Got one client that’s having trouble with their Redi-Mix company. That company swears that their only pump mix is a 2″ slump, 4000 psi and people run that through 2″ hoses and spray it for pools and such all the time. My local concrete guys were concerned that the 3″ slump we specified for my stairs wouldn’t even make it through the hose–no way they woulda allowed us to order 2″ slump. The company in question down in FL won’t change the mix unless the client signs a waiver relieving them of responsibility. Clients also specified 3/8″- gravel and got some 1/2″+ in the sample. They’re worried about pumping this.
Anyone have any insights? Any explanation of the different things being said by each company? I’ve never had this happen with a Redi-Mix company before.
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I won't be much help, but some 1/2" stone thru a 3/8" screen is a given, (and it isn't gravel, it is stone. I also suspect it is crush, and some 1/2" will get thru, especially if the screens are worn).
As for the slump, they say they pump it all the time, where is the problem? Are they saying they can't do 4k lbs if you increase the slump? Do you need 4k? Is the site going to dictate a greater slump to pump well?
Sorry for 3 questions for every answer, but that is the norm for me.
They don't say THEY pump it...they say PEOPLE pump it. The 4000 psi is standard for a pump mix from what I've seen. But 2" slump is not standard from what I've seen. The test batch dropped off at their site (from a 2 yd batch) didn't look to them like it'd pass through ANY pump. I wasn't there, so I'm working with second-hand info. They're on a tight sched and worried that getting 6 yds of a too stiff mix will throw them off and have a domino effect. So I guess what I'm looking for is evidence that other people regularly pump/spray their mix for a 2" hose at a 2" slump.
OK, I'm learning. Recommendations for shotcrete seem to be 2" to 6" slump (or, 3-5 depending on who the "expert" is), typically (by some) with 2" as delivered by the truck, adjustable on-site to address local conditions, such as type of aggregate, pump, etc. If the Redi-Mix company says they'll deliver it at 2 and allow on-site adjustment (as they did on their test batch) then they seem within the parameters of what I've learned elsewhere.
I think most readi-mix companies are not dealing with the low-slump work that you do. Most pumping is with a high slump for slabs. A piston type pumper should handle a stiff mix with the low slump you need without problems....that's not a mistake, it's rustic
I suppose, one would ask the person who is pumping the mud. Around here you will either pump a grout mix with no gravel/rock in it, just sand, for the gravel would ruin the pump, hose is I believe 2", or you would pump redi-mix/concrete with a boom truck, with either a 4" or 6" hose. Both of these guys want the mud wet, the wetter the better. Best of Luck in your research, Jim J, I'am not real clear on the waiver, just what all is guaranteed in the first place. I do understand the more water, less strenght, whacha doing with it??