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While PLC can increase or decrease any given concrete property relative to OPC from the same plant, the variations are relatively minor. 
Customers want assurance that PLC will result in good fresh and hardened concrete properties. They expect PLC concrete to be just as easy to work with and produce the same level of quality they have come to expect of all their concrete. Over the years, many studies have shown that there is not much effect on properties of concrete as a result of adding limestone to a mix via PLC. And differences that arise are usually dependent on the fineness of the limestone. This is because cement manufacturers optimize PLC to achieve a similar performance to ordinary portland cement. 


In other words, research confirms that PLC works like its OPC counterpart, both for fresh behavior and for hardened properties. A summary of effects on concrete is here:

 

  • workability – PLC can increase or decrease water demand higher and there is no significant increase in demand for chemical admixtures

  • bleeding – increasing the fineness of the limestone decreases the bleeding rate, but is generally of no concern

  • setting time – there can be a slight effect, a general decrease in initial and final set time with increasing fineness of limestone, but it is not a concern even at up to 15% addition rate for limestone

  • heat of hydration – in general, a slight increase in HOH can be observed at early ages (up to 48 hours) but these differences are less significant at later ages 

  • compressive strength – limestone additions at 10% to 15% can increase early-age strength due to increased particle packing, and long-term strength may also be slightly increased

  • scaling and freeze-thaw resistance – proper air-void systems, curing, and strength level are used to impart resistance to cold exposures and deicing chemicals, just as with OPC concrete mixes

  • sulfate resistance – low water-cement ratio (or water-cementitious materials ratio) and moderate- or high-sulfate cement designations (MS, HS) are appropriate controls for sulfate exposures, just as they are with OPC mixes

  • alkali-silica reactivity – SCMs are used with PLC mixes to reduce potential expansion when used with reactive aggregates, just as they are with OPC mixes

For further information on PLC research reports, please consult our experts

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