The mix ratio of concrete in the quota is allowed to be adjusted. For example: the original cast-in-place concrete of the quota is C20, but when it is actually C30, you can change C20 to C30; you must not adjust the internal mix of fine aggregate without permission. Ratio; this quota is stipulated. Regarding the issue of adding additives, I think it should belong to the construction technical measures. First of all, it should be measures taken to better complete the project. There are two aspects: 1. Construction technology requirements. 2. Construction environment or equipment requirements. Secondly, for which party is the best benefit pursued by the measures taken, that is, for the construction unit or for the construction unit? As for the adjustment issue you mentioned, I personally think that in principle, it should be calculated according to special construction measures; if not To implement the quota, the additives can only be increased with the agreement of both parties. There is no theoretical basis for the deduction of cement savings. Unless actual calculations, actual usage and supplementary unit prices of costs are made in accordance with special construction measures.
(1) Whether the cement ore is stable leads to whether the mineral components are stable, which affects the adaptability of concrete admixtures to cement.
(2) The cement production process, such as shaft kilns and rotary kilns, how well the quenching measures in the cooling system are controlled, the temperature during gypsum grinding, etc., lead to the mineral components and crystal phase state in the cement. The morphology of gypsum changes, thus affecting the adaptability of admixtures to cement.
(3) The ability to adsorb admixtures in cement: C3A>AF>C3S>C2S. The cement hydration rate is directly related to the mineral components.
(4) After the cement is stored for a period of time, the temperature drops, which improves the high-temperature adaptability of the concrete admixture. Moreover, f-CaO absorbs water in the air and converts into Ca(OH)2, which absorbs water in the air. The CO2 is converted into CaCO3, thereby reducing Mwo, improving the workability of concrete, slowing down the slump loss of fresh concrete, and slightly prolonging the setting time of concrete.
(5) The water requirement of ordinary Portland cement is slightly larger than that of slag cement, and its water retention is good, but its slump loss is generally faster.
(6) Cement with higher C3A content has fast slump loss and good water retention.
(7) Hydrophilic admixtures in cement have good water retention; pozzolanic cement has poor water retention and is prone to bleeding.
(8) Temperature and humidity directly affect the adaptability of concrete admixtures to cement.
(9) The gradation of sand and stone in the mix ratio and the proportion of sand, stone, water and glue also affect the adaptability of concrete admixtures to cement.
In addition to concrete In addition to appropriate strength, it should also be based on special requirements for use, including resistance to freezing, water penetration, chloride ion penetration, shrinkage, carbonization, steel corrosion, sulfate resistance, compressive fatigue deformation, and alkali aggregate reaction. etc., collectively referred to as durability.
Impermeability:
Refers to the ability of concrete to resist the penetration of liquids and gases. Because there are interconnected pores and capillaries inside the concrete, as well as honeycombs and holes caused by insufficient vibrating, liquids and gases can penetrate into the concrete. The intrusion of moisture and air will cause steel bars to rust, and the intrusion of harmful liquids and gases will Deterioration of concrete will affect the quality and long-term safe use of concrete.
The impermeability of concrete is represented by the impermeability symbol P. For example, P4 means that under the corresponding 0.4N/㎜2 water pressure, 6 cylindrical or conical test blocks of specified sizes used for the impermeability test still remain impermeable to 4 test blocks. The impermeability grades of concrete are generally divided into P4, P4, P6, P8, P10, and P12.
Frost resistance:
Refers to the ability of concrete to resist freezing. Concrete is often damaged by freezing in cold areas, especially in environments where it is exposed to both water and freezing.
This is because the water that penetrates into the concrete expands by 9% in volume after being frozen by ice, which puts considerable pressure on the pores and capillaries inside the concrete. If the temperature rises, the ice will melt, and this will happen again and again. As the ground freezes and thaws, the concrete will eventually fail. The frost resistance of concrete is represented by the frost resistance code F.
If the strength of the test block subject to freezing and thawing is not reduced by more than 25% compared with the strength of the test block not subject to freezing and thawing, the frost resistance is deemed to be qualified. The anti-freeze label is expressed by the maximum number of repeated freeze-thaw cycles that the test block can withstand. According to the number of freeze-thaw cycles, concrete frost resistance grades are generally divided into: F15, F25, F50, F100, F150 and F200.
Erosion resistance:
Refers to the corrosion resistance of concrete in various corrosive liquids and gases. The media that corrode concrete are mainly sulfate solution, acidic water, active and or pressurized soft water, sea water, concentrated solutions of alkali, etc.
Heat resistance:
Refers to the fact that under the action of high temperature, the internal structure of concrete will not be damaged, the strength will not be significantly lost, and it has certain chemical stability.
Why do the same concrete admixtures blend with different types of cement, and the same cement mixed with different types of admixtures will cause the above problems? Through analysis, the author believes that the main reason is that the admixtures are not compatible with the cement. Adaptation, so what is the adaptability of cement and admixtures? We can define it this way: the concrete prepared by using admixtures that have been tested to meet the technical standards and cement that has also been tested to meet the technical standards can produce the desired results. If the effect is good, this kind of cement is considered to be suitable for this kind of admixture; on the contrary,If it cannot produce the desired effect, it is considered that this kind of cement is not suitable for this kind of admixture
Therefore, in the actual production process, we recommend that the cement should be added as much as possible before construction during construction. The concrete admixtures and cement are sent to the laboratory for adaptability testing. Then apply it in actual production and construction, thereby reducing cement and other raw materials!
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