Page 17

2014FallShotcreteEMag

Fig. 1: Typical setup for dry-mix shotcrete operations Table 1: Difference between dry-mix and wet-mix process Dry-mix process Wet-mix process Pros Instantaneous adjustment of shooting Known w/cm consistency Delivery hose lighter to move Rebound and dust are lower Start-stop operations simple High volume output Cons High volume output sometimes difficult to Higher rebound manage Low volume output Use (and dosage) of accelerator on site hose. Air is added at the nozzle, through an air- binder content is sometimes used (Prudêncio Jr. ring, to propel the material at high velocity onto 1998). Accelerator dosage has to be carefully the surface ensuring sufficient compaction. As all planned as it reduces long-term resistance and components are mixed together prior to pumping, durability of concrete (Neville 2008). wet-mix concrete is usually delivered on site by a standard ready-mix truck and is fed directly into Dry-Mix Shotcrete the pump. Dry-mix shotcrete is fundamentally different With the exception of the set-accelerator, all from its wet-mix counterpart. In this process, all admixtures are blended before pumping. When the solid materials (gravel, sand, cement, addi- needed, the set-accelerator is added at the nozzle tives, fibers, admixtures) are transported through through a separate valve by using a special admix- the hose using compressed air. Water is added ture pump. Normal dosage of accelerator usually through a water ring at the nozzle or shortly before ranges from 2.5 to 6%, but a dosage of >10% of depending on the type of nozzle used. No matter the Shotcrete • Fall 2014 15


2014FallShotcreteEMag
To see the actual publication please follow the link above