MULTI-NATIONAL CEMENT producer Lafarge faces massive compensation claims after admitting this week that 'rogue staff' at one of its cement works faked test results on more than 1Mt of cement.
It said that as a result it had been supplying customers with cement containing higher than certifi ed levels of soluble alkalis for two years.
It is understood that this has exposed some major highway structures and a large basement in south west England to an increased risk of alkali silica reaction (ASR).
The cement was supplied to customers in the south west from Lafarge's Westbury works in Wiltshire between September 2002 and December 2004.
'Lafarge recently discovered that alkali test data at its Westbury works had been deliberately mis-reported during this period, ' it said in a statement.
'As a result, a number of ready mixed concrete producers inadvertently supplied non-conforming concrete to customers in the south west of England.' Lafarge said that alkali levels in the cement produced between these dates were well above levels agreed with customers, putting structures at risk from alkali-silica reactivity - better known as 'concrete cancer'.
Alkali levels in the Lafarge product are understood to have shot up when its Westbury plant started using chalk, one of its main raw materials, from a new quarry.
Cement users have always relied on the producers' test certifi ates for reassurance on the chemical composition of the cement they receive.
'We use the alkali levels declared by the cement makers to design our mixes so the levels of soluble alkalis in the concrete are safe', said British Ready Mixed Concrete Association (BRMCA) technical director Tom Harrison.
'If the cement is actually more alkaline than we believe then mixes with high cement content could be liable to ASR. , ' he said.
Lafarge said that as soon as an internal audit uncovered the false data it documented the true alkali levels in cement produced over this period. It then supplied them to the ready mix producers.
The readymix industry has launched a huge exercise to trace all mixes that could be vulnerable, referring to detailed computer records of concrete supplies held by concrete depots.
Harrison said this exercise was complicated by the variability of the alkali levels in cement supplied over the period.
He pointed out that only mixes with high levels of Westbury Type 1 cement content - more than 450kg/m 3 - were at risk. Mixes containing pulverised fuel ash (PFA) or ground granulated blastfurnace slag (GGBFS) are expected to be safe.
'Less than 1,000m 3 have so far been identifi ed as being at risk, ' Harrison said. 'Unfortunately, high cement content usually equates to high assumed performance. The concrete under threat includes highway structures and a large basement.' Precast concrete producers also use high cement contents in many of their products.
But precast manufacturers body British Precast chief executive Martin Clarke said that the Westbury problems should have no signifi cant effect on this sector.
'Producers in the south west use non-reactive limestone aggregates in most of their products, ' he added.
Lafarge said on Tuesday that alkali levels at Westbury were now under control, after a change in the raw material blend.
It refused to be drawn on the fate of the rogue employees, saying only 'appropriate corrective action has been taken; it is inappropriate for us to comment on individuals.' Concrete industry bodies such as the BRMCA and the Concrete Centre have applauded Lafarge for publicising its problems and for working with its customers to identify at risk structures.
But the tracing exercise has absorbed a lot of manpower, and the ready mixed producers expect Lafarge to cover the costs.
'We are bound to receive claims from our customers as well, and these will be passed on to Lafarge, ' said Harrison.
Lafarge has accepted responsibility for the long term monitoring of suspect structures and has retained Halcrow and Arup to offer independent advice to concerned end users.