Finally, towards the end of January, the dig was complete. The digger was taken off site, and the ground could now be prepared for the first, and the most significant, concrete pour. Lower drainage runs were dug out, sumps and manholes put into place, service ducts installed. Then the steel reinforcement crew came in and set about creating the reinforcement cages. The engineer’s solution for the concrete slab avoided the use of groundbeams and used carefully placed reinforcement to create a thin substructure.
On Tuesday 8 February we were all up bright and early. It was cold (0 degrees) and foggy (very atmospheric), but the forecast was set to get warmer through the day, which it did (reaching 9 degrees and, most crucially remaining at this temperature overnight) and the pour went ahead. Kate went down to site at 7.30am (the builders had been there since 6am, undertaking the final preparations), and the concrete pump boom was in place and they were getting ready to pour. The boom reached over the neighbouring site, an impressive piece of kit which was apparently capable of pumping concrete up eleven storeys. Kate went back up, and Jonny went down, then we all went to have a look as the concrete was being poured into the boys’ bedroom area before they went off to school and pre-school.
Throughout the day over 30 cubic metres of concrete was pumped, poked, tamped and hand trowelled. At last, we were out of the mud. This concrete slab represented the top of our table-like substructure – the legs being the piles, which reach down to 11 metres.
In the knowledge that cement has very high CO2 emissions associated with it, we used a concrete mix with a cement replacement component. This meant that the slab took a little longer to harden properly, yet the mix is still very strong.
There are two more pours to go – one for the upper slab to the front of the building and the rear retaining walls, and then the last to deal with the retaining wall to the front of the house, and steps to the front and rear courtyards. The blinding is down and the steel reinforcement is currently being prepared for the rest of the ground floor, and we hope to pour week beginning 21 February.
The final pour will be several days’s later again. The slab and its retaining walls is a very involved structure; setting out an accurate base for the steel and timber frame elements to follow.