Cement Market Expansion

Construction began in mid April on what will be the largest cement storage terminal in Texas and one of the largest in the United States. A little over a year ago, Ash Grove Texas Cement Co. and Alamo Cement Co. formed a joint venture, which has been named Houston Cement Co., in order to build this

Both companies had begun developing their own plans to build additional import cement storage terminals at this port, but realized that they could build bigger and better by combining their resources. Ash Grove has been operating a 70,000 metric-ton facility for eight years at the Port of Houston and wanted to expand; Alamo owned an 88-acre tract about three miles away.

Headquartered in Overland Park, Kansas, Ash Grove is the largest American-owned cement producer in the United States, operating plants in nine Midwestern and Western states. Ash Grove Texas was formerly North Texas Cement Co. Alamo Cement, one of the U.S. cement industry's original producers, has been in business in San Antonio since 1880, where they operate a 1.4-million-ton-per-year capacity plant.

When completed a year from now, in spring 2006, the six-silo terminal will boast a capacity of 100,000 metric tons and an annual throughput capacity of 1.5 million metric tons (mtpy). Ash Grove will oversee operation of the facility, led by Houston Cement President Jim Gatens. The two companies' respective customer sales will be maintained separately.

Although North, Central and South Texas have been blessed with plentiful limestone deposits for the manufacture of cement, the Greater Houston area, which is one of the largest cement markets in the United States, has always had to rely on product shipped by rail or sea.

"All the cement we sell stays within 100 miles of Houston," Gatens added. "To allow us to source product from all over the world, we need to have adequate storage facilities. We are currently importing primarily from South Korea and Greece. Right now, the lead time from the date we purchase until the ship arrives is 60 to 70 days. A lot can happen in 70 days. We could have a week's worth of rain." Operating a terminal at maximum capacity, such as Ash Grove's existing Houston facility, poses logistics issues that tie closely to the weather and consumption.

"The new terminal will have 30-percent more storage than our existing domed facility," said Gatens. "We have also purchased a new, bigger ship unloader that will allow us to off load ships faster. We can now off load 8,000 tons per day with our pneumatic loader, meaning that we can off load a 40,000-ton capacity ship in five days. The new BMH Siwertell auger unloader, which is one of the largest made, will off load 12,000 tons per day, meaning we could off load the same sized ship in three to four days."

Dock

Earth work is proceeding quickly on the $42-million project, which broke ground in April. The Orion Marine Group division of Houston-based Orion Construction has the responsibility of building the mooring dock for the facility.

Preparation involves constructing a mile-diameter levee, creating a 30-acre placement zone to contain material that will be dredged from the ship channel. Three draglines will work for one month moving dirt from borrow pits within the zone to construct the 15-foot-tall levee. The clay bottom will make a sufficient seal for the bottom, so no additional lining material will be placed down, according to James Buntrock, project manager for Orion.

"We will use a hydraulic dredge off-shore to pump the material into the levee," said Buntrock. "From between the ship channel and where the dock is going to sit, we will dredge about 400,0000 cubic yards of material."

Most of the silt will be retained within the levee, he described, while a spillway structure will channel water into a retention pond where more silt will be allowed to settle. "The clean water will then be allowed to flow back into the ship channel."

Orion is also reinforcing the shoreline on the property to prevent erosion by the wake from passing ships. Cable-locked concrete revetment mat topped with grass will reinforce the slope to the natural grade, about 15 feet above sea level.

Silos

Continental Construction Co. of Memphis, Tenn., has been contracted to construct the silos and facilities. In order to support the huge six-silo concrete structure on this sandy terrain, two Continental Construction Co. crews operate two crane-mounted auger units installing 1,450 auger cast piles beneath the silo area. Ricky Howard of Orion operates the Trimble Geodimeter to lay out the pier grid by satellite navigation. The Continental crew then drills the 16-inch-diameter piers 74 feet into the subgrade. The auger allows the crew to drill the pier, then pump grout down through the center of the auger.

"We add plasticizer to the mix to make it more 'soupy' so that it will flow into the hole more easily and the reinforced steel cage can be inserted," explained Kenny Stratham, site project manager for Continental. "They begin pumping grout into the hole before they begin drawing up the auger. This allows them to maintain the pressure of a 5-foot head of grout above the bottom of the auger. From experience, the crew knows the number of pump strokes that will place 150 cubic feet of grout under the auger."

Once the 74-foot pier is filled with concrete grout, a 20-foot rebar cage and 60-foot #8 steel bar are lowered into the shaft, then securely tied to a saw horse where they hang suspended until the mix sets. The Continental crew has been able to complete 32 piers per day with this method.

One year from now, six concrete silos, each 66 feet in diameter and 186 feet tall, will tower over the Houston ship channel. The mechanical rooms atop the structure will bring their height to 220 feet.

"The silo walls will be continuously slip formed and poured," explained Aaron Bufmack, Ash Grove project engineer. "It will take about 10,300 yards of concrete just in the slipping of the 19-inch-thick silo walls. Below that, 5,500 yards will be used for the reinforced concrete foundation mat.

The six silos will be fed by one of the largest rail-mounted Siwertell auger loaders made. Once the dock is completed, Continental Construction will install the unloader and conveyor under the direction of a BMH Marine representative from Sweden. The totally enclosed conveyor will eliminate dust and spillage as the powdery cement travels from the cargo ship to the storage facility.

The new unloader and larger storage capacity will facilitate the separation of cement by source. "We keep each cement separate according to our three suppliers," Gatens explained. "Our cement is Type 1/2 and all state approved, but our customers don't like to mix cement on spec work."

The plans have been designed to speed trucks through the terminal via three truck-loading lanes. Ash Grove representatives estimate that the time for loading a standard 25-ton capacity bottom dump hauler will be reduced to 3-1/2 minutes at this facility, a major improvement for contractors' haulers.