Today's Non-Shrink Grouts
Well before Orville and Wilbur Wright took to the air and changed the way our nation traveled, deep in the smoky environs of America's mighty industrial plants another developing trend was evolving that would have a profound affect on the way manufacturing plants were assembled. That trend was a method by which heavy manufacturing equipment and machinery could be set and aligned to an unheard of tolerance of several thousandths of an inch. Working with little more than a trowel, a bucket, a supply of cement, sand and water, millwrights of that day gave us the foundational principles for what we now call non-shrink grout.
Plant engineers of yesterday and today need machinery and equipment to be stable and well anchored in order to operate efficiently and safely. A special material is needed to fill the space between a pre-set equipment base plate and its concrete foundation in order to effectively transfer the static and dynamic loads of that machinery into the foundation. In the early years plant engineers did not know how to define or specify this performance, but they knew how to test for it. Rather than specifying a material, they required a proof test for the grout being installed. After the grout had been installed and allowed to harden, the base plate was tapped with an iron bar; if it produced a ringing sound the grout was in contact with the base plate and passed. If the sound produced was a dull sound, this indicated the grout had shrunk and was not in contact with the base plate. The dull sounding base plate would then be rejected and become the source of much local discontent.
Dry pack sand and cement grouts
In the early 1900's grout placement techniques assured a low water cement ratio and thus ample strength. Grouts of that day were made up of cement, sand and water. The ratio of the ingredients was a key factor that determined whether or not a grout could be placed without shrinking. The grout was placed between the base plate and the foundation concrete by tamping it in place. This procedure required the grout to have a consistency of damp sand. The grout had to be very cohesive in order to hold the sand grains in place during the tamping operation. This required high cement content. The combination of high cement factor and low water content produced a high strength grout that would not shrink in the plastic state.
Aside from water/cement ratio, there was one other factor that determined whether or not a grout would be both strong enough and also be able to overcome its natural tendency for drying shrinkage. That factor was the way the grout was tamped or packed under the base plate. To properly dry pack a grout, unlike a flowable or fluid grout, a large amount of physical energy is required during the placement operation in order to squeeze out the voids in the grout. If voids are allowed to remain, the grout will not develop its full strength potential as it hardens. All cementitious grouts, mortars, and concretes will undergo a strength increase as their density is increased by compaction during placement.
Dry pack grouts produced during this era were not corrected for drying shrinkage and, over time, would shrink. One might ask, "How did they produce a material that would maintain contact with both the base plate and the concrete foundation?" The answer was quite simple. When grout was dry packed into place it required such force that it caused the grout to become slightly compressed. As the grout hardened and dried out, rather than shrinking, the compressed grout, being somewhat elastic, became slightly less compressed and thus did not shorten in height (shrink). Instead it remained in contact with both the base plate and the concrete foundation. It may be helpful to think of the grout acting somewhat like a compressed spring between the base plate and the foundation concrete.
Those early millwrights with their buckets, trowels and very stiff grout, were able to develop a method for precise base plate alignment that would remain state of the art for many decades. But while the science was good, the art was often lacking. One might say the devil was in the details; the details of getting the grout properly and consistently compacted under the base plate. The quality of workmanship became a very important issue. Not unlike today, there were good crews and there were crews that were somewhat less attentive to details. Many failures were the results of poor workmanship. A more user-friendly method would have to be developed!
A new term, thixotropy, which is the method by which fluid grouts prevented bleeding and aggregates from settling, would redefine non-shrink grout research efforts.
Not only were manufacturers and plant engineers alike concerned about shrinkage, we were also concerned about expansion; when it occurred, and how much. Conditions known as plastic state expansion and hardened state expansion took on new meanings and raised new concerns. Also of importance was working time and shelf life.
ASTM C 1107, the work of many years and many people.
What was needed was a comprehensive non-shrink grout specification. The work of ASTM in developing comprehensive specification for the construction industry was now need. It became the task of ASTM to provide us with just such a specification for grout. I can personally attest to battles that took place in the ASTM's subcommittees in which non-shrink grout specifications and test methods were conceived and written. We had only our experiences and observations to build on. As I remember, the hours were long and the tempers were often short. After 15 years or so, we came to a consensus of opinion and published three documents: ASTM C 1090, the test method for determining the volume changes of grout in the hardened state; ASTM C 827, the test method for determining the volume changes of grout in the plastic state; and ASTM C 1107, a comprehensive non-shrink grout specification soon became recognized worldwide as "the non-shrink grout specification".
Many non-shrink grout manufacturers used this information as a benchmark for product development, even before it was passed. It was not until 1989 that ASTM C 1107 was finalized and published. With ASTM C 1107 in place, many of the questions raised by this new technology were answered. Soon after ASTM C 1107 was published, The U.S. Army Corps Of Engineers replaced the content of CRD C 621, their older specification and the industry standard up until that time, with ASTM C 1107.
These new grouts no longer depended on the rusting of iron or the production of gas to produce expansion. These new systems, for the most part, used the knowledge of the chemistry of cement to produce expansion in the cementitious portion of the grout. Free water and aggregate were held in place by a new thixotropic mechanism. This new technology gave us a non-shrink grout that could be economically poured into place, that would harden in contact with both the base plate and the foundation concrete, and expand after hardening, compressing the grout. In spite of its early fluid consistency, the compressive strength of many of these grouts was twice the foundation requirements. These expansive thixotropic cementitious grouts not only met the principles that the "bucket toting millwright" had proven many years ago, but also gave us a non-shrink grout that was very much less dependent on the skill of the installing crew and therefore much more consistent and reliable.
L&M grouts are a result of the past with a strong look to the future With all the improvements made over all previous systems, there was still one common shortcoming: all but one of these grouts had short working times of less than 20 minutes. That exception was CRYSTEX by L&M Construction Chemicals. Early on in its development program, L&M learned the secret of designing and producing a non-shrink grout that met all the requirements of ASTM C 1107. Equally important was its response to the needs of our installing contractors with a long working time grout; one that could be placed for up to one hour in a wide placement temperature range of 45° to 100°F. This proved to be a significant labor saving feature for the installing contractors and made CRYSTEX the favorite of both plant engineer and millwright alike. Later on, L&M continued to meet the needs of its contractor customers, by producing a fluid non-shrink grout with a shorter working time and but with an extended trim time. That product, PREMIER, is a precision grout that allows producing a non-shrink grout that met all the requirements of ASTM C 1107. Equally important was its response to the needs of our installing contractors with a long working time grout; one that could be placed for up to one hour in a wide placement temperature range of 45° to 100°F. This proved to be a significant labor saving feature for the installing contractors and made CRYSTEX the favorite of both plant engineer and millwright alike. Later on, L&M continued to meet the needs of its contractor customers, by producing a fluid non-shrink grout with a shorter working time and but with an extended trim time. That product, PREMIER, is a precision grout that allows the early trimming of grout shoulders. Many years after their development, both CRYSTEX and PREMIER are still on the cutting edge of technology providing plant engineers the reliability of state of the art grouting technology, while saving contractors money by reducing material wastage and reducing valuable placement time.
© 2001 L&M Construction Chemicals, Inc. | ConcreteNews Spring 2001.