Measures to Alleviate the Adverse Effects of Soil on Polycarboxylate Superplasticizer

2019-08-15 16:36:49

Polycarboxylate water reducing agent has been continuously developed in recent years, and its synthesis conditions have changed from high temperature conditions to low temperature conditions, and its performance has also evolved from a single function of water reduction and moisture retention to functionalization.

The reason for its development is mainly due to the compatibility of water reducing agent and cement and the problem of sand and gravel.

Especially in recent years, as natural sand and gravel materials are gradually consumed, sand and stones with a large amount of mud are increasingly used to mix concrete.

However, the general polycarboxylic acid water reducing agent is sensitive to soil, and when used in concrete, the water reducing agent is easily adsorbed by the soil.

This means that the proportion of the water reducing agent that really works is reduced.

In response to the adverse effects of soil on concrete, domestic and foreign scholars have gradually studied the measures to inhibit or resist soil.

(1) Wash the sand before using the sand. However, this kind of thinking not only increases the labor, machinery and water costs, but also the operation is very cumbersome, and is not suitable for large-scale engineering and construction.

(2) By increasing the amount of polycarboxylate water reducing agent to meet the needs of the work.

However, the increase of the amount of polycarboxylate water reducing agent not only increases the production cost of concrete, but also may cause adverse consequences such as excessive concrete setting time, bleeding, and segregation.

(3) Adding a small molecule sacrificial agent to allow small molecules to quickly adsorb onto the clay particles to occupy the active site, so that the added water reducing agent molecules are adsorbed on the cement particles to achieve the purpose of dispersion.However, the small molecule adsorbents generally used in this method are cationic, and the polycarboxylate water reducing agents are generally anionic.When they are used together, precipitation may occur.

(4) Synthetic anti-mud polycarboxylate water reducing agent, usually introducing a functional group such as a sulfonic acid group, a phosphoric acid group, an amide group or an ester group into a water reducing agent molecule,These functional groups reduce the adsorption of high-valent metal ions in the soil on the polycarboxylic acid-based water reducing agent by adsorption and complexation, thereby improving the utilization rate of the water reducing agent.

Therefore, starting from the molecular structure of the polycarboxylate superplasticizer, a polycarboxylate superplasticizer suitable for high-sludge aggregates and simple reaction process is developed by introducing functional groups capable of reducing clay adsorption.It is of great significance for the promotion and application of polycarboxylate superplasticizer in the ready-mixed concrete industry.

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