grout vs mortar in reinforced masonry

huangyhg

grout vs mortar in reinforced masonry
i am looking for an article that a contractor (he is bright, but not an engineer) could read to give the reasons why it is important to make sure that grout is used to fill the cells of reinforced masonry rather than the cells being simply packed with mortar.  he tells me that mortar is used for this purpose all the time and he has never seen a problem with it.  he says that without evidence of problems, it will be a hard sell to make sure his subs use grout the right way.  does anyone know of something that i can show him that shows the actual in-use effects in a wall built this way?
i have plenty of small articles showing the importance of vibrating the grout to make sure it fills all voids, but nothing to show that replacing the grout with mortar has had adverse effects on strength or durability.
the building code will point out that grout is required and what astm spec it must meet.  i imagine you would have similar requirements in your code if you are not in the us.  if mortar does not meet the required astm it cannot be used, per the building code. done.  do note though that mortar is commonly used to fill the cells of reinforced fence brick.  
go to maconline.com, click on "grout", then on "what is grout".  here you find that grout has a slump of 8 to 10 inches, mortar, 5 to 8 inches.  the difference is that grout can be poured and will fill the cells, while mortar is too stiff and will leave voids that weaken the wall.
engineering -
refer the "well meaning" contractor to the national concrete masonry association tek note series (ncma.org).
there is no reference in any building code i am aware of that allows mortar to be used as a substitute for grout in filling cmu cells. contractors do it all the time but that doesn't mean its correct.  i would expect that mortar used to fill cells will shrink more and bond less well to both bars and block than properly placed coarse or fine grout.  
if you specified the specified strength of your structural masonry construction (f'm) and it's 1500 psi or higher....
the masonry won't qualify as structural masonry unless f'm is met and usually by unit stength design.  the mortar, probably "s" won't by definition cover this.  so... now the contractor is taking the project in the direction where unit strengths must be met by field testing in order for code to be met.  now the contractor has to feel comfortable enough that his mortar will meet grout spec by field testing(probably 2000 psi for f'm=1500psi which is the most typical).  
the reality of the situation is that you might shoot yourself in the foot trying to get the masons to change their practice.  i've seen a bunch of times where grout-as-you-go masons just can't deal with pumped grout and you would have a better product if you just let them mortar it in. some masons will try to skip bond-beams in inconvenient locations for scaffolding or too near another bond beam when truck grout comes. that is just one example of many possibilities.
in my experience, (this may raise some eyebrows) the mason should have no issue with working in a batch of site grout every couple of courses by mixing portland cement in lieu of mortar cement or masonry cement. with a good mix (use the damn measuring box!) and occasional grout compression test specimen, you should get above 3000psi and feel comfortable justifying f'm.
i know you shouldn't allow them to substitute concrete for grout because it doesn't bond to the units. it may be that you also get a reduced bond with mortar when compared to what is required for grout.
units meeting the astm c90 minimum strength and mortar meeting astm c470 requirements can be assumed to have a f'm of 1500 psi. from a practical standpoint, mortar has a very minor effect on prism strengths(f'm) when compared to the unit strength of the cmu, if you use the prism test method.
by all means avoid getting highter strength masonry by using high strength grout and/or mortar. it is far more economical, safer and easier to justify and test by using higher strength masonry units. this puts the higher stregth material at the out fibers of the section and eliminates the errors of using an average strength. - cmus can also be tested before they are in place, resulting in increased reliability, which is a luxury you do not have with many other materials like concrete.
the reason for using grout and not mortar is because of specifications! - it is as clear as that.
mortar is designed to be workable with a trowel, not to "fill" voids. grout also makes the constructability of the wall more reliable because of the ability to fill all the voids and the proven lower in-place shrinkage.
additional
i bet my house the blocks are on-site already.
i'm assuming the mortar mix is a 3:1 sand to cement mix (mortar cement or masonry cement).  i think that's a safe assumption because that is the easiest (and i think cheapest) to do.  switching the masonry/mortar cement bag to a bag of portland makes  fine grout per table 2103.10 of the ibc, not concrete.  ok, so it's still concrete... but it's not hi-test.
if i'm wrong,... that's my landlord's problem.
haynewp:
i've never heard that concrete should not be used for grout and i've seen a lot of masonry constructed with 3,000 psi for grout.  
astm c476 specifies that portland cement is an acceptable cementitious material.  the only other requirements in c476 is the cement to aggregate ratio, and a minimum compressive strength of 2,000 psi.
if that is the case, then what exactly is the problem with using 3,000 psi concrete as grout?