The development of high-strength and high-performance concrete has made great contributions to the development of national large and medium-sized key engineering projects such as highway bridges, hydropower projects, nuclear power plants, railway lines, and roads. This is all inseparable from the contribution of concrete admixtures, but different concrete admixtures have different application fields. If the selection is incorrect, it will cause adverse effects. How to choose concrete admixtures during project construction?
1. Differences in climate
Preparation of water reducing agent for winter construction measures. Due to the low temperature in winter, the slump damage is small, but the strength will be limited. To achieve early strength and cold protection, the more economical and reasonable method is to use early strength concrete, use early strength agent, early strength admixture or admixture composite early strength agent. Preparation of water reducing agent for summer engineering construction. In summer, due to the high temperature of raw materials, mixing and transportation of concrete, the water evaporates quickly, so the slump loss is large, and the concrete is easy to harden. Concrete will not thicken underwater, and dry lumps will make it easy for cracks to form in the early stage of hardening of the concrete and problems such as poor integration between the various layers of concrete. Therefore, it is extremely reasonable to add retarder or retarder admixture during summer engineering construction.
2. Differences in asphalt mixtures
When gravel and river pebbles are used as seasonings, they have a great impact on the fluidity and cohesion of the concrete mixture. When gravel is used as stone, although cement, stone powder and fine sand are strong and strong, the gravel has water chestnuts and is not easy to flow, so the amount of water-reducing agent added needs to be increased accordingly. Fine asphalt mixtures are coarse sand, coarse sand and fine sand. Different fineness modulus has a great impact on the adhesion of the concrete mixture and also affects the amount of water-reducing agent added. When the sand is coarse, the fluidity is poor and the intake is relatively increased; when the sand is fine, the fluidity is good and the intake of water-reducing agent is relatively reduced.
3. Differences in water bodies
Tap water for mixing concrete and cement mortar generally uses drinking water and clean water from wells, rivers, lakes and streams without harmful substances (ph value Not less than 4), but swamp water, peat surface water, processing plant sewage and water with high mineral content cannot be used. Do not use sea water or other salt-containing water to mix concrete.
4. Differences in admixtures
When admixtures are added to concrete mixed with early strength agents, the actual early strength effect will be slightly lower than those that do not match the admixtures. . In concrete that should be added with a retardant, the same effect can be achieved with less or no mineral admixtures. It is also important to pay attention to the compatibility between the accelerating agent and mineral admixtures. The admixture will increase the initial and final setting time of the accelerating agent. In other words, when the admixture is used in large amounts, the adaptability to the water-reducing agent must be taken into consideration.
5. Differences in incorporation methods
The admixture incorporation methods are roughly divided into first-incorporation method, simultaneous incorporation method, water retention method, and post-incorporation method. It is better to use naphthalene series high-efficiency water reducing agent and then mix it; to use lignocalcium admixture, it is better to mix it at the same time. According to different mixing methods, the amount of water-reducing agent can be determined through trial mixing. Accurate measurement and verification. Although the intake of water reducing agent is small, it has great harm to the properties of concrete. If there is a problem with the weighing silo and excessive mixing occurs, it will not only be economically uneconomical, but may also lead to serious engineering safety accidents. If the calcium intake exceeds 0.5% of the concrete quality, excessive gas will be introduced and the initial setting will be delayed, reducing the initial compressive strength of the concrete.
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