A quick update
Tower Crane
The good news is that the tower crane got successfully installed on Saturday and Sunday, the construction went very smoothly and though long days the Red and White livery of the crane in John Holland stands out against all the yellow cranes across Perth.
What this does mask is a drama with the strength of the concrete which led to lot of running around. The pile cap design required a strength of 30 Mpa, however 3 and 6 day test cylinder strengths were 16 Mpa and 23 Mpa accordingly. This result of the 6 day test was delivered at 12pm on the Friday. This resulted in the requirement for some urgent core samples to be taken from the pile cap. Fortunately the lab stayed open for us and the results came in at an average of 30.5Mpa….phew…..at this point half of the site had been shut and a 250tonne crane was on site. If the installation had been delayed it would have been costly!!
Stair Core 3
The reason for the ridiculous number of piles in Stair Core 3 has not been driven by the loads but by an error in design (a problem made worse by construction being so close to completed design). I can’t write too much as this is the subject of an ongoing investigation and litigation but it seems there were number of errors in the design calcs which under designed the initial piles. This resulted in the extra piles which you can see. Stair core 4 carries a similar amount of load but you will see has much fewer piles.
Of note – a frequent cry from sub contractors is the level of overdesign and redundancy being specified in the design, Often I will hear the sub contractors saying they have not seen such a large pile cap or pile with so much reinforcement. A lot of this is driven by the requirement to be the last building standing in the case of a natural disaster and the seismic loading!!
PT/TMJs
The post tender interviews went well – I was assisted by the works package manager in the end which was helpful as both our brains were fried after repeating the same meeting 3 times. The major contentious issue is the supply and install of Temporary Movement Joint shear connectors. All 3 PT sub contractors complained bitterly that they were not the right sub contractor to install these items. (The value of these items is now about 50% of the overall contract value)
The reason why these have been included is that they were never included in the superstructure works package scope and John Holland are trying to do a regain by slipping this $1,000,000 extra into the PT works Package (another ball dropping moment from the procurement team).
Concreting in the heat
Being in a hot climate and seeing as where the Corps is building at the moment I took the opportunity to attend a lecture by the Institute of Concrete yesterday on “Beating the Heat –Concreting in extreme temperatures.”
This may well ensure that I spend the rest of my career in the wilds of Scotland or Norway or some such cold place but I learnt loads. From simple wins like the best way to cool the concrete is to cool the aggregate by spraying with water and shading the aggregate prior to use. To the sci fi method of using liquid nitrogen (maybe beyond the scope of the Corps). I also now have a better understanding of plastic shrinkage (from bleed rates, evaporation nomographs to use of Aliphatic Alcohol) and again the simple to very advanced ways of mitigating this (anyone heard of internal curing before?)
Holdfast Training Services Trial Blog 
Hi Steve, Rob Ridley’s thesis was on early age thermal cracking prediction and control which covered predicting the effects heat would have on large concrete pours (albeit in a marine environment). Interestingly, one of his conclusions was that Oz doesn’t have the codes to do this particularly well and he had to rely on extrapolating from UK codes to work out what was going to happen.
Ah yes, Internal curing 🙂 he says sagely. Presumably using prewetted light weight aggregate (potential cost uplift…) needs careful design and QA to ensure w/c ratio and consistence works out but very effective with PFA and other cement replacement binders. DId they discuss addition of water as ice or slush? and need to control overnight temperature variations and rate of cooling? Any good material comming out of it for me???
PT/TMJ Why isn’t this simply being introduced as an extra to the structural package. It would probably cost as much ‘cos you’re over a barrel but at least it wouldn’t burden the piling contractors with an aspect that they will not be happy with. They will charge throught the nose for it becasue to them it represents abnormal risk?
Oh and in passing, the issue of concrete test results has just passed through this office re Carillion stuff on site – it’s about understanding averages and material saftey factors and not looking at individual numbers… BS EN206-1:2000 Section 8 and Annex B. Glad you’re crane worked out.
Steve, I’ve been involved in discussions about internal curing here as a means to reducing thermal cracking. We are using a 50MPa mix (cylinders not cubes) which is hitting 50Mpa at 3 days (consistently). 28 day strength is hitting 100+MPa. This is cooking off so fast that it goes from tacky to surface dry in an instant and the cracks also appear immediately if you miss the change point and don’t wet it down for curing.
Roy,
Are you targetting 100MPa or 50 MPa at the 28 day point? how is the internal curing being specified?
Richard, 50MPa is the target. There is no internal curing but it was something I suggested to reduce the possibility of thermal cracking. Unfortunately we are tied to using concrete that has been approved by Bechtel and they shuddered at the thought of internal curing. Bechtel tend to be very straight down the line and are quick to raise non-conformance reports at the drop of a hat. It is a dead end unfortunately on the MOF.