New Plasticizer for Shotcrete

Cyrill Spirig, Corporate Product Engineer Tunneling & Mining

Until recently, mainly standard superplasticizers were used for the production of shotcrete. No consideration was given to the fact that the requirements for a superplasticizer used for the production of shotcrete are quite different than for the production  conventionally placed concrete. The additional requirements are the result of the mechanical application of shotcrete. Shotcrete which can be sprayed with lower pump pressure is kind to the machine and reduces wear. At the same time the accelerator can be injected more easily. Thanks to its long open time, shotcrete can be transported long distances without loss of workability. The easy combination with Sika accelerators guarantees high early strengths.

Shotcrete

Contrary to conventionally placed concrete, shotcrete is not being cast, but sprayed onto the substrate. Traditionally, the dry mix is conveyed pneumatically. In the modern method, the concrete is conveyed in a dense stream to the nozzle with a double pump and, after the addition of an accelerator pneumatically sprayed onto the substrate.

Requirements to Superplasticizer for Shotcrete

In the past, superplasticizers were mainly aimed at the requirements for conventionally placed concrete, with emphasis on water reduction. Shotcrete however places additional requirements on a superplasticizer. Since shotcrete is mechanically conveyed, the wear of the equipment plays a decisive role. High pump pressure produces high wear. Therefore, superplasticizers used for shotcrete in the dense stream mode must reduce pump pressure to reduce wear costs and extend the machine’s life span.

Shotcrete is mainly used for protection work in civil engineering and tunnel construction. Especially in tunnel construction, there are long transportation distances from the batching plant to the spraying location. A superplasticizer for shotcrete must therefore also guarantee a long open time.

Once the shotcrete is applied, it must develop strength fast to be able to guarantee the safety of the work force at the excavation point. Long open time and fast strength development face each other diametrically. To overcome this contradiction, superplasticizers for shotcrete must contain additional components which, in combination with an accelerator support and further strength development.

With Sika ViscoCrete SC-305 we have made a decisive step forward in shotcrete technology and gained technical market leadership in the field of superplasticizers for shotcrete. Samples for trials can be ordered with Sika Schweiz AG. Tests are an absolute must for every shotcrete “guru” of the Sika family. The results will thrill you.