There is movement in concrete. Like other building materials, the unglamorous-if-ubiquitous slabs of cemented stone, slag, and sand constantly expand and contract in reaction to temperature and moisture. Concrete, which provides the basic infrastructure to buildings, dams, highways, and airport runways, tends to buckle and crack.
Working to mitigate structural failures in concrete is a decades-old endeavor that has ushered in a raft of new raw materials. In turn, these new materials have necessitated new chemistry in concrete admixtures--the chemical additives used to add strength, regulate setting time, and guard against the elements. In recent years, environmental and other government regulations have prompted a new round of formulation and the introduction of synthetic chemistry to better manage the mix.
Polycarboxylates, in particular, are gaining wide acceptance as dispersants in admixtures. The polymer chemistry can be used to customize admixtures by regulating flow rate, drying time, and other variables to meet the needs of specific construction jobs. Admixture makers say the new chemistry supports strong and durable concrete at lower admixture usage levels than traditional dispersants such as ß-naphthalene sulfonate and lignosulfonates.
Producers point to cost savings in both the final project and maintenance as justification for the increased cost of advanced admixtures. In most cases, they claim there is an immediate payback in that the new products allow builders to work with grades of concrete that had been unfeasible for any number of reasons prior to the advent of new admixture chemistry.
Polycarboxylate admixtures were first introduced in the early 1990s by Nippon Shokubai in Japan, where building standards address the high likelihood of earthquakes and the challenges of building tall structures in limited areas. Degussa, W.R. Grace, and Sika, the leading suppliers of admixtures in the U.S. and Europe, have since introduced admixtures with polycarboxylates, and observers say the chemistry is starting to catch on worldwide.
"Over the last six years, we have moved into synthesized chemistry rather than selling what historically have been by-products of other industries blended and formulated to enhance performance," says L. Michael Shydlowski, chief executive officer of Degussa Admixtures, the former MasterBuilders unit of the German chemical conglomerate.
The new chemistry has led to more precise concrete formulation, Shydlowski explains. Using natural by-products, such as ß-naphthalene sulfonate, lignosulfonates, and even corn syrup, formulators would sometimes have to add both accelerators and retardants to the same product to regulate performance, he says. The introduction of polycarboxylate chemistry has eliminated this problem. "By synthesizing new chemistry, you are really able to design a molecule that serves a specific purpose," he says.
Polycarboxylates also add strength, Shydlowski says, and cut the amount of water needed to pour concrete by 10 to 15%.
HAVING THE ABILITY to better control setting time is a major advantage, Shydlowski says. "It is more user-friendly, less dependent on a skilled workforce. Frankly, in the construction industry, we are often struggling to get skilled workers these days. People don't want to work in concrete."
Degussa introduced its Glenium line of water-reducing admixtures in 2000. The company has also introduced a line of polycarboxylate additives for highway repair that enables patches to harden to withstand 400 lb per square inch in four hours. The company, which recently demonstrated the performance of the new 4 x 4 Concrete admixtures for Department of Transportation Secretary Norman Y. Mineta, sees fast-setting highway concrete as key to growth.
Degussa has worldwide admixture sales of $900 million and sales growth of 6 to 8% annually, Shydlowski says, compared with 3% overall growth in the U.S. concrete market.
Grace has seen similar growth driven by new polycarboxylate chemistry. "There has been a historically high level of innovation in concrete and admixtures," says James Gado, marketing director for specialty construction chemicals. Much of the activity, especially in Europe, has been driven by regulations to control the emission of chromium(VI) and carbon dioxide from concrete, as well as by a drive for plant efficiency improvements, Gado says.
Grace's Adva Superplasticizer, an admixture based on polycarboxylate chemistry, was introduced in the mid-1990s. The firm's construction chemicals division had worldwide sales of $450 million last year and is experiencing 10% annual growth, he says, spurred by the increased acceptance of new technology.
Philippe Jost, director of U.S. marketing for construction chemicals at Sika, another major supplier of admixtures, says polymer chemistry has been an active area of formulation since it emerged in the 1990s. "The polymers we used in 1997 have disappeared," Jost says. "There have been a lot of new developments. As our chemists understand the technology better, they are able to develop better, more efficient products that are more targeted to specific industries."
Jost says the momentum behind Sika's ViscoCrete polycarboxylate admixtures is the flexibility it affords contractors. "You can customize polymers for special applications, such as precast bridge or parking garage beams," he says. "Contractors may want to use forms on 24-hour cycles, or they may want long workability in ready mix."
ADMIXTURE FORMULATORS are beginning to take on alkaline silica reactivity (ASR), a condition in which alkali in cement attacks silica-based aggregates to form gels that can absorb water and crack concrete. The use of nonreactive aggregates has been the main line of defense, but many quarries supplying such stone have been depleted, and transportation from distant quarries is prohibitively expensive. A growing approach is the use of lithium salts to neutralize the silica, allowing contractors to select from a broader range of aggregate materials.
FMC Lithium has been working in construction chemicals for the past 10 years, says Claudio Manissero, sales and marketing manager for the lithium division's construction business. He expects the use of lithium compounds to be boosted by increases in government funding for repair of bridges, airports, and highways under the $318 billion transportation bill passed in February.
According to Manissero, the neutralization provided by lithium provides a permanent bulwark against ASR. The other common ASR-fighting additive, fly ash, provides an alternative silica source for the alkali to react with--but only when the cement is being poured. Admixtures with lithium add about $6.00 per cubic yard to the $75- to $110-per-cubic-yard cost of ready-mix concrete containing nonreactive aggregate.
Airport runways and taxiways are a major application for lithium, given that water absorption can result in "pop-up": segments of cracked runway surface that can be sucked into jet engines. "This is a major issue, especially for the military," Manissero says.
Despite recent advances in performance, Manissero acknowledges continued resistance to paying the additional cost for high-tech concrete additives. Shydlowski agrees that the question of what the market will bear is a sticky one in concrete admixtures. Upfront materials costs can blind builders to far more significant costs in future construction and maintenance. "It's a fundamental problem for concrete," Shydlowski says.