Reply to the discussion by William G. Hime of “The use of tension testing to investigate the effect of w/c ratio and cement type on the resistance of concrete to sulfate attack”

Abstract

This brief discussion contains the original authors' replies to a commentary on their study (Boyd and Mindess, 2004) on concrete specimens that were cast and partially immersed in a solution for varying periods of time up to 1 year. The study found that water/cement (w/c) ratio had a greater influence on the resistance of the concretes to than did cement type. In addition, the pressure tension test appeared to be more sensitive than the compressive strength test in detecting internal damage, particularly at early ages. In the commentary, Hime contended that the term sulfate attack is not adequately defined, nor is the distress under investigation necessarily confined to at all; it may be due to physical salt due to precipitation of sodium as either thenardite or mirabilite or both. Hime also noted that the authors fail to provide any explanation why the tests fail to show any loss from the initial measurement of the prisms in sodium solution, except for one type of cement studied. Boyd and Mindess reply to these concerns by claiming that Hime has misunderstood the intent of the original paper, which was to examine the use of a novel tension testing technique to determine the extent of internal damage to concrete. The paper was not intended to deal with the mechanisms of attack. Boyd and Mindess do note, however, that in common engineering usage, sulfate attack is the term used for chemical processes involving ions reacting with the components of the cement paste, such as the formation of ettringite, gypsum, thaumasite, and sodium dihydrate. The authors conclude by turning down Himes' offer to carry out a further microscopic investigation of the research specimens; said specimens have been discarded.