Commercial concrete construction is inseparable from concrete admixtures. Concrete admixtures are chemical materials added before or during concrete mixing to improve the performance of fresh concrete or hardened concrete. The application of admixtures promotes The rapid development of commercial concrete has achieved considerable technical, economic and social benefits. Concrete companies have also developed rapidly, but the quality of employees varies. Some concrete companies lack strict management of the production process, resulting in product quality problems, seriously affecting the quality of construction projects, and also bringing unpredictable consequences to the companies themselves. Loss, the following quality problems caused by excessive amounts of concrete admixtures are discussed and analyzed through several cases. There are still many misunderstandings in actual construction applications, which affect the application effect of admixtures in commercial concrete construction. Engineering accidents caused by improper use of admixtures also occur from time to time.
1. The metering of admixtures was out of control and abnormal conditions occurred in the concrete
Case:
A certain project was pouring C25 concrete for a layer of beams, slabs and columns, and the mixer truck arrived at the construction site to unload the materials. During the inspection, it was found that the slump of the concrete was obviously too large and there was segregation. There was yellow liquid emerging from the surface of the concrete. After it was placed in the bucket truck and left to stand for 20 to 30 minutes, the phenomenon of sticking to the bottom appeared, and the surface bleeded seriously and turned yellow.
Cause analysis:
Before producing this batch of concrete, the operator discovered that there was an abnormality in the measurement of concrete admixtures, and promptly notified the mechanic to come and check. It was found that the problem was with the sensor. , so a new sensor was replaced, but the scale was not calibrated in time. The succeeding operator continued production without knowing it, which resulted in the above-mentioned problems. After calibrating the scale, it was found that the measurement deviation was more than double, resulting in a serious excess of additives.
Disposal:
All the concrete trucks with this abnormal phenomenon will be scrapped.
Preventive measures:
(1) Strengthen the repair and maintenance of all parts of the mixing station, pay special attention to the maintenance of the metering part to prevent a certain part of the production from getting out of control. For maintenance involving metering Or replacement, especially the replacement of the scale body, scale body connectors and sensors, the scale must be recalibrated and can be used only after it is normal.
(2) Mixing station operators and testers must increase their sense of responsibility, and unqualified products or concrete in abnormal conditions must not be carelessly shipped out of the factory.
(3) Strengthen personnel management and improve the handover system.
2. The butterfly valve of the concrete admixture scale failed, causing the admixture to leak and cause excess, resulting in concrete quality problems
Case:
A municipal bridge The project was to pour C40 concrete for paving the bridge deck. The pouring started at 6:00 that morning. There were a total of 4 trucks of 30m³ concrete, and all the pouring was completed around 9:30. On the morning of the second day, the construction unit discovered that the concrete poured by the last truck had not yet completely set. The first three trucks were normal, and it did not completely set until the evening of the second day, which greatly exceeded the normal setting time.
Reason analysis:
According to the on-site operator of the construction unit, the slump of the last truck of concrete arriving at the construction site was significantly larger than that of the first three trucks, because it did not affect pumping and construction. I didn’t care. Based on the on-site conditions and the conditions during pouring, the technicians of the mixing station initially determined that the cause was caused by excessive amounts of concrete admixtures. After careful inspection, it was found that the butterfly valve of the admixture scale was not closed tightly, and the scale leaked during the production process. Because it was not discovered in time, it resulted in an excess of admixture.
Treatment:
Notify the construction unit to add fence protection to prevent trampling, and continue to strengthen maintenance. Although the concrete setting time is delayed, it will not affect the final quality of use.
Preventive measures:
(1) Strengthen equipment maintenance and upkeep, and establish a regular equipment inspection system.
(2) Strengthen the professional quality training of operators and quality inspection personnel, and enhance the work responsibility education of relevant personnel.
(3) Problems must be discovered and solved early to avoid unqualified concrete from leaving the factory.
3. Excessive external mixing of retarding admixtures resulted in abnormal phenomena in the concrete
Case:
During the summer construction of a mixing station, a power outage occurred at the construction site. In the past 4 hours, the slump loss of the concrete was too great. In order to increase the slump without increasing the water-cement ratio, the mixing station used additives to adjust the slump. However, due to excessive amounts of additives, the concrete slumped 12 times after construction. No condensation for hours.
Cause analysis:
The concrete admixture used in summer concrete production is a composite admixture with a retardant component. If you blindly use admixtures to adjust concrete slump, The drop rate will inevitably bring the retarding component into the concrete, causing the retarding component to be excessive and the concrete setting time to be greatly lengthened.
Handling:
Notify the construction unit to postpone the formwork removal time and prohibit people from stepping on it, and continue to strengthen maintenance. Although the concrete setting time is delayed, it will not affect the later strength of the concrete.
Preventive measures:
(1) When excessive slump loss occurs, mixing station technicians should analyze the cause and adjust the slump in an appropriate amount even if admixtures are added. Admixtures can be added appropriately or a small amount of water can be added according to the specific conditions. Construction workers should not add water at will to prevent the reduction of concrete strength due to an increase in the water-cement ratio.
(2) Can beConcrete that is difficult to adjust to meet slump requirements is downgraded to other construction sites, and those that are truly unusable are scrapped.
Concrete quality problems caused by concrete admixtures are not uncommon in reality. Through the analysis of the above cases, we must pay more attention to the use of admixtures. As technical personnel of concrete enterprises, we should have an in-depth understanding and mastery of the performance and use methods of admixtures; managers should strengthen admixture-related equipment, especially Routine maintenance and repair of measuring equipment; operators must closely monitor the occurrence of abnormal situations and strictly detect and handle them promptly; quality inspection personnel should increase the frequency of sampling and handle abnormal situations in a timely manner to prevent problematic concrete from leaving the factory. In short, to avoid or reduce the occurrence of problems, we must strictly manage, pay attention to details, establish and improve relevant management systems, improve the professional level and work responsibility of relevant practitioners, work more on pre-control, and strictly implement prevention Suffer before it happens.
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