Causes and solutions of deterioration of concrete polycarboxylic acid water reducing agent

At present, the commonly used water reducing agent is polycarboxylic acid system water reducing agent. Compared with other types of water reducing agents, it has the advantages of strong molecular designability, high water reduction rate, good slump retention, low chloride ion and alkali content, and pollution-free production and use. In practice, it is generally compounded with defoamer, retarder, air-entraining agent, etc., to meet the different technical performance requirements of concrete. Among the retarder sodium gluconate or sucrose and polycarboxylic acid system water reducing agent compounding, can improve the water reduction rate, slow slump loss, and improve the water reducing agent and cement adaptability. But also often due to the addition of sodium gluconate and quickly deteriorate, lightly reduce the performance, or lead to complete failure of water reducing agent, which brings many uncertainties to the use of engineering or directly lead to engineering accidents, and even cause many legal disputes. Especially in the high temperature weather, it is more likely to appear this phenomenon. In order to prevent the deterioration of polycarboxylic acid water reducing agent and lead to performance changes and even engineering accidents, Nanjing Tianshi Blue Shield will analyze the causes and put forward effective measures to prevent the deterioration of polycarboxylic acid water reducing agent from the production and application point of view.
　　There are two main reasons for the deterioration of polycarboxylic acid water reducing agent: one is the influence of temperature, and the other is sodium gluconate.
　　The influence of temperature: In summer, the water reducing agent is easy to deteriorate, such as blackening, odor, flocculation, bacterial spots, etc. The higher the temperature of the storage environment of polycarboxylic acid water reducing agent, the more likely to deteriorate. When the ambient temperature rises, the Brownian motion intensifies and the heat energy becomes larger, leading to chain decomposition and reduction of water reducing agent effectiveness. Higher ambient temperature makes it easier for bacteria and mold to grow in the liquid, while the growth and reproduction of microorganisms are accelerated, which leads to moldy water reducing agent.
　　The most suitable temperature for most mold reproduction is 25-30 ℃, the optimum growth temperature of Aspergillus flavus is about 37 ℃, the optimum temperature for the production of toxicity is 28-32 ℃. And most bacteria suitable for reproduction temperature is 25 ~ 40 ℃.
　　The impact of sodium gluconate: there are three main production processes of sodium gluconate: one is the immobilized cell and immobilized enzyme method, the second is the biocatalytic method, and the third is the microbial fermentation method. Currently commonly used is the microbial fermentation method, is a fungal fermentation and bacterial fermentation process, which is more commonly used Aspergillus niger strain M276 fermentation production of sodium gluconate. The use of Aspergillus niger fermentation to produce sodium gluconate will produce Aspergillus niger, gluconic acid residues. These residues provide nutrition for the reproduction of microorganisms, when the ambient temperature is more suitable, microorganisms, bacteria will accelerate the reproduction of water reducing agent that appears black mold phenomenon occurs.
　　Polycarboxylic acid system water reducing agent deterioration of prevention and solution measures
　　Practice has proved that the deterioration of polycarboxylic acid water reducing agent will have a certain degree of impact on its quality, which can seriously lead to concrete quality accidents. The domestic compounding production plant takes a fluke attitude towards the setting of anti-mildew function of polycarboxylic acid water reducing agent, and adopts the way of quick supply and quick use to ensure the quality of water reducing agent by constantly replenishing "fresh water reducing agent" to the site (factory) water reducing agent storage tank, but this is very unscientific and unreliable. When the project schedule is affected, the use of water reducing agent speed can not be controlled, the stock of water reducing agent in the summer that is easy to appear corruption, deterioration. Prevention of water reducing agent corruption, deterioration, the following measures can be taken.
　　1, the use of high purity of sodium gluconate
　　There are more manufacturers of sodium gluconate on the market, manufacturers should provide sodium gluconate in Aspergillus niger, gluconic acid residue test report. Manufacturers with strict production control system can effectively control the residues of glucose and Aspergillus niger in the production process, thus reducing the risk of corruption and deterioration of polycarboxylic acid water reducing agent compounded with sodium gluconate.
　　At present, the price difference between industrial grade sodium gluconate and food grade sodium gluconate is about 1000~2000 RMB/ton, but the purity of food grade sodium gluconate is higher and the amount in water reducing agent is less, so you can choose food grade sodium gluconate instead of industrial grade.
　　2、Add a certain amount of preservative
　　Adding a certain amount of preservative in the production process of polycarboxylic acid water reducing agent can effectively prevent the corruption and deterioration of polycarboxylic acid water reducing agent. At present, the main preservatives on the market are sodium nitrite, sodium benzoate and isothiazolinone. Isothiazolinone is a more widespread, efficient, low toxicity, non-oxidizing fungicides, applicable pH value is wide, used for water reducing agent mold sterilization is more ideal. The amount of preservative added is (0.5-1.5) kg per ton of polycarboxylic acid system water reducing agent.
　　Tips: reduce the use of formaldehyde, nitrite, try to use high-quality fungicides compounding! There are some water reducing agent manufacturers will use formaldehyde, sodium benzoate and strong oxidizing nitrite, etc. for corrosion. Although its relatively low cost, but the effect is not good, while formaldehyde will also escape with time, temperature, pH and other factors change, there is still corruption and deterioration.
　　3、The importance of storage environment of polycarboxylic acid water reducing agent
　　Try to store polycarboxylic acid water reducing agent in a cool and ventilated environment, avoid direct sunlight exposure. Avoid using metal products, otherwise the corrosion of metal materials will also cause the polycarboxylic acid water reducing agent to change color or even deteriorate. For example, stainless steel cans will make the stored water reducing agent become red, iron cans will make the stored water reducing agent become green, copper cans will make the stored water reducing agent become blue, etc.
　　4、Rational estimation of polycarboxylic acid water reducing agent usage
　　In some projects, the speed of polycarboxylic acid water reducing agent is not easy to control due to the project progress and weather conditions. In some projects, polycarboxylic acid water reducing agent has been placed on site for more than 3 months or even longer, and corruption and deterioration happens from time to time. Therefore, it is recommended that manufacturers should communicate with the project office before delivery about the progress and cycle of product use, so as to ensure that the consumption and replenishment of polycarboxylic acid water reducing agent are in dynamic balance.
　　Finally, for the deteriorated water reducing agent in principle is not to be used again, especially the water reducing agent has been smelly, moldy, flocculation. However, slight deterioration of the water reducing agent, can be used to quickly kill the preservative for corrosion treatment. Concrete mixing experiments should be conducted again to prevent the water reducing agent function failure.