THE INFLUENCE OF THE TYPE OF ANTI-FOAMING ADMIXTURE AND SUPERPLASTICIZER ON THE PROPERTIES OF SELF-COMPACTING MORTAR AND CONCRETE

Beata Łazniewska-Piekarczyk,Janusz Szwabowski

doi:10.3846/13923730.2012.698908

Beata Łazniewska-Piekarczyk, Janusz Szwabowski

Open Access

https://doi.org/10.3846/13923730.2012.698908

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Abstract

To prevent excessive air entrainment, superplasticizers (SPs) should not only be compatible with cement, but also should not create the air-entraining effect in mortar. In order to counteract excessive air entrainment, anti-foaming admixtures (AFAs) can be used to prevent the formation of air bubbles. This paper investigates the influence of the type, amount and time of introduction of AFAs on air-entrainment, rheological properties and workability loss of self-compacting mortar. The research results prove that AFAs decrease air-content in mortar. Mortar containing an AFA does not undergo segregation, as is the case with mortars of a similar degree of fluidity with no AFA and incorporating an SP only. Moreover, mortar with an AFA keeps initial consistency for longer in comparison to mortar with a SP only. The properties of hardened mortar mixes are also investigated. The research results show that AFAs do not have a significant influence on the compressive strength of mortar mixtures. The compressive strength of mortar mixtures incorporating an AFA is similar to mortar with a non-air-entraining SP. Moreover, AFAs increase significantly the flexural strength of mortar. In most cases, AFAs do not decrease the absorbability of mortar. Only two types of AFAs increase slightly the absorbability of mortar. In order to explain this phenomenon, a research was performed investigating the porosity structure according to the EN 480-11 (1999) and SEM analyses of two types of self-compacting concrete (SCC): one made of mortar with an AFA and the other without AFA. The freeze-proof resistance of SCC (made of the same mortar mixes) was also investigated according to PN-88/B-06250 (2003). The results show that the type of AFA and SP significantly influences porosity characteristics and frost-resistance of SCC.

Highlights

One of the important properties of self-compacting concrete (SCC) is self liberation of air bubbles introduced during concrete mixing (Kamal et al 2002; Khayat 2000; Szwabowski, Łaźniewska-Piekarczyk 2009)
Beyond the saturation point of anti-foaming admixtures (AFAs), there was no further reduction in air volume of mortar and SCC
− A polyalcohol-based AFA was highly effective in decreasing air content in mortar, increasing its flow diameter and decreasing its flow time without any segregation

Summary

Introduction

One of the important properties of self-compacting concrete (SCC) is self liberation of air bubbles introduced during concrete mixing (Kamal et al 2002; Khayat 2000; Szwabowski, Łaźniewska-Piekarczyk 2009). Research results (Neville 2000; Grodzicka 2005) proved that larger air voids, formed e.g. because of too low compacting, cause higher decrease of concrete strength than smaller air voids produced by an air-entraining agent For this reason, it is important to eliminate the airentraining effect of a SP, because under its influence large air voids are formed (Szwabowski, Łaźniewska-Piekarczyk 2008b; Fagerlund 1999). It is advisable to carry out proper tests aiming to verify the influence of different types of AFAs on the properties of fresh and hardened self-compacting mortar mixes. The results of such investigations are presented in the paper. The porosity structure characteristics of two types of self-compacting concrete (made of M1, M2 and M2-f mortar mixes) were examined in accordance with the EN 480-11 (1999) and SEM analysis procedures

PCP PCE abcdef

Admixure type

Findings

Conclusions