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  1. #1
    Senior Member Rank = Mature Champion Ant62's Avatar
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    Concrete base mix

    Im just sat here perusing through endless info about concrete etc for the base and the i fo seems to be basically the same...
    So what i was wondering.

    The pond bottom a C25 mix or a C35 mix is there and preference..



  2. #2
    Moderator Rank = Supreme Champion Feline's Avatar
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    I used C35. It's going to have to withstand many tonnes of weight and possibly torsional forces on the slab, so best not to take any chances IMO.

    I didn't go for any fibres in mine as the consensus seemed to be that they would help avoid surface cracking but not make the base structurally any stronger. If you're going to insulate and glass it then the surface itself is not very important.

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  4. #3
    Senior Member Rank = Mature Champion Ant62's Avatar
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    Aye there is some weight for the base to hold thats for sure.....
    It is something that if it requires a few more ££££ spending upon it and the rest has to be put on hold for a shirt period then its worth it imho.

    Its pays to do it correctly the first time.....
    Last edited by Ant62; 26-02-2017 at 11:33 AM.

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    Senior Member Rank = Grand Champion Doghouse Riley's Avatar
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    This might not apply, but with a deep liner pool all you need for the base is a screed of two or three inches of fine concrete mix.
    "I know" as mine has that and is now thirty years old.
    "The information's out there,
    You only have to let it in." (Jesse Stone)

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    Extreme Koi Member Rank = Rokusai TAC's Avatar
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    Much depends on the ground it's sitting on as to what is best.

    Mine was sand and ballast so no need to over board also 50mm of insulation was used on mine, my mix was knock up in a mixer with fibres.

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  10. #6
    Senior Member Rank = Mature Champion Ant62's Avatar
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    Fibres or not....
    Ive read many posts on various searches about concrete bases and some say add fibres and many say dont bother...
    So which is it yes or no......

  11. #7
    Extreme Koi Member Rank = Rokusai AlanF's Avatar
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    No.
    As Feline said earlier
    they would help avoid surface cracking but not make the base structurally any stronger
    The biggest factor is the base you are laying it on. If you think it is unstable then metal re-enforcing mesh must be used, two layers in extreme conditions.

  12. #8
    Extreme Koi Member Rank = Rokusai TAC's Avatar
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    The concept of using fibers as reinforcement is not new. Fibers have been used as reinforcement since ancient times. Historically, horsehair was used in mortar and straw in mudbricks. In the 1900s, asbestos fibers were used in concrete. In the 1950s, the concept of composite materials came into being and fiber-reinforced concrete was one of the topics of interest. Once the health risks associated with asbestos were discovered, there was a need to find a replacement for the substance in concrete and other building materials. By the 1960s, steel, glass (GFRC), and synthetic fibers such as polypropylene fibers were used in concrete. Research into new fiber-reinforced concretes continues today

    Fibers are usually used in concrete to control cracking due to plastic shrinkage and to drying shrinkage. They also reduce the permeability of concrete and thus reduce bleeding of water. Some types of fibers produce greater impact–, abrasion–, and shatter–resistance in concrete. Generally fibers do not increase the flexural strength of concrete, and so cannot replace moment–resisting or structural steel reinforcement. Indeed, some fibers actually reduce the strength of concrete.

    The amount of fibers added to a concrete mix is expressed as a percentage of the total volume of the composite (concrete and fibers), termed "volume fraction" (Vf). Vf typically ranges from 0.1 to 3%. The aspect ratio (l/d) is calculated by dividing fiber length (l) by its diameter (d). Fibers with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio. If the fiber's modulus of elasticity is higher than the matrix (concrete or mortar binder), they help to carry the load by increasing the tensile strength of the material. Increasing the aspect ratio of the fiber usually segments the flexural strength and toughness of the matrix. However, fibers that are too long tend to "ball" in the mix and create workability problems.

    Some recent researchindicated that using fibers in concrete has limited effect on the impact resistance of the materials.This finding is very important since traditionally, people think that ductility increases when concrete is reinforced with fibers. The results also indicated that the use of micro fibers offers better impact resistance to that of longer fibers.
    The High Speed 1 tunnel linings incorporated concrete containing 1 kg/m³ of polypropylene fibers, of diameter 18 & 32 μm.

 

 

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