Compatibility of cementitious materials and admixtures.
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Compatibility of cementitious materials and admixtures.

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    • Abstract:
      Growing demand for creating more sustainable and durable concretes lead to the increased usage of various cementitious materials and 

      chemical  admixtures  in the mixtures. However, the  increased usage of these  components resulted  in more  complex mixtures that 

      sometimes cause unexpected incompatibility problems. This report summarizes the results of the investigation of the parameters that 

      may lead to workability problems, early age hydration irregularities and difficulties in achieving quality air void system in both plain and 

      fly ash cementitious mixtures. The present research work was performed in three major phases and the statistical modeling was used to 

      aid in interpretation. 

            Phase I involved evaluation of more than 100 different paste and mortar mixtures with respect to potential slump loss and hydration 

      irregularities. The results showed that cements with high C3A and low SO3 content were more prone to incompatibility problems. It was 

      also observed that mixes with  lignin based water reducing  agent (WRA) had higher tendency for rapid stiffening than mixes with 

      polycarboxylate  type superplasticizer  (PCSP).  Increased replacement  of  cement  by  class  C  ashes resulted  in the  development  of 

      abnormal secondary peaks in semi‐adiabatic calorimetry curves and accelerated the setting behavior. 

            The focus of phase II was on identifying material combinations that can result in problems related to air void generation and stability. 

      The experiments were conducted on 18 different systems and included determination of foam drainage and foam index parameters. 

      The results show that the amount of air entrainers required to obtain target air percentage, increased with the increase in the fly ash 

      content  in the mixture.  Lignin  based WRA  had,  in  general,  a  higher  air  entraining  effect than the super‐plasticizer when  used  in 

      combination with air entrainers. Also, five out of the six mixtures with most unstable air void system, identified using the foam drainage 

      experiments, contained the PCSP. 

            The third (and final) phase of the study involved production of 10 concrete mixtures to verify the incompatibility findings from the 

      paste and mortar experiments performed in phases I and II. The observations from the concrete testing were in agreement with the 

      findings from the paste and mortar testing. 

            Statistical modeling (performed using the material properties and results from phase I) identified the total C3A, SO3 and Na2Oequ 

      contents of the binder system along with dosage of PCSP (if present in the mixture) as statistically significant in predicting the initial set 

      time and area of spread (measured using the mini‐slump test). 

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