Holdfast Training Services Trial Blog

The last 2 weeks has seen the stage 1 backfill at Dickson Rd Abutment A completed and I can finally get the subcontractor back in this week to erect the scaffold to then start steel fixing and forming the wingwalls. I estimate we have lost nearly 4 weeks from this delay but having spoken to the FRP subcontractor supervisor we are both confident of gaining at least 2 weeks back on the programme especially as summer seems to have arrived half way through winter!?

To be honest this delay has been useful as I’ve been busy with other work. The defects work on the three other bridges in my section are close to completion with minor  outstanding work like handrails, anti-grafitti guard and underbridge drainage close to completion. The conduit issue at Scalabrini has been shelved at the moment as I have also taken over from another engineer who left last week. I now have responsibility for all the bridge works outside of the two stations which includeds a total of 9 bridges and 18 retaining walls. The majority of work is of course complete but there are a number of defects/issues to close out and some minor work to complete.

I have also been given a HV/LV substation to complete which I have been focusing on last week. This includes padmounts, conduit runs and 6 pits which are situated on the western side of a high pressure gas main. This gas main has been a sticking point for many months and has been the cause of delay of installing rail track due to the client having not submitted the appropriate notice for a concrete protection slab to be constructed. The gas main is highly sensitive and comes with a great deal of red tape but the appropriate clearance has now been granted so work can commence. This means we need to have the substation area complete by 9 Sept when work is scheduled to begin. We have managed to pour the padmounts easily enough and have poured the base of one of the pits and I hope to pour the walls and the base of another pit by the end of the week. An issue I realised on Sat when going through the drawings with a quiet few minutes was a small note that said the concrete for the pit must contain a Xypex waterproofing additive. The handover I got from the engineer who had had this job for well over a month consisted of very little but ‘read these’ and having been initially told two of the pits must be complete by the end of last week – this gave me about 4 days since being handed the job – I cracked the whip to get productivity up – looking back it was at the expense of knowing the finer detail. The fact that it wasn’t briefed to me on the handover made me feel that the pits would be straight forward so thought lets get some concrete in that hole. I also noticed that a betonite/asphalt tape was required to be wrapped around the conduits that entered the pits which would swell on contact with water and stop/slow any ingress of water through the joints. This also made me wonder way it didn’t mention it for the construction joints between the base and walls so I have decided to order more of it and place it at the CJ’s as well. I have been quite frustrated at the inconsistency and lack of detail of the drawings which has made a simple looking job a lot more difficult. The construction manager wasn’t too concerned about my confession this morning about the concrete so I will continue as is with the Xypex batched in with any further works.

Other major works in the future include a RW that has settled and the corner has been crushed as it sits on the edge of a pile cap of Byron Rd bridge. Remedial work will have to include breaking out this corner and re-establishing the joint to not only that RW but three others that sit on the Pile Cap which haven’t yet crushed but may do in the future. The RW above these have also settled and a 50mm+ gap has opened up between panels which also needs filling to maintain noise wall integrity.

There are also some slip form traffic barrier’s to construct at two further bridges but as I will have some further barriers to do at both Dickson and Eastwood which were initially in the scope of works of the civil team I will try to do all the slip forming works together around Oct time. I have to speak to the subcontractor yet and contribute to producing the contract with the commercial team before any of this happens so that will at least give me time to do this and to also write the AMS.

The concrete strength issue of Dickson Rd piles continues with a few developments. The main development is the Project Verifier (who works for RMS as it is a road bridge) noticed that on the third day of four a different concrete mix was delivered. I really should have picked this up when we poured but I was mainly loooking to see that we received B80 (RMS spec) 50MPa 220mm slump tremie mix which we did. What I failed to notice is the different mix code on three of the dockets so I must accept a small part of the blame. However, this was not the mix I ordered which I have proved and why they decided to change the mix on the third day and then revert back to the correct mix the day after is a bit of a mystery. Both mixes are 50MPa with the same slump but the ‘rogue’ mix has a higher cement content and lower w/c ratio. I looked back at all the 10 batches I received for the piles to compare them and you can see that the concrete supplier has fairly consistently cocked up the batching. The first two rogue mixes were batched identically to the previously mix so it appears even though it states a different mix code the mix is practically the same as the project approved mix. The third rogue mix batch was in line with the design mix and is probably the one which will cause an issue with the designer. The project approved mix should have a Total Cementitious Content (TCM) of 515 Kg/m3 with a w/c ratio of between 0.3-0.4 but as you can see from the table below most of the batches don’t conform to this. The one rogue mix that is actually correct should have TCM of 635Kg/m3 with a w/c ratio of between 0.27-0.32 but the project requirements state that TCM should not be over 550 for durability purposes so this is the batch that may be a problem. The origianal issue of strength inconsistency has just about been put to bed as the project approved mix is a 50MPa product at 56 days even though the designer states in the drawings that this strength must be achieved at 28 days. Since there is no 50MPa at 28 days product approved for this project  the deisgener has taken the 56 days results, applied the corrective value to convert to 28d strength (1.19 for blended concrete) and is happy that the strength achieved is satisfactory. The issue of some of the results losing strength between 28-56d has largely been brushed aside as I expected and the test samples have been blamed. However with this new information which I submitted to the deisgner through the RFI process this morning we wait to find out what implications there may be. The main issue that has been raised is the potential of thermal cracking due to the high cement content in pile A3  and therefore the issue has now become one of durability where as initially it was of concrete compressive strength.

Outside of work we have celebrated our little mans 1st birthday which to be honest he may not have realised! We and friends had a good celebration anyway with cake, beer and champagne. We also completed the City2Surf run or walk in our case this sunday which is apparently the most popular run in the world. It is certainly one of the most scenic as you go from Hyde Park in the centre of Sydney and finish at Bondi beach. I registerd with JHG so got to wear a JHG running top and sun visor – I saved a visor for you westy! It all finished with a BBQ on the beach in the JHG/Thiess/Leightons corporate tent which was a good way to end the day. As Westy has mentioned we are doing Tough Mudder in Oct which I might add I signed up to before Mr West but I’ll have to share with you his text he sent when asking if I was up for it. It certainly confused me – not that I’m saying you wouldn’t do well in a model competition mate! Not sure I’ve been called Benjo before either!