A kiln for Castle in Flintshire

Mowlem was awarded the 3.2m civil engineering contract for the Kiln 4 project at Castle Cement's Padeswood Plant in late February 2003. Construction work began on 17 March and essentially consists of numerous large heavily reinforced concrete bases, subterranean service tunnels, drainage, roads and hardstandings, totalling 12,500m^sup 3^ of ready-mixed concrete.

The work is divided into two main sections: the first consisted of the three kiln support piers, completed in July, the second refers to the cyclone pre-heater tower base and sub-structure, completed in August. The site team identified completion of the service tunnels as an early requirement. These were originally programmed for later in the year, but the team considered these deep excavations to be at risk from bad weather. Construction of these tunnels would also make large areas of the site inaccessible, affecting progression of the other works.

Foundations

The site is compact, orientated east-west, with the existing plant on the north boundary and a large landscaped mound to the south. The new kiln and pre-heater tower occupy the centre of the site. They are surrounded by other structural foundations including those for the sub-structure, coal mill, cemfuel storage tanks, transfer towers, clinker coolers, bag filters, duct supports and other lesser support foundations (see Figures 1 and 2). All piling took place under a previous works package.

The largest reinforced concrete foundation was required for the cyclone pre-heater tower. This was over 4m deep and covers approximately 28 28m. Placing this concrete in a single pour would have involved pouring over 3000m^sup 2^ of concrete, and the mix design would have had to incoiporate cement replacements to reduce hydration heat. With the agreement of the client and their designers, Mowlem decided to split the pour into four, with three horizontal construction joints (see Figure 3).

The benefits

Considerable safety benefits were derived adopting this technique. Horizontal joints were carefully positioned below the reinforcement lap positions, where possible. This made it easier to fix the higher level reinforcement as this took place during progression of the concrete pours. This method eliminated the hazards to the steel-fixers of fixing reinforcement at height, added stability to the reinforcing cage and negated the requirement for internal scaffolding. It significantly reduced the amount of chairs needed for the upper reinforcing mat, thereby saving approximately 12 tonnes of reinforcement. Formwork use was rationalised as forms were used four times. There was no requirement for joiners to work at height, and consequently access scaffolds were not used as the structure was back-filled after completion of the pours.

Concluding remarks

Both the kiln pier towers and the cyclone pre-heater substructure have been completed on programme. Early completion of the service tunnels has enabled the mechanical work to commence on schedule with unrestricted access. Mowlem has now substantially completed the civil engineering contract on time and below budget by engaging in value-engineering exercises with the client's team. Mowlem has been engaged by Castle Cement to undertake further essential modification work for commissioning of the new kiln within the existing plant whilst the mechanical and electrical works progress on Kiln 4 (see Figure 4).