Concrete has come a long way, but most people think of concrete as a modern day building material.

Imagine the Great Wall of China, built between 220 B.C. and the 1600s. The materials used are those available near the site of construction. Near Beijing, for example, the wall is constructed from quarried limestone blocks. In other locations it may be quarried granite or fired brick. Where such materials are used, two finished walls are erected with packed earth and rubble fill placed in between with a final paving to form a single unit. In some areas the blocks were cemented with a mixture of sticky rice and egg whites. In the extreme western desert locations, where good materials are scarce, the wall was constructed from dirt rammed between rough wood tied together with woven mats. If the wall were built today using current materials, it might be called the Concrete Wall of China and would have required only 10 years to build.

Assyrians and Babylonians used clay as cement in their concrete. Egyptians used lime and gypsum cement. During the Roman Empire, Romans used concrete made from Quicklime, pozzolanic ash and an aggregate made from pumice that was very similar to modern portland cement concrete. Concrete became a high-tech material for Romans and Egyptians when they added volcanic ash to the mix and found that this mix allowed it to set under water. Similarly, the Romans knew that adding horse hair to ash made concrete less liable to shrink during the curing process and adding blood made it more frost-resistant.

Today, concrete is composed of cement, water, aggregates, admixtures that give the concrete certain characteristics, and other additives. The use of recycled and reused materials as concrete additives is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is pulverized fly ash that's recycled from the ash by-products of coal power plants. Fly ash strengthens concrete and significantly reduces the amount of quarrying and landfill space to bury the ash. Another additive is slag, a by-product of blast furnaces that is blended with cement or used alone and slows the curing process in cooler weather. Researchers also have added other materials to create concrete that has characteristics such as conducting electricity or producing a shine to the finish.

In the last several years, concrete had to be produced fast and furiously for the increasing amount of building projects around the world. According to Industrial Info Resources, cement producers are expanding their facilities to meet the high demand of U.S. concrete projects with an estimated value of $3.6 billion in the first four months of 2006.

Local contractors have seen the increase in the need for concrete and the advancement in concrete technology. Shafer Contracting Company, Inc. is one of the largest concrete contractors in Minnesota and works mostly on government projects for the Minnesota Department of Transportation. Currently, Shafer is the contractor providing concrete on the highway reconstruction of I-35E and I-694 in St. Paul known as "Unweave the Weave" project.

Greg Pelkey, vice president at Shafer, said that although Shafer's plants, acquired in the 1960s and early 1970s, have not changed much, the materials used and the chemistry involved in concrete production have. For example, "the latest innovation is high-performance concrete, started about seven years ago, that's classified as a 60-year design," said Pelkey. "What concrete manufacturers have done is take the concrete and, where it failed initially, altered the design to alleviate the early failures. One of the changes was to reduce the permeability and make concrete denser. Another change is taking away the standard carbon steel dowels and replacing them with stainless steel dowels in laying concrete on roads to prevent decay in the concrete after years of use.

"Concrete producers also increased the air content to make concrete more durable." Since this change and the first project that used high-performance concrete seven years ago, Pelkey said contractors are still waiting to see if high-performance concrete is better. "Minnesota is very fortunate that the DOT takes a very proactive approach to the pavements and the designs."

MnDOT does have its standards that concrete contractors must follow on all its projects. For example, water content in the concrete mix must be below .40 of the total mixture to provide higher strength. With new digital computers that are programmed to make the batches of concrete, Shafer can provide more accurate proportions in its mixtures to its customers and in its own projects.

Matt Zeller, executive director of the Minnesota Concrete Pavement ­Association (MCPA), agrees that MnDOT is more receptive to using concrete for more pavement projects. The department recently included a section on its website devoted to pavement design and recently added an updated concrete portion that Zeller helped write. Zeller and MnDOT then developed a chart using soil factors to determine concrete thickness for low-volume roads that are usually in smaller cities and rural areas and were not paved with concrete.

"The advances in concrete materials and production led to more acceptance and convinced MnDOT to use concrete for all types of roads," said Zeller.

But smaller cities and rural areas also see increases in concrete construction projects. Consolidated Redi-Mix, Brookings, S.D., bought out a smaller concrete mix plant and began its business in January. Matt Wagner, plant manager, said its business has increased in five months. Seventy percent of its work is delivering ready mix to its contractor customers, and the remaining business involves its own crew building foundations and paving concrete.

Wagner thinks that improvements in concrete technology have made it more attractive as a building material. "Our plant makes the mixes that have different strengths, consistencies and aggregates, certified by state and federal laws, for our customers' needs," he said. Admixtures have changed the most with improved chemicals that have broadened concrete's applications, he emphasized, and adding an accelerator in high enough doses can act as an antifreeze for better longevity of concrete, especially in the cold winters in South Dakota.

"Methods used to cast concrete have improved enough for Consolidated to work in winter. Hot water can be transported to the job site, and ground heaters can help the crew dig four to eight feet below ground to work on foundations," said Wagner.

In Bloomington, Minn., PCL Construction's general superintendent, Harry Whitman, agrees that concrete has changed for the better, but its use can be limited. He is currently working on an entertainment facility that is attached to Mystic Lake Casino, about 40 miles south of Minneapolis, and the first concrete pour for the foundation was in January. The two-story structure used concrete for its foundation and lower level walls. The upper level, which includes the dome of an open theater area, had to be built from structural steel, not concrete, because of the weight with no support.

As technology continues to advance, concrete will become easier to produce, faster to cure, and will require less time to complete a project.

Now, about those pyramids in Egypt ...