Application of Gunning Mix Concreties
Concrete gunning refractors must be kept in a dry and moist-free place, avoiding any damage to the package and 2 pallets on top of each other at most.
During the application of gunning concretes temperature of air and the water that will be used must be between +5/+30°C. While our gunning concretes may be applied with spud and plastering, they are mostly suitable for gunning method application. There is need for one gunning machine for gunning method. Our gunning concretes can be applied with two types of machine.
1st Type Machine : Shotcrete Machine. The concrete is mixed with water in a mixer included In these machines and ready plaster is gunned.
In 2nd Type gunning machines, dry cocrete is gunned directly through a nozzle with water and pressurized air.
In gunning machines that have a rotor capacity up to 2 liters, minimum 6-7 bar pressure and 4-5 m3 / min. flow dry air is needed. And, in machines with higher rotor capacity the need for air flow is higher. Especialy, air used in 2nd type machines must be dry. If the air is not dry, concrete is plugged early and this my result in congestion in machine nozzles and pipes.
If the air does not have enough bar pressure and flow it may result in rebound loss in gunning cocretes. The surface of the gunned cocrete is skewed before freezing and made even with a wooden spud. It must be definitely damped with water (water cure) during freezing. As there is a heating with exothermic reaction in the concrete during freezing; to prevent this, concrete is tamped through the water channel of gunning machine during freezing.
Gunning concretes are preferably left to rest for 48 hours and at the end of 48 hours they are exposed to dry out application wiht a heating program.
Points to Consider in the Application of Gunning Concretes:
1. Specially produced refractor gunning machines must be used preferably.
2. There is a need for 6-7 bar pressure and 4-5 m3/min. flow dry air according to the gunning machine that is used.
3. Special gunning overalls and goggles must be worn during gunning application.
4. There must be distance of 0,5 - 1 meter between the nozzle and application surface. Rebound loss increases at closer or further gunning applications.
5. When the gunned concretes start to plug, they must be skewed and surface of the concrete must be trimmed with a wooden spud.
6. In order to prevent the exothermic reaction that will happen during freezing, the concrete must be damped through the water channel of gunning machine during freezing.
7. The concrete must definitely be dried out with a drying program.
Use vibrators with vibration table or those connected to mold from outside for shapes small in size and with thin sections. Vibratiors should be of 16 to 18 thousand VPM frequency and secured tightly to the molding to provide full vibration. We recommend submerging vibrators of 17.000 VPM frequency, 7.26 diameter and 0.58/kg centrifugal force on places of 30 cm larger sections. For sections thinner than 30 cm you should use 0.54/kg centrifugal force and 1.2 to 5 cm diameter vibrators.
Short termed vibration should be applied on mortar placed over with sufficient anchorage (taking 1 to 2 minutes for 16.000 - 18.000 VPM). After casting is complete, mortar left for drying shall start to be in gear within 2 to 4 hours. Hand check the surface to see hardness, if so, irrigate from outside, cover by damp cloth and leave.
Following factors are known to negatively effect density, durability and hardening features of concrete :
a) Additions made;
b) Dirt and/or hot water;
c) Cement waste material and/or dirty mixing machines;
d) Excessive water input;
e) Prolonged mixing
DRYING AND HEAT CURING
Heat cure program for high alumina concrete should be applied given in annex booklet.