Regen durability

Using Regen as a cement substitute in concrete increases its durability and resistance to deleterious reactions.

Resistance to deleterious reactions

Sulfates occur naturally in the ground and  can sometimes have a harmful effect on  concrete, causing it to crack and disintegrate.  The main reactions are known as ettringite and  thaumasite. The use of Regen in concrete greatly  increases resistance to sulfate attack. This is well  recognised by codes and standards. In the latest  version of the British Standard for concrete  (BS 8500), the only option recommended for the  most severe sulfate exposure is a concrete with a  cement replacement of at least 66 per cent GGBS. 

Ettringite - The primary sulfate reaction that causes  disruption of hardened concrete is associated with  one of the minor compounds in Portland cement,  tricalcium aluminate. This can combine with sulfate  ions that have penetrated the concrete and form  a new hydrate (ettringite), which occupies a  volume greater than the original constituents.  This generates high internal stresses in the  concrete that can cause it to crack and disintegrate. 

Thaumasite - Another form of sulfate attack,  called thaumasite attack, has been recognised  as a problem after the discovery of its effects  on some M5 motorway bridges. Thaumasite is a  product, which forms at temperatures below 15°C  through a reaction between cement paste hydrates,  carbonate and sulfate ions. Its formation reduces  the cement paste to a soft mulch, undermining the  concrete's durability and stability.

Alkali-silica reaction (ASR) - A reaction between  the hydroxyl ions in the pore water within a concrete,  and certain forms of silica which are present in  some aggregates. This produces a gel which  imbibes pore fluid and expands; this expansion  induces internal stress of such magnitude, that it  causes extensive cracking of the concrete, known  as map cracking. The damage occurs in parts of  the concrete structure exposed to moisture. Regen  significantly reduces the risk of ASR occurring  and with some reactive aggregates is the only  recommended preventative measure. The resistance  of Regen to ASR is a function of the reduced  available alkali and the refined pore structure.

Chloride attack

Chlorides damage concrete by breaking down  the passive layer that protects steel reinforcement.  This layer is formed on the surface of the steel as  a result of the high alkaline environment produced  by hydrating cement. Certain types of concrete are  more vulnerable to attack because it is easier for  the chloride ions to reach the steel reinforcement.  When CEM I Portland cement hydrates, the  resultant pores are relatively large and can  easily allow chloride ions to penetrate into the  heart of the concrete and attack the embedded  metal. The result is rapid corrosion of the steel  reinforcement which can take the form of  localised pitting or general corrosion.  To prevent the penetration of chloride ions, a  dense concrete of very low permeability needs  to be produced and this can be achieved by  incorporating GGBS.  Where structures are subject to attack from  chlorides from an external source, a minimum  of 50 per cent GGBS should be used, with a  higher proportion used in areas where high  levels of chlorides will be encountered.

Heat of hydration

The hydration of cement is an exothermic reaction.  The use of Regen reduces the heat of hydration.  High temperatures in concrete can generate  stresses that could result in early-age thermal  cracking. This cracking is known to have caused  issues with some structures, so the use of Regen  is recognised as an effective solution to the  problem. Minimising heat of hydration to reduce  thermal cracking is of critical importance in mass  concrete pours. Regen was used successfully in  the construction of The Shard in London, the UK’s  largest ever concrete pour.  The percentage of Regen used directly affects  the heat of hydration; a replacement level of  around 70 per cent is recommended for large pours.  A temperature reduction of up to 40 per cent can  be achieved with a 70 per cent replacement level.

Setting times

Concrete produced with a proportion  of Regen has a slightly longer setting  time than cement-only concrete.  In practice, these extended setting  times give greater opportunity for  working the concrete, and provide  more flexibility on site to compensate  for any delivery delays or adverse  working conditions.  Concrete with a cement content  containing 50 per cent Regen will  have a setting time of approximately  half an hour longer than cement-only  concrete, although this can be  affected by the water/cement  ratio and ambient temperature.  We recommend carrying out tests  to ensure the correct mix ratios.