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Importance of lime in construction industry

  • 1.  Importance of lime in construction industry

    Posted 01-07-2021 05:47 AM
    Despite lime to be used in ancient time...... Why after advancement of cement it is still in use? In short, what are pros and cons of lime?

  • 2.  RE: Importance of lime in construction industry

    Posted 01-08-2021 09:19 AM
    I suspect it all depends on what it is intended to be used for. As a stabilizer in road construction, the option to use cement vs. lime depends on the particular properties of the material. For example, the general "rule of thumb" is that for highly plastic materials (materials with high PI; clayey materials), and where it is also required to reduce the PI, lime is generally preferred (pozzolanic reaction with clay particles, to render material less plastic and improve bearing strength properties). For less plastic materials (PI < 15; typical more sandy materials), and where strength properties (bearing strength) needs to be improved, the hydraulic reactive properties of cement as additive will be more effective.

    But, as will all additives, there are pro's and con's to both. As cement is a hydraulic reaction, it requires activation with moisture in the materials, and generally, process time from adding and mixing in the cement to final compaction and finishing of layer needs to be carefully controlled (typically 8 hours or less).

    Lime on the other hand, can (should ideally) be mixed in and allowed time for the pozzolanic reactions to take place, and only then shaped and compacted. This allows more time to complete construction. One of the major drawbacks of lime, in my opinion, is that it required careful handling on site, especially during spreading and mixing (causes "lime-burn" when gets on skin), so is a safety concern. Also to keep in  mind, the specific gravity (SG) of lime is approx. half of that of cement, so need double the bulk quantity than that of cement to attain the same percentages. This can however be both a disadvantage (if ordered in bags, it needs double the amount), but in turn, it facilitates the mixing process, especially if lower percentages of chemical additive is needed.

    Trust this provides some clarification.

    Gerhard du Toit, PE (TX), Pr-Eng (SA)
    Pavement Engineering Group Manager, Transportation, Northeast
    D +1-978-905-2496
    M +1-512-915-2332
    [email protected]

    250 Apollo Drive
    Chelmsford, MA, USA
    T +1-978-905-2100

  • 3.  RE: Importance of lime in construction industry

    Posted 01-08-2021 12:03 PM
    Cement is a great product, it can and has been used successfully for years.  The same is true for lime.  Lime stabilization is an effective, economical, safe, and environmentally friendly process.  TXDOT recommends the use of cement for clay soils that have a P.I. less than 15 and recommends using lime in clay soils that have a P.I. greater than 15.  To use lime in a lower P.I. material would require the addition of fly ash to create the environment for producing water-insoluble hydrates known as Calcium-Silicate-Hydrates (CSH) and Calcium-Aluminate-Hydrates (CAH), which are essentially the same hydrates that form during the hydration of Portland Cement.  Lime is a better product to use for fat clays than cement because it reduces the P.I. much more effectively.  Over the last number of years there have been projects where lime and cement have been used in conjunction with one another to treat soils (separate application process for both).  The lime is used to reduce the swell potential to an acceptable level (normally less than 1%) and then the cement can be applied to gain more strength if desired. Lime can offer a psi of somewhere normally between 150 psi and 300 psi depending on how reactive the soil is, where cement can achieved a much higher psi if desired.  However, for subgrade treated soils you normally don't want to target a stiffness much more than 200 psi due to the potential of getting it to rigid and unforgiving, especially if you are sitting on more clay soils below in your active zone which can be 10' to 15' deep in Texas.  The two most devastating forms of distress in flexible pavements are bottom-up fatigue cracking and rutting.  The addition of lime can permanently change the clay soils, stabilizing and strengthening them into high performance pavement foundations.  The chemical transformation from the lime reduces the soil  plasticity and expansiveness making the material more workable.  It also creates a great working platform that is resistant to water migration from the remaining clay soils below that attracts water which could then migrate up into the rest of your pavement structure if it were not for the water resistant layer.  Positive drainage should always be an important factor for any design and pavement structure.  Call me at 254-723-5463 or email me at [email protected] should you want to discuss further.  Thanks!

    Kelvin Reinhardt A.M.ASCE
    Executive Director/VP
    Lime Association of Texas
    McGregor TX