From the manufacturer of loading mixer truck, the consequences of insufficient concrete strength are the reduction of concrete impermeability, durability, cracks and deformation of components, and the decline of bearing capacity. 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 clarify the causes of insufficient concrete strength and what measures should be taken to control it. There are two common reasons for insufficient concrete strength:

水泥質量不好是造成混凝土強度不足的關鍵因素。

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

石子質量不好包括石子強度低、體積穩定性差、石子形狀與表面轉態。在混凝土試塊試壓時，有時會發現石子被壓碎了，這說明石子強度低于混凝土的強度，導致混凝土實際強度下降。有些由于多孔燧石、頁巖、帶有膨脹粘土的石灰巖等制成的碎石子，在干濕交替或凍融循環作用下，常表現為體積穩定性差，而導致混凝土強度降低。針片狀石子含量高影響混凝土強度。石子表面光滑則無法與水泥砂漿結合好，也會影響混凝土強度。

Poor stone quality includes low stone strength, poor volume stability, stone shape and surface transformation. During the pressure test of concrete test block, it is sometimes found that the stone is crushed, which shows 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, resulting in the reduction of concrete strength. The high content of needle flake stone affects the strength of concrete. If the stone surface is smooth, it cannot be combined with cement mortar, and it will also affect the strength of concrete.

砂子配制混凝土用砂子的粗細程度按細度模數分為粗、中、細3個等級，配制混凝土宜優先選用中砂。砂子質量的好壞可用細度模數、含泥量、泥塊含量等幾項指標來評定。其中含泥量、泥塊含量對混凝土強度影響。這是因為泥塊遇水會呈現漿狀，膠結在一顆或數顆砂子表面，在混凝土中與水泥起著隔離作用，從而影響了水泥與石子的粘結力

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