2 / 2017-05-31 04:23:26

Investigation of the Influence of PCE-superplasticizers on the robustness of concrete air content

Air content, Superplasticizer, Air-entraining, Admixtures, Cement, Mix Design, Testing.

Air content is an extremely important aspect of today’s concrete performance and durability characteristics. High air contents are necessary in most severe frost environment. According to the Finnish concrete code, the target value for total air content varies between 4% and 5.5% for XF - exposure classes. Lately, research results showed that elevated air contents have been observed in fresh air-entrained concrete measurements at construction site and also from the samples drilled from structures. The highest air content measured from the samples taken from the structures have exceeded 15%. The high air content has caused deficiencies in the compressive strength and other mechanical properties of concrete structures.
The key question is how to properly entrain the desired air content and how these can be stably kept in the concrete (from fresh to hardened state). There are many factors in the procedure of concrete production that can influence the stability air bubbles in concrete. One of the factors affecting the stability of air content in concrete could be the use of combination of air entraining agent (AEA) and polycarboxylate ether (PCE) –superplasticizers admixtures, where the PCE superplasticizers show air-entraining functioning.
The objectives of this study is to investigate the stability of air-entrainment in concrete using different types of PCE superplasticizers, air-entraining agents and concrete mix design. The study include (i) a state-of-the-art literature review about the air-entraining functioning of PCE-based superplasticizers and (ii) laboratory work to investigate the effects of the concrete composition and admixture combination on the stability of the air entrainment in fresh and hardened concrete. Concrete compositions with three cement types and different maximum aggregate sizes are investigated. A polycarboxylate ethers based superplasticizers and air entraining agent admixture combinations from seven different admixture producers are used. Also the effect of different mixing periods and compaction times on the stability of air content in concrete is performed.
The result of this study will set requirements of the concrete mixtures so that a stabile protective pore system can be achieved.