1. Cement

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.

2.石子石子質量不好包括石子強度低、體積穩定性差、石子形狀與表面狀態。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。

2. Poor stone quality, including low stone strength, poor volume stability, stone shape and surface state. 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.

3.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。

3. The thickness of sand for preparing concrete is divided into three grades: coarse, medium and fine according to the fineness modulus. Medium sand should be preferred for preparing concrete. 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.

二.未嚴格按照配合比施工及施工工藝不正確。

II The construction is not in strict accordance with the mix proportion and the construction process is incorrect.

1.用水量比較常見的有攪拌機上加水裝置不準確；不扣除砂、石子的含水量，甚為了方便施工在澆筑地點上任意加水。這一現象除了對水嚴格計量外，還應根據現場當時砂、石子的含水率將試驗室配合比換算為施工配合比，而按試驗室配合比施工是不正確的。

1. The water consumption is common, and the water adding device on the mixer is inaccurate; The water content of sand and stone is not deducted, and even water is added at the pouring site for the convenience of construction. In addition to the strict measurement of water, the laboratory mix proportion should also be converted into the construction mix proportion according to the water content of sand and stone at that time, and the construction according to the laboratory mix proportion is incorrect.

2.外加劑摻量不準確普通型減水劑，如木質素磺鈣、糖鈣等摻量過大是常發生的摻量不準確現象。超摻嚴重時，會造成對混凝土強度的不足，值得注意的是，摻量少也會使28d強度達不到要求，但長齡期強度仍可達到空白混凝土強度。

2. The dosage of admixture is inaccurate. It is a common phenomenon that the dosage of ordinary water reducing agents, such as calcium lignosulfonate and calcium sugar, is too large. When the over mixing is serious, it will cause the deficiency of concrete strength. It is worth noting that a small amount of mixing will also make the 28d strength fail to meet the requirements, but the long-term strength can still reach the strength of blank concrete.

3.其他原因如外加劑使用不當；砂石計量不準確和水泥用量不足；攪拌不佳、時間過短造成攪拌不均勻；因模板問題造成的水泥漿漏失；養護不當，如早期缺水干燥、冬期受凍等原因都會造成混凝土強度不足。

3. Other reasons, such as improper use of admixture; Inaccurate measurement of sand and gravel and insufficient cement consumption; Poor mixing and short time cause uneven mixing; Cement slurry leakage caused by formwork problems; Improper curing, such as water shortage and drying in the early stage and freezing in winter, will cause insufficient concrete strength.