Vibrationspåverkan på färsk betongs hållfasthet : En studie av vibrationens inverkan på färsk betong och dess effekt på hållfastheten i det härdade stadiet.

Sammanfattning: Concrete is a durable and long-lasting material that plays an important role in many areas of application such as infrastructure and housing. In order for the fresh concrete to have good stability and meet the desired strength and durability requirements, it needs to be well processed so that it fills the form and encloses the reinforcement well. Vibration is used to achieve good workability, as air voids and cavities can degrade the properties of the concrete. Although vibration input is an important part of concrete processing, too much vibration can increase the risk of major separations such as stone separation, mortar separation and water separation. Therefore, it is important not to overdo the vibration time, but to use only the time necessary to achieve a concrete that meets all requirements. In this way, potentialproblems with separations can be avoided while ensuring that the concrete is correctly processed. The purpose of this thesis is to study the effect of vibration on the strength of fresh concrete. The thesis has been conducted through literature studies, laboratory experiments on vibration effects on fresh concrete and interview studies to answer the study's questions. The effect of vibration has been investigated experimentally using different concrete mixtures by vibrating the concrete for different time intervals using different techniques. The aim of the study is to understand the effect of vibration on fresh concrete based on different parameters such as varying air content and time to achieve good concrete strength. The goal is also to clarify which factors can affect the vibration inflow during concrete pouring at a work site. The results indicate that concrete with a loose consistency is more sensitive to vibrations than concrete with a denser consistency. The results from the compressive strength tests revealed that concrete mixture 1 exhibited good strength compared to concrete mixture 2. This observation is clearly evident in figures 16 and 17. The reason for this is considered to be that concrete with a loose consistency is more prone to segregation, leading to lower compressive strength. Furthermore, the study shows that a lower air content in the concrete resulted in higher strength compared to concrete with higher air content and the same aggregate material. Regarding the impact of vibration, the study presented an uncertain result due to the limited number of test cubes, which made it difficult to draw clear conclusions. Therefore, future studies with a larger number of specimens are suggested to further investigate the impact of vibration on the strength development of concrete. Regarding the factors affecting the vibration intake of concrete workers at the workplace, it was found that it mainly depends on the worker's experience in vibration work.