KING Shotcrete Solutions Introduces Ultra-Rapid Strength Gain Dry-Mix Shotcrete
It has already been shown that rapid strength gain dry-mix shotcrete utilizing calcium sulfo-aluminate (CSA) cement and providing about 20 MPa (2900 psi) after only 2 hours, can be effectively produced and placed in mining applications. As it is actually used as a standard part of the excavation ground control system, the use of such rapid strength gain dry-mix shotcrete can be a very efficient and robust solution. This product provides ultra-rapid support and reduces the mining/tunneling cycle by reaching the re-entry criteria much faster than with traditional Portland cement based, dry-mix shotcrete using set-accelerators.
In this context, the use of this ultra-rapid strength gain shotcrete appears to be a very attractive solution for emergency repairs in civil applications, for which rapid strength gain materials such as mortars or concretes are already employed. This product allows for shortened construction schedules due to restricted lane closure times on bridges and roadways, and restricted access time in tunnels.
Based on its experience with durable shotcrete and the use of CSA cement in shotcrete, KING is introducing a durable, rapid strength-gain, dry-mix shotcrete for emergency repairs, called KING RS-D1. This product is a CSA cement based, dry-mix shotcrete. All testing conducted on KING shotcrete products is performed on samples that have been shot to represent the exact properties of the in placed material. All KING shotcrete made with CSA cement are powered by Rapid Set® cement technology.
KING RS-D1 provides very good shooting characteristics. All nozzlemen who tested it, said that the mixture was easy to shoot, that the consistency was easy to adjust, and that the product adhered very well to the receiving surface. The testing completed at Laval University showed a lower rebound rate than the current KING Portland cement based formulations. As expected, KING RS-D1 reaches its final set after 15 to 20 minutes after placement. Then, it rapidly develops compressive strength, reaching more than 13.5 MPa (2000 psi) after only 1 hour, 20 MPa (3000 psi) after 3 hours, 40.0 MPa (5800 psi) after 7 days, and finally more than 50.0 MPa (7250 psi) after 28 days.
The boiled water absorption and the volume of permeable voids are two of the first durability properties typically analysed when performing tests in the shotcrete industry, in order to provide an indication of the quality of the in-place shotcrete. The absorption results obtained for KING RS-D1 and the associated shotcrete quality indicators proposed in the literature (and generally accepted in the industry) (Austin & Robins, 1995), indicate that KING RS-D1’s quality of the placed shotcrete was good.
The rapid chloride penetration test (RCPT) results also confirm low chloride ion penetrability, a characteristic which will provide excellent protection against corrosion of the steel reinforcement. In addition to the outstanding results presented previously in terms of strength development, material quality and chloride ion penetrability, KING also tested freeze-thaw resistance. Testing has shown that the freeze-thaw resistance is excellent with results of 100% when performing the classic ASTM C 666 freeze and thaw testing.
The air void system characteristics measured for KING RS-D1 is lower than 300 μm, explaining the excellent freeze and thaw resistance obtained. It is also important to note that CSA based cements are proven to provide a lower shrinkage when compared to a similar Portland cement based system. The testing showed shrinkage of only 400 μm/m after 28 days when tested accordingly to ASTM C 157, which is lower than with typical shotcrete.
It is now possible to use a CSA cement based, dry-mix shotcrete that provides ultra-rapid compressive strength development, lower rebound, good in-place material quality, low chloride ion penetrability and excellent freeze-thaw resistance. With all of these great characteristics, it is now possible to repair concrete structures on a tight schedule without compromising the long-term durability of the repair. To learn more about this product, view the Technical Data Sheet or contact your KING Technical Sales Representative.