Mix Design Selection For Old and New Generation of SuprePlasticizers

Determination the optimal mix design plays an important role in order to gain the maximum characteristic strength. This research was conducted as a case study for Manjil tunnel project located in Qazvin-Rasht highway. For this purpose, 18 concrete mix designs were prepared at the study phase of the project with specifications such as conventional water-to-cement ratios of 0.4, 0.5 and 0.6, the use of two generations of new and old conventional superplasticizer in Iran (naphthalene sulphonate and polycarboxylate ether types, respectively) with cement weight percentages of 0.2, 0.4 and 0.6. Superplasticizers are used to increase the fluidity of concrete without adding excess water. The naphthalene sulphonate is a polymeric molecule formed by condensation of naphthalene sulfonic acid and formaldehyde, in which the hydrophilic groups are mainly sulfonic groups. It has been demonstrated that polycarboxylate ether can mitigate plastic shrinkage of matrix because of the reduction of the build-up rate of capillary pressure by polycarboxylate ether. Finally, the optimal water-to-cement ratio and superplasticizer weight percentage were determined. Concrete mix designs with different ages of curing were made (0, 3, 7, 14 and 28 days).