Some high profile infrastructure projects are falling apart.

Acid attack on concrete structures used as sewerage storage / treatment, industrial chimneys and bridge support is causing them to literally fall apart. This issue is of greatest concern to asset owners of sewerage treatment works, acid based manufacturing processes and structures in acid sulphate soils.

Deterioration occurs when the concrete is exposed over a long period of time to an acid solution. Softening of the cement paste allows a 'loosening' of the binding effect of the paste on the concrete aggregates. In some structures this can affect the outer 50mm of the structure significantly reducing the effective protective cover to embedded steel reinforcement. Corrosion of steel then can proceed at an accelerated rate leading to further loss of structural integrity.

A recent ACCI (Australian Centre for Construction Innovation, UNSW) investigation found acid attack is also an issue well above ground. Concrete flue gas waste chimneys in a major industrial complex were deteriorating due to acid attack. Deterioration was so severe that demolition was seriously considered.

Research into this problem has lead to new concrete mix designs that significantly reduce the adverse effects of acid attack.

The ACCI has reproduced the action of aggressive acid environments in laboratory trials and found some standard concretes can lose up to 45 % compressive strength over an extended period of exposure. By comparison new mix designs using blended cements containing silica fume, fly ash or ground slag have superior integrity and marginal reduction in compressive strength.

In recent years there has been an increasing trend of specifying a service life of 100 years for important concrete infrastructure projects. Resistance to chemical deterioration is therefore a key issue to be addressed at mix design stage if service life is to be optimised.

For further details contact Professor Marton Marosszeky at the Australian Centre For Construction Innovation, UNSW on Ph: 0412 446 916