Concrete conservation : an analysis of a British historical pillbox

Abstract

This study was based entirely upon a British historical concrete pillbox built in Manikata in the late 1930's. Since the main aim of the dissertation was to recommend a suitable repair methodology, it was essential to carry out a study on the concrete's constituents, a visual inspection of the surfaces, and non/destructive testing for a more in depth study of the structure. Visual inspection gave an indication that the pillbox is undergoing weathering processes possibly triggered by chloride contamination and carbonation. This was examined further by carrying out non/destructive testing. Cover meter results suggested that the structure provided adequate protection to the embedded reinforcement. Changes in the gradients from UPV graphs show that a few irregularities in the walls are in fact present. Most of the Half cell potential readings imply that corrosion of reinforcement in tested locations have a 50% chance of actually being actively corrosive. Visual analysis of concrete core samples confirms that the concrete is homogenous and well compacted. Due to these characteristics compression strengths up to 46N/mm2were reached. Regardless of the state the pillbox is in due to weathering, the concrete in most areas is still in mint condition. Charters and literature by conservation bodies were utilised to justify necessary repairs to the structure. Traditional patch repairs with inorganic inhibitors, crack sealing epoxies, and the application of sealants to prevent ingress of water were considered to be effective repair strategies for the pillbox, without breaching the recommendations of conservation principles.