The application of common problems in concrete quality has become an essential link in concrete construction. The concrete in the mixing plant is often prone to some problems during the mixing process, which brings trouble to the construction progress and quality. This article analyzes the reasons for the loss of slump and unstable slump of pumped concrete, and provides a series of solutions.
1. Cause of occurrence
(1) The poor adaptability of concrete admixtures to cement leads to rapid loss of concrete slump.
(2) The dosage of concrete admixtures is insufficient, resulting in unsatisfactory retarding and plastic retention effects.
(3) The weather is hot, and some additives fail at high temperatures; Fast evaporation of water; Bubble overflow causes rapid loss of slump in freshly mixed concrete.
(4) The initial concrete slump is too small and the unit water consumption is too low.
(5) Poor coordination between the construction site and the mixing plant resulted in prolonged tank truck pressure and congestion, resulting in excessive loss of concrete slump.
(6) The measurement error of the concrete mixing weighing system is large and unstable.
(7) Changes in moisture content of coarse and fine aggregates.
(8) Cement mixing warehouse storage and mixed use.
2. Solution
(1) Adjust the formula of concrete admixtures to make them compatible with cement. Before construction, it is necessary to conduct compatibility tests between concrete admixtures and cement.
(2) Adjust the concrete mix ratio, increase or decrease the sand rate and water consumption, and adjust the initial slump of the concrete to over 200mm.
(3) Add an appropriate amount of fly ash to replace some cement.
(4) Increase the amount of concrete admixture appropriately, and adjust the retarding component in the admixture (especially when the temperature is much higher than the normal temperature).
(5) Prevent water from evaporating too quickly and bubbles from overflowing too quickly.
(6) Choose slag cement or volcanic ash cement.
(7) Improve the water retention and cooling devices of concrete transport vehicles.
(8) The accuracy of measuring equipment should meet relevant regulations and have a certificate of conformity issued by the legal metrology department. Self inspection should be strengthened to ensure accurate measurement.
(9) Strengthen the detection of aggregate moisture content, and adjust the mix proportion in a timely manner when changes occur.
(10) Cement entering the warehouse should be stored and used separately according to the manufacturer, variety, and label.
3. Summarize experience
Regarding the issue of slump loss in pumped concrete, especially in pumped concrete and underwater pile foundation concrete. Through learning, exploration, and experimentation, a set of practical problem-solving methods has been summarized.
Communicate with the additive manufacturer to improve and adjust the retarder components in the additive;
Adjust the construction time of concrete and try to avoid not working under high temperatures;
When the construction road conditions are poor and the distance is long, the secondary feeding of additives is used;
Construction using a large amount of fly ash concrete mix ratio.
The thorny problem of causing concrete slump loss has been greatly solved.
Regardless of the reason for the decrease in slump, which results in the inability to pump or the inability to meet the construction requirements, we can use additives to adjust it to achieve the required slump, eliminate the bad habit of randomly adding water to expand the slump, and fundamentally determine the quality of concrete!
