Construction World October 2017

PROJECTS & CONTRACTS

Old paper mill’s NEW LEASE ON LIFE Sika’s specialised products were used recently in a major concrete rehabilitation project at Sappi Ngodwana Paper Mill, situated 50 km from Mbombela in Mpumalanga. One of the oldest paper mills in South Africa, Ngodwana is also one of the largest.

Sappi (the South African Pulp and Paper Industries Limited) required a highly durable solution that would be able to withstand an adverse operational environment at its Ngodwana Paper Mill, and DPA Specialist Consulting Engineers had no hesitation in specifying four Sika products to cover all aspects of the necessary concrete repairs. Sika MonoTop-610, a cementitious, polymer-modified, one component bonding slurry and primer with active corrosion inhibitors, was used for protection of all steel reinforced concrete. With excellent adhesion to steel and concrete, Sika MonoTop-610 meets ZTV-SIB requirements for corrosion protection. Due to its excellent workability characteristics and thixotropic behaviour, Sika MonoTop-615 HB was used for thick layer repairs to concrete slab soffits at the mill. Sika MonoTop-615 HB is a high build, cementitious, polymer-modified, one component repair and reprofiling mortar containing silica fume and Ferrogard corrosion inhibitor. Both Sika MonoTop products are easy to mix, with adjustable consistencies and are

sprayable by the wet spray method. Since no shutdown time was allocated to the contractor Structural Maintenance Services, applications of Sika products were carried out while the mill was fully operational. All floor areas were repaired using Sikacrete-214, a free-flowing, high strength micro concrete with a maximum aggregate size of 9 mm. It is typically used for casting sections or members where the volumes required are too large for conventional grouts or too small and inaccessible for normal concreting procedures. Economical, easy to mix, apply and finish, Sikacrete-214 provides excellent adhesion and rapid strength development with high resistance to freeze/thaw cycling. It is shrinkage compensated and vapour permeable. Although in operation since 1966, it was not until 2013 that Ngodwana Paper Mill entered the Dissolving Wood Pulp (DWP) market using a process known as the kraft or sulphate process. For this reason, consultants specified sulphate- resistant Sika MonoTop-412 S, a one- component, fibre-reinforced, low shrinkage, structural repair mortar that meets the

The situation before repairs.

Damaged concrete was repaired using Sika Monotop 610.

requirement of Class-R4 of EN 1504-3. This specialised product was applied to all areas subjected to high sulphate attack. Providing superior workability characteristics, Sika MonoTop-412 S can be applied manually up to 50 mm thick and requires no bonding primer. It is suitable for preserving or restoring passivity and is tested for application under live dynamic loading. Ngodwana Mill not only complies with responsible and sustainable forestation practices and is FSC (Forest Stewardship Council) accredited, but is also uniquely designed to minimise fresh water usage, a significant factor considering the current drought conditions in South Africa. In this regard, as an integrated pulp and paper mill, Ngodwana performs in the top fifth percentile worldwide. Besides the adverse working environment for the project, severe time and budget constraints were also imposed, making this a challenging project that was significantly expedited by the superior quality of Sika products, which have no doubt extended the operational future of Ngodwana Mill. 

Sika Monotop 516 was used for the concrete slab repairs.

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CONSTRUCTION WORLD OCTOBER 2017