synthetic fibre suggestions

[david656]

hi
we casted cubes beams and cylinders using 1.75% 2.0% and 2.25%polypropylene fibers by weight of cement and are going to perform basic destructive tests'
any suggestions on specific results to look for?

 

[civilperson]

Should also cast control cubes with equal cement and no fiber. Compare compressive strength.

 

[Prepakt1]

Try nylon fibres also, they have a much higher tensile strength

 

[Ron]

Look for variations in fiber distribution. 2% poly fiber is a lot! It will only enhance some properties of the concrete...it won't replace conventional reinforcement.

 

[Ussuri]

A lecturer at my University told us how he used pine needles as a matrix in concrete.

 

[concretemasonry]

Keep in mind that the amount of fibers will affect the apparent slump from a traditional slump test. Specifications may have to be altered.

The idea of casting companion samples without fibers is great.

Fibers, especially in high percentages, can affect the amount of water for proper placement and finishing. As usual mixing time (excessive?) and even distribution will be a factor.

The trick will be to get correalation of the lab tests for strengths with field performance.

 

[david656]

thanks for the previous replies..

well we have casted a pair of beams , a cylinder and 3 cubes without the fibre also.. so do you think there will be any improvement in compressive strength(wit & without the fibre)

all the casted members have nominal reinforcement in them.

will the first cracking time differ??
and what other tests can we perform??

 

[concretemasonry]

Due to the shapes and probable aspect ratios of the samples you probably will not be able to relate the results for the different shape samples if you are just applying a compressive load in some way.

A set or average of two samples will not provide a high degree of comfidence. If you cast additional samples, you will also have a problem with a curing factor and assurance that the same materials were used.

What do you mean by nominal reinforecement? Is this in addition to the fibers? If you are casting reinforcement in the sample, you will not be measuring the properties of the concrete itself. It was always fun to add a rebar to a cylinder, but the results were worthless.

Beams are normally tested in flexure to measure tensile strength or the effects of the reinforcement amount and placement. Depending on the load application and dimensions your failure could be measuring different properties.

Cylinders are normally twice as high as the diameter and compression testing usually results in a shear failure.

Cubes, having idential height and width, will give you results closer to pure compression with less measurable effect of the fibers.

Dick

 

[david656]

thanks dick,

well we used nominal reinforcement in form of #8mm rebars in the beams only...
will the fibers help in increasing the compressive strrength of the concrete(the 28days submerged strength)....

 

[civilperson]

The fibers will have little or no effect on flexural or compressive strength of the specimens.

 

[i387]

Try a mix that has no aggregate, but a very high fiber content (50% cement / 50% fiber by volume). It's an impractical mix design because of cost. It is however VERY strong.

Has anyone else tried this? What have your results been?

 

[concretemasonry]

It has been done with shredded newspapers.

Fireproof, very resistant to bullets and is strong.

Like all of these type of products, the mixing type and time are the most critical item. A lot of little balls of fibers do not add to the strength.

Dick