By: Allen Zeyher
Highway construction is struggling to maintain a healthy
pace in an economy that stubbornly remains sluggish.
Portland cement consumption was 5% lower in May 2002 than in
May last year, according to the latest statistics from the Portland Cement
Association (PCA). It was the third consecutive month of lower consumption. For
the first five months of the year, portland cement consumption was down 1.5%
from last year, and that is consistent with PCA's prediction for the year
as a whole.
Public construction in June was down 3.8% from May,
according to PCA.
Highway construction spending in June was down 4.2% from
May, the lowest level so far this year, down 16.7% from last June and down 3.3%
for the first half of the year, compared with 2001.
Ron Blech has seen those economic concerns play out in the
concrete plant market in the past year.
"The market was slowing at best" even before
Sept. 11, the vice president of sales at RexCon, a Milwaukee-based division of
Rose Industries Inc., told Roads & Bridges.
"After that, things went very, very dead for a short
time," Blech continued. "Now we see good quote activity. The economy
has maybe bottomed out, and we see people that have projects to do that are
coming back into the marketplace knowing they have to buy, and we do have some
plant sales."
Another trend Blech sees is toward plants that take up less
space, so they can fit into tighter jobsites.
"We see a lot of different ways to economize in the
overall plant installation and operation," he said.
With the various mixes required for high-performance
concrete to get higher strength, decreased moisture permeability or faster
curing, many contractors are buying concrete plants with more silos for storing
different types of material.
"Everybody's wanting a third compartment or a
third storage capacity," said Blech. His customers are requesting more
compartments and more storage in general.
As far as instrumentation, Blech mentioned that RexCon is
now often called on to provide a moisture probe for the sand bin. The probe
measures the moisture in the sand and sends a signal to the plant's
computer, which automatically adjusts the amount of water it adds to achieve
the right mixture.
Just add water… and cement, sand and stone
RexCon's new HD-12 concrete plant
provides a 12-cu-yd aggregate batcher with four 20,000-lb load cells. The
67-cu-yd, 100-ton aggregate bin is made of 1?4-in.-thick steel, with a
3?8-in.-thick bottom for added durability. The bin is equipped with eight
double-clamshell batching gates, one individually controlled pair per
compartment. All gates are cylinder operated and solenoid controlled. Optional
aggregate bins are available with 150- and 200-ton capacities.
The HD-12's single-compartment gravity cement bin has
a rated storage capacity of 2,120 cu ft or 100 ton. Low-pressure bin flow pads
improve cement aeration. Optional cement silo compartment splits and silo
additions are available.
The HD-12 also is equipped with a 30-in.-wide three-ply
conveyor belt powered by a 20-hp motor with a 350 ft/minute belt speed.
RexCon also designs its own RC3 universal concrete batching
control system RC3 can be retrofitted into any existing plant,
according to the company, and can interface with a varitey of truck dispatch and
accounting systems. Information such as formulas, plant configuration and
ticket archives can be stored in any industry-standard format and viewed on
another computer.
Hyper mix
The Hyper-Mobile Concrete Batching and Mixing Plant, with a twin-shaft mixer, has the ability to rapidly and uniformly mix zero-slump concrete, cement-treated base, RCC and other low-slump materials.
The four-trailer plant from Guntert & Zimmerman, Ripon,
Calif., can be set up and operational in less than a day without the need for a
crane or foundations under most site conditions. All plant ladders and
platforms fold up for transport. Separate motor control cabinets are provided
on each trailer, minimizing cable hookup time.
The mixer trailer becomes the plant foundation with the aid
of the trailer air bags. In some soft ground conditions, concrete sleepers or
mats may be required under the mixer trailer to ensure a stable silo
foundation. In some seismic areas, a reinforced or shorter silo structure and
concrete foundations with foundation bolts may be required.
The twin-shaft compulsory mixer reaches 85% of the maximum
mix quality after only 15 seconds, according to the company, and 95% uniformity
after 30 seconds. The crossover of two mixing circles creates a high degree of
turbulence, ensuring effective dispersion of the cement particles.
Expandable mix
The mobile Pacesetter 1236 from CMI
Johnson-Ross Corp., Champaign, Ill., has modular aggregate and cement sections,
and additional sections can be added to increase storage capacity. The plant is
adaptable to central mix with the Johnson-Ross tilt-drum mixer.
The Pacesetter also comes equipped with a cement screw
batcher, which provides precise pre-blending of all materials prior to charging
the mixer.
The plant has a production rate of 200 cu yd/hour in
transit-mix configuration or 250 cu yd/hour in central-mix configuration.
Aggregate storage capacity is 40-226 cu yd or 54-305 ton. Cement storage
capacity is 1,000-5,400 cu ft or 36-253 ton. The batcher's rated capacity
is 12 cu yd.
Johnson-Ross' Ranger 750 mobile batch plant is designed for the paving contractor, according to the company. The plant
features dual 12-cu-yd, self-erecting, tilt-drum mixers and individual batchers
for up to four aggregates and two cements (overhead).
The plant has an hourly capacity of 750 cu yd. It consists
of five main individual mobile units, including an aggregate section with
radial action transfer conveyor.
Pick your flavor
Mobile batch plants from Helco Co., Cortland, Ohio, come in
three varieties. The SBS-5 has a batch plant capacity of 120 cu
yd/hour and a batcher capacity for aggregate and cement of 5 cu yd. There are
three compartments for aggregate for a total of 34 cu yd of storage.
The SBS-10 has a batch plant capacity of 200 cu
yd/hour and a batcher capacity for aggregate and cement of 10 cu yd.
The HM-105 has a batch plant capacity of 105 cu
yd/hour and a batcher capacity of 4.5 cu yd of aggregate and 4.5 cu yd of
cement. The plant has three storage bin compartments with six gates and a total
capacity of 38 cu yd.
The company's Golden Hawk control system
has standard features such as a full manual backup system, automatic sand
moisture compensation, aggregate moisture compensation, multi-level password
security, inventory reporting, delivery ticket printing and automatic multiple
batching.
Crave to pave
State-of-the-art components have been combined with
innovations in batch plant design in the MG-12CP Mobile Gravity 12 Central Mix
Paving Plant, according to Erie Strayer Co., Erie, Pa. The plant
includes a 12-cu-yd mobile tilt mixer, high-profile paving blades, a 50-cu-yd
mobile aggregate bin, three individual aggregate batchers, a 12-cu-yd cement
batcher and a 715-bbl mobile two-compartment cement silo.
The MG-11C also is a central-mix paving plant
with an hourly output capacity of 366 cu yd. It includes a 10-cu-yd mobile tilt
mixer, high-profile paving blades, a 50-cu-yd mobile aggregate bin, a 10-cu-yd
aggregate batcher, a 12-cu-yd cement batcher and a 715-bbl mobile
single-compartment cement silo.
The MC-11C is a self-erecting mobile
central-mix paving plant with an output capacity of 400 cu yd/hour.
Sophisticated hydraulics eliminate the need for a large crane at the time of
erection and dismantling. The plant is ideal for quick moves, according to the
company, where short pours at high production are required. It includes a
10-cu-yd mobile tilt mixer, high-profile paving blades, a 50-cu-yd mobile
aggregate bin, a 10-cu-yd aggregate batcher, a 10-cu-yd cement batcher and a
300-bbl in-truss cement bin.
Horizontal mixing
The Model LP-12B-80/4-1000/2 batch plant is a
new product from The Vince Hagan Co., Dallas. It includes 12-cu-yd cement and
aggregate batchers, a 1,000-bbl two-compartment cement silo, an 80-ton
four-compartment aggregate bin and two silo-top dust collectors.
The company's latest mixer, a horizontal shaft spiral
blade mixer produces a forced mix that does not rely on gravity
the way tilt mixers do. Hagan's horizontal shaft spiral blade mixer can
produce up to 450 cu yd/hour, based on 30-second mix times. The mixer is
available in four capacities up to 10 cu yd.
