What Is Shotcrete Additive

SHOTCRETE

Shotcrete is a self-trapping concrete sprayed onto a surface with high air pressure. In order to be able to apply shotcrete, it should be able to set early and gain strength. For this purpose, set accelerators are used in shotcrete.

Shotcrete is applied in two ways; dry mix systems and wet mix systems. In a dry mix system, a dry mix of cement, aggregate and set accelerators in powder form is filled into a machine. Then it is delivered from hoses to nozzles with the help of compressed air. Water required for hydration is added to the nozzle. In the wet mixing system, the cement is filled into the aggregate machine. The water and liquid outlet accelerator is added to the nozzle. In the wet mix system, as in normal concrete applications, a mixture of chemical admixtures with controlled water/cement ratio is prepared and pumped from the hose to the nozzle with appropriate machines. The pressurized air required for spraying and liquid set accelerator mixtures are added to the concrete in the nozzle.

Where to Use Shotcrete?

Dry mix and wet mix shotcrete are used in the tunnels, mines, hydropower projects, slope stabilizations, and rock and ground support.

Set accelerators of shotcrete can be divided into three groups; sodium silicates, aluminates and alkali-free set accelerators. Depending on the cement type and desired set strength and strength values, shotcrete admixtures are used at a ratio of 3-10% of the cement weight. Although set accelerators cause positive impacts, they also create (especially sodium silicates and aluminates) certain downfalls in ultimate strengths. For that reason, the dosage of the accelerator is very important and should be as low as possible.

The additives of shotcrete are mostly white and cream colored and are in powder and liquid form. Its density is 1,1 kg/lt at 20 ° C.

What are the Effects of Shotcrete Admixtures?

Effects on Fresh Concrete: Fast setting, vertical and horizontal hold in thick layers with reduced rebound ratio, cohesion increase.

Effects on Hardened Concrete: 20-25% reduction in ultimate concrete strength, insufficient durability, reduction in freezing and thawing resistance, high hydraulic shrinkage.