Masonry Magazine October 1995 Page. 41
MASONRY BOND STRENGTH
Continued from Page 22
Conformance to ASTM C 270 provides best available technical input as to mortar preparation, yielding optimum bond strength without affixing a minimum bond strength criterion.
Compliance with Industry Association recommendations address specific considerations, such as unit laying procedures and care of masonry during and after completion.
Examples include prewetting absorptive brick, unit laying techniques, tooling of joints, and cleaning of completed masonry. Although recommendations are not mandatory, unless required, these recommendations form the industry standard.
The method of unit bedment deserves special attention. To attain maximum bond strength, mortar must completely "wet-out" the units surface area, so extent of bond is complete. Furrowing, although common, and beveled mortar joints to reduce mortar droppings must be balanced with complete extent of bond desires.
Full head and bed mortar joints, with intimate contact between the two materials, are desired. Joint cut-off and tooling, further promoted extent of bond.
Protection of masonry, from a bond strength consideration, involves assisting the materials of construction perform in their intended manner. Masonry segments exposed to drying conditions require moist curing: masonry segments exposed to freezing conditions require protection, such as heat during the early period after construction.
Recommendations
It's recommended that all in the masonry industry recognize those specification requirements that indirectly influencing bond strength. These should be faithfully practiced. These recommendations include:
Designers should select masonry mortar type for specific applications using Table X1.1 in ASTM C 270, while avoiding high strength mortars to promote workability, intimate contact of mortar with unit and extent of bond.
Masonry contractor should request and receive Certification of Compliances for all all masonry materials. The Certificate should reflect test results of material showing compliance with a national standard.
Dealing with Conflict
CONFLICT HAS TAKEN ON negative connotations, but the truth is conflict is neither good nor bad. Conflict is a natural by-product of human interaction. In fact, it can stimulate creativity and increase motivation. It's all in how you manage conflict.
How should you deal with conflict on the job? Typically, managers choose one of three strategies. I'll discuss each in turn, moving from the least effective to the most effective.
Compromise-The least effective strategy for dealing with conflict is compromise. Conventional wisdom says that if you want to work with people you've got to compromise. But if everyone gives in a little, that means no one gets what they really want. Sure, you can compromise on unimportant issues. In most cases, however, it's impossible-or impractical to compromise on anything serious.
Competition-Outside of the firm, competition is desirable. Inside the firm, however, it's not desirable. We don't want one team to win over another. This is the problem with using sports analogies on internal issues. Competition isn't about how you play the game, but rather who wins. When Dallas humiliated Buffalo in the Super Bowl, Buffalo didn't come out as the second best team in the country. They came out as losers.
Collaboration The most effective strategy, and the one that requires the greatest amount of time, is collaboration. Only through collaboration can you build the essential team ingredient-trust. Trust is the best predictor of an individual's satisfaction with a company. Without trust, team members can't be counted on to do their part.
If you manage conflict on important issues with compromise or competition, you'll find that relationships within your company will deteriorate. Collaboration is the only strategy for successfully dealing with conflict over the long term.
Mix mortars for 3 to 5 minutes in a mechanical batch mixer. Avoid prolonged mixing, especially when air-entrained materials and cold weather conditions are common.
Mix mortars with maximum amount of water to produce a workable consistency.
Recognize bond strength of mortar to masonry unit as a significant but numerically evasive property of masonry and comply with general requirements incorporated within specifications to promote bond strength.
Know performance characteristics of materials so masonry performance can be upgraded. Avoid rapid drying of early age masonry: moist cure masonry at end of work day when drying weather conditions prevail.
All member of the design, materials and construction team should contribute toward perfecting an understanding of masonry.
"The unfortunate thing about research is that today's knowledge of procedural effects was not incorporated during yesterday's research."
Bibliography
[1] Palmer. L.A. and Parsons, D.A. "A Study of the Properties of Mortars and Bricks and Their Relation to Bond." USDOC BS Journal of Research, vol. 12, May, 1934, pp. 609-644. (Note: credited Figure not contained in document, but mortar codes BVI and CIII are described.)
[2] Kuenning. W.H. "Improved Method of Testing Tensile Bond Strength of Masonry Mortars," ASTM Journal of Materials, Vol., No. 1, 180-202 (March 1966).
[3] Hestrom, E.G., Tarhini, K.M., and Thomas, R.D. "Flexural Bond Strength of Concrete Masonry Prisms Using Portland Cement and Hydrated Lime Mortars," TMS Journal, Vol. 9, No. 2, Feb. 91, pp. 8-23.
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MASONRY-SEPTEMBER/OCTOBER, 1995 41