Network Rail traffic (i.e NR works trains)

[HOOVER29]

Leicestershire granite is probably the best there is. No coincidence that 3 off the busiest quarries ie Stud Farm, Mountsorell & Bardon are in the county & ship out to destinations a far away as Carlisle & south London

 

[DarloRich]

Leicestershire granite is probably the best there is. No coincidence that 3 off the busiest quarries ie Stud Farm, Mountsorell & Bardon are in the county & ship out to destinations a far away as Carlisle & south London

That isnt the sole or even main reason.

 

[Ken H]

No, you are confusing a lime mortar and Portland cement. Lime putty results from slaking calcined limestone and mixing it with sand. Portland cement (which sets under water) needs clay minerals in it as well as the lime fraction. Adding aggregate to either of these gives concrete. Different aggregates have different effects on the concrete, as my link explained.
Look at the wikipedia page that Ken H linked: it says

So if I get a bag of el-cheapo cement from B&Q, will it be Portland?

What if I get a load of readymix? I thought portland was expensive posh stuff.

Last time I had anything to do with concrete was on a building site in the late 1970's. I was chain man (engineers labourer) and I had to do slump tests (1) and make the cubes to go off to the lab for testing. This was structural concrete in a tower building.

Must have done something right, cos the building is still there, the old lloyds bank on the corner of park Row

There was also a lot of talk about how much vibrating was done. They worried about 'over vibrating'.

They also worried about the overnight temperature. They didnt want newly poured concrete to freeze.

but they let a 17 yr old kid do the test stuff, and do vibrating. different times....

Haven't had anything to do with concrete since 1978. not much call for slump tests in IT!

(1) Slump test. You fill a metal cone (pointed end to the top, but the point removed) with concrete and compact it with a rod, a fixed number of pokes. Then you remove the cone and measure the difference in the height of the cone and the height of the unsupported concrete. I assume it was measuring moisture content. Had to record the test in a book. If it wasnt in limits the batch was rejected and the newly poured concrete had to be removed - happened once!

 

[furnessvale]

Leicestershire granite is probably the best there is. No coincidence that 3 off the busiest quarries ie Stud Farm, Mountsorell & Bardon are in the county & ship out to destinations a far away as Carlisle & south London

Leicestershire "granite" is a strong stone but I believe it is not a true granite.

However, the strength to price ratio is sufficiently in its favour to enable it to be used as ballast for the vast quantities needed by NR.

A true granite such as Shap, is now just too expensive.

 

[furnessvale]

Surely not? Limestone is relatively weak compared to most igneous rock and quite a lot of metamorphic ones (which is why worktops are made of marble and not limestone.) I'm certain that concrete made with granite or similar aggregate will be stronger than one made with limestone, but at least the limestone version won't get this:
https://en.wikipedia.org/wiki/Alkali–silica_reaction which has done for a lot of concrete.
The actual mineral content of cement (after roasting and grinding then rehydration) is weird, but I just remember that Portland cement needs clay minerals in it, which is why some cement works on pure limestone or chalk have to import clay rocks of some sort!
p.s. it seems that the actual strength of the aggregate is less important than other factors: https://www.engr.psu.edu/ce/courses/ce584/concrete/library/materials/aggregate/aggregatesmain.htm says

Failure of concrete is more to do with a failure of the bond between the various components, Cement, sand and aggregate, rather than the actual aggregate failing eg shattering. Limestone is apparently better at maintaining this bond.

I say apparently because, although I used various concretes as a bridge engineer, I was no expert on the mixes and was happy to accept the specialists work when they designed a mix for a certain strength. Of course, we tested the mixes before use, even visiting the batching plants to make test cubes etc before allowing installation on site.

 

[Ken H]

Failure of concrete is more to do with a failure of the bond between the various components, Cement, sand and aggregate, rather than the actual aggregate failing eg shattering. Limestone is apparently better at maintaining this bond.

I say apparently because, although I used various concretes as a bridge engineer, I was no expert on the mixes and was happy to accept the specialists work when they designed a mix for a certain strength. Of course, we tested the mixes before use, even visiting the batching plants to make test cubes etc before allowing installation on site.

One thing puzzled me. You make your test cubes, and leave overnight. then you break the mould and bung in a tank of water, i think that was kept at a constant temperature with an immersion heater. Then they went away for testing.
I was told it takes 14 days for concrete to cure properly. until then its not at final strength.
So they test the cubes at 14 days.
One fails. What then? because there could well be more of the structure built upon the dodgy concrete. I think we poured more concrete every day. The shuttering came off the morning after the pour and hessian was draped over the exposed concrete and wetted. but steel fixers and chippies moved in quickly for the next section. I think a new pour joins better to the old pour if the old pour isnt too old. They did use retardant and scabbling to make the different pours mate.

This is a building totally made of concrete cast in situ, not made out of factory manufactured sections.

Again, this is from a long memory

 

[AndrewE]

So if I get a bag of el-cheapo cement from B&Q, will it be Portland?

What if I get a load of readymix? I thought portland was expensive posh stuff.

I think virtually everything now called "cement" is Portland cement, in that it will set under water. Apart from "Low-CO2 cement" which I think is ground blast furnace slag, and like Pozzolan, sets when ground and then wetted. You have to pay a premium to get lime suitable for making mortar and you pay even more to find a brickie who will work with it.

 

[furnessvale]

One thing puzzled me. You make your test cubes, and leave overnight. then you break the mould and bung in a tank of water, i think that was kept at a constant temperature with an immersion heater. Then they went away for testing.
I was told it takes 14 days for concrete to cure properly. until then its not at final strength.
So they test the cubes at 14 days.
One fails. What then? because there could well be more of the structure built upon the dodgy concrete. I think we poured more concrete every day. The shuttering came off the morning after the pour and hessian was draped over the exposed concrete and wetted. but steel fixers and chippies moved in quickly for the next section. I think a new pour joins better to the old pour if the old pour isnt too old. They did use retardant and scabbling to make the different pours mate.

This is a building totally made of concrete cast in situ, not made out of factory manufactured sections.

Again, this is from a long memory

Me too for the long memory! I am sure we tested cubes at 7 days and 14. The whole process was more an exercise in deterrent for a contractor using dodgy materials. We never had a failure in the 12 years I was involved that I can recall but that is why cubes were cast in 3s to allow for dodgy tests. 2 out of 3 was a pass. Mind you, a series of 2 out of 3 would have resulted in a stern word to the contractor had it occurred..

 

[kilonewton]

In my experience, the concrete mixes usually achieve strength well in excess of the specification for that mix. I have worked on a project where we had one load tested which didn't achieve the 7 day strength, but did achieve the 28 day strength. But it was one load out of 10 in that particular pour, and of 100s of that particular mix on the project. Put it down to a rogue load.
Client tried to make a song & dance about it, but that was for commercial reasons, as sometimes quality gets imbroiled in when it shouldn’t.

 

[w1bbl3]

So if I get a bag of el-cheapo cement from B&Q, will it be Portland?

Retail bags from B&Q or builders merchants are actually really expensive vs bulk cement for commercial use, but no it won't be "pure" portland. In the wonderful world of cements old fashioned portland cement is CEM I, modern ordinary portland cements are CEM II which depending on the letter afterwards will contain between 5% and 45% of other stuff. Typically Limestone, PFA or GGBS.

What if I get a load of readymix? I thought portland was expensive posh stuff.

Depends on the specified usage, time of year and location but something like the GEN or RC/C mixes will be CEM II or CEM III based so anything from 95% to 20% pure, the strength will be whatever is specified just way the concrete gains strength will different with the blastfurnace slag mixes (CEM III) gaining strength for more slowly but ultimately likely to be far stronger. In mid summer you wouldn't for example want to use a CEM I mix as it's likely suffer from excessive plastic shrinkage, equally in mid winter CEM II or CEM III with high cement replacement content are likely to suffer from frost damage.

Ignore pozzolan mixes cause they are very very rare in this country at least.

One thing puzzled me. You make your test cubes, and leave overnight. then you break the mould and bung in a tank of water, i think that was kept at a constant temperature with an immersion heater. Then they went away for testing.
I was told it takes 14 days for concrete to cure properly. until then its not at final strength.
So they test the cubes at 14 days.
One fails. What then? because there could well be more of the structure built upon the dodgy concrete. I think we poured more concrete every day. The shuttering came off the morning after the pour and hessian was draped over the exposed concrete and wetted. but steel fixers and chippies moved in quickly for the next section. I think a new pour joins better to the old pour if the old pour isnt too old. They did use retardant and scabbling to make the different pours mate.

The warranty age for ready mix is 28 days so you wouldn't worry that much if target strength hasn't been achieved at 14 days, unless your doing something like post tensioning where the concrete needs to gain strength in very predicable way. If at 28 days it's not reached strength then your first port of call would be to the batching plant advising the mix supplied is potentially defective and you would hopefully still have spare cubes that could be crushed at 56 days which is point where the concrete will stop gaining strength. Beyond that and you'd ask the engineers to check the design to see if it still works based on the actual achieved strength and if not look at designing additional strengthening. Only if it doesn't work and strengthening is not possible would you then demolish back to the last known good concrete, the contractor will at this point be discussing restitution costs with the concrete supplier and their insurer.