Madrid Engineering won the 2015 Project of the Year

project of the yearMadrid Engineering won the 2015 Project of the Year at the Engineering Awards Banquet held February 24th at the Polk County Historical Museum in Bartow. The banquet is held annually during National Engineers Week, the third week of February (in honor of George Washington, a pioneer of engineering and surveying in the US). The Florida Engineering Society, Ridge Chapter jointly holds the banquet with the American Society of Civil Engineers Ridge Branch. In addition to Engineer of the Year and Young Engineer of the Year awards, each society may select a Project of the Year.
Madrid Engineering’s project involved stabilizing the parking lot at the Lowe’s on Lakeland Highlands Boulevard. The property that had previously been mined for phosphate and consisted of a mixture of loose sand and very soft clay. “Miners refer to the clay as ‘slimes’”, according to Larry Madrid, PE, president of Madrid Engineering Group, Inc., “but the correct term is ‘waste phosphatic clay’. It is a waste product from phosphate mining, created when the phosphate rock is separated from the sand and clay in the ore-bearing stratum”. This clay is very soft, very wet, has high plasticity and very little strength, according to Madrid.

Most importantly, when the Lowes facility was built, the building itself was supported by pilings, but the parking lot settled, moved and flexed due to consolidation soft clays up to 40 feet thick below the parking lot. As a result, there were low areas in the parking lot that developed over time due to excessive settlement, and after storm events the water would pond there several inches deep. Madrid Engineering reviewed previous data, soil borings and reports, and came up with a unique remediation plan: excavate the near surface clays, process/mix it on site to chemically stabilize the soil, and place the stronger, stabilized soil back into the excavated area. This technique is called shallow soil mixing (SSM) and is an established geotechnical construction technique.

However, Madrid Engineering’s innovative twist for this project is that the chemical stabilizer is PhosphoCrete™, which was invented in Madrid’s soils laboratory. “I’ve done a lot of research on this area over the years. When we add just a small amount of PhosphoCrete to the clays an immediate chemical reaction called hydration literally pulls moisture out of the clay, making it much stiffer than the initial peanut butter consistency”, said Madrid. “Then, over time a second reaction called a pozzolanic reaction slowly cements the material, making it 10 times stronger or more. In effect, we are creating a bridge of stiff material overlying the very soft clays, and this helps to spread out vehicle loads and minimize settlement.”

According to Madrid, Phosphocrete™ was invented more than 10 years ago and this is just the second project to use it, mostly because of the downturn in the economy. But he hopes it will become more widely used as formerly mined land is developed in Polk and surrounding counties. “Our proprietary mix design saved the contractor about 34% in cost compared to the traditional “excavate and replace” method which would have replaced the soft clays with sand and rock or crushed concrete in the hole. That’s a significant cost savings. Rock is an expensive material and crushed concrete is a commodity that fluctuates in price. Sand is plentiful but all three materials weigh significantly more than the clays we were excavating, so it would induce even more long term settlement. The Phosphocrete has almost the same density of the clays that were excavated, so it added no weight and expect no significant long term settlement. Finally, since we mixed it on-site and re-used the clays, we avoided trucking costs to dispose of the unsuitable materials, lowered our carbon footprint by avoiding miles driven, and provided a sustainable, long-term solution.”

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The project team was as follows:

Owner: Lowe’s Home Improvement
Civil Engineer: Chastain Skillman, Inc.
Geotechnical Engineer: Madrid Engineering Group, Inc.
General Contractor: Marcobay Construction
Geotechnical Contractor: Certified Foundations, Inc.

For more information on PhosphoCrete™, call Larry Madrid, PE, D.GE, F.ASCE or visit | www.madridengineering.com