Affordable Superstrong Concrete for Bridges

Ultra-high performance concrete mixes cost $360-650 per cubic yard and have compressive strength from 22,500 PSI to 29000 PSI. There are proprietary makers of stronger concrete with costs of $2000 per cubic yard. There have been test blocks of concrete with strengths of 60000 PSI. Regular concrete is usually at 3000-5000 PSI compressive strength.

The Federal Highway Administration is studying how to make stronger concrete at lower cost in high volumes for bridges and other infrastructure.

Four UHPC matrices with fine aggregates only and three UHPC matrices including coarse aggregates were recommended using locally available materials from three different regions. The three regions included the Northeast, the upper Midwest, and the Northwest. Their material costs without fiber reinforcement ranged between about $360 and $500/yd3 ($470 and $650/m3) and $355 to $380/yd3 ($460 and $500/m3) for fine and course UHPC, respectively. The workability of these mixes can facilitate the use of these UHPCs in many structural applications. The compressive strength of the recommended UHPC matrix mixes ranged from 22.5 to 29 ksi (155 to 200 MPa)and exceeded the minimum required compressive strength of 20 ksi (138 MPa).

Future research efforts are suggested to tailor the weight ratio of cement to silica fume to supplemental material of 1:0.25:0.25 in terms of performance versus cost ratio. A reduction in the amount of the most expensive material and an increase in the amount of the least expensive material might lead to a further improvement in performance versus cost. This optimization was not the scope of this research project and has been left for future research efforts.

Adding fiber reinforcement of 1.5 percent by volume to the UHPC matrix increases the costs by about $470/yd3 ($615/m3). This value, when combined with the cost of the cementitious matrix, results in a total material cost for a fiber-reinforced UHPC of about $850/yd3 ($1,110/m3). More research effort is needed to find an alternative cost effective solution to provide sustained tensile strength and enhanced ductility due to the high costs of fiber reinforcement. This can be achieved by finding an alternative fiber reinforcement of lower cost and by reducing the required amount of fiber reinforcement through improved material utilization. A more effective fiber material utilization could be obtained by tailored matrix fiber bond and by combining continuous reinforcement with discontinuous fiber reinforcement.

Background on Concrete

Pounds per square inch (psi) measures the compressive strength of concrete. A higher psi means a given concrete mixture is stronger. Stronger is usually more expensive. Stronger concretes are also more durable, meaning they last longer.

The ideal concrete psi for a given project depends on various factors, but the bare minimum for any project usually starts around 2,500 to 3,000 psi. Each concrete structure has a normally acceptable psi range.

Concrete footings and slabs on grade typically require a concrete of 3,500 to 4,000 psi. Suspended slabs, beams, and girders (as often found in bridges) require 3,500 to 5,000 psi. Traditional concrete walls and columns tend to range from 3,000 to 5,000 psi, while 4,000 to 5,000 psi is needed for pavement. Concrete structures in colder climates require a higher psi in order to withstand more freeze/thaw cycles.

Traditional concrete costs about $90-125 per cubic yard as a ballpark figure. All prices are up currently with inflation in material costs. Concrete slab cost will vary by region. Expect a fee of about $60 per load for delivery from a concrete truck for concrete cost.

How UHPC compares to traditional concrete:

Tensile strength—UHPC has a tensile strength of 1,700 psi, while traditional concrete typically measures between 300 and 700 psi.

Flexural strength—UHPC can deliver more than 2,000 psi in flexural strength; traditional concrete normally has a flexural strength of 400 to 700 psi.

Compressive Strength—The advanced compressive strength of UHPC is particularly significant when comparing to traditional concrete. While traditional concrete normally has a compressive strength ranging anywhere from 2,500 to 5,000 psi, UHPC can have a compressive strength of up to 10 times that of traditional concrete.

After just 14 days of curing, UHPC has a compressive strength of 20,000 psi. This number increases to 30,000 psi when fully cured for 28 days. Some mixes of UHPC have even demonstrated a compressive strength of 50,000 psi.

SOURCES – Federal Highway Administration
Written By Brian Wang, Nextbigfuture.com