The polycarboxylate water-reducing agent is a graft copolymer having a comb-like molecular structure, the main chain is an alkyl carbon chain having a carboxyl functional group, and the side chain is a polyoxyethylene (and/or polyoxypropylene) structural unit having a different length.
The carboxyl group in the main chain of the polycarboxylate superplasticizer is adsorbed by electrostatic attraction and cement particles,Polyoxyethylene units of different lengths in the side chain prevent other cement particles from approaching by steric hindrance and achieve their dispersion of cement.Compared with naphthalene-based water reducers, polycarboxylate superplasticizers have a stronger dispersing ability for cement and exhibit a higher concrete water reduction rate.Its water reduction rate is over 40%, which can significantly reduce the amount of concrete mixing water.
The water consumption of concrete can determine the water-to-binder ratio (water-cement ratio), and the water-to-binder ratio (water-cement ratio) directly affects the mechanical properties of concrete.The water-cement ratio rule considers that the 28d compressive strength of concrete is directly proportional to the reciprocal of the water-cement ratio.In order to ensure the compressive strength of concrete, production technicians usually use a smaller water-to-binder ratio.
In order to improve the economics of concrete, reducing the water consumption of concrete is the most effective way to reduce the water-to-gel ratio of concrete.
The reduction of concrete mixing water will affect the workability of the fresh concrete, and the polycarboxylate water reducing agent can effectively ensure the workability of the concrete mixture.Furthermore, the organic unity of the polycarboxylic acid water reducing agent and the concrete water consumption is realized.
The change in the water consumption of concrete not only determines the concrete water-to-binder ratio, but also affects the concrete-to-slurry ratio of the concrete.As with the water-binder ratio, the slurry-to-bone ratio is also an important factor that must be considered in the design of the concrete mix ratio.The ratio of the slurry to the concrete mixture is the ratio of the total amount of the mixing water and the cementitious material to the total volume of the aggregate. The change of the ratio of the slurry to the concrete affects the workability and volume stability of the concrete.Compared with the density of the cementitious material (cement: about 3.0 g/cm3; fly ash: 1.9 to 2.4 g/cm3; mineral powder: about 2.6 g/cm3), the density of water (1.0 g/cm3) is Much smaller than them,
In the case of the same mass, the change in water consumption has the greatest effect on the total volume of the slurry.Under the condition that the total amount of the rubber material is kept constant, the reduction of the water consumption will inevitably lead to a decrease in the volume of the slurry of the mixture, which affects the workability of the fresh concrete.Therefore, when reducing the water-to-binder ratio by reducing the water consumption of the concrete, the total amount of the rubber should be adjusted to ensure that the ratio of the slurry to the concrete is constant.However, concrete production personnel often neglect the effect of water consumption on the ratio of slurry to bone, which causes the volume of the slurry to vary greatly with the change of water consumption.
In order to ensure the workability of concrete, concrete production personnel have put forward higher technical requirements for polycarboxylate water reducer.The polycarboxylate water reducing agent not only has strong cement dispersing ability, but also needs to have a good plasticizing ability for the concrete mixture, so that the workability of the concrete has a strong dependence on the performance of the polycarboxylate water reducing agent.