A reply to Bryant Mather's discussion of the paper “a review of alkali-silica reaction and expansion mechanisms, 2. Reactive aggregates”

CEMENT and CONCRETERESEARCH. Vol. 6, pp. 815-816, 1976. Pergamon Press, Inc. Printed in the United States.

A REPLY TO BRYANTMATHER'S DISCUSSION OF THE PAPER "A REVIEW OF ALKALI-SILICA REACTION AND EXPANSIONMECHANISMS,

2.

REACTIVEAGGREGATES"*

Sidney Diamond School of Civil Engineering Purdue University, West Lafayette, IN 47907 I thank Mr. Mather for calling attention to certain ambiguities which seem to have appeared in the review, and hope that they can be ironed out without difficulty. Professor G i l l o t t ' s position, which I found to have merit, is that sufficient evidence exists for the notion that at least three kinds of alkali-aggregate attack can be distinguished: a) the "classical" a l k a l i - s i l i c a attack, b) alkali-carbonate attack, c) the new proposed category of " a l k a l i - s i l i c a t e " attack, the silicates involved being primarily relatively coarse-grained phyllosilicates found in a variety of rock types - "graywackes, phyllites, a r g i l l i t e s , siltstones, e t c . " , and also (confusingly)"argillaceous dolomitic limestones." There was no attempt to discredit the well-established alkali-carbonate reaction as a category. The extent to which actual reaction in a given argillaceous dolomitic rock may be a reaction with the carbonate (involving dedolomitization or other response) or a reaction purely with the phyllosilicate portion of the rock, i.e. an a l k a l i - s i l i c a t e reaction, would presumably be a subject for investigation in each case. The proposed a l k a l i - s i l i c a t e reactions seem to be marked by (a) slow response, and (b) formation of only small or negligible amounts of reaction gel. These characteristics may not absolutely distinguish such reactions from specif i c instances of a l k a l i - s i l i c a reaction, which may also occur slowly and form l i t t l e gel. In my mind the absolute distinguishing factor is that the reaction is one that takes place between alkali pore solutions and phyllosilicates, instead of one taking place between alkali pore solutions and "thermodynamically metastable s i l i c a . " This may be d i f f i c u l t to prove in many instances, since both categories of reactants may be present in the aggregate. The proposed a l k a l i - s i l i c a t e reaction category is distinguishable from distress due to swelling of (usually fine-grained) clay in weak, clayey aggregate due to water absorption; such response does not require the presence of alkaline solutions, and indeed would be inhibited by alkali solutions as concentrated as those found in the pores of concrete made from high alkali cements. I f , as Mr. Mather suggests, there may not actually be any reaction between alkali pore solutions and phyllites then the category invoked is an empty one

CCR 6, 549 (1976). 815

816

Vol. 6, No. 6 S. Diamond

and we are wasting our time. However, competent workers have reported cases in which such reactions do seem to occur and give rise to distress in concrete. I f these reports are correct, then the new category is "useful" to prevent further confusion. This does not mean that we understand the mechanisms involved in such reactions; and as Mr. Mather r i g h t l y pointed out, I do not think that the suggest. ions so far advanced are p a r t i c u l a r l y convincing. I t r u s t that this restatement c l a r i f i e s the points raised by Mr. Mather and appreciate the opportunity to make the c l a r i f i c a t i o n . In private correspondence Mr. Mather has kindly pointed out several typing errors in the references of the original paper as reproduced in CCR, for which I apologize. The errors are as follows: I.

Reference 4 should refer to "Part 14," not "147."

2.

Reference 9 should be date 1975.

3.

Reference 12 should be page referenced to p. 87.

4.

The f i r s t author of Reference 16 is Robert Folk, not Falk.