We are carrying out work to restructure a building. My question is how I can ensure that the cast concrete has filled the hollow part under existing structural elements that the project does not allow us to damage.
Hello: It seems that you have an interesting problem. For my answer to your problem, I hope to have interpreted it correctly: I understand that in the restructuring work that you mention in your mail, it requires you to paste some spaces that are under structural elements that the project requires do not want to affect or hurt. If this is the case, you may find the following recommendations useful:
In order to carry out the emptying of the concrete under a particular structural element, I want to think that under said structural element there is a recess to be filled. If this is the case, a space through which the fresh concrete will be discharged must exist or be constructed. The initial problem is then to allow one or more points to exit the air from the gap as the concrete enters the structural element, and in turn this will depend on the lower uniformity of said structural element. The more uneven the lower face is, the greater the chance of air being trapped, this problem is generally solved by small holes, which are placed on the higher levels of the lower face.
Another problem that occurs in these cases is the placement of fresh concrete itself, which is why it is necessary to use additives. As already known, there are self-leveling types additives on the market, which allow the concrete surface to remain at the same level during casting as it is introduced under the existing structure. It may be necessary to take into account an additive to obtain a uniformly fluid (super solidification) concrete mixture, in order to fill all the wells perfectly, as well as self-compacting since it cannot be easily vibrated.
In some cases it may be useful for the exterior level of the cast concrete to be slightly higher than the fill gap in order to ensure better contact between existing and new concrete. It should not be forgotten that the concrete used should not have a retraction that allows the formation of voids in the contact area.
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My final recommendation, is that for this type of problem, it is best to have the technical support and advice of a good company manufacturer of additives and reinforcements for concrete, and / or a specialist engineer, if you are not expert In that area.