Masonry Grout Specimen testing

[sapperDAK]

I am in the process of revising our report format for compressive strength testing of masonry grout specimens to bring it in compliance with the requirements of ASTM C 1019. Unfortunately, I cannot find any documentation of how to describe the failure of grout specimens, as required in paragraph 12.1.8 of the Test Method. Unlike concrete cylinders, which have clearly indicated failure types (1 thru 6), I cannot find any similar graphical depiction of grout specimen failures. Can someone tell me is this description intended to be a narrative entry on the strength test report or is there a standard graphical depiction?

 

[Ron]

If you are using cylindrical specimens, they can be described the same as for full size concrete cylinders.

There are generally only two descriptions for a cube failure: cone and shear

 

[concretemasonry]

You should not be using samples cast in non-absorbent molds, but should use the recommended sample cast methods described in ACI 530, which are the industry basis for most modern masonry testing.

The code and specifications commentary may give you some insight into the specifications.

Strength is not normally a factor unless it gets too high, but you need some sort of "hook" to hang your hat on. A call to one of the engineers at the National Concrete Masonry Association (NCMA) may be able to give you some information since they sit on all the codes and standards committees. If there is something missing in the ASTM procedure, it will give them an opportunity to make changes in the current ASTM standards.

Dick

 

[BigH]

I've noted on many of our small cubes that we get "columnar" looking failures. We are testing the "cast" faces (i.e., turnin the cube on its side.)

 

[concretemasonry]

sapperDAK -

The failure description (12.1.7), is only narrative.

Section 12.2 refers to information on the masonry units used to make a suggested masonry unit molded shape. That is for the engineer to determine if the mold is compatible with the units the wall is built from.

If you are using a "non-standard" mold system such as non-absorptive molds, you must fully describe (Section 12.3) the molds, sizes and proportions, correction values and coefficient of variation so the specifier can determine if it complies with the specifications that are based on the the molding method described in detail in ASTM C1019.

There is always the danger of falling into the trap of treating grout as concrete samples are treated. Concrete is placed in non-absorbent forms, while grout is placed in forms (masonry units) that absorb the excess water. Grout testing is an attempt to identify the grout in place.

All design methods, codes, specifications and testing standards are based on the tradition methods supported by years of documentation. Because of the combination of high required water contents and absorptive, it is a totally different "animal".

The grout is meant to transfer the loads from the masonry units into the steel reinforcement and are not intended to to increase the vertical compressive strength on the masonry wall. If the grout is too strong the properties of the wall are different when constructed and the load distribution is different and can lead to unpredictable failures.

If non-absorptive molds (steel, coated cardboard, etc.) of different aspect ratios, the results could require a higher strength, which is not desirable. This is the reason for the extra documentation on the mold configuration, dimensions, corrected compressive strengths and coefficient of variation, that is a source of complication and increased lab liability when the results must be compared to the methods described in C1019.

Dick