Making tiny bubbles in very alcaline Portland cement ?

[Externet]

Hi.   Your headache is back.

What chemical compound can be mixed with Portland cement, that when gets wet will generate effervescence of either nitrogen, oxygen, hydrogen, air, carbon dioxide, whatever other small enough gas bubbles, staying in suspension a while until mix sets/cures creating sort of pumice or aerated concrete ?

[KJW]

This actually seems like a bad idea to me.

 

[LaurieAG]

4 hours ago, Externet said:

Hi.   Your headache is back.

What chemical compound can be mixed with Portland cement, that when gets wet will generate effervescence of either nitrogen, oxygen, hydrogen, air, carbon dioxide, whatever other small enough gas bubbles, staying in suspension a while until mix sets/cures creating sort of pumice or aerated concrete ?

The process was first developed in the mid 1020's.

https://en.wikipedia.org/wiki/Autoclaved_aerated_concrete#Manufacturing

Quote

When AAC is mixed and cast in forms, aluminium powder reacts with calcium hydroxide and water to form hydrogen. The hydrogen gas foams and doubles the volume of the raw mix creating gas bubbles up to 3 millimetres (1⁄8 in) in diameter—it has been described as having bubbles inside like "a chocolate Aero bar".[24] At the end of the foaming process, the hydrogen escapes into the atmosphere and is replaced by air, leaving a product as light as 20% of the weight of conventional concrete.

 

[chenbeier]

Quote

The process was first developed in the mid 1020's.

What is 1020's. Do you mean 1920's, do you.

[naitche]

Look up Aircrete

[studiot]

3 hours ago, Externet said:

Hi.   Your headache is back.

What chemical compound can be mixed with Portland cement, that when gets wet will generate effervescence of either nitrogen, oxygen, hydrogen, air, carbon dioxide, whatever other small enough gas bubbles, staying in suspension a while until mix sets/cures creating sort of pumice or aerated concrete ?

Forst of all what do you mean by concrete, ie what is your application ?

I ask this because american practice is to use the word cement for what we call concrete on this side of the atlantic.

I am replying using the european terminology.

Concrete contains inert filler material called aggrgate and binding materials, which are often portland cement as you say.

OK so why do you want aerated concrete ?

There are three basic reasons for doing this. All use air entrainment (air is the entrained gas, the link gives many types of foaming agents, mostly fancy organic compounds)

https://www.sciencedirect.com/topics/engineering/air-entraining-agent

 

Firstly to produce lightweight concrete for structural reasons.
 

Since this concrete is also structural,  lightweight aggregate is used along with normal grading. You can even go as far as polystyrene aggregate replacement in suitable parts of the structure. Polystyrene beads are entrained in the mix.

 

Secondly for frost resistance on non reinforced mass concrete.

Here larger sized aggregate is often used (40mm and down or even bigger as opposed to 20mm or 10mm and down) as this is cheaper. These would be stones of normal weight.

Medium air entrainment would be added at mixing
We call this 'bus bay concrete' but I can't see you needing any where you are.

Finally air entrainment is used in the concrete to make lightweight thermally insulating building blocks
All these blocks are again lightweight and there are various grades.
However since the prime purpose of such blocks is insulation rather than structural a variety of pulverised aggrgegates are used, depending upon what is available in the area of manufacture.
These pulverised aggregates are often already partly entrained so need less air entrainment with the binder.

 

Does this help?

 

 

[TheVat]

14 hours ago, Externet said:

Hi.   Your headache is back.

What chemical compound can be mixed with Portland cement, that when gets wet will generate effervescence of either nitrogen, oxygen, hydrogen, air, carbon dioxide, whatever other small enough gas bubbles, staying in suspension a while until mix sets/cures creating sort of pumice or aerated concrete ?

Extra lime.  Makes stucco. Regular concrete is made of cement, water and sand. Stucco is made of these ingredients as well, plus lime. One big difference between the two home exteriors is that when dry, stucco is breathable - it has tiny pores that allow water to evaporate from behind it so that moisture doesn't build up and cause rot.  (and yes, Americans do distinguish between cement and concrete, as Euros do.  As does everyone, I had thought, since they are two different materials)  

[exchemist]

10 hours ago, LaurieAG said:

The process was first developed in the mid 1020's.

https://en.wikipedia.org/wiki/Autoclaved_aerated_concrete#Manufacturing

 

Yup, and this stuff has subsequently proved to be a disaster, as it fails after a few decades, often without warning.

[Externet]

Thanks, gentlemen.

LaurieAG : is the powder aluminium Al and nothing else ?  No oxides, no sulphates, no Al compounds but just metallic Al ?    OK, that is then a viable good clue and answer 👍, as already in proven manufacturing processes of air-entrapped concrete blocks.

 

Studiot :  Concrete as = Portland cement + sand + crushed stone + water with incorporation or not of fibers.  For manufacturing of building materials as blocks (not to pour structural columns nor beams, but walls) without the addition of already foamed liquids after wetting but with a dry compound added to the dry mix.

In my ignorant terms, imagine sodium bicarbonate in the mix that would be later hydrated and create a foamy mix then. (But I believe such CaCO3 does not work in alkaline)

Expanded polyestyrene beads nor fancy organic compounds addition not convenient to consider as the aim is more artisan aimed process with some improvement of thermal insulation characteristics and with less weight.

In other not-artisanal approach, perhas with interlocking convenience to use less mortar or glue, manageable by robotic mechanical placement. 🤔  Yes, you always help good.

 

[TheVat]

38 minutes ago, exchemist said:

Yup, and this stuff has subsequently proved to be a disaster, as it fails after a few decades, often without warning.

I would guess water infiltration, in improperly sealed blocks or where a sealant has been breached, would be a serious problem in rainy/humid climes.  Here in the States, it also would not meet R-value requirements in the UBC unless the walls were very thick.  You'd probably have to add an interior layer of insulation, with an interior cavity wall.  Seems like a lot of trouble.

[toucana]

2 hours ago, TheVat said:

I would guess water infiltration, in improperly sealed blocks or where a sealant has been breached, would be a serious problem in rainy/humid climes.  Here in the States, it also would not meet R-value requirements in the UBC unless the walls were very thick.  You'd probably have to add an interior layer of insulation, with an interior cavity wall.  Seems like a lot of trouble.

The widespread use of RAAC (Reinforced Autoclaved Aerated Concrete) in public buildings - especially in school buildings - became the subject of a major political scandal in the UK in May 2023, where over 100 hundred schools had to be closed following investigations after a structural beam collapse brought down a roof at a primary school in Gravesend Kent in 2018.

https://www.independent.co.uk/news/uk/home-news/school-closures-raac-concrete-closed-b2403208.html

The structural risks of using RAAC which first became popular as a cheap building material in the UK during the 1950s had begun to be flagged up from 1995 onwards by professional engineers who described RAAC as a “ticking time bomb” in British schools.

Quote

 

RAAC has been shown to have limited structural reinforcement bar (rebar) integrity in 40 to 50 year-old RAAC roof panels, which began to be observed in the 1990s.The material is liable to fail without visible deterioration or warning. The material is not the root cause, rather inadequate roof maintenance, which permits water infiltration, and decisions by building owners as to repair or the replacement of existing roofs, which is a part of cost-benefit analysis.

https://en.wikipedia.org/wiki/2023_United_Kingdom_reinforced_autoclaved_aerated_concrete_crisis

 

The crisis deepened in May 2023 when the UK government announced that 7 hospitals in England which were largely constructed with RAAC were not safe to operate beyond 2030 and would need to be rebuilt. Large numbers of RAAC compromised buildings were subsequently identified across the country, including some on university campuses, public theatres, and even at the Palace of Westminster.

[LaurieAG]

14 hours ago, exchemist said:

Yup, and this stuff has subsequently proved to be a disaster, as it fails after a few decades, often without warning.

Sorry, 1920's. I have worked in a materials testing laboratory and sub standard products which have been manufactured with poor materials and poor procedures usually fail when tested. On the other hand properly quality assured products will last until their design life says so unless they are used in sub standard construction methods.

[studiot]

13 hours ago, Externet said:

.

In other not-artisanal approach, perhas with interlocking convenience to use less mortar or glue, manageable by robotic mechanical placement. 🤔  Yes, you always help good.

 

 

Not sure whether you are looking at the blocks or the mortar for your foamed concrete ?

As @LaurieAG says getting the materials science of both of these components right is very important to the performance of the building.

Further there are big differences in the requirements for the blocks and the mortar (which does not function as a glue for the blocks, concrary to popular belief).

Cowboy builders sometimes add ordinary wahing up liquid to mortar as a cheap easy to obtain alternative to the proper plasticiser.
this works OK for the blocklaying time but is deleterious to the mortar in the long term.

 

14 hours ago, TheVat said:

Extra lime.  Makes stucco. Regular concrete is made of cement, water and sand. Stucco is made of these ingredients as well, plus lime. One big difference between the two home exteriors is that when dry, stucco is breathable - it has tiny pores that allow water to evaporate from behind it so that moisture doesn't build up and cause rot.  (and yes, Americans do distinguish between cement and concrete, as Euros do.  As does everyone, I had thought, since they are two different materials)  

 

Yeah Liverpool Catherdral is a famous example of failure to observe proper masonry practice.