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Title: Influence of Synthetic Zeolite on Delayed Ettringite Formation – Preliminary Investigation

Author(s): Stephen O. Ekolu

Publication: Symposium Paper

Volume: 326


Appears on pages(s): 9.1-9.10

Keywords: delayed ettringite formation; heat treatment; sulphate; expansion; compressive strength

DOI: 10.14359/51710979

Date: 8/10/2018


Investigations were conducted to evaluate the effects of synthetic zeolite additive on delayed ettrintite formation (DEF) in heat cured cementitiuous systems. Mortar prisms 25 x 25 x 285 mm (1 x 1 x 11.4 in.) were prepared at water-cement ratio (w/c) = 0.5, using portland cement CEM I 42.5 N,R. Sulphates were introduced into the mixtures by adding 2%, 3% and 5%SO3. Also, a commercially available synthetic zeolite additive PWC was added to cement at proportions of 1%, 0.5% and 2.5%PWC. The mortar specimen were heat-treated at 95oC (203oF) then stored in water.

It was found that heat treatment led to higher early strength gain as expected but increase in sulphate concentration correspondingly caused reduction in early strength development. There was a marked increase in early strength of heat-cured mortars containing PWC. Use of 2.5% PWC in expansive mortars led to five-fold increase in expansion at 90 days. Accordingly, preliminary results indicate a possibility of adverse effect of PWC on DEF in cementitious systems, especially when used in elevated proportions. Further investigations are needed to conduct detailed evaluation of PWC effect on DEF.