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The relationship between high efficiency water reducing agents and concrete and its components
Blog The relationship bet
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As a third-generation high-performance water reducer, polycarboxylate superplasticizer is often used in combination with small amounts of retarding, air-entraining, defoaming and viscosity-modifying components, to meet the different technical performance requirements of concrete. However, the high temperature in summer makes it easy for water-reducing agents with added retarding components (such as sodium gluconate and sucrose) to deteriorate, seriously affecting their effectiveness. How to solve it?
At the initial stage of deterioration of polycarboxylate superplasticizer, there are light colored fuzzy or cotton like bacterial spots on the liquid surface, which then develop into discrete island shaped floating objects, and occasionally string shaped bubbles emerge; When the deterioration is severe, the plaque will cover the entire liquid surface, and the solution will present suspended solids in dark green, brown, and black colors, accompanied by the generation of rancid and foul smelling gases. This kind of deterioration is mainly caused by mold growth.
The deterioration of polycarboxylate superplasticizer is mainly caused by the compounded sodium gluconate. In industrial production, Aspergillus niger fermentation is commonly used to produce sodium gluconate. After Aspergillus niger fermentation is complete, a large amount of Aspergillus niger residue will be produced, with a wet weight of 2%- 3% of the total sodium gluconate solution. Black mold residue contains nutrients and various components.
In the production of sodium gluconate, if production control is not strict, residues of glucose and Aspergillus niger are inevitable, which also provide nutrients for the reproduction of microorganisms. Under suitable natural conditions (nutrients, temperature, humidity, oxygen, pH), microorganisms have an astonishing reproduction rate and can reproduce one generation in about 20-30 minutes. When extremely rare breeding conditions overlap, the phenomenon of “mold explosion” occurs. The blackening of deteriorated water reducing agents is caused by the fermentation of black mold in unqualified sodium gluconate products.
On the other hand, the mold growth of polycarboxylate superplasticizers is also related to their storage environment. Higher temperatures will intensify the movement of large molecular chains. Once the dissociation energy of chemical bonds is exceeded, chain decomposition, irregular breakage, and thermal decomposition will occur, leading to an accelerated degradation rate of the polymer. Similarly, the higher the temperature, the greater the activity of microorganisms, and the faster the mold growth rate of water-reducing agents.
There is also literature showing that improper storage conditions, such as severe temperature rise in storage space, lack of ventilation, and humidity, can lead to the melting of large monomers, and the local temperature of monomers is too high, accelerating the rearrangement reaction of related monomers, resulting in a serious decrease in the double bond amount of large monomers and severe performance degradation.
In the production process of polycarboxylate superplasticizers, adding a certain amount of preservatives can effectively prevent spoilage and deterioration. At present, the main preservatives on the market are sodium nitrite, sodium benzoate, and isothiazolinone.
Among them, isothiazolinone is a widely used, efficient, low-toxic, non-oxidizing fungicide with a wide range of pH values. It is ideal for use as a water-reducing agent for mold prevention and sterilization. The amount of preservative added is 0.5-1.5 kilograms per ton of polycarboxylate superplasticizer.
Try to store polycarboxylate superplasticizer in a cool, well-ventilated place out of direct sunlight. I conducted a test in which one portion of polycarboxylate superplasticizer was placed in a cool storage bottle out of direct sunlight, and the other portion was placed in a storage bottle exposed to direct sunlight. It was found that the superplasticizer placed in the storage bottle, when exposed to direct sunlight, quickly became moldy and blackened.
In addition, non-metallic materials should be used as storage containers for polycarboxylate superplasticizers whenever possible; otherwise, corrosion of metal containers can cause discoloration or even deterioration of the superplasticizer. Stainless steel cans can turn stored water reducing agents red, iron cans can turn stored water reducing agents green, copper cans can turn stored water reducing agents blue, and so on.
In some engineering projects, due to factors such as project progress and weather conditions, the speed of use of polycarboxylate superplasticizers is often difficult to control. Some polycarboxylate superplasticizers used in engineering projects may be left on construction sites for more than 3 months or even longer, and spoilage may occur.
It is recommended that the manufacturer communicate with the engineering project department about the product’s usage and cycle before delivery to achieve planned use and ensure that the consumption and replenishment of polycarboxylate superplasticizer are in dynamic balance.
Currently, some water-reducing agent manufacturers use formaldehyde, sodium benzoate, and highly oxidizing nitrites to prevent corrosion. Although it is relatively low-cost, the effect is poor. At the same time, formaldehyde will also escape with changes in time, temperature, pH value, and other factors, and still exhibit decay and deterioration. Try to use high-quality fungicides in combination. For water reducing agent storage tanks that have already decayed, they should be cleaned before adding new polycarboxylate water reducing agents.
In addition, for polycarboxylate superplasticizers that have already become moldy but show only a relatively mild degree of mold, there are also related methods for processing and recycling, such as heating treatment or the addition of hydrogen peroxide or liquid alkali. The research findings in the relevant literature show that, after treatment, moldy polycarboxylate superplasticizer can restore its original performance, with a color similar to the original product and an odor that can be removed.
The relationship between high efficiency water reducing agents and concrete and its components
Blog The relationship bet
