高速公路

高速公路的横幅
混凝土在美国的建筑中扮演了重要的角色.S. 在过去60年的州际公路系统. The national focus has shifted from building new highways to maintaining and repairing the existing highway network. 

Recent advances in concrete technology enable highway contractors to rehabilitate the nation's 160,000 mile national highway system to extend its useful life with minimal disruption of traffic.


混凝土公路的历史

The first concrete highway constructed in the United 状态s was a 24-mile long, 的9英尺宽, 5英寸厚的混凝土路面,建在松崖附近, 阿肯色州, 1913年,福特T型车问世5年后. By 1914, concrete had been used to pave 2,348 miles  of roadway. Highway construction received a significant push forward two years later when President Woodrow Wilson signed the first Federal-Aid Highway Act directing the federal government to help states finance 道路建设. In 1919, Oregon became the first state to level a fuel tax on gasoline to finance road construction. Today this is still the primary method of financing 道路建设 and maintenance. 宾夕法尼亚收费高速公路, 建于20世纪30年代的铁路上, was the first major intercity turnpike or toll road in the United 状态s and was constructed of concrete.

高速公路的身体图片Significant technical and design developments during the 1930s and 1940s made concrete paving faster, 更便宜的, 、更持久. Road designers stopped requiring contractors to build roads that were thicker at the edges—concrete highways were generally six inches thick at the middle and eight- or nine-inches thick at the edges—and permitted construction with a uniform concrete depth, 节省时间和金钱. 设计师开始要求用碎石做底座, 碎石, 或者在20世纪30年代末将矿渣埋在混凝土公路下, 当重型卡车交通的增加导致泵, a phenomenon in which a concrete slab loses support and cracks as wet clay and soil particles underneath shift and are pumped from beneath the slab at its edges.

In the 1940s, some highway departments began to use soil-水泥 as a subgrade for highways. 在这个时候, contractors also changed their method of creating pavement joints. Rather than forming the joints when the concrete was fully plastic by lumping it up to either side of the joint, contractors began sawing the concrete once it was partially hardened to create a smoother joint. This change in procedure helped create more even highway surfaces, 并消除了熟悉的“撞击”, “颠簸”司机感觉在一些老化的板接头.

在这个时候, 混凝土路面也出现了结垢的问题, 剥落表面的剥落或剥落, 哪些研究确定是冻融循环的结果, 通过使用除冰盐加速. Studies showed that the introduction of tiny air bubbles in the concrete mix could reduce the problem. This led to the development of air-entrained concrete, now used in virtually all U.S. 道路建设. The invention of the slip-form paver in 1949 was another milestone in the development of concrete paving technology, as it allowed road crews to place wide sections of concrete continuously and therefore far more efficiently than before. Slip-forming is now used for highway paving projects in almost every state.

Many consider the construction of the interstate highway system, 在二十世纪六七十年代, 是混凝土铺路的全盛时期, 以及道路建设. 但就在数千英里的混凝土公路建成之时, 研发工作继续进行, 改进混凝土浇筑和养护方法. 在1976年,美国.S. Congress recognized the need to specifically finance maintenance of the highway system, 并批准了3R项目的联邦资金:修复, 康复, 和重修的. 

新施工技术

Several relatively new techniques make it possible for concrete contractors to rehabilitate and resurface highways efficiently with minimum traffic interruption. 其中包括快速混凝土路面技术, in which high-early-strength concrete is used to allow reconstructed roads to open more quickly. While conventional concrete mixes might require a curing time from five to 14 days, fast-track concrete can meet roadway opening strengths in 12 hours or less. 尽管成分的组合是不同的, high-early-strength concrete commonly includes a higher proportion of the standard Type I 水泥 to water or contains high-early-strength 水泥, 被称为III型水泥. III型水泥实际上与I型水泥相同, 只是III型水泥颗粒被磨得更小. 水泥颗粒越小,表面积就越大, allowing more 水泥 contact with the water in the concrete mix, 这意味着水合作用更快. 一般, fast-track concrete provides good durability because most of these concretes are air entrained and have a relatively low water content—factors that improve strength and decrease the chloride or salt permeability that damages steel reinfor水泥 and contributes to deterioration. 

Another relatively new technique that promises to improve highway smoothness and longevity is dowel retrofitting of existing concrete pavement that has undowelled slab joints. 自1980年以来, the slab joints of most new concrete highway pavements in areas where heavy loading is anticipated have been dowelled with 18-inch long smooth steel bars. The dowels bridge the joint sawed between the pavement slabs and help transfer traffic loads from one concrete slab to the next. The retrofitting technique involves cutting slots across the pavement joints, 插入酒吧, 用快轨混凝土混合料修补缝隙, 然后用钻石打磨路面以获得光滑的路面. Department of 运输 officials in Washington—the first state to undertake dowel retrofitting on a large scale—expect to extend the life of some of the state's 30-year-old concrete highways by 10 to 15 years using the new technique.