The first steps in the development of Shotcrete were taken nearly a century ago. Since then, countless structures have been built, restored and reinforced using this unique concrete placing method.
The invention of ‘spraying concrete and mortar onto a surface at high velocity’ in 1907 is credited to well-known naturalist Dr. Carl E. Akeley. The machine (and process) was introduced at the Cement Show, in Madison Square Garden, N.Y., in 1910. Patents on the equipment and method were granted in 1911, and the process immediately became popular in the industry.
The issue of patents and registration of the term “Gunite,” soon after allowed widespread use of the technology. Related companies were formed in various parts of the world and “Gunite” grew rapidly from 1912 through the 1930’s. After World War II, the use of “Gunite” continued to grow rapidly as new technology such as the introduction of the rotary gun for gunnite were introduced.
It is at this time that the description Shotcrete was introduced as an all-inclusive term for both the wet-mix and dry-mix methods. In pool construction, however, shotcrete refers to wet mix and gunnite to dry mix. In this context, these terms are not interchangeable.
During the 1970’s, technical advancements in materials and equipment brought marked improvements to uses for gunite construction. Perhaps the most significant step in this period was the development of efficient concrete pumps that could be used for wet mix shotcrete application.
In the 1980’s, admixtures were developed to provide almost total control of consistency, hydration and in-place performance of wet shotcrete. Packaging of dry shotcrete (gunnite) materials and admixture developments, such as air entraining for dry shotcrete (gunite) , also enhanced the performance of the dry process. The introduction of steel fibres provided the possibilities of integral reinforcement to meet specific requirements for structural repairs and underground support applications. During these years, the progress in the method of shotcreting has been the result of practitioners who both investigated and evaluated the performance of materials for shotcrete. recently, because of the relationship between the industry and the research community, developments in shotcrete have increased dramatically, and many qualities of the process have been improved.
In the dry-mix process, the dry sand and cement mixture is blown through a hose using compressed air, with water being injected by the nozzle man at the nozzle to hydrate/wet the mixture, immediately before it is discharged onto the receiving surface. The concrete mixture is by pneumatic pressure from a cement gun, hence “gun”-ite. Gunnite has a high rebound factor and as such should not be used in thick pass structural elements where the encasement of this waste rebound will lead to poor quality concrete. The fluctuation in strengths due to inconsistent hydration are also of concern in structural concrete. However with proper placement methods and the use of a rebound blower it is very suited to concrete repair and smaller swimming pool construction. Equipment costs are low.
The wet-mix process is so named because the materials are pre-batched with the correct dosage of the mix design including water. This results in a more consistent verifiable concrete with far less rebound/waste than gunite. A higher work rate can also be achieved with shotcrete pumps. Wet Shotcrete is ideal for structural concrete construction and usually results in time and cost savings over conventional shutter & pour methods. Equipment costs are high.
Shotcrete Africa SCP utilises both methods choosing the one that lends itself best to site and project conditions. We only use imported best of breed REED wet & dry shotcrete equipment.
Shotcrete Africa SCP are not pool builders, however due to our excellent and guaranteed quality we are preferred shotcrete applicators for Pool companies like Blue Lagoon pools who are responsible for the pools seen on our site.