Beijing Dongke United Technologies Co.,Ltd.

What should be paid attention to in the preparation of low and medium strength concrete with polycarboxylate superplasticizer?

polycarboxylate superplasticizer

As a water-reducing agent with excellent comprehensive performance, polycarboxylate superplasticizer has a lower dosage and a higher water-reducing rate, and the mixed concrete has good slump retention performance. polycarboxylate superplasticizer has more advantages than traditional naphthalene and aliphatic water reducers when mixing high-strength concrete. Since polycarboxylate superplasticizer has a higher water reducing rate, even if the dosage is reduced when formulating medium and low strength concrete, it is possible to obtain a higher water reducing rate than naphthalene-based and aliphatic water reducing agent. 

The high water reduction rate of polycarboxylate superplasticizer reduces the water consumption of concrete, and the total slurry of concrete is reduced when the water-to-binder ratio remains unchanged, which affects the working performance of concrete. Therefore, when using polycarboxylate superplasticizer to prepare low-strength grade concrete, its dosage must be strictly controlled. 

When preparing low-strength grade concrete, a phenomenon will be found: when the amount of water reducing agent is slightly too large, the concrete mixture will have bleeding, segregation and other poor workability. If the admixture is too small, the concrete mixture is likely to have insufficient fluidity and poor slump retention effect, which makes it difficult to meet the construction requirements. In addition, due to the poor quality of sand and gravel used in low-strength grade concrete, the amount of polycarboxylate superplasticizer increased, and the cost-effectiveness was reduced.

In order to better use polycarboxylate superplasticizer in low-strength concrete, the author believes that the following points should be noted for your reference

  1. Reduce the solid content of polycarboxylate superplasticizer
  • The higher the solid content of the polycarboxylate superplasticizer, the lower the content of the polycarboxylate superplasticizer to achieve the same water-reducing rate. When formulating low- and medium-strength grade concrete, if a polycarboxylate superplasticizer with a higher solid content is used, the water reduction rate is too high and the water consumption is reduced. Once the water consumption increases, concrete bleeding will occur. When formulating low- and medium-strength grade concrete, the required water reduction rate is low. The use of high solid content polycarboxylate superplasticizer will often result in too low admixture content. The lower the water-reducing agent consumption, the lower the water-reducing agent consumption And the more sensitive the water consumption, the less convenient the production control. For example, if the amount of polycarboxylate superplasticizer fluctuates by 0.5kg/m3 or the water consumption fluctuates by 5kg/m3, the concrete mixture will undergo major changes, sometimes even segregation, bleeding, hardening, and even blockage during construction. Pipe, sometimes the concrete mixture becomes unable to meet the workability required by the construction.
  • Therefore, when using polycarboxylate superplasticizer to produce low- and medium-strength grade concrete, it is advisable to control the solid content of polycarboxylate superplasticizer at 8%-10% (when the mixing amount is 1.8%, the water-reducing rate is controlled at 20% Below) to facilitate concrete production control. The low solid content polycarboxylic acid reduces the sensitivity of the amount of water reducing agent and water consumption. In the concrete production process, even if the water content of sand and gravel fluctuates, it can effectively control the workability of concrete to produce greater fluctuations.