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