Baseljets use of portland cement

[michael]

I noticed in one of the Victoriana programs last night that Baseljet’s brickwork sewers were constructed using Portland cement rather than the more common lime of the day and apparently they are as good now as when they were built.

I just wanted to know why in this case the Portland cement hasn’t trapped water, spalled the bricks and damaged the structure as we commonly here about on this site?

 

[MdB]

I didn't see the program but trapping water is the whole point for sewers. I would have thought also that frost is rather unlikely in sewers so damp bricks are unlikely to be damaged through spalling.

(But then again, I am a complete non expert on this so the above is just my thoughts)

 

[Gareth Hughes]

Bazalgette was building a sewer, not a house - Hard bricks as well as hard mortar, no intention of making a "breathing" structure, and an absence of frost.

 

[michael]

These sewers are large brickwork arched tunnels with the sewer running like a river in the bottom third/half of the tunnel. I think it would have been and probably still is quite rare for the tunnels to be completely full to the roof with water except in extreme circumstances. The atmosphere however must be very damp. I would have thought that the main threat is water ingress from the ground above not from the sewer itself..

Thanks for your thoughts. I guess frost is the key word here. Maybe Portland cement and old bricks might work adequately well in warmer, drier climates than ours where frost is not an issue.

However, you do mention ‘hard bricks’? Were the firing techniques available then to create bricks harder than Portland cement mortar? I’ve always understood that the mortar should always be weaker than the brick.

Obviously no flexibility was required in the sewage structures either which surprises me with the forces of surrounding ground movement which I would have thought could crack bricks if too much resistance is put up.

I wonder why he didn’t use hydraulic lime. Didn’t they once build harbour walls with that stuff?

 

[chuckey]

Portland cement hardens much quicker then lime, so the work could progress at more or less 10X the speed.
Frank

 

[Jon Maine]

These sewers are large brickwork arched tunnels with the sewer running like a river in the bottom third/half of the tunnel. I think it would have been and probably still is quite rare for the tunnels to be completely full to the roof with water except in extreme circumstances. The atmosphere however must be very damp. I would have thought that the main threat is water ingress from the ground above not from the sewer itself..

Thanks for your thoughts. I guess frost is the key word here. Maybe Portland cement and old bricks might work adequately well in warmer, drier climates than ours where frost is not an issue.

However, you do mention ‘hard bricks’? Were the firing techniques available then to create bricks harder than Portland cement mortar? I’ve always understood that the mortar should always be weaker than the brick.

Obviously no flexibility was required in the sewage structures either which surprises me with the forces of surrounding ground movement which I would have thought could crack bricks if too much resistance is put up.

I wonder why he didn’t use hydraulic lime. Didn’t they once build harbour walls with that stuff?

Bricks similar to these http://www.ketley-brick.co.uk/about-ketley-bricks.htm would have been used. hard cement would indeed not pose a problem with strong hard bricks like this, albeit an older version of them.

Of course don't go thinking cement is new 1900 years ago it was used to create the dome on top of the Pantheon which holds the record for the worlds largest un-reinforced concrete dome even today.

For sewers hard bricks and hard mortar in solid ground are ideal.

 

[Jon Maine]

Portland cement hardens much quicker then lime, so the work could progress at more or less 10X the speed.
Frank

Agreed, very likely to be at least that much quicker than lime, I seem to remember that Bazalgette had a well oiled machine going, putting these in at a speed we would be challenged to match in todays technological era ( probably due to health and safety constraints now).

Although the use of hydraulic or a pozzolan could have sped up the use of lime a bit.

I suspect a combination of rapid set and early set strength were why he used it.

 

[Gervase]

OPC was being made in some quantities on Tyneside and on the banks of the Thames by the 1840s, and the first major project which saw its use was the tunnel under the Thames built by Brunel (That's the dad of IK Brunel) that is still used today by the London Underground.
It was expensive, and used mainly for important civil engineering projects that require great strength and a very fast set. Made from chalk and clay fired at a higher temperature than lime, it was pretty similar to the OPC in use today.
Even when it became cheaper in the later 19th century it wasn't used for much other than civil engineering work and for pouring large slabs for foundations. Builders were more than happy to stick with lime (though the lime with which the great sprawl of British cities was built was not quite the same as your standard hydrated or hydraulic available today. It was the equivalent of an NHL1 lime; very slightly hydraulic, but with most of the attributes of a hydrated lime. Singleton Birch now makes an NHL1 lime for those who want to repair late Victorian brickwork). What brought OPC into prominence was the Great War; both in terms of the loss of skills and because OPC production had been geared up astronomically, and a market had to be found for it.

 

[Penners]

The only contribution I feel qualified to make to this learned discussion is this. If Bazalgette didn't make the sewers out of breathable materials, I, for one, am very grateful.

 

[Jon Maine]

The only contribution I feel qualified to make to this learned discussion is this. If Bazalgette didn't make the sewers out of breathable materials, I, for one, am very grateful.

Breathable = miasma UGHHHHHH!! or so many thouht then 8)