|
|
|
Saturday, October 31, 2009 |
|
Repairs to No.1 Concrete Silo at Harmony Central Plant, Virginia
:: News
|
 |
Source: Leon Mentz
The two 6 000 ton gold-ore silos at Harmony’s Central Plant Refinery in Virginia were originally constructed in 1986. They were lined with railway tracks to absorb the impact of the ore and to reduce the wear on the silo wall when discharging the ore into the outlet hoppers.
The continuous impact of the incoming ore was concentrated mainly on two areas of the silo wall, resulting in a gradual reduction of the wall thickness. This, combined with the friction of the discharging ore and the failure of the railway tracks, led to the sudden disintegration of a 2m diameter section of the silo wall.
In early June 2009 Stefanutti Stocks Civils began to rehabilitate the first silo as specified by Walker Ahier Holtzhausen Engineering Consultants.
The scope of work included:
• removal of damaged and loose concrete;
• replacement of missing reinforcing steel;
• installation of new rail liner brackets;
• guniting the silo wall to its original profile;
• installation of new rail tracks; and
• post tensioning of the silo.
Our first task on site was to provide a safe platform inside the silo on which our scaffolding was to be erected. The 3.5m deep openings over the three discharge hoppers and the overhanging dead box material made access for the scaffold erection unsafe and virtually impossible. “In order to create a level platform, we manually relocated the 400 m3 of dead box material into the voids over the hoppers,” says Leon Mentz, site agent. Due to the unstable nature of the ore, our team was attached to life-lines by means of safety harnesses, and suspended from the top of the silo.
The principal activity of the project was the guniting of the wall once the brackets were in place. The criterea for the material used was that it had to obtain 70 MPa in compressive strength after 28 days. A specialized pre-bagged, ready-to-use, fibre-reinforced cementitious mortar mix, containing a unique blend of selected cements, micro-particles and a combination of admixtures is being utilized. This material provides a long lasting durable surface and the micro-particles reduce rebound thereby lowering costs. “Strength tests during installation indicated that we had surpassed the compressive requirements, by attaining results in excess of 80 MPa,” said Leon.
The contract is on track for completion in early November 2009.
|
|
|
|
|
|
|
|
|