Tests on concrete columns at Mater Dei Hospital last summer have uncovered evidence of previous failed repair works, Times of Malta has learnt.
Repair works had been done to stop corrosion of the steel reinforcement inside the columns by water that was absorbed through the concrete. The water absorption rate was also found to be more than double what was expected of high quality concrete in place for 20 years.
The tests formed part of the exercise undertaken by Arup, a UK engineering firm, last summer to determine the strength of the concrete which was used in the construction of Mater Dei.
Evidence of the repair works carried out in the past was found in the service tunnel situated below the emergency building, which formed part of the initial structures erected in the first half of 1996.
The report seen by this newspaper said the undated repair works had not been effective in stopping the corrosion and the mortar used was also dropping off the columns. This led to “a progressive reduction of column capacity”, the report concluded.
Carbonation was well advanced and in some parts had even reached the steel reinforcement
Arup was commissioned by the Health Ministry to carry out wide-ranging tests after preparatory studies done before the construction of additional floors over the building to accommodate more hospital beds had found weak concrete.
The report said concrete was impacted by a high level of carbonation – physical changes to concrete as a result of water absorption.
“Carbonation was well advanced and in some parts had even reached the steel reinforcement,” the report said. In some places moisture had reached a depth of 40mm when the level of carbonation for good quality concrete that was 20 years old was expected to be less than 20mm.
The consequence of the advanced carbonation was the increased risk of corrosion to the steel reinforcement in the concrete. Arup said this was particularly important in the basement areas and the plant rooms where columns experienced high humidity.
While increased carbonation had no impact on the strength of concrete, it was a sure sign of low-grade concrete that used limestone aggregate rather than hard stone, the report pointed out. “Higher levels of carbonation can be attributed to a higher water-to-cement ratio, poor compaction and porous materials [limestone].”
The report said it was not known from construction documentation made available whether quality checks performed between 1996 and 2000 during the construction phase had found limestone aggregate in the concrete.
Had the quality tests – normally performed by crushing concrete cubes – been performed on the same concrete that was used in the columns, they would have shown that the mix contained limestone.
The tests done by Arup confirmed that in many areas of the accident and emergency department the strength of the concrete used was well below that required for a hospital building.
More than half the columns also failed seismic checks when Mater Dei had to be earthquake-proof and all columns at basement level were found to be “working below the adopted design stress”.
The Arup results indicate that the hospital builders were in breach of the initial 1992 contract signed with the government when the project was still known as San Raffaele Hospital.
The agreement seen by Times of Malta had specified that the hospital development had to “allow for expansion above the floor space proposed”, something that turned out to be impossible years later because of the low-grade concrete used.
The original contract had also made it incumbent on the builders to take into consideration seismic criteria when designing loads. This condition was also breached because the structure failed to be quake-proof.
The construction of the accident and emergency department began late in 1995 and most of the weak concrete was poured between March and May 1996.
The four main concrete suppliers were Blokrete, Tal-Magħtab, Mixer Ltd and Devlands.
Subsequent studies by Arup on the rest of the hospital found weaknesses in other areas.
kurt.sansone@timesofmalta.com