| Case Name |
Impossibility to cast concrete by use of high-performance AE ( Air Entrained ) water reducing agent under the freezing point. |
| Pictograph |
|
| Place |
The cold region. |
| Location |
The construction of PC superstructure constructed in the cold region in winter. |
| Overview |
In the cold region, they tried casting the concrete which added high-performance AE water reducing agent but the slump wasn't stabilized, and the installation work was suspended. |
| Incident |
In the construction of PC ( prestressed concrete ) superstructure in a cold region in winter, when it was intended to cast the concrete which added high-performance AE water reducing agent, the slump (the index which shows the softness of the concrete ) wasn't stabilized when the concrete had arrived at the field , quality control of it became impossible, and the installation work was suspended. |
| Sequence |
High-performance AE water reducing agent has been adopted for general PC superstructure construction since its decreasing amount of water effect and holding slump is high, etc.
This winter-construction had been required from the order point of time, and measures against cold and test blending. etc. were carried out.
The slump wasn't stabilized, because the temperature of the installation day was considerably lower than the test blending day, and the mixed quantity of high-performance AE water reducing agent wasn't appropriate. |
| Cause |
The temperature of the installation day was considerably lower than the test blending day, and the mixed quality of high-performance AE water reducing agent wasn't appropriate.
In cases when the concrete has a low content of high-performance AE water reducing agent, expression of effect became lack of stability.
The slump became unstable by the ability of the mixing equipment ( mixer ). |
| Response |
The reexamination scouring was carried out. |
| Countermeasures |
To ensure a steady implementation of thermal management to concrete.
To test that blending by the real machine is carried out.
To recognize that in the low temperature, effect of the superscription on the slump increases because the high-performance AE water reducing agent dosage decreases. |
| Knowledge Comment |
To ensure a steady implementation of thermal management to concrete!!!
To recognize rightly admixture ingredient sensitivity also the high-performance AE water reducing agent, and that it selects the admixture ingredient with the appropriate performance!!!
To test that blending by the real machine is certainly carried out after the decision of the mixture!!! |
| Background |
It is considered that there was the recognition shortage for the comparatively new material.
As discussed previously, it is important to recognize rightly admixture ingredient sensitivity also the high-performance AE water reducing agent, and that it selects the admixture ingredient with the appropriate performance. And it is necessary to do knowledge improvement for the admixture ingredient of practicing engineer and ready-mixed concrete manufacturer engineer. |
| Sequel |
The reexamination blending showed the following facts.
The effect of the concrete temperature is large for the performance of the high-performance AE water reducing agent.
The effect becomes unstable when the dosage of the water reducing agent is little.
The slump becomes unstable by the ability of mixing equipment ( mixer ). |
| Incidental Discussion |
The reexamination scouring was carried out, and it was realized again that there was the knowledge shortage for the use of the high-performance AE water reducing agent. |
| Reason for Adding to DB |
In order to anticipate that the similar trouble will be generated in the future too. |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Ignorance, Insufficient Knowledge, Insufficient Analysis or Research, Insufficient Prior Research, Planning and Design, Poor Planning, Usage, Operation/Use, Bad Event, Chemical Phenomenon
|
|
| Number of Deaths |
0 |
| Number of Injuries |
0 |
| Physical Damage |
At the beginning 40% of the installation schedule quantity has been discarded. |
| Financial Cost |
About \1,500,000 ( discarded ready-mixed concrete quantity is made to be about 100m3, and it costs amount of money material cost ). |
| Field |
Civil Engineering
|
| Author |
TANAKA, Miyo (Japan Prestressed Comcrete Constructors Association)
|
