Modern concrete technology traces its history back to the middle of the 19th century with the discovery of Portland cement and the art of using steel rods to reinforce concrete. In the early days, exclusively fixed forms were used – but the construction became complicated and expensive when it came to the erection of tall structures. The idea gradually emerged of using a low form – about 3 to 5 feet high – and making it slide upwards at such a rate that the concrete would have time to harden sufficiently not to flow out beneath the form.
The form was raised by means of screw jacks, which climbed up vertical rods and were completely manual in operation. One man could look after up to 5-7 jacks of this type. On major works 20-30 men per shift could be required – just to carry out the lifting operation.