Saint-Gobain Weber Concrete Repair is the Solution for Chertsey Lock

Published by Jackie Biggin for Weber in Communities

In the refurbishment of Chertsey Lock, on the River Thames, Saint-Gobain Weber, leading UK formulator and manufacturer of innovative materials in the external wall insulation, render, tile fixing, flooring and construction mortars sectors, has supplied a significant quantity of high specification structural repair concrete.

The busy lock, to the west of Walton-on-Thames and east ofStaines, is popular amongst river users.  Over the years, unavoidable wear and tear from boats and the river itself has caused deterioration of the lock chamber.  As part of the Environment Agency’s commitment in maintaining the River’s many structures, which amounts to more than 2000 assets on the River Thames alone, work commenced in November 2011 to extend the life of the lock by at least 30 years and return it to its former glory.  The main contractor was Jackson Civil Engineering of Ipswich,Suffolk.

Over 1500 25kg bags of Saint-Gobain Weber’s weber.cem spray DS, a polymer-modified, dry-spray, cement-based concrete, were required to complete the project.  The lock was fully drained to gain access to the walls and applicators Currall Lewis & Martin (Construction) Limited of Oldbury, West Midlands, applied weber.cem spray DS by a process of ‘guniting’, a high pressure method of spraying concrete on to vertical and horizontal surfaces.

Initial works at Chertsey Lock involved the removal of the existing cement based lock wall at a depth of 75mm.  This was carried out with hydrodemolition but discovery of a 50mm mesh reinforcement resulted in the need to change the method of removal.  The Environment Agency permitted the walls to be saw cut and broken out by hand which allowed the programme of works to continue on schedule and negated the need to monitor the risk of water contamination.

After removal of the concrete, resin injection works to 200 linear metres of cracked walls was carried out.  New reinforcement mesh was fixed to the walls and batons to the bottom edge to terminate the concrete spraying works. 

“After power washing the walls to remove any loose debris we pre-dampened the area in preparation for spraying,” says Mike Fullerton, infrastructure manager, Currall Lewis & Martin (Construction) Limited.  “We used weber.cem spray DS for the reinstatement work which achieves less rebound than any other dry spray system we have tried.  We bulked out in one pass to a depth of 80mm to accommodate the new levels set by the timbers installed by Jackson Civil Engineering Limited.”  The freshly sprayed walls were dragged back with a feather edge rule to level the material and lightly sprayed with water after the initial set of around one hour, to provide a good surface for the final pass of 30-40mm of weber.cem spray DS.

A further process of levelling was required before sealing the surface to the specified finish.  The work area was immediately installed with protective polythene sheeting and secured for 24 hours to prevent rapid dehydration of the cement from strong winds during the curing process.

From a test panel 750 x 750 x 100mm, Currall Lewis & Martin took five core samples which were independently laboratory tested for strength.  “We had two cores crushed at seven days to ensure we had reached the required strengths.  Results revealed strength values of 49.5 N/mm² and 58.8 N/mm².”

Spraying works to the quoin ends of the lock were also carried out requiring precision and accuracy.

Waste levels within the rebound material were below those indicated on Saint-Gobain Weber’s data sheets indicating a superbly mixed product and experienced application.  “As a result we were able to save money on the quantity of material used as well as the programme savings of time and labour on cleaning up the rebound and the expense of skip hire for take away.”

The formulation of weber.cem spray DS, which contains inert limestone aggregates and dust suppressants, has been especially designed for dry process spray application to give high early strength in 2 – 3 hours, reduced rebound and maximum application thickness.  It achieves a compressive strength of up to 56.3 MPa in 28 days, tested to BS EN 12390-3:2002 at 20^OC, and a flexural strength of 9.8 MPa, tested to BS 1881-118:1983.  weber.cem spray DS is highly resistant to shrinkage and chloride penetration. 

weber.cem spray DS is used extensively in repairing large areas of highway structures including bridge columns, piers, parapets, tunnels and viaducts; to marine structures including sea walls and docks; to fire damaged concrete structures as well as rock and embankment stabilisation, and the structural encasement of steel sections and pylons.

To enable the restoration of the lock the Environment Agency carried out a fish rescue to minimise the impact on the environment.  Over 150 fish were caught and released to the river outside of the lock chamber in preparation for the engineering work.  The successful completion of the project will ensure that many thousands of people can navigate the River Thames with confidence and peace of mind.

Further information and technical support is available from Saint-Gobain Weber on 08703 330 070, or 028 9334 3700 in NI or ROI, or visit www.netweber.co.uk and register for a copy of the Construction Solutions Handbook.  A free download of the new weber.app for iPhone and iPad users is available from the iTunes app store, and from Google Play for android smartphones and tablets.