'It's quite scary' Alarm among parents at school forced to shut over safety warning

Willowbrook Mead primary academy on the outskirts of Leicester was a hive of activity yesterday morning as staff moved tables, chairs and bookcases from brick buildings into a nearby portable cabin.

- Jessica Murray

But the activity was not the usual hustle and bustle of a new academic year. Just two days into the new term, Willowbrook Mead was forced to close its doors to students while safety works are carried out.

It is one of a number of schools that have had the beginning of term plunged into chaos after the government found more than 150 schools had buildings made from potentially dangerous reinforced autoclaved aerated concrete (Raac), which has been assessed as being at risk of collapse.

"It was a bit of a surprise, the kids have just gone back to school, and we just found out yesterday," said Mohammad Younis, who has a 10-year-old daughter at the school.

"It is alarming if something like this is there in a lot of schools It was considered an innovative, lightweight material that allowed the country to rebuild quickly and cheaply after the second world war.

But reinforced autoclaved aerated concrete (Raac) is now at the centre of a mounting national crisis after the failure to properly maintain mid-century building stock forced schools to close just before term was due to begin.

Raac was principally used in roofs - and less regularly walls and floors - between the 1950s and 1990s. It was lower-priced and easier to shape than traditional "dense" concrete, and was not made with coarse aggregate.

Instead it was aerated, giving it a "bubbly" effect like the inside of an Aero chocolate bar - and was about a quarter of the weight of normal reinforced concrete.

But even then it was considered less durable, with a lifespan of about 30 years. By the 1990s, structural engineers found Raac was beginning to struggle with age - especially on the roofs where they were primarily used.