Engineered Sands Production
Experience with Dry Engineered Sand
From Research to Reality
Luck Stone carried out multiple trials of local natural sands against that produced in each of their quarry sites. The best engineered sand results were from crushing diabase (trap rock) at their Goose Creek site. They purchased a Barmac B9100 VSI for Goose Creek in 1998 as they could foresee the increasing request for shaped aggregate and the possibility of producing quality engineered sand from this site. After the Barmac’s installation, the site produced a ‘high fines’ engineered sand with 14 % passing 75 μm (200 mesh). Luck Stone initiated the Aggregates Research Institute (ARI) to help establish the quality of the engineered sand.
During this period, Luck Stone branded the engineered sand as Advanta concrete sand. However, due to the higher than ASTM C33 allowed minus 75 μm (200 mesh) compared to natural sand, it proved difficult to gain acceptance for this engineered sand with customers. To try and encourage acceptance of Advanta sand, Luck Stone decided that blending with natural sand to decrease the minus 200 would allow their customers to establish confidence in the new sand.
Blends were produced by mixing the concrete sand with natural sand from Luck Stone’s Caroline pit. Customers were generally still resistant to the new sand. In order to encourage the use of the concrete sand Luck Stone specified its use on a major construction project at their Goose Creek plant. As a result of this work and the performance of the concrete during finishing customers began to use the material in mixes for low risk uses. The blended sand was eventually accepted by customers but blending costs proved to be high due to the cost of transportation of natural sand.
Controlling the Ultrafines to Produce 100 % Engineered Concrete Sand
Luck Stone decided they needed to reduce the amount of minus 75 μm (200 mesh) present in Advanta concrete sand for customers to accept a 100 % engineered sand. A dual AC22.5GI air classifier was installed at Goose Creek in 2005 to control the minus 75 μm (200 mesh), creating an improved Advanta concrete sand to meet their customers’ needs.
After several years Luck Stone determined to advance the concrete sand strategy to other production plants where markets were present. To do this, they decided the best solution was to conduct large-scale testing using a portable Barmac B6100 VSI, screen and a transportable gravitational inertial air classifier to prove the viability with Luck Stone’s customers. By changing the Barmac VSI’s rotor speed they were able to adapt the different mineralogies of the stone to perform similarly to the natural sands in the same area.
The portable plant was installed at Luck Stone’s quarry sites and then fed with sufficient material to produce 1000 to 1500 tons of Advanta concrete sand for the specific customers to try at full production through their ready-mix plants. They would feed it fresh screenings to shape them and then de-dust them to provide enough test material for their customers to conduct full-scale production testing as a means to determine real-time production benefits outside of a laboratory setting. After completion of experimentation, this transportable test plant is now producing Advanta concrete sand consistently at one of Luck Stone’s plants.
With the success of the trials, a decision was made to establish Advanta concrete sand production at the Goose Creek, Virginia location. This decision was based on both market demand and location geology. The dual AC22.5GI was installed in 2005 and is fed with crushed sand from the Barmac B9100. The dual AC22.5GI air classifier processes up to 100 t/h of sand, producing both concrete sand as well as mineral filler supplement (used in hot mix asphalt; specifically SMA) from the -200 mesh.
Several of the Luck Stone plants are producing Advanta concrete sand today and the strategy is to continue introducing this product to their concrete customers. This is a testament to Luck Stone’s tenacity and foresight in introducing Advanta concrete sand in spite of the difficulties from both customer resistance to change and unfavorable ASTM specifications.
In 2010 Metso purchased the Buell air classification technology from Fisher-Klosterman. Metso intends building on the success that this long-established air classification technology has had in the USA. It is being offered along with existing Metso technologies to create highly efficient and adjustable solutions to engineered sand production globally.
This article has been adapted from the original paper written by Luck Stone’s R.L. Weingart (Director: Materials Management & Research) on Luck Stone’s investigation into dry classification for asphalt sand. With his generous help, it has been updated to include Luck Stone’s advances with dry processing engineered concrete sand.