concrete grinding

[a2mfk]

A couple of weekends ago I rented a grinder to do a couple of different jobs. While I had it I took care of a troublesome control joint at our office with about a half inch of vertical displacement, it was quite a tripping hazard. Anyway, I thought this was an interesting cross sectional view of a typical concrete slab. There was a lot of aggregate and larger diameters, and this concrete compared to other slabs I have ground before was exceptionally durable and abrasion resistant. There was almost no edge chipping, and it took about 20 minutes of back and forth grinding just to do about four feet, about 5 times longer than similar joints.

Anyway, this is what it looks like if you ever specify grinding down the joints on one of your jobs. It is pretty easy to create a smooth transition across the joint, but it does look a bit odd because of the color change. I think a whole slab done like this and then a clear seal would be an awesome looking floor or patio, industrial looking, and similar to terrazzo.

 

[a2mfk]

another view

 

[Ron]

two different concrete mixes. Either a repair with good bond or separate truck with different mix placed while concrete on right still plastic.

Agree.…..makes nice surface

 

[a2mfk]

Sorry about my explanation Ron, it wasn't very clear after I reread it. I meant that this concrete, for whatever reason, was exceptionally tough compared to the other concrete slabs I have ground before. I only did one joint at our office, which was built in 1969. They must have had some really good limestone aggregate, and a lot of it over 1" diameter, and as you can see the coarse aggregate was dense. We did a few joints at a coworker's house, and did 5x the lineal feet in half the time, it wasn't nearly as tough.

The other odd observation came when I was grinding the surface of a kitchen and adjoining laundry room, and the kitchen was such a pain in the butt and slow going, but the laundry room was a breeze, much softer material. Now the only thing I noticed was the linoleum I removed from the kitchen did not come up easy and I had to scrape a lot of glue and material off of it, while the laundry again was a piece of cake with the linoleum peeling right off and no residue left on the slab surface. I wonder if the glue was the difference and had gotten into the concrete pores in the kitchen and had greatly increased the abrasion resistance? Anyway, I really wish I had rented the scarifier instead of the rotary grinder.

 

[Ron]

a2....older concrete can be extremely tough! The scarifier would have given you a much rougher surface finish!

Concrete in your area in the 60's and 70's was produced from limerock from the Newberry and Ocala areas. Those formations are dolomitic and contain a lot of flinty chert particles, therefore many areas were harder than the formations in south Florida and in some cases even harder than the Brooksville aggregates. Also finishers hadn't learned about adding water 'till you had soup. They actually cared about quality. Imagine that.

 

[civeng80]

Them were the days for real concrete.
Probably 4:2:1 mix and mixed by hand.