水泥和混凝土 - 它们是一样的吗？

许多人认为水泥和混凝土是相同的产品 - 它们不是。

水泥是一种干粉化学品，当与水混合时，慢慢反应形成新的硬质固体化合物。另一方面，混凝土是水泥混合水和各种尺寸的聚集体的混合物。水泥和水形成糊状物，糊状物在硬化时粘在一起。

混凝土在其新鲜混合状态下是一种可塑性可行的混合物，其几乎可以形成为几乎任何所需的形状。它开始在混合时慢慢加强，但仍然塑料仍然可行几个小时。这是一个足够长的时间，让它放置并完成。

在其初始集合之后，如果潮湿持续存在，则继续增加几个月的强度。

WHAT IS CONCRETE?

混凝土有两个组件;18新利官网登录在线汇总和粘贴。

聚集体一般是两种尺寸;细腻粗糙。

Fine aggregates are those with particle sizes smaller than about 5mm, commonly known as sand, which can be natural or manufactured. Coarse aggregates are those with particle sizes greater than about 5mm. Gravel, crushed stone and blast furnace slag are among the most commonly used coarse aggregates.

Paste is composed of cement, flyash, water and sometimes entrained air. The cementing property of the paste results from a chemical reaction between the cement and water. This reaction is called hydration. It is a reaction that requires time and favourable conditions of temperature and moisture.

“固化”是在足够长的时间内提供有利的温度和湿度条件，以便允许水合过程接近完成。

With proper curing, hydration takes place very rapidly at first, and then decreases slowly for a long time. This allows the concrete to develop good strength and durability.

Remember, concrete needs continued moisture to harden properly. It should not dry out too quickly.

混凝土的力量

The compressive strength of concrete, measured by how much force is required to crush it, is important in the design of structures. In pavements and other slabs on ground, the design is usually based on flexural strength, (i.e; how much force the concrete can withstand in bending before it breaks). In either case, the principal factors affecting strength are the water-cement ratio and the extent to which hydration has progressed.

The addition of too much water to concrete (beyond the intended mix design) will reduce strength and durability of the concrete, even if it is properly placed, finished and cured.

PROPERTIES OF FRESH CONCRETE

虽然新鲜混合的混凝土仍然只有短时间才能留下塑料，但其性能很重要，因为它们影响了硬化混凝土的质量和成本。

塑料一致性的混凝土（中等坍落度）不会崩溃，因为它被排出，但没有比细粒的粗骨分离的流动迟钝。这种稠度的混合物适用于大多数工作。

The ease or difficulty of placing and consolidating concrete is called workability.

Concrete should be workable; it should not be so stiff or so wet that segregation occurs; nor should it bleed excessively.

出血是水的运动到新放置混凝土的表面。水的过度出血到表面上增加了表面的水柱比。可能导致耐久性较差的弱层，特别是如果在存在过量水而在过多的水中发生完成操作。

WHAT DO YOU ORDER?

用新鲜混合成分的立方米体积购买和出售混凝土。混凝土规格通常包括对固化28天的测试气缸的某种设计强度水平的要求，或者它们基于指定水泥含量的处方。

Other characteristics such as slump and air content are also requested.

是什么使得很好的混凝土？

您不需要成为一个具体的分析师。但是，您应该知道每个混合设计都建立了一定的质量，您应该熟悉构成良好混凝土的内容：

1. Cement and water combine chemically to bond the sand and coarse aggregate together. Flyash may also be used as a cementing material, but always in combination with cement. The volume of water added to a certain volume of cement determines, to a large extent, how strong the hardened concrete will be. Most concretes are designed with a certain cement content and enough water to make the mass workable. Reducing the mixing water content makes the batch stronger and the addition of water makes the batch weaker.
2. Fine and coarse aggregate of a predetermined quality is added to the cement-water paste in the batch to give bulk to the batch. They contribute significantly to the quality of the concrete. If all fine aggregate (sand) is used to make a one cubic metre batch, a large amount of cement-water paste is needed to coat and bond the particles. By adding coarse aggregate to the batch instead of a portion of the sand, the mixing water demand can be kept lower. This works to produce better quality concrete at an economical cement content.
3. 混合剂 - 许多这些（通常组合）用于赋予新鲜或硬化混凝土的特定品质。有些混凝土使混凝土设置更快或更慢，或使其更加密集​​，或使其更强大或更耐用。最常见的是空气夹带剂，在混凝土中开发数百万微小的气泡;另一个是超级塑化，这增加了新混凝土的流动能力。这些提高了耐用性和可加工性。减水混合剂也很常见。

它们有助于生产中型坍落度，可行的混凝土，较少所需的混合水。超塑性体是一种相对较新的混合物，可以大大增加较小剂量的坍落度。一旦添加到混凝土中，这种坍落度增加将持续长达2小时，混凝土最终恢复原来的坍落度。它的主要用途是 -

a）流动混凝土（180 mm加坍落度），便于放置，劳动力节省和良好的表面光洁度

b）卓越的泵送性中等坍落度混凝土（100 mm - 140 mm坍落度）

c）由于含水量降低，普通坍落度混凝土（80 mm）给出了非常低的收缩。