Iano's backfill

Self-Consolidating Masonry Grout

PCA Masonry Today (Winter 2004/2005) devotes its two main articles to a relatively new material self-consolidating grout (SCG). Like its close relative self-consolidating concrete, SCG is a cementitious grout material formulated with special additives to achieve very high-flow, low-slump properties without the addition of excess water to the mix. The most significant benefit of using SCG in grouted masonry construction is its ability to flow easily through complex, extended void spaces and around densely spaced reinforcing within the masonry assembly. This simplifies the masonry construction, speeds the grouting process, and greatly reduces the chance of voids or partially filled cores in the completely construction.

According to Characteristics of Self-Consolidating Grouts, an SCG mix has a lower water-cement ratio and includes superplasticizing admixtures (polycarboxylates) to increase its workability or flow in comparison to conventionally formulated grout. When the standard test for slump is applied to SCG, the test is more accurately termed a “flow test”. When the test cone is lifted, the SCG typically spreads out in a shallow pool or “pat” roughly 22 to 30 inches in diameter. In addition to verifying adequate flow, the pat is also checked for absence of segregation, bleed water, or aggregate clumps--all signs of deficiencies in the mix that could lead to poor quality in the finished construction.

Other common tests that are used to ensure the quality of both conventional grout and SCG construction include compressive strength testing of cured samples, and the post-placement inspection of strategically located openings in the masonry assembly to confirm the full flow of grout throughout the intended spaces within the masonry.

Grout Goes Straight on Prison Project discusses additional benefits of SCG in grouted masonry construction. While SCG itself may cost 8% to 11% more than conventional grout, it can be placed in roughly half the time. This reduces off-loading time for the ready mix trucks that deliver the grout to the construction site and speeds construction. Additional labor savings accrue from the absence of any need to vibrate SCG to ensure proper consolidation, and potential savings in the simplification of the masonry construction due to the high-flow capabilities of SCG.

More information
Grouting of reinforced brick masonry construction is discussed on page 294, and grouting of concrete masonry unit construction on pages 324 - 328 of the textbook. Additional information is also contained in Chapter 10, Masonry Loadbearing Construction.
The concrete slump test, the compressive strength testing of test cylinders, and the use of self-consolidating concrete are discussed on pages 477 - 478.

Light-Transmitting Concrete

Concrete casts new light in dull rooms, Optics.org, 11 March 2004, reports on a new concrete composite with optical fibers that is reportedly as strong as traditional concrete but also highly translucent. Dubbed LiTraCon, the material consists of cast blocks with an embedded array of optical fibers that allow light to pass through walls constructed of the material. According to twenty-seven year old inventor Áron Losonczi, “Thousands of optical glass fibers form a matrix and run parallel to each other between the two main surfaces of every block. Shadows on the lighter side will appear with sharp outlines on the darker one. Even the colours remain the same.”

See also Luccon.

Pop Quiz!

The accompanying photo shows a reinforced concrete masonry wall under construction. When the author observed this wall during a recent site visit, he immediately instructed the contractor to take corrective action.

Can you identify the problem and what corrective action was required? Use the comment link below to submit your answer.

Hints: No work is currently taking place on the wall. The problem is nonstructural, and does not relate to temporary bracing.

Masonry/Tilt-Up Hybrid Construction

Masonry or Tilt-Up?, Concrete Construction November 2003, reports on a new system for combining unit masonry elements into tilt-up concrete construction. The system, licensed under the Chameleon Cast Wall System name, opens up new possibilities for facing concrete walls constructed using the tilt-up method.

For an explanation of the tilt-up concrete construction method, see page 537 in the textbook. Tilt-up's main advantage is its cost savings through the elimination of most of the usual formwork required for wall construction.

In this new hybrid system, concrete masonry facing units are first laid face down on the casting bed. These unit facers are specially-fabricated 2-inch thick concrete masonry units with keyed backs. Next sand is broomed into the joints between facers, to prevent the concrete that will be poured next from seeping through to the face of finished wall. Subsequent construction follows normal tilt-up procedures: first placement of reinforcing, then concrete placement, and after initial curing, raising of the cast wall section into position.

Masonry unit facers for this hybrid system can come in any of the various finishes, textures, and colors normally available with standard CMU, and can be laid up in any pattern or bond. Chameleon Cast Wall licenses the system to facer manufacturers. They also provide test data documenting the system's durability and structural performance, and provide construction crew training.

Debate Over Fire Testing

The National Concrete Masonry Association's Fire Safety page provides a provocative collection of information related to fire-resistant construction, the relative merits of masonry construction in comparison to more light-weight materials, and the responsibility of design and construction professionals for building safety. For any instructor looking to bring an added dose of currency and relevance to their classroom, this page offers a great opportunity for classroom presentation, student research, and discussion. A few of the most interesting items on this page include:

• Are Architects, Engineers and Code-Writing Officials Friends of the Firefighter?, by Vincent Dunn, Deputy Chief FDNY (ret.), argues that the building industry and design profession have been complicent in a gradual decline in building safety standards. This is a challenging, yet worthwhile article.
• NCMA Fires at Gypsum Wall Assemblies provides a thorough and clear description of the ASTM E 119 fire-resistance test, and challenges whether this test is appropriate for comparing the relative fire-performance of masonry and gypsum wallboard partitions.
• Fire Video (Windows Media Player or Quicktime) is a 6-minute video that includes dramatic footage of both gypsum wallboard and masonry partitions undergoing ASTM E 119 testing.

This image shows a gypsum wallboard partition subjected to hose stream testing as part of an ASTM E 119 fire-resistance test.

The debate surrounding ASTM E 119 seems to focus primarily on the hose stream portion of this test, how and when it is applied, and what it is meant to simulate. For an alternative point of view regarding the role of the hose stream test in E 119, see for example, The Gypsum Association's Fire Resistance Testing topical paper. This paper draws on historical background and comparable international standards (that have dropped hose stream testing) to suggest that the masonry associations may be misrepresenting the importance of the hose stream test in assessing fire resistance.

See also this site's wtc archive for additional articles related to lessons from this event.

09 - Concrete and Stone Masonry Links

This article contains external links to resources on the Web relevant to Chapter 9 Concrete and Stone Masonry.

MasonrySystems.org

The industry association-sponsered web site provides a useful variety of information regarding wall system selection guidelines, wall system examples, and more.

NCMA Concrete Masonry Fire Safety

National Concrete Masonry Association downloadble articles and video discussing the performance advantages of masonry-constructed fire partitions. The free video provides an excellent overview of the ASTM E-119 fire test in action. This site provides many more useful resources.

NCMA e-TEK

National Concrete Masonry Association's technical information bulletins related to masonry design, construction, materials and evaluation