Influence of cement mineral composition
The shrinkage of C3A, C3S, C2S and C4AF in Portland cement is C3A > C3S=C2S > C4F. The increase of C3A and C3S content in cement clinker will increase the self-shrinkage and drying shrinkage of concrete and increase the chance of cracking. The calorific value of C3A is the highest, and the high heat of hydration accelerates the slump loss of concrete.
Influence of cement fineness
Increasing the specific surface area of cement is to increase the hydration rate, so as to improve the early strength of concrete. And the greater the fineness of cement, the worse the frost resistance of concrete, and the lower the tensile strength. More importantly, the increase of cement fineness makes the compatibility of cement and superplasticizer worse. With the increase of cement fineness, the saturation point of superplasticizer is greatly increased, and the amount of superplasticizer needed to reduce the slump loss of concrete is also greatly increased.
Effect of Gypsum Morphology on compatibility of Superplasticizer and cement
Different forms of gypsum have little difference in testing the produced cement according to cement standards, but a single addition of superplasticizer will be completely different. this is due to the different solubility of reducing sugar and polyol to dihydrate gypsum and anhydrite (anhydrous gypsum) and fluorogypsum.
Effect of soluble alkali
Many studies have proved that alkali sulfate in cement, that is, soluble alkali, has a very important influence on the adaptability of admixture and cement. Studies have shown that when the mass fraction of C3A is less than 8% and the soluble alkali content of cement is high, the workability of concrete and workability is good, and the slump loss is small. When the soluble alkali is very low, the concrete and workability lose quickly. For cement with low soluble alkali content. The initial slump can be obtained by increasing the content of superplasticizer, but the loss is still very fast. When a little more amount is added above the saturation point, the precipitation and secretion will be obviously high.
The influence of other factors of cement
Cement temperature, cement aging time, type and content of fillers and other factors will affect the working performance of concrete. The higher the temperature of cement is, the worse the plasticizing effect of superplasticizer is.
Fly ash mainly changes the workability of concrete, because of fine particles, mainly fill the gap of cement, there are some crystal beads, play the role of ball, increase fluidity. With the increase of the amount of fly ash, the quality of fly ash in the market is uneven. Generally, grade II is used for concrete below C50 and grade I for concrete above C50. Due to the shortage of fly ash, many commercial concrete use grade III fly ash or even raw ash. Due to the large fineness of grade III fly ash and original ash, high burning loss and high water storage capacity, concrete and workability become worse, and the strength of concrete is reduced.
Granulated blast furnace slag powder can increase the initial fluidity of slurry and reduce the fluidity loss. Mainly due to different manufacturers, so different chemical composition, different fineness, resulting in different water demand of mineral powder, the contribution to the strength of concrete is also different.
Sand and stone
The effects on polycarboxylate superplasticizer include:
1. the mud content and mud block content of sand are high, and the mud composition in concrete absorbs superplasticizer, which leads to great loss of concrete. the high fineness modulus of superplasticizer mainly affects the workability of concrete, and the water absorption of sand leads to the water consumption of concrete.
2. Mud content, mud block content, particle size and stone powder content of stones.
The particle size of stone determines the water consumption, and the content of stone powder has a great influence on the workability of concrete, which mainly changes the composition of powder below 0.315mm in concrete and affects the workability of concrete.
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