Flowing without loss: SCG challenges the traditional beliefs about grout

Masonry Construction, Sept, 2004 by Rick Yelton

Have you ever worked a project where you needed to do something different in order to make a profit? B.J. Grubbs, a foreman for Del's Masonry, a Denver-area contractor, recently had that very experience.

Work was progressing nicely on the new Eire (Colorado) Junior/Senior High building. Walls were going up smoothly and workflow seemed steady. But an unanticipated change in the general contractor's schedule presented Grubb's crew with a new problem.

To keep the project on schedule, Grubb's crew needed to quickly complete a set of high, grouted interior walls. Not only was there the problem of completing the higher lifts ASAP, but here was the additional hassle of limited head space under the roof. "We decided that our best plan was to erect the wall and then pump grout from the top in high lifts," said Grubbs.

The contractor called his supplier to set up the grout pours. Learning of the challenge, the ready-mix concrete salesman suggested trying something new called self consolidating grout (SCG) to help speed up the process. "The suggestion caught me by surprise because we normally ordered the basic 3/8-inch pea gravel mix," said Grubbs.

The change order required approval of the GC's engineer, so Grubbs prepared a test panel using the new grout product. Grubbs first impression wasn't all that memorable. "When it first came down the chute, the mix looked a little rockier, but not that much different from what we normally used," stated Grubbs.

But when the real pours came, Grubb's opinion of the new product was much different. Despite its harsher look, the product flowed very well and moved easily using a 3-inch trailer pump.

But it was on the wall where Grubbs noticed the major difference compared to conventional masonry grout. The new product made that portion of the job go a lot faster, according to Grubbs As the grout filled the cells, the SCG kept its composition and the crew didn't need to vibrate the mixture to keep it moving. "It flowed through the tightest reinforcing cell,' said Grubbs.

There was another benefit from the choice to go a different grout way. Strength gains on the compressive tests were excellent. The GC was happy because after 7 days, the grout had the strength it was supposed to have in 28 days,

"I can't say SCG is the most exciting innovation I've seen in 30 years as a mason, but it sure did make that job go much better," remembered Grubbs.

The SCG Grubbs was referring to is a new concept in mix design that is slowly being introduced into selected markets. SCG is an engineered construction material that is based on a mix design technology developed for its cousin, self consolidating concrete. Mason contractors in many areas now have the opportunity to use an engineered material for a grout designed to increase flowability without sacrificing compressive or bond strength.

The theory and technologies behind self consolidating materials are the hottest topic in the field of concrete mix design. The technology to craft performance mixes is gaining wide acceptance. For example, since self consolidating concrete mix design technology was introduced to the marketplace about 4 years ago, it has captured more than half the yardage of the precast concrete production market.

Marketing a high-performance material like SCG to masonry contractors will be a tough sell. After all, ready-mix producers and admixture manufacturers have been touting superplasticizers and grouting aids for many years.

SCG is truly different. The engineering concept behind SCG combines gap-graded aggregate gradations and polymer admixtures to achieve fluidity and workability. The result is a grout that performs the same way with each pour. It might be something you can use to solve your problem.

Flowing paste

Experienced mason foremen like B. J. Grubbs know how "good grout" looks. It is a paste-like substance that spreads evenly when placed on a horizontal surface. Another quality of good grout is that after it spreads on the surface, there isn't an outer ring of bleed water.

But achieving this perfect mix consistently is hard. Sometimes there is consistency changes from truck-to-truck. Or if the pour goes slow, even the material in the truck can change.

These cases are where the science used to create SCG fits in. Material design engineers have developed a product that meets even the toughest inspection of the mason contractor's most experienced foreman.

Engineers are in the process of developing ACI and ASTM definitions for SCG. Based on a definition for self-consolidating concrete currently under ballot at ACI, "Self-consolidating grout can flow around reinforcement and consolidate within a wall or column under its own weight without additional effort, while retaining its homogeneity."

Mason contractors need to review three key points in this definition.

First, according to the definition, SCG meets the specifications for grout as outlined in ASTM C 476-02, "Standard Specification for Grout for Masonry." SCG can be either fine or coarse, but in most cases it is course. And it must achieve a 28-day strength of 2000 psi, and it must be proportioned and mixed following the standard's requirements.