The Influence Of Air Entraining Agent on Bond Strength

Mortar bond strength bricks and mortar

From University of Newcastle. This is a study on the effects of banned additives like detergents, soft drinks and air entraining agents. For the full paper see the link at the bottom of this page:

Air entraining agents are widely used in Australia to impart plasticity to the fresh mortar. The entrainment of a large quantity of air into the mortar affects the hardened mortar properties, in particular the mortar-to-unit bond strength [1,2]. This report represents a summary of the investigations carried out at the University of Newcastle to evaluate the effects of air entraining agents on bond strength and mortar microstructure [3,4,5]. These investigations formed part of a major joint research project between CSIRO and the University of Newcastle investigating the mechanisms of bond formation in masonry.

Air entraining agents (AEA) are used to improve the workabilily of rnortars made with sands which are often graded poorly. The improved workability is achieved by the introduction of minute air bubbles into the mortar mix and through the reduction of the mortar's bulk density. AEA are used to partially or completely replace hydrated lime in conventional cement:lime:sand mortars. Reductions in masonry bond strength often result with dramatic reductions occurring when the mortars are overdosed with AEA. AEA overdosing from inaccurate batching, as typically very small quantities are required, or driven by the desire to produce a more workable mix than is possible with the recommended dose. Even with low levels of overdosing, the bond strength may be reduced and not meet the characteristic flexural tensile strength requirement of 0.2 MPa specified in AS3700:199S t6l. In extreme cases little or no bond is achieved.

The results from two investigations into the effects of AEA on masonry bond strength and mortar microstructure investigations using optical and scanning electron microscopy techniques are described in the following sections. These investigations represent a preliminary study across a wide range of AEA concentrations and, a detailed study of the mortar microstructure and brick/mortar interface characteristics in the AEA bond strength sensitive range of AEA addition.

Read the Full Paper Here.


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