mortar vs grout in block cells ?? 1

[boffintech]

The code limits the size of mortar protrusions in the cells and requires that the cells be reasonably clean prior to grouting. The code even refers to mortar droppings as "debris".

Masons invariably argue that type S mortar has a higher compressive strength than grout so it doesn't matter that 4to6" of mortar is slopped in the cells or that there are giant mortar protrusions.

Why is their argument invalid?

ACI-530 SPECIFICATION FOR MASONRY STRUCTURES 3.5 E. Consolidation — Consolidate grout at the time of placement.

1. Consolidate grout pours 12 in. (305 mm) or less in height by mechanical vibration or by puddling.
2. Consolidate pours exceeding 12 in. (305 mm) in height by mechanical vibration, and reconsolidate by mechanical vibration after initial water loss and settlement has occurred.

ACI 530 COMMENTARY ON SPECIFICATION FOR MASONRY STRUCTURES 3.5 E. Consolidation — Consolidation of grout is necessary to achieve complete filling of the grout space. Reconsolidation returns the grout to a plastic state and eliminates the voids resulting from the water loss from the grout by the masonry units.

ACI 530 SPECIFICATION 3.2 D. Debris — Construct grout spaces free of mortar dropping, debris, loose aggregates, and any material deleterious to masonry grout.

ACI 530 COMMENTARY 3.2 D. Debris — Continuity in the grout is critical for uniform stress distribution. A clean space to receive the grout is necessary for this continuity. Inspection of the bottom of the space prior to grouting is critical to ensure that it is substantially clean and does not have accumulations of materials that would prevent continuity
of the grout.

 

[concretemasonry]

boffintech -

You have a hit a hot subject when it comes to cleanliness/applicability of grout cells. Everything you cited from ACI 530 is totally applicable. A practical condition exists in the intellegent application of the standard.

In general, it makes little difference whether the mortar is Type M, S or N. Grout is not used for the strengthening the wall for compressive strength purposes. The masonry units really control this. The grout is used to transfer the loads in the rebars to the masonry units and vice-versa. Strong grout is not necessarily better.

What is really required is that the bottom of the cell is reasonably clean. A few solid chunks do little to prevent the bond. Obviously, 4-6" of even 10,00 psi chunks is grossly excessive and a sign of poor workmanship.

Excessive mortar extrusions do not decrease the wall strength, but they can interfere with complete grouting if proper prcedures are followed.

A bigger problem occurs when the wrong shape units are accepted or not specified for use. Designers rarely are concerned with the shapes that can be used for superior quality construction. There are units that are completely modular when it comes to cell alignment that makes grouting much easier and can cost. Too often, U.S. designers are in the "Dark Ages" in this area and many block producers are guilty of the same error. Foreign (non-U.S.) engineers often shake their heads at the details and practices they see here. Some were coming out of the Russian/East European countries that are trying to improve their traditional precast construction by using more masonry.

The consolidation, placement methods and new materials are in a state of flux from a code standpoint, so the current ACI 530 is the way to go unless it comes to accepantance of other newer materials and procedures.

Unfortunately, some of the present grouting practices are a carry-over from the period when grout was used to increase the compressive strength of the wall when the masonry units did not have sufficient uniform strengths. Bacause of this, the poor habit of over grouting and not enforcing practical limits has been continued.

I have been seen complexes of 15 to 20 story loadbearing buildings where there was superb quality control and virtually no clean-outs were used because of excellent plans and the use of good training, inspection equipment and techniques. - Unfortunately, the U.S. has not caught up yet.

Dick

 

[hokie66]

The mortar droppings are not compacted, and are in truth debris. When you clean them out, they can usually be removed by hand. Compacted grout is required to provide bond for lapping bars.

 

[concretemasonry]

The loose mortar spillage is debris and the question is what is allowed for the structure. Obviously, the old practice of cleanouts, washing, flushing and dusting is a little on the obcessive side and unnecessary.

The right design, construction practices coupled with the right units and good inspection can eliminate the need for cleaning. They do it internationally, why not here?

 

[hokie66]

They may "do it internationally" in some countries, but in Australia we still use cleanouts. Our masons are sloppy, and nothing will change that.