Masonry Magazine August 1996 Page. 19
Competitive
Depending on the design, steel in the wall is cut anywhere from 15% to 25% for another cost savings. Because most CMU walls are solidly grouted in California, another savings is realized in that thinner walls take less grout. Labor savings were the biggest savings realized when most walls shifted to 8" instead of 12" block.
The Technical Coordinating Committee for Masonry Research (TCCMAR), a research program supported by the National Science Foundation and the masonry industry, has also introduced research information to promote Limit States Design for masonry. This technique of designing walls to actual rate level of capability and performance, not the minimum level, allows engineers to design more economical walls. When the engineer can calculate how a wall will react with expected stresses, he is designing a real wall, not a theoretical case study. Real world designs are more cost effective designs.
Because masonry is a labor intensive trade, the concrete block industry is always looking to create a masonry unit that will reduce labor costs. As our industry grows, new block designs not only provide form but function as well. You will not find as many shapes available in other parts of the world as you do in the United States. Channeled bond beam units for placement of horizontal steel, half units and corners to maintain a running bond, and open ended units to facilitate placing units around vertical steel are just some of the special shapes that have become regular inventory in most concrete block plants.
Mortarless block has also been introduced over the years. By eliminating the head (vertical) and/or bed (horizontal) mortar joints from the wall, quite a labor saving can be realized. One type of mortarless block eliminates only the head joints. This type of unit was approved in the 1985 Uniform Building Code in Section 2404 (d) 4 which states: "Head joints of open end units with beveled ends need not be mortared. The beveled ends shall form a grout key which permits grout within 5/8 inch of the face of the unit. The units shall be tightly butted to prevent leakage of grout." The head joint is the most labor-intensive mortared joint. It takes a quality craftsman to apply the proper amount of mortar to the ends of the masonry unit and then place it correctly in the wall. Tooling the joints after the block are installed is another labor step in completing the wall. Savings of up to 15% on the overall wall cost have been reported on this type of mortarless unit.
Another type of mortarless block is the "dry stack" which completely eliminates all mortared joints in the wall. Some of these dry stack block use either a surface bond system or a grouted cell system to provide structural integrity. By eliminating mortar from the wall system, you can significantly reduce the overall cost of the wall. The expenses of materials needed to make the mortar and of labor costs for producing and installing the mortar are deleted.
The Haener Mortarless Inter locking Masonry Building System is unique in the development of dry-stack technology. It is a three block system composed of a corner, stretcher and half block, all manufactured to exact tolerances +/-1/16 inch in both height and length. The blocks are all made out of the same materials used to make conventional CMU's and meet all the requirements of ASTM C90 which is the standard specification for load-bearing structural concrete masonry units. The interlocking of the units is achieved through specially designed nubs which interlock together within the cell of the block.
In a recent case study on the Haener Mortarless System done in the Portland, Oregon area, the cost of a conventionally built masonry wall was compared to a Haener block wall. The case study used 6 masons and 4 tenders as the work force. The conventional wall took 18 work days to complete while the Haener wall was completed in 6.4 days. This represented a 64% savings in labor costs. Add to this savings the cost of the materials used in mortar and the job cost savings increases even more. And this does not take into account that the Haener System can be laid during inclement weather, which is the source of a lot of job cost overruns.
Finally something has to be said about building materials that use up our valuable natural resources. Concrete block manufacturers looked at this problem many years back and have been quietly creating ways of recovering valuable aggregate supplies. One significant way has been by crushing broken block, brick and concrete to acceptable sieve sizes and recycling this crusted aggregate back into the block. The test results have proved that this aggregate adds a higher compressive strength to the block because of the added cement content. The cities in which these manufacturers operate are also benefiting from this recycling process because now some construction waste can be diverted from the cities overflowing landfills.
Contact the local concrete block supplier in your area for more information about the advantage of masonry for your next project. Gina Adams, Architectural Representative, CDT, CSI, of RCP Block & Brick, Inc., San Diego, Ca. Phone 619/460-7250, Fax 619/460-3726.
MASONRY-JULY/AUGUST, 1996 19