and preventative maintenance.
The selection of the maintenance method for repairs prevention depends primarily on the cause of deterioration . For steel construction the main cause of deterioration is corrosion and regular maintenance painting should be carried out to prevent the steel from corroding . If corrosion does occur then the only repair option is to grit blast back to shiny metal before r
epainting . An assessment of load carrying capacity should be carried out if corrosion has resulted in a significant reduction of steel section .
The selection of repair and prevention methods for concrete construction is more complex because there are numerous causes of concrete deterioration .The deterioration of reinforced concrete can be conveniently sub-divided into deterioration of the concrete and deterioration of the steel reinforcement . The main causes of concrete deteriorationreactive翻译 are sulphates , free-thaw cycles and alkali-silica reaction(ASR) . Deterioration can also be related to poor mix design and construction process such as compaction and curing . These types of deterioration can only be prevented by actions taken at the time of construction ; there are no effective preventative actions that can be taken after construction. For example where the environment is known to contain significant quantities of sulphide it is sensible to consider the use of sulphate resisting Portland cement . In regions experiencing large numbers of freeze-thaw cycles frost damage to concrete can be prevented by adding air entraining agent to the concrete mix . Frost damage is worse in concrete that is saturated with salty water so techniques such as waterproofing membrane
s and silane treatments may be helpful . Alkali-silica reaction between aggregates and the alkali in cement can be prevented by avoiding the most reactive types of aggregate and by keeping the alkali content of the cement below the designated limit . To set up damaging stresses in concrete the ASR requires water so procedures to reduce the water content such as waterproofing membranes and silane treatments may help . If these forms of concrete deterioration take place the only viable repair method is concrete replacement which may be extensive especially for ASR where entire sections can be affected . Sulphate and freeze-thaw damage normally occur only in the cover zone of the concrete . It is important to note that deterioration of the concrete will increase the risk of corrosion to the reinforcement because steel depassivators , like chlorides and carbon dioxide , will be able to move more easily through the concrete to the reinforcement .
Deterioration of the reinforcing steel is caused by corrosion and can be prevented by actions taken at the time of construction and for a period after construction . Preventative techniques that can be applied at construction include the use of epoxy coated mild steel , stainless steel of carbon or glass fibre reinforcement , inhibitors , cathodic protection , anti-
carbonation coatings , silane treatments and waterproofing membranes . All of these techniques , except the last three , directly protect the reinforcement against corrosion and to date , have been used only occasionally largely on grounds of cost . Waterproofing membranes , silane treatments , and anti-carbonation coatings are applied to the concrete and are designed to slow down the ingress of carbon dioxide and chlorides into the concrete thereby increasing the age of the structure when the reinforcement begins to corrode . These techniques can be used after construction because they are applied to the concrete surface and they should be effective , providing corrosion of the reinforcement has not already begun . It is important not to overlook the importance of well compacted and cured, low water : cement ratio concrete in preventing reinforcement corrosion.
When corrosion of the reinforcement occurs it result in a loss of steel section and/or cracking, spalling and delamination of concrete due to the stresses produced as a result of the low density of rust compared with density of the steel . Reinforcement corrosion repair methods have two main functions , to crete replacement ; cathodic protection ; desalination ; realkalization.
Concrete replacement has to be used to repair the damage caused by corrosion regardless of which technique is used to stop corrosion . Concrete replacement can also be used to stop corrosion although this involves the removal of all the carbonated and chloride contaminated concrete even though it is physically sound . This often means that concrete repairs to stop corrosion are not economically viable . Cathodic protection can be applied at any time to stop corrosion caused by carbonation or chlorides . It functions by making the reinforcing steel cathodic with respect to an external anode system . Cathodic protection requires a permanent electrical installation . Desalination can be used to stop corrosion caused by chlorides and it works by migrating chloride ions towards an external anode and away from the reinforcing steel in an electric field ; this process takes about 6 weeks . Realkalization stops corrosion caused by carbonation and it works by migrating sodium ions from an external anolyte into the concrete where in combination with the hydroxyl ions generated on the reinforcing steel due to the electric field , the alkalinity is raised to a level where the steel re-passivates . Realkalization takes about 4 weeks . Desalination ,realkalization and concrete repair are not normally used in conjunction with a
preventative treatment such as silane or an anti-carbonation coating to increase the life of the repair .Cathodic protection does not require additional preventative measures because it is a permanent installation , but the anodes do require periodic replacement.
大桥维修技术
大桥的基本的维修大体上包括加强和更换桥的基本元素。加强技术包括焊接电镀连接，外部后拉等从而来增加桥贴面的刚度。元素替换可以用于甲板和横梁，码头和圆柱。对基本维修的主要目的是为了提高负荷承载能力，容量的不足则是次要考虑的。如果仅仅是要提高载荷量的话，维护时可以被仅限制在提高承载量上，但如果情况恶化的话，维修还必须包括维修保养和预防性维护。
避免维修所采取的维护方法选择主要取决于恶化的原因。对于钢结构恶化的主要原因是腐蚀，定期的保养喷漆应该被实施，以防止钢被腐蚀。如果确实发生腐蚀那么唯一的选择是在重新修整回闪亮的金属上铺设砂砾。承载能力应该被重新评估评估，如果钢腐蚀让钢剖面有明显的减少。
修复和预防混凝土施工方法的选择更为复杂，因为有无数的混凝土劣化的原因。恶化的钢筋混凝土原因可以简单地分为混凝土恶化和钢筋恶化分歧两种。混凝土劣化的主要原因是硫酸盐，免费冻融循环和碱硅酸反应（ASR）。恶化也可以和设计和施工不良有关，如压实和养护。阻止这些类型的恶化只能在建造时采取行动;在建成后没有有效的预防方法。例如在环境是已知含有大量的硫化物，明智的考虑是使用抗硫酸盐硅酸盐水泥。在经历冻融循环大批冻害是的具体地区，加入引气剂在混凝土配合使用可以预防冻害。冰霜伤害在建筑实体中是严重的，饱和盐水，诸如防水卷材和硅烷处理技术可能会对此有所帮助。碱硅酸水泥之间的聚合和碱反应是可以预防避免产生聚合反应类型并可以保持在指定的限制以下水泥碱含量。要设置在混凝土应力破坏的ASR需要水，所有程序以包括减少诸如防水卷材和硅烷处理可以帮助含水量。如果这些具体形式发生恶化，唯一可行的修复方法是具体的更换可在广泛的ASR整个部分，特别是可能会影响。硫酸盐和冻融破坏，通常只发生在混凝土保护区。重要的是要注意，具体的恶化，将腐蚀的风险增加因为钢容易被氧化，氯化物和二氧化碳一样，将能够通过移动的钢筋混凝土更容易。
对钢筋腐蚀造成的恶化，并且可以通过在建设时间和建设时期后所采取的行动阻止。可在施工中的应用的预防性技术包括环氧涂层低碳钢，碳或玻璃纤维增强材料，抑制剂，阴极保护，
防碳化涂料，防水卷材硅烷处理和不锈钢的使用。所有这些技术除了最后三，直接保护不受腐蚀，并且迄今为止，已被用于成本只是偶尔的理由主要是加固。防水卷材，硅烷处理，防碳化涂层应用到具体的，其目的是减缓到混凝土，从而增加了结构加固时的年龄开始腐蚀的二氧化碳和氯化物进入。这些技术可用于施工后，因为它们应用到混凝土表面，他们应该是有效的，提供的钢筋腐蚀还没有开始。重要的是不要忽略了坚实完好，并治愈的重要性，低水：可防止水泥混凝土钢筋锈蚀率。

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