经过Gregory Havel
Concrete is a mixture of sand, several sizes of aggregates such as gravel and small stones, Portland cement that is added in a quantity that is known to produce concrete of a certain strength when it has aged and cured, and enough water so that it will slide down a chute or concrete pump easily into forms without being so loose that it cannot retain its shape with the help of the forms until it has set.
Plain concrete that has cured has compressive strength but little strength in tension or shear.
To increase concrete’s tensile and shear strength, it is reinforced frequently. Several types of concrete reinforcement are used to achieve greater strength in different applications and environments.
Photo 1 shows the floor of a factory addition before the concrete was poured. Near the middle of the photo, the existing wall of the factory is visible, with steel rebar dowels drilled into the edge of the existing floor to bind it to the new floor that will be poured.
（（1) Photos by author.
前景显示塑料泡沫绝缘板放在砾石底座上，上面放有塑料湿度屏障和焊接电线网to reinforce the new concrete floor to reduce the possibility that it will crack. The “V” of steel rebar that is visible on both sides of the square tubular column is connected to the column and uses the concrete floor to help stabilize the column. Welded wire mesh is available in light gauge in cylindrical rolls and in heavier gauges; they are shipped in flat sheets because they are too stiff to roll.
照片2显示了垫子steel reinforcing rodsorbars (rebar)这将加强地下混凝土罐的底部和侧面。这些是普通的，未涂层的钢，脊滚入杆上，以帮助混凝土粘合到它们上。
（2）
These rebar are spliced with lap joints connected with steel tie wire. Rebar crossing at right angles are tied with the same kind of wire to provide stability to the mat of rebar and increase its strength. The multiple mats of rebar in the floor are separated by chairs (supports) of smaller rebar, heavy wire, or brick-sized concrete masonry units. The rebar for the sides of the tank will be connected by lap joints tied with steel wire and the rebar in the roof of the tank.
Photo 3 shows preshapedepoxy-coated rebar这将用于桥梁或驻车结构中的圆柱和横梁，这些桥梁将暴露于各个方面的天气。
（3）
This epoxy coating is sprayed on at the steel mill after the rebar is formed by conventional means and after the surface of the rebar has been abraded and cleaned of any rust or oil residue that would prevent the epoxy coating from sticking to the steel. This coated rebar is connected by lap joints and tie wire, which must be sprayed with an aerosol epoxy coating to prevent rust from forming where there is no epoxy paint or where the paint is chipped.
According to architectural and engineering journals,高强度合金钢钢筋可用，具有相同尺寸的强度；传统的钢筋尺寸更大。这种类型的钢筋是制造的，具有与常规钢钢筋相同的外观，并使用膝关节和钢带线安装。使用较小尺寸的钢筋，每磅钢合金的成本增加被节省的体重所抵消。制造商指出，这种高强度的钢筋可用于火评级的钢筋混凝土墙和地板天花板组件，而不会影响实验室测试炉中组件的性能。
建筑和工程期刊还讨论了开发和测试plastic rebar（用玻璃或碳纤维加固）用于海洋环境，其他类型的腐蚀性环境中的结构和bamboo fiber reinforced plastic rebar。This could eventually replace conventional steel rebar in some applications and would be considered “sustainable” building material.
照片4显示了一个地板fiber-reinforced concrete。该纤维以预定比例添加到混合器中的混凝土中，以提高固化混凝土对裂纹的电阻。
（4）
合成纤维通常是聚乙烯，尼龙或聚丙烯（照片5），可以单独使用或与焊接钢丝网或钢筋组合使用。为了更大的强度，也可以使用通常使用钢或不锈钢线的金属纤维。
（（5)
用金属纤维加固的混凝土地板比普通混凝土更具导电性，并且很容易消散静电。因此，它有时在燃油泵周围的路面和对静电敏感的区域内的建筑物内部的地板中使用。
钢电缆或“tendons”can also be used to reinforce concrete for specific applications. “Pre-tensioned” or“pre-stressed” concrete是将张力施加到由钢混凝土形式支撑的肌腱上的结果。当混凝土倒入形式并通过形式的外部加热迅速固化时，将混凝土粘合到电缆肌腱上。当混凝土固化时，电缆肌腱上的张力将释放，并且收缩肌腱将混凝土拉在一起，从而在长期跨越100英尺（30.48米）的长跨度中具有很大的强度。此过程用于制造“ Tees”，“双T恤”，空心的混凝土木板，梁，梁和其他结构混凝土形状。
照片6显示了拆除建筑物中的一块预应力的混凝土破裂。在这张照片中，这块空心核心混凝土木板的底部位于顶部，其三个大型电缆腱直接粘合到混凝土上。从预应力混凝土顶部的较小的单肌腱明显地躺在地面上。
（（6)
张贴后混凝土is the result of applying tension to steel cable tendons in kraft-paper or plastic sleeves that have been embedded in concrete poured on a form supported by falsework, much like structural concrete with steel rebar. After the concrete is cured, each tendon is anchored to the concrete at one end, and a hydraulic machine attached to one end of each tendon applies tension to it, which is permitted by the tendon’s ability to move freely inside its sleeve. After the proper amount of tension is applied, the tendon is connected to the opening in the concrete with a bolted-on cylindrical wedge anchor in each tendon sleeve. The tendons are then cut off and the openings around them are filled and protected with a concrete patch. This type of reinforcement gives great strength to a relatively thin structural slab that is flat on both top and bottom.
Photo 7 shows the underside of a post-tensioned concrete floor that spalled when tension was applied to tendons that were not perfectly straight. The black-sleeved tendons are under tension and caused the spalling when they straightened. The gray-sleeved tendons are not yet under tension. The concrete around them will chip away, tension will be reapplied, and they will be embedded in an epoxy concrete mixture that will bond to the concrete and tendon sleeves.
（（7)
图8显示了后张混凝土的边缘floors that have been tensioned, and the ends of the tendons and their anchors are sealed in the concrete. These concrete patches concealing the ends of the tendons appear as round “dots” on the edge of the floor slabs.
（（8)
Research and development will result in additional types of reinforcement for concrete. Knowledge of the methods used to reinforce concrete, especially in structural systems, is of interest to firefighters simply because the less mass the structural system has, and the thinner the covering of concrete over the reinforcement of steel or other materials, the less fire resistive it is likely to be.
如果我们被要求违反地板系统，也必须能够识别我们所处理的混凝土结构的类型。在预压力或张紧的混凝土地板上切割一个或多个电缆肌腱会削弱地板，并可能导致大面积地板的塌陷，即使距离我们工作的地方一距离。
For more information on the materials and methods used to reinforce concrete, do an Internet search for any of the terms “in quotation marks” or in bold type.
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Gregory Havel是伯灵顿镇（WI）消防局的成员；退休的副局长兼培训官；以及一名40年的消防人员资深人士。他是威斯康星州认证的消防教练II，消防官II和消防检查员；Gateway技术学院消防计划的兼职讲师；Scherrer Construction Co.，Inc。的安全总监Havel拥有圣诺伯特学院的学士学位，在设施管理和建筑建设方面拥有40多年的经验，并在FDIC和其他场所举办课程。
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