Just another day in the shotcrete world out in Portland’s Forest Park for an emergency repair. 40% slope…steep! https://www.instagram.com/p/CHqHYJglKQf/?igshid=7e9afvb18fai
Shotcrete is a precise mixture of graded sand, aggregate and cement that we call the “mix design”.
The sand is often mined or manufactured (we use only virgin sand, no manufacured). The quality of the sand is critical in shotcrete and allows for longer pushes and higher pressures if correct.
The aggregates we use are generally 1/2″ or smaller and include a lot of buckshot and fines down to #10 or less.
The cement is Portland type I/II provided locally from Ashgrove out of Durkee, Oregon. Shotcreter’s only uses American Made Portland Cements.
The ratios we have determined through the years is roughly 25% agg and 75% sand and over 800 lbs. of cement along with some admixes.
The admixes that make shotcrete a reliable component for the installers and crew are critical.
Shotcreter’s has on hand high-end super plasticizers, air entrainments, water reducers and pumping aids.
Shotcrete and sprayed concrete are used to facilitate getting massive amounts of material on a vertical or overhead surface safely and effectively.
Shotcrete has no bounds or limits thanks to the pneumatics that propel it onto a surface, thus eliminating expensive formwork.
Shotcrete also makes the working environment for the crew safe by allowing the machines to do the work. The use of high pressure hydraulics and high volume pneumatics achieves a process that no other method can replicate or achieve.
Shotcrete and sprayed concrete are ideal for erosion control and bank side rehabilitation where the earth needs some stabilization.
Sea walls benefit from shotcrete by decreasing the time needed for erection and completion, thus increasing the safety of the crew.
Old URM (un-reinforced masonary) structures and buildings can now be revitalized and refurbished thanks to the structural properties of shotcrete.
Shotcrete is very versatile due to the ability to drag around the hose that is the delivery mechanism. Instead of limiting the scope of the project due to no access, the hose used for shotcrete applications can be reached out 300′.
300′ of placement hose/line allows for the heavy equipment to stay parked away from the jobsite if necessary and also opens up the rainy season for many construction uses.
Is shotcrete strong? In a simple answer: YES!
Shotcrete has nearly 2x the amount of cement that a normal redi-mix load would have. Cement is the main component for strength in shotcrete and concrete.
Shotcrete is also strong thanks to the airline that supplies the “punch” for the material being sprayed or embedded.
The physical properties of spraying concrete or shotcrete exceed normal concrete thanks to the “punch” or the impaction from velocity.
Normal concrete is poured and placed, but it does not get “punched”. The punching effect of shotcrete increases the density of the concrete and materials.
Concrete that is denser, by nature, is stronger in many aspects. Shotcrete and spraying concrete increases the density of the materials thanks to the “punch” of the pneumatics.
Normal (conventional) concrete does not use pneumatics to be applied, lacking the impaction and punch.
When normal concrete gets tested, the aim is to achieve 3,000 p.s.i., when crushed with a special testing apparatus. When testing shotcrete, the aim exceeds 4,000 p.s.i. and lot’s of times much higher!
Sprayed Concrete is an effective method of delivering vast amounts of high-strength concrete via high-pressure air and hydraulics.
Shotcreter’s has it’s own fleet of specialized mixer trucks that we developed alongside a fleet of truck mounted line pumps. Spraying concrete is what we do!
Sprayed concrete is synonymous with wet-mix shotcrete or dry-batch gunite. We only provide wet-mix shotcrete at Shotcreter’s.
Wet-mix shotcrete is very similar to the normal concrete we are accustomed to seeing, except it has been tailored with specific chemicals and ingredients to achieve the characteristics of shotcrete.
Shotcrete will have less aggregate than normal concrete, and more sand. Shotcrete will have nearly 2x the amount of cement and cementious materials. Also shotcrete, since we are spraying it, needs to have some chemical properties that achieve a tacky state when appplied.
Sprayed concrete (shotcrete) is great for vertical work (walls and embankments) and also works great for flat installations like pipelines.
Shotcrete and sprayed concrete are the most acceptable method for safely building tunnels and aquaducts worldwide.
Shotcrete on general is 2-3x the cost of conventional concrete. Why does shotcrete cost more than normal concrete?
Shotcrete is a special blend of sand and aggregate just like concrete, except the difference is the amount of cement (much higher), and the special admixes to ensure it’s performance.
Admixes like air entrainment help with the freeze/thaw effect from the elements.
Admixes like super-plasticizer help with the pumping characteristics and getting the material through the system effectively.
Admixes like a water-reducer help with attaining high-early strength by reducing the amount of water in the mix design and thus increasing the cement-to-water ratio.
Admixes like VMA (viscosity modifying admix) help with the workability of the product
All those admixes are essential for an optimal shotcrete mix that can make it’s way through the system of hoses and machinery, be applied efficiently with a workable result.
To narrow down the cost Shotcrete, a few steps are required to get an accurate estimate of the project.
Shotcrete requires additional manpower, machinery and preparation for the product to work in the manner as prescribed. Most shotcrete projects need mobilization of the crew and calculations made from dimensions available either via onsite visitation or from a set of plans.
Smaller shotcrete projects generally begin around $2,000 and go much higher depending on the project.
Shotcrete is sold by the Cubic Yard and most likely only 7 to 8 cubic yards are delivered each truck. One of the tricky aspects of shotcrete is how tacky it can be to the equipment and delivery trucks.
Shotcrete by nature is suppose to be tacky and have the properties of adhesion, thus the cost of cleanup is higher.