Polycarboxylic acid water reducing agent as the third generation of high-performance water reducing agent, in order to meet the different technical performance requirements of concrete, often used with a small number of slow-setting components, air-entraining components, defoaming components, viscosity modification components, etc. after compounding. However, the summer temperature is high, adding the water reducing agent of slow-setting components (such as sodium gluconate, sucrose) is prone to deterioration, which seriously affects the use effect. How to solve it? Deterioration phenomenon and causes of polycarboxylic acid water reducing agent deterioration at the beginning, the liquid surface with light-colored fluffy or cotton wool-like spots, and then developed to a discrete island-like floating objects, and from time to time there are strings of bubbles; deterioration is serious, the spots will cover the entire liquid surface, the solution shows a thick green, brown, black suspended matter, and accompanied by the generation of sour odor gas. This deterioration is mainly caused by the role of mold. Polycarboxylic acid system water reducing agent deterioration is mainly caused by the compounded sodium gluconate. Industrial production of sodium gluconate is commonly used in the fermentation of Aspergillus niger. Aspergillus niger fermentation will produce a large number of Aspergillus niger residue after the end of its wet weight is 2%-3% of the total sodium gluconate solution. Aspergillus niger residue contains nutrients and a variety of components. In the production of sodium glucose, if the production control is not strict, there will inevitably be residues of glucose and Aspergillus niger, which also provide nutrients for the reproduction of microorganisms. Under suitable natural conditions (nutrients, temperature, humidity, oxygen, pH), microorganisms have an amazing reproduction rate of about (20-30) min to reproduce one generation. When the extremely rare reproduction conditions once the chance encounter and superimposed on each other, “mold explosion” phenomenon that appears. The deterioration of the water reducing agent blackening, is caused by the fermentation of Aspergillus niger in the unqualified sodium gluconate products. On the other hand, the mold of polycarboxylic acid water reducing agent is also related to its storage environment. Higher temperature will intensify the movement of macromolecular chain, once more than the dissociation energy of the chemical bond, chain decomposition, irregular fracture and thermal decomposition, etc., resulting in faster deterioration of the polymer. Similarly, the higher the temperature, the greater the microbial activity, the faster the water reducing agent mold. It is also shown in the literature that improper storage conditions, such as storage space temperature rises severely, not ventilated, and humid, leading to melting of macromonomers, and the local temperature of the monomer is too high, so that it accelerates the rearrangement reaction of the relevant monomer, leading to a serious decrease in the amount of macromonomer double bond and serious performance degradation.
Prevention and solution measures for deterioration of polycarboxylic acid water reducing agent will have an impact on its quality, which will seriously lead to concrete quality accidents. It is recommended to take the following measures.
(1) The choice of high-quality sodium gluconate as a slow coagulation component currently on the market sodium gluconate manufacturers. Manufacturers with strict production control system can effectively control the residual amount 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.
(2) Compounding a certain amount of preservatives in the production process of polycarboxylic acid water reducing agent compounding a certain amount of preservatives, can effectively prevent the corruption of polycarboxylic acid water reducing agent deterioration. At present, the main preservatives on the market are sodium nitrite, sodium benzoate and isothiazolinone. Isothiazolinone is a more extensive, high-efficiency, low toxicity, non-oxidizing fungicide, 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.
(3) Pay attention to the storage environment as much as possible to store polycarboxylic acid water reducing agent in a cool, ventilated, non-direct sunlight place. A test was done, one copy of polycarboxylic acid water reducing agent was placed in a cool, non-direct sunlight storage bottle, and the other copy was placed in a storage bottle with direct sunlight, and it was found that the water reducing agent placed in the storage bottle with direct sunlight quickly turned black and moldy. In addition, polycarboxylic acid water reducing agent storage containers try to use non-metallic materials, otherwise the corrosion of metal materials will also cause water reducing agent discoloration or even deterioration. Such as stainless steel cans will make the stored water reducing agent turn into red, iron cans will make the stored water reducing agent turn into green, copper cans will make the stored water reducing agent turn into blue, etc.
(4) Reasonable estimate of the amount of polycarboxylic acid water reducing agent used in the project Some projects, due to the progress of the project, the weather environment and other factors, the use of polycarboxylic acid water reducing agent speed is often not easy to control. In some projects, the polycarboxylic acid water reducing agent is placed on the site for more than 3 months or even longer, and the 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 the consumption and replenishment of polycarboxylic acid water reducing agent in a dynamic balance.
(5) reduce the use of formaldehyde, nitrite and other preservatives currently have a part of the water reducing agent manufacturers use formaldehyde, sodium benzoate and strong oxidation of nitrite and other preservatives. 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. Try to use high-quality fungicide compounding, for the water reducing agent storage tank has been corrupted, should be cleaned and then replenished with new polycarboxylic acid system water reducing agent. In addition, for the moldy but mildew degree of polycarboxylic acid water reducing agent, there are also related methods to deal with the recovery, such as heating treatment or mixed with hydrogen peroxide or liquid alkali method. The conclusion of the relevant literature shows that after treatment, the moldy polycarboxylic acid water reducing agent can restore the original performance, color and the original product close to the odor can be removed.
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