Which concrete grade is better for casting into plastic and silicone molds. Crack -safe is important! :)

[dorydirect]

High-strength concrete grade is more ideal than a low-strength grade when casting into molds such as plastic bowls and silicone molds? I am using 0.3mm gravel along with sea sand as aggregates.
Crack -safe is important!
Many thanks!

 

[MAR]

High-strength concrete grade is more ideal than a low-strength grade when casting into molds such as plastic bowls and silicone molds? I am using 0.3mm gravel along with sea sand as aggregates.
Crack -safe is important!
Many thanks!

Well your answer is good

 

[dorydirect]

Well your answer is good

Thanks for your replay Mohammed my friend, i used M10 Grade do you recommend something else?

 

[Dnyan Deshmukh]

Thanks for your replay Mohammed my friend, i used M10 Grade do you recommend something else?

May i know for what purpose you want to cast mold - is it for concrete cubes or cylinder for testing compressive strength or you want it for architectural purpose.

Are you using sea sand for structural concrete too?

Plastic molds are good for casting concrete cube sample and they are crack resistant too.

If you are talking about the formwork, i do not have any idea about it.

 

[dorydirect]

May i know for what purpose you want to cast mold - is it for concrete cubes or cylinder for testing compressive strength or you want it for architectural purpose.

Are you using sea sand for structural concrete too?

Plastic molds are good for casting concrete cube sample and they are crack resistant too.

If you are talking about the formwork, i do not have any idea about it.

Thanks for your replay!

I am casting concrete candle holders, the can go to about 1 cm so i am looking for a grade or a custom mix that will prevent cracks as much as possible in the future.
I am using sea sand but also have "regular" construction sand( dry), so i can use it if needed.

Regards,
Dor

 

[Dnyan Deshmukh]

Thanks for your replay!

I am casting concrete candle holders, the can go to about 1 cm so i am looking for a grade or a custom mix that will prevent cracks as much as possible in the future.
I am using sea sand but also have "regular" construction sand( dry), so i can use it if needed.

Regards,
Dor

Can you post the photo of mold for easy understanding.

 

[dorydirect]

Can you post the photo of mold for easy understanding.

Something like this bowl thickness of bowl inside bowl mold

 

[Dnyan Deshmukh]

You can use 100% Polyphenylene Ether (PPE) fibers 6 to 12 mm long for reducing / eliminating the cracking in concrete / mortar.

Cracking due to shrinkage mostly occurs during first 3 hours, taking extra care will eliminate cracks (re-trowelling once the concrete / mortar is set will also help in reduction in cracks at top surface)

Fibers will help in providing high resistance to cracking in its lifetime.

To make it more stronger you can also additional make a GI wire reinforcement mesh inside of it.

Do use sea sand after verifying it properties and effect on this type of concrete / mortar.

Use super plasticizers admixture in it at 0.5 to 1 % dosage by weight of cement to provide high workability at lower water cement ratio (using a less water and achieving the workability / flow of concrete will help in achieving high strength at lower cement content)

Hope this data will help you in your experiment.

you stated your can height is 1 CM = 10 mm - i would suggest you to use cement paste only to produce this kind of element ( i am very confuse about the dimension of this object).

Use of flyash or GGBS by partly replacing cement will make your product as green product.

You can also experiment with bacteria which seals the cracks on its own by reacting with water.
at below article you will get brief about it

Self Repairing Concrete - No Maintenance

Hello to All, I came across the new inventions which are going on in construction Industry. Creating a concrete which repairs itself. Concrete is porous material (porosity depends on mix design), so if not protected will start degrading over period of time. To protect the concrete we...

civil4m.com

You can also search on internet for detailed research papers (this may make your product non crackable for its whole life)

 

[dorydirect]

You can use 100% Polyphenylene Ether (PPE) fibers 6 to 12 mm long for reducing / eliminating the cracking in concrete / mortar.

Cracking due to shrinkage mostly occurs during first 3 hours, taking extra care will eliminate cracks (re-trowelling once the concrete / mortar is set will also help in reduction in cracks at top surface)

Fibers will help in providing high resistance to cracking in its lifetime.

To make it more stronger you can also additional make a GI wire reinforcement mesh inside of it.

Do use sea sand after verifying it properties and effect on this type of concrete / mortar.

Use super plasticizers admixture in it at 0.5 to 1 % dosage by weight of cement to provide high workability at lower water cement ratio (using a less water and achieving the workability / flow of concrete will help in achieving high strength at lower cement content)

Hope this data will help you in your experiment.

you stated your can height is 1 CM = 10 mm - i would suggest you to use cement paste only to produce this kind of element ( i am very confuse about the dimension of this object).

Use of flyash or GGBS by partly replacing cement will make your product as green product.

You can also experiment with bacteria which seals the cracks on its own by reacting with water.
at below article you will get brief about it

Self Repairing Concrete - No Maintenance

Hello to All, I came across the new inventions which are going on in construction Industry. Creating a concrete which repairs itself. Concrete is porous material (porosity depends on mix design), so if not protected will start degrading over period of time. To protect the concrete we...

civil4m.com

You can also search on internet for detailed research papers (this may make your product non crackable for its whole life)

Thanks a lot for this information my friend.

I tried to used fibers but it seems to really made the mix not workable. i will buy a superplastizer and try again with it, thanks

The casting of 10-20 mm is usually the thickness of the end concrete bowl that is coming out of the plastic mold.
i tried to do ratio of 1 cement 1 sand 2 with but it was too rocky...
any suggestion on a different mix ratio with aggragate(without it i find my casting easily breaks)

thanks!

If you happen to go to mars to bring that soil take me with you!


Thanks again,
Dor

 

[Dnyan Deshmukh]

What is the size of bowl diameter and height.

Are you using any kind of reinforcement in it like putting cage / mesh of MS or GI wire.

For doing casting like this when concrete is mixed, it should be stiff (almost no workability) then add admixture in it to gain workability which will make mix little plastic.

Put the mortar / concrete in mould and to make it compact use vibrating table, due to vibration it will get compacted completly.

You need to make trials with different combination to arrive at best.

Making flowable mix with water will always lead to low strength.

Less amount of water gives higher strength.

As i am not sure about what it is but imagining its not more than 100mm in dia and height.

You can try following for mix

By weight
Cement - 1 part
GGBS (if available) - 0.5 part
Sand - 2.5 part
Water - 20% to 30% of cement + ggbs
Admixture - as per requurement to make mix little plastic.

After mixing pour it in mould up to 1/3rd then do compact it on table vibrator or by giving any kind of vibration.

Indication of compaction - when no bouble comes from it and look like accumulation of liquid started on top ( record the time required for it so that you xan automate this process)

Then fill remaining mould in 2 parts with same process

Finish the top of it to desired level.

After 24 hours de-mould it and put it in water for atleast 7 days.

After 7 days it will be ready for use.

Main thing - keep water as low as possible in mix.

You can also visit to nearest precast concrete yard to understand how they do cast concrete and what workability they kept.

 

[dorydirect]

What is the size of bowl diameter and height.

Are you using any kind of reinforcement in it like putting cage / mesh of MS or GI wire.

For doing casting like this when concrete is mixed, it should be stiff (almost no workability) then add admixture in it to gain workability which will make mix little plastic.

Put the mortar / concrete in mould and to make it compact use vibrating table, due to vibration it will get compacted completly.

You need to make trials with different combination to arrive at best.

Making flowable mix with water will always lead to low strength.

Less amount of water gives higher strength.

As i am not sure about what it is but imagining its not more than 100mm in dia and height.

You can try following for mix

By weight
Cement - 1 part
GGBS (if available) - 0.5 part
Sand - 2.5 part
Water - 20% to 30% of cement + ggbs
Admixture - as per requurement to make mix little plastic.

After mixing pour it in mould up to 1/3rd then do compact it on table vibrator or by giving any kind of vibration.

Indication of compaction - when no bouble comes from it and look like accumulation of liquid started on top ( record the time required for it so that you xan automate this process)

Then fill remaining mould in 2 parts with same process

Finish the top of it to desired level.

After 24 hours de-mould it and put it in water for atleast 7 days.

After 7 days it will be ready for use.

Main thing - keep water as low as possible in mix.

You can also visit to nearest precast concrete yard to understand how they do cast concrete and what workability they kept.

Thanks for your in depth answer.
I dont know what GGBS i tried to look online but not sure where i can find it in israel and what they call it here
the mix you suggest has no aggragres, is this ok?

Thanks,
Dor

 

[Dnyan Deshmukh]

GGBS or GGBFS is a waste / bi-product from steel manufacturing industry, you can get more in details about it at below link

How GGBS used for replacing cement in concrete is Made inside Steel manufacturing Factory

How GGBS is Made inside Steel manufacturing Factory On our planet, Iron is not found in pure state, we call it as ore. Iron Ores are often oxidized and mixed with Silicates (sand). During manufacturing of steel these ores are heated above 1600 degree centigrade in the furnace, there are many...

civil4m.com

If it is not available at your place you can use flyash too.

If the mold is not bigger than 100mm in diamensions, using a cement sand mortar to cast it, wont make an issue (the strength of the cement is calculated by making a mortar cube only).

cement testing mortar proportion is 1:3
where 1 part is cement and 3 parts are sand.

You can safely use 1:3 proportion for casting your candle stand mould, provided you control water cement ration and mix is not made very plastic or flowable for casting by addition of water.