The manufacturer of concrete mixer said that the consequence of insufficient concrete strength is that the impermeability of concrete is reduced, the durability is reduced, the components appear cracks and deformation, and the bearing capacity is reduced. In serious cases, it will affect the normal use of buildings and even cause accidents. In view of the harm caused by insufficient concrete strength, it is very necessary to find out the causes of insufficient concrete strength caused by concrete and what measures should be taken to control it. There are two common reasons for insufficient concrete strength

水泥质量不好是造成混凝土强度不足的关键因素。

The poor quality of cement is the key factor of insufficient concrete strength.

石子石子质量不好包括石子强度低、体积稳定性差、石子形状与表面状态**。在混凝土试块试压时，有时会发现石子被压碎了，这说明石子强度低于混凝土的强度，导致混凝土实际强度下降。有些由于多孔燧石、页岩、带有膨胀粘土的石灰岩等制成的碎石子，在干湿交替或冻融循环作用下，常表现为体积稳定性差，而导致混凝土强度降低。针片状石子含量高影响混凝土强度。石子表面光滑则无法与水泥砂浆结合好，也会影响混凝土强度。

The poor quality of stones includes low strength, poor volume stability, shape and surface state. During the pressure test of concrete test block, sometimes it is found that the stone is crushed, which indicates that the strength of stone is lower than that of concrete, resulting in the decrease of actual strength of concrete. Some crushed stones made of porous chert, shale and limestone with expansive clay often show poor volume stability under the action of dry wet alternation or freeze-thaw cycle, which leads to the decrease of concrete strength. The high content of needle flake stone affects the strength of concrete. If the stone surface is smooth, it can not be well combined with cement mortar, which will also affect the strength of concrete.

砂子配制混凝土用砂子的粗细程度按细度模数分为粗、中、细3个等级，配制混凝土宜优先选用中砂。砂子质量的好坏可用细度模数、含泥量、泥块含量等几项指标来评定。其中含泥量、泥块含量对混凝土强度影响。这是因为泥块遇水会呈现浆状，胶结在一颗或数颗砂子表面，在混凝土中与水泥起着隔离作用，从而影响了水泥与石子的粘结力

According to the fineness modulus, the sand for concrete preparation can be divided into three grades: coarse, medium and fine. Medium sand should be preferred for concrete preparation. The quality of sand can be evaluated by fineness modulus, mud content and mud lump content. Among them, the content of mud and mud block have great influence on the strength of concrete. This is because the mud will appear slurry when it meets with water, which is cemented on the surface of one or several sand particles, and plays an isolation role with cement in the concrete, thus affecting the adhesion between cement and stone

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