Concrete additives are a kind of chemical substances added in the process of making concrete, and cement, sand and stone are important raw materials constituting concrete. The mixing amount is generally not more than 5% of the cement quality. It can be divided into superplasticizer, expansion agent, air-entraining agent, accelerator and retarder, among which superplasticizer accounts for the most. In 2017, it accounted for 66.61% of the total output of concrete admixtures, followed by an expansion agent, accounting for 21.55 %.
Superplasticizer is a concrete admixture that can reduce the amount of water used for mixing while maintaining the slump of the concrete. Most of them belong to anionic surfactants, such as lignin sulfonate and naphthalene sulfonate formaldehyde polymer. After adding the concrete mixture, it has the function of dispersing the cement particles, which can improve its workability, reduce the unit water consumption and improve the fluidity of the concrete mixture; or reduce the unit cement consumption and save cement.
History of Superplasticizer
In recent years, engineering construction has become more and more demanding on the performance of concrete, and the design strength of concrete is getting higher and higher; the previous lignin type water reducing agent and naphthalene sulfonate type water reducing agent have low water reduction rate, and the performance of concrete construction The improvement is not great. The construction requirements cannot be met at all. To save energy and reduce the weight of the building, the strength of concrete used in building structures is getting higher and higher. High-strength and high-performance concrete require additives to have the functions of high water reduction and greatly improved solid performance. Engineering and market demands have spawned a third-generation high-performance water-reducing agent-polycarboxylic, acid-based water-reducing agent.
The basic role of superplasticizer
(1) Improve the workability, slump and fluidity of concrete.
(2) Improve the mechanical properties of concrete.
(3) Save cement and reduce costs.
(4) Improve the durability of concrete.
The superplasticizer does not react chemically with cement. The role of superplasticizer on concrete is mainly through the plasticizing effect of freshly mixed concrete so that the concrete can increase the fluidity or keep the slump unchanged under the same water consumption. Can reduce the water-cement ratio of concrete.
Superplasticizers are mostly anionic surfactants, lignin sulfonates, Tsai series, melamine sulfonate formaldehyde condensates, etc. Anionic surfactants are widely produced and applied, with low cost and good plasticizing effect.
Polycarboxylate superplasticizer has many unique technical performance advantages:
(1) Low admixture and high water reduction rate;
(2) Good fluidity retention of concrete mixture; good compatibility with cement;
(3) The shrinkage of the prepared concrete is small, which is beneficial to improve the volume stability and durability of the concrete;
(4) Environmentally friendly and pollution-free during production and use, it is a green and ecologically friendly admixture.
What happens if you use too much polycarboxylate superplasticizer?
For the amount of polycarboxylate superplasticizer added, it is generally mentioned that it must not be added in excess. Otherwise, the consequences will be very serious, because it is often used with concrete, so the impact on concrete is greater. What are the implications of adding too much water reducer?
(1) There are many types of polycarboxylate superplasticizer, every kind of water reducer has different components, different functions, and the consequences after an overdose will not be the same.
(2) If it is a polycarboxylate superplasticizer with only water-reducing function, the excess will only cause an excessive slump of the concrete, or segregation, bleeding, and compaction.
(3) If there is too much polycarboxylate superplasticizer with retarded air entrainment, excessive retardation and excessive gas content will cause the concrete to set too slowly, and the gas content will be high, resulting in the decrease of concrete strength.
(4) When polycarboxylate superplasticizer is added in excess to concrete, the phenomenon of excessive slump and stone segregation will occur.
(5) If the amount of polycarboxylate superplasticizer exceeds the specified amount, the concrete will generally become brittle.
Polycarboxylate superplasticizer added too much would cause problems such as concrete slabs. Although the water reducer can remove part of the water in the concrete and can properly change the properties of the concrete, once the excess is added, the performance of the concrete will improve greatly.
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