ABSTRACT
At the end of the Second World War the condition of railway tunnels in the United Kingdom was poor after six years of reduced maintenance; in particular, the mortar in the brickwork joints had seriously deteriorated owing to attack by the sulphur dioxide from steam locomotives. A method of mechanizing the cleaning and repointing operations was developed, starting in 1951 with an aerated mortar which had good flow properties because of its air content of 20%. This was fairly successful except at locations where the locomotive exhaust was sufficiently severe to attack the new mortar before it had cured properly. A better mortar was then developed, using pulverized fuel ash (PFA) and a non-ionic wetting agent, with minimum air entrainment to give good flow and minimal reaction between the ordinary Portland cement (OPC) and the wetting agent. With the mix now used (see Section 14.3) the likelihood of alkali-aggregate reaction is avoided, and tests on the mortar after immersion for five years in extremely high magnesium sulphate concentrations have shown it to be unaffected owing to its pozzolanic nature.
