For what you are doing, its probably marginal, however we know that this material, subject to any deviation from a designed and tested mix, can and will produce adverse results. Technically speaking, it needs to be done within a certain tolerance ie; additional water for lower slump, admixtures, pump design mixes and so on.
If in fact that amount of portland has begun the hydration process, (clumps) you have "technically" changed the water/cement ratio for the measured quantity in the bag. How much, well that depends on how much of the mix absorbed enough moisture, and I suppose, chemically, you could determine how much of the portland has reacted or how far along its been hydrated. Thats putting things under a microscope, and I think all who participate in the discussions you have posted (which I find highly interesting, and enjoy participating in) realize that most things you are doing, it just may not make too much difference. Its still an unknown to be honest, only way to really know is testing.
If in fact a certain portion of the portland in the bag, be it clumps or not, was compromised, its hard to say for that particular measured quantity, how much tolerance there is for something like that and what the result would be for compressive strength. This would be an interesting test, like (remember Puddles ?) did with the welding processes and the bending/breaking etc. You could create test cylinders per ASTM criteria, from the compromised mix, say after the clumps were pulverized and dispersed evenly into the mix. Break tests would prove out its effect on compressive strength, and that would truly answer this question as to the effects on a small measured quantity of an already designed and tested mix. I think it would be more along the lines of less portland cement in the mix. I also look at it from another view, it could also then be inert, weakened, to the point where its just filler, or an increase of small fine aggregate, which if was done to a design mix, you would proportionally have to add more portland to bond more aggregate, very small fines in this case. The mix is a uniform and measured quantity of all materials, change things and its performance may easily change as well, requiring testing to determine the results. I think what was in the bag has the possibility to bind, just maybe not as strong as if it were new material.
In the construction industry, with a stuctural material such as concrete, anytime there is deviation, or any compromise of this material, in my mind, a red flag pops up, hence my views as posted here, its just something you do not fool with. At home or in non critical situations, it may be fine, but I did see you took high notice of results or performance with this material where it spalled or did not perform abrasively, given what you describe. That is precisely why we do not, in good project management practice, tolerate deviation with concrete unless the engineer of record approves and it proves out through ASTM test criteria.
I did see mention of a wire brush being used, this may leave iron deposits onto the abrasive material, and leave rust stains, often times with masonry you want to use another brush type, so as not to leave rust stains.
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