Nowadays, more concrete is used, especially in the summer. Sometimes the concrete pump truck comes out with a small slump. Concrete companies often choose to add admixtures on site to increase the slump.
Dosage issue
Various admixtures often have a most suitable dosing amount, which is based on the quality of the admixture and the conditions of the concrete and stone it is used in. of. If the dosage is too small, the admixture will not have the required effect and cannot achieve the expected goal; if the dosage is too high, it will not only fail to achieve the expected goal, but will also have relative effects. Therefore, before use, the best dosage should be confirmed through experiments. When the expected target cannot be exceeded, the dosage should be changed and the amount of concrete, stone, and water needs should be adjusted to achieve the optimal effect.
Effective use of admixtures
To effectively use various admixtures, at least the following points must be ensured to ensure the quality of project construction.
(1) Accurate dosage. During project construction, admixtures must be added accurately according to the designed dosage. If it is a liquid, the liquid concentration value must be measured accurately; if it is a granule, it should be added evenly and accurately so that the deviation is controlled within ±2%.
(2) Evenly blended, we must find ways to jointly distribute the admixture throughout the entire mix, so that it can fully mobilize its efficacy and avoid adverse effects caused by excessive concentration. If the granular agent is added together with concrete, it should be spread out and the dry mixing time should be appropriately increased; the liquid agent should also be spread evenly to avoid local concentration problems
(3) The mixing process is not consistent It’s okay to be messy. For concrete mixed with several types of admixtures, special attention should be paid to the order in which they are mixed. Some may be added first, some may be added last, and some may be added after being transported to the site. Therefore, there is a certain order in adding admixtures and cannot be messed up.
(4) The admixture should be replaced in time as the season changes (the working temperature is different). Different admixtures have different characteristics. As mentioned earlier, a certain company encountered problems due to incorrect operation of admixtures during the construction process of an overpass prestressed beam. Due to the winter 13 to 1 season , the temperature is already below zero, but we still use high-efficiency water-reducing admixtures used in autumn. This kind of admixture has a certain retarding effect, and the cold-proof effect is not very good. When the temperature is relatively low, the solidification rate is slower. As a result, it does not condense for 28 hours and the compressive strength progress is slow. Therefore, from autumn to winter construction, the type of concrete admixture should be changed in advance. In winter, anti-cold and early-strength admixtures should be used to fully prepare for winter construction.
Experiences of using admixtures
In order to make good use of concrete admixtures and bring them into full play, certain measures should be taken during use.
(1) Do a good job in comparing and selecting admixtures. When selecting the type of admixture, it should be determined based on the technical characteristics of the concrete, construction technical conditions, construction season, purpose of use, and technical and economic comparisons, and should not be used blindly. There are many types of admixtures. When choosing the place of origin, you need to conduct actual research. You should choose some genuine products from large manufacturers with certain manufacturing history and experience. Do not listen to some brand advertisements, otherwise, it will cause financial and financial losses. Extravagant waste of energy and time.
(2) In the process of evaluating the adaptability of admixtures to concrete. Before the application of admixtures, the adaptability of the admixtures to commonly used concrete should first be evaluated to prevent the addition of admixtures from causing rapid setting problems in the concrete and resulting in safety accidents. The evaluation is based on the cement slurry external diffusion experiment and confirms that the good adaptability to water reduction has a large external diffusion and a small one. During the construction process, when changing concrete types or using concrete from different manufacturers, first conduct concrete adaptability tests to avoid accidents. According to statistics, many companies do not conduct concrete adaptability tests when changing concrete types or using concrete from different manufacturers during the construction process. This can easily lead to safety accidents and should be taken seriously.
(3) The work of improving the mix proportion of concrete mixed with admixtures is in progress. First, carefully prepare the standard mortar mix ratio for ordinary concrete, and then based on this, determine the most suitable dosage of admixtures, and determine the best mortar mix ratio based on the 29-d compressive strength.
(4) Ensure accurate dosage at the construction site. In order to make the dosage of admixture accurate, some simple and feasible measures should be adopted at the construction site. For non-commercial concrete mixing stations, when choosing the powder method, according to the mixing quantity per plate and the dosage size of admixture, use 1 Fix the container for mixing, or choose to weigh the amount of admixture in each plate of concrete in advance and put it into a small bag, and then add the bag accurately during construction to ensure that each plate of concrete is filled with water. The accuracy of adding additives prevents side effects caused by inaccurate amounts.
(5) Ensure even mixing. Certain measures should also be taken to ensure the joint distribution of admixtures in the concrete mix. When choosing the powder method, first sprinkle it on the mixing material as much as possible without concentrating it in a certain position. Fifth, increase the mixing time appropriately, usually by 40 seconds, but the total mixing time does not exceed 3mln. For the admixture dissolved in the incoming water, prepare it into an aqueous solution with a certain concentration, and then stir it.��Fully automatic metering and adding water to the mixer, so that the additives can be evenly dispersed into the mixture without increasing the mixing time.
(6) Designate a dedicated person to take charge. In order to ensure the quality of mixing, when using admixtures, a dedicated person is assigned to take charge every time. Before the actual operation, these employees are first specially trained to carefully explain the mixing method to ensure the accuracy of the dosage. </p
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